The special magnetic transition in Fe_x/(In_2O_3)_(1-x) granular films

摘要

Fe/In_2O_3 magnetic granular films have been prepared by radio frequency sputtering (rf) method. The results reveal that the nanometer-sized Fe grains uniformly disperse in the amorphous matrix In_2O_3 for the as-deposited samples. At room temperature, the Fe_(0.35)/(In_2O_3)_(0.65) film shows a super paramagnetic behavior and 5.2% magneto resistance (MR) ratio is obtained. The susceptibility measurements manifested that the blocking temperature is 50 K. Blow a certain freezing temperature T_f about 10K, the film transits from ferromagnetic state to a composite-cluster state in which the Fe atoms dispersed randomly in In_2O_3 severs as intermedia to couple the Fe grains together. In this case, the MR ratio of the film increases dramatically and a maximum giant magneto resistance (GMR) ratio up to 82.4% is obtained at 2.2 K, which is quite different to the MR effect at room temperature. The mechanism of this GMR is attributed to the increase of the hopping mobility of carriers under the applied magnetic field.