Field geometry dependence of magnetotransport in epitaxial La2/3Ca1/3MnO3 thin films

In-plane and out-of-plane magnetoresistance measurements on epitaxial ∼200 nm thin (0 0 1)-oriented films of high oxygen pressure DC-sputtering grown manganite La2/3Ca1/3MnO3 were carried out. Single crystal (0 0 1)-SrTiO3 substrates were used. The samples featured a Curie temperature TC∼260K and a magnetic moment μ(T→0K)∼3μB per Mn atom. Magnetocrystalline anisotropy with the easy axes lying on film plane was evidenced by recording the in-plane and out-of-plane magnetization loops at temperatures, below TC, in magnetic field strengths up to 5 T. Evidence for anisotropic magnetotransport in these films was provided by electric measurements in a wide temperature range up to 6 T magnetic field strengths applied both perpendicular and parallel to the film plane. In both applied magnetic field geometries, current and magnetic field were maintained perpendicular to each other. Neither low-field magnetoresistance nor large magnetoresistance hysteresis were observed on these samples, suggesting that the tensile strain imposed by the substrate in the first monolayers has partially been released. In addition, by rotating the sample 360° around an axis parallel to film plane, in magnetic fields ⩾2T, a quadratic sinusoidal dependence of the magnetoresistance on the polar angle θ was observed. These results can be consistently interpreted using a generalized version of the theory of anisotropic magnetoresistance in transition-metal ferromagnets.