Helimagnetism Explained

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. 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[1]) 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. On the other hand, if the multiple is irrational, the magnetism is incommensurate, like the updated MnO2 structure.

Helimagnetism was first proposed in 1959, as an explanation of the magnetic structure of manganese dioxide.[2] Initially applied to neutron diffraction, it has since been observed more directly by Lorentz electron microscopy.[3] Some helimagnetic structures are reported to be stable up to room temperature.[4] 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.[5]

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. For these itinerant helimagnets, the direction of the helicity can be controlled by applied electric currents and magnetic fields.[6]

Helimagnetic materials
MaterialTemperature rangeSpace group
β-MnO2[7] < 93 KP42/mnm
FeGe,< 278 KP213
MnGe[8] < 170 KP213
MnSi,[9] < 29 KP213
FexCo1−xSi (0.3 ≤ x ≤ 0.85)[10] [11] P213
Cu2OSeO3[12] < 58 KP213
FeP[13] < 120 KPnma
FeAs[14] < 77 KPnma
MnP[15] < 50 KPnma
CrAs[16] < 261 KPnma
CrI2[17] < 17 KCmc21
FeCl3[18] < 9 KR
NiBr2[19] < 22 KRm
NiI2[20] < 75 KRm
Cr1/3NbS2[21] [22] < 127 KP6322
Tb[23] 219–231 KP63/mmc
Dy[24] 85–179 KP63/mmc
Ho[25] 20–132 KP63/mmc

See also

Notes and References

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  2. Yoshimori . Akio . A New Type of Antiferromagnetic Structure in the Rutile Type Crystal . Journal of the Physical Society of Japan . Physical Society of Japan . 14 . 6 . 1959 . 10.1143/jpsj.14.807 . 807–821. 1959JPSJ...14..807Y .
  3. Uchida . Masaya . Onose . Yoshinori . Matsui . Yoshio . Tokura . Yoshinori . Real-Space Observation of Helical Spin Order . Science . American Association for the Advancement of Science (AAAS) . 311 . 5759 . 2006 . 10.1126/science.1120639 . 359–361. 16424334 . 2006Sci...311..359U . 37875453 .
  4. Zhang . S. L. . Stasinopoulos . I. . Lancaster . T. . Xiao . F. . Bauer . A. . Rucker . F. . Baker . A. A. . Figueroa . A. I. . Salman . Z. . Pratt . F. L. . Blundell . S. J. . Prokscha . T. . Suter . A. . Waizner . J. . Garst . M. . Grundler . D. . van der Laan . G. . Pfleiderer . C. . Hesjedal . T. . 5. Room-temperature helimagnetism in FeGe thin films . Scientific Reports . Springer Science and Business Media LLC . 7 . 1 . 2017 . 10.1038/s41598-017-00201-z . 123. 28273923 . 5427977 . 2017NatSR...7..123Z . free.
  5. Schoenherr . P. . Müller . J. . Köhler . L. . Rosch . A. . Kanazawa . N. . Tokura . Y. . Garst . M. . Meier . D. . Topological domain walls in helimagnets . Nature Physics . Springer Science and Business Media LLC . 14 . 5 . 2018. 10.1038/s41567-018-0056-5 . 465–468. 1704.06288 . 2018NatPh..14..465S . 119021621 .
  6. Jiang . N. . Nii . Y. . Arisawa . H. . Saitoh . E. . Onose . Y. . Electric current control of spin helicity in an itinerant helimagnet . Nature Communications . Springer Science and Business Media LLC . 11 . 1 . 2020-03-30 . 2041-1723 . 10.1038/s41467-020-15380-z . 1601. 32231211 . 7105454 . free .
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  9. Stishov . Sergei M . Petrova . A E . Itinerant helimagnet MnSi . Physics-Uspekhi . Uspekhi Fizicheskikh Nauk (UFN) Journal . 54 . 11 . 2011-11-30 . 10.3367/ufne.0181.201111b.1157 . 1117–1130. 2011PhyU...54.1117S . 122357363 .
  10. Watanabe . Hideki . Tazuke . ichi . Nakajima . Haruo . Helical Spin Resonance and Magntization Measurement in Itinerant Helimagnet FexCo1−xSi (0.3≤x≤0.85) . Journal of the Physical Society of Japan . Physical Society of Japan . 54 . 10 . 1985. 10.1143/jpsj.54.3978 . 3978–3986. 1985JPSJ...54.3978W .
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  12. Seki . S. . Yu . X. Z. . Ishiwata . S. . Tokura . Y. . Observation of Skyrmions in a Multiferroic Material . Science . American Association for the Advancement of Science (AAAS) . 336 . 6078 . 2012 . 10.1126/science.1214143 . 198–201. 22499941 . 2012Sci...336..198S . 21013909 .
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  16. Selte . Kari . Kjekshus . Arne . Jamison . Warren E. . Andresen . Arne F. . Engebretsen . Jan E. . Ehrenberg . L. . Magnetic Structure and Properties of CrAs. . Acta Chemica Scandinavica . Danish Chemical Society . 25 . 1971 . 0904-213X . 10.3891/acta.chem.scand.25-1703 . 1703–1714. free .
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  18. Kang . Byeongki . Kim . Changsoo . Jo . Euna . Kwon . Sangil . Lee . Soonchil . Magnetic state of FeCl 3 investigated by NMR . Journal of Magnetism and Magnetic Materials . Elsevier BV . 360 . 2014 . 0304-8853 . 10.1016/j.jmmm.2014.01.051 . 1–5.
  19. Adam . A . Billerey . D . Terrier . C . Katsumata . K . Magariño . J . Tuchendler . J . Magnetic resonance experiments in NiBr2 at high frequencies and high magnetic fields . Physics Letters A . Elsevier BV . 79 . 4 . 1980 . 0375-9601 . 10.1016/0375-9601(80)90369-2 . 353–354.
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  23. Book: Palmer . S. B. . Baruchel . J. . Farrant . S. . Jones . D. . Schlenker . M. . The Rare Earths in Modern Science and Technology . Observation of Spiral Spin Antiferromagnetic Domains in Single Crystal Terbium . Springer US . Boston, MA . 1982 . 978-1-4613-3408-8 . 10.1007/978-1-4613-3406-4_88 . 413–417.
  24. Herz . R. . Kronmüller . H. . Field-induced phase transitions in the helical state of dysprosium . Physica Status Solidi A . Wiley . 47 . 2 . 1978 . 10.1002/pssa.2210470215 . 451–458. 1978PSSAR..47..451H .
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