The low-temperature magnetoresistance of ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ (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 $\mathbf{H},$ while $T_m$ versus $\mathbf{H}$ curves showed maxima at around 2 T. We have fitted the resistivity versus temperature data for all $\mathbf{H}$ 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.

• Received 8 December 2000

DOI:https://doi.org/10.1103/PhysRevB.65.094407