Marc Janoschek: Tales of topology as told by neutron and X-ray scattering — Microscopic Insights into Magnon and Skyrmion Hall Effects

Marc Janoschek

Paul Scherrer Institute & Universität Zürich

"Tales of topology as told by neutron and X-ray scattering — Microscopic Insights into Magnon and Skyrmion Hall Effects"

Abstract: Magnetic skyrmions are nano-sized, topologically non-trivial magnetic textures. The low electrical current density required to set skyrmions in motion highlights their potential for future race-track memory, spintronics, and neuromorphic computing devices. This efficient motion of skyrmions is a result of their coupling to the conduction electrons via the spin-torque transfer effect. Here the topological charge C carried by skyrmions acts as a fictious magnetic field and leads to a topological Hall effect and a transverse motion of electrons. In this talk, I will first report on our recent extensive inelastic neutron scattering study, which demonstrates that magnons— bosonic quasiparticles that do not carry an electrical charge—equally experience a topological Hall effect when traveling across a skyrmion lattice texture. In the second part, I will focus on the skyrmion Hall effect, which describes the deflection of skyrmion motion transverse to the direction of an electrical drive current. The transverse motion represents a major hurdle for devices as it limits skyrmion speeds and results in a need for higher drive currents. A solution, proposed by theory, is to create pairs of antiferromagnetically coupled skyrmions. The compensated topological charges +C and −C of this skyrmion pair implies a net straight trajectory preferable for devices. Using neutron diffraction and resonant elastic X-ray scattering, we have uncovered a new topological state of matter— a skyrmion lattice characterized by compensated topological charges arising from antiferromagnetically coupled skyrmion lattice layers (AFM-SkL) consistent with the absence of topological Hall resistivity observed in this phase.