Magnetic susceptibility: instrumentation and analytical applications

Anal. Chem. 1980, 52, 199R-214R

They had very limited stability in aqueous solution with a consequent loss of catalytic activity. This was changed with the introduction of immobilized enzymes (10-12). Free or water-soluble enzymes were immobilized or made insoluble by combination with some inert matrix either by entrapment or chemical reaction to ensure insolubility. In either case, it was shown that enzymes retained activity for long periods of time. Thus, it has been noted that a single sample of immobilized glucose oxidase has been used for several thousand determinations ( I O ) . The new developments and the proliferation of publications and patents on immobilized enzymes have led to widespread use and intensive work with automated instrumentation and enzyme electrodes. The high-speed and rather sophisticated instrumentation has, of course, been a tremendous asset in the clinical chemistry laboratory. Enzyme electrodes have probably been the most interesting application of immobilized enzymes. These electrodes have been the combination of an insoluble enzyme with some porous organic polymer which is used as a coating for an electrochemical sensor. These have been especially useful in such systems as whole blood or biological media, where sample preparation has been a major problem. T h e format of this article continues to be that which was

used previously. Again, as was done in the last review, the enzyme nomenclature follows the recommendations of the International Commission of Enzyme Nomenclature (13). LITERATURE CITED

(1) (2) (3) (4) (5)

M. M. Fishman and H. F. Schiff, Anal. Chem., 44, 543R (1972). M. M. Fishman and H. F. Schiff, Anal. Chem., 46, 367R (1974). M. M. Fishman and H. F. Schiff, Anal. Chem., 48, 322R (1976). M. M. Fishman, Anal. Chem., 50, 261R (1978). H. A. Bergmeyer, Ed., "Grundlagen Enzyme Analysis", Gawehn, Karlfried, Verlag Chemie, Weinheim, Germany, 1977. (6) H. A. Bergmeyer, Ed., "Principles of Enzymes Analysis", Verlag Chemie, Weinheim, Germany. 1978. (7) T. M. S. Chang. Ed., "Biomedical Applications of Immobilized Enzymes Proteins", Plenum, New York, 1977. (8) "Methods in Enzymology", Vol. 55 and 56, Academic Press, New York, 1979. (9) A. Meister, Ed., "Advances in Enzymology and Related Areas of Molecular Biology", Vol. 46, 47, 48, 49, Wiley, New York, 1978, 1979. (10) J. Everse, et al., Methods Biochem. Anal., 25, 135 (1979). (11) G. G. Guilbault, and M. H. Sadar, A c c . Chem. Res., 12, 344 (1979). (12) I. Chibata, Ed., "Immobilized Enzymes, Research and Development", Halstead, New York, 1978. (13) Enzyme Nomenclature (1978). Recommendations of the Nomenclature Committee of the International Union of Biochemistry on the nomenclature and classification of enzymes, Academic Press, New York. 1979.

Magnetic Susceptibility: Instrumentation and Analytical Applications Including Bioscience, Catalysis, and Amorphous Materials L. N. Mulay" and Indumati L. Mulay Department of Materials Science and Engineering, [136 Materials Research Laboratory], The Pennsylvania State University, University Park, Pennsylvania 16802

INTRODUCTION: SCOPE OF T H I S REVIEW I n this tenth review on magnetic susceptibility, we survey important trends in instrumentation and applications, especially in the realm of analytical chemistry including bioscience, catalysis, and amorphous magnetic materials. T h e last two categories are becoming technologically very important in recent years. I t will be shown in this tenth review that magnetic susceptibility techniques have proved to be extremely useful in the characterization of these systems a t the micro- and macroscopic levels, dealing with their electronic and bulk structures, analysis of various components present, and so on. T h e first nine reviews appeared during 1962 to 1978 (98,105-112). This 1980 edition covers literature mostly from about January 1978 to December 1979 and some earlier work. In response to a n editorial plea, we have made this review more concise than the previous ones. In doing so, it seemed imperative that we depict the exceptionally novel trends in the instrumentation and applications area and eliminate some that we covered before, without, of course, implying in the least that these are no longer important. Hence, we shall not review the work on lunar samples, which was adequately covered before (108, 109) and work on charge-transfer complexes of the TTF-TCNQ type, which show promise of emerging as new superconductin materials (110). It should be noted that books by Mulay andkoudreaux (102) and excellent reports survey the transition metal and rare earth complexes. The reports (55) are published by the Chemical Society, London. Since this review is concerned with instrumentation and analytical applications, we have focused relatively more attention on practical aspects of instrumentation and have attempted to point out the truly novel trends in the hope that experimentalists will explore challenging 0003-2700/80/0352-199R$05.00/

avenues of instrumentation for specific problem-oriented research and that they will not remain chained to otherwise outmoded techniques. Since classical methods, such as the Faraday and the Gouy techniques, quite surprisingly, continue to be very reliable for the measurement of weak susceptibilities and, since these are relatively less expensive than some of the modern gadgetry, we shall continue to incorporate important modifications and tricks-of-the-trade reported by ingenious workers. Unfortunately, owing to limitations of space, we shall not be able to survey various temperature controlling and measurement devices. Furthermore, while curtailing our usual coverage of the general field of instrumentation, we have stressed applications which are expected to be of special appeal to analytical chemists. Since structural analysis is an important aspect of analytical chemistry, we have included typical examples of such analysis. This was also done in response to requests from our readers. We urge our readers to refer to our earlier reviews (10S112) concerning the scope of areas such as solid state science (that is, chemistry and physics of solids), which is somewhat synonymous with materials science and engineering, in order t o appreciate their interdisciplinary role in science and technology, and to appreciate the relevance of these areas to societal needs and their relationship to analytical chemistry. It should be noted that a few developments in instrumentation and their applications are reviewed under the section on "Applications". The "cgs-emu" and S.I. units are discussed a t the end of this review. GENERAL LITERATURE Abstract Services a n d New Journals. References should be made to our earlier reviews (107-112) concernin abstract services. A number of topical conferences such as t t e annual

o e! 1980 American Chemical

Society

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MAGNETIC SUSCEPTIBILITY

meetings on magnetism and magnetic materials (popularly known as the 3M conference), the International Conference on Magnetism (Intermag), Conferences on Amorphous Magnetic Materials, superconductivity and so on are held almost every year within and outside the USA. The proceedings of these conferences are published generally in the Journal of Applied Physics and the Magnetic Transactions of IEEE (Institute of Electrical and Electronic Engineers). These journals are more easily available in most libraries than the specialized proceedings, which were earlier published by the American Institute of Physics and were found to be very expensive and less accessible to most readers. Monographs, Books, Contributed Chapters, and Reviews. A number of books of special interest to the magnetochemist and materials scientists appeared during the past few years. Konig and Kremer (71) have compiled valuable information dealing with (a) magnetic diagrams for transition metal ions and (b) Ligand field energy diagrams. Cracknell (29)and Pekalsi (124) have written books dealing respectively with magnetism in crystalline materials and magnetism in metals and metallic compounds. Watson (170) has reviewed the many applications of magnetism; the materials aspects of permanent magnets in theory and practice have been surveyed by McCaig (93). Magnetic properties of solids by Crangle (30) and magnetic bubble memory technology by Chang (24) represent important aspects of materials science and magnetic technology. The followin books should prove useful to the geoscientists: (i) Magnetohycfrodynamics and magnetohydrostatic methods of mineral separation, which contains excellent information on the magnetic susceptibility of minerals [by Andres (2)]; (ii) Geomagnetic dia nosis of the magnetosphere by Nishida (120). Dubrov (38) cfiscusses the geomagnetic field and life, whereas Davis e t al. (32) consider magnetism-blue print of life. (iii) Liu (81) has edited a volume on the industrial applications of magnetic separation containing excellent theoretical and practical aspects of low field and high gradient field magnetic separation (commonly abbreviated HGMS). This new area of research and technological development, like “superconductivity” is emerging as a subdiscipline of magnetics. The theoretical aspects do consider the magnetic susceptibility of various components to be separated and as such should prove useful to the magnetochemists. [See, for example, an excellent paper by Luborsky in ref. ( S I ) ] . The components to be separated range all the way from red cells (containing hemoglobin) from blood, the separation of diamagnetic metal cans (made of aluminum) from trash, the removal of pollutants such as pyrite (FeS2)from coal, to the beneficiation of minerals such as magnetite (Fe,O,) from taconite which contains other iron bearing components such as iron-silicate, siderite (iron carbonate) and so on. This relatively new realm of magnetic separation provided a great stimulus t o magnetics research during the past decade. Last of all, we must mention experimental magnetism by who have edited chapters on neutron Kalvius and Tebble (64), diffraction in relation to magnetic densities and magnetic excitations in solids, magnetic anisotropy, magnetostriction, and magnetic resonance. Books on molecular diamagnetism and molecular paramagnetism by Mulay and Boudreaux (102) continue t o prove useful to the magnetochemists. Bernier and Poix (10) have reviewed the theories, equipment, and applications of magnetochemistry. The three reviews are in French, which unfortunately do not include references to original work. Mulay (101) in his Italian article describes basic principles and selected applications of magnetochemistry, which are based mostly on the work carried out in his laboratory. Two reviews on the magnetic and other electronic properties of the light actinides have been written by Kalvius (64) and Dunlap (39). Magnetochemistry of inorganic compounds with 484 references are surveyed by Gregson (55). A review with no references on the possibilities offered by static magnetic measurements (Curie and NBel temperatures) and by magnetic resonance methods has been written by Mekhandzhiev (95). Magnetocrystalline anisotropy of (ionic) oxides have been extensively compiled in a 118-page article by Kuwaleski and Rudowicz (77). Bando (4) d’iscusses the chemistry of ma netic materials without citing references to original papers. +he physical chemistry division of IUPAC (60)lists reference (standard) materials available from various national laboratories with relevant data for 25 physicochemical 200R

ANALYTICAL CHEMISTRY, VOL. 52, NO. 5, APRIL 1980

properties, which would be useful, in our opinion for magnetochemical research. In our last review (112),we described an area of research, which is relatively new to magnetochemists This is concerned with the effect of pressure as a parameter in elucidating the magnetic properties and electronic structures (accompanied by valence fluctuations) in various systems. In this area, the following review should prove useful: (i) Pressure effects on one-dimensional charge transfer conductors such as TTFTCNQ by Jerome et al. (61), (ii) Fluctuating Valence States by Jorgensen (62),and (iii) Pressure effects in dilute magnetic alloys by Schilling (137). Cerdonio (22) has written a review with 35 references on the magnetic susceptibility and structure of metalloproteins and model systems. He points out that the new superconducting magnetometers (see section on “SQUIDS” under Instrumentation may give new impulse to unravelling the complex structures of metalloproteins (Hb and hemocyanin), their equilibria, and kinetic features of conformational changes and bonding energies. [See earlier reviews (109-112)]. St. Lorant (149a) has reviewed the advances in biomagnetism since 1968. Biomagnetism deals with the effects of (dc) static and (ac) fluctuating magnetic fields (even of low intensity) on various biosystems. Potential biological hazards associated with human exposure to magnetic fields are discussed. Generally, publications on biomagnetism discuss the so-tospeak magnetic properties of various biosystems. In this respect St. Lorant’s (149a) review should prove useful to bioscientists. The following topics have been reviewed in considerable detail: (i) The magnetic properties and crystal chemistry of rare-earth sulfides [Plug (129)],(ii) Magnetic and electronic transitions in rare-earth alloys [Nikitin (119)],(iii) Magnetic susceptibilities and band structure of transition metal compounds, such as nitrides and carbides, [Calais ( I S ) ] , (iv) Magnetic properties of liquid and metal alloys [March and Sayers (87)],(v) Spin susceptibilities and the theory of itinerant antiferromagnetism [Cade and Young ( 1 7 ) ] ,(vi) Metamagnetism [Stryjewski et al. (152)], (vii) The determination of magnetic structures [Prandl (131)],(viii) Physical methods (such as magnetic susceptibility, ESR, NMR, and Mossbauer Spectroscopy) for studying the structure of coordination compounds [Yatsimirski ( I S O ) ] . Research on magnetically “soft” materials (which show a narrow B vs. H loop, and are difficult to magnetize permanently) and on “hard” materials (which show a broad B vs. H loop and are used for permanent magnetic applications) continues to show a flurry of activity, which is of importance to materials scientists. These materials now include the amorphous materials also. In Tables I and I1 we have compiled selected references t o reviews dealing with such materials.

INSTRUMENTATION Modifications of the Gouy Magnetic Balance. A plan is presented for converting a double-pan balance in conjunction with a permanent magnet into a Gouy balance. The apparatus would be most useful for lecture demonstrations and in the undergraduate laboratory. In our opinion, its usefulness as a research tool is doubtful [Viswanathan ( I S Z ) ] . Antipin and Ergin ( 3 ) give a description of the electronic scheme which, along with an analytical balance automatically compensates a change of mass within f1800 mg. By using this apparatus, a null method is given for weighing. Electronic damping time is less than 0.1 s. Error in measurement is -0.01%, with registration of a change of magnetic susceptibility of cgs unit. The apparatus appears to be based on the Gouy principle. A modification of the Gouy compensating tube is described in which the filler tube has been isolated in a separate piece with ground glass joints, enablin the lower compartment to be emptied, cleaned, and filled wit ease before the air trap and filler tube are replaced [Zimmerman and Duffy (184)]. Another design for the compensating type Gouy tube is given by Davis (33). A shallow long groove is etched with 40% H F in the ground surfaces of both the cone and socket of the lower compartment. By alignment of the grooves, excess solvent may be expelled, after which the tube is closed by turning the stopper. Reference should be made to Mulay’s publications (99,100)which describe other modifications.

1


L. N. Mulay is a professor of Solid State Science in the Materials Science and Engineering Department at The Pennsylvania State University since 1967 and served as chairman of the corresponding interdiscipiinary program from 1967-1972. He took his Ph.D. (1950) in physical chemistry from the University of Bombay. He held various research and teaching positions in chemistry at Northwestern and HaNard Universities before joining the faculty at Penn State in 1963 as an Associate Professor. Dr. Mulay is the author of over 140 research publications and a monograph on "Magnetic Susceptibility". He is the cc-editor of two new treatises on the "Theory and Applications of Molecular Diamagnetism and Paramagnetism" (Wiley, New York, N.Y., 1976). He is internationally recognized for his many contributions to magnetics. His research interests have centered on magnetic probes, such as susceptibility, broad-line NMR. EPR, and Mossbauer spectroscopy for the characterization and structural elucidation of solids at the macro and microscopic levels. Dr Mulay, has traveled widely and contributed to international meetings and research conferences. He is a member of several professional organizations and was chairman of the Central Pennsylvania Section of the ACS (1965). Recently he was elected a Fellow of the Royal Institute of Chemistry, London and a Senior member of IEEE (Inst. Elec. Electronic Engineers). He has been a regular contributor to Analytical Chemistry's Fundamental Review issue since 1962. Ms. Indumatl L. Mulay has been a research associate and collaborator in the Materials Research Laboratory and the biophysics dept at The Pennsylvania State University since 1963. She received a B.S. in chemistry and M.S. in biochemistry (1953) from the University of Bombay. She also earned an M.S. (Radcliffe College) in 1957 and a PhD. in biology (Cincinnati) and did postdoctoral research at the University of Cincinnati before joining Penn State. Her main research interests include radiation genetics, trace metal analysis, EPR studies on cancer tissues, and the effect of magnetic fields on biological matter. She has published several papers and reviews in these areas and contributed a chapter to a book on biomagnetism. She is a member of several professional organizations. She has been a regular contributor to Analytical Chemistry's biennial Fundamental Reviews since 1964.

Modification of the Faraday Magnetic Balance. Nelson and Villa (115) have shown that a new hang-down fiber for the Faraday magnetic susceptibility setup made of 50% nylon and 50% quartz is accurate and precise in the measurement of susceptibilities down to 12 K. The 100% nylon fiber previously employed was shown to deteriorate a t the low temperature range. Also, new molar susceptibilities for the calibration standard [HgCo(NCS),] are given down to 12 K. A thermocouple has been used by Williamson (174) as the suspension in a magnetic susceptibility balance. This construction is described and some measurements providing an assessment of the performance of the balance are given. Van den Bosch e t al. (161) describe another method determining the position of a small solid sample which is suspended, by thin Cu wires, from a microbalance in a Dewar. The shrinkage of the wires a t low temperatures is reproducible to within f0.15 mm. Tweedle and Wilson (157) have constructed a Faraday balance, from commercially available components. I t is convenient to operate and capable of high-resolution measurements on metalloprotein solutions, over a 6.5-300 K temperature range. The measurements are as accurately determined as for other, more expensive devices that usually require superconducting magnetic equipment. As an example, the temperature dependence of the magnetic susceptibility of metmyoglobin fluoride is reported and compared to other available data. The commercial components consist of a Cahn R.G. electrobalance, with an extended glass bottle enclosure, a sa phire hang-down suspension, a helium flow type cryostat ma& by Air Products, Bethlehem, Pa. (model LT 3-110 with a DMX-19 cold shroud), and an electromagnet with the Faraday type pole tips [cf. Mulay (99,loo)].The authors have designed a miniature bulb type container and a plastic leak-

Table I.

Reviews on Bulk (Solid) Magnetic Materials topic

Permanent magnetic materials and applications Rare earth (RE) cobalt magnets such as SmCo,, the REtransition metal ( 2 : 2 7 ) alloys (contains reviews on chemical and physical analysis of powdered RE-Co alloys and magnets) Ferromagnetism of iron all the way u p t o the surface (discusses surface magnetism along with Mossbauer spectroscopy) Developments in soft magnetic materials Micromagnetism in hard magnetic materials Magnetic, photoinduced magnetic and electromagnetic properties of ferrites with the spinel and garnet structures Trends in the development of permanent magnet materials, such as rare-earth Co alloys, ductile magnets, eg., Fe-Cr-Co alloys, low cost Mn-A1 type

ref. Schuler ( 14 2 ) Goldschmidt "Informiert" (52)

Shinjo (147)

Chen ( 2 5 )

Kronmuller (74) Metselaar (96)

Zillstra ( 18 3 )

alloys

Production and properties of ferrite powders for making flexible (plastic reinforced) magnets with a glossary of magnetic terms. Magnetjc materials including ferrites for a specialized

Kerekes (67)

Abarenkova et al. ( 1 )

purpose

Magnetic and transport properties of the rare earths Why is iron magnetic?

McEwen ( 9 4 ) Stearns ( 1 5 0 )

proof cap for holdin sample solutions. The authors discuss the elimination of vitration arising from many sources. The aerodynamic noise was minimized by making measurements in a helium atmosphere of 1 to 10 Torr. The authors give experimental results for 340 mL of 1-28 mM solution of Met-M6(F) protein. Another sensitive apparatus is described by Tveryanowich (156). This allows the magnetic susceptibility to be determined as 2 components, 1 independent of and 1 dependent on the field intensity. The apparatus is based on the Faraday-Hugh method. The theory behind the apparatus is described. Korin (72) discusses methods for measuring magnetic susceptibilities of different samples, and an experimental Faraday magnetometer with the resolution of 2 x emu/g for a 20-mg sample is described in some detail. The apparatus has proved to be extremely accurate for very small samples. Flanders and Graham (50) report on the construction of a novel Faraday magnetometer, in which the force acting on the sample is increased by a factor of 500 as compared to the usual systems with an electromagnet which enerally ives fields (H)of 10 kOe and a gradient (dH/d.zT of a few t u n dred Oe/cm arising from special tapered pole-caps or gradient coils (cf., Mulay (loo)].The increased sensitivity in the new apparatus is obtained by using a Bitter type High-Field solenoid which gives hi her fields (H) up to 120 kOe and gives a field gradient (Cwfdz), 50 times greater than the conventional electroma nets, by working a t the end plane(s) of the solenoid bore, wfere the field starts to taper off. With the Bitter Solenoid system, the field, the field gradient, and the magnetization of the sample are all parallel along the vertical axis of the solenoid. Thus the sample experiences a force along the vertical axis only; thus the annoying situation is circumvented in which the sample experiences a lateral force toward one pole piece of the electromagnet giving rise to the unwanted frictional forces. Another unique feature of the solenoid magnetometer is that a strain-gauge force sensor is used with N


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Table 11. Amorphous Magnetic Materials topic (i)

(ii) (iii)

(iv) (v) (vi)

Amorphous magnetic materials. (This is a n excellent review dealing with the preparation, structure, magnetic properties, and applications of a number of amorphous magnetic materials. It contains several specific and general references up to 1 9 7 6 ) Theory of spin glasses: a review with 80 references. Theoretical studies of rare-earth amorphous alloys Some fundamental aspects of amorphous magnetism Amorphous magnetism: theoretical aspects Random magnetism

(vii) Amorphous magnetic order

Applications of amorphous alloys

(xii) (xiii) (xiv)

(xv) (xvi)

Amorphous metallic materials and their magnetic properties Amorphous magnetic layers with cylindrical domains Magnetic and structural aspects of some amorphous systems (Gd-Co alloys) The micromagnetic properties of an amorphous alloy Amorphous ferromagnetic materials quenched from the melt Amorphous ferromagnetic materials deposited from vapor or liquids Spin glasses: recent experiments and systems Magnetic properties of amorphous alloys

ref.

Luborsky (85)

Binder ( 1 2 ) Ferrer et al. (47)

Wohlfarth (176) Krey (73a) Tahir -Khe li (155) Coey, J. M. (27) Lubors ky (84) Fahlenbrach (46) Batskichev et al. (7) Cargill (19 )

Evetts. et al. (45)

Hubert (58) Dietz (35) Mydosh (113) Flanders et al. (49)

a wide measuring range of forces of -30 to +30 g corresponding to f30 X lo3 dyne for displacements of *0.06 mm. The sensor consists of four gauges connected as a bridge; it is driven a t about 500 Hz and the bridge unbalance is measured with an amplifier locked into the same frequency, which eliminates the effects of vibration. Measurements a t constant temperature, but a t varying fields, are recorded by using an electronic divider. The force 0,which is proportional to the magnetization ( g = xH,where x is the susceptibility) is measured in terms of the signal voltage. The authors recommend the use of standards of known susceptibility (e.g., HgCo(CN),) or of known saturation magnetization (e.g., pure nickel or iron). The paper is well written with a simple mathematical analysis of the technique. It is indeed possible to use a superconducting solenoid in place of the Bitter type solenoid, which requires very high currents to produce fields of 120 kOe. In our opinion, both types of magnets are rather expensive in terms of initial investment and operational costs, which pose a limiting condition for their widespread use. The authors give factual results obtained with -15 mg of iron, -225 mg of paramagnetic H Co(CN), and for -42 mg of an amorphous alloy (Fe1dW80 A computer-controlled Faraday balance has been constructed, calibrated, and tested by Kulick and Scott (75). Magnetic moment and susceptibility measurements can be performed a t fields S 1 5 . 5 kG, and a t temperatures 2-300 K. Gradient coils in the magnet gap permit separate variation of the field and its inhomogeneity. The system is interfaced to a computer which collects data from the electrobalance and thermometer, and controls the magnitude of the applied field and the sign of the field gradient. An independent programmer controls the temperature in such a way that computermonitored sweeps of temperature are achieved with optimal thermal equilibration. The design of the gradient coils is based on a paper by Lewis [cf., Mulay ( l o o ) ] .The crucial part of the apparatus is the Perkin-Elmer Model AR-2 microbalance

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with a digital AD-2 control unit which provides a true 0.1-pg sensitivity in the sense that it is not only stable in that digit but the reading is reproducible on successive gradient reversals and from one field sweep to another, barring other sources of noise. The paper gives a block diagram for computer interfacing, a flow chart for data acquisition showing the temperature sweeping and field sweeping modes. Typical results for a brominated conducting polymer (SN,Bro,&)and a highly paramagnetic polymer containing chromium ions are iven. This is a good paper which has incorporated all the cfetails needed for constructing a sensitive and reliable automatic recording Faraday balance. Inductance Bridges Including Nuclear Magnetic Resonance (NMR) Techniques. An ac inductance bridge for the measurement of the absolute value of the paramagnetic susceptibility is described by Zibold and Korn (182). With this apparatus, the susceptibility of quench-condensed films is measured in situ in the temperature range 2.5-300 K. The applied ac magnetic field varies between 0.5 and 11.5 mT a t frequencies of 11-5500 Hz. Direct current fields up to 11.5 mT can be applied parallel to the ac field. Ma netic moments of fi 2 pB are detected a t 2.2 m T (ac) ancf1100 Hz. This sensitivity allows the study of films about 1 pm thick with various magnetic additions, e.g., Mn, Fe, and Co in nonmagnetic host metals. As an example, the initial susceptibility x of amorphous Au&3i1$e6 and of polycrystalline Aug2Fe8was measured. x has a similar behavior in both cases showng that there is only minor influence on x,whether the nonmagnetic matrix is amorphous or crystalline. Mattock (92) has outlined techniques for the measurement of magnetization and susceptibilities to accuracies of f 5 X lo2 A m-l and f 3 X respectively, in 17-T, 0.7-ms pulsed magnetic fields. The unique features are the use of copper-beryllium wire in the search coils to reduce eddy current effects and a sinusoidal field pulse to obtain symmetric ma netization curves from which an origin can be found, incfependent of remanent magnetization and long-term drift. Brodbeck et al. (16) have constructed a versatile ac mutual inductance bridge, which uses integrated circuit operational amplifiers (op-amps) for the measurement of magnetic susceptibilities of ferro-, ferri-, and paramagnetic samples. The circuit employs op-amps both for balancing the bridge and for detecting the differential signal from the sample coil. The response of the circuit is linear over a wide range of sample susceptibilities, and is calibrated directly in absolute units (emu) using a multiturn digital potentiometer. The sensitivity of the instrument for weak paramagnetic samples is f 3 X emu/g. Calibration curves showing the room-temperature susceptibility as a function of the weight of Fe304and Fe(NH4)2(SO4)2:6 H 2 0 are given. The possibility of making susceptibility measurements as a function of temperature is 'unfortunately not described. Similarly, it is not clear how measurements can be made of saturation magnetization or of magnetization as a function of an applied field, which are of importance in the characterization of ferro- or ferrimagnetic materials. Kumano and Ikegami (76) have designed a semiautomatic Hartshorn bridge to improve the complicated adjusting procedures of the bridge in the measurements of magnetic susceptibilities. The bridge is useful for a continuous recording of the susceptibility of a sample, especially when it varies with time. The authors discuss the problems associated with the stability of inductance bridges and describe useful circuitry for obtaining long range stability. The paper does not describe the adaptability of the apparatus for measurements of the susceptibility as a function of temperature and fails to report calibration data on standard samples. Whitmore and coworkers (172) have designed a solid-state mutual inductance bridge suitable for low-temperature thermometry and susceptibility measurements. The design features an electronically simulated variable mutual inductance. Particular care is taken to reduce spurious capacitive effects. The bridge is highly stable and linear. I t has a resolution of over the range 15 pH to 150 mH, and a noise limited sensitivity of 55 IP-' nH with a 1-s time constant, where I , is the rms primary current in mA. Application t o thermometry and results obtained with cerous magnesium nitrate (x = 4.14 X T-' emu/g) are discussed. SQUID (Superconducting Q u a n t u m Interference Device) Magnetometers. Nave and Huary (116) describe a SQUID susceptometer for submicrogram samples, such as


actinides. A dc magnetic susceptometer incorporating a superconducting quantum interference device as a magnetic flux sensor was conducted with sensitivity to measure the magnetic susceptibility of submicrogram samples as a function of temperature. For a 2-pg actinide sample, the minimum measurable dimensionless susceptibility is approximately cgs in a 2000-G field. The sensitivity was determined in a series of calibration experiments by using samples of P b spheres a t 4.2 K. Pick-up coils insensitive to changes in spatially uniform fields and fields with a constant first derivative were used to reduce noise. The field was trapped in a N b cylinder to roduce a uniform stable applied field. The flux produced y the sample in the pick-up coils is proportional to the magnetic susceptibility of the sample and is a function of the sample position. Calibration of a SQUID magnetometer has been carried out using aluminum metal of high purity (5 and 6 nines) which is machined into cylinders of 2.2-mm diameter and 6.2-mm long [Steelhammer and Symko (151)]. Actually the very weak nuclear paramagnetism of Al, which obeys the following Curie law is employed:

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Magnetization,

(M) = NgN2wX2Id m - H/ 3k T , where gN, p N , and I correspond respectively to the nuclear Land6 factor, the moment, and the spin of the A I nucleus. The calibration procedure was carried out over the ultra-cryogenic range 9 mK to 1.5 K and in a field of 150 Oe. The calibration procedure is recommended for studies on very dilute alloys with very weak (electronic) paramagnetic susceptibilities. Ketchen and co-workers (68) describe a thin-film SQUID gradiometer, that is a device for measuring the magnetic field gradients. T h e gradiometers can be generally adapted for magnetic susceptibility measurements, especially of weakly paramagnetic or diamagnetic materials, which distort the magnetic flux within a superconducting magnet. The authors (68)give a detailed description of the design, fabrication, and performance of planar thin-film dc SQUIDS and planar gradiometers in which a dc SQUID is incorporated as a null detector. Each gradiometer was fabricated on a planar substrate and measured an off-diagonal component of changes in the magnetic field gradient. The gradiomete;. with the highest sensitivity had 127 X 33 mm loops that could be connected in parallel or in series: The sensitivities were 2.1 X and 3.7 X Tm-' Hz-'/', respectively. The intrinsic balance of the gradiometers was about 100 ppm for fields arallel to their plane, and a balance of about 1 ppm could e achieved for fields perpendicular to their plane. When the series-loop gradiometer was rotated through 360' in the Earth's field, the output returned to its initial value to within an amount corresponding to a balance of 1 ppm. Possible improvements in sensitivity are discussed. Another high performance UHF-SQUID magnetometer is described by Long e t al. (83). These authors have constructed a lumpedcomponent stabilized point contact SQUID magnetometer, biased a t 430 MHz and utilizing a cooled (4.2 K) GaAs F E T preamplifier. The system incorporates a full-bandwidth (5-10 MHz) flux-locked loop and has an overall flux sensitivity of 1X @,,/(HZ)'/~,corresponding to an energy sensitivity -4.5 X 10- J/Hz. Reference should be made to a paper by Best and Rothe (111, who have designed and built a 7TNbTi split coil superconducting magnet for susceptibility (and Mossbauer Spectroscopic) measurements. T o r q u e m e t e r s f o r the M e a s u r e m e n t of Magnetic Susceptibility Anisotropy. Ellwood (41) gives an elegant comparison with mathematical rigor of the precision of torque and spinner magnetometers for basaltic specimens. Although the paper is directed toward the interests of geoscientists, it contains valuable information of general interest to all magneticists. Five replicate measurements of the low-field anisotropy of magnetic susceptibility (AMS) of 10 basaltic samples were made using a torque magnetometer and a Digico spinner magnetometer to compare the azimuthal precision for these instruments. AMS measurements of 100 additional basaltic samples are used to compare magnitude determinations between the two devices. I t is shown that although analyses using the torque magnetometer are more time consuming than similar measurements using the Digico spinner magnetometer (1.5 h as opposed to less than 4 min), the

E

precision of the torque magnetometer is superior. The lower precision of the spinner magnetometer is due to an increasin inability to resolve individual axial directions when the AM! maximum (K,) and intermediate (Kb) magnitudes or Kb and minimum (K,) magnitudes become more and more similar. This problem is compounded by a tendency for the spinner AMS device to assign initially lower values to AMS magnitudes than are calculated from torque magnetometer data. The instruments gave similar results for measurements on two samples constructed from homogeneous dispersions of equidimensional magnetite grains. Robertson (134) discusses a simple absolute method for calibrating spinnin magnetometers. For specimens having to IO-' A mP, and a dipole moment of a volume of m2 the probable error of the method is approximately 1%. He uses a coil carrying direct current to simulate a rock specimen. This method has been applied to a coil-type spinning magnetometer with a rotation frequency of 5 Hz, a specimen size of m3 and a resolution of 2 X lo-* A m2. The success of the method depends upon a judicious choice of components and a technique which substantially reduces the effect of large systematic errors. Usher and Reid (160) have developed a new method of measuring the absolute direction of the Earth's magnetic field comprised of a cylinder with a radial hole spinning about its axis on air bearings. The device acts like a single-turn coil and a misalignment between the spin axis and the direction to total field causes currents to flow in the cylinder which are detected by static quadrature coils fixed to the instrument frame. The signals are phasesensitively rectified and fed back to small Helmholtz coils to cancel the small fields producing the misalignment. When combined with an absolute scalar instrument, the vector magnetometer provides complete and continuous absolute vector information, and could find application as a standard observatory instrument. Potton (130) has assessed a new technique for measuring the magnetocrystalline anisotropy torque of a single crystal under stress, in which the specimen is incorporated as one layer of an anisotropic laminated plate, by measurements on a (100) nickel disk. A mathematical analysis of the torquemeter and constructional details of the strain (pressure) cell are given. A capacitance torquemeter for use in a superconducting split-pair magnet over the temperature region 4 to 300 K has been devised by Birss and Shepherd (13). This torquemeter is capable of accurate, absolute measurements of the torque curves arising from the magnetocrystalline anisotropy of ferromagnetic single crystals in an applied magnetic field. A ''null" method is used in which the rotation against a stiff flat-spring suspension is measured by a capacitance technique. The torquemeter is suitable for use in a wide temperature range (4-300 K) and in high magnetic fields (up to 4 T). A detailed experimental investigation of the system is made and some preliminary results on a basal plane terbium sample and a (111) plane nickel sample are reported. An automatic torque magnetometer has been developed by Larsen and Livesay (79) for use in highpressure hydrogen. It can sustain pressures ranging from vacuum to 200 atm of hydrogen gas a t sample temperatures greater than 400 "C. This magnetometer, which uses an optical lever position sensor and restoring force technique has an operating range of 2.0 x IO3 dyne cm to 1.6 x dyne cm. An accompanying di ital data collection systems extends the sensitivity of 1 X 10- dyne cm as well as increasing the data handling capacity of the system. The magnetic properties of thin films in high-temperature and high-pressure hydrogen environments can be studied using this instrument. Miscellaneous (and New) Techniques. Hendrickson et al. (56) have developed a very novel resonant torsional apparatus for contactless measurements of electrical conductivity and magnetic susceptibility of solids. Owing to its use of modulation spectroscopy, the technique achieves considerable enhancement of sensitivity compared to previous contactless methods. Conductivities in the range mho/cm t o lo4 mho/cm can now be measured by the contactless technique. Measurements of magnetic susceptibility as low as lo-'* can be made. This sensitivity allows for investigation of magnetic impurities as dilute as 1 part in lo7. In samples which display both phenomena of electrical conductivity and magnetic susceptibility, the two effects can be sorted out via analysis of frequency and/or temperature dependence. The present apparatus has potential for considerable improvement. The

Q


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TabTe 111. Magnetic Characterization of Selected Metal and Metal-Oxide Catalysts topic

conclusions and comments

Magnetic characterization of Ni on alumina-graphite substrates: studies on u vs. H I T and coercivity ( H , ) as a function of the reducing (sintering) temperature.

Range of superparamagnetic particle sizes is determined from low field and high field approximations of the Langevin equation. A catalyst with a higher loading of Ni (57.3 wt %) is found t o be thermally more resistant t o the formation of multidomain particles. Work on chemisorption and catalytic activity is in progress. Ferromagnetic component from superparamagnetic particles is separated and their particle size is determined. A catalyst with a higher content of Ni ( 6 7 % ) is found t o be thermally resistant to the formation of single domain anisotropic and multidomain particles. Methanation reaction on sintered samples is reported and the “magnetically structure” sensitive aspects are discussed. Magnetization volume isotherms of adsorbed hydrocarbons and comparison with adsorbed H, indicated the presence of the same surface species NiCH=CHNi for ( b ) (e), and (d). Hydrogenation of adsorbed acetylene ( d ) was studied. Low coverages lead to chemisorption; higher additions caused hydrogenation. Magnetic measurements indicate a surface reaction accompanied by a decrease in the number of bonds between adsorbate and metal surface. IR spectra are discussed. Preparation of Ni/SiO,-Al,O, with preimpregnated Na is described. Magnetic susceptibility and H, adsorption showed that the Ni dispersion was relatively unaffected by the Na treatment and by poisoning of the surface. Several types of hydrogenation and hydrogenolysis were studied. The Curie temp ( Tc ) of Ni is almost independent of particle size for average particle diameters down to 2.5 nm ( 2 5 A ) . Shift in T , occurs in partially reduced samples or on oxygen chemisorption. Consequences of these observations are discussed in terms of chemical and electronic characterization of dispersed Ni catalysts. A theoretical model is described for determination of the fractions of free and associated magnetic ions in solid solutions (such as Coo-MgO) by using the dependence of the Weiss constant on the magnetic-ion concentration. By using thus obtained distribution functions, the adsorption of CO and the oxidation of the adsorbed CO on Coo-MgO and NiOMgO were explained qualitatively. x depends nonmonotically on the metal concentration. The magnetic behavior is probably due to the formation of metal clusters of Pt. The variation of x can be used to estimate the dimensions of the finely dispersed clusters. With all the metals studied, the same regularities were found t o apply for the formation of the crystalline phase in the preparation of the supported catalyst, and, consequently, the dependence of the magnetic

Magnetic and catalytic properties of nickel catalysts for the methanation reaction: studies on u vs. H I T and H , as a function of reducing temperature and effects on methanation activity.

Magnetic and IR measurements on ( a ) CH,, ( b ) C,H,, (c) H,C=CH,, and ( d ) HC=CH, adsorbed on silica supported nickel. Studies over a range of temperature ( - 2 0 to + 25 “C).

The activity of nickel on sodium neutralized silicaalumina: magnetic measurements, hydrogen adsorption, hydrogenation, and hydrogenolysis. Aspects of poisoning with H,S.

Effects of particle size and degree of reduction on the magnetic properties of dispersed Ni catalysts: magnetization and ferromagnetic resonance measurements.

Use of magnetic ion distribution for explaining certain adsorption and catalytic properties of cobalt(I1) oxide-magnesium oxide and nickel(I1) oxide-magnesium oxide solid solutions.

Magnetic susceptibility of catalysts: relation between magnetic susceptibility and metal dispersivity in the Pt-silica gels. Studies on the susceptibility (x) of Pt-silica gels (0.1 to 10 wt % Pt) and temperature (300-650’ K). The temperature dependence (300-600 K ) of magnetic susceptibility of metals (Pt, Re, Rh, and Cd) supported on 7-alumina.

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ref. Yamamura and Mulay ( 1 79)

Everson, Mahajan, Walker, and Mulay ( 4 4 )

Erkelens and Wosten ( 4 2 )

Huang and Richardson (57)

Derouane et al. ( 3 4 a )

Shestakov et al. ( 1 4 6 )

Sverdlova et al. ( 1 5 4 )

Dobrotvorskii et al. (36)


Table I11 ( C o n t i n u e d ) topic

conclusions and comments

susceptibility on the concentration of the deposited metal also were qualitatively the same. The most appreciable quantitative differences exist between metals with an even and an odd number of electrons in the atom. Temperature dependence of the magnetic Electron microscopy and magnetic susceptibility of Gd clusters in Faujasite type measurements of the reduced Gd zeolites zeolites show formation of Gd particles with extremely narrow particle size distribution and diameters < 1.3 nm. These particles are paramagnetic even at 5 K and 1 tesla. ( l o 4 Oe) Magnetism and catalysis A brief review of selected aspects of magnetic properties in relation to catalysis. Emphasis is on the author's work on Ni which shows how to obtain particle size distribution of superparamagnetic particles assuming certain distribution functions. Magnetic and Mossbauer spectroscopic investigations Fe ions added during the preparation of on iron doped sodium-A-type zeolite the zeolite instead of ion-exchange. Superparamagnetic particles (diam. < 100 A ) formed within the zeolite. Magnetic, ESR, Mossbauer, etc. studies on the Preparation is described. The structures formation of highly dispersed iron oxides from of the particles change with varying faujasi t e conditions of calcination. At 600 "C the Fe3+ions give a superparamagnetic species and y-Fe,O, outside the cavities: reactions are not described. Magnetic study of well defined silica supported Preparation of the catalysts is described. Ni-Cu catalysts. Saturation magnetization ( u s ) at 4 K and Curie points showed that a homogeneous alloy is formed. Metallic particle size varied between 6 and 13 nm. Magnetic effects of H, and 0, chemisorption were similar t o bulk concentration in contrast with the surface enrichment in Cu generally found in Ni-Cu catalysts. Hydrogen titration is discussed. Magnetic and Mossbauer spectroscopic studies on Catalyst preparation is described. At the activation of hydrogen on Fe-MgO catalysts. room temperature, H, adsorption caused a small decrease in u s . Above 4 7 0 K, adsorbed H, was activated according t o the reversible redox scheme Fen+ + nH,ds + Fe + nH' with n probably equal t o 0. Magnetic and Mossbauer spectroscopic studies on Decomposition of Fe( CO), in the zeolite the dispersion of iron species in ( a ) Linde 1 3 X initially produced a paramagnetic zeolite and ( b ) in glassy carbon matrices, dispersion of Fe3+ions, which on obtained by the decomposition of organometals. annealing produced a fine dispersion of e-Fe,O, species. These were confirmed by Mossbauer spectroscopy. Addition of ferrocene during the synthesis of glassy carbon gave iron carbides, such as Fe,C. Magnetic susceptibility ( K ) of small Pd particles A new method for the correction of supported on silica gel and alumina at 1 2 0 and thermomagnetic impurities in Pd is 298 K as a function of metal dispersion ( D ) over developed to give the true value of K , a range of 0.1 t o 0.8. The samples are exposed t o 30 kPa of H, for 1800 s at 150 and 298 K which marks the major paramagnetic susceptibility of Pd. The corrected values ( K sp ) decrease linearly with increasing D , and can be extrapolated t o a temperature independent value at complete dispersion, D = 1. This value is said t o be the surface susceptibility, which is found to be the same for all samples. Their preparation is described.

ref.

Schmidt et al. ( 1 3 8 )

J. T. Richardson ( 1 3 3 )

Bara, Brandt, e t al. (5)

Wiedemann, Schmidt, and Gunser ( 1 73)

Dalmon ( 31 )

Dutartre et al. (40)

Mulay e t al. ( 1 04)

Ladas, Dalla Botta, and Boudart ( 7 8 )


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Table I11 ( C o n t i n u e d ) topic Susceptibility and ESR of PdII supported o n Y zeolites by ion exchange: electron microscopy and X-ray diffractometry.

Hydrogenation of olefins, etc., over CrO, jSi0, catalysts: characterization by susceptibility, EPR and UV-visible spectroscopy. Magnetic and Mossbauer spectroscopic studies on Fe and Fe-Co in silicalite and ZSM substrates.

conclusions and comments Particle size and the distribution studies show that not all Pd particles are atomically dispersed. The temperature dependence of a new EPR line (g = 2.16) for the reduced samples gives a maximum a t significant temperatures depending on the particle size. Results are confirmed by susceptibility. The structure, degree of dispersion and valency of Cr in the catalysts were studied. The starting, reduced and used catalysts were studied. Evidence for the forrnation of various Fe-Co, Fe-C, and Fe-0 species was found in the reduced and used catalysts.

author gives a detailed mathematical analysis of the apparatus, its constructional details, and typical results obtained for a stock aluminum sample and anthracene. A variable temperature multimode magnetometer is described by Winter et al. (175) for use with a high field superconducting solenoid in a liquid helium environment. Measurements can be made at temperatures ranging from 1.5 to 300 K. Three modes of operation are possible: integrating fluxmeter, ballistic magnetometer, and variable temperature. The probe permits quick, efficient sample exchange. Constructional aspects for magnetization measurements and for recording the hysteresis curves for SmCoj at various temperatures are given. Smith and Burilla (149) describe a novel Hall effect hysteresigraph which provides a much more rapid measurement of the coercivity of amorphous bubble films than any previously used method. This device utilizes the Hall effect to sense the film magnetization and has sufficient sensitivity and stability that coercivities as low as -1 Oe can be readily measured. Although this device cannot provide an absolute measurement of saturation magnetization, approximate values of this quantity can be inferred from the saturation field indicated by the hysteresis loop. A probe-contact arrangement is employed which permits measurements to be made even on films having an insulating passivation layer. Peuzin and co-workers (127)describe a simple and sensitive apparatus which allows the routine measurement of the magnetization of small ferrite samples using the well-known extraction method. In contrast to the classical extraction method, however, this device makes use of a high-permeability magnetic circuit that serves both to apply the bias field and to collect the sample flux. This design, together with a signal sampling technique, allows an unusually high sensitivity for this type of method (magnetic moment resolution is 5 X Fern). The apparatus is described in detail and a brief theory of its function is given. Finally, the usefulness of the device is illustrated by some measurement results referring to GaYIG spheres that are used in ferrimagnetic resonators. Eaton and Eaton ( 4 0 ~have ) devised magnetic susceptibility balance in which the change in the weight of the magnet is measured. The same information is duplicated in two journals. In their apparatus, Hicorex (cobalt rare earth) permanent magnets are used to construct a magnet with a weight which is within the capacity of standard analytical balances. A NMR type sample tube (5-mm 0.d.) is employed. Using HgCo(SCN), as the standard, three measurements of the gram susceptibility of [Ni(en) ]S203a t 298 K gave x = (10.9 & 0.3) X lo4 (literature v a h e a t 298 K, 10.8 X 10%). The weight change due to the empty sample tube was -5% of the total weight change for [Ni(en),]Sz03and -1.5% of the total weight change for HgCo(SCN)4. An important limitation of the apparatus appears to be the measurement of susceptibility a t various temperatures. T h e moving magnet balance is based on the Rankine principle [cf., Mulay (99, loo)],which is not explicitly stated (and does not appear t o have been recognized) by the authors. Their apparatus and another [Schneider and Ertel (140)] described below are elegantly suited for lecture demonstration and undergraduate instruction. The other apparatus uses a permanent magnet with truncated pole pieces 206R


ref.

Schmidt, Nauman, and Gunsser (139)

Groeneveld et al. ( 5 5 ~ ) Lo, Rao, Mulay, et a1 ( 8 2 )

which give a field gradient away from the central region. In the “pendulum mode”, a solid ferro- (or ferri-) magnetic material is attracted toward the magnet. The displacement is measured accurately on an appropriate scale. In the “bubble mode”, a closed glass tube containing a paramagnetic solution of Ni(N03)2in ethyl alcohol with an air bubble is tilted in the vicinity of the gradient field until the bubble breaks through the “magnetic barrier”. The angle of inclination is measured accurately. The authors (140) show how such measurements, in addition to the mapping of the field gradient can be used to obtain paramagnetic susceptibilities. The original paper should be consulted for understanding t h e beauty of magnetostatic principles in terms of the (Faraday) field profiles, magnetic forces acting on various materials, etc., which have been elegantly described by the authors (140) along with a brief historical perspective of magnetism and conversion from the cgs-emu t o the SI units. A compensation ballistic method and apparatus for thermomagnetic analysis of ferromagnetic catalysts has been constructed by Visokov and Iranov ( 1 6 1 ~ )Curie . temperature in static and dynamic conditions, changes of magnetic properties (magnetic state, Tkthermomagnetic hysteresis, etc.) could be measured. T h e ferromagnetic catalysts were of different particle sizes. Investigations were carried out between 293 K and Tkof the samples, ensuring magnetic saturation. Since the original (Bulgarian) article was not available, we cannot determine if attempts were made by the authors to obtain the sizes of very small catalytically active superparamagnetic particles. Another apparatus is described by Li et al. (80) for the determination of susceptibility in strong fields and for magnetization approaching saturation in polycrystalline ferromagnetic materials. I t can supply a field up to 4500 Oe. By using a compensation method for a specimen of 5-mm diameter, a sensitivity of 1 X G/Oe-V can be achieved. At 300-2700 Oe by using high-purity Ni samples, an accuracy of 1 3 % was obtained for susceptibility measurements. The magnetic properties of rare earth magnets Sm(CoFeC&, Sm(CoFeCuMn)i, and Ce(CoFeCu), were studied by using a pulsed high magnetic field and a n electromagnet by Sat0 and co-workers (136). T h e temperature dependence of magnetization curves of Sm(CoFeCuMn)7both parallel and perpendicular to the c axis were measured a t several temperatures from 4.2 to 600 K. The anisotropy constant K1 of Sm(CoFeCuMn), was also determined at 4.2-480 K. The relation between coercivity H,(V and K , ( V is discussed. The use of a “large drop method’ for measuring the susceptibility of melts is outlined by Seleznev and co-workers (141). Further details of their Russian article were not available to us a t the time when this review was written. An improved viscometer method is presented by Lassocinski and Zeman (79a) for the determination of the magnetic susceptibility of a liquid with a complete exclusion of the dissolved oxygen effect. The method is excellent even in determining the magnetic susceptibilities of diamagnetic liquids, giving results accurate to within 10.05%. T h e influence of air (or oxygen) is also discussed. Errors in Magnetic Measurements and Reference


Materials for Calibration. The influence of real experimental conditions on the accuracy of the Faraday method for susceptibility measurements is discussed by Napijalo and Zegarac (114). They point out that the measurement of the magnetic susceptibility by the Faraday method is usually carried out by neglecting the effect of dimensions of the sample, the sample holder, and the rod supporting the sample holder in the magnetic field. The theoretical analysis of the method presented shows that, owing t o the effect of these dimensions, the forces, measured in the corresponding experiment, do not have their maximum in the positions corresponding to the maximum H.dH/dz, as usually assumed. T h e positions of the force maximum are different for the sample holder, for the investigated, and for the standard sample. The results are presented of measurements performed with CuS04.5H20 and with graphite in two series of experiments which entirely confirm the conclusions of the theory. T h e existence of this effect can substantially affect the susceptibility measurements. Reference should be made to earlier reviews, etc. which outline other relevant corrections, discussed by Martin et al. and Stewart [cf., Mulay (100) and Mulay and Mulay (110, I l l ) ] . Zell e t al. (181) discuss the elimination of the magnetic contribution of the sample holder in the Faraday balance. They show that the force of the sample holder of a Faraday-magnetometer can be reduced below the sensitivity of the balance a t all temperatures and fields by shaping both the holder and field symmetry, with respect to a horizontal plane. Better reproducibility, smaller errors, and considerable savings of labor are obtained. Zolotarevskii and Snezhnoi (185)show possibility for the experimental determination of the magnetic susceptibility of t h e paramagnetic matrix component xo in the case when the quantity of ferromagnetic inclusions can be varied. The equation defining the amount of ferromagnetic phase P, is analyzed, transformed, and graphically presented in coordinates P, vs. susceptibility x. The interception of the straight line Pa vs. x when extrapolated to P, = 0 on the x axis gives the respective value of xo in magnetic fields strong enough to saturate the sample. The method was experimentally tested with Mohr’s salt containing Fe-Si (3%) alloy powder in 4.52, 6.85, and 8.45 kOe fields. Experimental points were well within the straight line, the maximum error being 1-2%. Similar experimental results were obtained with the austenitic steel N25G3, containing the magnetic phase martensite, formed during mechanical deformation. Measurements of susceptibilities a t low temperatures for three sulfates K2A2(S04)3, where (A = Mn, Co, and Ni) are reported by Waszczak, (169). These compounds will be most useful as reference materials for the calibration of all types of magnetometers (Faraday, Gouy, V.S.M., SQUIDS, etc.). He reports that these samples follow Curie-Weiss behavior from 300 K to approximately 4.2 K with antiferromagnetic 8 values near 10 K. T h e effective moments obtained are 5.62 pB for A = Mn, 4.21 pB for A = Co, and 2.94 pB for A = Ni. The Mn compound was also measured from 4.2 to 1.6 K; the data suggest the onset of antiferromagnetic ordering a t 1.75 K.

APPLICATIONS Magnetic Titration. Seltmann and Gunsser (143) describe a typical application based on redox and substitution reactions. They discuss several model reactions. In one instance, nickel was determined by titration of paramagnetic Ni(NH3)62C with 0.5 M KCN to give diamagnetic Ni(CN)42-. The determination of I- by titration with 0.5 N K2Cr207/H2S04 is based on the difference in the paramagnetic properties of Cr2072-and [Cr(H20)6]2(S04) . The magnetic susceptibility was measured by using a Gouy Lalance. The magnetic titration was evaluated bv ulottine the force in magnetic field vs. the reciurocal of the ”total vohme. Magnetokinetics of Oxidation and Diffusion. In continuaGon of their earlier work, Marusak and Mulay (91) studied the magnetokinetics of oxidation of pyrite, (FeS2),as a function of particle size (90-120 wm) and temperature, T (400-500 “C). In addition to considering the formation of u and y FezO , the formation of Fe2(S04)3and superparamagnetic a-Fepd3 was studied. The yield of the sulfate was found to increase with decreasing particle size of FeS2. From the slope of the magnetization (M) vs. time ( t ) curves for the oxidation of pyrite, values of (dM/dt) were obtained for particles in the range 150-250 pm. From the plots of (dM/dt) L

vs. 1/T an activation energy of -7 kcal/mol was obtained for the reaction: ( 1 / 2 ) cu.Fe203 + 2SO2 FeS + (11/4) O2

-

The value (7 kcal/mol) thus obtained compared favorably with the values reported by earlier workers using thermogravimetric analysis. The structures of various components involved were identified by using Mossbauer spectroscopy and X-ray diffraction. In another application, Marusak and Mulay (89,901 studied the magnetokinetics of diffusion of iron atoms during the X phase transition in FegSlo. The antiferromagnetic to ferrimagnetic phase transition in a pyrrhotite (FegSlo),which occurs around 480 K is known as the X transition, apparently because of the shape of the thermomagnetic curve in which the magnetization (a) is plotted against the temperature (2‘). These authors (89, 90) studied the magnetization “growth curves” a t a fixed temperature while approaching the transition around 480 K. The “growth curve” yields values of (dM/dt), which in turn was correlated to (NvA)/t) and ( N v P ) / twhere ) NV(*)and NVm)refer to the number oh vacancies (of iron atoms) in the sublattices A and B, respectively, of FegSlo. Using absolute rate reaction theory, the authors (89, 90) obtained a constant ( d ) , along the c axis for the diffusion coefficient of iron atoms into the vacancies (and vice versa); cm2/s in fairly reathe value for d was found to be sonable agreement with values obtained from more sophisticated radioactive tracer techniques. T h e X transition was also elucidated by Mossbauer spectroscopy. Other Magnetokinetic and Reaction Studies. Khundkarr and co-workers (69) have studied the reactions of H2S with Fe2O3 and FeO under different conditions and the magnetic properties of the products were determined. Possible modes of the reactions are outlined. Fe2S3formed from highly ferromagnetic y-Fe203 has less tendency to decompose into FeS and FeSz as compared to the Fe2S3formed from ignited Fe20B. FeS is the main product of the reaction between FeO and H2S. The unusually high magnetic susceptibility of the reaction product is explained by the presence of a small amount of either ferromagnetic Fe304 or Fe7S8. T h e FeO phase used in the reaction was produced in situ by the decomposition of FeC204. T h e successive decomposition of (diamagnetic) MgSO4:xHzO where x = 0, 1, 2 . . . 7 has been followed by Skokanova et al. (148) using magnetic susceptibility techniques. The observed values for changes in susceptibility (Ax) were found to differ from those calculated on the basis of the additivity law. This disagreement can be explained by the presence of the thermally independent Van Vleck’s polarization paramagnetism xp,which is calculated for the individual hydrates of MgS04.iH20for i = 0, 1, . . . 7. The part of the polarization paramagnetism xp,of the overall values of x c, due to the effect of water of crystallization is determined. d n the basis of this information, the deviation from the spherical symmetry, caused by hydration of the MgS04 mol., is interpreted. Neumeister and Jaeniche (117) have investigated the formation of copper oxide (Cu150) using a dual purpose thermomagnetic and thermogravimetric apparatus. T h e oxidation of C u 2 0 and Cu was studied a t 200-540 “C. During oxidation of Cu20,CuO is formed exclusively if the concentration of Cu vacancies in the C u 2 0 is high. If the C u 2 0 samples are tempered before oxidation, both CuO and Cu1,,O (Cu3O2) are formed. The ratio of both oxides depends on temperature and oxidation time. Periodic changes in the composition of the layer are explained by rearrangements by which mechanical stresses during oxidation are removed. The oxidation law: Am t” with n K0.5 (e.g., cubic laws) is to be expected if a concentration gradient of Cu vacancies is formed within Cu20 during the preparation. During oxidation of Cu, the oxide Cu3O2 is observed up to 360 “C. If evaporated Cu layers on quartz are oxidized a t 200 “C, the oxide layer is formed stepwise. The primary product is Cu20 which later is transformed into Cu302. Finally Cu302disappears completely, whereupon CuO is formed. The range of stability of Cu302 is greater than was found previously. Bauer and Baranowski (8)have developed a magnetic microdevice for the study of formation and decomposition of NiFe hydride when Fe is added to Ni in high pressure hydrogen up to 20 kbar. The device consists of a sample holder with fixed measuring coil, a mobile controlling coil and a n embedded SmCo5 magnet to supply the external field. The hydride

-


207 R


Table IV. Selected References on Magnetic Studies on Carbon topic

conclusions: comments

ref.

Effect of interlayer interactions on the diamagnetism The temperature dependence of x of pre- Volpilhak and Horau (16 3 ) of graphitic ribbons: discussion of 2 and 3 graphic carbons is calculated by dimensional models in terms of magnetic London’s theory applied to a 3susceptibility ( x ) dimensional lattice. In this case the x per mass is proportional to the ribbon width ( L )when the lattice is smaller than 100 A and reaches a constant value when L > 300 A . The critical L values are a function of P o / ? ’ , where the two resonance integral parameters describe the interaction between 2 C atoms in the same layer and in 2 neighboring layers. The parameterization of the diamagnetic susceptiA model involving discrete energy levels Volpilhak and Horau ( 1 6 4 ) bility-temperature curves for pregraphitic carbons is given for the parameterization of the (ribbon width, 30-100 A). Comparison of magnetic susceptibility of pregraphitic experimental results and a theoretical model. carbons (graphitic ribbon width 30-100 A ) as a function of temperature. The agreement achieved between calcd. and exptl. results deteriorated when the size of the samples was > l o 0 P, because of the interactions between graphitic planes involving nonlinear variations. The analogy between expressions involving continuum and discrete levels could be related t o the analogy of magnetic susceptibility curves as the no. of arom. rings increases until the graphite structure is reached. Effect of density fluctuations on the physical A number of Dhvsical DroDerties. such as Carmona and Delhaes ( 2 0 ) properties of disordered carbon. paramagnetic susceptibiiity, chemical composition, density, specific heat of an anthracene char were investigated during the carbonization process. A simple physical picture based on density fluctuations is proposed to explain the observed results. Use of electronic properties for characterizing The use of electrical conductivity ESR- Wang et al. ( 1 6 7 ) structural features of carbon materials. spectral, and magnetic susceptibility measurements for studying crystal defects, the density and the degree of orientation of crystals in carbon materials is discussed. EPR spectroscopy and magnetic susceptibility Studies on natural and a synthetic Paersch et al. ( 1 2 2 ) of graphites at high temperatures extruded graphite are reported. The anisotropy of the polycrystalline graphites was smaller than that of a monocrystalline graphite. The physical meaning of the degeneracy temperature derived was not clear. [This is explained by Mulay et al. See ref. ( 102a). A lower degeneracy temperature means a more “metallic character]. x was calculated from a simple density of states model. The results are explained on the basis of a smaller band overlap in the modified band structure. Low temperature magnetic and thermal properties Cormona et al. ( 2 1 ) The magnetization and magnetocaloric of an amorphous carbon. effect of amorphous carbon, produced as anthracene chars at >1500 ” C were studied. The magnetization measured at 0 . 1 - 4 . 2 K in fields of 0.8-70 kOe follows the Currier-Weiss law with B = 0.8 and c = 38 X The sp. heat between 0.15 and 2 K was also detd. The magnetic measurements showed that the char behaves as a spin glass. Pshenichkin et al. ( 1 3 2 ) Temperature dependence of the diamagnetic The temperature dependence of x of susceptibility (x) and electronic structure of various electron acceptor additives ( B carbon fibers with additives. (Fibers made and F ) is reported. The x of B-doped from acrylic, rayon fibers, and polyacrylonitrile) fibers is increased with increasing B content. Laminated graphitized fibers from polyacrylonitrile with MoCl,, NiCl,, and CuCl, gave increased 208R

ANALYTICAL CHEMISTRY, VOL. 52, NO. 5 , APRIL 1980


Table IV ( C o n t i n u e d ) conclusions: comments

topic

Diamagnetic susceptibility, Hall effect, etc., studies on boron doped turbostratic graphites.

Magnetic susceptibility and structural formation of high modulus carbon fibers doped with boron.

Temperature-field dependence of the magnetic susceptibility of carbon materials ( 2 papers). Magnetic susceptibility of graphite-potassium intercorlation compound C,K.

electrical conductivity, which is related to the formation of charge transfer complexes with metal chlorides. Kawamura el. al. (65) The effect of boron doping on the galvanomagnetic properties and diamagnetic susceptibility of turbostatic carbon was studied. B doping can influence the Hall coeff. of the sample, but the neg. magnetoresistance is insensitive to boronation. The changes in diamagnetic susceptibility are related t o the depression of the Fermi level. Fialkov et al. ( 4 8 ) Elastic modulus and density of carbon fibers are discussed. Fibers containing 0.3 to 0.5% B have a layered structure parallel t o the fiber axis. Addition of B changed significantly the electronic structure of carbon fibers which was confirmed by diamagnetic properties. The diamagnetic susceptibility of carbon fibers decreased sharply and the temp.-dependence of the diamagnetism decreased with increasing B content which suggested a maximum B concentration related to the formation of a saturated solid solution. These appear to be a general review, the Pesin e t al. (125, 1 2 6 ) English translation of which was not available, Koike e t al. ( 7 0 ) The critical temperature T,, and the angular and temperature dependences of the upper critical field H c 2 in highly oriented pseudo-single crystals of C,K have been studied by using a magnetic susceptibility measurement. The magnetic susceptibility abruptly changes around 139 mK at zero field. The angular dependence of H,, shows a very large anisotropy.

formation can be followed by measuring the changes in magnetic moments of thin foil samples. Crabtree and Moll (28) have investigated the temperature, pressure, and magnetic field dependence of the reaction: Ni(C0)4 Ni 4CO

-

+

They did not find any evidence for an “oscillatory” dependence of the rate on the strength of the magnetic field. I t should be noted that studies on the effects of magnetic fields on chemical (and biochemical) reactions is attracting considerable attention. In many instances, these effects are measured in terms of the changes in magnetic susceptibility (or magnetization) of the reactants and products. T h e chemical abstracts continue to record an ever increasing number of such studies. A typical example is given by Rowe e t al. (135),who have briefly surveyed earlier work on the system Fe203(haematite) Fe 0, (magnetite) Fe (iron) at (C550 “C). T h e authors studied the reduction of NiO to Ni using a Cahn type thermomagnetic balance [cf., Mulay ( l o o ) ] .No significant effect of an external field on the above reduction was detected. However, Mulay et al. (103) have shown by thermodynamic calculation and experiment that an external field does affect chemical equilibrium if the difference between the net susceptibilities of reactants and products is very great. Analysis of Gases and Vapors. Twisselman and Gast (159) have devised a lightweight and compact paramagnetic gas analyzer for oxygen with short response time, which incorporates several new concepts. The magnetic susceptibility of the gas is measured by admitting a laminar gas flow to flat test bodies in a narrow gap between parallel poles of a magnet; t h e pressure differences arising from the different partial pressure of oxygen in places with different magnetic field strengths are measured with a magnetic torsion balance. In optimized geometry, the interference moments disappear. The

-

-

ref.

error arising from flow forces is 10.05% oxygen for flow rates of 5-30 L/h. The 90% response time is 0.5-1 s. The hollow test bodies made of nonmagnetic Au-Ni foils are corrosionresistant. An improved viscometer method has been developed by Sueoka and Ikeda (153)for the determination of the magnetic susceptibility of a paramagnetic gas and found to be of use in the analysis of a paramagnetic gas mixed with a diamagnetic gas. T h e magnetic susceptibilities of oxygen and NO were determined to within &0.5% using a saturated solution of NaCl as the working liquid. Sharnopolskii (145) has obtained a patent for his thermomagnetic compensation type gas analyzer. T h e gas analyzer consists of a measuring chamber in the form of a bracket-shaped gas channel consisting of two branches (in one of which a sensing element is located), a device for generating a compensation flow of a thermal convection, and a measuring device. To make possible the compensation a t any concentration of examined component, the device generating the compensation flow was located in the branch of the gas channel with the sensing element. This description of the patent does not clarify the magnetic principles involved. Tveryanovich (156)describes an improved pendulum magnetometer suitable for measuring the susceptibility of weak magnetic materials and paramagnetic vapors. Sealed quartz ampules laced in a Pt furnace were used for measuring the susceptigility of vapors a t 0.1--30 atm. The susceptibility of amorphous AszSe was determined by using this apparatus, which appears to be useful for quantitative analysis. New techniques for the quantitative determination of dissolved oxygen have been recently developed which are based on magnetic susceptibility measurements. In one instance, the oxygen uptake and release by green algae induced by light absorption or deprivation has been studied by Oman and co-workers (121). These authors have constructed a device for automation of both the simple and the differential magANALYTICAL CHEMISTRY, VOL. 52, NO. 5, APRIL 1980

* 209 R


netic diver balance. By using a mechanically chopped laser beam and double-beam system, a large proportional sensitivity of the controller and considerable stability over a relatively long period of time were attained. The inherent sensitivity of the balance was retained, and automatic measurements for several days were made possible. The applicability of the device was tested on a differential magnetic diver balance by measuring the change in reduced weight during a histochemical reaction and by measuring oscillations in oxygen uptake and release by green algae. Delpuech et al. (34) have outlined a technique for the determination of magnetic susceptibilities, Axv of oxygen by using a field-axis variation NMR technique. This technique was applied to the titration of oxygen in benzene or hexafluorobenzene solutions contained in sealed sample tubes under pressures of 1-6 atm. The validity of the method was checked by usin both nuclei of each solvent, Le., ‘H (at 90 and 250 MHz) ancf13C {‘HI (22.63 and 62.86 MHz) for ‘?F (84.67 and 250 MHz) and 13C (19F} for C6Fs. The sensitivity limit is ex ected to be AxI = 0.03 X 10 and [O,] = m ~ l - d m (for - ~ H or 19F nuclei). This method may be used for a remote control of the oxygen content in solvents for oxygen pressures higher than 1 atm. Studies of aqueous solutions of NiCl, showed that susceptibilities of paramagnetic compounds in solution can be measured by NMR spectroscopy by using the method of simple substitution. These studies by Chopard-Casadevall (26) allow determination of the value of the calibration factor ( A )relative to the combination of tube and probe. Magnetic susceptibilities of Co salts in organic solvents were determined by using this method. The susceptibility of a paramagnetic ion is not modified by the presence of a substrate undergoing pseudo-contact effects due t o the presence of this ion. This method is particularly useful to determine the paramagnetism of air- and water-sensitive solutions. Analysis of Magnetic Species in Various Systems. The concentration of various inclusions in synthetic diamonds has been carried out by Bogatyreva and co-workers (14) using magnetic susceptibility measurements. The results were found t o agree well with those obtained by neutron activation analysis on inclusions such as Mn, Ni, Fe, Cr, Co, Na, and La. Concentrations of ferromagnetic and Paramagnetic species in synthetic diamonds and their effect on absorption activity was further investigated by Bogatyreva et al. (14). These workers point out that such measurements can be used to magnetically separate diamond powders into fractions with uniform composition. Ergin et al. (43) report a magnetochemical study of the solvation of alkali-metal halides in acetamide. They show t h a t the ion--solvent bond is less directional than the solvent-solvent (hydrogen bond). Candea and co-workers (18a) have analyzed the diamagnetic and paramagnetic components in amorphous silicon. They conclude that the susceptibility of the crystal rather than the amorphous phase is anomalous. Phase-Transitions. As outlined in our earlier reviews, the work by Mulay’s group (cf., 105-112) successfully used magnetic susceptibility (and EPR) to elucidate the electronic and structural phase transitions in the oxides of titanium (TinOSn.J. Work along these lines has been continued by other workers. For example, Marezio et al. (88) report a detailed study on single crystals of Ti509 The interpretations are based on the disordering of the constrained antiferromagnetism in Ti3+-Ti3+ pairs proposed by Mulay e t al. (cf., 105-110). The transition from Pauli paramagnetism to band ferromagnetism in very thin nickel films is reported by Bergmann (9). Thermomagnetic analysis of magnetic phases of natural pyrrhotites has been studied by Hucl and his associates (59). S t u d i e s o n Oxygen a n d Ozone. Mulay and Keys first showed t h a t two (or more) O2 molecules in the triplet state adsorbed on the surface of y-alumina dimerized to the “04” species (or other polymeric species) with subnormal magnetic moments arising from weak antiferromagnetic coupling [cf., Mulay and Boudreaux (102b)l. Gregory (53) has shown that oxygen adsorbed on porous Vycor glass, a heterogeneous substrate, displays properties of an amorphous antiferromagnet. However, no antiferromagnetic ordering transition is seen for submonolayer coverages in the temperature range studies (1.S-95K) although these coverages have paramagnetic Curie temperatures as large as -50 K. In another paper, Gregory (54) discusses experimental studies on the magnetic susceptibility of adsorbed phases of oxygen. The observed

c&;

P

210 R

ANALYTICAL CHEMISTRY, VOL 52, NO. 5, APRIL 1980

behavior is seen to be influenced both by the restricted geometry of the oxygen films and by microscopic properties of the substrates. Borman et a!. (14a) describe the appearance of a “ferromagnetically” ordered monolayer of oxygen on the surface of gold. The interaction of nitrogen on the gold surface and the effects of a magnetic field are considered. Magnetic properties of ozone (03), such as the magnetic moment of its first excited state have been reported by Mack and Muenter (86),who used molecular beam spectroscopy to study the Stark and Zeeman effects in 03.Nicol e t al. (118) discuss various phases of oxygen. Applications to Bioscience. Pauling (123)has shown that a simple theory of the diamagnetic anisotropy of noncyclic planar groups of atoms with resonance structures (mobile electrons) leads to the value -5.36 x lo4 cgs-emu for the molar diamagnetic anisotropy of the peptide group. Pauling’s outstanding contributions to our understanding of molecular diamagnetism, and their applications to numerous molecular systems have been reviewed by Mulay and Boudreaux ( 1 0 2 ~ ) . In his early work, Pauling showed that the observed diamagnetic anisotropy of proteins may be attributed in part to induced ring currents in the aromatic side chains of residues of phenylalanine, tyrosine, and tryptophan. Worcester ( 177), however, has recently pointed out that polypeptides that do not contain aromatic residues, including poly(L-glutamicacid), poly(?-ethyl-L-glutamate), and poly(L-lysine hydrobromide), also show magnetic orientation. Pauling (123) has attributed this to the diamagnetic anisotropy of the peptide groups, which are planar because of the resonance between two valence-bond structures:

Worcester assumed for the value of A K (the difference in molar magnetic susceptibility with the magnetic field normal to the plane of the group and that with the field in this plane), cgs emu/mol equal to that the unreliable value -8.8 X reported by Lonsdale for the carboxylic ester group. An experimental value, from recent measurements on poly(yethyl-L-glutamate), is -5.2 f 0.4 X lo4, which agrees well with Pauling’s value, calculated from the Pauli expression; taking into account a correction for the incomplete resonance of the peptide group. Reference should be made to Pauling’s original papers to understand the beauty and simplicity of his resonance theory which gives remarkably good agreement between the calculated and observed values of the diamagnetic anisotropy (S). Cerdonio (22)has reviewed the magnetic susceptibility and structure of metalloproteins and model systems. In another article (23), he discusses the room temperature magnetic properties of oxy- and carbon-monoxyhemoglobin. We quote below the abstract of his paper. “The magnetic susceptibility and the density of human oxy-(HbOz) and carbon-monoxyhemoglobin (HbCO) solutions of various concentrations have been measured a t room temperature, with pure water used as a calibrant. Solutions of unstripped and stripped HbOz a t p H 7.2 in unbuffered water solvent were always found to be less diamagnetic than pure water, whereas solutions of HbCO in identical conditions were always found to be more diamagnetic than pure water. After correcting for concentration-dependent density changes and assuming the HbCO samples to be fully diamagnetic, the paramagnetic reduction of the diamagnetic susceptibility of HbOz corresponds to a molar susceptibility per heme (xMheme)of 2460 f 600 X lo4 cgs/mol.” Reference should be made to our last review (112) in which we discussed the research carried out by Pauling and other workers in this area. Philo (128) has published a dissertation dealing with the “magnetic susceptibility of biomolecules”, with discussions of (1) Kinetics of the hemoglobin-CO reactions, (2) temperature dependence of the diamagnetism of water, and (3) susceptibility of phospholipid bilayer dispersions. Barbanera and co-workers (6) have set up a second-derivative gradiometer together with an RFSQUID magnetometer for the detection of magnetic fields generated by the human heart. A preliminary version of the device has successfully worked without a magnetically shielded room in a noisy environment. A first balancing of the ra diometer has been attempted. The effect of the r e s i j u i ambient 50-Hz magnetic field has been reduced electronically.

MAGNETIC SUSCEPTIBILITY -

Table V. Frequently Used Symbols, Nomenclature, and Factors Used for Conversion from the cgs-emu (Gaussian) to the mksa-SI (Systemme’ International) Units in Magnetism. (For complete details, see chapters on “Units in Magnetism” by Mulay in Ref. I 0 2 ( a ) o r 1 0 2 ( b ) ) = 3.14;4n = 12.56; 114n = 0.0796; 1 0 3 / 4 n = 79.61

n

A = Ampere ( o r “Ampere turns”)

k g = kilogram

B = Magnetic flux or induction 0 or p B = Bohr Magneton (3hi4nrnc) c = velocity of light

m = meter (= 100 cm) (“m” also used for “mass” in general or “mass of the electron”) A4 or I = Magnetization mol (or M ) = Molar (or Atomic) N = Avogadro’s number Oe = Oersted 0 = Flux Quantum (hci2e) p = density (gicm’ or kg/rn’) s = second; u = Magnetizationig T = Tesla u = volume Wb = Weber (unit for magnetic pole) = 10’ Maxwells (unit for B)

cm = centimeter

x = general symbol for magnetic susceptibility e = charge on the electron g = gram G = Gauss h = Planck’s constant (sometimes used for henry, the unit for inductance) H = magnetic field (i.e,, intensity or strength of the field; sometimes used for henry) k = Boltzmann’s constant K = susceptibility per unit volume I

An important point that should be noted at the outset is that in emu, the permeability of free space p = 1 and is dimen. sionless, whereas in SI p = 4n X kg ms” A-*. However the relative permeability, p , = ( p o b s / p u )equals one and is dimensionless in both systems. Conversion from Gaussian to SI Units Multiply the number for Gaussian quantity unit flux density, B G magnetic field strength, H

Oe

103/4n

volume susceptibility, (dimensionless)

emu/cm3

4n

K

mass susceptibility, xp molar susceptibility,a

To obtain the number f o r

by

SI quantity

flux density, B

unit T = Wb/m2

magnetic field strength, H rationalized volume susceptibility,

Aim dimensionless

K

4n x 10-3 rationalized mass susceptibility,

emu/g (E cm3/g) emuimol (E cm3/mol) 4 n x

K~

rationalized molar susceptibility,

m3/kg m3/mol

Kmole

¬e

magnetization, M or I (per cm’)

G or Oe

magnetization, M

103

magnetization, M

Aim

1 pB/atom or pB/form. unit, etc.b

magnetization, M

pB/atom for pB/form. unit, etc.b

magnetic moment of a dipole, p

erg/G or Oe.cm3

magnetic moment of a dipole,

Am

demagnetizing factor, N

dimensionless

10-3

m

1/4n

rationalized demagnetizing factor, AT dimensionless

a Also called atomic susceptibility. Molar susceptibility is preferred since atomic susceptibility has also been used to refer t o the susceptibility per atom. “Natural” units, independent of unit system. However, the numerical value of the Bohr magneton does depend o n the unit system.

A typical magnetocardiogram and a simultaneously recorded electrocardiogram are shown. Reference should be made to an earlier section on analysis of dissolved oxygen which depicts a few selected applications on the determination of oxygen in biosystems. Dooley and co-workers (37) have remeasured the magnetic susceptibility of Rhus uernicifera laccase over the temperature range 5-260 K. In contrast to the previous results linear x vs. T’behavior was observed. The susceptibility of Limulus polyphemus oxyhemocyanin has also been measured in the range 5-260 K. Only weak paramagnetism, attributable to dissolved oxy en and a small amount of paramagnetic impurities, was okerved. Analysis of the data establishes a lower limit of 550 cm-’ for J , consistent with the earlier work. The temperature dependence of the susceptibility of laccase is uantitatively accounted for by the presence of 2 paramagnetic u ions (types 1 and 2) per enzyme molecule. Curie law behavior a t low temperatures rules out significant interaction between the 2 Cu types, indicating that these redox centers are well separated (several angstroms) and are not connected by bridging ligands. Formulation of the type 2 site as binuclear Cu(I1) required J 2 500 cm-’. Moss and his associates (97)have investigated the susceptibility of cytochrome oxidase in the 4.2 to 1.5 K ran e. Sixteen low temperature measurements on 8 indepenfent (beef heart) cytochrome oxidase samples from 2 separate laboratories yielded magnetic sus-

8

ceptibility data compatible with a model of spin-coupled Fe and Cu ions. The data in the 1.5-77 K range match those attained at higher temperatures and the predictions of the spin-coupled model. Measurements of reduced samples confirm the high spin nature of 1 Fe atom. No obvious uncoupling of the antiferromagnetic Fe--Cu interaction is detected in partly reduced samples. Direct evidence for antiferromagnetically coupled Fe(III):Cu(II) pair in cytochrome oxidase has been obtained by Tweedle and co-workers (157). The enzyme is shown to possess 2 magnetically isolated spin (S = centers and spin-couples (S= 2) center. The S = 2 center is said to arise from an antiferromagnetically coupled pair Fe:Cu binuclear complex of total S = 2 with -J 2 200 cm-’. A thorough interpretation of magnetic data is given which leads to a fully consistent picture. As analogues of Co(II1) complexes of bidentate azotyrosine in proteins, several bidentate azophenol complexes of Co(I11) were prepared by White and Legg (171). These were characterized by magnetic susceptibility, visible spectra, and proton magnetic resonance. A detailed description of the stereochemistry was possible in one of the mixed ligand complexes. These model systems are being investigated by magnetic and other probes in a program involving the site specific modification of proteins with substitution inert metal ions. Kinetic and magnetic properties of Co(II1) ion in the active site of carbonic anhydrase has been studied by Shinar ANALYTICAL CHEMISTRY, VOL. 52, NO. 5, APRIL 1980

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and Navon (14th). T h e oxidation of Co(I1) and Co(II1) is found to be inhibited by specific inhibitors of carbonic anhydrase. Reduction reactions with BH4- and dithionate ion are discussed. T h e Co(II1) ion is the corresponding carbonic anhydrase and Co(II1) carboxypeptidase A was found to be diamagnetic, which indicated a near octahedral symmetry. An unusual investigation of magnetic iron particles (ferrofluids) introduced in the tissue, combined with a study of microwaves and lasers has been proposed as a combined test model for investigation of hyperthermia treatment of cancer. This work is described by Goldmann and Dreffer ( 5 1 ) . Magnetic Characterization a n d Activity of Catalysts. An important problem especially in heterogeneous catalysis is the characterization of the catalyst (that is, the active catalyst as well as the support and any components formed between these two) a t the macro- and microscopic levels and then to establish a correlation between the properties of the catalysts and their activity with respect to one or more reactions. Magnetic parameters studied as a function of the field (H) and temperature (7') provide an appropriate avenue for such studies, especially with regard to transition metal and metal-oxide type catalysts (including the rare-earth type materials). Interest in magnetic characterization of a wide variety of catalysts continues to grow. Because of limitations of space we have compiled succinctly a selected list of examples in Table 111. In addition to the selected citations in Table 111, reference should be made to a n excellent review on supported metal crystallites by Wynblatt and Gjostein (178) who discuss magnetic properties and structure of small particles. Reference should also be made to the following: (i) a chapter by Selwood (144)on the effect of a magnetic field on the catalyzed nondissociative parahydrogen conversion rate on catalysts such as alumina, lanthana, lutecia, yttria, the paramagnetic rareearths, chromia, cobalt monoxide, manganese monoxide, chromium dioxide, europium monoxide, and metallic nickel; (ii) a series of specialist periodic reports on Catalysis [Senior reporter Kemball (SS)], which review work up to 1977 on (a) catalysis of well-defined metal surfaces and nonmetallic substrates, (b) reactions of hydrocarbons on alloy and bimetallic catalysts, (c) catalysis on faujasite structures, (d) reactions on metal sulfide catalysts, and (e) the hydrogenation of CO on heterogeneous catalysts. M a g n e t i c C h a r a c t e r i z a t i o n of Carbon. Many oxides, such as A1203 and SiOz have been used for several years as supports for metal (or metal-oxide) catalysts. In recent years, carbon has attracted considerable attention as a support for catalysts [Walker and co-workers (166)] and has found numerous applications in commercial catalysts. Different forms of carbon such as the graphite, graphitic carbons, and "glassy" carbons have unusual structural and electronic properties. A number of papers on this topic in relation to the technological applications of carbon continue to appear in the journal "Carbon" and in a series of volumes, entitled "The Chemistry and Physics of Carbon". In the writers' magnetics laboratory at The Pennsylvania State University, work is in progress (104) on the characterization of carbons doped with various additives and on metal catalysts supported on carbon. In view of the growing interest in this fascinating material, we have compiled a selected list of references, dealing especially with the magnetic characterization of carbon and some aspects of its electronic theory, Table IV. Symbols, nomenclature, and conversion factors are given in Table V.

OBITUARY We regret t o announce the untimely demise of Laurence A. Marusak a t the age of 26. Dr. Marusak, who did his doctoral research with one of us (L.N.M.), made excellent contributions to magnetics research on the Fe-S system (89-91 ).

ACKNOWLEDGMENT We thank Dawn Gates, Kathy Ishler, Lois Annechini, Sandy McBride, Pat Tate, and Jeannie May for their cheerful assistance in typing our manuscript efficiently and in helping us meet the manuscript deadline, The work cited in Ref, (82) was by the "" Department Of Energy 'Ontract DE-AC-22-79 PC10350 to L. N. Mulay a t The Pennsylvania State University. A N.S.F.-Erg traineeship supported the 212R


research cited in references 89, 90, and 91. LITERATURE CITED

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Anal. Chern. 1980, 52, 2 1 4 R - 2 5 8 R

Mass Spectrometry A. L. Burlingame" and Thomas A. Baillie Biomedical Mass Spectrometry Resource, Space Sciences Laboratory, University of California, Berkeley, California 94720,and School of Pharmacy, University of California, San Francisco, California 94 143

Peter J. Derrick Department of Physical Chemistry, La Trobe University, Melbourne, Victoria, Australia 3083

0. S. Chizhov Laboratory of Physical Methods of Analysis of Organic Compounds, N. D. Zelinsky Institute of Organic Chemistry, Academy of Sciences of USSR, Moscow I179 13, USSR

OVERVIEW T h e chronicle of achievements involving innovative uses of mass spectrometry in investigations of both molecular structure and function forms an impressive testament to the value of this technique in the fields of chemistry, biology, and medicine. The great utility of mass spectrometry is independent of the atomic and molecular constitution of the substances being analyzed, provided that these substances (whether pure compounds or components of highly complex mixtures) can be transformed into gas-phase positive and negative ions which retain the elemental and structural composition of their neutral parent molecules. T h e inherent sensitivity and accompanying specificity of mass spectrometry remain unsurpassed by other physicochemical techniques for the qualitative and quantitative analysis of a wide spectrum of molecular structures. Only radioimmunoassay (RIA) procedures rival mass spectrometry for quantitative applications in those situations where a unique substrate is to be considered to which a favorable antibody exists. In truth, these two ultrasensitive techniques are complementary: for relatively small stable substances, mass spectrometry has the clear advantage in cases where relatively low sample throughput is acceptable, while for unstable and/or larger biological substances, RIA is favored and has high throughput capacity. 214 R

0003-2700/80/0352-214R$05.00/0

The father of the field, J. J. Thomson, clearly stated the salient advantages in 1913 (A5): . . . "I have described at some length the application of Positive Rays to chemical analysis; one of the main reasons for writing this book was the hope that it might induce others, and especially chemists, to try this method of analysis. I feel sure there are many problems in Chemistry which could be solved with far greater ease by this than by any other method. The method is surprisingly sensitive-more so even than that of Spectrum Analysis, requires an infinitesimal amount of material and does not require this to be specially purified: . . ." [later ( A 6 ) ]''. . . the rays are registered on the photograph within much less than a millionth of a second after their formation, so that when chemical combination or decomposition is going on in the gas in the tube, the method may disclose the existence of intermediate forms which have only transient existence, as well as that of the final product, and may thus enable us to get a clearer insight into the processes of chemical combination." With sometimes considerable analogy to the experiences of the Three Princes of Serendip, the practice of mass spectrometry entails creation of ions, separation of ions, and measurement of ions or, if one likes, sample preparation, spectrum determination, and substance identification. While mass spectrometry has been the method par excellence for the study of the qualitative and quantitative composition of volatile and easily derivatized substances in the molecular 1980 American Chemical Society

Magnetic susceptibility: instrumentation and analytical applications

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