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

Abstract

New muon-spin-relaxation (\ensuremath{\mu}SR) results on magnetite are reported and discussed in light of earlier M\"ossbauer, neutron, and \ensuremath{\mu}SR results. Modification of the \ensuremath{\mu}SR 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 (${T}_{V}$). Together with theoretical evidence, these data support Mott's suggestion that above ${T}_{V}$ magnetite is in the Wigner-glass state.