Nonadiabatic small polarons, positive magnetoresistance, and ferrimagnetism behavior in the partially inverse Mn2−xV1+xO4 spinels

Abstract

We present experimental results of electrical resistivity (ρ), magnetoresistance (MR), Seebeck coefficient (S), and magnetic susceptibility (χ) experiments at high temperature on the spinel Mn2−xV1+xO4 series with x=0, 13, and 1, prepared by solid state reaction. The Rietveld analysis of neutron powder diffraction (NPD) patterns confirm the expected cubic symmetry (SG: Fd-3m) with cell parameters around 8.5 Å. We also precisely calculate the distribution of Mn/V cations, in the tetrahedral and octahedral sites, for the whole series showing an important degree of inversion. The magnetic susceptibility and electrical transport properties show ferrimagnetic and semiconductor behaviors, respectively. A large difference detected between the activation energies for S and ρ indicates the presence of small polarons and the temperature dependence of ρ is well fitted with the nonadiabatic polarons model. All the samples present positive MR at room temperature, in particular, the highest value (around 1%) was observed in the MnV2O4 sample.