Skyrmion helicity, which defines the spin swirling direction, is a fundamental parameter that may be utilized to encode data bits in future memory devices. Generally, in centrosymmetric ferromagnets, dipole skyrmions with helicity of −π/2 and π/2 are degenerate in energy, leading to equal populations of both helicities. On the other hand, in chiral materials where the Dzyaloshinskii–Moriya interaction (DMI) prevails and the dipolar interaction is negligible, only a preferred helicity is selected by the type of DMI. However, whether there is a rigid boundary between these two regimes remains an open question. Herein, the observation of dipole skyrmions with unconventional helicity polarization in a van der Waals ferromagnet, Fe5−δGeTe2, is reported. Combining magnetometry, Lorentz transmission electron microscopy, electrical transport measurements, and micromagnetic simulations, the short‐range superstructures in Fe5−δGeTe2 resulting in a localized DMI contribution, which breaks the degeneracy of the opposite helicities and leads to the helicity polarization, is demonstrated. Therefore, the helicity feature in Fe5−δGeTe2 is controlled by both the dipolar interaction and DMI that the former leads to Bloch‐type skyrmions with helicity of ±π/2 whereas the latter breaks the helicity degeneracy. This work provides new insights into the skyrmion topology in van der Waals materials.

A simple, reliable, and self-switchable spin−orbit torque (SOT)-induced magnetization switching in a ferromagnetic single layer is needed for the development of next generation fully electrical controllable spintronic devices. In this work, fieldfree SOT-induced magnetization switching in a CoPt single layer is realized by broken multiple inversion symmetry through simultaneously introducing both oblique sputtering and a vertical composition gradient. A quantitative analysis indicates that multiple inversion asymmetries can produce dynamical bias fields along both z-and x-axes, leading to the observed field-free deterministic magnetization switching. Our study provides a method to accomplish fully electrical manipulation of magnetization in a ferromagnetic single layer without the external magnetic field and auxiliary heavy metal layer, enabling flexible design for future spin−orbit torque-based memory and logic devices.

Magnetic skyrmions are topologically protected spin textures that were found to be promising candidates for next-generation spintronic devices owing to their small size and unique current-induced dynamics.Increasing skyrmions density at designated locations in a controllable manner is a prerequisite to further improve the recording density of magnetic memory devices and relevant spintronics. Here, we demonstrate that a sharp increase in skyrmion density in magnetic multilayer films can be purposefully realized at a site-specific position by ion irradiation, which has industrial applicability. The Cs-scanning transmission electron microscopy and micromagnetic simulation results indicate that the skyrmions density can be sharply increased five times after applying an exposure with an irradiation dose of 1.5 × 10 14 Ga + /cm 2 , and the magnetic field required to create skyrmions is also reduced. The intrinsic physical mechanism of increasing skyrmion density is found to mainly originate from the formation of disorders through Ga + irradiation, which can induce a decrease in the nucleation energy barrier of skyrmions. We further show that the artificial skyrmion patterns with tunable density can be intentionally written at specific sites by using a Ga + ion beam. This work should contribute a significant step toward eventually realizing the practical recording application of magnetic skyrmions.

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Understanding the nucleation and growth process of carbon nanotubes (CNTs) is important for guiding their efficient and controllable synthesis in industry. However, the intrinsic mechanism that controls the formation of carbon nanotubes is still controversial. Here, using in‐situ transmission electron microscopy (TEM), we demonstrate the dynamic catalytic growth of multilayered graphite crystallites and single‐walled carbon nanotubes (SWCNTs) from the Co2C catalyst nanoparticles (NPs) at the atomic resolution. The dissociative carbon atoms arrive at the nucleation sites on the surface of small and large NPs by the surface and bulk diffusion, respectively. These two different diffusion modes are found to be the essential prerequisite for growing single‐walled carbon nanotubes (SWCNTs) or multilayered graphite crystallites. The small NPs utilize crystal self‐rotation to expose the (111) plane for efficiently capturing carbon atoms, while the large NPs use self‐reshaping on (111) facets to provide atomic steps as active nucleation sites. Density functional theory (DFT) calculations indicate that the observations are in good agreement with the growth mechanism of graphite structures involving the preferential selectivity of crystal facets. Our results may open up the possibility of adjusting the size and crystal orientation of cobalt‐based catalyst particles to efficiently synthesize the SWCNTs with high quality.