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.