Spin Waves and Magnetic Exchange Hamiltonian in CrSBr.

CrSBr is an air-stable two-dimensional (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. An experimental study is presented to determine the CrSBr magnetic exchange Hamiltonian and bulk magnon spectrum. The A-type antiferromagnetic order using single crystal neutron diffraction is confirmed here. The magnon dispersions are also measured 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, the fitted Hamiltonian is used to predict the presence of chiral magnon edge modes with a spin-orbit enhanced CrSBr heterostructure.