Dynamical and Reversible Control of Topological Spin Textures

Recent observations of topological spin textures brought spintronics one step closer to new magnetic memories. Nevertheless, the existence of Skyrmions, as well as their stabilization, require very specific intrinsic magnetic properties which are usually fixed in magnets. Here we address the possibility to dynamically control their intrinsic magnetic interactions by varying the strength of a high-frequency laser field. It is shown that drastic changes can be induced in the antiferromagnetic exchange interactions and the latter can even be reversed to become ferromagnetic, provided the direct exchange is already non-negligible in equilibrium as predicted, for example, in Si doped with C, Sn, or Pb adatoms. In the presence of Dzyaloshinskii-Moriya interactions, this enables us to tune features of ferromagnetic Skyrmions such as their radius, making them easier to stabilize. Alternatively, such topological spin textures can occur in frustrated triangular lattices. Then, we demonstrate that a high-frequency laser field can induce dynamical frustration in antiferromagnets, where the degree of frustration can subsequently be tuned suitably to drive the material toward a Skyrmionic phase.

Figure 1

Magnetic properties of the $\mathrm{Si}(111):\{\mathrm{Sn},\mathrm{Pb}\}$ systems as functions of the laser field strength $Z$ for different frequencies $\mathrm{\Omega }=3\tilde{U}$, $5\tilde{U}$: exchange interactions $J$ (top left), DMI (bottom left), ratio $J/D$, which is proportional to a Skyrmion radius (bottom right). Dashed black curve corresponds to the case of zero direct exchange and shows the important role that $J^D$ plays in a phase transition and manipulation of the Skyrmionic structure. Top right panel shows NN and next-NN exchange interactions of Si(111):C, where we take “unrealistic” case of $t_1=t_2=t_3$ to make the difference in anti-FM–FM transition more visible. All units are given in meV.

Figure 2

Stable Skyrmionic phase for the Si(111):Sn as a function of laser field amplitude $Z$ and magnetic field $\tilde{B}=B/J_{A=0}$ given in units of the initial exchange interaction $J_{A=0}$, $\mathrm{\Omega }=4\tilde{U}$.

Figure 3

Hopping amplitudes $t_{2(3)}/t_1$ as the function of the amplitude $Z$ of the laser field for the values $J_1/|J_{2(3)}|$ that correspond to the Skyrmionic phase. Frequency of the laser field is $\mathrm{\Omega }=3\tilde{U}$.