Low field magnetoresistance in intrinsic granular system La_1-xBa_xMnO₃

The La_1-xBa_xMnO₃ for 0.5≤x was found to be an intrinsic magnetic granular system composed of ferromagnetic/metallic phase and insulating phase. Owing to the magnetic granularity, the La_1-xBa_xMnO₃ system for 0.5≤x shows a three-dimensional percolation-type conduction behavior with a percolation threshold of x_p=∼0.85 (i.e. ferromagnetic volume fraction, θ_p(%), of ∼17%) and a large low field magnetoresistance (MR). The MR of 12-16% at 500 Oe and 77 K was found in the granular ferromagnetic region over a wide range of doping 0.5≤x≤0.75, and the MR was found to become small for x<0.5 and x>0.75.