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

We present a detailed analysis of magnetoresistance in tetragonal thin films of ferromagnetic La0.7Ca0.3MnOδ grown by atomic layer-by-layer molecular-beam epitaxy. The field and temperature dependence of the resistivity ρ show an explicit dependence only on the fractional magnetization M/Msat and are consistent with a single approximate form ρ≅ρ(0)exp[-C(M/Msat)2] for small and intermediate magnetization both above and below the Curie temperature (TC). The microscopic magnetization and susceptibility (χ) have been inferred from the low-field magnetoresistance above TC with χ following a Curie-Weiss form. We observe a sharp transition in the low-field (H) dependence of ρ from quadratic (∝H2) above TC to linear (∝H) below, consistent with a temperature-independent ρ(M). Finally we show that within a simple model this temperature-independent form for ρ reproduces the behavior of the measured low-field sensitivity below TC. copyright 1996 The American Physical Society