Effect of in-plane epitaxy on magnetotransport properties of (La0.5Sr0.5)CoO3 thin films

We have systematically studied the temperature- and magnetic field-dependen t resistance in (La0.5Sr0.5)CoO3 (LSCO) films with various degrees of in-pl ane texturing using the biaxially oriented LSCO on CeO2/YSZ/SiO2/Si substra tes. We find that the ferromagnetic transition temperature, T-c, is much th e same in all samples while the resistive transition exhibits metallic beha vior (dR/dT>0) in the epitaxial LSCO to semiconducting behavior (dR/dT<0) i n the poorly textured LSCO. The magnetoresistance (MR) in the epitaxial LSC O on a LaAlO3 substrate displays two distinct regions; the low field hyster etic MR related to the magnetization hysteresis and the high field linear n egative MR due to the suppression of spin fluctuations. In contrast, the MR in the biaxially textured LSCO sample shows only the hysteretic behaviors at low fields and no linear MR at high fields. Compared to the polycrystall ine-doped LaMnO3 which shows an enhanced MR at low fields, the MR in the bi axially oriented LSCO does not exhibit such characteristics. We attribute t his to the differences in the spin polarization between LSCO and the doped LaMnO3. (C) 1998 American Institute of Physics. [S0003-6951(98)03931-X].