Spin waves and magnetic exchange Hamiltonian in CrSBr

TL;DR

This study experimentally determines the magnetic exchange interactions and magnon spectrum in CrSBr, a 2D magnetic semiconductor, revealing a ferromagnetic intra-plane model and enabling predictions of chiral magnon edge modes.

Contribution

It provides the first detailed experimental determination of the magnetic exchange Hamiltonian and magnon spectrum in CrSBr, a promising 2D magnetic material.

Findings

CrSBr exhibits A-type antiferromagnetic order confirmed by neutron diffraction.

Magnon dispersions fit well to an intra-plane ferromagnetic Heisenberg model with seven exchanges.

Predicted chiral magnon edge modes in a spin-orbit coupled CrSBr heterostructure.

Abstract

CrSBr is an air-stable 2D van der Waals semiconducting magnet with great technological promise, but its atomic-scale magnetic interactions -- crucial information for high-frequency switching -- are poorly understood. We present an experimental study to determine the CrSBr magnetic exchange Hamiltonian and bulk magnon spectrum. We confirm the $A$-type antiferromagnetic order using single crystal neutron diffraction. We also measure the magnon dispersions using inelastic neutron scattering and rigorously fit the excitation modes to a spin wave model. The magnon spectrum is well described by an intra-plane ferromagnetic Heisenberg exchange model with seven nearest in-plane exchanges. This fitted exchange Hamiltonian enables theoretical predictions of CrSBr behavior: as one example, we use the fitted Hamiltonian to predict the presence of chiral magnon edge modes with a spin-orbit enhanced CrSBr heterostructure.