Ultrafast Magnetic Vortex Core Switching Driven by the Topological Inverse Faraday Effect

We present a theoretical discovery of an unconventional mechanism of inverse Faraday effect which acts selectively on topological magnetic structures. The effect, topological inverse Faraday effect, is induced by the spin Berry’s phase of the magnetic structure when a circularly polarized light is applied. Thus a spin-orbit interaction is not necessary unlike that in the conventional inverse Faraday effect. We demonstrate by numerical simulation that topological inverse Faraday effect realizes ultrafast switching of a magnetic vortex within a switching time of 150 ps without magnetic field.

Figure 1

(a) Feynman diagrams representing the effective magnetic field generated by a TIFE. Solid line represents the electron’s Green’s function, and wavy line represents the electric field ($\mathit{E}$) of the incident circularly polarized light. Contributions (a1) and (a2) are linear and second order in spin gauge field (${\mathit{A}}_S$, denoted by dotted line), respectively. (b) Schematic depiction of the TIFE induced by a circular polarization $\mathit{\epsilon }\times {\mathit{\epsilon }}^{*}$ and spin chirality $\mathbf{\Phi }$. The induced magnetic field ${\mathit{H}}_{\mathrm{TIFE}}$ is parallel or antiparallel to the local spin direction $\mathit{n}$. (c) Profile of effective magnetic field $H_{\mathrm{TIFE}}$ [Eq. (6)], induced for a vortex as a function of distance from the core center $r$. The light intensity is $L=0.3\times {10}^{-18}{\mathrm{Tm}}^2$.

Figure 2

Phase diagram of vortex core reversal for a disk with radius of $1\mu \mathrm{m}$ and thickness of 20 nm at $T=100\mathrm{K}$. $L$ is proportional to the laser intensity. The region colored by blue represents negative value of averaged magnetization $⟨M_z⟩$ indicating switching of a core, while the red region represents no switching.

Figure 3

Time dependence of the averaged magnetization during the core switching process for several temperatures, $T=0.1$, 1, 10, and 100 K. The intensity of the light is $L=0.6\times {10}^{-18}\mathrm{T}{\mathrm{m}}^2$. Inset: Dependence of switching time to temperature.

Figure 4

Thickness dependence of the switching time and the threshold intensity ($L$) for core switching.