Ultrafast dynamics of 4f electron spins in TbFeCo film driven by inter-atomic 3d–5d–4f exchange coupling

Abstract

The ultrafast demagnetization dynamics of 3d and 4f spins, respectively, in FeCo and Tb of TbFeCo alloy film are studied independently by employing a dual-color time-resolved magneto-optical Kerr spectroscopy. The demagnetization dynamics of 3d and 4f spins are independently probed, respectively, by 800 and 400 nm light. Two-step demagnetization dynamics are observed for both the 3d and 4f spins under the excitation of 800 nm laser. In particular, the onset of 4f spin dynamics presents a delayed time with respect to the one of 3d spin dynamics. Those results clearly reveal a strong inter-atomic 3d-5d-4f exchange coupling which drives the first-step subpicosecond ultrafast demagnetization process of 4f spins, and a spin(4f)-lattice coupling which drives the second-step slower demagnetization process of 4f spins. A numerical calculation based on four temperature model reproduces the coupling characteristics in the demagnetization dynamics, and reveals the energy evolution dynamics among the different subsystems. These results provide a direct demonstration of strong coupling dynamics between the two spin subsystems in rare earth-transition metal alloy occurring within subpicosecond timescale, and show a new approach for ultrafast control of 4f spins via an indirect excitation.

Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co88Tb12 thin film with stripe domains

“…The fits, presented in Fig. 3, provide a quantitative description of the demagnetization process and allow to draw several conclusions: First, within experimental resolution (90 fs), we do not observe any significant delay between the demagnetization onset of Co and Tb atoms [37]. Second, the two magnetic sublattices exhibit very similar demagnetization amplitudes.…”

Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co$_{88}$Tb$_{12}$ thin film with stripe domains

“…The fits, presented in Fig. 3, provide a quantitative description of the demagnetization process and allow to draw several conclusions: First, within experimental resolution ( 50 fs), we do not observe any delay between the demagnetization onset of Co and Tb atoms 37 . Second, the two magnetic sublattices exhibit very similar demagnetization amplitudes.…”

Ultrafast Laser Modulation of Local Magnetization Orientation in Perpendicularly Exchange-Coupled Bilayer

“…Considering the light penetration depth, the polar Kerr signal in our experiment mainly comes from the out-of-plane magnetization component in the upper half part of GdFeCo layer. Note that for RE-TM materials, the Kerr signal probed at 800 nm is contributed from the magnetic moment of TM atoms [18], namely FeCo atoms here. As shown in Figure 1A, the out-of-plane polar Kerr hysteresis loop presents the hard-axis hysteresis of GdFeCo layer.…”

“…Amorphous ferrimagnetic rare earth-transition metal (RE-TM) alloy films, such as GdFeCo and TbFeCo, are one kind of the most-concerned materials for ultrafast magnetic applications [16][17][18]. Typically, GdFeCo and TbFeCo can be used as the free and pinning layers, respectively, in perpendicular ECCs due to their dissimilar spin-orbit coupling and perpendicular magnetic anisotropy (PMA) [2,19].…”