Colossal Magnetoresistance in La0.7Ca0.3MnO3-δ: Comparative Study of Single-Crystal and Polycrystalline Material

Abstract

The magnetoresistance (MR) and transport properties of both single-crystal and polycrystalline samples of La0.7Ca0.3MnO3-δ (LCMO) have been investigated to elucidate their magneto transport behaviors near and below the Curie temperature TC. We find that negative MR is heavily dependent upon the surface morphology in the low-temperature, ferromagnetic regime. The polycrystalline sample postannealed at 1400 °C under the oxygen atmosphere exhibits large low-field MR in the whole temperature range below TC, which is about 20% at 0.5 T. On the other hand, the single-crystal sample shows the remarkable suppression of resistivity only at the narrow temperature region near TC. We suggest that the MR found in the polycrystalline sample is dominated by the tunneling of spin-polarized electrons between grains below TC while the MR in the single crystal is mainly ascribed to the suppression of spin fluctuation. The difference in the MR property between the single-crystal and polycrystalline samples is discussed in te...