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 Å thick were grown on LaAlO₃(100), MgO(100) and SiO₂/Si(100) substrates by RF magnetron sputtering. Changes in the resistivity and magnetoresistance of the films on LaAlO₃ (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 _0.82Ca_0.1Sr_0.08MnO₃ film were a₀=5.466 Å, b₀=5.392 Å, c₀ =7.725 Å. 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_SC-M) of the epitaxial films on LaAlO₃ (100) increased and the resistivity decreased as the amount of Sr was increased. For the epitaxial La_0.82Ca_0.1Sr_0.08MnO₃ film on LaAlO₃, 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