Magnetic Domain Walls Displacement: Automotion Versus Spin-Transfer Torque

From the magnetization dynamics equation, a domain wall that changes structure is predicted to undergo a displacement by itself, a phenomenon called automotion. We experimentally demonstrate this effect in soft nanostrips, by transforming under spin-transfer torque a metastable asymmetric transverse wall into a vortex wall. Displacements more than three times larger than under spin-transfer torque only are measured for 1 ns pulses. The results are explained by analytical and numerical micromagnetics. Their relevance to domain-wall motion under spin-transfer torque is emphasized.