A μSR study of valence fluctuations in Fe3O4

New µSR measurements on Fe3O4, showing a temperature shift of the "247 K anomaly" in applied fields, demonstrate muon-conduction-electron cross-relaxation and yield a 0.11 eV barrier for near-neighbor B-site electron transfer above the Verwey transition. µSR relaxation rates and the possibility of molecular-polaron formation are discussed

Experimental evidence for a Mott-Wigner glass phase of magnetite above the Verwey temperature

New muon-spin-relaxation (µSR) results on magnetite are reported and discussed in light of earlier Mössbauer, neutron, and µSR results. Modification of the µSR anomaly (observed at 247 K in zero field), when an external magnetic field is applied, provides evidence that the anomaly results from cross relaxation between the muon Larmor precession and the electron-correlation process in the B sublattice. The combined results strongly indicate that phonon-assisted electron hopping is the principal conduction mechanism above the Verwey transition temperature (TV). Together with theoretical evidence, these data support Mott’s suggestion that above TV magnetite is in the Wigner-glass state