Anomalies in the structural and magneto-transport properties of thin films of Bi substituted La[sbnd]Ca[sbnd]Mn[sbnd

Abstract

The effects of Bi-substitution on structural, magnetic, and transport properties of polycrystalline and RF sputtered thin films of LaCaMnO are reported. Films of La0.62Bi0.05Ca0.33MnO3 sputtered on (1 1 1)Si are polycrystalline whereas textured films with (1 1 0) orientation are obtained for (1 0 0)Si. In bulk polycrystalline samples, Bi substitution leads to (i) a very small decrease in the lattice constant and (ii) a large reduction in the Curie temperature Tc (230 K vs. 240 K for La0.67Ca0.33MnO3). The films, however, show a 0.4% decrease in the lattice constant and a relatively high Tc (= 262–266 K) due to reduced MnOMn bond lengths. Although the magnetic parameters are identical for polycrystalline and oriented films, electrical resistivity ρ and MR data for the (1 1 0) textured films show the following anomalous features: (i) a semiconductor like conduction and the absence of the metal-semiconductor transition observed near Tc in polycrystalline bulk samples and thin films, (ii) a two-order of magnitude increase in low temperature ρ 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 films of the oxides.