Giant Magnetoresistance in Granular Perovskite La_0.8Sr_0.2MnO₃

The electric and magnetic properties in granular perovskite La_0.8Sr_0.2MnO₃ have been investigated. A giant magnetoresistance (GMR) has been observed at temperatures well below T_C, the Curie temperature, associated with crystal intrinsic magnetic properties. The granular GMR effect is also isotropic but shows some characteristics different from those in the films and crystals of similar perovskites. This suggests an effect of interfacial spin-dependent tunneling in the granular perovskite at temperatures much lower than T_C. In addition, with the reduction of grain size, an evident superparamagnetic behavior has been observed.