Cation ordering in transition-metal oxides often drastically modifies their properties. We focus on A-and-B-site-ordered quadruple perovskite-structure oxides AA'3B2B'2O12, in which transition-metal ions are included at the A', B, and B' sites in an ordered manner. In such compounds A'-A', A'-B, A'-B', and B-B' interactions compete with each other and play important role in giving rise to unusual properties. The A-and-B-site-ordered quadruple perovskite CaCu3Fe2Sb2O12with magnetic Fe3+at the B site and nonmagnetic Sb5+at the B' site was successfully synthesized under a high-pressure and high-temperature condition. The B-site Fe3+spin sublattice adapts a tetrahedral framework and the Fe3+-Fe3+antiferromagnetic interaction causes geometrical spin frustration as seen in the double perovskite Ca2FeSbO6. With the introduction of Cu2+into the A' site, the frustration is relieved by strong antiferromagnetic A'(Cu2+)-B(Fe3+) interaction, leading to a ferrimagnetic ordering below 160 K. When B'-site Sb5+was replaced with Re5+, another A-and-B-site-ordered quadruple perovskite CaCu3Fe2Re2O12was synthesized by a high-pressure technique. The compound contains magnetic Fe3+at the B site and Re5+at the B' sites, and strong antiferromagnetic A'(Cu2+)-B'(Re5+) interaction overcomes the A'(Cu2+)-B(Fe3+) interaction, leading to a ferrimagnetism with the ferromagnetic A'(Cu2+)-B(Fe3+) spin arrangement below 550 K. More importantly, the electronic structure of CaCu3Fe2Re2O12is half metallic and the compound shows large magnetoresistance by the spin-dependent transport.
Layered (Cu,Fe) oxides of double perovskite structure: Correlation between structural and magnetic-property changes inBaY(Cu0.5Fe0.5)2O5+δupon high-pressure heat treatment
