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 Tpeak=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.

Epitaxial La0.7Ca0.3MnO3-δ thin films have been grown on LaAlO3(100) substrates by magnetron sputtering. By vacuum annealing at temperatures below 600 °C, oxygen-deficient films with ferromagnetic ordering temperatures, TC, between 130 K and 270 K have been prepared. Oxygen deficiency reduces the Mn4+ content, i.e. the charge carrier density of the films. Effective oxygen diffusion was observed at temperatures as low as T = 80 °C. Resistance, magnetization and magnetoresistance behaviours of the films are reported. Our results are consistent with a magnetically phase-separated ground state - a mixture of ferromagnetic metallic and antiferromagnetic insulating regions - of La0.7Ca0.3MnO3-δ for an Mn4+ concentration below ~20%. The electrical transport in the oxygen-deficient films, e.g. the non-monotonic temperature dependence of the resistance, the large magnetoresistance at T

No abstract