Spectra of the various Fe oxides

The very low Neel temperature (77 K) of lepidocrocite ensures that this compound is paramagnetic at RT. The Mossbauer spectrum at RT consists of a doublet with a AEq of 0.53 mm s . Magnetically ordered lepidocrocite shows a sextet with a Bhf of 45-46 T at 4K that is lower than that of any other Fe oxide (Johnson, 1969 Murad Schwertmann, 1984). 

Ferrihydrites from ferritin also show a range of TbS, depending on the source organism (human limpet bacterial) (Webb St.Pierre, 1989) (see Fig. 17.3). The Tb of a 2-line ferrihydrite dropped from 50 to 25K when citrate was added at a level of ci-trate/Fe -0.08 (Zhao et al. 1994). Particle interactions in aggregates also affect the Mossbauer parameters. 

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