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垂直共振磁场下三维磁性纳米圆盘的自旋波模式及其动力学
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Abstract:
本文采用微磁模拟的方法研究了不同厚度的坡莫合金纳米圆盘在垂向交变磁场作用下所激发的自旋波模式。当坡莫合金纳米圆盘厚度与半径相比不可忽略时，磁矩不再沿着厚度方向均匀分布，形成了中间大两头小的橄榄球状涡核，这与退磁能与交换能的相互竞争密切相关。我们发现除了常见的径向自旋波模式外，还存在着厚度方向驻波模式与径向自旋波模式的混合模式，其频率要远大于低阶径向自旋波模式的本征频率。当圆盘厚度足够大时，可以观察到厚度方向的高阶驻波模式与径向自旋波模式的混合模式，却难以观察到纯粹的径向自旋波模式。当我们给这种混合模式施加一个相位匹配的垂向共振外磁场时，涡旋态极性更容易发生翻转。
We studied the spin wave modes in permalloy nanodisks with different thicknesses under the ex-citation of a perpendicular ac magnetic field, using micromagnetic simulations. When the thickness of permalloy nanodisks is comparable to its radius, the magnetic moments are nonuniform along the disk thickness, forming a football-like vortex core in which middle part is larger than the ends, due to competition between demagnetization energy and exchange energy. And we observe not only the excitation of radial spin wave modes, but also hybridization of standing wave along the disk thickness with radial spin wave modes. The eigenfrequencies of such hybrid modes are much larger than the low-order radial spin wave modes. When the thickness of the disk is large enough, we observe hybridization of the high-order standing wave with radial spin wave modes, but near absence of pure common radial spin wave mode. By applying a perpendicular phase-matched resonant magnetic field, the vortex polarity can be easily switched.
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