Impedance, dielectric, and magnetic properties study of La2CrMnO6 ceramics

Abstract

Double perovskite La2CrMnO6 (LCrMO) ceramics was prepared using solid state reaction technique sintered at 1433 K in ambient air. Wide range impedance spectroscopy study conducted in 20 Hz – 1 MHz over 85–440 K range allowed for separation of grain bulk and grain boundary effects. Electrical features corresponded to grain bulk and grain boundary properties were investigated. The features of imaginary part of impedance indicated electrical relaxation phenomenon occurrence in LCrMO. The temperature dependence of most probable relaxation times, τZ, obtained from impedance spectra collected below 120 K were fitted using Arrhenius relation and the activation energy equal to 0.14 eV was estimated. The Kramers-Kronig transform of the dielectric permittivity enabled to distinguish relaxation process over 85–170 K temperature range. The variable range hopping of small polaron model was fitted with better accuracy to the dielectric relaxation times, τdiel, temperature dependence, which indicated occurrence of Fermi glass related to local disorder. AC and DC conductivity relaxation processes, which corresponded to grain bulk and grain boundary contributions, respectively, were discriminated. Magnetic susceptibility of LCrMO ceramics was measured over 5–300 K range. Bifurcation between zero field cooled and field cooled dependence occurred below ~120 K. Magnetization M(H) hysteresis loops were not dependent on temperature and exhibited low values of coercive field, ~108 Oe and remnant magnetization, ~6 emu g−1, over 5–200 K range. The magnetic spin glass features were deduced. We note that coupling between electric and magnetic properties was detected: anomaly around 87 K in magnetization, related to magnetic transition, is accompanied by deviation of dielectric relaxation times discerned from the VRH temperature dependence.