Two-dimensional ferromagnetic van der Waals CrC l3 monolayer with enhanced anisotropy and Curie temperature

Among the recently widely studied van der Waals layered magnets Cr X₃ (X =Cl , Br, I), CrC l₃ monolayer (ML) is particularly puzzling: it is shown by experiments to have only an in-plane magnetic easy axis and, furthermore, all previous first-principles calculation results contradict this. Through systematic first-principles calculations, we unveil that the in-plane shape anisotropy that dominates over the weak perpendicular magnetocrystalline anisotropy is responsible for the in-plane magnetic easy axis of CrC l₃ ML. To tune the in-plane ferromagnetism of CrC l₃ ML into the desirable perpendicular one, we propose substituting Cr with isovalent tungsten (W). We find that CrWC l₆ has a strong perpendicular magnetic anisotropy and a high Curie temperature up to 76 K. Our work not only gives insight into understanding the two-dimensional ferromagnetism of van der Waals MLs but also sheds new light on engineering their performances for nanodevices.