[10a-Z08-1~10] 10.2 Fundamental and exploratory device technologies for spin

▼ [10a-Z08-1] Optical spin-torque observed in FeCo / Pt bilayers

〇Satoshi Iihama^1,2, Shigemi Mizukami^3,2,4 (1.FRIS, Tohoku Univ., 2.CSRN, Tohoku Univ., 3.AIMR, Tohoku Univ., 4.CSIS, Tohoku Univ.)

Keywords:photo-spintronics, Light helicity induced magnetization dynamics

Manipulation of magnetization precession, namely magnon, with circularly-polarized light has attracted much attention, to date. Many of relevant studies have focused on magnon driven by the inverse Faraday effect in magnetic insulators or semiconductors. However, there have been few reports on metals. Recently Choi et al. reported magnetization precession driven by the circularly-polarized light in ferromagnet/heavy metals bilayers [1]. Then, they proposed new physics, optical spin-torque which is distinct from the traditional inverse Faraday effect. However, the physics of optical spin-torque is not clearly understood yet; thus, it is demanded to deeply understand the physics of this torque toward photo-spintronic applications. As a first step to further research, we study helicity dependence of laser-induced magnetization precession in FeCo / Pt bilayers. Thin film samples were prepared by magnetron sputtering. MgO / FeCo / Pt thin film layer were deposited on thermally oxidized Si substrate. The pulse width, wavelength, and repetition rate of the femtosecond laser pulse used were 120 fs, 800 nm, and 1 kHz, respectively. The helicity dependent magnetization precession in FeCo / Pt bilayer was clearly observed. The fitting to experimental data indicated that circularly-polarized laser makes magnetization initially tilt away from the film surface. This result is consistent with the previous observation and optical spin-torque proposed. Optical spin-torque is believed to be regarded as a damping-like torque, which is induced by a current of the spin-angular momentum in a nonmagnetic layer transferred from the circularly-polarized light. Indeed, we observed the remarkable dependence of this torque on the FeCo and Pt layer thicknesses, which will be discussed in detail.
[1] G. -M. Choi et al. Nat. Commun. 8, 15085 (2017), G. -M. Choi et al. Nat. Commun. 11, 1482 (2020).
[2] S. Iihama and S. Mizukami, manuscript in-preparation.