Increase in Tc and spin glass transition in La 0.9Ca0.1Mn1-yCryO3 (y = 0, 0.1 and 0.2)

Abstract

We report on the structural, frequency dependent ac susceptibility, dc magnetization and magnetoresistance (MR) measurements on polycrystalline samples of La0.9Ca0.1Mn1-yCryO3(y = 0, 0.1 and 0.2) prepared by sol-gel technique. For y = 0, a paramagnetic to ferromagnetic transition is observed at Tc= 136 K. Both for y = 0.1 and 0.2, Tcincreases from 136 to 180 K. For y = 0, the imaginary part of the ac susceptibility shows a broad transition at Tf< Tcwhich does not depend very much on the frequency. However, for y = 0.1 and 0.2, the frequency dependence resembles that of a spin glass. Though all the three samples show a semi-conducting behavior between 300 and 5 K, a negative MR is observed corresponding to Tcand Tf. The value of MR decreases for the Cr substituted samples. © 2004 Elsevier Ltd. All rights reserved.