Magnetoresistance in thin films and bulks of layered-perovskite La2-2xCa1+2xMn2O7

Epitaxial thin-film and polycrystalline bulk samples of ferromagnetic La2-2xCa1+2xMn2O7 (x = 0.3) with a layered perovskite structure have been examined with respect to their magnetotransport properties. In addition to a large magnetoresistance (MR) effect at temperatures around the metal-insulator transition, a-axis thin films exhibit unusual low-temperature MR behavior with apparent hysteresis in applied magnetic fields. The features in the bulk samples are a low-temperature MR effect without such hysteresis, and also an MR effect at high temperatures well above the metal-insulator transition temperature. The unique MR behavior depending on the sample form would reflect an anisotropic nature in the layered-perovskite ferromagnet with two-dimensional Mn-O networks. (C) 1997 American Institute of Physics.