Magnetic properties and giant magnetoresistance in Fe_0.35(In₂O₃)_0.65 granular film

Fe/In₂O₃ granular films have been prepared by the radio frequency sputtering method. The magnetic and transport measurements of a representative sample, Fe_0.35/(In₂O₃)_0.65, showed that there exist different magnetic states in different temperature regions. At room temperature, the film shows superparamagnetic behaviour, and a 5.2% magnetoresistance (MR) ratio was obtained. The susceptibility measurements showed that the blocking temperature is 50 K. Below a certain freezing temperature T_f of about 10 K, the film transits from the ferromagnetic state to the particle-spin-cluster state. In this event, the MR ratio of the film increases dramatically with decreasing temperature. A maximum giant magnetoresistance (GMR) ratio up to 506% is obtained at the metal-semiconductor transition temperature of about 2.2 K. The mechanism of this GMR is related to the interaction with the impurities influencing the local magnetization which is quite different to the spin-dependent tunnelling effect at room temperature.