Nanogranular Fe-Cu-Ag thin films: structure, microstructure and giant magnetoresistance

Fe(x)Cu(y)Ag(z) granular thin films with several compositions were prepared by dc magnetron sputtering. These films consist of small Fe magnetic particles embedded in a nonmagnetic CuAg matrix. Structure, microstructure, morphology and magnetotransport properties were studied. The compositions of these samples were determined by energy-dispersive X-ray analysis. X-ray diffraction results showed strong Ag(111) peaks and broad Cu(111) peaks in all the samples. The variation of the (111) lattice spacings indicates a partial intermixing of Fe, Cu and Ag atoms. Microstructural studies using transmission electron microscopy (TEM) on a selected sample showed only Ag reflections and no reflection from Cu and Fe. Both XRD and TEM studies did not reveal any diffraction peak due to Fe and Cu for this sample. The fitting of the experimental grain size data obtained from TEM micrograph to the lognormal distribution function has allowed an estimation of the average grain diameter of 3.7 nm. The surface image of the Fe22Ag78 film observed using a scanning electron microscope showed the presence of droplet like Ag particles on the film surface. The Cu substitution results in smooth films without any Ag particles on the surface. Surface morphology by atomic force microscopy shows that the Fe39Cu13Ag48 film has a surface roughness of 0.75 nm. Finally, we have obtained a maximum giant magnetoresistance ratio of 3.2% in these films measured at 300 K for an in-plane magnetic field of 20 kOe.