CoFe-based granular alloys: the role of the metallic matrix

Abstract

RF-sputtered CoFe-NM granular alloys (NM=Ag, Cu) with CoFe volume content, x v , ranging from 0.10 to 0.45 have been studied. These two series of samples show similar features depending on the synthesis conditions and post-deposition annealing treatments, revealing the strong dependence of magnetotransport properties on microstructure. Three different regimes have been observed as x v is increased: the classical giant magnetoresistance (GMR) regime at low ferromagnetic contents; at intermediate x v , a domain structure appears, and GMR and anisotropic magnetoresistance (AMR) together with domain wall scattering are observed; and a third regime at x v close but below the volume percolation threshold, where the two latter contributions still coexist, while the GMR contribution has been suppressed by strong magnetic correlations. The role of the metallic matrix is crucial to determine the crossover ferromagnetic contents between these three regimes, which depend on the relative immiscibility of CoFe either in the Ag or Cu matrices and the diffusivity of Ag and Cu. Moreover, the metallic matrix settles the degree of CoFe segregation, sample crystallisation and texture, which are responsible for the magnetotransport properties.