Regensburg 2022 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 20: Focus Session: Revealing Multidimensional Spin Textures and their Dynamics via X-rays and Electrons

MA 20.5: Hauptvortrag

Mittwoch, 7. September 2022, 11:45–12:15, H37

Determination of spin chirality and helicity angle by circular dichroism in soft x-ray absorption and resonant elastic scattering — •Gerrit van der Laan — Diamond Light Source, Didcot, UK

The depth profile of the full 3D spin structure of magnetic skyrmions below the surface of bulk Cu2OSeO3 was obtained using the polarization dependence of resonant elastic x-ray scattering (REXS) [AIP Advances 11, 015108 (2021)]. While the bulk spin configuration showed the anticipated Bloch type structure, the skyrmion lattice changes to a Néel twisting (i.e., with a different helicity angle) at the surface within a distance of several hundred nm. The experimental penetration length of the Néel twisting is 7x longer than the theoretical value given by the ratio of J/D. This indicates that apart from the considered spin interactions, i.e., Heisenberg exchange interaction J and Dzyaloshinskii-Moriya interaction D, as well as the Zeeman interaction, other effects must play an important role.

A new rule for the rotational symmetry invariance of the XMCD signal is presented [PRB 104, 094414 (2021)]. A threefold symmetric kagome lattice with negative spin chirality can give a nonzero x-ray magnetic circular dichroism (XMCD), despite a total spin moment of zero. A necessary condition is the existence of an anisotropic XMCD signal for the local magnetic atom. The maximum dichroism is not aligned along the spin direction but depends on the relative orientation of the spin with respect to the atomic orientation.