Manganese-mediated ferromagnetism in La2Fe1−x Mn2x Cr1−x O6 perovskite oxides

Abstract

We have investigated the structure and magnetic properties of the perovskite oxides of the formula La2Fe1−x Mn2x Cr1−x O6 (0 < x < 1.0). For 0 < x ≤ 0.5, the members adopt the orthorhombic (Pbnm) structure, where the transition metal atoms are disordered at the 4b sites and the MO6 (M = Fe, Mn, Cr) octahedra become increasingly distorted with increasing x. For 0.65 ≤ x < 1.0, the members adopt the rhombohedral (R-3c) structure that is similar to LaMnO3+δ (δ ≥ 0.1) where the MO6 octahedra are undistorted. While the magnetic properties of the latter series are largely similar to the parent LaMnO3+δ arising from the double-exchange (DE) between mixed valent MnIII/MnIV, the magnetic properties of the orthorhombic members show a distinct (albeit weak) ferromagnetism (T C ∼ 200 K) that seems to arise from a MnIII-mediated superexchange (SE) between FeIII/CrIII in the disordered perovskite structure containing FeIII, MnIII and CrIII.