MSc Anna Birk Hellenes

Q&A about altermagnetism

What are altermagnets?

Altermagets are magnetically compensated magnets that belong to a spin symmetry class which is completely distinct from that of ferro(ferri-)magnets and antiferromagnets. Altermagnets have alternating spin polarization in real and wave-vector space. This combination is not available in neither ferro(ferri-)magnets nor antiferromagnets [1].

What makes altermagnets interesting?

The symmetries of altermagnets dictate that their energy-wavevector dispersions are spin-polarized and spin-split. A combination of nonrelativistic quantum mechanical exchange and crystal fields that are naturally present in the system dictates the size of this spin splitting. In other words, the spin splitting in altermagnets is not a relativistic correction, and its size in energy could therefore be orders of magnitude larger than splittings due to spin-orbit coupling. In turn, altermagnets are candidates for hosting many unconventional spintronics effects, such as an unconventional anomalous Hall effect [2], spin currents, and giant/tunneling magnetoresistance [3], and this without creating large stray fields like in ferromagnets or requiring large spin orbit-coupling.

Is there experimental evidence of altermagnetism?

The anomalous (crystal) Hall effect, as well as spin current and torque, have already been measured in material candidates for altermagnets [4,5]. Such measurements indirectly point towards these systems being altermagnetic. Moreover, several materials researched in other fields, such as magnetic semiconductors and superconductors, also have altermagnetic symmetries [6].

[1] Šmejkal, L., Sinova, J., and Jungwirth, T., Phys. Rev. X 12, 031042 (2022)
[2] Šmejkal, L., González-Hernández, R., T. Jungwirth, and J. Sinova, Sci. Adv., 6, 23, 6 (2020)
[3] Šmejkal, L., Hellenes, A., González-Hernández, R., Sinova, J., and Jungwirth, T., Phys. Rev. X 12, 011028 (2022)
[4] Feng, Z., Zhou, X., Šmejkal, L. et al. Nat Electron 5, 735–743 (2022).
[5] Bose, A., Schreiber, N.J., Jain, R. et al. Nat Electron 5, 267–274 (2022).
[6] Šmejkal, L., Sinova, J., and Jungwirth, T., Phys. Rev. X 12, 040501 (2022)


Honored to receive poster prize at the European school of magnetism 2022 together with Elena Stetco, who herself won a price for writing the winning nomination. The topic of the poster was altermagnetism.

Talk, presenting work on giant magnetoresistance in d-wave altermagnets at the german physics society (DPG) meeting 2022.

My second paper, and my first in the field of spintronics, is published in Physical Review X February 2022.


Physical Review X

'Giant and Tunneling Magnetoresistance in Unconventional Collinear Antiferromagnets with Nonrelativistic Spin-Momentum Coupling'. Libor Šmejkal, Anna Birk Hellenes, Rafael Gonzáles-Hernández, Jairo Sinova, Tomáš Jungwirth. (2022)

Physical Review Letters

'Nonlocal conductance spectroscopy of Andreev bound states: Symmetry relations and BCS charges'. Jeroen Danon, Anna Birk Hellenes, Esben Bork Hanse, Lucas Casparis, Andrew P. Higginbotham, and Karsten Flensberg. (2020)

Research interests

  • Altermagnetism
  • Giant and tunneling magnetoresistance in magnets with zero net magnetic moment
  • Topological antiferromagnetic spintronics