Magnetic phase evolution in the LaMn_(1-x)Fe_xO_(3+y) system

摘要

We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn_(1-x)Fe_xO_(3+y), in the whole range 0.0≤x≤1.0, prepared by solid state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn-Teller distortion, thus favoring a ferromagnetic (FM) superexchange interaction between Mn~(3+)-O-Mn~(3+). For x=0.0 the oxygen excess (y ≈ 0.09) produces vacancies in the La and Mn sites and generates a fraction around 18% of Mn~(4+) ions and 82% of the usual Mn~(3+) ions, with possible double-exchange interaction between them. The Fe doping in this system is known to produce only stable Fe~(3+) ions. We find an evolution from a fairly strong FM phase with a Curie temperature T_C～ 160 K, for x=0.0, to an antiferromagnetic (AFM) phase with T_N=790 K, for x=1.0, accompanied by clear signatures of a cluster-glass behavior. For intermediate Fe contents a mixed-phase state occurs, with a gradual decrease (increase) in the FM (AFM) phase, accompanied by a systematic transition broadening for 0.2