Effect of Fe doping on high field magnetoresistance and low field magnetoresistance at zero field in polycrystalline La0.7Sr0.3Mn1-xFexO3 (x=0-0.12) thin films

Polycrystalline La0.7Sr0.3Mn1-xFexO3 thin films, with x = 0-0.12, have been prepared on (001)-Si substrates using pulsed laser deposition. The films consist of fine grains with an average size of 60-80 nm. For those films, the metal-insulator transition temperature, T-p, is much lower than the Curie temperature, T-C. The high field magnetoresistance, HFMR, is nearly temperature independent for x < 0.08, whereas the extrapolated low field magnetoresistance at zero field, LFMR*, decreases rapidly with increasing temperature. Moreover, Fe doping significantly decreases LFMR* and enhances HFMR at low temperatures. We propose that for the Fe-doped films, both the reduced spin polarization of conduction electrons and the increased spin-flip scattering are responsible for the decrease of LFMR*, while the weakened ferromagnetic spin interaction at the grain boundaries is responsible for the enhanced HFMR. (C) 2001 American Institute of Physics.