Complex spin dynamics in layered CrBr₃

Layered magnetic materials give rise to unconventional spin dynamics and electrically accessible resonance frequencies even for antiferromagnets. Towards this end, we investigated the rich spin dynamics in a layered CrBr₃ crystal using magnetic resonance phenomena. Compared to the other chromium trihalides (i.e., CrX₃, X = Cl, I), CrBr₃ possesses unique magnetic properties such as strong ferromagnetic intralayer exchange interaction and weaker interlayer ferromagnetic coupling due to competing ferromagnetic and antiferromagnetic exchange interactions at low temperature. Here, we show that magnetic excitation for the in-plane and out-of-plane directions of CrBr₃ give rise to distinct magnon modes. With the out-of-plane magnetic field, only one resonance mode (Kittle mode) is observed. However, we have identified three different modes in the CrBr₃ crystal when the applied field is in-plane. We explain the origin of different modes using micromagnetics including different anisotropy and intralayer and interlayer exchange energies. Our study shows that broadband microwave transmission spectroscopy can reveal the intricate spin dynamics phenomena in layered magnetic materials that originate from the interplay of intralayer and interlayer exchange energies.