Abstract

Novel nanoelectronic and spintronic devices based on advanced materials can play a role in the quest for GreenIT if they are stable and can transport and manipulate angular momentum with low power. Conventional devices based on ferromagnetic materials that have an s-wave spin symmetry have been proposed, where switching can be realized in engineered multilayers by energy-efficient approaches to manipulate topological spin structures in 2D and 3D [1].

We combine the enhanced stability of topological states due to chiral interactions with enhanced manipulation efficiency using novel spin orbit torques [2]. Using novel materials that exploit the orbital degree of freedom increases the switching efficiency drastically further [3]. We use 2D materials as well as chiral systems including chiral organic molecules and chiral nanographenes to stabilize chiral spin structures and manipulate them [4].

Enhanced stability is found going beyond s-wave magnets to systems with compensated magnetic moments that are insensitive to stray fields and also exhibit ultra-fast dynamics. Starting with synthetic antiferromagnetic materials we demonstrate new meron topological spin structures and enhanced topological spin structure dynamics [5].

Materials discovery based on theoretical symmetry analysis as well as experimental realization enable even in systems with fully compensated magnetic order spin-polarized Fermi surfaces. This includes non-collinear antiferromagnets [6] that can exhibit p-wave spin symmetry as well as collinear d-wave (e.g. RuO₂) and g-wave altermagnets (e.g. CrSb) where we reveal the spin-split bands [7]. In the altermagnet hematite that can host antiferromagnetic antiskyrmions we find that ultra-low damping enables long distance spin transport and the altermagnetic nature manifests itself in the crystal Hall effect [8]. Using d-wave altermagnetic orthoferrites, we can probe the spin split magnonic bands leading to non-reciprocal spin transport.

A particularly exciting class of materials are 2D van der Waals materials that can be fabricated with high quality down to the monolayer thickness regime. Such materials that exhibit these symmetries are particularly exciting as heterostructures of differently ordered magnetic and non-magnetic materials with atomically flat interfaces that lead to enhanced coupling effects [9].

Such systems are not only of interest from a fundamental science point of view but their stability, efficient manipulation and fast dynamics also hold prospects for a range of applications such as memory and unconventional computing [10].

References

[1] K. Everschor-Sitte et al., Perspective in J. Appl. Phys. 124, 240901 (2018); D. Han et al., Nature Mater. 18, 703 (2019).

[2] S. Woo et al., Nature Mater. 15, 501 (2016); K. Litzius et al., Nature Phys., 13, 170 (2017); Nature Electron. 3, 30 (2020).

[3] S. Ding et al., PRL 125, 177201 (2020); PRL 128, 067201 (2022); R. Gupta et al., Nature Commun. 16, 130 (2025)

[4] Y. Kapon et al., Nano Lett. 25, 306 (2025).

[5] T. Dohi et al., Nature Commun. 14, 5424 (2023).

[6] A. Rajan et al., arxiv:2304.10747; A. Bose et al., arxiv: 2401.16021 (Nano Lett. 2025).

[7] O. Fedchenko et al., Sci. Adv. 10, eadj4883 (2024); S. Reimers et al., Nature Commun. 15, 2116 (2024).

[8] R. Lebrun et al., Nature 561, 222 (2018); Nature Commun. 11, 6332 (2020); E. Galindez-Ruales et al., arxiv:2310.16907.

[9] Z. Chen et al., J. Am. Chem. Soc. 138, 15488 (2016); A. Balan et al., Adv. Mater. 2403685 (2024).

[10] J. Zázvorka et al., Nature Nanotechnol. 14, 658 (2019); K. Raab et al., Nature Commun. 13, 6982 (2022).     G. Beneke et al., Nature Commun. 15, 8103 (2024).

Biography

Mathias Kläui is professor of physics at Johannes Gutenberg-University Mainz and adjunct professor at the Norwegian University of Science and Technology as well as Fellow at the University of Tokyo.

He received his PhD at the University of Cambridge, after which he joined the IBM Research Labs in Zürich. He was a junior group leader of an ERC Starting Grant at the University of Konstanz and then became associate professor in a joint appointment between the EPFL and the PSI in Switzerland before moving to Mainz. His research covers from blue sky fundamental science to applied projects with major industrial partners. He has published more than 440 articles and was selected as a Clarivate Highly Cited Researcher in 2024. He is a Fellow of the IEEE, IOP and APS, IEEE, EurASc, the German National Academy of Science and Engineering and was selected as an IEEE Magnetics Society Distinguished Lecturer.

Contact details and more information at www.klaeui-lab.de