Low Field Magnetoristance and Inhomogenieties in La2/3Ca1/3MnO3 Films

La_2/3Ca_1/3MnO₃ films were prepared using a conventional paint-on method on alumina and monocrystalline TiSrO₃ substrates. A significant difference between the peak resistivity temperature T _p=178 K and the magnetic transition temperature T _c=240 K was found in contrast to single crystal samples. The behavior of the magnetoresistance with temperature also differs from that found in bulk samples. Although the films show significant granular morphology differences, their transport and magnetoresistive properties are very similar. Maximum magnetoresistance ratios of 16% and 10% at 0.3 T and 77 K were obtained for films deposited on alumina and TiSrO₃ substrates, respectively. Magnetization measurements above T _c show a nonlinear behavior, consistent with the presence of ferromagnetic inhomogeneities within the paramagnetic phase. These results suggest that, in addition to the importance of grain boundary scattering in determining the magnetoresistance at low fields, microscopic inhomogeneity plays a role in determining magnetotransport properties.