ANOMALIES IN THE STRUCTURAL AND MAGNETOTRANSPORT PROPERTIES OF THIN-FILMS OF BI SUBSTITUTED LA-CA-MN-O

The effects of Bi-substitution on structural, magnetic, and transport properties of polycrystalline and RF sputtered thin films of La-Ca-Mn- O are reported. Films of La0.62Bi0.05Ca0.33MnO3 sputtered on (1 1 1)Si are polycrystalline whereas textured films with (1 1 0) orientation a re obtained for (1 0 0)Si. In bulk polycrystalline samples, Bi substit ution leads to (i) a very small decrease in the lattice constant and ( ii) a large reduction in the Curie temperature T-c(230 K vs. 240 K for La0.67Ca0.03MnO3). The films, however, show a 0.4% decrease in the la ttice constant and a relatively high T-c(= 262-266 K) due to reduced M n-O-Mn bond lengths. Although the magnetic parameters are identical fo r polycrystalline and oriented films, electrical resistivity rho and M R data for the (1 1 0)textured films show the following anomalous feat ures: (i) a semiconductor like conduction and the absence of the metal -semiconductor transition observed near T, in polycrystalline bulk sam ples and thin films, (ii) a two-order of magnitude increase in low tem perature rho relative to the polycrystalline films and (iii) MR-values much higher than for polycrystalline films. These data are indicative of a giant anisotropy in the magneto-transport properties of thin fil ms of the oxides.