On the nature of grain boundaries in the colossal magnetoresistance manganites

Abstract

The electrical transport properties of grain boundaries in the epitaxial La2/3Ca1/3MnO3 − δ thin films have been studied as a function of temperature and applied magnetic field. Below the Curie temperature TC an additional grain boundary resistance, highly non-linear current-voltage curves, and a large magnetoresistive effect in the whole temperature regime below TC 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 TC 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.