Role of nonuniform magnetic barrier on the grain boundary magnetotransport in perovskite manganites

Based on surface induced phase separation and progressive disorder at the grain boundaries, a core-shell model is presented to describe the magnetoresistance of the grain boundaries in perovskite manganites. Considering the band-bending effects, the electronic structure of the grain boundary and its effects on magnetotransport are studied. Within this model, the dependence of the magnitude of low-field magneotresistance, the form of the high-field, and the crossover from low-field response to a high-field one, on the surface properties are examined explicitly. These results agree with experimental observations well.