The properties of isolated chiral skyrmions in thin magnetic films

TLDR

Chiral skyrmions were predicted over two decades ago, yet until recently they were only observed as condensates such as hexagonal lattices. This study reports experimental and theoretical investigations of isolated chiral skyrmions in PdFe/Ir(111) bilayers. Spin‑polarized STM and modeling show isolated skyrmions exist within a field‑dependent stability window bounded by strip‑out and collapse instabilities, and the governing equations apply universally to all chiral systems with broken mirror symmetry.

Abstract

Axisymmetric solitonic states (chiral skyrmions) have been predicted theoretically more than two decades ago. However, until recently they have been observed in a form of skyrmionic condensates (hexagonal lattices and other mesophases). In this paper we report experimental and theoretical investigations of isolated chiral skyrmions discovered in PdFe/Ir(111) bilayers two years ago (Science 341 , 636 (2013)). The results of spin-polarized scanning tunneling microscopy analyzed within the continuum and discrete models provide a consistent description of isolated skyrmions in thin layers. The existence region of chiral skyrmions is restricted by strip-out instabilities at low fields and a collapse at high fields. We demonstrate that the same equations describe axisymmetric localized states in all condensed matter systems with broken mirror symmetry, and thus our findings establish basic properties of isolated skyrmions common for chiral liquid crystals, different classes of noncentrosymmetric magnets, ferroelectrics, and multiferroics.