Complex Ferrimagnetism and Magnetoresistance Switching in Ca-Based Double Double and Triple Double Perovskites

Cation ordering in ABO3 perovskites can lead to interesting and useful phenomena such as ferrimagnetism and high magnetoresistance by spin polarized conduction in Sr2FeMoO6. We used high pressures and temperatures to synthesize the cation ordered AA′BB′O6 perovskites CaMnFeReO6, CaMnMnReO6, and Ca(Mn0.5Cu0.5)FeReO6. These have columnar A/A′ and rocksalt B/B′ cation orders, as found in the recently discovered double double perovskite MnNdMnSbO6, and partial Mn/Cu order over tetrahedral and square planar A′ sites in Ca(Mn0.5Cu0.5)FeReO6 demonstrates that triple double cation order is possible. Neutron diffraction reveals complex ferrimagnetic orders in all three materials; CaMnFeReO6 and Ca(Mn0.5Cu0.5)FeReO6 have large room temperature magnetizations with low temperature switching of magnetoresistance in the latter material, and CaMnMnReO6 displays a high coercivity of 1.3 T at low temperatures.