arXiv subjects

Erik Lysne

Publications and source records attributed to Erik Lysne.

4 recordsLinked to original sources

arXiv2026

Control of helix orientation in chiral magnets via lateral confinement

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.

cond-mat.mtrl-sci↗

arXiv2023

Large ordered moment with strong easy-plane anisotropy and vortex-domain pattern in the kagome ferromagnet Fe$_3$Sn

We report the structural and magnetic properties of high-quality bulk single crystals of the kagome ferromagnet Fe$_3$Sn. The dependence of magnetisation on the magnitude and orientation of the external field reveals strong easy-plane type uniaxial magnetic anisotropy, which shows a monotonous increase from $K_1=-0.99\times 10^6 J/m^3$ at 300\,K to $-1.23\times10^6 J/m^3$ at 2\,K. Our \textit{ab initio} electronic structure calculations yield the value of total magnetic moment of about 6.9 $μ_B$/f.u. and a magnetocrystalline anisotropy energy density of 0.406\,meV/f.u. ($1.16\times10^6 J/m^3$) both being in good agreement with the experimental values. The self-consistent DFT computations for the components of the spin/orbital moments indicate that the small difference between the saturation magnetisations measured along and perpendicular to the kagome layers results from the subtle balance between the Fe and Sn spin/orbital moments on the different sites. In zero field, magnetic force microscopy reveals micrometer-scale magnetic vortices with weakly pinned cores that vanish at $\sim$3\,T applied perpendicular to the kagome plane. Our micromagnetic simulations, using the experimentally determined value of anisotropy, well reproduce the observed vortex-domain structure. The present study, in comparison with the easy-axis ferromagnet Fe$_3$Sn$_2$, shows that varying the stacking of kagome layers provides an efficient control over magnetic anisotropy in this family of Fe-based kagome magnets.

cond-mat.mtrl-sci↗

arXiv2021

Magnetic and geometrical control of spin textures in the itinerant kagome magnet Fe$_3$Sn$_2$

Magnetic materials with competing magnetocrystalline anisotropy and dipolar energies can develop a wide range of domain patterns, including classical stripe domains, domain branching, as well as topologically trivial and non-trivial (skyrmionic) bubbles. We image the magnetic domain pattern of Fe$_3$Sn$_2$ by magnetic force microscopy (MFM) and study its evolution due to geometric confinement, magnetic fields, and their combination. In Fe$_3$Sn$_2$ lamellae thinner than 3 $μ$m, we observe stripe domains whose size scales with the square root of the lamella thickness, exhibiting classical Kittel scaling. Magnetic fields turn these stripes into a highly disordered bubble lattice, where the bubble size also obeys Kittel scaling. Complementary micromagnetic simulations quantitatively capture the magnetic field and geometry dependence of the magnetic patterns, reveal strong reconstructions of the patterns between the surface and the core of the lamellae, and identify the observed bubbles as skyrmionic bubbles. Our results imply that geometrical confinement together with competing magnetic interactions can provide a path to fine-tune and stabilize different types of topologically trivial and non-trivial spin structures in centrosymmetric magnets.

cond-mat.str-el↗

arXiv2021

Detection of Topological Spin Textures via Non-Linear Magnetic Responses

Topologically non-trivial spin textures, such as skyrmions and dislocations, display emergent electrodynamics and can be moved by spin currents over macroscopic distances. These unique properties and their nanoscale size make them excellent candidates for the development of next-generation logic gates, race-track memory, and artificial synapses for neuromorphic computing. A major challenge for these applications - and the investigation of nanoscale magnetic structures in general - is the realization of detection schemes that provide high resolution and sensitivity. We study the local magnetic properties of disclinations, dislocations, and domain walls in FeGe, and reveal a pronounced response that distinguishes the individual spin textures from the helimagnetic background. Combination of magnetic force microscopy and micromagnetic simulations links the non-linear response to the local magnetic susceptibility. Based on the findings, we propose a read-out scheme using superconducting micro-coils, representing an innovative approach for detecting topologically non-trivial spin textures and domain walls in device-relevant geometries.

cond-mat.mtrl-sci↗