Magnetoresistance analysis of nanoscale magnetic correlation in cosputtered Fe100-xAgx films

Granular films of composition Fe_100-xAg_x and nominal thickness 250 nm were prepared by dc plasma sputtering deposition in Ar atmosphere on Si substrates covered with naturally grown oxide. The in-plane film magnetization was measured between 4 K and 270 K using either a SQUID or extraction magnetometer. The magnetoresistance was measured by the four-contact method. All films exhibited isotropic negative magnetoresistance (GMR), whose intensity decreases monotonically with temperature, with no apparent saturation up to 50 kOe. The isothermal magnetic correlation range R_m roughly follows an exponential behavior as a function of the applied field. In this way, the field needed to destroy nanoscale magnetic correlation can be estimated as a function of both Fe concentration and temperature.