Magnetic properties of La0.55CaxSr0.45−xMnO3 perovskite manganite

Abstract

Conventional solid-state reaction technique was used to prepare the studied samples La0.55CaxSr0.45−xMnO3 (x = 0.0, 0.1, 0.2). Their structural and magnetic properties have been investigated to find the effect of calcium doping on the D.C. and A.C. magnetic properties of the compounds. Room temperature XRD investigations confirm rhombohedral structure with space group R-3c for all the samples. Lattice parameter is found to decrease with increase in Ca(x) content. Microstructure was examined from the images taken by Scanning Electron Microscopy (SEM) and chemical compositions were determined by an energy dispersive X-ray diffractometer (EDX). The zero-field cooled (ZFC) and field cooled (FC) DC magnetization measurements reveal paramagnetic (PM) to ferromagnetic (FM) transition in them upon cooling through their Curie temperature (TC). But the FM state coexists with the residual canted anti-ferromagnetic state rather than a pure FM state in the samples. The TC values are dependent on Ca(x) content of the samples. Moreover, XRD analysis and EDX data reveals the presence of Mn deficiency in the studied samples. Presence of minor secondary Mn3O4 phase creates this deficiency resulting a significant decrease in TC and strongly influences the magnetic properties. The values of A.C. permeability (μʹ) also depend on Ca(x) content as well as grain size that can be explained by Globus equation. However, μʹ values of the samples remain almost constant over a wide range of frequency which indicates the compositional stability of the perovskites. The magnetic modulus demonstrates the dynamics of their A.C. permeability by screening out the stray/any other effects in them. The Nyquist plots of magnetic modulus of the samples show the type of their magnetic relaxation.