A-Type Antiferrospin Ordering under the Antiferroorbital Order in Perovskite-Type Compounds

Abstract

The appearance of the A-type antiferrospin (A-AFS) order under the antiferroorbital (AFO) order observed in some perovskite-like compounds is studied theoretically to resolve discrepancies between existing theories and to clarify its mechanism in an open way. The various kinetic exchange interactions (KEI) between degenerate dγ orbitals of neighboring magnetic ions are derived not to violate the crystal symmetry with making no assumption on the transfer integrals. The KEI constants which are affected by the Hund coupling under the AFO order due to the joint effect of the cooperative Jahn–Teller effect (CJTE) and the orbital exchange interaction can explain successfully the appearance of the A-AFS ordering. The close relation between the AFO and A-AFS orders, the role of the CJTE, and the effect of the presence of the unfilled dε orbitals are clarified. The obtained results are consistent with the properties of the A-AFS order observed in LaMnO₃, MnF₃ and KCuF₃.