Anisotropic Gigahertz Antiferromagnetic Resonances of the Easy-Axis van der Waals Antiferromagnet CrSBr

We report measurements of the antiferromagnetic resonance modes in the van der Waals (vdW) antiferromagnet CrSBr. Weak interlayer exchange coupling between vdW layers gives resonances in the GHz range, making it easier to study their fundamental properties compared to antiferromagnets with THz-scale resonances. Unlike the other vdW magnets whose modes have been characterized previously (CrCl₃ and CrI₃), CrSBr has strong triaxial magnetic anisotropy. As a result, the quantum-mechanical hybridization between the two antiferromagnetic modes can be tuned via the angle of an in-plane magnetic field. The anisotropy also causes distinctly different types of resonance modes depending on the field direction with respect to the anisotropy axes. Fits to a two-sublattice Landau-Lifshitz model allow quantitative measurements of the anisotropy and interlayer exchange as a function of temperature. This work sets the foundation for future experiments regarding controlled manipulation of antiferromagnetic modes.