Raman scattering signatures of strong spin-phonon coupling in the bulk magnetic van der Waals material CrSBr

Magnetic excitations in layered magnetic materials that can be thinned down to the two-dimensional (2D) monolayer limit are of great interest from a fundamental point of view and for applications. Raman scattering has played a crucial role in exploring the properties of magnetic layered materials and, even though it is essentially a probe of lattice vibrations, it can reflect magnetic ordering in solids through the spin-phonon interaction or through the observation of magnon excitations. In bulk CrSBr, a layered A-type antiferromagnet (AF), we show that the magnetic ordering can be directly observed in the temperature dependence of the Raman scattering response (i) through the variations of the scattered intensities, (ii) through the activation of new phonon lines reflecting the change of symmetry with the appearance of the additional magnetic periodicity, and (iii) through the observation below the N\'eel temperature (TN) of second-order Raman scattering processes. We additionally show that the three different magnetic phases encountered in CrSBr, including the recently identified low-temperature phase, have a particular Raman scattering signature. This work demonstrates that magnetic ordering can be observed directly in the Raman scattering response of bulk CrSBr with in-plane magnetization and that it can provide unique insight into the magnetic phases encountered in magnetic layered materials.