Roles of adiabatic and nonadiabatic spin transfer torques on magnetic domain wall motion

Electric current exerts torques-so-called spin transfer torques (STTs)-on magnetic domain walls (DWs), resulting in DW motion. At low current densities, the STTs should compete against disorders in ferromagnetic nanowires but the nature of the competition remains poorly understood. By achieving two-dimensional contour maps of DW speed with respect to current density and magnetic field, here we visualize unambiguously distinct roles of the two STTs-adiabatic and nonadiabatic-in scaling behaviour of DW dynamics arising from the competition. The contour maps are in excellent agreement with predictions of a generalized scaling theory, and all experimental data collapse onto a single curve. This result indicates that the adiabatic STT becomes dominant for large current densities, whereas the nonadiabatic STT-playing the same role as a magnetic field-subsists at low current densities required to make emerging magnetic nanodevices practical.