@article{semenov_xu_boulton_kim_2023, title={Electrical control of Dzyaloshinskii-Moriya interactions in magnetic Weyl semimetals}, volume={108}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.108.134428}, abstractNote={The Dzyaloshinskii-Moriya interaction (DMI) is known to be responsible for multiple phenomena in magnetic materials. In the conventional description as a perturbation of the superexchange interaction by the spin-orbit coupling, the strength of the DMI is only weakly sensitive to the external fields, making its control difficult in spintronic applications. In this work, we show that an electrical modulation of the DMI may actually be possible in magnetic Weyl semimetals (WSMs). Specifically, it is theoretically illustrated that an antisymmetric indirect spin-spin interaction identified recently as an alternative mechanism for the DMI can result in the desired sensitivity to the external electric and magnetic fields via a redistribution of Weyl fermions among nodes of opposite chirality. This chiral anomaly enabled approach becomes particularly prominent in WSMs with inversion symmetry, in which the conventional DMI is not allowed. Numerical estimations suggest that moderate electric and magnetic fields of $\ensuremath{\sim}{10}^{3}--{10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{cm}$ and $\ensuremath{\sim}1$ T can induce a sufficiently strong change in the DMI. The impact of this externally modulated DMI on the manipulation of magnetic textures, including skyrmions in WSMs, is also discussed.}, number={13}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Xu, Xinyi and Boulton, James A. and Kim, Ki Wook}, year={2023}, month={Oct} }
 @article{xu_semenov_kim_2020, title={Spin wave generation via localized spin-orbit torque in an antiferromagnet-topological insulator heterostructure}, volume={128}, ISSN={["1089-7550"]}, DOI={10.1063/5.0010478}, abstractNote={The spin–orbit torque induced by a topological insulator (TI) is theoretically examined for spin wave generation in a neighboring antiferromagnetic thin film. The investigation is based on the micromagnetic simulation of Néel vector dynamics and the analysis of transport properties in the TI. The results clearly illustrate that propagating spin waves can be achieved in the antiferromagnetic thin-film strip through localized excitation, traveling over a long distance. The oscillation amplitude gradually decays due to the non-zero damping as the Néel vector precesses around the magnetic easy axis with a fixed frequency. The frequency is also found to be tunable via the strength of the driving electrical current density. While both the bulk and the surface states of the TI contribute to induce the effective torque, the calculation indicates that the surface current plays a dominant role over the bulk counterpart except in the heavily degenerate cases. Compared to the more commonly applied heavy metals, the use of a TI can substantially reduce the threshold current density to overcome the magnetic anisotropy, making it an efficient choice for spin wave generation. The Néel vector dynamics in the nano-oscillator geometry are examined as well.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Jul} }
 @article{semenov_xu_kim_2019, title={Controllable Dispersion of Domain-Wall Movement in Antiferromagnetic Thin Films at Finite Temperatures}, volume={11}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.11.064051}, abstractNote={The dynamics of a 90$^{\circ }$ domain wall in an antiferromagnetic nanostrip driven by the current-induced spin-orbital torque are theoretically examined in the presence of random thermal fluctuations. A soliton-type equation of motion is developed on the basis of energy balance between the driving forces and dissipative processes in terms of the domain wall velocity. Comparison with micromagnetic simulations in the deterministic conditions shows good agreement in both the transient and steady-state transport. When the effects of random thermal fluctuations are included via a stochastic treatment, the results clearly indicate that the dispersion in the domain wall position can be controlled electrically by tailoring the strength and duration of the driving current mediating the spin orbital torque in the antiferromagnet. More specifically, the standard deviation of the probability distribution function for the domain wall movement can be tuned widely while maintaining the average position unaffected. Potential applications of this unusual functionality include the probabilistic computing such as Bayesian learning.}, number={6}, journal={PHYSICAL REVIEW APPLIED}, author={Semenov, Yuriy G. and Xu, Xinyi and Kim, Ki Wook}, year={2019}, month={Jun} }
 @article{xu_li_semenov_kim_2019, title={Creation and Destruction of Skyrmions via Electrical Modulation of Local Magnetic Anisotropy in Magnetic Thin Films}, volume={11}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.11.024051}, abstractNote={Magnetic skyrmions are topologically protected spin textures that are promising as carriers of information for computing and storage beyond CMOS-based systems. An electrostatic approach to creating a skyrmion can be more energy efficient than those based on a driving current. In this work, formation and dissolution of N\'eel skyrmions are examined theoretically via electrical modulation of magnetic anisotropy, in both ferromagnetic and antiferromagnetic structures. Simulations clearly illustrate the feasibility of the mechanism, enabling local control for versatility in applications. Also noteworthy is that the dynamical processes involved are much faster in antiferromagnetic materials.}, number={2}, journal={PHYSICAL REVIEW APPLIED}, author={Xu, Xinyi and Li, Xi-Lai and Semenov, Yuriy G. and Kim, Ki Wook}, year={2019}, month={Feb} }
 @article{xu_semenov_kim_2019, title={Electrical generation and propagation of spin waves in antiferromagnetic thin-film nanostrips}, volume={114}, ISSN={["1077-3118"]}, DOI={10.1063/1.5094767}, abstractNote={Electrical generation of terahertz spin waves is theoretically explored in an antiferromagnetic nanostrip via the current-induced spin–orbit torque. The analysis based on micromagnetic simulations clearly illustrates that the Néel-vector oscillations excited at one end of the magnetic strip can propagate in the form of a traveling wave when the nanostrip axis aligns with the magnetic easy-axis. A sizable threshold is observed in the driving current density or the torque to overcome the unfavorable anisotropy as expected. The generated spin waves are found to travel over a long distance, while the angle of rotation undergoes continuous decay in the presence of nonzero damping. The oscillation frequency is tunable via the strength of the spin–orbit torque, reaching the terahertz regime. Other key characteristics of spin waves such as the phase and the chirality can also be modulated actively. The simulation results further indicate the possibility of wavelike superposition between the excited spin oscillations, illustrating its application as an efficient source of spin-wave signals for information processing.}, number={23}, journal={APPLIED PHYSICS LETTERS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2019}, month={Jun} }