Magnetic inhomogeneity in colossal magnetoresistive La 0.67Ca 0.33MnO 3− δ perovskite ceramics

Abstract

Magnetic inhomogeneity in colossal magnetoresitive lanthanum manganites and its effect on MR properties are reported. Polycrystalline bulk specimens of La 0.67Ca 0.33MnO 3 were prepared by solid state reaction and sol–gel route. By controlling materials processing parameters, CMR specimens with different magnetic quality ( M 0=91–93 emu g −1, T c=240–270 K) were obtained. The MR properties of these specimens were characterized to be a broad, rather than a sharp as in a typical CMR materials, transition of semiconductor to metal and multiple peaks in MR versus T curve, which was explained by the co-existence of several La 1− x Ca x MnO 3 phases with different magnetic transition temperature ( T c). The extent of inhomogeneity was in coincidence with the magnetic quality of the specimens. The magnetic inhomogeneity was found to severely degrade a field sensitivity at the temperature where the peak MR ratio was observed. The presence of paramagnetic secondary phase at the temperature was proposed to explain the degradation of field sensitivity.