Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance
Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance
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DOI：
10.1088/1367-2630/17/1/013019
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发表时间：
2015-01-15
影响因子：
3.3
通讯作者：
van der Laan, G.
中科院分区：
文献类型：
--
作者：
Stenning, G. B. G.;Shelford, L. R.;van der Laan, G.
交换耦合软磁层在数据存储中有着广泛的应用，其动态响应对数据存储具有重要意义。使用诸如铁磁共振（FMR）之类的体块技术，很难获得每一层的行为和精确影响。相比之下，基于同步辐射的x射线检测铁磁共振（XFMR）技术允许在0.5-11 GHz频率范围内进行元素特定和相位分辨的FMR测量。本文报道了一种交换耦合Ni0.81Fe0.19 (43.5 nm)/Co0.5Fe0.5 （30 nm）双层体系的磁化动力学研究，采用磁强计和矢量网络分析仪FMR，并结合XFMR在Ni和Co L-2 x射线吸收边缘进行了研究。外延生长的双分子层表现出两种主要的共振，即声光模式。FMR实验表明，两层的基特尔曲线不能孤立地考虑，但它们的建模需要考虑层间交换耦合。FMR的角依赖性表明，硬磁CoFe层和软磁nfe层的模态存在集体效应。XFMR进动扫描结果表明，声模以Co和Ni同相磁化的Ni信号为主，光模以Co和Ni反相磁化的Co信号为主。Co信号在Ni共振处的响应和Co信号在Ni共振处的响应均表现出振幅和相位的变化，这可归因于界面交换耦合。相位解析XFMR的一个有趣的方面是能够区分静态和动态交换耦合。NiFe/CoFe双分子层的元素特异性旋进扫描具有明显的静态交换耦合特征，其中一层的有效场沿另一层的磁化方向排列。
Exchange-coupled hard and soft magnetic layers find extensive use in data storage applications, for which their dynamical response has great importance. With bulk techniques, such as ferromagnetic resonance (FMR), it is difficult to access the behaviour and precise influence of each individual layer. By contrast, the synchrotron radiation-based technique of x-ray detected ferromagnetic resonance (XFMR) allows element-specific and phase-resolved FMR measurements in the frequency range 0.5-11 GHz. Here, we report the study of the magnetization dynamics of an exchange-coupled Ni0.81Fe0.19 (43.5 nm)/Co0.5Fe0.5 (30 nm) bilayer system using magnetometry and vector network analyser FMR, combined with XFMR at the Ni and Co L-2 x-ray absorption edges. The epitaxially grown bilayer exhibits two principal resonances denoted as the acoustic and optical modes. FMR experiments show that the Kittel curves of the two layers cannot be taken in isolation, but that their modelling needs to account for an interlayer exchange coupling. The angular dependence of FMR indicates a collective effect for the modes of the magnetically hard CoFe and soft NiFe layer. The XFMR precessional scans show that the acoustic mode is dominated by the Ni signal with the Co and Ni magnetization precessing in phase, whereas the optical mode is dominated by the Co signal with the Co and Ni magnetization precessing in anti-phase. The response of the Co signal at the Ni resonance, and vice versa, show induced changes in both amplitude and phase, which can be ascribed to the interface exchange coupling. An interesting aspect of phase-resolved XFMR is the ability to distinguish between static and dynamic exchange coupling. The element-specific precessional scans of the NiFe/CoFe bilayer clearly have the signature of static exchange coupling, in which the effective field in one layer is aligned along the magnetization direction of the other layer.