Manipulation of the spin helix in FeGe thin films and FeGe/Fe multilayers

TL;DR

This study investigates how the spin helix in FeGe thin films and FeGe/Fe multilayers can be manipulated using magnetic fields and boundary conditions, revealing deformation and control mechanisms of chiral magnetic states.

Contribution

It demonstrates the manipulation of the spin helix in FeGe thin films through applied fields and boundary exchange coupling, providing new insights into controlling chiral magnetic states.

Findings

Helix reverses by deforming into a helicoidal form under magnetic field.

Boundary exchange coupling with Fe layer controls spin reversal.

Helical states can be manipulated by boundary conditions and external fields.

Abstract

Magnetic materials without structural inversion symmetry can display the Dzyaloshinskii-Moriya interaction, which manifests itself as chiral magnetic ground states. These chiral states can interact in complex ways with applied fields and boundary conditions provided by finite sample sizes that are of the order of the lengthscale of the chiral states. Here we study epitaxial thin films of FeGe with a thickness close to the helix pitch of the helimagnetic ground state, which is about 70 nm, by conventional magnetometry and polarized neutron reflectometry. We show that the helix in an FeGe film reverses under the application of a field by deforming into a helicoidal form, with twists in the helicoid being forced out of the film surfaces on the way to saturation. An additional boundary condition was imposed by exchange coupling a ferromagnetic Fe layer to one of the interfaces of an FeGe layer. This forces the FeGe spins at the interface to point in the same direction as the Fe, preventing node expulsion and giving a handle by which the reversal of the helical magnet may be controlled.