核壳磁性纳米盘中的反常自旋波动力学
Unusual spin-wave dynamics in core-shell magnetic nanodisks
摘要：
利用微磁学模拟方法研究了垂直于盘平面的振荡场驱动下核壳磁性纳米盘中涡旋态的自旋动力学。该纳米盘包括半径为100 nm的Py（Fe 0.2Ni 0.8）核，被50 nm厚的Fe壳包围。傅里叶变换分析表明，Py核和Fe壳分别在基模和高阶径向模处主导自旋波振荡。对于调谐到基本本征频率的振荡驱动场，Py/Fe界面有效地将自旋波激发限制在Py核心区域中。与均匀圆盘相比，这种效应导致明显更快的涡核（VC）反转。我们的工作表明，高阶模式可以驱动更快的VC反转比基本模式，在均匀磁盘中获得的结果形成鲜明对比。随着激发水平高达30 mT，我们发现强非线性自旋波动力学的系统，这导致模式频率红移，因此观察到的最快速的VC反转低于本征频率和VC开关在很宽的频率范围。
英文摘要：
We investigated the spin dynamics of a vortex state in a core-shell magnetic nanodisk driven by an oscillating field applied perpendicular to the disk plane by means of micromagnetic simulations. The nanodisk comprises a Py (Fe0.2Ni0.8) core of 100 nm in radius, surrounded by a 50 nm thick Fe shell. Fourier transform analyses show that the Py core and the Fe shell dominate spin-wave oscillation at the fundamental and higher order radial modes, respectively. For oscillating driving field tuned to the fundamental eigenfrequency, the Py/Fe interface effectively confines spin-wave excitation in the Py core region. This effect leads to significantly more rapid vortex core (VC) reversal in comparison to homogeneous disks. Our work demonstrates that the higher order modes can drive much faster VC reversal than the fundamental mode, in sharp contrast to the results obtained in homogeneous disks. With excitation levels up to 30 mT, we find strong nonlinear spin-wave dynamics in the system, which results in mode frequency redshifting, therefore the observation of the most rapid VC reversals below eigenfrequencies and VC switching in wide ranges of frequencies.
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