Thermal Magnon Hall Effect in FM/AFM Skyrmionic Structures

Abstract

Inspired by Onose et al,, who observed the thermal magnon Hall effect in pyrochlore ferromagnetic structures, the present master Thesis investigates the same effect of magnons in stable, rectangular, ferromagnetic and antiferromagnetic skyrmionic lattices. Our analysis is based on a Hamiltonian which consists of the following four terms: an exchange interaction, an easy axis anisotropy, the Dzyaloshinskii-Moriya interaction and an external magnetic field. Transformations on the initial Hamiltonian in order to obtain the non-interacting magnonic spin-wave Hamiltonian, and the standard method of diagonalisation, allow us to numerically compute the effective magnetic field that the magnons feel, which is essential ingredient to compute the transverse thermal conductivity. The results found for both ferromagnetic and antiferromagnetic lattices show the presence of the Hall effect of magnons at low temperatures. Although a direct comparison between ferromagnets and antiferromagnets is impossible, since they differ in the size as well as in the number of skyrmions, we do compare the two configurations to conclude that the antiferromagnetic structure exhibits a stronger thermal Hall effect.