Using symmetry analysis and density functional theory calculations, we uncover the nature of the Dzyaloshinskii-Moriya interaction in monolayer ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$. We show that while such an interaction might result in small distortions of the magnetic texture in the short range, in the long range it favors in-plane Néel spin spirals along equivalent directions of the crystal structure. Whereas our results show that the observed Néel skyrmions cannot be explained by the Dzyaloshinskii-Moriya interaction at the monolayer level, they suggest that a canted magnetic texture shall arise at the boundary of ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ nanoflakes or nanoribbons and, most interestingly, that homochiral planar magnetic textures could be stabilized.

We theoretically predict that vanadium-based Janus dichalcogenide monolayers constitute an ideal platform for spin-orbit torque memories. Using first-principles calculations, we demonstrate that magnetic exchange and magnetic anisotropy energies are higher for heavier chalcogen atoms, while the broken inversion symmetry in the Janus form leads to the emergence of Rashba-like spin-orbit coupling. The spin-orbit torque efficiency is evaluated using optimized quantum transport methodology and found to be comparable to heavy nonmagnetic metals. The coexistence of magnetism and spin-orbit coupling in such materials with tunable Fermi-level opens new possibilities for monitoring magnetization dynamics in the perspective of nonvolatile magnetic random access memories.

We present the magnetic and optical properties of various combinations of ordered spin state configurations between low‐spin (LS) state, intermediate‐spin (IS) state, and high‐spin (HS) state of LaCoO₃. In this study, we use the state‐of‐the‐art first principles calculations based on generalized gradient (GGA) + Hubbard U approach. The excited‐state properties of different spin configurations of LaCoO₃ such as the X‐ray absorption spectra, optical conductivity, reflectivity, and electron energy loss are calculated. We have demonstrated that the optical spectra results can be used for analyzing the spin state of Co³⁺ ion. The first specie is the local excitation of IS cobalt ions in the LS ground state. The second excitation leads to the stabilization of the mixed IS/HS Co³⁺ metallic state. At low temperature, the comparison between O 2p and Co 3d projected density of states with the experimental valence band spectra indicates significant IS Co³⁺ ions and this is in sharp contrast to the HS state which is negligible. The line shape of O 2s and Co 3d core level spectra are well reproduced in this study. The present results are in excellent agreement with the available experimental data. The variation in the spectra of different configurations of LaCoO₃ suggests a changing in the spin state as the temperature is enhanced from 90 to 500 K. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012

While some of the most elegant applications of topological insulators, such as the quantum anomalous Hall effect, require the preservation of Dirac surface states in the presence of time-reversal symmetry breaking, other phenomena such as spin-charge conversion rather rely on the ability for these surface states to imprint their spin texture on adjacent magnetic layers. In this Rapid Communication, we investigate the spin-momentum locking of the surface states of a wide range of monolayer transition metals ($3d-\mathrm{TM}$) deposited on top of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ topological insulators using first-principles calculations. We find an anticorrelation between the magnetic moment of the $3d-\mathrm{TM}$ and the magnitude of the spin-momentum locking induced by the Dirac surface states. While the magnetic moment is large in the first half of the $3d$ series, following Hund's rule, the spin-momentum locking is maximum in the second half of the series. We explain this trend as arising from a compromise between intra-atomic magnetic exchange and covalent bonding between the $3d-\mathrm{TM}$ overlayer and the Dirac surface states. As a result, while Cr and Mn overlayers can be used successfully for the observation of the quantum anomalous Hall effect or the realization of axion insulators, Co and Ni are substantially more efficient for spin-charge conversion effects, e.g., spin-orbit torque and charge pumping.