8-FeOOH magnetic properties

Magnetic properties of feroxyhyte (8-FeOOH) Phys. Chem. Min. 22 333-341 Bender-Koch, C. Morup, S Madsen, M.B. ... 

Pemet, M. Obrados, X. Fontcuberta, J. Joubert, J.C. Tejada, J. (1984) Magnetic structure and superparamagnetic properties of 5-FeOOH. IEEE Trans. Magn. Mag. 20 1524-1526... 

Rickardite-type compounds with much lower occupancy of the octahedral sites are Fe2.io-2.36Te2 (219, 220), Fe2.iSe2 (221, 222) and Fe2.iS2 (223) to which the PbO type is often attributed. In the PbO or LiOH type, however, the octahedral sites are completely empty. FeS is in fact reported to exist also with exact 1 1 stoichiometry (224). Whereas there is no question that ferrimagnetic (220) Fei.iTe and also Fei.osSe are metallic because of their stoichiometry, FeS is claimed to be non-metallic (224). If the absence of a magnetic moment is due to Fe—Fe bonds (Fe—Fe = 2.60 A) then these bonds should lead to metallic properties too. It is tempting to ascribe the observed resistivity to the presence of thin films of FeOOH or Fe(OH)2. 

P-Fe20s has been obtained by dehydration of P-FeOOH in high vacumn at 170 °C (Braun and Gallagher, 1972). s-FeaOs ean be produced by the reae-tion of alkaline potassium ferrieyanide solution with sodium hypochlorite. It is also obtained (together with a mixture of other iron oxides) in an electric arc under an oxidizing atmosphere (Buttner, 1961). Its magnetic and thermal properties have been investigated by Dezsi and Coey (1973). 

The inconsistencies were explained by Dezsi and Fodor [43], who found that three out of five deposits of natural a-FeOOH and a synthetic sample all gave a unique hyperfine pattern, while the other two did show clear evidence of two fields. The latter result was found to be true of samples containing excess water deposits of stoichiometric a-FeOOH do not show evidence for more than two magnetic sublattices. The Neel temperature was found to be only 367 K, and relaxation occurred at up to 30° below this. It would appear that the defect structure and particle size are both important in determining the properties of a specific sample. 

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