Low-temperature resistivity minima in colossal magnetoresistive La_0.7Ca_0.3MnO₃ thin films

The low-temperature magnetoresistance of La_0.7Ca_0.3MnO₃ (LCMO) thin films has been investigated using a four-probe dc technique with a 5 T superconducting magnet. Thin film samples of LCMO were prepared in situ using a pulsed laser deposition technique. The results obtained from the high-resolution low-temperature (5-50 K) measurements, carried out on various samples differing widely in their resistivities, have shown distinct minima at T_m in the resistivity versus temperature plots for all fields. The depth of the resistance minima was found to increase with an increase in applied magnetic field H, while T_m versus H curves showed maxima at around 2 T. We have fitted the resistivity versus temperature data for all H to an expression that contains three terms, namely, residual resistivity, inelastic scattering, and electron-electron (e-e) interaction and Kondo effects. We conclude that the e-e interaction effect is the dominant mechanism for the negative temperature coefficient of resistivity of these colossal magnetoresistance (CMR) materials at low temperatures.