Jan Masell

Three‐dimensional (3D) topological spin textures host rich internal structures in thickness dimensions and enable emergent topological phenomena. However, whether their layer‐resolved textures and internal singularities fundamentally modify intralayer interactions lies beyond rigid‐tube interaction models and remains unexplored. Here we show that, in 3D hybrid skyrmion‐antiskyrmion strings, the layer‐dependent topology gives rise to interactions with a sign change across the film thickness, producing a switch between attraction and repulsion both among different layers within each texture and between neighboring 3D strings. This vertically asymmetric attractive‐repulsive interaction drives a tunable transition between square and triangular string lattices, in agreement with our experiment. Computational simulations identify quadrupolar Bloch points as internal topological junctions whose vertical migration mediates the intralayer competition between repulsive skyrmion segments near the surfaces and attractive antiskyrmion segments in the interior. We further show that the averaged topological charge quantifies the relative thickness fractions of the two competing topological segments and robustly captures the lattice phase boundary over a broad range of magnetic parameters. These findings highlight the importance of the surface‐bulk difference in topological materials and establish vertically asymmetric interactions as an intrinsic mechanism for topological phase control in 3D magnetic systems.

In this paper, we demonstrate how altermagnets can be simulated in the recently released micromagnetic simulation package mumax+. We have added a new magnet class for d-wave altermagnets and demonstrate how mumax+ is able to reproduce the analytical solutions for line profiles of the Néel vector and net magnetization for a Bloch domain wall. Next, we show simulation results of the magnon dispersion relation and its dependence on the anisotropic nature of the exchange interaction. Finally, we study the motion of a Néel skyrmion by applying a spin transfer torque. Altermagnets were implemented by extending the pre-existing code base for antiferromagnetic simulations. The object-oriented design of mumax+ allows for a correct calculation of the magnetostatic field in multi-sublattice systems, a feature that many other micromagnetic simulators lack.

Helimagnetic materials offer a versatile platform for spin-based device concepts owing to their long-range, tunable spiral order. Here, we demonstrate controlled manipulation of the helimagnetic propagation vector q by geometrical confinement, using FeGe as a model Dzyaloshinskii–Moriya interaction (DMI)-driven chiral magnet. Micromagnetic simulations based on the nonlinear sigma model reveal that open boundaries give rise to a chiral surface twist acting as an effective surface anisotropy, which dictates the preferred helix orientation in the absence of magnetostatic shape effects. This geometry-induced anisotropy is quantitatively captured by an analytical model derived from the DMI boundary condition. Magnetic force microscopy measurements on focused-ion-beam structured FeGe confirm the predicted orientation behavior and establish geometry-controlled helimagnetic order as a robust, tunable mechanism for steering DMI-stabilized spin-spiral states. The concept provides a general route toward device-level control of chiral magnetic order in non-centrosymmetric systems.

A fundamental question in condensed matter physics concerns how topological electronic states are influenced by many-body correlations, and magnetic Weyl semimetals represent an important material platform to address this problem. However, the magnetic structures realized in these materials are limited, and in particular, no clear example of an undistorted helimagnetic state has been definitively identified. Here, we report clear evidence of a harmonic helimagnetic cycloid with an incommensurate magnetic propagation vector Q in the Weyl semimetal GdAlSi via resonant elastic X-ray scattering, including rigorous polarization analysis. This cycloidal structure is consistent with the Dzyaloshinskii–Moriya interaction prescribed by the polar crystal structure of GdAlSi. Upon applying a magnetic field, the cycloid undergoes a transition to a novel multi-Q state. This field-induced, noncoplanar texture is consistent with our numerical spin model, which incorporates the Dzyaloshinskii–Moriya interaction and, crucially, anisotropic exchange interactions. The perfectly harmonic Weyl helimagnet GdAlSi serves as a prototypical platform to study electronic correlation effects in periodically modulated Weyl semimetals.

Helimagnetic materials offer a versatile platform for spin-based device concepts owing to their long-range, tunable spiral order. Here, we demonstrate controlled manipulation of the helimagnetic propagation vector q by geometrical confinement, using FeGe as a model DMI-driven chiral magnet. Micromagnetic simulations based on the nonlinear sigma model reveal that open boundaries give rise to a chiral surface twist acting as an effective surface anisotropy, which dictates the preferred helix orientation in the absence of magnetostatic shape effects. This geometry-induced anisotropy is quantitatively captured by an analytical model derived from the DMI boundary condition. Magnetic force microscopy measurements on focused-ion-beam structured FeGe confirm the predicted orientation behavior and establish geometry-controlled helimagnetic order as a robust, tunable mechanism for steering DMI-stabilized spin-spiral states. The concept provides a general route toward device-level control of chiral magnetic order in of non-centrosymmetric systems.

Antiferromagnetic states with a spin-split electronic structure give rise to spintronic, magnonic and electronic phenomena despite (near-)zero net magnetization^{1,2,3,4,5,6,7}. The simplest odd-parity spin splitting—p wave—was originally proposed to emerge from a collective instability in interacting electron systems^8,9,10,11,12. Recent theory has identified a distinct route to realize p-wave spin-split electronic bands without strong correlations^13,14, termed p-wave magnetism. Here we demonstrate an experimental realization of a metallic p-wave magnet. The odd-parity spin splitting of delocalized conduction electrons arises from their coupling to an antiferromagnetic texture of localized magnetic moments: a coplanar spin helix whose magnetic period is an even multiple of the chemical unit cell, as revealed by X-ray scattering experiments. This texture breaks space-inversion symmetry but approximately preserves time-reversal symmetry up to a half-unit-cell translation—thereby fulfilling the symmetry conditions for p-wave magnetism. Consistent with theoretical predictions, our p-wave magnet shows a characteristic anisotropy in the electronic conductivity^13,14,15. Relativistic spin–orbit coupling and a tiny spontaneous net magnetization further break time-reversal symmetry, resulting in a giant anomalous Hall effect (Hall conductivity >600 S cm⁻¹, Hall angle >3%), for an antiferromagnet. Our model calculations show that the spin-nodal planes found in the electronic structure of p-wave magnets are readily gapped by a small perturbation to induce the anomalous Hall effect. We establish metallic p-wave magnets as an ideal platform to explore the functionality of spin-split electronic states in magnets, superconductors, and in spintronic devices.

Topological magnetic (anti)skyrmions are robust string‐like objects heralded as potential components in next‐generation topological spintronics devices due to their low‐energy manipulability via stimuli such as magnetic fields, heat, and electric/thermal current. While these 2D topological objects are widely studied, intrinsically 3D electron‐spin real‐space topology remains less explored despite its prevalence in bulky magnets. 2D‐imaging studies reveal peculiar vortex‐like contrast in the core regions of spin textures present in antiskyrmion‐hosting thin plate magnets with S₄ crystal symmetry, suggesting a more complex 3D real‐space structure than the 2D model suggests. Here, holographic vector field electron tomography captures the 3D structure of antiskyrmions in a single‐crystal, precision‐doped (Fe_0.63Ni_0.3Pd_0.07)₃P (FNPP) lamellae at room temperature and zero field. These measurements reveal hybrid string‐like solitons composed of skyrmions with topological number W = −1 on the lamellae's surfaces and an antiskyrmion (W = + 1) connecting them. High‐resolution images uncover a Bloch point quadrupole (four magnetic (anti)monopoles that are undetectable in 2D imaging) which enables the observed lengthwise topological transitions. Numerical calculations corroborate the stability of hybrid strings over their conventional (anti)skyrmion counterparts. Hybrid strings result in topological tuning, a tunable topological Hall effect, and the suppression of skyrmion Hall motion, disrupting existing paradigms within spintronics.