Talk:Altermagnetism

The 2024 research was on properties of MnTe and RuO2. Alanapertum (talk) 11:16, 15 February 2024 (UTC) Reply

As a comment on the above diagram request. Some of the cited works are licensed under Creative Commons 4.0 attribution, which means that the figures in them can be uploaded into Commons and used here (perhaps in a simplified form). Jähmefyysikko (talk) 14:12, 16 February 2024 (UTC) Reply

Do the figures need to be all centered? It is unusual for a Wiki article.--ReyHahn (talk) 11:22, 18 February 2024 (UTC) Reply

The formulation "altermagnetism was first experimentally observed" is not really suitable. Altermagnetism is a mathematical concept (it is a classification of periodic structures based on non-relativistic symmetries) which in itself cannot be "experimentally observed". On the other hand, the class of systems called altermagnets is endowed with certain physical properties which of course can be observed. One of that properties is the spin-splitting. Another property is the anomalous Hall effect which was observed even earlier (in 2023). Similarly, the formulation "previously theorized to exist" (with reference to works from 2022) is not appropriate. Spin splittings (of materials which fall into altermagnetic class in today's terms) were theoretically discussed before, e.g. PRB 102, 014422 (2020) and earlier, but first PRX 12, 031042 (2022) came with the non-relativistic classification of collinear systems into ordinary antiferromagnets, altermagnets and remaining ferro-/ferrimagnets.

Hello, I made major extension of the article based on info provided by the co-authors of several referenced articles and they also sent me the following clarifying information:

"According to the references in main text ["The existence of a new kind of magnetism has been confirmed"], the unusual anomalous Hall effect and d-wave magnetisation in RuO₂ was proposed in 2019 (arXiv:1901.00445, doi: 10.1126/sciadv.aaz8809) and first observed in 2020, not 2023 (arXiv:2002.08712, Nature Electronics 5, 747, (2022)). However, the effects could not be explained in a unified and general way before the prediction of altermagnetism from symmetries[[https://doi.org/10.1103%2Fphysrevx.12.040002 doi:10.1103/physrevx.12.040002], [https://doi.org/10.1103%2FPhysRevX.12.031042 doi:10.1103/PhysRevX.12.031042]] which also allowed to identify many more properties and altermagnetic materials including experimentally confirmed MnTe." Sandwort (talk) 13:46, 18 February 2024 (UTC) Reply

Yes, the observation of the anomalous Hall effect (AHE) in RuO2 pre-date those in MnTe. Since the main discussion was now linked to Nature 626, 517 (2024) reporting ARPES on MnTe, I quoted the 2023 measurement of AHE in MnTe but the point is that term "experimental observation of altermagnetism" linked to year 2024 is not suitable since earlier works reported AHE before and that can also be taken as "experimental observation" even if, arguably, not as nice as the spin-resolved ARPES. The Sci. Adv. article (whose arxiv is 1901.00445) uses other terminology but in today's terms it would probably have the word 'altermagnet' in its title. I continue in the discussion below. Kvyb6672 (talk) 20:22, 18 February 2024 (UTC) Reply

What's the difference with altermagnetism and other magnetic states? How is it different from an antiferromagnet? ReyHahn (talk) 10:14, 18 February 2024 (UTC) Reply

Both altermagnets and antiferromagnets are protected by crystal symmetry to have zero net magnetization. The distinction is that antiferromagnets are Kramers degenerate whereas altermagnets are not. Igor Mazin's editorial can be cited for this (https://doi.org/10.1103/PhysRevX.12.040002). Jähmefyysikko (talk) 10:35, 18 February 2024 (UTC) Reply

Hello, I made major extension of the article based on info provided by the co-authors of several referenced articles and they also sent me the following information to your question:

"The references also discuss that the symmetry class and order parameters of altermagnets are different from those in antiferromagnets and ferromagnets. In ferromagnet there is a net magnetization, in altermagnet there is an anisotropic d,g, or i-wave magnetization [[https://doi.org/10.1103%2Fphysrevx.12.040002 doi:10.1103/physrevx.12.040002], [https://doi.org/10.1103%2FPhysRevX.12.031042 doi:10.1103/PhysRevX.12.031042]] and an antiferromagnet does not have a net magnetization. The mentioned reference[doi:10.1103/physrevx.12.040002] by the experts from APS have written: "While antiferromagnets have staggered magnetic order in the coordinate space, the magnetic order of altermagnets is staggered both in the coordinate space and in the momentum space. This distinction is as fundamental, and as important, as the familiar antiferromagnetic-ferromagnetic dichotomy." Sandwort (talk) 13:38, 18 February 2024 (UTC) Reply

This distinction should appear in the lead in some simplified form.--ReyHahn (talk) 16:34, 18 February 2024 (UTC) Reply

It is misleading to simply state 'order parameters of altermagnets are different from those in antiferromagnets and ferromagnets' - an expert will understand the correct meaning but it is easy to get confused. Spin-splittings which depend on direction of k-vector also occur in non-collinear antiferromagnets; these can be told apart from altermagnets (which are a subset of collinear magnetics) but this information gets lost when using compact statements (not to speak of simplified slogans). I believe the introduction of the article is now fine.

Regarding the question about difference between 'altermagnet and antiferromagnet': in traditional terminology, altermagnets (now a newly defined class) are a subset of collinear antiferromagnets. As explained in PRX 12, 031042, which proposes new terminology, all collinear systems can be broken down into (ordinary) antiferromagnets, altermagnets and remaining ferro-/ferrimagnets. This classification is done using non-relativistic spin-groups (determine the symmetry using this framework and then look into a list which says to which of the three classes the system belongs). Whether the distinction between any two of these three classes is "as fundamental, and as important, as the familiar antiferromagnetic-ferromagnetic dichotomy" is a subjective matter.

An easy way to tell the two apart, looking at collinear systems with zero net magnetisation, is the AHE. In the presence of spin-orbit interaction, the anomalous Hall effect is allowed by symmetry in altermagnets. Kvyb6672 (talk) 21:11, 18 February 2024 (UTC) Reply

The alternating spins shown in the first Figure sure look antiferromagnetic to me! JHBrewer (talk) 16:47, 14 April 2026 (UTC) Reply

For antiferromagnet, up and down spin sublattices are related by a translation, but in the first figure, a translation does not transform the atoms into each other, as the orientations are not the same. Instead, the sublattices are related by a rotation, which is characteristic of altermagnets. The same rotation can also be done in the reciprocal space, and then it transforms the spin bands into each other. Jähmefyysikko (talk) 17:00, 14 April 2026 (UTC) Reply

This research starting to get picked up by the mainstream media, including an article in Financial Times on 11 December 2024. It would be helpful if there was a section with basic concepts, applications, etc. — Preceding unsigned comment added by 97.113.135.103 (talk) 16:50, 18 December 2024 (UTC) Reply

You are welcome to add it yourself.--ReyHahn (talk) 18:27, 18 December 2024 (UTC) Reply

I removed any claims about RuO2 being an altermagnet, because that claim has been disproven in two papers in 2024 (which are now added as references), which show in two independent experiments that Ruo2 is not magnetic, suggesting that previous measurements where on samples which had magnetic inclusions or defects. As such, this means that the case of RuO2 is at least controversial, and should therefore not be contained in an encyclopaedic article in my opinion (or at least it should be made clear that it is controversial). Pwstauk (talk) 20:25, 1 October 2025 (UTC) Reply

removed section 'Spin-splitting effect in altermagnets' for the same reason as stated before - as per current state of research, RuO2 is not an altermagnet. Pwstauk (talk) 14:51, 22 February 2026 (UTC) Reply