Physics of grain boundaries in the colossal magnetoresistance manganites

The electrical transport properties of grain boundaries in epitaxial thin f ilms of the perovskite manganites have been studied as a function of temper ature and applied magnetic field. Below the Curie temperature T-C an additi onal grain boundary resistance, highly nonlinear current-voltage curves, an d 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 deplete d below T-C due to an increase of the workfunction of the ferromagnetic gra in material adjacent to this layer. The related band bending and space char ge effects are important for the physics of grain boundaries in the mangani tes. (C) 2000 Elsevier Science B.V. All rights reserved.