STRUCTURAL, MAGNETIC AND TRANSPORT-PROPERTIES OF NIFEXAG(1-X) HETEROGENEOUS ALLOYS

We carried out a comprehensive study of structural, magnetic and electrotransport properties of as-deposited and annealed (Ni80Fe20)xAg(1-x) heterogeneous alloys prepared by sputtering. The NiFe atomic concentration was varied between 15% and 40%. These alloys consist of small magnetic particles (Ni80Fe20) embedded in a nonmagnetic matrix (Ag). The structures of these alloys were investigated by X-ray diffraction, scanning electron microscopy and high-resolution cross-section transmission electron microscopy. The magnetic measurements were made using SQUID magnetometry and ferromagnetic resonance. Magnetoresistance was measured with a conventional four-point probe between 1.5 K and room temperature in field range 0-6 T. Three contributions to the magnetoresistance of these granular alloys have been clearly identified: the spin-valve (or giant) magnetoresistance as in multilayers, scattering on magnetic fluctuations (as in any ferromagnetic metal around its magnetic ordering temperature), and anisotropic magnetoresistance. These three contributions have their own dependences on the size of the magnetic particles, on the degree of intermixing between Ni80Fe20 and Ag, and on temperature. We discuss the different shapes and amplitudes of magnetoresistance versus Ni80Fe20 concentration or temperature and their evolution upon annealing in terms of the relative roles of these three contributions. The magnetoresistance in multilayers (current in-plane or perpendicular to the plane) and granular alloys are also compared.