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SUMMARY:Merons\, bimerons and skyrmions in α-Fe2O3: from cosmology to spi
 ntronics - Prof Paolo Radaelli\, University of Oxford
DTSTART:20240213T160000Z
DTEND:20240213T170000Z
UID:TALK212206@talks.cam.ac.uk
CONTACT:Dr Nur Unal
DESCRIPTION:The field of quantum matter/quantum materials draws inspiratio
 n from a variety of theories\, seeking materials in which they can be embo
 died and verified.  In some cases\, the materials in question end up being
  rather useful\, though not necessarily in a way that is closely related t
 o the original research motivation.  A celebrated example [1] is the analo
 gy\, proposed by Wojciech H. Zurek\, between cosmological strings [2] and 
 vortex lines in the superfluid\, which suggested cryogenic experiments to 
 test cosmological string formation in 4He.  The work I will describe in th
 is talk started off as an attempt to seek the analogue of cosmological str
 ings in easy-axis antiferromagnets with low in-plane anisotropy\, leading 
 to an approximate U(1) symmetry.\n\nA well-known example of such materials
  is hematite (a-Fe2O3)\, which orders at a high Néel temperature (TN ~ 96
 0 K).  At room temperature and above\, the spins are aligned perpendicular
  to the high-symmetry trigonal axis and are also slightly canted due to th
 e Dzyaloshinskii-Moriya interaction\, giving rise to a ‘weak’ but meas
 urable net ferromagnetism.  Below the Morin transition temperature (TM ~ 2
 60 K)\, the spins flip out of plane and lose their canting\, leading to pe
 rfect antiferromagnetism and the loss of the net magnetic signal.  We reas
 oned that the above-Morin phase should be topologically rich and could in 
 principle support vortices\, while the easily accessible low-temperature p
 hase would be topologically ‘trivial’.  I will discuss our recent work
  [3\,4]\, in which we demonstrated that\, indeed\, hematite supports a ric
 h variety of topological textures (merons\, antimerons\, bimerons)\, which
  can be tuned in and out of existence simply by cycling temperature over a
  narrow range through TM or by application of biaxial/uniaxial strain [5].
   Remarkably\, these magnetic textures can be imaged in real space by X-ra
 y spectral microscopy (X-PEEM\, transmission X-ray microscopy and holograp
 hy [6]).  I will also discuss the recent collaboration with Cambridge coll
 eagues\, in which we imaged by N-V centre microscopy [7] the ‘emergent
 ’ multipolar charges associated with topological textures.  My final que
 stion is: can topological textures in hematite be at all useful?  I will a
 rgue that the answer may be yes\, particularly in the blooming field of an
 tiferromagnetic spintronics/skyrmionics.\n\nReferences:\n[1]    Zurek\, W.
  H. Cosmological experiments in superfluid helium? Nature 317\, 505–508 
 (1985).\n[2]    Kibble\, T. W. B. “Topology of cosmic domains and string
 s.” J. Phys. A: Math. Gen. 9\, 1387–1398 (1976)\;\n[3]    F. P. Chmiel
 \, N. Waterfield Price\, R. D. Johnson\, A. D. Lamirand\, J. Schad\, G. Va
 n Der Laan\, D. T. Harris\, J. Irwin\, M. S. Rzchowski\, C. B. Eom\, and P
 . G. Radaelli\, Nat. Mater. 17\, 581 (2018).\n[4]    H. Jani\, J. C. Lin\,
  J. Chen\, J. Harrison\, F. Maccherozzi\, J. Schad\, S. Prakash\, C. B. Eo
 m\, A. Ariando\, T. Venkatesan\, and P. G. Radaelli\, Nature 590\, 74 (202
 1).\n[5]    H. Jani\, J. Harrison\, S. Hooda\, S. Prakash\, P. Nandi\, J. 
 Hu\, Z. Zeng\, J.-C. Lin\, G. ji Omar\, J. Raabe\, S. Finizio\, A. V.-Y. T
 hean\, A. Ariando\, and P. G. Radaelli\, Nat. Mater  (2024 in press) arXiv
 :2303.03217 [cond-mat.mtrl-sci]\n[6]    J. Harrison\, H. k. Jani\, J. Hu\,
  M. Lal\, J-C Lin\, H. Popescu\, J. Brown\, N. Jaouen\, A. Ariando\, and P
 . G. Radaelli\, Optics Express 32\, pp. 5885-5897 (2024) \n[7]    A. K. C.
  Tan\, H. Jani\, M. Högen\, L. Stefan\, C. Castelnovo\, D. Braund\, A. Ge
 im\, M. S. G. Feuer\, H. S. Knowles\, A. Ariando\, P. G. Radaelli\, and M.
  Atatüre\, Nat. Mater 23\, 205-212 (2023)
LOCATION:Small Lecture Theatre\, Cavendish Laboratory\, J.J. Thomson Avenu
 e
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