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Spin-flop transition in atomically thin MnPS$_3$ crystals

The magnetic state of atomically thin semiconducting layered antiferromagnets such as CrI$_3$ and CrCl$_3$ can be probed by forming tunnel barriers and measuring their resistance as a function of magnetic field ($H$) and temperature ($T$). This is possible because the tunneling magnetoresistance originates from a spin-filtering effect sensitive to the relative orientation of the magnetization in different layers, i.e., to the magnetic state of the multilayers. For systems in which antiferromagnetism occurs within an individual layer, however, no spin-filtering occurs: it is unclear whether this strategy can work. To address this issue, we investigate tunnel transport through atomically thin crystals of MnPS$_3$, a van der Waals semiconductor that in the bulk exhibits easy-axis antiferromagnetic order within the layers. For thick multilayers below $T\simeq 78$ K, a $T$-dependent magnetoresistance sets-in at $\sim 5$ T, and is found to track the boundary between the antiferromagnetic and the spin-flop phases known from bulk magnetization measurements. The magnetoresistance persists down to individual MnPS$_3$ monolayers with nearly unchanged characteristic temperature and magnetic field scales, albeit with a different dependence on $H$. We discuss the implications of these finding for the magnetic state of atomically thin MnPS$_3$ crystals, conclude that antiferromagnetic correlations persist down to the level of individual monolayers, and that tunneling magnetoresistance does allow magnetism in 2D insulating materials to be detected even in the absence of spin-filtering.