Magnetoresistance scaling in MBE-grown La0.7Ca0.3MnO3 thin films

We present a detailed analysis of magnetoresistance in tetragonal thin films of ferromagnetic La0.7Ca0.3MnOdelta grown by atomic layer-by-layer molecular-beam epitaxy. The field and temperature dependence of the resistivity rho show an explicit dependence only on the fractional magnetization M/M(sat) and are consistent with a single approximate form rho approximate to rho(0)exp[-C(M/M(sat))(2)] for small and intermediate magnetization both above and below the Curie temperature (T-C) The microscopic magnetization and susceptibility (chi) have been inferred from the low-field magnetoresistance above T-C with chi following a Curie-Weiss form. We:observe a sharp transition in the low-held (H) dependence of rho from quadratic (proportional to H-2) above T-C to linear (proportional to H) below, consistent with a temperature-independent rho(M). Finally we show that within a simple model this temperature-independent form for rho reproduces the behavior of the measured low-field sensitivity below T-C.