An Investigation Of Electrical, Magnetic And Optical Properties Of La1-xCaxMnO3 (x= 0.0, 0.3, 0.5 And 0.7) System

Solid State Physics Lab, Department of Physics, National Institute of Technology Hazratbal Srinagar, J & K 190006, India

Adv. Mater. Lett., 2015, 6 (8), pp 749-755

DOI: 10.5185/amlett.2015.5875

Publication Date (Web): Aug 02, 2015

Copyright © IAAM-VBRI Press

E-mail: ksbhat.phy@gmail.com

Abstract

Results from a detailed investigation on the structural, optical, electrical and magnetic properties of polycrystalline bulk samples of La_1-xCa_xMnO₃ (x=0, 0.3, 0.5 and 0.7) synthesized by solid state reaction method are presented. The Rietveld analysis of the X-Ray diffraction (XRD) profiles clearly indicated that the XRD patterns are well fitted with orthorhombic structure. Raman spectral features revealed their finger print modes and irreducible representations at the brillouin zone center as per the group theory. It is also observed that as doping is increased, these compounds tend towards a cubic form. Ooptical band gap ‘E_g’ study reveals that the Eg decreases with Ca doping resulting in increase in conductivity. This is consistent with the resistivity measurements. In all the samples, except when x = 0.0 and 0.7, the resistivity at the highest temperature measured (ρ_{300 K}) is less than that at 5 K (ρ_5K), although for temperature T<Tp, the material shows a metal variation of ρ with temperature (d ρ/dT > 0) whereas the value of ρ_{300 K} decreases as x increases. Magnetization study revealed that temperatures corresponding to magnetic transitions Tc increases with doping. It is observed that the composition x = 0.5 show both a paramagnetic to ferromagnetic transition and an antiferromagnetic transition. An effort has been made to relate above observed results in the compound with the structural changes brought about by Ca doping.Possible mechanisms such as activated transport and Zener double exchange are used to understand the phase diagram of these materials.

Keywords

Manganites, magnetization, zener double exchange, activation energy.