Ultrafast optical manipulation of magnetic skyrmions

TL;DR

Ultrafast optical manipulation of magnetic skyrmions is addressed by introducing an inertial Thiele equation that includes an inverse Faraday effect (IFE) driven force under circularly polarized light. The model treats the skyrmion as a massive quasiparticle with mass $M_{sk}$, deriving the nonuniform IFE field $H_{IFE}(r)$ and the resulting force $F_{IFE}$ under Gaussian CPL, and showing how CW and pulsed excitation produce fundamentally different dynamics. The main findings are that (i) CW driving yields polygonal or spiral trajectories due to inertia, (ii) pulsed driving leads to post-pulse, sustained gyration revealing intrinsic relaxation, and (iii) the handedness and attraction/repulsion of skyrmions are controlled by the topological charge $Q$ and light helicity, with phase diagrams mapping oscillatory, transition, and overdamped regimes as functions of $\alpha$, $I_0$, $f$, and $M_{sk}$. The work provides a theoretical framework for designing all-optical protocols to create and steer topological spin textures on ultrafast timescales and has potential implications for spintronic devices.

Abstract

We theoretically investigate the inertial dynamics of magnetic skyrmions driven by circularly polarized light (CPL) via the inverse Faraday effect (IFE). By incorporating an inertial mass term into the Thiele equation and analytically deriving the optically induced magnetic fields and forces, we demonstrate fundamentally distinct dynamical regimes under continuous-wave (CW) versus pulsed excitation. Skyrmion inertia qualitatively transforms trajectories from smooth spirals to polygonal orbits under continuous driving, while enabling sustained post-pulse gyration that reveals the system's intrinsic relaxation dynamics. The handedness of the trajectory is determined by the topological charge and light helicity: left-circularly polarized (LCP) light attracts skyrmions toward the beam center, while right-circularly polarized (RCP) light repels them. Systematic parameter analysis reveals how Gilbert damping, optical intensity, frequency, and skyrmion mass control the transition between oscillatory and overdamped dynamical phases. Our work identifies inertia, topological charge, and light helicity as essential factors in ultrafast all-optical skyrmion manipulation and provides a theoretical model for designing topological spin textures with ultrafast light.

Figures (7)

• Figure 1: Schematic diagram of Gaussian CPL driving Néel-type skyrmion motion in chiral magnetic film through IFE. The origin of the Cartesian coordinate system ${\bf O}=(0, 0)$ is located at the center of the beam with $\boldsymbol{r} = (x, y)$. $\boldsymbol{R} = (X, Y)$ denotes the collective coordinate of a skyrmion. The inserts are the Gaussian beam profile (left) and a skyrmion configuration (right).
• Figure 2: The trajectories of skyrmions with $Q=\pm 1$ for the RCP/LCP light: (a)-(d) for CW CPL, and (e)-(h) for pulsed CPL, respectively. The skyrmions with mass (red) and without mass (blue) are included. The initial positions of skyrmions are all set to be 50 nm from the laser beam center. $\alpha=0.03$, and $t=10$ ns for the motion time of skyrmions. The black arrows indicate the skyrmion's motion.
• Figure 3: Velocity-time dynamics of the magnetic skyrmion under RCP/LCP light. (a) and (b) for CW CPL, and (c) and (d) for pulsed CPL, respectively.
• Figure 4: Parameter-dependent trajectory morphology of inertial skyrmions under CW excitation with (a) LCP light and (b) RCP light, respectively. $\alpha=0.03$, $I_1=6.37 \times 10^6$ W/m$^2$, $M_{\text{sk}}=M_0=10^{-23}$ kg, $f=\omega/2\pi=10$ GHz. The temporal evolution of trajectories is represented by a color map (red to green: $0-10$ ns), while black arrows indicate the initial direction of motion. In all simulations, the skyrmion's initial position is fixed at 50 nm from the beam center, and its topological charge is $Q=+1$
• Figure 5: Parameter-dependent trajectory morphology of inertial skyrmions under pulsed excitation for (a) LCP light and (b) RCP light, respectively, using consistent parameters and settings as shown in Fig. \ref{['Parameter-trajectory-cw']}.