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chsm.1984. 56. 293R-300R
Magnetometry: Aspects of Instrumentation and Applications Including Catalysis, Bioscience, and Geoscience 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
I. SCOPE OF THIS REVIEW In this twelfth review, we survey important trends in instrumentation and applications, especially in the realm of analytical chemistry including catalysis, bio- and geoscience, and materials science. All categories are becoming technologically very important in recent years. I t has been well established that magnetometry has proved to be extremely useful in the characterization of these systems a t the microand macroscopic levels, dealing with their electronic and bulk structures, analysis of various components present, and so on. The fmt eleven reviews on 'Magnetic Susceptibility" appeared during 1962 to 1982 (39,49-57). This 1984 version covers
_.
literature mostly from about J a n w 1982 to December 1983 and some earlier work. In response to an editorial plea, we have made this review more concise than the previous ones. In doing so i t seemed imperative that we depict the exceptionally novel trends in the applications of magnetometry. Readers will note that we have now adopted the term "Magnetometry", because it encompasses not only the principles of magnetism but also the measurement and applications of magnetic susceptibility ( x ) as well as of magnetization (M), which are usually studied as a function of temperature (77 and the applied field (If). The susceptibility ( x ) is simply equal to M JH; x can be expressed in units of per unit mass or volume. Factors for conversion from the 'cgs" to the 'SI" units for magnetic parameters are given in Table I.
11. GENERAL LITERATURE
A. Conference Pmceedingu Books,and Chapters. The
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research andtsamng p & m m in dnrmsny Q at NORhweslem and Haward Universities before ]ocnlng the lacuny at Psnn State in 1963 as an Awxlate Rofesoa. Dr. Mulay Is the a u m a 01 over 170 research publlcatlons and a monograph on "Magnetic 01 two , Susceptlbliy". He is me &or new beatloea on me '"Theory and AppIIcatlOns of Mckcular Diamapnstirm and Paramagnemm" (miey: MW yak. 1976). ~e is internationally recog nized lor his many mblbutbns to magnetics. His research intw& have centered on magnetic probes. such as susceptlblltty. broad-line NMR. EF'R. Llnd M&sbaua specboscopy lor me characterl2atbn and sbuctuai eiucldatlOn 01 sclm at the macro and mlaoscopic levels. Dr. Mulay has haveM widely and mblbuted to International meatlngs and research mfwenc88. Hip hubbies lncluje playlng me sitar and rtW 01 matwlals in relatbn to anClem cultures. such as Chlna. Indla. and Egypt. In recent years he has d e v s w a popular course along mesa lines. He is a member of oevwal potessbnal orga"l2Btio"S and was chakma" 01 the centra1 Pe""e.yka"la Sectbn of the ACS (19S5). He was w e d a Fdcw 01 the Royal Institute 01 Chmlstry, London. and B Senlor member 01 IEEE (Insmute 01 Elecmcal and ~ ~ ~~ngi-s). n i ci n recent years. vlsning scientls~from mainland ( ~ e puMk oll China. Indla, Japan. and USSR spent Umir study leaves in Roless a Mulay's Magnetics Labastory. He has been a regular mblbutor to Anatyiical Chemirhy'r Fundamental Review isow since 1962.
A
I1
mm. She parti+tes In U-eteachlng 01 B -se on "Matwlals in Ancient and MoQm CunVes". Her hDbbieS induje s l W of Lha CUnwe of Ametlcan Indians and wowing exotic plants Of Indla. hults. and vegetables. She is a -ba 01 several p o l e u i k m organiratlOns. She has been a regular hibutor to Anawical Chemiphy's biennlal Fundamental Reviews since 1964.
0003-2700/84/0355293R$O 1.5010
prweedings of the Magnetism and Magnetic Materials (3M) Conferences, which are held annually in the U.S.A. continue to appear in a special issue of the J. Appl. Phys. (usually in March following the conference) and in Special fiblications of the Am. Inst. Phys. The proceedings of the International Conferences on Magnetism (Intermag) which are held in various countries, including U.S.A. in alternate years, are published usually in special issues in journals such 89 the Inst. Elec. and Electronic Engineers (IEEE)-Mag Transactions and related publications. The invited lectures in all cases appear in about 8-page-long articles, which are indeed very informative and entertaining, and range all the way from "Advances in Magnetic Theory", "Technical Applications", "Magnetism Applied to Archaeology", and "Magnetism in Living Systems". Magneticists are urged to look up the myriads of entries each year in such proceedings, because they are sure to find information closely related to their own research. Needless to say, there is an information explosion, which seems to grow at an exponential rate. Hence, those who care to look a t the entries in Chemical Abstracts or Physical Abstracts are bound to feel that their heads are "spinning" after the literature survey is even partially completed. We found that it is easy to do a computer search for short topics, for instance, 'ferrites", "amorphous materials", etc., with reasonable success; however, in our experience a computer search of the literature has proved to be fruitless, because articles addressed to 'instrumentation" of a wide variety of apparatus (for instance, Faraday or Gouy balance, flux gate, vibrating or spinning magnetometers) seldom contain the phrase 'instrumentation of ..."..This comment is also true about "applications of magnetic measurements to ..., which is conspicuous by its absence. This situation has made computer retrieval of information impossible, and as such, the authors had to search through the voluminous evergrowing entries in Chemical, Physical, Biochemical, etc., Abstracts. On one oculssion after providing the key words (such as the PACS category of the J. Appl. Phys. and related journals), the computer output was as voluminous as the entries themselves, in the types of abstracts listed above. However, the situation is not hopeless; if only the PACS numbers were reformed to include specific citations for key words such as "magnetic instrumentation" and "applications of magnetism", the computer retrieval could be narrowed down to a window of accessibility for the type of information we have attempted to present in our earlier reviews. With the above disarming statement and in response to the (usual) plea from our editor, we plan to present exceptional advances in magnetic instrumentation and selected applications, by condensing considerable citations in a tabular form. 1 1984 Amaican Chemhl Society
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Table I. 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 42a or 42b) = 3.14; 4n = 12.56; ‘/4n = 0.0796; 103/4n = 79.61 A = ampere (or “ampere turns”) kg = kilogram B = magnetic flux or induction m = meter (= 100 cm) p or p~ = Bohr magneton (eh/4nmc) (“m” also used for “mass” in general or “mass of the electron”) (9.2731 x lo-’] erg/G) M or I = magnetization c = velocity of light mol (or M ) = molar (or atomic) cm = centimeter N = Avogadro’s number x = general symbol for magnetic susceptibility Oe = Oersted e = charge on the electron = flux quantum (hc/2e) g = gram P = density (g/cm3 or kg/m3) G = Gauss s = second; u = magnetization/g h = Planck’s constant (sometimes used for henry, T = Tesla the unit for inductance) u = volume H = magnetic field (i.e., intensity or strength of the field; Wb = Weber (unit for magnetic pole) sometimes used for henry) = l o s Maxwells (unit for B) k = Boltzmann’s constant K = susceptibility per unit volume An important point that should be noted at the outset is that in emu, the permeability of free space p = 1 and is dimensionless, whereas in SI p = 4n X lo-’ kg ms-* A‘Z. However the relative permeability, p r = ( p o b s / p 0 ) equals one and is dimensionless in both systems. $J
Conversion from Gaussian to SI Units multiply the number for Gaussian quantity unit flux density, B magnetic field strength, H volume susceptibility, K (dimensionless) mass susceptibility, x p molar susceptibility: Xmole
magnetization, M o r I (per cm3) magnetization, M magnetic moment of a dipole, p demagnetizing factor, N Bohr magneton, p or p B
G Oe emu/cm3
to obtain the number for SI quantity
by 103/4n 477
flux density, B magnetic field strength, H rationalized volume susceptibility
unit
T = Wb/m2 A/m dimensionless
K
emu/g (= cm3/g) 4n x 10-3 emulmol ( E cm3/mol) 4n x
rationalized mass susceptibility, K~ rationalized molar susceptibility,
G or Oe
magnetization, M (or polarization, J ) magnetization, M
pglatom or pB/form. unit, etc. b erg/G or Oe.cm3
103
(,IC 1
10-3
m3/kg m3/mo1
Kmole
magnetic moment of a dipole, m rationalized demagnetizing factor,
Aim T pB/atom for pB/form. unit, etc. A m2 dimensionless
dimensionless N ‘/4n 10-3 Bohr magneton p or p B (A m2)/mol erg/G a Also called atomic susceptibility. Molar susceptibility is preferred since atomic susceptibility has also been used to refer to the susceptibility per atom. “Natural” units, independent of unit system. However, the numerical value of the Bohr magneton does depend on the unit system. Magnetic polarization J is used in early literature; for this, the conversion factor (0)is and the SI unit is Tesla, With regard to books, Wohlfmth (81)has edited and added a third volume to his earlier 2 volumes on “Ferromagnetic Materials”, a handbook on the properties of magnetically ordered materials. One of us (L.N.M.) had the privilege of reviewing this third volume (in relation to the first two). An excerpt of our review (37) is given below. “This third volume should be read in the context of the previous two, which appeared in 1980. The editor, a pioneer in the field of modern magnetism, explains that the book is intended on the one hand as a comprehensive reference work and on the other as a textbook. In this reviewer’s opinion, the first of these purposes is served admirably, but the second is not, not even a t the most advanced level. At best, the volumes may be considered as “supplementary reading.” Even the “Handbook” designation is misleading. Thus,for instance, the information on magnetically ordered (i.e., ferro- and ferri-magnetic) materials is randomly scattered throughout the volumes, and considerable effort is needed to retrieve data relating to any particular group of substances. In a charitable spirit, the reader should take into consideration the editor’s disarming introductory comment, to the effect that “One man can no longer prepare a work of this nature, and the only possibility was to produce several edited uolumes containing reuiew articles, and it should be said that the contributors are indeed preeminently qulified. However, portions of the text have already appeared elsewhere, with minor modifications. The chapters are nevertheless consistent in their presentations, and there are many references. Volume I11 contains an excellent review by Enz on “Magnetism and 294R
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Magnetic Materials: Historical Developments and Present Role in Industry and Technology“ which would have had a more logical place in Volume I. There are also some gaps. Thus, for instance, Zijlstra (Chapter 2) discusses the theory of permanent magnets but, surprisingly, does not mention McCaig‘s book Permanent Magnets in Theory and Practice (Pentech Press, London, 1977), an elegant earlier treatise. Other chapters review work on ”Alnico Permanent Magnet Alloys” (Chapter 3, McCurrie), “Oxide Spinels” (Chapter 4, Krupicka and Novak), “Hexagonal Ferrites” (Chapter 5, Ko’ima), “Ferroxplana-Type Hexagonal Ferrites” (Chapter 6, ugimoto), “Hard Ferrites and Plastoferrites” (Chapter 7, Stablein), and “Sulphosphinels” (Chapter 8, Van Stapele). Most of these authors have given useful diagrams, SEM pictures of the microstructure of magnetic materials, and in several instances, examples of “structure-property” correlations. Chapter 9, by Campbell and Fert, is one of the rare contributions in the realm of magnetism that discusses transport properties; it includes topics such as resistivity and the Hall Effect, Electrical Resistivity of Pure Metals and Alloys, Magnetoresistance, Spontaneous Resistive Anisotropy, Thermoelectric Power, Nernst-Ettinghausen effect and Thermal Conductivity-all in relation to Fe, Co, and Ni and their alloys. Dilute Ferromagnetic Alloys and Platinum-Based Alloys are also covered, along with Amorphous AUoys. Volume I11 thus offers a wealth of information for theoretical and experimental ”magneticists,” for which the editor, authors and publishers deserve our thanks. Scholarly libraries should have this book (and the two previous volumes) at hand, even though
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Table I1 authors and references
topic (A) Compilation of Review Articles Magnetochemistry-advances in theory and experimentation. Molecular properties of a few organic molecules (molecular polarizability, diamagnetic susceptibility, etc. using empirical formulas). Magnetic properties of transition element oxides with the perovskite structure. Magnetic properties of ceramics ( 2 reviews), properties of ferrite, and methods of preparation and apparatus for magnetic measurements. Properties and application of magnetic liquids.
O’Connor (62) Pandey et al. (63) Berdyshev, A. A. (5) Kanamaru et al. (26) Charles et al. (8) Romani et al. ( 6 7)
Johannson et al. (25) and Freeman (16)
An excellent review is presented, which surveys instrumentation for measuring magnetic fields emanating from the human body and other biological systems. Various sensors such as induction coils, fluxgates, optically pumped magnetometers, balancing coils, etc. There are many more aspects to list here. Electronic (magnetic) structure of actinides under high pressure. Freeman has reviewed effects of positive and negative pressure on bulk solids and synthetic materials (submicron level films) and magnetism of superconducting C-15 compounds.
(B) Selected Reviews on Materials Novak, P. (61) Rossat-Mignod et al. (68) Mydosh (60)
Roy (6 7u) Ford (15) Schilling (69a)
Electronic structure of magnetic systems: calculations of magnetic properties of d-functional formalism for calculations of magnetic properties of transition metals (bulk and with impurities). Magnetic properties of cerium monopnictides. Present experimental research in Spin Glasses: frequency dependent susceptibility, magnetization ESR, etc. (this author, who has developed expertise in spin glasses, has written a number of reviews in various journals with new information in each article); see our earlier reviews (56, 57)). Spin glasses: magnetically disordered systems Spin glasses. Results in magnetism under high pressure reviewed. Eschange interactions, magnetic ordering temps; magnetic susceptibility of weak itinerant magnetic and strongly Stoner-enhanced systems, etc.
(C) Selected Reviews on Theoretical Developments Diamagnetic crystal and molecular anisotropies of naphthacene. The molecular anisotropies of condensed systems for aromatic orthorhombic or molecular systems is examined and extended to napthacene. Uncertainties in the early (1938) measurements are removed and good fit with those of other compounds is shown. Diamagnetic susceptibility and electron static polarizability from Ivanov-Smolenski et al. (24) X-Ray data. Calculations for alkali halides and alkaline earth oxides are shown to agree with magnetic data. Gupta et al. (20) Semiempirical calculation of diamagnetic susceptibilities of organotin compounds. Results on a large number of compounds with the formula R,SnR’,-, are given where R = Me, R’ = SEt, SPr, SBu, etc. with n = 2,3, and R = Et, Pr, Bu, R’ = C1, n = 3 , R = Me, R‘ = Sme, n = 2. Parameters were calculated from experimental values of diamagnetic susceptibilities of homologous stannanes. Good agreement between semiempirical and experimental values is shown. The overall goal of this type of work is not clear. Baba (3) Statistical theory and ionic model for alkali metal halide molecules. A model is used for calculating equilibrium distances ( R ) and dissociation energies ( D )for halides of first-row elements. With appropriate approximations, the R and D values and the diamagnetic susceptibilities are shown to agree with existing experimental data. Hurd (23) The author has attempted t o clarify the distinction between the wellknown types of magnetic order (e.g., para-, ferro-, and ferri-, antiferro-, metal and superparamagnetism) with the “new” varieties such as spero-, speri-, aspero-, mictro-, etc. magnetisms with their interrelations. One has to study 28 references cited to understand the intricacies. Sobry et al. (73)
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the cost is high”. Similarly, L.N.M. (38) reviewed Cyrot’s book (12). Again, a brief outline of this review is presented below. “Since the advent of “Amorphous Magnetic Materials” about two decades ago, there has been a prolific growth of
interest in this area, because of the unique properties associated with these materials, some of which have been exploited for technological applications. However, since about 1966, when Conyers Herring wrote his famous book Erhange Interactions Among Itinerant Electrons (Academic Press, New ANALYTICAL CHEMISTRY, VOL. 56, NO. 5, APRIL 1984
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Table 111. Analysis of Biosystems author and reference Kondorskii et al. ( 3 0 )
topic Magnetic susceptibility of single erythrocytes was studied in a homogeneous field. Oxygenized erythrocytes showed a x 0.75 x whereas the deoxygenized showed a x 0.45 x The methomoglobin (97%)containing species Mulay and Mulay ( 4 7 , 4 8 ) had developed a showed a value -0.54 X technique for single normal and cancer cells and had found significant differences in such tissue ( 4 8 a ) . Reference should be made to their paper.
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Vilenchik ( 7 9 )
Mockler et al. ( 3 6 )
Melnik ( 3 3 )
Schardt et al. ( 6 9 )
Cope (11)
Brittenham et al. ( 6 )
Vasak et al. ( 7 8 )
Smith et al. ( 7 2 )
Huang Ya-Ping et al. (22)
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Rhodopsin frog retinal rods show a high diamagnetic susceptibility anisotropy even in a low field ( l o 3 Oe or 8 X lo3 Am-’); however, the velocity of reorientation is very slow. Malignant transformations changes the properties of membrane proteins, their membrane orientation, physical state of lipids containing the proteins. Under certain conditions these changes lead to selective effects (not specified) of the field on the growth of cancer cells in vitro and in vivo. Thermodynamic considerations of various parameters are discussed. Mulay and Mulay ( 4 8 a ) had shown that magnetic fields retard the growth of certain cancer cells. Authors discuss the active site of allantoic purple acid phosphatase and a model complex for strongly coupled di-iron sites. Model complexes such as [Fe(ebpN)],O, containing di-iron sites are proposed for the behavior of the enzyme. Magnetic susceptibility analysis suggests the presence of Fe-0-Fe linkage. Reference should be made to a paper by Mulay and Selwood (cf. 4 2 b ) and Chapter 4 in Mulay and Boudreaux’s bood (cf. 4 2 b ) for a discussion of dimeric species of Fe, when Fe(C10,) is hydrolyzed. Magnetic analysis coupled with IR, Electronic, and EPR spectroscopy have been used to show that caffein adducts of Cu(I1) acetate and Cu(I1) chloracetates have strongly coupled antiferromagnetic interactions. Caffein is a therapeutic agent with analyptic activity. The antiferromagnetic exchange interaction (-25) between the singlet and triplet states of Cu(CH,COO),-caffein is much higher than any observed values for well-characterized Cu(I1) acetate complexes. Binuclear and other clusters have been discussed in Chapter 7 of Mulay et al.’ s book on molecular paramagnetism ( 4 2 b ) . The authors have isolated, purified, and characterized high valent complexes from a manganese porphyrin based catalytic hydrocarbon activation system. Magnetic analysis gave an effective Bohr magneton number = zero for [N,Mn(IV)TPP],O. Other evidence suggests the presence of Mn-0-Mn linkages in such complexes. The molecular structure is said to remain unchanged in the solid as well as in the solid state. The crystal and molecular structure of Mnbiocomplex is presented. In our last review ( 5 7 ) we surveyed the interesting work on magnetic monopoles presented by Cope. Most of his work has been published in bio-oriented journals, and is likely to escape the attention of chemists and physicists. Cope advocates startling concepts. For instance, in the present paper, he points out the following observations/interpretations concerning magnetically induced anisotropy of magnetic susceptibility is possible at room temperature as in organic superconductors. He suggests that the curves of dependences on time and on applied field strength of magnetically induced anisotropy of susceptibility resemble the curves for room-temperature remanent magnetization in various dyes and in powdered graphite. These observations are interpreted in terms of the concept that anisotropic lattices of magnetic flux are trapped in these organic materials, as observed in nonhomogeneous type 2 superconductive materials at low temperature. Magnetic susceptibility measurements on Fe stored in 110 patients (with hepatic liver disease) and in 20 normal subjects using a SQUID susceptometer. The authors discuss several medical aspects and conclude that magnetic analysis of Fe stores provide a new quantitative technique for the early detection of hereditary hemochromatosis and for rapid evaluation of treatment for transfusional overload. The authors present evidence for the presence of metal [Co(11)] thiolate clusters in rabbit liver metalthionein-1 in which all 7 sites are occupied by Co(I1). The microsymmetry of these sites is discussed in detail by EPR and magnetochemical analysis. The loss of paramagnetism with temperature reflects antiferromagnetic coupling of neighboring Co(I1) ions, brought about by a superexchange antiferromagnetic mechanism via the thiolate bridging ligands. Magnetic-susceptibility cx) of (a) native and (b) thionene oxidized Mo-Fe protein from A z o b a c t e r uinelandii nitrogenase was measured by the NMR technique [cf. Mulay, L. N. and Martha Haverbusch ( 4 5 ) ] . The difference between the magnetic properties of (a) and (b) is discussed in terms of a model for the spin states of the Fe in Mo-Fe protein. (EPR and Mossbauer spectral results were also obtained.) The x results suggest that the effective moment for the paramagnetic centers correspond to 5’ = ”*. These authors also used a NMR method for measuring the magnetic susceptibility (x) of fluoride binding to cytochrome c-Fe(II1) heme octapeptide. (See reference cited above for the NMR method.) The authors propose a model for anion binding to the active site of high-spin ferric heme proteins. The temperature dependence of x was measured and thermodynamic parameters for the appropriate species in equilibrium were obtained. They suggest that bonded interactions between the distal histidine and the ligand may contribute to the
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Table I11 (Continued) author and reference Timkovich et al. ( 7 6 )
Kirschvink (29)
topic stabilization of the hemoprotein-ligand complex. The NMR technique seems to have been popular for measuring magnetic susceptibility of various bio and other systems. This is exemplified by the authors’ studies on Pseudomonas aeruginosa cytochrome cd,. They found x to obey the Curie-Weiss law for the ferricytochrome; however ferrocytochrome showed an increase in the paramagnetic x with temperature. We suggest that if one assumed some sort of antiferromagnetic coupling between two Fe(I1) centers (or between adjacent “molecules”), one would expect an increase in x with T below the Ned1 temperature for such centers or clusters. The author has written a fascinating paper entitled “The Horizontal Magnetic Dance of the Honeybee (Apis mellifera).” This is compatible with a singledomain ferromagnetic magnetoreceptor. In our last review ( 5 7 ) ,we surveyed the evidence for the presence of ferromagnetic particles in bacteria. A recent discovery has shown that biochemically precipitated Fe,O, particles are found in bees. The author suggests that the bees may use a simple compass organelle for magnetoreception. When dancing to the magnetic directions on a horizontal honeycomb, bees clearly showed a magnetic alignment behavior. The receptors emu or magnetite volumes near cm3. The have moments of 5 X results are analyzed statistically and the author suggests that the subspherical single-domain crystals are held symmetrically in their receptors. A magnetic orientation energy of 6 kT in the geomagnetic field is estimated and a model is proposed for the magnetoreceptor, consistent with the constraints discussed in the paper. These authors have pointed out that the basic equation used for determining magnetic susceptibility of paramagnetic solutions by the “Concentric tubes” NMR technique is incorrect and has been used for 20 years. They have derived a correct equation. Reference should be made to their paper and to citations ofprevious workers. Their comments d o not apply to diamagnetic solutions as reported by Mulat et al: ( 4 5 )
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Orrell and Sik (62a)
York, 1966), as part of Rado-Suhl’s series on “Magnetism,” there has been no single book which encompassed different types of “new” magnetic materials, such as “spin glasses,” “amorphous magnetic alloys,” the so-called “mictomagnets”, and so on. This volume contains six chapters, which not only deal with the above topics, but also provide an elegant introduction to “Itinerant Magnetism“ (by Gautier). Coqblin has covered the important realm of “Intermediate Valence and Kondo Effects in Anomalous Rare Earths.” “Spin Glasses” are discussed in detail by Rammel and Souletie, and “Magnetism and Amorphous Magnetic Alloys” is reviewed by Chappert. A valuable addition is provided on “Magnetic Processes in Ferromagnets” by Kleman. Pierre has covered rare earth and intermetallic compounds. All the authors are preeminently qualified to write these chapters, which fill in the gaps of knowledge left by other researchers, who have written many topical reviews in journals, etc., devoted to magnetism, materials science, and solid state physics. There is a fair consistency in the style of writing among all chapters, except that one author (Pierre) has listed references in alphabetical order, without numbering them. This is a minor inconvenience to the reader, considering the quality of the contents of the chapter. The most remarkable feature is that the book contains a total of over 1300 references, including papers published through 1980. Considering the monumental effort involved, the editor and publishers should be congratulated for making the volume available in such a short time. The book is based on lectures given a t the School of Magnetism of Metals and Alloys, which was organized a t les Houches in February 1980. The ramifications of modern magnetism are many, and are expected to bring forth new concepts, terminology, theories and applications. Cyrot’s textbook of magnetism should prove very attractive to all magneticists who wish to keep abreast of new findings in the field. The text is written a t a very advanced level, and is meant for specialists with appropriate mathematical background.” Luborsky (31) has covered extensively the topic of “Amorphous Metallic Alloys”. Kaneyoshi (27) has also written a book on a similar subject. In addition, Hasegawa (21) has also reported advances in the realm of amorphous materials. Scattered information on the diamagnetic and paramagnetic effects in relation to phase diagrams and applications of alloys has appeared in a number of books by Pollock (65)and others. Weltner’s book (80) should be of interest to chemists.
As we pointed out in our earlier reviews (56, 57), “amorphous magnetic materials” have attracted considerable attention because of their technological applications in the large-scale applications of magnetically soft materials for transformer cores and other electrical devices. Analytical chemists should note that such amorphous systems consist of metal-metalloid compositions, and their professional contribution to these relatively new materials lies not only in analyzing the elemental composition but most importantly in measuring the magnetic parameters, such as the remanent and finally the magnetization (a,) the coercive force (H,) magnetic energy product (I3.H). B. Topical Reviews. A number of reviews have appeared during the past 2 years. In Table 11,we summarize first those which would be of interest to chemists in general; in later subsections we summarize publications of general interest to the magneticists.
111. INSTRUMENTATION It would be appropriate to make a general comment that even a cursory survey of development of instrumentation for magnetic property measurements has been diverted from the classical Gouy and Faraday balances (40,41)to the modifications of the relatively new and more expensive “superconducting quantum interference device” (SQUID) and the “vibrating sample magnetometers” (VSM). This situation may be attributed to new electronic technologies, including minicomputers/processors, etc. (We wish to refrain from using cliche’s such as “high technology” and “high-tech industry”,) Nevertheless, in terms of low cost, the Faraday balance (based on the Cahn Company’s microbalances) continues to be the most versatile apparatus for measurement on bulk solids, liquids, or solutions and even for measuring anisotropies not only of single crystals but also of thin films. Most importantly, these can be used for in situ measurements, on dia-, para-, ferro-, antiferro-, ferri-, etc. magnetic type materials. Mulay and co-workers (44)havc developed special sample holders for use with their Faraday balance. These were made of microscope slides about 1 x 1 cm to hold thin films of iron nitrides in such a way that the anisotropy parallel or perpendicular to the FeN columns could be measured with great accuracy. In particular, measurements were made on discrete (thin film) phases of Fe4N, tFeaN, and Fe4N + aFe. These displayed superparamagnetic behavior, which was confirmed by Mossbauer measurements. Their technological significance ANALYTICAL CHEMISTRY, VOL. 56,
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in catalysis has been pointed out and, in subsequent papers (not reviewed here), they have pointed out the use of such f i s as candidate materials for magnetic recording. Reference should be made to a paper by Gron et al. (19),who measured the temperature dependence of Gd-Co alloy films using the principles of operation of “8 magnetic balance”. The meaning of this terminology is not clear to the writers, because the original paper was not available at the time of writin this review. A data logging system for a.c. magnetic suscepti ility measurements and the temperature dependence of T b is illustrated by McKenna et al. (32). A simple method for determining anisotropies of diamagnetic susceptibilities of liquids by use of proton NMR spectroscopy is outlined by Diehl et al. (13). Manometric measurements of susceptibilit of liquids such as 3He in high magnetic fields is outlined y Meservey and co-workers, who have stressed that a nonclassical resonance method was adapted for measuring the nuclear susceptibility of and nuclear relaxation in 3He. Although their sophisticated experiments were aimed at studying the properties of exotic materials such as 3He, one should consider the applicability of their instrumentation for measuring dia- and paramagnetic susceptibilities of organic and inorganic liquids/solutions. Reference should be made to a paper on the same topic by Brooks et al. (7). Foner and co-workers (Zieba) continue to give an elegant design analysis of the VSM (vibrating sample magnetometer). In a recent paper (82), they describe with mathematical rigor the “detection coil, sensitivity function, and sample geometry effects on VSM”. They point out the applicability of the analysis to induction and force methods. Gerber and coworkers (17) describe the design features of a simple and relatively inexpensive homemade vibrating sample magnetometer. These include signal electronics which employ an analog divider rather than the usual electromechanical feedback circuit and a method for gas cleaning during sample changes allowing long experiments at liquid helium temperatures in a superconducting solenoid.
IV. APPLICATIONS (A) Coordination Compounds and Organometallic Compounds. Since this area is very prolific and is reviewed
structural deformation of tetrahydral and octahydral coordination of Fe sites in Fe203. The formation of dimeric and trimeric species in clusters is suggested by Chaumant and co-workers (9). (Reference should be made to earlier work by Mulay and Collins (43).) Another analysis of s lat cooled oxides containing varying concentrations (n)Fe3 is also reported by the same authors (9); systems such as BaOB2O3-Fe2O3-yFe2O3 were analyzed. With varying 1 In I8 dimers and trimers of Fe with antiferromagnetic interactions are detected. Synthesis and magnetic analysis of such systems is relevant to the glass industry, and we hope that magnetic susceptibility measurements could be used not only as a uality control tool but also for developing new types of colored) glasses with improved mechanaical properties. Borelli et al. (5a)have developed glass-encapsulated materials (96% porous glass with Fe and/or Mn, Co, Ni) which on magnetic analysis showed high coercivities (>10000 Oe) and magnetizations at high fields (0.131 emu/g at 25 “C). Borelli-Corning Glass patent describes methods of synthesizing these new types of glasses and techniques of analysis. Mydosh and co-workers (60) have analyzed Co- and Mn-aluminosilicate glasses at high temperatures. The magnetic analysis is interpreted in terms of the Bohr magneton number of Mn and Co and deviations from the Curie-Weiss law, based on the nearest-neighbor and next-nearest-neighbor exchange interactions for the Mn and Co systems. Magnetic analysis of carbon fibers was deduced by McClure et al. (34). They assumed a model of long, longitudinally folded, monolayer ribbons of graphite. Theoretical hints are given for unravelling the fiber structure from magnetic susceptibility vs. temperature data. An apparatus for the electromagnetic detection of oxygen in a gas stream has been patented by Amouriq ( I ) . It uses Si02s heres (with adsorbed oxygen) which is surrounded by an inluctance coil. (C) Geoscience Applications. Senftle and his associates (71)have shown that when coal is pulverized in a steel grinder, abraded steel particles cause ferromagnetic contamination (-0.02 w t %). When such coal particles were analyzed in a VSM some of the superparamagnetic Fe particles moved through the pulverized coal and formed “multidomain” clusters, which affected the magnetic properties of the coal. Strictly speaking one is sup osed to rigidly pack any powdered material in the sample hol& of the VSM, so that no particles would “rattle” at a frequency other than that of the VSM. Hence, the results quoted by the authors need to be examined in detail. Onufrionok et al. (61a)discuss the high-temperature magnetic properties of a series of synthetic pyrrhotites above their Ne61 temperature and found no ordering of Fe ion vacancies. Their reference to the Ned temperature indicates that most or all of their pyrrhotites were antiferromagnetic. This is not strict1 true. Mulay et al. (46) showed that the conversion of Fe (antiferromagnetic) to Fe,S, displays a X transition, whick takes place via the interchange of Fe3+ions and vacancies in Fe9Slo. The use of a proton precession magnetometer (that is ‘H NMR spectrometer) to detect buried (steel) drums is illustrated by Tyagi and his group (77a). Their technique should prove very useful to conscientious workers in the U.S. (and other) Environental Protection Agencies, where hazardous waste is quite often (sometimes secretly) dumped by (unethical) industries, causing irreparable damage to the health of humans and animals. The room-temperature magnetization of some Canadian chysotile and UICC asbestos samples is reported by Stroink et al. (74). (D) Analysis of Biosystems. In addition to the myriads of investigations of magnetic thin films, and magnetic materials such as ferrites (which are not reviewed here), magnetic analysis of a number of biomaterials has been reported. One may surmise that this effort is prompted by the newly emerging bioengineering technology. Since a vast number of magnetic analyses have been reported during the past two years, we have succinctly summarized a few selected studies, in Table 111.
in specialist periodical reports of the Chemical Society, London, no attempt will be made here to review such materials. However, a few complexes of biological interest will be reviewed in later sections. (B) Magnetic Analysis of Materials. Magnetic analysis of splat-cooled glasses such as nFe203(1-n)[Ba0,B2031 and others in the ternary system have been analyzed in terms of
V. APPLICATIONS TO CATALYSIS In continuation of the research on Fe and Fe-Co dispersions on the ZSM-5 and silicalite zeolites, reviewed before (57), Mulay and co-workers (59)have characterized Fe/Mordenite catalysts by magnetic (and Mossbauer) techniques. Iron oxide dispersions were made by decomposing Fe3(C0)12on mor-
fl
i
All readers should see an important paper on NMR by Orrel and Sik (62a) given at the end of Table III. Pesch (64) has measured the low coercivities of 80% NiFe d o y using a VSM in conjunction with a hysteresigraph, which employ the classic torroid specimens. A rotating sample ma netometer has been successfully developed by Flanders a n t Fischer (14) to measure contactless magnetoresistance with a rotating sample ma netometer. A discussion is presented by Zieba and Foner b 3 ) on the superconducting image effects observed with a superconducting VSM. Measurement of static magnetization using ESR spectrometer is outlined by Schultz and Gullikson (70). Surprisingly, their method is said to be applicable to samples which do not show an ESR signal. This paper will be indeed helpful to those who perform magnetization as well as ESR experiments. High-sensitivity magnetization measurements under pulsed high magnetic fields is reviewed by Toshiru and co-workers (77). In the same reference, Gersdorf et al. (18) have given an account of the high magnetic field facility at the University of Amsterdam. The magnetic susceptibility of stycast 1266 Epoxy, a lowtemperature binder has been found to be diamagnetic from 2.5 to 400 K in a field of 5 kOe. Its chief use is in the fabrication of sample holders for the S UID magnetometers, because it has a negligible temperature ependence. This work was reported by Azvedo (2). Karmazsin and co-workers (28) have developed a simple apparatus for measuring the Curie temperature of ferromagnetic materials, which uses a platinum coil as a sensor; this in turn can be coupled to a thermodilatometer. a-Fe2O3 and yFe203transitions, etc., have been studied. An apparatus for monitoring the burden conditions in a blast furnace is reported by Sumimoto Metal Industries (75).
2
298 R
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 5, APRIL 1984
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MAGNETOMETRY
denites (that is aluminosilicates with cage structures) with varying ratios (12, 17,20 and 60) of Si02/A1203. This ratio governs the number of Bronsted acid sites, and it is highest at a ratio of 17. For 15% Fe species on mordenite (ratio = 20) a saturation magnetization (a,) of 73 emu/g was found, which agreed well with that of y-FezOa. This was also confirmed by Mossbauer spectroscopy. The a, decreased as the “ratio of Si02/A1203”decreased from 60 to 17 and again increased when the ratio was further lowered. These results showed the presence of an interaction between the Bronsted acid sites (H+)and the iron oxide. The average particle sizes were calculated from the low field and high field approximations of the well-known Langevin function. These varied from 50 to 14 8, reaching a minimum value (14 8,) when the ratio was 17. Thermomagnetic measurements were made to elucidate the transitions in iron oxides and the growth of superparamagnetic oxides. In an earlier review (57) we described briefly the work on Fe/carbon and Fe/V3G (graphitized carbon catalysts). In continuation of this work a new approach was developed by Walker, Vannice, and Mulay [see original ref in (57)]. They doped Cabot’s Monarch carbon blacks with boron so as to change the basic nature of the carbon support itself and see if any changes would ocw in the hydrogenation of CO to CHI, by dispersing Fe on such carbons. Since boron has one electron less than carbon (ls22s22p2with a sp2hybridization), it seemed reasonable to expect that boron could enter the carbon or graphitized carbon substitutionally and thus change ita band parameters such as the degeneracy temperature To = kEf (where Ef is the Fermi level), the effective electron mass m*,etc. Thus Fe3+ ion (via Fe(NO& impregnation) was dispersed on various carbons and carbons graphitized at two different temperatures (2073 and 3779 K). Mulay and Prasad Rao (58)characterized carbons with a nominal loading of
