Low temperature electrical resistivity of polycrystalline La0.67Sr0.33MnO3 thin films

Electrical transport properties of La0.67Sr0.33MnO3 polycrystalline thin films are studied in the temperature range 13−300  K and in magnetic fields up to 3  kOe. It is found that the resistivity of the sample with ellipsoidal grains exhibits an insulating behavior at low temperature. Detailed analysis of experimental data shows that the Variable Range Hopping model cannot apply to this sample. Negative magnetoresistance is explained by assuming that the transport occurs through the mechanism of inter-granular (insulating) as well as granular (metallic) paths connected in series. By qualitatively comparing the relative fractions of these channels, we explain the resistivity behavior in each temperature range.