Hematite magnetic properties

I 6 Electronic, electrical and magnetic properties and colour 6.3.4.6 Hematite... 

Fig. 6.7 Temperature dependence of the magnetic properties of hematite. Tc = Curie temperature,Tm = Morin temperature, pm = paramagnetic region, wfm = weakly ferromagnetic region afm = antiferromagnetic region. The insets show simulated Mossbauer spectra of hematite in the paramagnetic, weakly ferromagnetic and antiferromagnetic states (Murad, 1988, with permission).

Like X-ray diffraction patterns, neutron and electron diffraction patterns provide averaged information about the structure of a compound. Details of these techniques are given in works by Hirsch et al. (1965) and West (1988). Neutron diffraction involves interaction of neutrons with the nuclei of the atoms. As the neutrons are scattered relatively evenly by all the atoms in the compound, they serve to indicate the positions of the protons in an oxide hydroxide. This technique has been applied to elucidation of the structure and/or magnetic properties of goethite (Szytula et al., 1968 Forsyth et al., 1968), akaganeite (Szytula et al., 1970), lepidocrocite (Oles et al., 1970 Christensen Norlund-Christensen, 1978), hematite (Samuelson Shirane, 1970 Fernet et al., 1984) and wiistite (Roth, 1960 Cheetham et al., 1971 Battle Cheetham, 1979). A neutron diffractogram of a 6-line ferrihydrite was recently produced by Jansen et al. (2002) and has helped to refine its structure (see chap. 2). 

The industrial dust deposited in the metropolitan area of Shanghai consisted of high-coercivity (hematite) and low-coercivity (magnetite/maghemite) particles, usually < 10 pm in size. Four different dust sources could be distinguished on the basis of magnetic properties (Shu et al. 2000). Given previously reported links between... 

K. Morup, S. (2000) Magnetic properties of hematite nanoparticles. Am. Phys. Soc. 

Aust. J. Soil Res. 23 543-567 Flanders, P.J. Remeika, J.P. (1964) Magnetic properties of hematite single crystals. Phil. 

Dunlop, D.J., Magnetic properties of fine-hematite, Ann. Geophysique, 27, 269, 1971. 

Ozaki, M., Ookoshi, N., and Matijevic, E., Preparation and magnetic properties of uniform hematite platelets, J. Colloid Interface ScL, 137, 546, 1990. 

Bocqnet S (1996) Snperparamagnetism and the Mossbaner spectrum of goethite a comment on a recent proposal by Coey et al. J Phys Condensed Matter 8 111-113 Bodker F, Hansen MF, Bender Koch C, Lefmann K, Morap S (2000) Magnetic properties of hematite nanoparticles. Phys Rev B 61 6826-6838... 

Brown, N.E., Navrotsky, A., Nord, G.L., Baneijee, S.K. (1993) Hematite (Fe203)-ilmenite (FeTiOs) solid solutions Determinations of FeTi order from magnetic properties. Am Mineral 78 941-951 Burton, B.P. (1987) Theoretical analysis of cation ordering in binary rhombohedral carbonate systems. Am Mineral 72 329-336... 

Nord, G.L., Lawsort, C.A. (1989) Order-disorder transition-induced twin domains and magnetic properties in ihnenite-hematite. Am Mineral 74 160-176... 

Ishikawa Y (1962) Magnetic properties of the ilmenite-hematite system at low temperature. J Phys Soc Japan 17 1835-1844... 

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... 

Berry et al. [206] investigated the structural and magnetic properties of Sn-, Ti-, and Mg-substituted a-Fe203. Ti" + ions in Ti-substituted hematite (10% Ti), which occupy both the substitutional and interstitial sites, reduced the HMF... 

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