Professor Thorsten Hesjedal FInstP

Abstract:

<jats:p> Magnetic skyrmions are spin textures with nontrivial topology that form two-dimensional hexagonal lattices (SkX) in chiral magnets. Element-specific reciprocal-space characterization of skyrmion lattices with soft x-rays commonly relies on transmission geometries, which require thinning of bulk crystals and can modify their magnetic properties. Here, we show that resonant elastic x-ray scattering in a grazing-incidence geometry (GIREXS) provides a nondestructive and geometrically flexible probe of skyrmion lattices in bulk materials. Using MnSi as a model system, GIREXS resolves the helical, conical, and skyrmion-lattice states through their characteristic magnetic satellite peaks and yields the skyrmion wave vector. By operating just above the critical angle ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:msub> <a:mrow> <a:mi>α</a:mi> </a:mrow> <a:mrow> <a:mi mathvariant="normal">c</a:mi> </a:mrow> </a:msub> <a:mo>≈</a:mo> <a:mn>1.6</a:mn> <a:mo>°</a:mo> </a:mrow> </a:math> in MnSi at the Mn <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:msub> <d:mi>L</d:mi> <d:mn>3</d:mn> </d:msub> </d:math> edge), the method achieves a probing depth of approximately <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mn>3</f:mn> <f:mrow> <f:mtext>  </f:mtext> <f:mi>nm</f:mi> </f:mrow> </f:math> , tunable up to approximately <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mn>20</h:mn> <h:mrow> <h:mtext>  </h:mtext> </h:mrow> <h:mi>nm</h:mi> </h:math> via the incidence angle, while maintaining full reciprocal-space access to the in-plane magnetic correlations. The grazing-incidence approach circumvents the structural Bragg-peak constraints that limit conventional reflection resonant elastic x-ray scattering (REXS) at fixed soft-x-ray energies. Our measurements establish GIREXS as a practical method for studying magnetic superstructures in bulk crystals, providing direct reciprocal-space access to magnetic satellite reflections and a basis for future depth-controlled, element-selective investigations of complex spin textures. </jats:p>

Abstract:

<jats:title>Abstract</jats:title> <jats:p> Chiral soliton lattices (CSLs) emerge from the competition between Dzyaloshinskii–Moriya interaction, anisotropy, and magnetic fields. While well established in monoaxial helimagnets, their role in materials with anisotropic, direction-dependent chirality remains poorly understood. Here, we report the direct observation of a crossover from π to 2π soliton lattices in the non-centrosymmetric Heusler compound Mn <jats:sub>1.4</jats:sub> PtSn. Combining Lorentz transmission electron microscopy, resonant elastic X-ray scattering, and micromagnetic simulations, we identify a π-CSL as the magnetic ground state—rather than the expected spiral phase—which evolves into a classical 2π-CSL under increasing out-of-plane fields. This transition is governed by an interplay between uniaxial magnetocrystalline anisotropy and magnetostatic interactions, qualitatively captured by a double sine-Gordon model. Our framework extends to materials with <jats:italic>D</jats:italic> <jats:sub> 2 <jats:italic>d</jats:italic> </jats:sub> , <jats:italic>S</jats:italic> <jats:sub>4</jats:sub> , <jats:italic>C</jats:italic> <jats:sub> <jats:italic>n</jats:italic> <jats:italic>v</jats:italic> </jats:sub> , or <jats:italic>C</jats:italic> <jats:sub> <jats:italic>n</jats:italic> </jats:sub> symmetries in the thin-film limit, providing a unifying route to engineer magnetic phase diagrams in chiral systems with implications for soliton-based spintronics and topological transport. </jats:p>

Abstract:

The collective precession of magnetization manifests itself as magnon modes. These modes are governed by complex-valued vectorial eigenfunctions, which have remained experimentally challenging to observe. Here we introduce X-ray magnetic vector chronoscopy (XMVC), a time-resolved resonant scattering method that reconstructs the full magnetization dynamics with angular resolution of 0.1° (±0.01°). Applied to a synthetic antiferromagnetic multilayer (Si/NiFe (8 nm)/Ru (0.8 nm)/CoFeB (5.5 nm)), XMVC enables magnon state tomography, by directly measuring the nanoscale vectorial eigenfunctions of hybridized modes arising from magnon–magnon coupling. This approach provides full access to the system’s non-Hermitian Hamiltonian, revealing the complex-valued coupling strengths and non-orthogonal eigenbases. These results establish XMVC as an experimental platform for studying nanoscale spin systems by extracting the eigenfunctions of the system.