Communicating skyrmions as the main mechanism underlying skyrmionium (meta)stability in quasitwodimensional chiral magnets
Abstract
We reexamine the internal structure of skyrmioniums stabilized in quasitwodimensional chiral magnets with easyaxis uniaxial anisotropy. Skyrmioniums are particlelike states of two nested skyrmions with opposite polarities contributing to zero topological charge. The physical principles of skyrmionium stability are drawn from both the analytical analysis with a trial function and from numerical simulations within the framework of micromagnetism. We deduce that the radii of the internal skyrmion with the positive polarity and the ringshaped external skyrmion with the negative polarity are mutually dependent, which constitutes the paradigm of communicating skyrmions. For large central skyrmions, the skyrmionium transforms into a narrow circular domain wall, whereas for small internal radii, the ring expands, which occurs at the verge of collapsing into an ordinary isolated skyrmion. We show that skyrmioniums may form lattices of two varieties depending on the polarity of the internal skyrmion. At the phase diagram (magnetic field)(uniaxial anisotropy), both skyrmionium lattices share the same area with onedimensional spiral states and remain metastable solutions for the whole range of control parameters. By expanding at the critical line, skyrmionium lattices do not release isolated skyrmioniums. Isolated skyrmioniums of just one type exist apart from the corresponding lattice in a narrow field region restricted by the critical line of expansion from below and by the line of collapse above.
 Publication:

arXiv eprints
 Pub Date:
 April 2024
 DOI:
 10.48550/arXiv.2404.10189
 arXiv:
 arXiv:2404.10189
 Bibcode:
 2024arXiv240410189N
 Keywords:

 Condensed Matter  Mesoscale and Nanoscale Physics;
 Mathematical Physics