MAGNETIC INHOMOGENEITY IN COLOSSAL MAGNETORESISTIVE LA0.67CA0.33MNO3-DELTA PEROVSKITE CERAMICS

Magnetic inhomogeneity in colossal magnetoresitive lanthanum manganite s and its effect on MR properties are reported. Polycrystalline bulk s pecimens of La0.67Ca0.33MnO3 were prepared by solid state reaction and sol-gel route. By controlling materials processing parameters, CMR sp ecimens 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 ch aracterized to be a broad, rather than a sharp as in a typical CMR mat erials, transition of semiconductor to metal and multiple peaks in MR versus T curve, which was explained by the co-existence of several La1 -xCaxMnO3 phases with different magnetic transition temperature (T-c). The extent of inhomogeneity was in coincidence with the magnetic qual ity of the specimens. The magnetic inhomogeneity was found to severely degrade a field sensitivity at the temperature where the peak MR rati o was observed. The presence of paramagnetic secondary phase at the te mperature was proposed to explain the degradation of field sensitivity . (C) 1998 Elsevier Science B.V. All rights reserved.