Microstructure and Giant Magnetoresistance in Fe–Cu Thin Films Prepared by Cluster-Beam Deposition

Giant magnetoresistive Fex Cu100-x granular thin films have been prepared by cluster-beam deposition. The magnetoresistance (MR) ratio of the as-deposited films decreases monotonically with increasing Fe content. High resolution transmission electron microscopy of a low Fe content (x=12) sample shows chemically-homogeneous, fine grains having a fcc structure. The film with x=28 exhibits, however, distinct chemical heterogeneity, where bcc Fe clusters are formed in the Cu matrix. The film with a higher Fe content (x=53) consists mostly of the bcc phase with a small amount of the fcc phase. Mössbauer spectroscopy indicated that this MR behavior can be ascribed to the change in the magnetic state of Fe clusters with increasing the Fe content of the films: from cluster-glass to antiferromagnetic, and then to ferromagnetic states. After annealing, phase separation occurs in all specimens, and the grain size increases markedly, resulting in the suppression of the MR ratio in the low Fe content region.