Isotropic relaxation of the hyperfine field and intercluster interactions in ferrihydrite

Abstract

A theory for the fluctuations of the magnetic moment of the grains in ferrihydrite is developed, and their influence on the Mossbauer spectra is studied in the range of temperatures between 26 K and 65 K. The evolution of the spectra can be interpreted in terms of isotropic relaxation, in spite of the fact that they are not ordinary relaxation spectra. The results make it clear that superferromagnetic relaxation is present.

Occurrence and Constitution of Natural and Synthetic Ferrihydrite, a Widespread Iron Oxyhydroxide

“…The general features of the Mössbauer spectrum of ferrihydrite were reviewed by Murad, , and interpretations of specific aspects of the spectra of synthetic ferrihydrite and corrosion-derived ferrihydrite were given by Chadwick et al, Madsen et al, Arshed et al, and Cianchi et al , Pollard et al . provided a comparison of the spectra of goethite, lepidocrocite, akaganéite, and 2-line and 6-line ferrihydrite at low temperatures and in the presence of applied magnetic fields.…”

“…The general features of the Mo ¨ssbauer spectrum of ferrihydrite were reviewed by Murad, 160,161 and interpretations of specific aspects of the spectra of synthetic ferrihydrite and corrosion-derived ferrihydrite were given by Chadwick et al, 162 Madsen et al, 163 Arshed et al, 164 and Cianchi et al 165,166 Pollard et al 167 provided a comparison of the spectra of goethite, lepidocrocite, akagane ´ite, and 2-line and 6-line ferrihydrite at low temperatures and in the presence of applied magnetic fields. Wide hyperfine field distributions (half widths about 60 kOe) and low quadrupole splittings (<0.1 mm/s) were found to be indicative of ferrihydrite, though higher quadrupole splitting values (to 0.9 mm/s) are commonly reported.…”

A comparative Mössbauer study of the mineral cores of human H-chain ferritin employing dioxygen and hydrogen peroxide as iron oxidants

“…The spectra with either O 2 or H 2 O 2 conform to those of superparamagnetic ferrihydrite[28][29][30][31] with a blocking temperature around 20 K. Specific features include broad spectral absorption lines, characteristic of poor phase crystallinity, and asymmetrically broadened magnetic hyperfine absorption lines. In order to obtain least-squares fits with acceptable χ 2 values, experimental spectra required at least the superposition of two iron subsites, both in the collapsed superparamagnetic state seen at high temperature (120 K) and in the low temperature (4.2 K) magnetically split state.…”