Increase in Tc and spin glass transition in La 0.9Ca 0.1Mn 1− yCr yO 3 ( 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 La 0.9Ca 0.1Mn 1− y Cr y O 3 ( y=0, 0.1 and 0.2) prepared by sol–gel technique. For y=0, a paramagnetic to ferromagnetic transition is observed at T c=136 K. Both for y=0.1 and 0.2, T c increases from 136 to 180 K. For y=0, the imaginary part of the ac susceptibility shows a broad transition at T f< T c which 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 T c and T f. The value of MR decreases for the Cr substituted samples.