이번 학기 첫번째 콜로퀴움은 성균관대학교 에너지학과 최경민 교수님을 모시고 개최함을 안내드리오니, 참석 부탁드립니다.

                                                             아            래

1. Title: Optical spin generation in metals and its application for ultrafast spin torque

2. Speaker: 최경민 교수님(성균관대학교 에너지학과)

3. Date & Time: Sep. 9(Wed.)  2026.  4:30 PM

4. Place: Natural Science 1,  Room No. 31214

5. Abstract:

Spintronics aims for an efficient generation and transport of spin angular momentum. Conventionally, spin generation has been achieved by a spatial separation of spin-up and spin-down in electrons, such as spin filter effect and spin Hall effect. In addition, spin generation can be originated from spin angular momentum transfer between different quasiparticles of electrons, photons, phonons, and magnons.

In this seminar, I present optical spin-orbit torques (OSOT) in heavy metal/ferromagnet heterostructures [1], which is a combined process of optical spin generation in a heavy metal and spin transfer torque on ferromagnet. OSOT can excite both spatially uniform precession of magnetization and spatially propagating spin waves. Especially, measurement of dynamics of standing spin waves allows determination of exchange stiffness and damping of spin waves [2, 3].

OSOT can be mediated by magnons. Inserting an antiferromagnetic insulator of NiO in between the heavy metal and ferromagnet, we investigate the optically driven magnon torque. From the quantitative comparison of the optical and electrical magnon torque, we determine the spin transfer efficiency and relaxation length of magnons [4].

OSOT can induce fast dynamics of antiferromagnet. Antiferromagnets manifest high resonance frequencies owing to strong exchange coupling. We investigate the spin-torque-driven dynamics of Mn3Sn, noncollinear antiferromagnet. From the interaction between the spin current and antiferromagnet, we determine the spin absorption efficiency and spin coherence length of antiferromagnet [5]. In addition, we also investigated spin-torque-driven dynamics of ferrimagnet of CoGd, which has antiferromagnetic coupling between Co moment and Gd moment. OSOT triggers ferromagnetic-like dynamics, whose frequency of ~GHz, and the torque direction is determined by the net magnetization [6]

[1] G.-M. Choi, J. H. Oh, D.-K. Lee, S.-W. Lee, K. W. Kim, M. Lim, B.-C. Min, K.-J. Lee, and H.-W. Lee, Nature Commun. 11, 1482 (2020).

[2] G.-M. Choi, D.-K. Lee, K.-J. Lee, and H.-W. Lee, Phys. Rev. B 102, 014437 (2020).

[3] Y.-G. Choi and G.-M. Choi, Appl. Phys. Lett. 121, 012404 (2022)

[4] K.-H. Ko and G.-M. Choi, Phys. Rev. B 111, 134422 (2025).

[5] W.-B. Lee, H.-W. Ko, S. W, B.-G. Park, K.-J. Lee, and G.-M. Choi, Nature Nanotech. 20, 487 (2025)

[6] H.-S. Kim and G.-M. Choi, APL Mater. 14, 031115 (2026)