Ferromagnetic interactions in Mn3+ based perovskites.

La0.7Sr0.3Mn(3+)0.85Sb(5+)0.15O3 and La0.7Sr0.3Mn(3+)0.8Sb(5+)0.1Ge(4+)0.1O3 compounds with dominantly isovalent Mn3+ ions were studied by neutron powder diffraction and magnetization measurements. The compounds are basically ferromagnetic, with magnetic moments slightly above of 3 µB/Mn. Upon temperature decrease, the compounds exhibit structural transition from a rhombohedral phase to orbitally disordered orthorhombic one. The structural transitions occur well above the temperature of magnetic ordering (Tc ≈ 130 K). It is suggested that the ferromagnetic state is governed by the positive part of superexchange interactions Mn(3+)‒O‒Mn(3+), which is enhanced by Mn(eg)‒O(2p) hybridization.