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Helimagnetism

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Lorentz TEM image of helical spin stripes in iron germanide (FeGe) at 90 K

Helimagnetism is a form of magnetic ordering where spins of neighbouring magnetic moments arrange themselves in a spiral or helical pattern, with a characteristic turn angle of somewhere between 0 and 180 degrees. It results from the competition between ferromagnetic and antiferromagnetic exchange interactions.[1] It is possible to view ferromagnetism and antiferromagnetism as helimagnetic structures with characteristic turn angles of 0 and 180 degrees respectively. Helimagnetic order breaks spatial inversion symmetry, as it can be either left-handed or right-handed in nature.

Strictly speaking, helimagnets have no permanent magnetic moment, and as such are sometimes considered a complicated type of antiferromagnet. This distinguishes helimagnets from conical magnets, (e.g. Holmium below 20 K[2]) which have spiral modulation in addition to a permanent magnetic moment. Helimagnets can be characterized by the distance it takes for the spiral to complete one turn. In analogy to the pitch of screw thread, the period of repetition is known as the "pitch" of the helimagnet. If the spiral's period is some rational multiple of the crystal's unit cell, the structure is commensurate, like the structure originally proposed for MnO2.[3] On the other hand, if the multiple is irrational, the magnetism is incommensurate, like the updated MnO2 structure.[4]

Helimagnetism was first proposed in 1959, as an explanation of the magnetic structure of manganese dioxide.[3] Initially applied to neutron diffraction, it has since been observed more directly by Lorentz electron microscopy.[5] Some helimagnetic structures are reported to be stable up to room temperature.[6] Like how ordinary ferromagnets have domain walls that separate individual magnetic domains, helimagnets have their own classes of domain walls which are characterized by topological charge.[7]

Many helimagnets have a chiral cubic structure, such as the FeSi (B20) crystal structure type. In these materials, the combination of ferromagnetic exchange and the Dzyaloshinskii–Moriya interaction leads to helixes with relatively long periods. Since the crystal structure is noncentrosymetric even in the paramagnetic state, the magnetic transition to a helimagnetic state does not break inversion symmetry, and the direction of the spiral is locked to the crystal structure.

On the other hand, helimagnetism in other materials can also be based on frustrated magnetism or the RKKY interaction. The result is that centrosymmetric structures like the MnP-type (B31) compounds can also exhibit double-helix type helimagnetism where both left and right handed spirals coexist.[8] For these itinerant helimagnets, the direction of the helicity can be controlled by applied electric currents and magnetic fields.[9]

Helimagnetic materials
Material Temperature range Space group
β-MnO2[3][4] < 93 K P42/mnm
FeGe,[6] < 278 K P213
MnGe[10] < 170 K P213
MnSi,[11] < 29 K P213
FexCo1−xSi (0.3 ≤ x ≤ 0.85)[12][13] P213
Cu2OSeO3[14] < 58 K P213
FeP[8] < 120 K Pnma
FeAs[15] < 77 K Pnma
MnP[16] < 50 K Pnma
CrAs[17] < 261 K Pnma
CrI2[18] < 17 K Cmc21
FeCl3[19] < 9 K R3
NiBr2[20] < 22 K R3m
NiI2[21] < 75 K R3m
Cr1/3NbS2[22][23] < 127 K P6322
Tb[24] 219–231 K P63/mmc
Dy[25] 85–179 K P63/mmc
Ho[26] 20–132 K P63/mmc

See also

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References

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  1. ^ Blundell, Stephen, ed. (2001). Magnetism in condensed matter. Oxford master series in condensed matter physics. Oxford New York: Oxford University Press. pp. 99–100. ISBN 978-0-585-48360-3.
  2. ^ Perreault, Christopher S.; Vohra, Yogesh K.; dos Santos, Antonio M.; Molaison, Jamie J. (2020). "Neutron diffraction study of magnetic ordering in high pressure phases of rare earth metal holmium". Journal of Magnetism and Magnetic Materials. 507. Elsevier BV: 166843. Bibcode:2020JMMM..50766843P. doi:10.1016/j.jmmm.2020.166843. OSTI 1607351.
  3. ^ a b c Yoshimori, Akio (1959). "A New Type of Antiferromagnetic Structure in the Rutile Type Crystal". Journal of the Physical Society of Japan. 14 (6). Physical Society of Japan: 807–821. Bibcode:1959JPSJ...14..807Y. doi:10.1143/jpsj.14.807.
  4. ^ a b Regulski, M.; Przeniosło, R.; Sosnowska, I.; Hoffmann, J.-U. (2003-11-03). "Incommensurate magnetic structure of β−MnO2". Physical Review B. 68 (17). American Physical Society (APS): 172401. doi:10.1103/physrevb.68.172401. ISSN 0163-1829.
  5. ^ Uchida, Masaya; Onose, Yoshinori; Matsui, Yoshio; Tokura, Yoshinori (2006). "Real-Space Observation of Helical Spin Order". Science. 311 (5759). American Association for the Advancement of Science (AAAS): 359–361. Bibcode:2006Sci...311..359U. doi:10.1126/science.1120639. PMID 16424334. S2CID 37875453.
  6. ^ a b Zhang, S. L.; Stasinopoulos, I.; Lancaster, T.; Xiao, F.; Bauer, A.; et al. (2017). "Room-temperature helimagnetism in FeGe thin films". Scientific Reports. 7 (1). Springer Science and Business Media LLC: 123. Bibcode:2017NatSR...7..123Z. doi:10.1038/s41598-017-00201-z. PMC 5427977. PMID 28273923.
  7. ^ Schoenherr, P.; Müller, J.; Köhler, L.; Rosch, A.; Kanazawa, N.; Tokura, Y.; Garst, M.; Meier, D. (2018). "Topological domain walls in helimagnets". Nature Physics. 14 (5). Springer Science and Business Media LLC: 465–468. arXiv:1704.06288. Bibcode:2018NatPh..14..465S. doi:10.1038/s41567-018-0056-5. S2CID 119021621.
  8. ^ a b Sukhanov, A. S.; Tymoshenko, Y. V.; Kulbakov, A. A.; Cameron, A. S.; Kocsis, V.; et al. (2022-04-20). "Frustration model and spin excitations in the helimagnet FeP". Physical Review B. 105 (13). American Physical Society (APS): 134424. arXiv:2201.10358. Bibcode:2022PhRvB.105m4424S. doi:10.1103/physrevb.105.134424. ISSN 2469-9950. S2CID 246276036.
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  14. ^ Seki, S.; Yu, X. Z.; Ishiwata, S.; Tokura, Y. (2012). "Observation of Skyrmions in a Multiferroic Material". Science. 336 (6078). American Association for the Advancement of Science (AAAS): 198–201. Bibcode:2012Sci...336..198S. doi:10.1126/science.1214143. PMID 22499941. S2CID 21013909.
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  16. ^ Forsyth, J B; Pickart, S J; Brown, P J (1966). "The structure of the metamagnetic phase of MnP". Proceedings of the Physical Society. 88 (2). IOP Publishing: 333–339. Bibcode:1966PPS....88..333F. doi:10.1088/0370-1328/88/2/308. ISSN 0370-1328.
  17. ^ Selte, Kari; Kjekshus, Arne; Jamison, Warren E.; Andresen, Arne F.; Engebretsen, Jan E.; Ehrenberg, L. (1971). "Magnetic Structure and Properties of CrAs". Acta Chemica Scandinavica. 25. Danish Chemical Society: 1703–1714. doi:10.3891/acta.chem.scand.25-1703. ISSN 0904-213X.
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  19. ^ Kang, Byeongki; Kim, Changsoo; Jo, Euna; Kwon, Sangil; Lee, Soonchil (2014). "Magnetic state of FeCl 3 investigated by NMR". Journal of Magnetism and Magnetic Materials. 360. Elsevier BV: 1–5. doi:10.1016/j.jmmm.2014.01.051. ISSN 0304-8853.
  20. ^ Adam, A; Billerey, D; Terrier, C; Katsumata, K; Magariño, J; Tuchendler, J (1980). "Magnetic resonance experiments in NiBr2 at high frequencies and high magnetic fields". Physics Letters A. 79 (4). Elsevier BV: 353–354. doi:10.1016/0375-9601(80)90369-2. ISSN 0375-9601.
  21. ^ Kuindersma, S.R.; Sanchez, J.P.; Haas, C. (1981). "Magnetic and structural investigations on NiI2 and CoI2". Physica B+C. 111 (2–3). Elsevier BV: 231–248. doi:10.1016/0378-4363(81)90100-5. ISSN 0378-4363.
  22. ^ Miyadai, Tomonao; Kikuchi, Katsuya; Kondo, Hiromitsu; Sakka, Shuzo; Arai, Masatoshi; Ishikawa, Yoshikazu (1983-04-15). "Magnetic Properties of Cr1/3NbS2". Journal of the Physical Society of Japan. 52 (4). Physical Society of Japan: 1394–1401. Bibcode:1983JPSJ...52.1394M. doi:10.1143/jpsj.52.1394. ISSN 0031-9015.
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  24. ^ Palmer, S. B.; Baruchel, J.; Farrant, S.; Jones, D.; Schlenker, M. (1982). "Observation of Spiral Spin Antiferromagnetic Domains in Single Crystal Terbium". The Rare Earths in Modern Science and Technology. Boston, MA: Springer US. pp. 413–417. doi:10.1007/978-1-4613-3406-4_88. ISBN 978-1-4613-3408-8.
  25. ^ Herz, R.; Kronmüller, H. (1978). "Field-induced phase transitions in the helical state of dysprosium". Physica Status Solidi A. 47 (2). Wiley: 451–458. Bibcode:1978PSSAR..47..451H. doi:10.1002/pssa.2210470215.
  26. ^ Tindall, D. A.; Steinitz, M. O.; Kahrizi, M.; Noakes, D. R.; Ali, N. (1991). "Investigation of the helimagnetic phases of holmium in ac-axis magnetic field". Journal of Applied Physics. 69 (8). AIP Publishing: 5691–5693. Bibcode:1991JAP....69.5691T. doi:10.1063/1.347913.
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