Magnetic and electrical properties of Mn-substituted (La0.85Ag0.15)CoO3 compounds

Abstract

Abstract In this work, we have studied the influence of Mn substitution at the Co site of (La0.85Ag0.15)CoO3 on magnetic and electrical transport properties. Single phase samples of (La0.85Ag0.15)(Co1−yMny)O3 for y = 0, 0.05, 0.10, 0.15, 0.20, 0.30 and 0.40 have been prepared by solid state route. The X-ray diffraction (XRD) patterns recorded at room temperature show that these samples for y = 0–0.3 crystalize in rhombohedral structure with R 3 ¯ c space group, while for y = 0.4, it transforms into orthorhombic structure with Pbnm space group. The lattice parameters increase systematically with Mn concentration due to the substitution of larger Mn3+ ions at Co3+ site. Temperature variation of magnetization data and their analyses show that all samples exhibit ferromagnetic transition with a large increase in transition temperature (TC) upon Mn substitution, i.e. from 3.4 K for y = 0–211.0 K for y = 0.4. Such increase in TC is explained in terms of improved double exchange interactions across Co3+-O2−-Co4+, Co3+-O2−-Mn3+ and Mn3+-O2−-Mn4+ networks. The presence of considerable irreversibility between zero field cooled and field cooled magnetization data and the lack of saturation of magnetization data even at 10 T field is explained in terms of domain-wall pinning effect and the presence of competing antiferromagnetic interaction. Eventhough the electrical resistivity falls several orders of magnitude upon Mn substitution, no metal-insulator transition is observed.