[22a-P09-1~14] 10 Spintronics and Magnetics(Poster)

▲ [22a-P09-12] Optical-helicity induced magnetization dynamics in [Co/Pt] multilayer thin films with perpendicular magnetic anisotropy

〇Satoshi Iihama^1,2,3, Kazuaki Ishibashi^4,2, Shigemi Mizukami^2,3,5 (1.FRIS, Tohoku Univ., 2.AIMR, Tohoku Univ., 3.CSRN, Tohoku Univ., 4.Tohoku Univ., 5.CSIS, Tohoku Univ.)

Keywords:Photo-spintronics, Photo-induced spin dynamics

Recently, photon spin injection into heavy metal thin films attracts attention as a way of manipulation of magnetization in ferromagnetic/heavy metal thin films [1,2]. A torque is induced by spin angular momentum transfer from the heavy metal layer to the ferromagnetic layer. Thus, the amplitude of magnetization precession increases with decreasing ferromagnetic layer thickness. Ferromagnetic multilayers (MLs) with perpendicular magnetic anisotropy (PMA), such as [Co/Pt], are promising candidates for opto-magnetic memory media [3]; therefore it is demanded to understand optical-helicity effect on magnetization dynamics for such MLs. Here, we report optical-helicity induced spin-transfer torque effect in [Co/Pt] multilayer thin films with PMA. The MLs of Pt(3) / [Co(0.6)/Pt(1)]_N / Pt(2) (thickness is in nm) were deposited on thermally oxidized silicon substrates by means of DC magnetron sputtering technique. Optical pump-probe technique was employed. Wavelength and pulse duration of a laser pulse are about 800 nm and 120 fs, respectively. Figure 1(a) shows out-of-plane magneto-optical Kerr hysteresis loops for the ML films with different stack number N. All the ML films exhibit PMA. Figure 1(b) shows the temporal magnetization dynamics observed in ML film with different pump laser helicities, where an in-plane magnetic field of 2 T was applied and pump fluence was F_p = 8.4 J/m². Magnetization precessions were clearly observed and those initial phases were reversed with the helicity of the laser pulse, indicating optical-helicity induced torque on magnetization in MLs. The details of the optical-helicity induced torque on the MLs will be discussed in the presentation.
[1] G. -M. Choi et al. Nat. Commun. 11, 1482 (2020). [2] S. Iihama et al. Nanophotonics, 10, 1169 (2021).
[3] C. -H. Lambert et al. Science 345, 1337 (2014).