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Ferromagnetic Switching of Knotted Vector Fields in Liquid Crystal Colloids

Qiaoxuan Zhang, Paul J. Ackerman, Qingkun Liu, and Ivan I. Smalyukh
Phys. Rev. Lett. 115, 097802 – Published 28 August 2015
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Abstract

We experimentally realize polydomain and monodomain chiral ferromagnetic liquid crystal colloids that exhibit solitonic and knotted vector field configurations. Formed by dispersions of ferromagnetic nanoplatelets in chiral nematic liquid crystals, these colloidal ferromagnets exhibit spontaneous long-range alignment of magnetic dipole moments of individual platelets, giving rise to a continuum of the magnetization field M(r). Competing effects of surface confinement and chirality prompt spontaneous formation and enable the optical generation of localized twisted solitonic structures with double-twist tubes and torus knots of M(r), which exhibit a strong sensitivity to the direction of weak magnetic fields 1mT. Numerical modeling, implemented through free energy minimization to arrive at a field-dependent three-dimensional M(r), shows a good agreement with experiments and provides insights into the torus knot topology of observed field configurations and the corresponding physical underpinnings.

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  • Received 17 May 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.097802

© 2015 American Physical Society

Physics Subject Headings (PhySH)

Polymers & Soft Matter

Authors & Affiliations

Qiaoxuan Zhang1,2, Paul J. Ackerman1,3, Qingkun Liu1, and Ivan I. Smalyukh1,2,3,4,5,*

  • 1Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
  • 2Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, USA
  • 3Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder, Colorado 80309, USA
  • 4Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
  • 5Renewable and Sustainable Energy Institute, National Renewable Energy Laboratory and University of Colorado, Boulder, Colorado 80309, USA

  • *Corresponding author. ivan.smalyukh@colorado.edu

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Issue

Vol. 115, Iss. 9 — 28 August 2015

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