Colossal magnetoresistance in cluster glass-like insulator La0.67Sr0.33(Mn0.8Ni0.2)O3

Substitution of Ni for Mn in La0.67Sr0.33MnO3 (LSMO) lowers the Curie temperature T-C from 365 K for LSMO to 194 K for La0.67Sr0.33(Mn-0.8 Ni-0.2)O-3, which exhibits a cluster glass-like state. The oxide is insulating under both zero field and 60 kOe, but application of the magnetic field induces colossal magnetoresistance (CMR) especially at low temperature. Far below T-C, the compound's field dependence of resistivity has a very similar shape with that of metallic perovskite manganite at relatively high temperature when the spin fluctuation grows stronger. The results indicate that the ferromagnetic superexchange between Ni and Mn, is helpful for the overall ferromagnetic exchange components just overcoming the generic antiferromagnetic exchange components, which leads to the presence of the cluster glass-like state. The reduction of the magnetic disorder and the suppression of the spin fluctuation in Mn-O layer by the external magnetic field are suggested to explain the CMR effect in this insulating compound (C) 1999 American Institute of Physics. [S0021-8979(99)36008-4].