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

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Abstract
Giant magnetoresistance (GMR) is reported in Ag1−xCox(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 Ag0.67Co0.33 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 Ts≳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.