On the nature of grain boundaries in the colossal magnetoresistance manganites

The electrical transport properties of grain boundaries in the epitaxial La 2/3 Ca 1/3 MnO 3 − δ thin films have been studied as a function of temperature 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 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 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 manganites.