Increase in T_c and spin glass transition in La_(0.9)Ca_(0.1)Mn_(1-y)Cr_yO_3 (y=0,0.1 and 0.2)

摘要

We report on the structural, frequency dependent ac susceptibility, dc magnetization and magnetoresistance (MR) measurements on polycrystalline samples of La_(0.9)Ca_(0.1)Mn_(1-y)Cr_yO_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.