Oriented 3D Magnetic Biskyrmions in MnNiGa Bulk Crystals

Xiyang Li; Shilei Zhang; Hang Li; Diego Alba Venero; Jonathan S White; Robert Cubitt; Qingzhen Huang; Jie Chen; Lunhua He; Gerrit van der Laan; Wenhong Wang; Thorsten Hesjedal; Fangwei Wang

doi:10.1002/adma.201900264

Oriented 3D Magnetic Biskyrmions in MnNiGa Bulk Crystals

Adv Mater. 2019 Apr;31(17):e1900264. doi: 10.1002/adma.201900264. Epub 2019 Mar 13.

Authors

Xiyang Li^{1

2}, Shilei Zhang³, Hang Li^{1

2}, Diego Alba Venero⁴, Jonathan S White⁵, Robert Cubitt⁶, Qingzhen Huang⁷, Jie Chen⁸, Lunhua He^{1

9}, Gerrit van der Laan¹⁰, Wenhong Wang^{1

2

9}, Thorsten Hesjedal³, Fangwei Wang^{1

2

9}

Affiliations

¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
² School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 101408, China.
³ Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, UK.
⁴ ISIS, STFC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK.
⁵ Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232, Villigen, Switzerland.
⁶ Institut Laue-Langevin, 6 rue Jules Horowitz, 38042, Grenoble, France.
⁷ NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899, USA.
⁸ China Spallation Neutron Source, Dongguan, 523808, China.
⁹ Songshan Lake Materials Laboratory, Dongguan, 523808, China.
¹⁰ Magnetic Spectroscopy Group, Diamond Light Source, Didcot, OX11 0DE, UK.

Abstract

A biskyrmion consists of two bound, topologically stable, skyrmion spin textures. These coffee-bean-shaped objects are observed in real space in thin plates using Lorentz transmission electron microscopy (LTEM). From LTEM imaging alone, it is not clear whether biskyrmions are surface-confined objects, or, analogous to skyrmions in noncentrosymmetric helimagnets, 3D tube-like structures in a bulk sample. Here, the biskyrmion form factor is investigated in single- and polycrystalline-MnNiGa samples using small-angle neutron scattering. It is found that biskyrmions are not long-range ordered, not even in single crystals. Surprisingly all of the disordered biskyrmions have their in-plane symmetry axis aligned along certain directions, governed by the magnetocrystalline anisotropy. This anisotropic nature of biskyrmions may be further exploited to encode information.

Keywords: MnNiGa; biskyrmions; disorder; small-angle neutron scattering.

Abstract

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