MAGNETIC AND ELECTRONIC-PROPERTIES OF THE MAGNETORESISTIVE PEROVSKITES LA0.67-XBIXCA0.33MNO3

Magnetotransport, magnetic susceptibility and ferromagnetic resonance (FMR) studies of La0.67-xBixCa0.33MnO3 perovskites with x = 0.03 to 0. 16 are reported. The magnetoresistivity ratio shows a peak in all samp les corresponding to the Curie transition. In samples with x greater t han or equal to 0.13 a second peak at lower temperature is seen in the magnetoresistivity, Magnetic susceptibility measurements show Curie l ike behavior for all samples. Samples with low Bi content show a diffe rence between field cooled and zero-field cooled measurements at low t emperature. This difference diminishes with increasing x, FMR spectra show a single resonance above T-c. Samples with small Bi content show two resonances just below T-c but these resonances cannot be clearly r esolved at lower temperatures due to line broadening. These two resona nces also become less resolved with increasing x. No anomalous behavio r corresponding to the low-temperature peak in the magnetoresistivity is seen in the magnetic susceptibility or FMR measurements. Results ar e interpreted in terms of the effects of Bi on the structure of grain boundaries. (C) 1998 Elsevier Science B.V. All rights reserved.