A thermodynamic theory for thermal-gradient-driven domain wall motion

Spin waves (or magnons) interact with magnetic domain walls (DWs) in a complicated way that a DW can propagate either along or against magnon flow. However, thermally activated magnons always drive a DW to the hotter region of a nanowire of magnetic insulators under a temperature gradient. We theoretically illustrate why it is surely so by showing that DW entropy is always larger than that of a domain as long as material parameters do not depend on spin textures. Equivalently, the total free energy of the wire can be lowered when the DW moves to the hotter region. The larger DW entropy is related to the increase of magnon density of states at low energy originated from the gapless magnon bound states

Domain wall propagation due to the synchronization with circularly polarized microwaves

Finding a new control parameter for magnetic domain wall (DW) motion in magnetic nanostructures is important in general and in particular for the spintronics applications. Here, we show that a circularly polarized magnetic field (CPMF) at GHz frequency (microwave) can efficiently drive a DW to propagate along a magnetic nanowire. Two motion modes are identified: rigid-DW propagation at low frequency and oscillatory propagation at high frequency. Moreover, DW motion under a CPMF is equivalent to the DW motion under a uniform spin current in the current perpendicular to the plane magnetic configuration proposed recently by Khvalkovskiy et al. [Phys. Rev. Lett. 102, 067206 (2009)], and the CPMF frequency plays the role of the current