On the nature of grain boundaries in the colossal magnetoresistance manganites

The electrical transport properties of grain boundaries in the epitaxial La 2/3Ca1/3MnO3-delta thin films have been studied as a function of temperatur e and applied magnetic field. Below the Curie temperature T-C an additional grain boundary resistance, highly non-linear current-voltage curves, and a large magnetoresistive effect in the whole temperature regime below T-C ar e found. The results can be explained consistently by the presence of a dis ordered, a few nm wide paramagnetic grain boundary layer that is depleted b elow T-C due to an increase of the work function 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 manganite s.