Skyrmions and chiral bobbers: evolution from 2D to 3D with film thickness*

Theoretical studies of chiral magnets have focused on either 3D systems with broken bulk inversion symmetry or quasi-2D systems with broken surface inversion. Building on our earlier theoretical results [1] and motivated by recent experiments [2] of B20 thin films grown on substrates, we model the behavior of materials with two types of Dzyaloshinskii-Moriya interaction (DMI) that arise from broken bulk inversion and broken surface inversion. We investigate the T=0 phase diagram as a function of field H, anisotropy K, and sample thickness L. We highlight the importance of surface twists in quasi-2D systems. We also show how skyrmion tubes in very thin films evolve into chiral bobbers confined to the interface in thicker samples. The role of interfacial DMI in stabilizing chiral bobbers and stacked spirals is emphasized. The important role of magneto-crystalline anisotropy and demagnetization factors will also be discussed and comparison with experiments presented.

[1] J. Rowland, et al., Phys. Rev. B 93, 020404(R) (2016)
[2] A. S. Ahmed, J. Rowland, et al., arXiv:1706.08248 (2017)