8-FeOOH Neel temperature

The high pressure form of FeOOH is more compact than any other iron oxide hydroxide, hence it has a higher than usual Neel temperature of 470 K. At room temperature, high pressure FeOOH is antiferromagnetic with a collinear spin arrangement parallel to the c-axis (Fernet et al., 1973). High-pressure FeOOH is completely miscible with CrOOH. Substitution with Cr reduces T to the extent that with 80%... 

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. 

D. Chambaete, E. De Grave, On the Neel temperature of -FeOOH structural dependence and its Implications. J. Magn. Magn. Mater. 42, 263-268 (1984)... 

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