Effects of deposition temperature on the giant magnetoresistance of as-deposited Ag-Co thin films

Giant magnetoresistance (GMR) is reported in Ag1-xCo x(x=0.26-0.53) films cosputtered on Si at 28-354 °C from separate Ag and Co targets. GMR ratios (10 kOe maximum field) as high as 0.55 and 0.24 at 5 and 295 K, respectively, are achieved for the Ag0.67Co 0.33 films deposited at a substrate temperature, Ts, of 125 °C. The GMR ratio increases slightly when the Ts increases from 28 to ≅125 °C, and decreases substantially at T s≳175 °C. The resistivity of these films decreases monotonically with increasing Ts and levels off to a value ≅3× of Ag at Ts≥250 °C. The films deposited at lower Ts consist of essentially a metastable Ag-Co solid solution, while those deposited at higher Ts consist of separate fcc Ag and fcc Co. The coercivity of these films increases rapidly at Ts≫125 °C, consistent with the growth of single-domain ferromagnetic Co particles in this Ts range. The Ts dependence of GMR ratios is interpreted based on spin-dependent interfacial scattering arising from the Ts dependence of the size and number of ferromagnetic Co particles within the electron mean free path.