Origin of spin-glass and exchange bias in La1/3Sr 2/3FeO3-γ nanoparticles

Abstract

The structure and the magnetic properties of nanopowdered samples of La1/3Sr2/3FeO3-γ with average particles size d in the range of 67-367nm prepared by a sol-gel method were investigated in detail. The samples were characterized by X-ray diffraction, scanning electron microscopy, specific heat, Mössbauer spectroscopy, ac susceptibility, and magnetization measurements. Exchange bias with vertical magnetization shift was found in all samples. Charge ordering and antiferromagnetism were observed close to 200K for large particles (d ≥304nm) samples, while for particles with intermediated and smaller values (d ≤156nm) a cluster-glass like behaviour and a short range charge ordering were seen near 115K and 200K, respectively. The spin-glass like and exchange bias behaviour in nanopowdered samples of La1/3Sr2/3FeO 3-γ are associated to compact Fe3+ antiferromagnetic (AF) clusters caused by an oxygen deficiency, which was found to be higher in the samples with the smallest average particles sizes. The effect of exchange bias and vertical magnetization shifts are explained by a simple model involving the interaction of one AF phase with a canted AF phase. © 2014 AIP Publishing LLC.