A-site magnetism in quadruple perovskite structure oxides

Quadruple perovskite structure oxides with a chemical formula AA’₃B₄O₁₂ can accommodate transition-metal ions at both A’ and B sites. When the B site is occupied by non-magnetic cations, the magnetic interactions between the spins at the orthogonally-oriented A’-sites provide a variety of non-trivial magnetic structures in the cubic symmetry sublattices. CaCu₃Ge₄O₁₂ and CaCu₃Sn₄O₁₂ show ferromagnetism of the A’-site Cu²⁺ (S = 1/2) spins due to Cu–Cu direct-exchange interaction, whereas CaCu₃Ti₄O₁₂ shows the G-type antiferromagnetim, where the antiferromagnetic Cu–O–Ti–O–Cu superexchange interaction overcomes the Cu–Cu direct-exchange interaction. In the solid solution system of CaCu₃(Ge-Ti-Sn)₄O₁₂, very unusual ferromagnetic-antiferromagnetic-ferromagnetic spin-structure change was observed. In LaMn₃V₄O₁₂, on the other hands, the nearest neighboring Mn²⁺ high spins (S = 5/2) align with each other with an angle of 120 degrees. The electrons of V at the B site are delocalized and do not apparently contribute to the magnetic behavior. In CaFe₃Ti₄O₁₂ and CaCo₃Ti₄O₁₂ with respectively the A’-site Fe²⁺ (S = 2) and Co²⁺ (S = 3/2) spins, the magnetic structures consist of three interpenetrating mutually orthogonal magnetic sublattices. The fourth nearest neighbour spin exchanges as well as spin orbit coupling play an essential role for stabilizing the unusual spin structures.