Dominance of shape anisotropy in a CrOCl monolayer enables deterministic strain switching of the magnetic easy axis.

A CrOCl monolayer is a two-dimensional ferromagnetic semiconductor successfully synthesized in recent years, but the origin and tunability of its magnetic anisotropy have not been systematically studied. Our calculations reveal a pronounced triaxial anisotropy in the CrOCl monolayer, establishing the y-axis as the easy axis, with the z- and x-axes serving as the intermediate and hard axes, respectively. Our core finding is that shape anisotropy arising from the long-range magnetic dipole-dipole interaction plays a dominant role in the total magnetic anisotropy energy, exceeding the contribution from the magnetocrystalline anisotropy induced by spin-orbit coupling (SOC), while the opposite relationship is commonly assumed in conventional two-dimensional magnets. Besides, we find that uniaxial strain is an effective control method, which can reversibly switch the magnetization easy axis between the in-plane y-axis and the out-of-plane z-axis. The easy-axis switching feature of strain control makes CrOCl an alternative material system for multi-axis magnetic switch devices. This study clarifies the decisive role of shape anisotropy in the CrOCl monolayer and establishes its connection with strain-controlled magnetic behavior, providing a feasible route for magnetic-state engineering of two-dimensional ferromagnetic semiconductors.