Physics of grain boundaries in the colossal magnetoresistance manganites

Abstract The electrical transport properties of grain boundaries in epitaxial thin films of the perovskite manganites have been studied as a function of temperature and applied magnetic field. Below the Curie temperature T C an additional grain boundary resistance, highly nonlinear current–voltage curves, and a large magnetoresistive effect in the whole temperature regime below T C are found. The results can be explained consistently by the presence of a disordered, a few nm wide paramagnetic grain boundary layer that is depleted below T C due to an increase of the workfunction of the ferromagnetic grain material adjacent to this layer. The related band bending and space charge effects are important for the physics of grain boundaries in the manganites.