Surface-induced phase separation in manganites: A microscopic origin for powder magnetoresistance

摘要: Through the analysis of magnetic properties and nuclear resonance response La2/3Ca1/3MnO3 ceramics with different grain sizes, we have found that poorly conducting regions, some ferromagnetic weakly magnetic, are located at surface grains. We state these regions constitute tunnel barrier responsible for low-field magnetoresistance usually observed in powders half-metallic oxides. In addition, spin disorder accompanying coexistence phases magnetoelectronic character could contribute to large high-field also typical such ceramic samples. From a more general perspective, findings can be relevance understand microscopic origin phase separation manganites.