Enhancement of Magnetoresistance in Granular CrO₂/Polystyrene Composites

We present a study of magnetotransport in CrO₂/polystyrene (PS) composites over a range of polystyrene concentration (0-30 wt.%). In the experiment, an obvious enhancement in magnetoresistance (MR) is observed at 77 K and at room temperature as the half-metallic CrO₂ particles are encapsulated with a thin layer of insulating polystyrene. The enhanced MR can be interpreted in terms of spin-dependent intergranular tunneling with 4-nm-thick PS barrier. Moreover, it is found that the novel PS barrier contributes to room-temperature MR more significantly than that at 77 K. Temperature dependence of resistance is good agreement with ～ T^-1/4 in the temperature range from 77 to 298 K.