Incommensurate Antiferromagnetic Order in Weakly Frustrated Two-Dimensional van der Waals Insulator CrPSe₃

Although magnetic order is suppressed by a strong frustration, it appears in complex forms such as a cycloid or spin density wave in weakly frustrated systems. Herein, we report a weakly magnetically frustrated two-dimensional (2D) van der Waals material CrPSe₃. Polycrystalline CrPSe₃ was synthesized at an optimized temperature of 700 °C to avoid the formation of any secondary phases (e.g., Cr₂Se₃). The antiferromagnetic transition appeared at T_N ≈ 127 K with a large Curie-Weiss temperature θ_CW ≈ -301 K via magnetic susceptibility measurements, indicating weak frustration in CrPSe₃ with a frustration factor of f (|θ_CW|/T_N) ≈ 2.4. Evidently, the formation of a long-range incommensurate antiferromagnetic order was revealed by neutron diffraction measurements at low temperatures (below 120 K). The monoclinic crystal structure of the C2/m symmetry is preserved over the studied temperature range down to 20 K, as confirmed by Raman spectroscopy measurements. Our findings on the incommensurate antiferromagnetic order in 2D magnetic materials, not previously observed in the MPX₃ family, are expected to enrich the physics of magnetism at the 2D limit, thereby opening opportunities for their practical applications in spintronics and quantum devices.