A-site ordered quadruple perovskite oxides AA′3B4O12

The A-site ordered perovskite oxides with chemical formula AA'3B4O12 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 0-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 (LaCu33+Fe43+O12 -> LaCu32+FE43.75+O12) 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.