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

• Published in: Chemistry of materials 2000-11, Vol.12 (11), p.3509-3515
• Main Authors: Hong, Chang Seop, Kim, Wan Seop, Chi, Eun Ok, Lee, Kyu Won, Hur, Nam Hwi
• Format: Article
• Language: English
• Subjects: Colossal magnetoresistance; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity phenomena in semiconductors and insulators; Electronic transport in condensed matter; Exact sciences and technology; Galvanomagnetic and other magnetotransport effects; Magnetic properties and materials; Magnetotransport phenomena, materials for magnetotransport; Physics
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm0003931

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 T C. 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 T C, 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 T C. We suggest that the MR found in the polycrystalline sample is dominated by the tunneling of spin-polarized electrons between grains below T C 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 terms of oxygen inhomogeneity and granular effects affected by interfacial melting.