Talk:Altermagnetism

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

Requested diagrams

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)

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

Experimental observation

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[doi:10.1103/physrevx.12.040002, 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)

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)

Antiferromagnetism

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)

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)

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 [doi:10.1103/physrevx.12.040002, 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)

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

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)