Magnetic Properties of REMe0.5Mn0.5O3(RE = Rare Earth Element, Me = Ni, Co)

Magnetic properties of REMe 0.5 Mn 0.5 O 3 with Me = Ni and Co are investigated for a series of rare earth (RE) elements. In both systems with Me = Ni and Co, the Curie temperature ( T C ), below which the magnetic moments of Me 2+ and Mn 4+ allign ferromagnetically, decreases remarkably as RE goes from La to heavier elements; from 295 K for RE = La to 50 K for Lu with Me = Ni, and from 250 K for La to 95 K for Ho with Me = Co. The decrease of T C is interpreted as due to the bond angle (θ) dependence of the superexchange interactions between Me 2+ and Mn 4+ through O 2- ; T C is roughly linear to cos 2 θ as predicted by a simple theory [C. Boekema et al. : Int. J. Mag. 3 (1972) 341], but a distinct deviation from the linear relation is observed for the late RE elements. The magnetic moments of RE ions appears only in a low temperature region, typically below 30 K. Qualitative discussion on the exchange interactions involving RE is presented.