Magnetic Field Tunable Raman Scattering and Zone-Folding Phonons in Two-Dimensional Magnet CrSBr.

Abstract

The discovery of two-dimensional (2D) magnets has attracted significant attention in both fundamental research in low-dimensional physics and potential applications in spintronics. CrSBr, an A-type antiferromagnetic (AFM) van der Waals material with intralayer ferromagnetic (FM) order along the <i>b</i> axis, stands out as one of the most extensively studied 2D magnetic materials due to the strong coupling between its electronic structure and magnetic properties. Here, we demonstrate a deep connection between the magnetic order and Raman scattering of phonons in CrSBr. By applying a magnetic field along the easy axis, an abrupt change of Raman intensity is observed in the transition from the AFM to FM state for both bulk and few-layer CrSBr, which is attributed to the modification of the energy detuning between the excitation light and the near-resonant exciton. In addition, at the <i>a</i>-axis spin-canted state, we observe three strong zone-folding phonon modes of the three dominant A_g modes, which are absent at both AFM and FM states. Furthermore, we find that the FM magnetic order can introduce off-diagonal terms into the Raman tensors, which can dramatically modify the polarization patterns of the Raman modes and lead to different scattering intensities for the left and right circularly polarized light. Our findings underline the profound impact of the magnetic order on the Raman scattering intensity, activity of zone-folding phonons, and polarization properties in CrSBr and expand the scope of magneto-optical effects in 2D magnetic materials.