Spin exchange Hamiltonian and topological degeneracies in elemental gadolinium

TL;DR

This paper investigates the magnetic exchange interactions in elemental Gadolinium using neutron scattering, revealing RKKY behavior and exploring topological degeneracies and tunable properties in ferromagnets.

Contribution

It provides a detailed measurement of exchange interactions in Gadolinium and discusses how topological features can be manipulated with magnetic fields.

Findings

Exchange interactions follow RKKY oscillations.

Magnon spectrum measured over entire Brillouin zone.

Topological degeneracies can be tuned with magnetic field.

Abstract

We present a comprehensive study of the magnetic exchange Hamiltonian of elemental Gadolinium. We use neutron scattering to measure the magnon spectrum over the entire Brillouin zone, and fit the excitations to a spin wave model to extract the first 26 nearest neighbor magnetic exchange interactions with rigorously defined uncertainty. We find these exchange interactions to follow RKKY behavior, oscillating from ferromagnetic to antiferromagnetic as a function of distance. Finally, we discuss the topological features and degeneracies in Gd, and HCP ferromagnets in general. We show theoretically how, with asymmetric exchange, topological properties could be tuned with a magnetic field.