Dynamics of skyrmionic states in confined helimagnetic nanostructures
Dynamics of skyrmionic states in confined helimagnetic nanostructures
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DOI：
10.1103/physrevb.95.014433
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发表时间：
2017-01-30
影响因子：
3.7
通讯作者：
Fangohr, Hans
中科院分区：
文献类型：
--
作者：
Beg, Marijan;Albert, Maximilian;Fangohr, Hans
在受限的螺旋磁纳米结构中，在没有外磁场和磁晶各向异性的情况下，以不完整和孤立的skyrmion态形式出现的skyrmion态可以作为基态出现。在这项工作中，我们研究了薄膜FeGe圆盘样品中Skyrmion态的动力学性质（共振频率和相应的本征模）。在基于有限元的微磁模拟中，我们采用了两种不同的方法：特征值法和衰荡法。本征值法允许我们识别所有的谐振频率和相应的本征模式，可以存在于模拟系统。然而，使用特定的实验上可行的激发只能激发有限的本征模集。正因为如此，我们执行振铃模拟，类似的实验设置使用面内和面外激励。此外，我们还报道了共振频率与外加偏磁场和圆盘样品直径的非线性关系，并讨论了skyrmion态可能的反转模式。我们比较了不完整的skyrmion和孤立的skyrmion状态的功率谱密度，并观察到几个关键的差异，可以有助于在样品中存在的状态的实验识别。我们测量FeGe吉尔伯特阻尼，并使用它的值，我们确定什么本征模可以预期在实验中观察到。最后，我们表明，忽略退磁能量的贡献或忽略的磁化变化的膜外方向，虽然没有改变本征模的磁化动力学显着改变其谐振频率。除了有助于理解skyrmionic态物理学，这个系统的工作可以作为一个指导的实验识别skyrmionic态在有限的helmagnetic纳米结构。
In confined helimagnetic nanostructures, skyrmionic states in the form of incomplete and isolated skyrmion states can emerge as the ground state in absence of both externalmagnetic field andmagnetocrystalline anisotropy. In this work, we study the dynamic properties (resonance frequencies and corresponding eigenmodes) of skyrmionic states in thin film FeGe disk samples. We employ two different methods in finite-element based micromagnetic simulation: eigenvalue and ringdown method. The eigenvalue method allows us to identify all resonance frequencies and corresponding eigenmodes that can exist in the simulated system. However, using a particular experimentally feasible excitation can excite only a limited set of eigenmodes. Because of that, we perform ringdown simulations that resemble the experimental setup using both in-plane and out-of-plane excitations. In addition, we report the nonlinear dependence of resonance frequencies on the external magnetic bias field and disk sample diameter and discuss the possible reversal mode of skyrmionic states. We compare the power spectral densities of incomplete skyrmion and isolated skyrmion states and observe several key differences that can contribute to the experimental identification of the state present in the sample. We measure the FeGe Gilbert damping, and using its value we determine what eigenmodes can be expected to be observed in experiments. Finally, we show that neglecting the demagnetization energy contribution or ignoring the magnetization variation in the out-of-film direction-although not changing the eigenmode's magnetization dynamics significantly-changes their resonance frequencies substantially. Apart from contributing to the understanding of skyrmionic states physics, this systematic work can be used as a guide for the experimental identification of skyrmionic states in confined helimagnetic nanostructures.