Influence of grain size on the electronic and the magnetic properties of La0.7Ca0.3MnO3-δ

Polycrystalline La0.7Ca0.3MnO3-delta (LCMO), prepared by a solid-state reaction, was annealed at different temperatures T-A. The variation of T-A was responsible for observed changes in the physical properties, including a shift in the metal-insulator transition temperature, which is explained by variation in the oxygen content. At low temperatures the magnetization of LCMO samples was also observed to be dependent on T-A. A reduction of the grain boundaries leads to enhancement of both the magnetization and the sensitivity for low-field magnetoresistance. By using Mn L-3-edge x-ray absorption, it was also found that the Mn3+/Mn4+ ratio increases with the grain size, and that the oxygen content in LCMO is governed by the grain boundaries. (C) 2004 American Institute of Physics.