Joachim Deisenhofer

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Their crystallographic parity-broken symmetry and collinear antiferromagnetic order makes Fe2Mo3O8 and Co2Mo3O8 the perfect basis for a rich buffet for hungry condensed-matter scientists: The low-energy THz excitations of Fe2Mo3O8 reportedly exhibit a hybrid taste of chiral phonon [1] and magnon-polaron [2] states when probed via magneto-Raman measurements or neutron scattering, respectively. However, we could describe their THz absorption spectra and optical magnetoelectric effects such as the non-reciprocal directional dichroism [3] by using an advanced single-ion approach to the Fe2+ multiplet states [4]. The rich physics of Fe2Mo3O8 can be additionally spiced up by a combination of slight Zn doping and magnetic field [5, 6], where a metastable ferrimagnetic phase can be created with a peculiar magnetization reversal [7]. In addition to warming up some of these tasty but already published snacks, I will serve our recent findings on
strong Faraday effects of the THz-excitations in Fe2Mo3O8 and on our comparison of spin-group and magnetic-point group description of phonon selection rules in Co2Mo3O8 as an altermagnetic candidate [8]. Enjoy the meal

1] F. Wu, S. Bao, J. Zhou, Y. Wang, J. Sun, J. Wen, Y. Wan, and Q. Zhang, Fluctuation-enhanced phonon magnetic moments in a polar antiferromagnet, Nature Physics https://doi.org/10.1038/s41567-023-02210-4 (2023).
[2] S. Bao, Z.-L. Gu, Y. Shangguan, Z. Huang, J. Liao, X. Zhao, B. Zhang, Z.-Y. Dong, W. Wang, R. Kajimoto, M. Nakamura, T. Fennell, S.-L. Yu, J.-X. Li, and J. Wen, Direct observation of topological magnon polarons in a multiferroic material, Nature Communications 14, https://doi.org/10.1038/s41467-023-41791-9 (2023).
[3] S. Reschke, D. G. Farkas, A. Strini´c, S. Ghara, K. Guratinder, O. Zaharko, L. Prodan, V. Tsurkan, D. Szaller, S. Bord´acs, J. Deisenhofer, and I. K´ezsm´arki, Confirming the trilinear form of the optical magnetoelectric effect in the polar honeycomb antiferromagnet Co2Mo3O8,
npj Quantum Mater. 7, 1 (2022).
[4] K. V. Vasin, A. Strini´c, F. Schilberth, S. Reschke, L. Prodan, V. Tsurkan, A. R. Nurmukhametov, M. V. Eremin, I. K´ezsm´arki, and J. Deisenhofer, Optical magnetoelectric effect in the polar honeycomb antiferromagnet Fe2Mo3O8, Physical Review B.
[5] T. Kurumaji, S. Ishiwata, and Y. Tokura, Doping-tunable ferrimagnetic phase with large linear magnetoelectric effect in a polar magnet Fe2Mo3O8, Phys. Rev. X 5, 031034 (2015).
[6] Q. Chen, A. Miyake, T. Kurumaji, K. Matsuura, F. Kagawa, S. Miyahara, Y. Tokura, and M. Tokunaga, Multiple Magnetoelectric Plateaux in Polar Magnet Fe2Mo3O8 https://doi.org/10.48550/arXiv.2309.10583 (2023).
[7] S. Ghara, E. Barts, K. Vasin, D. Kamenskyi, L. Prodan, V. Tsurkan, I. K´ezsm´arki, M. Mostovoy, and J. Deisenhofer, Magnetization reversal through an antiferromagnetic state, Nature Communications 14, 10.1038/s41467-023-40722-y (2023).
[8] F. Schilberth, M. Kond´akor, D. Ukolov, A. Pawbake, K. Vasin, O. Ercem, L. Prodan, V. Tsurkan, A. A. Tsirlin, C. Faugeras, P. Lemmens, K. Penc, I. K´ezsm´arki, S. Bord´acs, and J. Deisenhofer, Optical phonons as a testing ground for spin group symmetries https://doi.org/10.48550/arXiv.2508.09793 (2025).

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Uni Augsburg
PH2
Contact: Markus Grüninger / Matteo Cacco