Role of Interface Transport in the Magnetoresistance of Strained Rare Earth Manganite Thin Films*

We are studying the temperature and field dependence of magnetoresistance in epitaxial thin films of rare earth manganites which are subject to lattice mismatch strain, with the goal of investigating the possible role of transport across strain-induced internal interfaces. We will present our results, comparing La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) thin films grown on by Pulsed laser deposition on different substrates with varying degrees of compressive or tensile lattice mismatch. Strained films of thickness $\sim $ 10 nm, show a large magnetoresistance in fields $<$ 1 Tesla, which continues to increase with decrease in temperature, similar to magnetoresistance associated with grain boundary transport. The temperature dependence of MR in these films does not correlate with the temperature dependence of resistivity and thus seems to originate from effects other than Mn spin alignment. Lattice mismatch strain is known to suppress the insulator-metal transition and enhance charge and orbital ordering, leading to the coexistence of insulating and ferromagnetic metallic phases. Our results suggest possible contributions to the magnetoresistance from transport across the interfaces between the different phases.