Ferromagnetic cuprates CaCu3Ge4O12 and CaCu3Sn4O12 with A-site ordered perovskite structure

A-site ordered perovskites CaCu3Ge4O12 and CaCu3Sn4O12, which are isostructural to antiferromagnetic CaCu3Ti4O12, were found to be ferromagnets. The special alignment of the CuO4 planes in the perovskite structure plays an important role in the magnetic properties of Cu2+ spins. Direct exchange interaction gives rise to the ferromagnetic behavior in CaCu3Ge4O12 and CaCu3Sn4O12, whereas involvement of Ti-3d orbitals produces the antiferromagnetic superexchange interaction in CaCu3Ti4O12. This finding demonstrates that either ferromagnetic or antiferromagnetic behavior can appear within the same structural framework.