Investigation of magnetic interactions and transport mechanism in Al−substituted La0.4Bi0.6MnO3 manganites

Abstract

In this paper, the effect of Al substitution on structural, magnetic, electrical and magnetotransport properties of the polycrystalline La0.4Bi0.6Mn1−xAlxO3 (where, x = 0.01, 0.05 and 0.1) have been investigated. Powder X-ray diffraction measurement and Rietveld refinement technique revealed that all the samples crystallize into orthorhombic structure having Pnma space group. The X-Ray photoemission spectra (XPS) measurements have been carried out on the samples to understand the core level states of Mn, Al and O in the samples. The lattice parameters and grain size are found to decrease with increasing Al concentration which is also evident from scanning electron micrographs. The magnetic measurements suggest the ferromagnetic nature along with trivial charge ordered phase present in the samples. Interestingly the suppression of charge ordering is observed with increasing Al substitution at Mn site. Frequency dependent ac susceptibility measurements reveal dynamic fluctuations due to cooperative interactions between antiferromagnetic domain pinning effects giving rise to spin-glass property. Electrical resistivity measurements reveal the semiconducting behavior of the sample in the entire temperature range studied. Analysis of resistivity data with temperature suggests that for T>(θD/2, the Debye temperature) the electrical transport is governed by non-adiabatic small polaron hopping mechanism. Whereas for T≤θD/2 the conduction process follows Shklovskii-Efros variable range hopping mechanism. Further the MR studies explain the grain contribution on the observed electrical transport properties.