Influence of Co doping on properties of Pr0.8Na0.2Mn(1-y)CoyO3 perovskites

The influence of the cobalt substitution for manganese ions in the series of the perovskites Pr0.8Na0.2Mn(1-x)CoxO3 (0≤x≤0.1) was investigated. The study of electric and magnetic properties was carried out on sintered polycrystalline samples. The composition of x=0.04 exhibits an insulator to metal-like (I-M) transition at ∼106 K, connected with a ferromagnetic arrangement. For x=0.1, however, an insulating behavior persists down to low temperatures in spite of the transition to the bulk ferromagnetism. The observed properties are related to an acting of the cobalt ions as point defects. They disturb the tendency to charge ordering and instead of the antiferromagnetic arrangement typical for x=0 ferromagnetic double-exchange interactions Mn3+-O2--Mn4+ and Mn3.5+δ-O2--Co2+, decisive for the resulting behavior, arise