pubs.acs.org/Langmuir © 2009 American Chemical Society
Hierarchical Superparamagnetic Magnetite Nanowafers from a Resin-Bound [Fe(bpy)3]2+ Matrix Mrinmoyee Basu,§ Arun Kumar Sinha,§ Sougata Sarkar,§ Mukul Pradhan,§ S. M. Yusuf,† Yuichi Negishi,‡ and Tarasankar Pal*,§ †
BARC, Mumbai, ‡Tokyo University of Science, Japan, and §Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India Received October 5, 2009
The brilliant red [Fe(bpy)3]2þ complex upon immobilization on a strongly acidic cation exchanger or in situ formation of the same cationic complex onto a resin matrix and subsequent modified hydrothermolysis (MHT) at ∼110 °C produces unusually stable hierarchical magnetite (Fe3O4) nanowafers. The slow hydrothermolysis, oxidation, and subsequent dehydration of the complex on the solid-liquid interface produce stable hierarchical nanostructures. The isolation of neat Fe3O4 (uncapped) particles from the resin matrix as hierarchical nanowafers was achieved by magnetically stirring a CH3CN suspension of nanocomposites. The solid resin support not only aids nanowafer formation on its surface but also provides unique stability to the magnetite particles, where nanowafer oxidation is largely retarded. The utility of the as-prepared porous nanocomposite and characterization of the nanoparticles are promising for nanotechnological and soft ferromagnetic applications.
Introduction Metallic magnetic oxides having different shapes and sizes have received considerable attention because of their theoretical and technological applications.1 Among those magnetic oxides, superparamagnetic iron oxide nanoparticles with appropriate surface chemistry can be used for numerous in vivo applications, especially for MRI contrast enhancement, tissue repair, mineral separation, heat transfer, electrophotography, immunoassay, detoxification of biological fluids, hyperthermia, drug delivery, sensors, cell separation, and cancer therapy.2 Over the years, researchers have employed different routes to facilitate the large-scale synthesis of nanostructured materials using hydrothermal processing to achieve this goal.3 Similarly, organometallic precursors, emulsion liquid membrane systems, reverse micelle methods, a solid template method, chemical vapor deposition, electron and ultrasound irradiation, chemical precipitation from microemulsions, microwave synthesis, thermal decomposition, vapor-liquid-solid methods, and a sol-gel technique have also been used.4 In the past decade, the synthesis of superparamagnetic nanoparticles has been intensively carried out not only for fundamental scientific interest but also for many technological applications.1 Magnetic nanomaterials have received much attention because of their potential applications in perpendicular data recording and spintronic devices, e.g., spin injection electrodes in tunneling magnetoresistance *Corresponding author. E-mail:
[email protected]. (1) (a) Battle, X.; Labarta, A. J. Phys. D: Appl. Phys. 2002, 35, R15. (b) Kodama, R. H. J. Magn. Magn. Mater. 1999, 200, 359. (2) (a) Lawaezeck, R.; Menzel, M.; Pietsch, H. Appl. Organomet. Chem. 2004, 18, 506. (b) Levy, L.; Sahoo, Y.; Kim, K.-S.; Bergey, E. J.; Prasad, P. N. Chem. Mater. 2002, 14, 3715. (c) Gao, S.; Shi, Y.; Zhang, S.; Jiang, K.; Yang, S.; Li, Z.; TakayamaMuromachi, E. J. Phys. Chem. C 2008, 112, 10398. (d) Jeong, U.; Teng, X.; Wang, Y.; Yang, H.; Xia, Y. Adv. Mater. 2007, 19, 33. (e) Zeng, H.; Li, J.; Liu, J. P.; Wang, Z. L.; Sun, S. H. Nature 2002, 420, 395. (f) Rooth, S. J. Magn. Magn. Mater. 1993, 122, 329. (g) Sonti, S. V.; Bose, A. J. Colloid Interface Sci. 1995, 170, 575. (3) (a) Taniguchi, T.; Nakagawa, K.; Watanabe, T.; Matsushita, N.; Yoshimura, M. J. Phys. Chem. C 2009, 113, 839. (b) Hu, C. Q.; Gao, Z. H.; Yang, X. R. Chem. Phys. Lett. 2006, 429, 513. (4) (a) Sugimoto, T.; Muramatsu, A.; Sakata, K.; Shindo, D. J. Colloid Interface Sci. 1993, 158, 420. (b) Ueda, M.; Shimada, S.; Inaga, M. J. Eur. Ceram. Soc. 1996, 16, 685. (c) Tamaura, Y.; Ito, K.; Katsura, T. J. Chem. Soc., Dalton Trans. 1983, 1983, 189.
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(TMR) devices.5 Among these magnetic materials, magnetite (Fe3O4) is the most infamous and important member of the ferrite family. Generally, most research has been focused on magnetite nanoparticles. Fe3O4 is a very important functional material because of advantages such as its magnetic properties, chemical stability, biocompatibility, and low toxicity. Magnetite, with a space group of Fd3m, is a cubic crystal of the spinel series. There are two distinct iron sites in the structure, namely, Fe(III) ions located at the tetrahedral sites and Fe(II) ions and Fe(III) ions equally distributed at octahedral sites of the spinel-type structure. Owing to its structure, magnetite is a typical semimetallic material. Fe3O4 nanoparticls (NPs) have attracted interest in the fields of biomedicine and magnetic sensing.6 The physical and chemical properties of magnetite nanocrystals are greatly affected by the synthesis route, and for this reason, various approaches have been employed to produce magnetite to obtain the expected properties. In past decades, magnetite particles have usually been obtained by the coprecipitation of Fe2þ and Fe3þ from alkaline solution, which is a common, simple technique for the preparation of Fe3O4 nanomatrices. Given that the particles obtained with the coprecipitation method have a broad size distribution, numerous other methods are currently being developed to produce NPs with a tight size distribution.7 Water-in-oil emulsions are currently being used to synthesize superparamagnetic iron oxide nanoparticles with a narrow size range and uniform physical properties because of the ability to control the size and shape of the nanoparticles.8 The oil and water (5) (a) Zhang, D.; Liu, Z.; Han, S.; Li, C.; Lei, B.; Stewart, P. M.; Tour, M. J.; Zhou, C. Nano Lett. 2004, 4, 2151. (b) Batlle, X.; Cuadra, P. J.; Zhang, Z. Z.; Cardoso, S.; Freitas, P. P. J. Magn. Magn. Mater. 2003, 261, L305. (c) Zhang, Z. Z.; Cardoso, S.; Freitas, P. P.; Batlle, X.; Wei, P.; Barradas, N.; Soares, J. C. J. Appl. Phys. 2001, 89, 6665. (6) (a) Gu, H.; Xu, K.; Xu, C.; Xu, B. Chem. Commun. 2006, 941. (b) Mornet, S.; Vasseur, S.; Grasset, F.; Duguet, E. J. Mater. Chem. 2004, 14, 2161. (c) Choi, J. W.; Ahn, C. H.; Bhansali, S.; Henderson, H. T. Sens. Actuators, B 2000, 68, 34. (7) (a) Kang, Y. S.; Risbud, S.; Rabolt, J. F.; Stroeve, P. Chem. Mater. 1996, 8, 2209. (b) Freid, T.; Shemer, G.; Markovich, G. Adv. Mater. 2001, 13, 1158. (8) Zhang, D. E.; Tong, Z. W.; Li, S. Z.; Zhang, X. B.; Ying, A. Mater. Lett. 2008, 62, 4053.
Published on Web 11/09/2009
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Figure 1. Formation of the magnetic Fe3O4 nanowafers on resin beads (black) from resin-immobilized [Fe(bpy)3]2þ(red).
phases often contain several dissolved components; therefore, the selection of the surfactant (and cosurfactant) depends upon the physicochemical characteristics of the system. Several types of surfactants, such as cationic, anionic, or nonionic, can be used. Unfortunately, the functional group of the ionic surfactants in the hydrated core seems to limit the capability of forming highly crystalline magnetite nanoparticles. Thermal oxidation of pure iron has been used to produce hematite (Fe2O3) nanowires and nanobelt arrays under different oxygen atmospheres.9 These methods are often plagued by undesired contaminants or the need for post-treatment. Templating is commonly employed for the controlled production of materials with ordered structure having the desired properties. In the past, templates such as aluminum oxide, carbon nanotubes, polymer fibers, and egg-shell membranes have also been employed.10 To the best of our knowledge, no reports have been published on the synthesis of an exceptionally stable wafer such as a magnetic material on a solid resin matrix by modified hydrothermolysis (MHT)11 without the need for any extra stabilizing agent. The reported method is a novel and cost-effective chemical route to producing waferlike porous magnetite (Fe3O4) nanocomposites on the gram level without high-temperature calcinations (Supporting Information). The morphology has been characterized by different physical methods such as FTIR, XRD, Raman, FESEM, and TEM. The magnetic moment reveals that the as-prepared Fe3O4 nanocomposite has a very low coercivity at room temperature, which is an indication of its similar, soft ferromagnetic properties. This article also reports the need-based isolation of neat Fe3O4 nanoparticles from the composite for the complete mineralization of a cationic dye, Rhodamine B, under UV irradiation.
Characterizations Two methods for the gram-level syntheses of iron oxide nanoparticles have been reported, following a similar synthesis protocol exploiting [Fe(bpy)3]2þ-immobilized resin beads. The resin beads became black in color and magnetic (Figure 1) in nature upon 8 h of modified hydrothermolysis (Scheme 1). In acetonitrile, the particles were successfully striped off of the solid resin matrix using magnetic flyers under stirring (Scheme 2), leaving the original spherical resin beads as residue. The percentage yield (90%) of iron oxide was determined gravimetrically. Black magnetic particles were collected, washed, and dried in air and retained for further characterization. On the contrary, MHT of an aqueous solution of [Fe(bpy)3]2þ produced unstable Fe3O4. (9) Ding, Y.; Morber, J. R.; Snyder, R. L.; Wang, Z. L. Adv. Funct. Mater. 2007, 17, 1172. (10) Xiong, S.; Wang, Q.; Chen, Y. J. Appl. Polym. Sci. 2009, 111, 963. (11) Sinha, A. K.; Jana, S.; Pande, S.; Sarkar, S.; Pradhan, M.; Basu, M.; Saha, S.; Pal, A.; Pal, T. CrystEngComm 2009, 11, 1210.
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FTIR spectral characteristics of the samples were recorded in reflectance mode with Nexus 870 Thermo-Nicolet instrument coupled with a Thermo-Nicolet Continuum FTIR microscope. A Raman spectrum was obtained with a Renishaw Raman microscope equipped with a He-Ne laser excitation source emitting at a wavelength of 633 nm and a Peltier-cooled (-70 °C) chargecoupled device (CCD) camera. The phase and purity of the product were determined by X-ray powder diffraction (XRD) using an X-ray diffractometer with Cu KR radiation (λ = 1.5418 Α°). At room temperature, the scans were recorded from the dry products in the range of 20-90°. XPS analysis was performed on an ESCA LAB MK II using Mg as the excitation source. The particle size, shape, and morphology of the nanoparticles were observed with a field-emission scanning electron microscope (FESEM) (Supra 40, Carl Zeiss Pvt. Ltd.), and an EDAX machine (Oxford link and ISIS 300) attached to the instrument was used to obtain the nanocrystal composition. TEM and HRTEM measurements of the metal oxide sols were performed on a Hitachi H-9000 NAR instrument on samples prepared by placing a drop of fresh metal oxide sols on copper grids precoated with carbon films, followed by solvent evaporation under vacuum. Finally, the Brunauer-Emmett-Teller (BET) surface area and pore size distribution were measured with an accelerated surface area and porosimetry system (ASAP 2020 V3.01 G) from N2 adsorption-desorption isotherms.
Results and Discussion The resin-bound solid-black particles remained stable for months, and the solid resin matrix offered stability to the magnetic particles. A magnetic stirring bar stripped off solid Fe3O4 from the resin surface as nanowafers, leaving the host resin beads clean. Then the presence of the Fe(II) species in the as -prepared solid nanowafer (obtained from acetonitrile) was confirmed from the chemical test performed with alcohol solutions of 2,20 -bpy and also with 1,10-phen. In both cases, characteristic colors of the charge-transfer complexes were obtained. However, the bulk Fe2O3 and nano Fe2O3 could not produce any such coloration. The Fe3O4 matrix was further authenticated from the spectroscopic (FTIR, Raman, and XPS) evidence. It may be mentioned that XRD information, elaborated on in the succeeding section, could vouch for the presence of iron oxide in the as-prepared matrix. Fe3O4, the magnetic nanomaterial prepared on the resin matrix, was isolated from the solid support while in acetonitrile solvent and magnetically stirred. Interestingly, the isolated particle remained physically bound to the magnetic stirring bar. The extracted magnetic particle was employed in the FTIR study. The FTIR spectrum of the as-prepared Fe3O4 particle in the region of 500-4000 cm-1 reveals a broad, weak band at about 586 cm-1 that corresponds to an Fe-O vibration. This may be ascribed to the incomplete crystallization of the sample. This incomplete crystallization again was confirmed by the XRD and also by the magnetic moment studies. It has been reported that the characteristic absorption band due to the Fe-O bond appears at about 570 cm-1 for magnetite particles.12 However, the band shifted to a higher wavenumber, 586 cm-1, for the sample prepared by method 1 (Supporting Information Figure S1a). A basic effect of the finite size of nanoparticles is due to the breaking of a large number of surface-atom bonds, resulting in the rearrangement of unlocalized electrons on the particle surface. (12) (a) Mandal, M.; Kundu, S.; Ghosh, S. K.; Panigrahi, S.; Sau, T. K.; Yusuf, S. M.; Pal, T. J. Colloid Interface Sci. 2005, 286, 187. (b) Xu, Z.; Shen, C.; Hou, Y.; Gao, H.; Sun, S. Chem. Mater. 2009, 21, 1778.
DOI: 10.1021/la903766p
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Basu et al. Scheme 1. Representation of Fe3O4 Nanowafer Formation on a Resin Surface
Scheme 2. Separation of Magnetic Nanowafers from a Resin Moiety
As a result, when particles were reduced to nanoscale dimensions, the absorption bands of the FTIR spectra shift to higher wavenumber. Therefore, the red shift of absorption bands of the Fe-O bond of magnetite particles is observed. The broad absorption peak at about 3445.54 cm-1 could be ascribed to the hydroxyl moiety. It is due to OH stretching, and a solitary band of O-H bending is located at 1650.73 cm-1. This showed that the surfaces of iron oxide particles had a large number of hydroxyl groups. In the case of the sample prepared by method 2, there also remains a broad band at 576 cm-1 corresponding to the Fe-O vibration of the Fe3O4 (Supporting Information Figure S1b) moiety. In Raman spectroscopy, the persistent exposure of the asprepared iron oxide sample to laser radiation has been shown to generate hematite. The reported laser power threshold values for hematite formation differ widely because they depend on operating conditions (wavelength, objective, time per scan, etc.). Tang et al.13a have studied the oxidation of magnetite in solution via the loss of optical absorption in the near-IR region. They concluded that this oxidation process is principally due to a temperature increase of several hundred degrees, not a photoeffect. The results of these studies vary significantly either in the number of observed Raman modes or in their positions and assignments. Recently, the 5838 DOI: 10.1021/la903766p
literature data were evaluated critically and systematized by Shebanova and Lazor et al.13b A certain discordance in the literature has been attributed to the transformations of magnetite, namely, into an orthorhombic phase or hematite. From the Raman study, we observe seven peaks (Supporting Information Figure S2). Some of them are characteristic peaks of magnetite, and some of them indicate the presence of as-prepared hematite nanomatrices. The peaks at 227 and 493 cm-1 (A1g) are due to Fe-O sym stretching. Stretching peaks at 293 and 410 cm-1 (Eg) are due to Fe-O symmetrical bending, and the peak at 610 cm-1 (Eg) is due to Fe-O symmetrical bending. Also, a distinct band at 1328 cm-1 has been observed. According to the reports of McCarty et al.13c and Shebanova et al.,13c this refers to a phonon overtone at 660 cm-1. Raman scattering at 1328 cm-1 is characteristic evidence for the presence of hematite (Fe2O3). Starting from the powder, laser-induced heating irreversibly gives pure hematite. The most intense band, at 658 cm-1, is attributed to the magnetite of the A1g mode, in close agreement with the literature.13d This residual peak at about 658 cm-1 indicates the incomplete phase transformation of magnetite to hematite upon laser irradiation. Preliminary attempts were made to determine the crystalline phase and degree of crystallinity by employing X-ray diffraction analysis of Fe3O4. The common crystalline phases of iron oxide include two related spinel structures, γ-Fe2O3 (maghemite) and Fe3O4 (magnetite), and a corundum-type structure, R-Fe2O3 (hematite).14a However, X-ray diffraction analysis cannot distinguish between Fe3O4 and γ-Fe2O3. As-prepared Fe3O4 on a solid support is not highly crystalline to X-rays. For the nanowafers of Fe3O4 prepared via method 1, there are six diffraction peaks (30, 35.4, 43, 53.5, 56.9, and 62.5, which is the standard pattern for crystalline magnetite (as evidenced from chemical tests, FTIR, and Raman studies) with spinel structure) (Supporting Information Figure S3a). These diffraction peaks at 30, 35.4, 43, 53.5, 56.9, and 62.5 correspond to the (220), (311), (400), (422), (511), and (440) crystal planes of the Fe3O4 lattice, respectively. The (13) (a) Tang, J.; Myers, M.; Bosnick, K. A.; Brus, L. E. J. Phys. Chem. B 2003, 107, 7501. (b) Shebanova, Olga N.; Lazor, P. J. Raman Spectrosc. 2003, 34, 845. (c) McCarty, K. F. Solid State Commun. 1988, 68, 799. (d) Legodia, M. A.; Waala, D. De. Dyes Pigments. 2007, 74, 161. (14) (a) Gole, A.; Stone, J. W.; Gemmill, W. R.; Loye, H.-C.; Murphy, C. J. Langmuir 2008, 24, 6232. (b) Tao, K.; Dou, H.; Sun, K. Chem. Mater. 2006, 18, 5273. (c) Peng, S.; Sun, S. Angew. Chem., Int. Ed. 2007, 46, 4155. (d) Stjerndahl, M.; Andersson, M.; Hall, H. E.; M. Pajerowski, D.; Meisel, M. W.; Duran, R. S. Langmuir 2008, 24, 3532. (e) Popovici, M.; Gich, M.; Roig, A.; Casas, L.; Molins, E.; Savii, C.; Becherescu, D.; Sort, J.; Suri~nach, S.; Mu~noz, J. S.; Baro, M. D.; Nogues, J. Langmuir 2004, 20, 1425.
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Figure 2. SEM images of the large wafers with different magnifications: (a) low, (b) medium, and (c) high.
XRD pattern of the sample confirms the structure of the Fe3O4 nanocrystal because the position and the relative peak intensity of the main peaks well matched those from the JCPDS card (19-0629) for Fe3O4.14b-e This confirms the spinel structure of the magnetic material. In the case of the prepared small nanowafers obtained from method 2, we have recorded a well-matched XRD spectrum having similar diffraction peaks to those recorded for the sample obtained from method 1. This observation confirms that the black material obtained from method 2 is Fe3O4 (Supporting Information Figure S3b), which is again in accordance with the relevant (chemical test, FTIR, and Raman) information. An XPS experiment is used to characterize the oxidation state of iron in the prepared nanomatrices because core electron lines of both ferrous and ferric ions have been detected and remain distinguishable from each other. It is noted that there exist two broad peaks at 724.2 and 710.85 eV (Supporting Information Figure S4a) assignable to Fe 2p1/2 and Fe 2p3/2, which agree well with the reported values for Fe3O4. Because of spin-orbit coupling, the Fe 2p core levels split into 2p1/2 and 2p3/2 components. The broadness of the Fe 2p peaks is ascribed to the existence of dual iron oxidation states (Fe2þ and Fe3þ) that have different but irresolvable binding energy. In the case of nano γ-Fe2O3, there also exist similar peak positions such as nano Fe3O4 but only one piece of information is carried by a shoulder peak or a satellite line in between Fe 2p3/2 and Fe 2p1/2 that is characteristic of Fe3þ in nano γ-Fe2O3. This satellite peak is not observed in Fe3O4,15 so the prepared sample is authenticated as Fe3O4, not γ-Fe2O3. The counterpart of iron is oxygen, whose binding energy of O 1s is 531 eV in Fe3O4 (Supporting Information Figure S4b). The sample obtained from method 2 (small nanowafer) was examined similarly to the case of the large wafer and proves to be Fe3O4. The shape and morphology of the prepared iron oxide were investigated with a scanning electron microscopy (SEM). (15) (a) Hui, C.; Shen, C.; Yang, T.; Bao, L.; Tian, J.; Ding, H.; Li, C.; Gao, H.-J. J. Phys. Chem. C 2008, 112, 11336. (b) Gao, S.; Shi, Y.; Zhang, S.; Jiang, K.; Yang, S.; Li, Z.; Takayama-Muromachi, E. J. Phys. Chem. C 2008, 112, 10398. (c) Moudler, J. F.; Stickle, W. F.; Sobol, P. E.; bonben, K. D. Handbook of X-ray Photoelectron Spectroscopy; Perkin-Elmer: Eden Prairie, MN, 1992. (d) Huang, K.-C.; Ehrman, S. H. Langmuir 2007, 23, 1419.
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Figure 3. SEM images of the small wafers with different magnifications: (a) low, (b) medium, and (c) high.
Figure 4. TEM and HRTEM images of (a, c) large wafers and (b, d) small wafers, respectively.
Figure 5. EDAX spectrum of (a) large wafers and (b) small wafers.
Figures 2 and Figure 3 represent the SEM images of the as-prepared iron oxide matrices at high, medium, and low DOI: 10.1021/la903766p
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Figure 6. Magnetic moment study: (a) M vs H and (b) M vs T.
magnifications. Figure 2 shows the morphologies of iron oxide prepared by method 1 whereas Figure 3 shows the morphologies of iron oxide prepared by method 2. They apparently bear different morphologies, but their surfaces all have tiny flakes responsible for porous structures. The images of both of the magnetite materials on the resin matrix indicate waferlike structures. Large wafers (thickness ∼100 nm) are obtained only from method 1 (Figure 2a-c), and small wafers (diameters ∼200 nm) are obtained only from method 2 (Figure 3a-c). SEM images confirm the waferlike structures of iron oxides. There exist many large wafers, arranged in an upward direction with their length in the micrometer region and their width in the nanometer (∼100 nm) region. These large wafers under high resolution account for many tiny flakes individually. Again, these small flakes are arranged in such a way that nanopores are produced in between two small flakes. Thus, there are many nanopores on each iron oxide wafer, resulting in porous hierarchical structures. Interestingly, macropores are produced in between the wafers as a result of the aggregated assembly of the large wafers. The wafers are composed of spherical magnetic particles and hence remain aggregated. To confirm the wafer structure and size distribution, TEM analysis was also carried out. The wafers are composed of spherical Fe3O4 (magnetic) particles and hence remain aggregated, so the size distribution could not be obtained from TEM images (Figure 4a,b). Careful analysis reveals the porous nature of the wafers. The lattice fringes are continuous from the core to the shell for both samples, confirming the perfect single-crystal epitaxial growth of the Fe3O4 layers. By analyzing the lattice fringes of the nanocrystal (Figure 4c,d), the lattice spacing between two planes is observed to be ∼0.29 nm, corresponding to the distance of two (220) planes of Fe3O4. EDAX analysis authenticates the elemental composition of the black wafer, confirming the Fe3O4 formation (Figure 5a,b). From the plot of the N2 adsorption/desorption isotherm and the corresponding pore size distribution of hierarchical nanowafers of Fe3O4, the surface area and pore diameter can be easily calculated. This measurement shows that the BJH adsorption average pore diameter of the wafers is 62.5 nm. The TEM image supports the porous nature of the nanowafers, and SEM analysis agrees well with the BJH adsorption result (Supporting Information Figure S5). Magnetic Moment Measurement. The M(H) curves for the Fe3O4 (large wafers) sample at room temperature and 5 K are shown in Figure 6a. A hysteresis loop, found at room temperature, reveals the superparamagnetic behavior of the resultant magnetic nanoparticles. The hysteresis loop (at room temperature) yields a saturation magnetization (Ms) value of about 0.897 emu/g, whereas the saturation magnetization value of bulk Fe3O4 is 92 emu/g. This indicates the reduction of the saturation 5840 DOI: 10.1021/la903766p
Scheme 3. Schematic Representation of Fe3O4 Formation
magnetization value from that of the bulk sample. The reduction in the saturation magnetization value signifies the decrease in the particle size. This is due to the fact that the energy of a magnetic particle in an external field is proportional to its size via the number of magnetic molecules in a single magnetic domain. The remnant magnetic induction (Mr) and coercivity (Hc) values for the present sample are about 0.077 emu/g and 40 Oe, respectively, both of which are lower than those of bulk Fe3O4.16 At low temperature (5 K), the hysteresis loop also shows ferromagnetic behavior with a saturation magnetization (Ms) value of about 1.186 emu/g and remnant magnetic induction (Mr) and coercivity (Hc) values of 0.269 emu/g and 172 Oe, respectively. The effects of size, structure ,and morphology are concerned with the magnetic properties of the nanomaterials. The disordered structure in amorphous materials and its interface has been shown to cause a decrease in the effective moment. The present system has a heterogeneous crystal structure where magnetic nanoparticles of Fe3O4 are embedded in the nonmagnetic matrix of an amorphous resin. The Fe3O4 nanoparticles also have incomplete crystallization (i.e., with a partial amorphous nature as authenticated by the XRD study). This type of structure could be responsible for the observed reduced values of the saturation magnetization, remnant, and coercivity. The magnetic moments of the nanoparticles undergo a superparamagnetic relaxation at temperatures higher than the blocking temperature (TB). In the absence of an applied magnetic field, when the sample is cooled at T
