Altermagnetism
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In condensed matter physics, altermagnetism is a type of persistent magnetic state in ideal crystals.[1][2][3][4][5] Altermagnetic structures are collinear and crystal-symmetry compensated, resulting in zero net magnetisation.[1][5][6][7] Unlike in an PT-symmetric collinear antiferromagnet, the electronic bands in PT-non-symmetric antiferromagnets (altermagnets) are not Kramers degenerate, but instead depend on the wavevector in a spin-dependent way due to the intrinsic crystal symmetry connecting different magnetic sublattices.[8][9][1][10] Related to this feature, key experimental observations were published in 2024.[11] It has been speculated that altermagnetism may have applications in the field of spintronics.[6][12]
Connection of altermagnetism to antiferromagnetism
[edit]It has been noted in[13][14][15] that altermagnetism is best understood by a spin-splitting of quasiparticles in a subset of collinear antiferromagnets that largely overlaps with piezomagnets[16] and weak ferromagnets.[17] It can also refer to noncollinear antiferromagnets with spin-splitting.
Collinear antiferromagnets are Néel-ordered magnets whose magnetic sublattices are related to each other by a combination of symmetries. There are PT-symmetric antiferromagnets, in which magnetic sublattices are connected by translation and/or inversion, and time-reversal operations. Such antiferromagnets are rare in Nature. In most antiferromagnets this symmetry is broken, and the magnetic sublattices are connected by a symmetry operation combining rotation, mirror reflection, or both, with time-reversal. The spin-splitting of quasiparticles, i.e. the altermagnetism, occurs in this class of antiferromagnets. Such antiferromagnets were experimentally discovered[18] in 1958 by A.S. Borovik-Romanov group when observing weak ferromagnetism in collinear antiferromagnets. I.E. Dzyaloshinskii developed the symmetry-based thermodynamic theory of weak ferromagnetism in 1958,[19] which was later microscopically expanded by T. Moriya via the Dzyaloshinskii-Moriya interaction.[20] E.A. Turov classified all antiferromagnets for all symmetry classes using magnetic space groups.[21] Importantly, it is understood that PT-symmetry must be broken in collinear antiferromagnets for weak ferromagnetism and piezomagnetism to occur. Weak ferromagnets might not necessarily have canting of the Néel order. It is rather broken PT-symmetry and other symmetries that define a weak ferromagnet and piezomagnet.
The spin-splitting effect in collinear antiferromagnets—initially predicted in 2016-2018 by T. Okugawa, K. Ohno, Y. Noda, and S. Nakamura[22][23] —was subsequently generalized across a broader class of collinear magnetic systems[6][7][24] leading to diverse nomenclature such as d-wave, g-wave, i-wave, and mirror-symmetric spin-splitting. These types of spin-splitting correspond to how the magnetic sublattices connect to each other. However, such spin-splitting also appears in compensated ferrimagnets. This implies that altermagnetism is a spin-splitting property of Néel-ordered magnets rather than a new state of matter.
The apparent novelty of altermagnets as being the third class of magnetically ordered systems[1] was debated (for example, this was noted in[25][26][27]); it stems from applying spin group theory, rather than magnetic space group theory, to the already understood set of collinear and non-collinear antiferromagnets. For example, despite being a traditional manifestation of piezomagnetism and weak ferromagnetism, a collinear antiferromagnet on a rutile lattice has recently been rebranded into an altermagnet. Or, hematite, the cornerstone of weak ferromagnetism, has recently been relabeled as a g-wave altermagnet. On the other hand, the field of altermagnetism has brought about the knowledge of antiferromagnetic spin-splitting of quasiparticles in collinear antiferromagnets.
Crystal structure and symmetry
[edit]In altermagnetic materials, atoms form a regular pattern with alternating spin and spatial orientation at adjacent magnetic sites in the crystal.[5][7]
Atoms with opposite magnetic moment are in altermagnets coupled by crystal rotation or mirror symmetry.[1][5][6][7][11][28][10] The spatial orientation of magnetic atoms may originate from the surrounding cages of non-magnetic atoms.[7][29] The opposite spin sublattices in altermagnetic manganese telluride (MnTe) are related by spin rotation combined with six-fold crystal rotation and half-unit cell translation.[7][11] Ruthenium dioxide (RuO2) was claimed to be an altermagnet,[7][28] but it was later confirmed in two independent studies that it is completely non-magnetic.[30][31]

Electronic structure
[edit]One of the distinctive features of altermagnets is a specifically spin-split band structure,[7] which was first experimentally observed in work that was published in 2024.[11] Altermagnetic band structure breaks time-reversal symmetry,[7][29] Eks=E−ks (E is energy, k wavevector and s spin) as in ferromagnets, however unlike in ferromagnets, it does not generate net magnetization. The altermagnetic spin polarisation alternates in wavevector space and forms characteristic 2, 4, or 6 spin-degenerate nodes, respectively, which correspond to d-, g-, or i-wave order parameters.[7] A d-wave altermagnet can be regarded as the magnetic counterpart of a d-wave superconductor.[32]
The altermagnetic spin polarization in band structure (energy–wavevector diagram) is collinear and does not break inversion symmetry.[7] The altermagnetic spin splitting is even in wavevector, i.e. (kx2−ky2)sz.[7][11] It is thus also distinct from noncollinear Rashba or Dresselhaus spin texture which break inversion symmetry in noncentrosymmetric nonmagnetic or antiferromagnetic materials due to the spin-orbit coupling.
Materials
[edit]Direct experimental evidence of altermagnetic band structure in semiconducting MnTe was first published in 2024.[11] Many more materials are predicted to be altermagnets – ranging from insulators, semiconductors, and metals to superconductors.[6][7] Altermagnetism was predicted in 3D and 2D materials[3][6][10] with both light as well as heavy elements and can be found in nonrelativistic as well as relativistic band structures.[7][11][29]
Properties
[edit]Altermagnets exhibit an unusual combination of ferromagnetic and antiferromagnetic properties, which more closely resemble those of ferromagnets.[1][5][6][7][10] Hallmarks of altermagnetic materials such as the anomalous Hall effect[29] have been observed before[33] (but this effect occurs also in other magnetically compensated systems such as non-collinear antiferromagnets[34]). Altermagnets also exhibit unique properties such as unconventional piezomagnetism[10] anomalous and noncollinear spin currents[10] that can change sign as the crystal rotates.[35]
Experimental observations
[edit]In December 2024, researchers from the University of Nottingham provided the first experimental imaging of altermagnetism, confirming its unique spin-symmetry properties. Using Nitrogen-vacancy center microscopy and X-ray magnetic linear dichroism (XMLD), they visualized spin-polarized currents arising from the crystal-symmetry-protected altermagnetic order. This order featured antiparallel spin alignment within distinct crystal sublattices, creating a compensating spin polarization without macroscopic magnetization.[36] These findings validated theoretical predictions and demonstrated the potential of altermagnetic materials in high-speed, low-energy spintronic devices.[37][38]
Connection of altermagnetism to antiferromagnetism and other states
[edit]It has been noted in[39][40][41] that certain altermagnets can be find in a subset of systems with collinear antiferromagnetic exchange. Altermagnets can exhibit previously known phenomena of piezomagnetism[16] and weak ferromagnets.[42]
Collinear antiferromagnets are Néel-ordered magnets whose magnetic sublattices are related to each other by a combination of symmetries. There are PT-symmetric antiferromagnets, in which magnetic sublattices are connected by translation and/or inversion, and time-reversal operations. Such antiferromagnets are rare in Nature. In most antiferromagnets this symmetry is broken, and the magnetic sublattices are connected by a symmetry operation combining rotation, mirror reflection, or both, with time-reversal. The spin-splitting of quasiparticles, i.e. the altermagnetism, occurs in this class of antiferromagnets. Such antiferromagnets were experimentally discovered[43] in 1958 by A.S. Borovik-Romanov group when observing weak ferromagnetism in collinear antiferromagnets. I.E. Dzyaloshinskii developed the symmetry-based thermodynamic theory of weak ferromagnetism in 1958,[44] which was later microscopically expanded by T. Moriya via the Dzyaloshinskii-Moriya interaction.[45] E.A. Turov classified all antiferromagnets for all symmetry classes using magnetic space groups.[46] Importantly, it is understood that PT-symmetry must be broken in collinear antiferromagnets for weak ferromagnetism and piezomagnetism to occur. Weak ferromagnets might not necessarily have canting of the Néel order. It is rather broken PT-symmetry and other symmetries that define a weak ferromagnet and piezomagnet.
The spin-splitting effect in collinear antiferromagnets—were known for a long time, however the charactersitic time-reversal breaking nature leading to diverse nomenclature such as d-wave, g-wave, i-wave, and mirror-symmetric spin-splitting was recognized only in recent studies. These types of spin-splitting correspond to how the magnetic sublattices connect to each other. However, such spin-splitting also appears in compensated ferrimagnets.
Various aspects of altermagnets[1] was debated[47][48][49]); it stems from applying spin group theory, rather than magnetic space group theory, to the in some cases already known systems previously understood as antiferromagnets. For example, despite being a traditional manifestation of piezomagnetism and weak ferromagnetism, a collinear antiferromagnet on a rutile lattice has recently been recongized to be a d-wave altermagnet. Or, hematite, the cornerstone of weak ferromagnetism, has recently been reclassified as a g-wave altermagnet. The field of altermagnetism has brought about the knowledge of time-reversal symmetry breaking spin-splitting of quasiparticles in systems with collinear antiferromagnetic exchange.
References
[edit]- 1 2 3 4 5 6 7 Mazin, Igor (2022-12-08). "Altermagnetism—A New Punch Line of Fundamental Magnetism". Physical Review X. 12 (4) 040002. Bibcode:2022PhRvX..12d0002M. doi:10.1103/physrevx.12.040002.
- ↑ Mazin, Igor (2024-01-08). "Altermagnetism Then and Now". Physical Review X. 17: 4. arXiv:2105.05820. Bibcode:2022PhRvX..12c1042S. doi:10.1103/PhysRevX.12.031042.
- 1 2 Mazin, Igor; González-Hernández, Rafael; Šmejkal, Libor (2023-09-05), Induced Monolayer Altermagnetism in MnP(S,Se)$_3$ and FeSe, arXiv:2309.02355
- ↑ Wilkins, Alex (14 February 2024). "The existence of a new kind of magnetism has been confirmed". New Scientist. Retrieved 2024-02-15.
- 1 2 3 4 5 Savitsky, Zack (2024). "Researchers discover new kind of magnetism". Science. 383 (6683): 574–575. Bibcode:2024Sci...383..574S. doi:10.1126/science.ado5309. PMID 38330121. Retrieved 16 February 2024.
- 1 2 3 4 5 6 7 Šmejkal, Libor; Sinova, Jairo; Jungwirth, Tomas (2022-12-08). "Emerging Research Landscape of Altermagnetism". Physical Review X. 12 (4) 040501. arXiv:2204.10844. Bibcode:2022PhRvX..12d0501S. doi:10.1103/PhysRevX.12.040501.
- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Šmejkal, Libor; Sinova, Jairo; Jungwirth, Tomas (2022-09-23). "Altermagnetism: spin-momentum locked phase protected by non-relativistic symmetries". Physical Review X. 12 (3) 031042. arXiv:2105.05820. Bibcode:2022PhRvX..12c1042S. doi:10.1103/PhysRevX.12.031042. ISSN 2160-3308.
- ↑ Noda, Y.; Ohno, K.; Nakamura, S. (2016). "Momentum-dependent band spin splitting in semiconducting MnO2: a density functional calculation". Physical Chemistry Chemical Physics. 18 (19): 13294–13303. Bibcode:2016PCCP...1813294N. doi:10.1039/c5cp07806g. PMID 27119122.
- ↑ Okugawa, T.; Ohno, K.; Noda, Y.; Nakamura, S. (2018). "Weakly spin-dependent band structures of antiferromagnetic perovskite LaMO3 (M = Cr, Mn, Fe)". Journal of Physics: Condensed Matter. 30 (7): 075502. doi:10.1088/1361-648X/aa9e70. PMID 29189206.
- 1 2 3 4 5 6 Ma, Hai-Yang; Hu, Mengli; Li, Nana; Liu, Jianpeng; Yao, Wang; Jia, Jin-Feng; Liu, Junwei (2021-05-14). "Multifunctional antiferromagnetic materials with giant piezomagnetism and noncollinear spin current". Nature Communications. 12 (1): 2846. arXiv:2104.00561. doi:10.1038/s41467-021-23127-7. ISSN 2041-1723.
- 1 2 3 4 5 6 7 Krempaský, J.; Šmejkal, L.; D'Souza, S. W.; Hajlaoui, M.; Springholz, G.; Uhlířová, K.; Alarab, F.; Constantinou, P. C.; Strocov, V.; Usanov, D.; Pudelko, W. R.; González-Hernández, R.; Birk Hellenes, A.; Jansa, Z.; Reichlová, H. (February 2024). "Altermagnetic lifting of Kramers spin degeneracy". Nature. 626 (7999): 517–522. arXiv:2308.10681. Bibcode:2024Natur.626..517K. doi:10.1038/s41586-023-06907-7. ISSN 1476-4687. PMC 10866710. PMID 38356066.
- ↑ Arrell, Miriam (February 14, 2024). "Altermagnetism proves its place on the magnetic family tree". ScienceDaily. Retrieved 2024-02-15.
- ↑ Mostovoy, Maxim (August 11, 2025). "Phenomenology of altermagnets". Applied Physics Letters. 127 (6): 060501. doi:10.1063/5.0283630.
- ↑ Solovyev, Igor V.; Nikolaev, Sergey A.; Tanaka, Akihiro (May 22, 2026). "Altermagnetism and weak ferromagnetism". npj Quantum Materials. 11 (1): 54. doi:10.1038/s41535-026-00900-9.
- ↑ Golubinskii, V. P.; Zyuzin, V. A. (February 24, 2026). "Anomalous Hall Effect in Metallic Collinear Antiferromagnets". JETP Letters. 123 (6): 341–349. doi:10.1134/S0021364025609844.
- 1 2 Dzialoshinskii, I. E. (1958). "The problem of piezomagnetism". Soviet Physics JETP. 6 (3): 621. Bibcode:1958JETP....6..621D.
- ↑ Dzyaloshinskii, I. E. (1958). "A thermodynamic theory of "weak" ferromagnetism of antiferromagnetics". Journal of Physics and Chemistry of Solids. 4 (4): 241–255. Bibcode:1958JPCS....4..241D. doi:10.1016/0022-3697(58)90076-3.
- ↑ Borovik-Romanov, A. S.; Orlova, M. P. (1957). "Magnetic properties of cobalt and manganese carbonates". Soviet Phys. JETP. 4 (4): 531–535.
- ↑ Dzyaloshinskii, I. E. (1958). "A thermodynamic theory of "weak" ferromagnetism of antiferromagnetics". Journal of Physics and Chemistry of Solids. 4 (4): 241–255. Bibcode:1958JPCS....4..241D. doi:10.1016/0022-3697(58)90076-3.
- ↑ Moriya, Tôru (1960). "Anisotropic Superexchange Interaction and Weak Ferromagnetism". Physical Review. 120 (1): 91–98. Bibcode:1960PhRv..120...91M. doi:10.1103/PhysRev.120.91.
- ↑ Turov, E. A. (1965). Physical Properties of Magnetically Ordered Crystals. New York and London: Academic Press.
- ↑ Noda, Y.; Ohno, K.; Nakamura, S. (2016). "Momentum-dependent band spin splitting in semiconducting MnO2: a density functional calculation". Physical Chemistry Chemical Physics. 18 (19): 13294–13303. Bibcode:2016PCCP...1813294N. doi:10.1039/c5cp07806g. PMID 27119122.
- ↑ Okugawa, T.; Ohno, K.; Noda, Y.; Nakamura, S. (2018). "Weakly spin-dependent band structures of antiferromagnetic perovskite LaMO3 (M = Cr, Mn, Fe)". Journal of Physics: Condensed Matter. 30 (7): 075502. doi:10.1088/1361-648X/aa9e70. PMID 29189206.
- ↑ Hayami, S.; Yanagi, Y.; Kusunose, H. (2019). "Momentum-Dependent Spin Splitting by Collinear Antiferromagnetic Ordering". Journal of the Physical Society of Japan. 88 (12) 123702. arXiv:1908.08680. Bibcode:2019JPSJ...88l3702H. doi:10.7566/JPSJ.88.123702.
- ↑ Mostovoy, Maxim (August 11, 2025). "Phenomenology of altermagnets". Applied Physics Letters. 127 (6): 060501. doi:10.1063/5.0283630.
- ↑ Solovyev, Igor V.; Nikolaev, Sergey A.; Tanaka, Akihiro (May 22, 2026). "Altermagnetism and weak ferromagnetism". npj Quantum Materials. 11 (1): 54. doi:10.1038/s41535-026-00900-9.
- ↑ Golubinskii, V. P.; Zyuzin, V. A. (February 24, 2026). "Anomalous Hall Effect in Metallic Collinear Antiferromagnets". JETP Letters. 123 (6): 341–349. doi:10.1134/S0021364025609844.
- 1 2 Fedchenko, Olena; Minár, Jan; Akashdeep, Akashdeep; D'Souza, Sunil Wilfred; Vasilyev, Dmitry; Tkach, Olena; Odenbreit, Lukas; Nguyen, Quynh; Kutnyakhov, Dmytro; Wind, Nils; Wenthaus, Lukas; Scholz, Markus; Rossnagel, Kai; Hoesch, Moritz; Aeschlimann, Martin (2024-02-02). "Observation of time-reversal symmetry breaking in the band structure of altermagnetic RuO 2". Science Advances. 10 (5) eadj4883. arXiv:2306.02170. Bibcode:2024SciA...10J4883F. doi:10.1126/sciadv.adj4883. ISSN 2375-2548. PMC 10830110. PMID 38295181.
- 1 2 3 4 Šmejkal, Libor; González-Hernández, Rafael; Jungwirth, T.; Sinova, J. (5 June 2020). "Crystal time-reversal symmetry breaking and spontaneous Hall effect in collinear antiferromagnets". Science Advances. 6 (23) eaaz8809. arXiv:1901.00445. Bibcode:2020SciA....6.8809S. doi:10.1126/sciadv.aaz8809. PMC 7274798. PMID 32548264.
- ↑ Hiraishi, M.; Okabe, H.; Koda, A.; Kadono, R.; Muroi, T.; Hirai, D.; Hiroi, Z. "Nonmagnetic Ground State in RuO2 Revealed by Muon Spin Rotation". Physical Review Letters. 132 166702. arXiv:2403.10028. doi:10.1103/PhysRevLett.132.166702.
- ↑ Keßler, Philipp; Garcia-Gassull, Laura; Suter, Andreas; Prokscha, Thomas; Salman, Z.; Khalyavin, Dmitry; Manuel, Pascal; Orlandi, Fabio; Mazin, Igor I.; Valentí, Roser; Moser, Simon. "Absence of magnetic order in RuO2: insights from μSR spectroscopy and neutron diffraction". npj spintronics. 2 50. doi:10.1038/s44306-024-00055-y.
- ↑ Šmejkal, Libor; Sinova, Jairo; Jungwirth, Tomas (2022-09-23). "Beyond Conventional Ferromagnetism and Antiferromagnetism: A Phase with Nonrelativistic Spin and Crystal Rotation Symmetry". Physical Review X. 12 (3) 031042. arXiv:2105.05820. Bibcode:2022PhRvX..12c1042S. doi:10.1103/PhysRevX.12.031042.
- ↑ Gonzalez Betancourt, R. D.; Zubáč, J.; Gonzalez-Hernandez, R.; Geishendorf, K.; Šobáň, Z.; Springholz, G.; Olejník, K.; Šmejkal, L.; Sinova, J.; Jungwirth, T.; Goennenwein, S. T. B.; Thomas, A.; Reichlová, H.; Železný, J.; Kriegner, D. (20 January 2023). "Spontaneous Anomalous Hall Effect Arising from an Unconventional Compensated Magnetic Phase in a Semiconductor". Physical Review Letters. 130 (3) 036702. arXiv:2112.06805. Bibcode:2023PhRvL.130c6702G. doi:10.1103/PhysRevLett.130.036702. PMID 36763381.
- ↑ Nakatsuji, Satoru; Kiyohara, Naoki; Higo, Tomoya (November 2015). "Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature". Nature. 527 (7577): 212–215. Bibcode:2015Natur.527..212N. doi:10.1038/nature15723. PMID 26524519.
- ↑ González-Hernández, Rafael; Šmejkal, Libor; Výborný, Karel; Yahagi, Yuta; Sinova, Jairo; Jungwirth, Tomáš; Železný, Jakub (2021-03-26). "Efficient Electrical Spin Splitter Based on Nonrelativistic Collinear Antiferromagnetism". Physical Review Letters. 126 (12) 127701. arXiv:2002.07073. Bibcode:2021PhRvL.126l7701G. doi:10.1103/PhysRevLett.126.127701. ISSN 0031-9007. PMID 33834809.
- ↑ Amin, O.J.; et al. (11 December 2024). "Nanoscale imaging and control of altermagnetism in MnTe". Nature. 636 (8042): 348–353. Bibcode:2024Natur.636..348A. doi:10.1038/s41586-024-08234-x. PMC 11634770. PMID 39663495.
- ↑ "New magnetic flow has potential to revolutionise electronic devices". Financial Times. 11 December 2024.
- ↑ Chen, X.Z. "Observation of Spin Splitting Torque in a Collinear Antiferromagnet RuO2". APS, Physical Review Journals. Physical Review Letters. Retrieved 13 May 2022.
- ↑ Mostovoy, Maxim (August 11, 2025). "Phenomenology of altermagnets". Applied Physics Letters. 127 (6): 060501. doi:10.1063/5.0283630.
- ↑ Solovyev, Igor V.; Nikolaev, Sergey A.; Tanaka, Akihiro (May 22, 2026). "Altermagnetism and weak ferromagnetism". npj Quantum Materials. 11 (1): 54. doi:10.1038/s41535-026-00900-9.
- ↑ Golubinskii, V. P.; Zyuzin, V. A. (February 24, 2026). "Anomalous Hall Effect in Metallic Collinear Antiferromagnets". JETP Letters. 123 (6): 341–349. doi:10.1134/S0021364025609844.
- ↑ Dzyaloshinskii, I. E. (1958). "A thermodynamic theory of "weak" ferromagnetism of antiferromagnetics". Journal of Physics and Chemistry of Solids. 4 (4): 241–255. Bibcode:1958JPCS....4..241D. doi:10.1016/0022-3697(58)90076-3.
- ↑ Borovik-Romanov, A. S.; Orlova, M. P. (1957). "Magnetic properties of cobalt and manganese carbonates". Soviet Phys. JETP. 4 (4): 531–535.
- ↑ Dzyaloshinskii, I. E. (1958). "A thermodynamic theory of "weak" ferromagnetism of antiferromagnetics". Journal of Physics and Chemistry of Solids. 4 (4): 241–255. Bibcode:1958JPCS....4..241D. doi:10.1016/0022-3697(58)90076-3.
- ↑ Moriya, Tôru (1960). "Anisotropic Superexchange Interaction and Weak Ferromagnetism". Physical Review. 120 (1): 91–98. Bibcode:1960PhRv..120...91M. doi:10.1103/PhysRev.120.91.
- ↑ Turov, E. A. (1965). Physical Properties of Magnetically Ordered Crystals. New York and London: Academic Press.
- ↑ Mostovoy, Maxim (August 11, 2025). "Phenomenology of altermagnets". Applied Physics Letters. 127 (6): 060501. doi:10.1063/5.0283630.
- ↑ Solovyev, Igor V.; Nikolaev, Sergey A.; Tanaka, Akihiro (May 22, 2026). "Altermagnetism and weak ferromagnetism". npj Quantum Materials. 11 (1): 54. doi:10.1038/s41535-026-00900-9.
- ↑ Golubinskii, V. P.; Zyuzin, V. A. (February 24, 2026). "Anomalous Hall Effect in Metallic Collinear Antiferromagnets". JETP Letters. 123 (6): 341–349. doi:10.1134/S0021364025609844.