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

RF-sputtered CoFe-NM granular alloys(NM = AE, Cu) with CoFe volume content, x(v), ranging from 0.10 to 0.45 have been studied. These two series of sam ples show similar features depending on the synthesis conditions and postde position annealing treatments, revealing the strong dependence of magnetotr ansport properties on microstructure. Three different regimes have been obs erved as x(v) is increased: the classical giant magnetoresistance (GMR) reg ime at low ferromagnetic contents; at intermediate x(v), a domain structure appears, and GMR and anisotropic magnetoresistance (AMR) together with dom ain wall scattering are observed; and a third regime at x(v) close but belo w the volume percolation threshold, where the two latter contributions stil l coexist, while the GMR contribution has been suppressed by strong magneti c 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 deg ree of CoFe segregation, sample crystallisation and texture, which are resp onsible for the magnetotransport properties. (C) 2000 Elsevier Science B.V. All rights reserved.