Ferromagnetic Cuprates, CaCu₃Ge₄O₁₂ and CaCu₃Sn₄O₁₂, with A-site Ordered Perovskite Structures

Abstract

We succeeded in synthesizing A-site ordered perovskites, CaCu₃Ge₄O₁₂ and CaCu₃Sn₄O₁₂, under high pressure and high temperature conditions. The magnetic measurements revealed that these compounds are ferromagnets in contrast to the isostructural antiferromagnet, CaCu₃Ti₄O₁₂. The ferromagnetism in CaCu₃Ge₄O₁₂ and CaCu₃Sn₄O₁₂ comes from the special alignment of CuO₄ planes in the perovskite structure. On the other hand, the involvement of Ti-3d orbitals in magnetic interactions give rise to the antiferromagnetic superexchange interaction and it overcomes the ferromagnetic direct interaction in CaCu₃Ti₄O₁₂. The finding demonstrates that either ferromagnetic or antiferromagnetic behavior can appear within the same structural framework.