We have theoretically and experimentally investigated magnetic resonance modes, i.e., optical mode (OM) and acoustic mode (AM), in two coupled ferromagnetic (FM) layers. We calculate the magnetization dynamics of the system by correlating each FM layer via exchange coupling (EC)-induced effective fields. Experimentally, we use CoFe/Ta/NiFe(Cu) trilayers in which the EC is tailored by varying the Ta spacer layer thickness and the saturation magnetization in the (NiFe)1–xCux alloy layer. The good agreement between theory and experiment clearly demonstrates that: 1) the resonance frequency of the OM can be significantly higher than that of the individual FM layer; 2) the intensity of the OM can be significantly enhanced by increasing the contrast in the saturation magnetization in two FM layers; and 3) the intensity of the OM, unlike the FMR of a single FM layer, increases with increasing applied magnetic field or frequency. By studying the EC as a function of spacer layer thickness and the saturation magnetization, we further verify that the Néel “orange-peel” coupling is a dominating mechanism in these trilayers, giving rise to coupling between FM layers.

中文翻译：

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交换耦合 CoFe/Ta/(NiFe)1′x Cu′ 三层膜中铁磁共振光学模式的调谐


我们从理论上和实验上研究了两个耦合铁磁（FM）层中的磁共振模式，即光学模式（OM）和声学模式（AM）。我们通过交换耦合 (EC) 感应的有效场关联每个 FM 层，计算系统的磁化动力学。实验上，我们使用 CoFe/Ta/NiFe(Cu) 三层，其中通过改变 Ta 间隔层厚度和 (NiFe)1-xCux 合金层中的饱和磁化强度来定制 EC。理论与实验之间良好的一致性清楚地表明：1）OM的谐振频率可以明显高于单个FM层的谐振频率； 2）通过增加两个FM层中饱和磁化强度的对比度可以显着增强OM的强度； 3) 与单个 FM 层的 FMR 不同，OM 的强度随着施加的磁场或频率的增加而增加。通过研究 EC 作为间隔层厚度和饱和磁化强度的函数，我们进一步验证了 Néel“橙皮”耦合是这些三层中的主要机制，从而引起 FM 层之间的耦合。