Influence of the substrate on growth and magnetoresistance of La0.7Ca0.3MnOz thin films deposited by magnetron sputtering

Off-axis radio frequency magnetron sputtering was employed to grow La0.7Ca0.3MnOz (LCMO) thin films onto three different types of substrates. The substrate strongly influences the structure and the colossal magnetoresistance effect of the obtained films. Single-crystalline thin films were prepared on LaAlO3 (100) substrates, showing a low value of residual resistivity and a metal-insulator transition at a temperature of up to T-peak=290 K. The latter value of the transition temperature is one of the highest reported so far on thin films of the La-Ca-Mn-O system. Films deposited onto Y-stabilized ZrO2 substrates and onto MgO substrates are polycrystalline and less textured. These films are characterized by a large negative magnetoresistance ratio MR=[R(H)-R(0)]/R(0) measured for small values of the magnetic field H. For H = 1.5 kOe, the MR was found to be approximately - 30%, - 20%, and - 8% at temperatures of 20, 77, and 180 K, respectively. The magnetoresistance of polycrystalline LCMO films shows two contributions, a low-field MR and a high-field MR, which are different in their dependence on temperature. The low-field MR is related to the magnetization process and can be attributed to scattering processes in domain walls or to tunneling of polarized charge carriers between the grains of the polycrystalline films. (C) 1998 American Institute of Physics.