Ground State Revealed by Layer-sensitive Magnetic Sensor

The recent identification of 2D magnetic CrI₃ adds a new building block to the family of 2D materials. While its monolayer was proven to be an intrinsic ferromagnetic insulator, its bilayer intriguingly exhibits vanishing magnetization. This implies a layered-antiferromagnetic spin arrangement, i.e. individual monolayers are ferromagnetic while the interlayer coupling is antiferromagnetic. Therefore, a probe to resolve the magnetization of individual monolayers is needed to reveal the bilayer CrI₃ ground state. Here we report magneto-optical spectroscopy studies on heterostructures of monolayer WSe₂ and bilayer CrI₃. Using the WSe₂ valley exciton photoluminescence, we achieve a layer-specific probe of the magnetization via proximity coupling of the WSe₂ to the CrI₃. We then employ magnetic circular dichroism to correlate with the total magnetization state of bilayer. Our results reveal that bilayer CrI₃ indeed has a layered antiferromagnetic configuration. We also reveal a spatially dependent coercivity phenomenon and discuss possible mechanisms.