Nanoparticle morphology in FeCo–SiO2 granular films with tunneling giant magnetoresistance

A series of FeCo–SiO2 granular films were prepared using a magnetron controlled sputtering system at room temperature. The nanoparticle morphology of FeCo particles and tunneling giant magnetoresistance in FeCo–SiO2 films were directly determined utilizing transmission electron microscope and conventional four probes method under room temperature, respectively. The results indicated that upon varying the volume fraction of magnetic FeCo particles, the tunneling giant magnetoresistance of as-deposited FeCo–SiO2 films increased and then decreased, reaching a maximum of about 4.8% at middle volume fraction of 30.5 vol.% FeCo. In addition, transmission electron microscope observation disclosed that FeCo–SiO2 films consist of FeCo nanoparticles dispersed in SiO2 matrix. For films with lower volume fraction of FeCo particles, the size distribution of FeCo particles satisfied a log-normal function. With increasing the volume fraction of FeCo particles, the size distribution of FeCo particles deviated gradually from a log-normal function. Meanwhile, the average size of FeCo particles increased monotonically with increasing the volume fraction of FeCo particles, leading to the fact that the tunneling giant magnetoresitance can reach a peak value at a certain middle particle size.