The emergence of magnetic order in monolayer van der Waals (vdW) materials has opened a new experimental platform for revisiting fundamental predictions of low-dimensional spin models. In particular, chromium trihalides provide a tunable family of layered magnets in which magnetic anisotropy evolves systematically from out-of-plane (CrI₃, CrBr₃) to in-plane (CrCl₃), enabling access to the two-dimensional XY limit. Recent reports of XY-type critical scaling in CrCl₃ near the transition temperature (TKT) suggest that this material may host Berezinskii–Kosterlitz–Thouless (BKT) physics, including topological spin textures and spin superfluidity.

Here, we realise monolayer CrCl₃ under ultra-high vacuum conditions, forming well-defined vdW interfaces suitable for surface-sensitive probes. Using X-ray magnetic circular dichroism (XMCD), we directly probe the magnetic anisotropy and ordering in the monolayer limit, confirming a strong preference for in-plane spin alignment consistent with XY behaviour. Despite the expected vanishingly small in-plane anisotropy, we observe robust magnetic signals that persist after the application of magnetic fields and at temperatures above TKT. These observations indicate deviations from the ideal XY model in the thermodynamic limit, highlighting the role of finite-size effects, slow spin dynamics, or residual symmetry-breaking interactions in stabilising magnetic correlations. Our results establish monolayer CrCl₃ as a promising platform for exploring two-dimensional magnetism and provide important constraints on the realisation of BKT physics in experimental vdW systems.