Reduction of Threshold Current for Domain Wall Depinning Using Gd Doping of Permalloy

The dependence of threshold current on applied magnetic field for domain wall depinning from a pinning potential in Gd doped permalloy wires is measured using pulsed current measurements. By increasing the Gd concentration we find a marked reduction in threshold currents. This is shown to arise due to the enhanced non-adiabatic spin-transfer torque: we calculate the non-adiabaticity parameter $\beta$ to be around 0.11 for 10% Gd concentration. On the other hand we show that the adiabatic spin-transfer torque is largely unaffected by Gd concentrations up to 10%.