交变共振磁场下横向磁畴壁的快速输运

Fast Motion of a Transverse Magnetic Domain Wall under an Alternating Resonant Magnetic Field

摘要: 我们采用数值模拟方法研究了铁磁性纳米条带中横向奈尔磁畴壁在交变磁场作用下激发的各种本征振动模式。我们选择外加交变磁场的方向分别沿纳米条带的长度、宽度和厚度方向，观察到了畴壁的扭转模式、呼吸模式、平移模式以及新颖的手风琴模式。当外加交变磁场沿条带宽度方向时，畴壁上下两端的宽度呈现反相位振动，我们将其命名为手风琴模式。进一步研究发现，在沿纳米条带长度方向施加恒定驱动磁场的同时，叠加共振频率的交变磁场以激发磁畴壁的扭转模式、平移模式或者手风琴模式，可以显著抑制沃克解体的出现，从而大幅提高磁畴壁的输运距离。畴壁的共振运动抑制沃克解体的机制在于这些特定振动模式能阻碍横向畴在其宽度较窄一端生成反涡核，从而避免了反涡核的旋进运动导致的横向畴形态复杂变化。

Abstract: Eigen resonant modes of transverse Neel magnetic domain wall in a ferromagnetic nanostrip stimulated by alternating magnetic field are investigated by micromagnetic simulations. We choose the direction of the applied alternating magnetic field along the length, width and thickness of the nanostrip, and we observe twisting mode, breathing mode, translational mode and novel accordion mode of the domain wall. When the alternating magnetic field is applied along the strip width direction, the widths of the domain wall top and bottom ends present an antiphase vibration, we named it accordion mode. Further research shows that, while applying a constant driving magnetic field along the length direction of the nanostrip, superposing simultaneously an alternating magnetic field of resonant frequency to stimulate the twisting mode, translational mode or accordion mode of the magnetic domain wall, could significantly restrain the appearance of the Walker breakdown, thus greatly improve the propagation distance of the magnetic domain wall. The mechanism that the resonant motion of the domain wall can suppress the Walker breakdown is that these specific vibration modes can impede the birth of anti-vortex core in the narrower end of the transverse domain wall, thus avoiding the complex transformations of the transverse domain which is caused by the precession motion of the anti-vortex core.