A -site ordered quadruple perovskite oxides

The A -site ordered perovskite oxides with chemical formula display many intriguing physical properties due to the introduction of transition metals at both A ′ and B sites. Here, research on the recently discovered intermetallic charge transfer occurring between A ′-site Cu and B -site Fe ions in LaCu₃Fe₄O₁₂ and its analogues is reviewed, along with work on the magnetoelectric multiferroicity observed in LaMn₃Cr₄O₁₂ with cubic perovskite structure. The Cu–Fe intermetallic charge transfer leads to a first-order isostructural phase transition accompanied by drastic variations in magnetism and electrical transport properties. The LaMn₃Cr₄O₁₂ is a novel spin-driven multiferroic system with strong magnetoelectric coupling effects. The compound is the first example of cubic perovskite multiferroics to be found. It opens up a new arena for studying unexpected multiferroic mechanisms. (topical review)