Magnetic phases evolution in the LaMn1-xFexO3+y system

TL;DR

This study explores how the magnetic phases of LaMn1-xFexO3+y evolve from ferromagnetic to antiferromagnetic as Fe content increases, revealing a mixed-phase region and cluster-glass behavior through structural and magnetic analysis.

Contribution

It provides a comprehensive analysis of magnetic phase evolution in LaMn1-xFexO3+y, including a model explaining exchange interactions and magnetic behavior across the entire Fe doping range.

Findings

Strong ferromagnetism at x=0 with T_C ~160 K

Transition to antiferromagnetism at x=1 with T_N=790 K

Presence of mixed-phase and cluster-glass behavior in intermediate compositions

Abstract

We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn1-xFexO3+y, in the whole range x=0.0 to 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 (SE) 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) of the FM (AFM) phase, accompanied by a systematic transition broadening for 0.2 < x < 0.7. A model based on the expected exchange interaction among the various magnetic-ion types, accounts very well for the saturation-magnetization dependence on Fe doping.