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

We carried out a comprehensive study of structural, magnetic and elect rotransport properties of as-deposited and annealed (Ni80Fe20)xAg(1-x) heterogeneous alloys prepared by sputtering. The NiFe atomic concentr ation was varied between 15% and 40%. These alloys consist of small ma gnetic particles (Ni80Fe20) embedded in a nonmagnetic matrix (Ag). The structures of these alloys were investigated by X-ray diffraction, sc anning electron microscopy and high-resolution cross-section transmiss ion electron microscopy. The magnetic measurements were made using SQU ID magnetometry and ferromagnetic resonance. Magnetoresistance was mea sured with a conventional four-point probe between 1.5 K and room temp erature in field range 0-6 T. Three contributions to the magnetoresist ance of these granular alloys have been clearly identified: the spin-v alve (or giant) magnetoresistance as in multilayers, scattering on mag netic 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 p articles, on the degree of intermixing between Ni80Fe20 and Ag, and on temperature. We discuss the different shapes and amplitudes of magnet oresistance versus Ni80Fe20 concentration or temperature and their evo lution upon annealing in terms of the relative roles of these three co ntributions. The magnetoresistance in multilayers (current in-plane or perpendicular to the plane) and granular alloys are also compared.