Recently the classification of magnetically order material was revisited and the application of spin symmetry groups allowed the identification of three distinct classes of collinear magnets [1]. In addition to ferromagnets and antiferromagnets a third class of magnets named altermagnets was introduced. These altermagnets are classified by a compensated magnetic structure, however, show anisotropic spin split band structure. In my talk I will show how altermagnetic materials can be identified and discuss the experimental verification of their spin split band structure on the example of MnTe [2] (see Figure). Furthermore various odd in magnetic field effects like the anomalous Hall effect and X-ray circular magnetic dichroism [3] where detected in altermagnets despite their magnetic compensation. In particular the anomalous Hall effect was so far used as experimental fingerprint of altermagnetismn in collinear compensated magnets like RuO₂ [4, 5], MnTe [6], and Mn₅Si₃ thin films [7, 8]. It can resemble the typical hysteretic transversal resistivity loops found in ferromagnets, however, in absence of any detectable magnetization and with strong anisotropy which is linked to the symmetry of the material.

Figure: (left) Schematic of MnTe structure with magnetic Mn atoms with opposite moment in red and blue. (right) Spin split bands observed in angle resolved photoemission spectroscopy measurements.

References:

[1] L. Šmejkal, J. Sinova, and T. Jungwirth, Phys. Rev. X 12, 031042 (2022)
[2] J. Krempaský, L. Šmejkal, S.W. D'Souza, DK, et al. arXiv:2308.10681 (2023)
[3] A. Hariki, T. Yamaguchi, D. Kriegner, et al., arXiv:2305.03588 (2023)
[4] Z. Feng, X. Zhou, L. Šmejkal, et al. Nat Electron 5, 735–743 (2022)
[5] T. Tschirner, R. D. Gonzalez Betancourt, T. Kotte, DK, et al, APL Materials 11, 101103 (2023)
[6] R. D. Gonzalez Betancourt, J. Zubáč, R. J. Gonzalez-Hernandez, et al., DK, Phys. Rev. Lett.0 130, 36702 (2023)
[7] H. Reichlová, R.Lopes Seeger, R. González-Hernández, DK, et al. arXiv:2012.15651 (2020)
[8] I. Kounta, H. Reichlova, D. Kriegner, et al. Phys. Rev. Materials 7, 024416 (2023)