Effect of dipolar interaction on exceptional points in synthetic layered magnets
Effect of dipolar interaction on exceptional points in synthetic layered magnets
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DOI：
10.1063/5.0049011
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发表时间：
2021-05
影响因子：
4
通讯作者：
T. Jeffrey;W. Zhang;J. Sklenar
中科院分区：
文献类型：
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作者：
T. Jeffrey;W. Zhang;J. Sklenar
在合成铁磁体和反铁磁体中，可以使用特殊的点来控制磁振子的能谱，在这些点上，光磁子和声波磁子结合成一个单一的分支。到目前为止，磁振子系统中的例外点现象主要是在基于耦合的Landau-Lifshitz-Gilbert运动方程的宏观自旋模型框架内预测和理解的。虽然这些方程可以很容易地线性化和求解，但它们不一定包含真实合成磁结构中存在的所有物理效应，如偶极相互作用。我们使用微磁模拟来模拟基于坡莫合金的合成磁体，它既包括偶极相互作用，也包括层间交换耦合，层间交换耦合决定了材料是铁磁还是反铁磁。对于所考虑的材料参数，我们预测当系统是铁磁性时，只存在一个例外点，而当材料是反铁磁性时，不会出现例外点。这些结果表明，当计算层状磁性材料中的异常点时，必须考虑层间交换场以外的相互作用，以准确地预测异常点的存在，而微磁模拟是执行这一任务的有用工具。
Within both synthetic ferromagnets and antiferromagnets, exceptional points, where optical and acoustic magnons coalesce into a single branch, can be used to control the magnon energy spectra. To date, exceptional point phenomena in magnon systems have been predominantly predicted and understood within the framework of macrospin models that are based upon coupled Landau–Lifshitz–Gilbert equations of motion. Although these equations can be readily linearized and solved, they do not necessarily incorporate all of the physical effects that are present in a real synthetic magnetic structure such as dipolar interactions. We have used micromagnetic simulations to model Permalloy based synthetic magnets that include both dipolar interactions, as well as the interlayer exchange coupling which determines whether or not the material is ferromagnetic or antiferromagnetic. For the material parameters considered in this work, we predict that only a single exceptional point is present when the system is ferromagnetic, and that no exceptional point appears when the material is antiferromagnetic. These results suggest that when calculating exceptional points within layered magnetic materials, interactions other than the interlayer exchange field must be accounted to accurately predict the existence of exceptional points, and that micromagnetic simulations are a useful tool to perform this task.