Transport properties and colossal magnetoresistance in epitaxial $La_{0.67}Cd_{0.33}MnO_3$ thin film

An optimal composition of $La_{0.67}Cd_{0.33}MnO_3$ was synthesized by ceramic route. The compound crystallized in a rhombohedral structure with lattice parameters a = 5.473(4) Å and $\alpha = 60^o37'$. Resistivity measurement showed an insulator-to-metal transition coupled with a ferromagnetic transition of around 255 K. Epitaxial thin films were fabricated on the $LaAlO_3 (100)$ substrate by a pulsed laser deposition technique. The psuedocubic lattice parameter a of the film is 3.873(4) Å. The insulator-to-metal transition of the film was observed at 250 K which is comparable with the bulk value. The film was ferromagnetic below this temperature. Magnetoresistance defined as $\Delta R/R_0 = (R_H-R_0)/R_0$ was over - 86% near the insulator-to-metal transition temperature of 240 K at 6 T magnetic field and over-30% at relatively low fields of 1 T. No magnetoresistance was observed at low temperatures in the film unlike in the polycrystalline sample, where about a 40% decrease in resistance was observed on applying 6 T magnetic field due to the spin dependent scattering at the grain boundaries