Creation and Annihilation of Skyrmions in the Frustrated Magnets with Competing Exchange Interactions

Noncollinear Magnetic Configurations in Frustrated Magnets

The exploration of materials with nanoscale noncollinear configurations has been continuously attracting attention due to the prospective applications in high-performance magnetic devices. Compared to ferromagnetic materials, noncollinear structures in frustrated magnets hold greater research value due to their smaller sizes and unique properties. However, an effective description of the nanoscale noncollinear domain structures in frustrated magnets is lacking. Here, we propose an approach based on a phase-field model to predict magnetic configurations in frustrated magnets within a square lattice system. The metastable domain structures have been determined under the competition between the nearest-neighbor ferromagnetic interaction and the third-neighbor antiferromagnetic exchange interaction. The conditions required for the stable existence of noncollinear phases have been theoretically derived. Additionally, we investigate the spin response to external fields for different J1 - J3 values, and we also examine the spin response to external fields for various values of J1 - J3, focusing on the emerging topological soliton states. Our research results not only hold crucial significance in facilitating an understanding of the complex characteristics of frustrated magnets but also offer theoretical guidance for further exploring the application potentials of these systems in diverse aspects such as emerging inductor devices and storage devices.

Magnetization dynamics in skyrmions due to high-speed carrier injections from Dirac half-metals

Recent developments in the magnetization dynamics in spin textures, particularly skyrmions, offer promising new directions for magnetic storage technologies and spintronics. Skyrmions, characterized by their topological protection and efficient mobility at low current density, are increasingly recognized for their potential applications in next-generation logic and memory devices. This study investigates the dynamics of skyrmion magnetization, focusing on the manipulation of their topological states as a basis for bitwise data storage through a modified Landau-Lifshitz-Gilbert equation (LLG). We introduce spin-polarized electrons from a topological ferromagnet that induce an electric dipole moment that interacts with the electric gauge field within the skyrmion domain. This interaction creates an effective magnetic field that results in a torque that can dynamically change the topological state of the skyrmion. In particular, we show that these torques can selectively destroy and create skyrmions, effectively writing and erasing bits, highlighting the potential of using controlled electron injection for robust and scalable skyrmion-based data storage solutions.

Skyrmion lattice formation and destruction mechanisms probed with TR-SANS

Magnetic skyrmions are topologically protected, nanoscale whirls of the spin configuration that tend to form hexagonally ordered arrays. As a topologically non-trivial structure, the nucleation and annihilation of the skyrmion, as well as the interaction between skyrmions, varies from conventional magnetic systems. Recent works have suggested that the ordering kinetics in these materials occur over millisecond or longer timescales, which is unusually slow for magnetic dynamics. The current work investigates the skyrmion ordering kinetics, particularly during lattice formation and destruction, using time-resolved small angle neutron scattering (TR-SANS). Evaluating the time-resolved structure and intensity of the neutron diffraction pattern reveals the evolving real-space structure of the skyrmion lattice and the timeframe of the formation. Measurements were performed on three prototypical skyrmion materials: MnSi, (Fe,Co)Si, and Cu2OSeO3. To probe lattice formation and destruction kinetics, the systems were prepared in the stable skyrmion state, and then a square-wave magnetic field modulation was applied. The measurements show that the skyrmions quickly form ordered domains, with a significant distribution in lattice parameters, which then converge to the final structure; the results confirm the slow kinetics, with formation times between 10 ms and 99 ms. Comparisons are made between the measured formation times and the fundamental material properties, suggesting the ordering temperature, saturation magnetization and magnetocrystalline anisotropy may be driving the timeframes. Micromagnetic simulations were also performed and support a scaling of the kinetics with sample volume, a behavior which is caused by the reconciling of misaligned domains.

Skyrmion driven by rotary magnetic field on the surface of magnetic nanotube: a Monte Carlo study

We report a Monte-Carlo simulation of the formation of skyrmions under a rotary magnetic field on a nanotube. The zero-field magnetic state is characterized as helical stripe domains swirling on the nanotube, with one to three periods depending on the ratio of Dzyaloshinskii-Moriya to ferromagnetic interaction and tubular size. Under a rotary magnetic field, the formation of skyrmions is in pair and the skyrmion number can be tuned. The movement of skyrmions is neither synchronous along with the rotary field, nor along a helical trajectory perpendicular to the rotary field. It is ascribed to that within a skyrmion pair, on one hand, the coupling between skyrmions is nonnegligible; on the other hand, different skyrmion pairs side by side are decoupled. This work predicts a way of nanotube-based skyrmion manipulation, and might develop the rotary information storage on energy- and space-saving modes or an edgeless racetrack memory.