Scientists from an international consortium have demonstrated experimentally and theoretically the altermagnetic character of the material Mn5Si3, proving the incomparable advantage of this type of zero-magnetization magnetic phase: the strong spintronic effects associated with it are based on non-relativistic physics.
Real space: Magnetic and crystalline structure of Mn5Si3. Reciprocal space: shifts in the electronic bands of majority and minority spins (s_z) (red and blue), and consequences on the Berry curvature (Omega_z), which displays hot spots that are the source of certain spintronic effects, such as the anomalous Hall effect.
Altermagnetism is a third class of magnetic materials. It complements and sometimes supplants the two usual classes: ferromagnetism (ferrimagnetism) and antiferromagnetism. An altermagnet (AM) is composed of magnetic moments alternately oriented in opposite directions, like a collinear antiferromagnet (AFM). Although devoid of magnetization, it nevertheless polarizes the electric current by shifting the electronic bands of the majority and minority spins, much like a ferromagnet (FM), but alternately. The secret lies in the fact that, unlike an AFM, the two sublattices of moments that make up the AM do not have the same electronic environment, so they are linked by rotational symmetry rather than translational or inversion symmetry. More generally, seen through the prism of symmetry groups, FM (& ferrimagnets), AFM and AM crystals belong to three distinct subgroups. In addition to the above-mentioned properties, the spin configuration of AMs gives them specific properties that are inaccessible to FMs and AFMs, such as compatibility with spin-polarized superconductivity. The discovery of this new class of materials opens up a whole new world of physics which is causing quite a stir in the scientific community.
To date, four AMs have been experimentally proven: RuO2; Mn5Si3; MnTe and CrSb. Among these materials, Mn5Si3 has the incomparable advantage of being composed of elements with weak spin-orbit coupling, making it possible to unequivocally link its AM character to the intrinsic, non-relativistic intermingling of the arrangement of magnetic moments with respect to its crystalline symmetries. Last but not least, Mn5Si3 is composed of abundant, inexpensive elements. Theory, a strong anomalous Hall effect (AHE) in the absence of magnetic field and magnetization, coupled with a clear influence of crystallinity, are all signatures of the altermagnetism of Mn5Si3. They are the subject of this pioneering paper, prepublished in arXiv barely a year after the theoretical prediction of AM.
The consortium is already looking ahead on many fronts: among other things, (i) it proposes a recipe for stabilizing the AM phase “under strain” of Mn5Si3 (Phys. Rev. Mat. 7, 024416 (2023)), (ii) it demonstrates the anisotropic character of the AHE (Phys. Rev. B in press, arXiv:2401.02275 (2024)) and (iii) the Nernst effect in Mn5Si3, despite the absence of magnetization (arXiv:2403. 12929 (2024)), and (iv) it suggests a related study on the influence of symmetries to detect phase transitions (arXiv:2311.14498 (2023)).
Team: Antiferromagnetic spintronics
Collaboration: CINaM (FRA), JGU – TUD – Uni. Konstanz (GER), FZU – Charles Uni. (CZECH)
Funding: ASTRONICS ANR-15-CE24-0015-01; MATHEEIAS ANR-20-CE92-0049-01; SPINMAT IRP CNRS.
Further reading: Observation of a spontaneous anomalous Hall response in the Mn5Si3 d-wave altermagnet candidate, H. Reichlova✉, R. L. Seeger et al., Nat. Commun. 15, 4961 (2024); https://doi.org/10.1038/s41467-024-48493-w
Contact at SPINTEC: Vincent Baltz
