  Most of the existing researches on the dynamics of a domain wall (DW) have
focused on the effect of DC biases, where the induced velocity is determined by
the bias strength. Here we show that AC biases such as a field or a current are
also able to move a DW via synchronization between the DW angle and the phase
of the AC bias. The resulting DW velocity is proportional to the driving
frequency of the AC bias, but independent of the bias strength, offering
potentially low-power operations of DW devices. The AC-bias-driven DW motion is
shown to exhibit a phase locking-unlocking transition, a critical phenomenon
akin to the Walker breakdown of a DC-bias-driven DW motion. Our work shows that
a DW can be driven resonantly by synchronizing its angle to AC biases, shedding
a light on hitherto overlooked utility of internal degree of freedom for
driving magnetic textures.
