Phase Transitions in Fe4+(3d4)-Perovskite Oxides Dominated by Oxygen-Hole Character

Abstract

The electronic properties of CaFe 1- x Co x O 3 , a perovskite system dominated by oxygen-hole character, were studied experimentally. A partial Co-substitution has been found to induce a serial transformation from a charge-disproportionated, antiferromagnetic (AF), insulating phase (Phase I, x <0.1) to a charge-melted, AF, metallic phase (Phase II, 0.1≤ x <0.2) and then to a ferromagnetic and metallic phase (Phase III, 0.2< x ≤0.5). Both the AF phases I and II have a screw spin structure with a propagation vector k //<111> , while the length of wave vector changes from | k |=0.161 a * at x =0 to | k |=0.13 a * at x =0.1. We ascribe the serial transformation to broadening of the oxygen-hole band with increasing Co content.