Satoh Takuya, Iida Ryugo, Higuchi Takuya, Fujii Yasuhiro, Koreeda Akitoshi, Ueda Hiroaki, Shimura Tsutomu, Kuroda Kazuo, Butrim V I, Ivanov B A
Department of Physics, Kyushu University, Fukuoka, 819-0395, Japan.
Institute of Industrial Science, The University of Tokyo, Tokyo, 153-8505, Japan.
Nat Commun. 2017 Sep 21;8(1):638. doi: 10.1038/s41467-017-00616-2.
Ultrafast control of magnets using femtosecond light pulses attracts interest regarding applications and fundamental physics of magnetism. Antiferromagnets are promising materials with magnon frequencies extending into the terahertz range. Visible or near-infrared light interacts mainly with the electronic orbital angular momentum. In many magnets, however, in particular with iron-group ions, the orbital momentum is almost quenched by the crystal field. Thus, the interaction of magnons with light is hampered, because it is only mediated by weak unquenching of the orbital momentum by spin-orbit interactions. Here we report all-optical excitation of magnons with frequencies up to 9 THz in antiferromagnetic CoO with an unquenched orbital momentum. In CoO, magnon modes are coupled oscillations of spin and orbital momenta with comparable amplitudes. We demonstrate excitations of magnon modes by directly coupling light with electronic orbital angular momentum, providing possibilities to develop magneto-optical devices operating at several terahertz with high output-to-input ratio.Light pulses can control magnetism in a material, and the effective creation of magnetic oscillations leads to spintronic devices with higher efficiency. Here, the authors increase the efficiency of magnon excitation by using a material in which orbital angular momenta are not quenched.
利用飞秒光脉冲对磁体进行超快控制，在磁学的应用和基础物理方面引起了人们的兴趣。反铁磁体是很有前景的材料，其磁振子频率可延伸到太赫兹范围。可见光或近红外光主要与电子轨道角动量相互作用。然而，在许多磁体中，特别是含铁族离子的磁体，轨道动量几乎被晶体场淬灭。因此，磁振子与光的相互作用受到阻碍，因为它仅由自旋 - 轨道相互作用对轨道动量的微弱去淬灭介导。在此，我们报道了在具有未淬灭轨道动量的反铁磁CoO中对频率高达9太赫兹的磁振子进行全光激发。在CoO中，磁振子模式是自旋和轨道动量具有可比振幅的耦合振荡。我们通过直接将光与电子轨道角动量耦合来演示磁振子模式的激发，为开发具有高输出输入比、工作在几太赫兹的磁光器件提供了可能性。光脉冲可以控制材料中的磁性，而有效产生磁振荡会导致具有更高效率的自旋电子器件。在此，作者通过使用一种轨道角动量未被淬灭的材料提高了磁振子激发的效率。
