Moessbauer study of quasi-particle spectrum in magnetite

The recoil-free absorption fraction in magnetite shows a series of dips at characteristic transition temperatures below 150 K, and are indicative of a complex charge-lattice coupling process. These results are ascribed to a spectrum of thermally excited charge complexes which behave as quasi-particles. A multitude of valence instabilities is considered in which four kinds of oxidation states are involved with charges of 3+, 2+, 4+ and 1+. A model is suggested for the electric conductivity which deals with the growth of the quasi-particle densities with rising temperatures, taking into account the probability for these densities to oscillate at phonon frequency. (Auth.)