Ultrasensitive Sagnac optical interferometry of magnetic spin dynamics

Magneto-optical measurements of two-dimensional antiferromagnets are a powerful tool for detecting spin dynamics with atomic precision. In A-type antiferromagnets like CrSBr, even-layer samples exhibit compensated magnetic moments that cancel out, while odd-layer samples contain an uncompensated magnetic layer, allowing for optical detection of the magnetization dynamics. We employ ultra-sensitive Sagnac interferometry, a highly precise optical technique that has recently been demonstrated to detect extremely small, current-induced magnetization changes, including second-order effects. This method is particularly effective for capturing small magnetization deviations resulting from spin-orbit torques that are otherwise difficult to observe.

Building on previous electrical measurements of highly local spin-orbit torque effects in bilayer CrSBr [1], we use Sagnac interferometry to verify these effects across CrSBr layers of varying thickness. By probing the layer-dependent magnetic behavior, we aim to uncover critical insights into the interplay between spin-orbit torques and spin dynamics in two-dimensional antiferromagnets, advancing the understanding of their potential for spintronic applications [2].