Wu Guanjie, Zhu Weihua, Zhu Zhendong, Xue Hongwei, Ren Yang, Liu Yaowen, Jin Q Y, Zhang Zongzhi
Department of Optical Science and Engineering, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), and Shanghai Ultra-Precision Optical Manufacturing Engineering Center, Fudan University, Shanghai 200433, China.
School of Physics and Astronomy, Yunnan University, Kunming 650091, China.
Phys Chem Chem Phys. 2019 Aug 14;21(30):16830-16837. doi: 10.1039/c9cp02902h. Epub 2019 Jul 23.
High frequency magnetic precessions with strong intensity are strongly desired in material systems for high performance magnetic memory or nano-oscillator applications with ultrafast manipulation speed. Here, we demonstrate an exchange-coupled asymmetric composite film structure of Ta/Pd/[Pd/Co]/Cu(t)/[Co/Ni]/Ta with adjustable strong perpendicular magnetic anisotropy and interlayer coupling strength, in which the dynamic magnetic properties are systematically studied by using time-resolved magneto-optical Kerr effect spectroscopy. It is demonstrated that the in-phase precession frequency is between those of the single hard magnetic [Pd/Co] and soft [Co/Ni] multilayers, which can be significantly enhanced for the strongly coupled case at t < 1 nm. Moreover, in the weakly coupled samples with t = 1.0-3.0 nm, besides the common in-phase acoustic mode, an out-of-phase optical mode occurs simultaneously with a frequency even higher than that of the hard magnetic [Pd/Co] layer. The optical mode precession frequency and amplitude show an unusual non-monotonic variation trend with the increase of t, which has been theoretically analyzed and attributed to the co-effect of decreased coupling strength and increased magnetic anisotropy field difference between the two multilayer stacks. Moreover, by adjusting t and the [Co/Ni] repetition number N, an optical mode of strong intensity can be actively achieved, even reaching 80% as compared to the acoustic mode. These results provide effective control and better understanding of magnetic dynamics in perpendicular composite films, which are of key importance for developing ultrafast spintronics-based devices.
在用于具有超快操纵速度的高性能磁存储器或纳米振荡器应用的材料系统中，强烈需要具有高强度的高频磁进动。在此，我们展示了一种Ta/Pd/[Pd/Co]/Cu(t)/[Co/Ni]/Ta的交换耦合不对称复合薄膜结构，其具有可调节的强垂直磁各向异性和层间耦合强度，其中通过使用时间分辨磁光克尔效应光谱系统地研究了动态磁性能。结果表明，同相进动频率介于单个硬磁[Pd/Co]和软磁[Co/Ni]多层膜的进动频率之间，对于t < 1 nm的强耦合情况，该频率可显著提高。此外，在t = 1.0 - 3.0 nm的弱耦合样品中，除了常见的同相声学模式外，还同时出现了异相光学模式，其频率甚至高于硬磁[Pd/Co]层的频率。光学模式的进动频率和幅度随t的增加呈现出异常的非单调变化趋势，这已通过理论分析并归因于耦合强度降低和两个多层堆叠之间磁各向异性场差增加的共同作用。此外，通过调节t和[Co/Ni]重复数N，可以有效地实现高强度的光学模式，与声学模式相比甚至可达到80%。这些结果为垂直复合薄膜中的磁动力学提供了有效的控制和更好的理解，这对于开发基于超快自旋电子学的器件至关重要。
