Orbital Hybridization and Magnetic Coupling of the A-Site Cu Spins in CaCu₃B₄O₁₂ (B = Ti, Ge, and Sn) Perovskites

Abstract

X-ray absorption spectroscopy (XAS) spectra near the O K-edge of A-site-ordered perovskite with A-site Cu(2+) (S = (1)/(2)) spins were measured. The spectra of ferromagnetic CaCu(3)Ge(4)O(12) and CaCu(3)Sn(4)O(12) showed hybridization between Cu 3d and O 2p orbitals, but magnetic circular dichroism measurement revealed that the O 2p orbital played a less important role in magnetic interaction. The XAS spectra of antiferromagnetic CaCu(3)Ti(4)O(12), on the other hand, showed strong hybridization of the Cu 3d, Ti 3d, and O 2p orbitals. These results demonstrated that direct exchange interaction of the Cu(2+) spins primarily determined the ferromagnetic ordering of CaCu(3)Ge(4)O(12) and CaCu(3)Sn(4)O(12), whereas the involvement of Ti 3d orbitals induced the antiferromagnetic property in CaCu(3)Ti(4)O(12).