Magnetic Properties of Iron Oxides

Compound Space group Lattice constants Magnetic properties Relerence(s) 

Ffematite (a-Fe203) Hexagonal (Rhombohedral) a = 5.03A c=13.8A Weakly ferromagnetic, Tc = 956K antiferromagnetic, Tm = 260 K, [15-17] 

It is well known, and also well documented, that iron oxides can be prepared in the form of nanoparticles. The majority of such studies [26-39] have concentrated on the size effects on the magnetic properties in different iron-oxide phases. Typically, it has been found that transition temperatures decrease with decreasing particle size. For example, in hematite the Morin transition shifts from Tm= 263 K in bulk to temperatures below 4K in particles smaller than 8-20 nm [33]. It is interesting to note that magnetic anisotropy rapidly increases for particles with diameters less than 

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Sohn B.H., Cohen R.E., and Papaefthymiou G.C., Magnetic properties of iron oxide nanoclusters within microdomains of block copolymers, J. Magn. Magn. Mater., 182, 216, 1998. 

The magnetic properties of iron oxides can be determined using Mossbauer spectroscopy, neutron powder diffraction and magnetometry (see Chap. 7). The characteristic parameters are the magnetic moment, the permeability, the saturation magnetization, the magnetic anisotropy constants and the Bhf (Tab. 6.2). 

M. Pregelj, P. Umek, B. Drolc, B. Jancar, Z. Jaglicic, R. Dominko, and D. Arcon, Synthesis, structure, and magnetic properties of iron-oxide nanowires, J. Mater. Res., 21,2955-2962 (2006). 

J. Chatteijee, Y. Haik, C.J. Chen, Size dependent magnetic properties of iron oxide nanopaiticles. J. Magn. Magn. Mater. 257, 113-118 (2003)... 

Toniolo, J.C., Taldmi, A.S., Bonadiman, R., Andrade, M.J., Beigmann, C.R Synthesis by the solution combustion process and magnetic properties of iron oxide (FesOa and a-Fe203) particles. J. Mater. Sd. 42,4785 791 (2007)... 

Coey, J.M.D. (1988) Magnetic properties of iron in soil iron oxides and clay minerals. In Stucki, J.W. Goodman, B.A. Schwert-mann, U. (eds.) Iron in soils and clay minerals. D. Reidel Publ. Co., 397-466... 

In addition to X-ray and neutron-diffraction structural characterization, the physical properties of iron oxides have been studied by a wide variety of techniques. Most common are conventional transport, optical, dielectric, calorimetric and magnetic measurements. In addition, NMR and Mossbauer are widely used. 

In a study of a series of iron-based spinels, Iwakura et al. [313] did not observe a correlation of chlorine evolution overvoltage with the magnetic properties of the oxide. In contrast, a dependence of overpotential on magnetic properties was observed for oxygen evolution. 

Bifunctional biolabels with magnetic and luminescent properties are highly desirable for in vitro and in vivo bioimaging. There are several strategies to use NPs to comprise such biolabels, such as core/shell NPs, for example, the magnetic cores of iron oxide doped with cobalt and neodymium and luminescent shells of Gd203 Eu (Dosev et al., 2005,2007). 

Thin film ceramic materials with important magnetic, optical, electronic, and mechanical properties are often highly anisotropic. Thus, the ability to control orientation is critically important in thin film applications. For many of the oxide materials, as well as Ae ionic materials, aqueous solution or sol-gel routes are the most convenient or the only method of preparation. Examples of these include barium titanate (BaTiOs) used in multilayer capacitors, lead-zirconate-titanate (Pb(Zr,Ti)03, "PZT") used as a piezoelectric material, and zinc oxide (ZnO) used in varistors. Thus, the use of substrates to control orientation can eliminate major problems in deposition of thin films. In some cases, e.g., the many magnetic and non-magnetic phases of iron oxide, the ability to control the phase formed is critical to production of the desired properties. While this can be controlled by solution conditions, the proper surface can add an additional and very effective mechanism of control. 

Figure 5b. Variation in the magnetic properties of metal clusters are investigated by measuring the depletion of a highly collimated cluster beam by an inhomogeneous magnetic field. Fe clusters and their oxides (FexO and Fex02) at several applied fields. The uniform depletion of Fe clusters indicates that their magnetic moments increase approximately linearly with number of atoms, as would be anticipated for incipient ferromagnetic iron. Unexpected, however, is the much larger depletion of iron oxide clusters.

An example of this process of data analysis is provided by the work of Yubero et al. (2000), who studied the structure of iron oxide thin films prepared at room temperature by ion beam induced chemical vapour deposition. Such films find important applications because of their optical, magnetic, or magneto-optical properties. They were produced by bombardment of a substrate with Oj or Oj + Ar+ mixtures, and Figure 4.15 shows RBS spectra of two iron oxide thin films prepared on a Si substrate by each of these bombardment methods. 

Tab. 6.2 Magnetic properties of the iron oxides (data from Coey, 1988, and Soffel, 1991 with permission)...

L.H. (1990) Magnetic properties of some selected, sod-related iron oxides and oxyhydroxides as probed by Fe Mossbauer spectroscopy. In Stanek, J. Pedziwiatr, A.T. (eds.) Condensed matter studies by nuclear methods. Proc. XXIV Zakopane School on Physics. 

H.V.Jr. Adams, J.B. (1993) Pigmenting agents in Martian soils Inferences from spectral, Mossbauer, and magnetic properties of nanophase and other iron oxides in Hawaiian palagonitic soil PN-9. Geochim. Cosmo-chim. Acta 57 4597-4609 Morris, R.V Golden, D.C. ShelfepTD. ... 

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