Anisotropic Magneto-Optical Raman Response Coupled with Magnetic Ordering in an A-Type Antiferromagnet.

Abstract

Magneto-optical effects serve as powerful tools for probing magnetic order and spin-related couplings, yet anisotropic spin-phonon coupling in low-dimensional systems remains underexplored. Here, we uncover an anisotropic magneto-optical Raman response in the A-type van der Waals antiferromagnet CrSBr, where intrinsic lattice anisotropy and quasi-one-dimensional magnetism enable anisotropic spin-phonon interactions. Using polarization- and angle-resolved Raman spectroscopy, we identify that the ratio |<i>b</i>/<i>a</i>| of the <i>A</i>_g² mode's Raman tensor elements undergoes a dramatic change across the Néel temperature, serving as a hallmark of the paramagnetic-to-antiferromagnetic phase transition. Under an out-of-plane magnetic field, this ratio varies continuously with spin canting, reflecting changes in spin configuration. Crucially, we elucidate that magnetic ordering selectively modulates the anisotropic electron-phonon coupling predominantly along the <i>b</i>-axis. Our work advances polarization- and angle-resolved Raman spectroscopy as a sensitive probe of anisotropic spin-phonon physics and pioneers the development of opto-spintronic devices with direction-selective magneto-optical functionality.