Microstructure and giant magnetoresistance of FeCo–Cu nanogranular films

A series of (Fe50Co50)xCu1–x granular films were prepared using a magnetron controlled sputtering system. The microstructure and giant magnetoresistance (GMR) of FeCo–Cu films deposited at room temperature and then annealed at various temperatures were investigated through transmission electron microscope and conventional four probes method under room temperature, respectively. The results revealed that all FeCo–Cu films consisted of fine FeCo granules uniformly dispersed in the Cu matrix and formed fcc structure. By a non-linear leastsquares method, the size distribution of FeCo granules in all as-deposited films satisfied a log-normal function. Upon varying the magnetic volume fraction (x), the GMR of asdeposited FeCo–Cu films reached a maximum of about 0.7% at the volume fraction of 31% FeCo, corresponding to the fact that the GMR has a non-monotonic relationship with the granule size. With increasing the annealing temperature, the GMR of films with lower volume fraction reached a peak at higher temperature, while for films with higher volume fraction the GMR reached a peak at lower temperature. In addition, the relationships between the full width at half maximum (FWHM) or the sensitivity of the GMR and the volume fraction were discussed in detail.