Electric properties of erbium cobaltites

Abstract

The temperature and electric, including magnetic-field, characteristics of ceramic samples Er1−xSrxCoO3−δ at temperatures ranging from room to liquid-helium temperatures and in magnetic fields to 4kOe applied perpendicular to the direction of the transport current have been investigated. Current-induced nonlinear features of percolation transport which are characteristics for a metal-insulator transition have been observed for weak currents. Regular behavior such as a decrease of the breakdown field with increasing concentration of divalent Sr and ordering effects with decreasing temperature have been observed for the first time. An anomalous increase of the conductivity and a large magnetoresistance effect in narrow Er and Sr concentration ranges, narrower and shifted more in the direction of the metallic phase than in lanthanum manganites, has been observed. The special behavior of the conductivity and the magnetoresistance, including nonlinear effects, are explained from a unified point of view—magnetostructural phase transitions, induced by a corresponding dopant concentration, temperature, or magnetic field, as well as the presence of a spin-dependent contribution, associated with double-exchange of delocalized electrons between heterovalent cobalt ions, to the mechanism of electron correlation.