Anomalous positive magnetoresistance effect in La0.67Ca0.33MnO3 microbridges

Microbridges were fabricated from the well epitaxial La0.67Ca0.33MnO3 films by the electron beam lithography (EBL) technology. The metal-insulator transition temperature (TP) decreases with the reduced bridge width, and the transition even disappears over the measured temperature range for the bridge with 500 nm width. The phenomena may be the result of the confined geometry, which will be dominated by the filamentary conduction. The most intriguing effect is the positive MR for the widths of 1.5, 1 μm under the 1 T magnetic field and it reaches around 25% at 175 K for the 1 μm bridge. The reason for the observation could be attributed to spin disorder enhanced electron-electron interactions at low temperatures, which can produce positive correction to the conductivity. The revealed size effect is valuable for getting further understanding about the mechanism of colossal magnetoresistance effect.