Effect of size disorder on the magnetic and transport properties of the (LaR) 0.55(CaSr) 0.45MnO 3 (R=Nd, Sm & Tb) compounds

Abstract

Electrical resistivity, magnetization and magnetoresistance (MR) measurements have been performed on ABO 3-type (LaR) 0.55(CaSr) 0.45MnO 3 (R=Nd, Sm and Tb) compounds, in which A-site size disorder varies but tolerance factor remains constant. The insulator–metal (I–M) transition temperature ( T p) and the Curie temperature ( T C) of these compounds decrease from ∼170 K for R=Nd to ∼120 K for R= Tb, which is consistent with increasing size disorder. All the samples exhibit maximum in MR at T p and an MR of 70–80% at 5 K. The reduced T p and T C and enhanced MR in these compounds vis-`a-vis the T p and T C of ∼230 K of the standard La 0.55Ca 0.45MnO 3 compound, may be attributed to the local structural distortions induced by enhanced A-site size-disorder.