Magnetoresistive and magnetic properties of RF-magnetron sputter deposited La-Ca,Sr-Mn-O films

Epitaxial and polycrystalline La-Ca,Sr-Mn-O thin films about 1000 /spl Aring/ thick were grown on LaAlO/sub 3/[100], MgO[100] and SiO/sub 2//Si[100] substrates by RF magnetron sputtering. Changes in the resistivity and magnetoresistance of the films on LaAlO/sub 3/ [100] substrate were investigated as the Ca and Sr ratio was varied. The crystal structure of the La-Ca,Sr-Mn-O films was determined to be orthorhombic perovskite. Lattice constants of the crystalline La/sub 0.82/Ca/sub 0.1/Sr/sub 0.08/MnO/sub 3/ film were a/sub 0/=5.466 /spl Aring/, b/sub 0/=5.392 /spl Aring/, c/sub 0/=7.725 /spl Aring/. When the amount of Sr was increased, the results of x-ray diffraction patterns showed no appreciable change of the lattice parameter. However, the semiconductor-metal transition temperature (T/sub SC-M/) of the epitaxial films on LaAlO/sub 3/ [100] increased and the resistivity decreased as the amount of Sr was increased. For the epitaxial La/sub 0.82/Ca/sub 0.1/Sr/sub 0.08/MnO/sub 3/ film on LaAlO/sub 3/, the temperature dependence of the resistivity under zero and 1.5 T applied fields showed that semiconductor-metal transition occurs at 246 K and the relative maximum magnetoresistance ratio was about 172% at 230 K.