Impact of Gd dopants on current polarization and the resulting effect on spin transfer velocity in Permalloy wires

A spin wave Doppler technique is used to measure the spin transfer velocity and the current polarization in current-carrying (Ni(0.80)Fe(0.20))(1-x)Gd(x) alloy wires. Reduced magnetization values with Gd doping suggest possible increases in the spin transfer velocity. Contrary to these expectations, we measured a decrease in the spin transfer velocity upon introducing Gd dopants. For a current density of 10(11) A/m(2), the measured velocities range from 6.0 m/s +/- 0.6 m/s for pure Permalloy (Ni(0.80)Fe(0.20)) to 2.6 m/s +/- 0.3 m/s for (Ni(0.80)Fe(0.20))(0.945)Gd(0.055). Interpretation of these values yields a current polarization ranging from 0.71 +/- 0.02 to 0.30 +/- 0.01 for the same compositions. These results reveal that Gd dopants in Permalloy have a more significant impact on the current polarization than on the material's magnetization for these alloy compositions. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3610517]