Nonlinear domain-wall velocity enhancement by spin-polarized electric current

The interaction between a dc spin-polarized electric current and a magnetic domain wall in a Permalloy nanowire was studied by high-bandwidth scanning Kerr polarimetry. The full functional dependence of wall velocity on electric current and magnetic field is presented. With the pinning potential nulled by a field, current-induced velocity enhancements exceeded 35 m/s at a current density of similar to 6x10(11) A/m(2). This large enhancement, more than 10 times that found in pinning-dominated experiments, results in part from an interaction that is nonlinear in current and independent of current direction.