Chiral Bobbers and Skyrmions in Epitaxial FeGe/Si(111) Films

TL;DR

This study demonstrates the formation of stable chiral bobbers at FeGe/Si(111) interfaces, revealing a thickness-dependent transition from skyrmions to bobbers, supported by experimental observations and micromagnetic simulations.

Contribution

It provides the first experimental evidence and theoretical validation that chiral bobbers are the stable ground state in FeGe films with interfacial Rashba DMI.

Findings

Chiral bobbers are stable at the FeGe/Si interface for film thicknesses greater than half the pitch length.

A transition from skyrmion phase to chiral bobbers occurs as film thickness increases.

Micromagnetic simulations confirm the stability of chiral bobbers with interfacial Rashba DMI.

Abstract

We report experimental and theoretical evidence for the formation of chiral bobbers - an interfacial topological spin texture - in FeGe films grown by molecular beam epitaxy (MBE). After establishing the presence of skyrmions in FeGe/Si(111) thin film samples through Lorentz transmission electron microscopy and topological Hall effect, we perform magnetization measurements that reveal an inverse relationship between film thickness and the slope of the susceptibility (d\c{hi}/dH). We present evidence for the evolution as a function of film thickness, L, from a skyrmion phase for L < LD/2 to a cone phase with chiral bobbers at the interface for L > LD/2, where LD ~ 70 nm is the FeGe pitch length. We show using micromagnetic simulations that chiral bobbers, earlier predicted to be metastable, are in fact the stable ground state in the presence of an additional interfacial Rashba Dzyaloshinskii-Moriya interaction (DMI).