Controlling magnetism in 2D CrI₃ by electrostatic doping

The atomic thickness of two-dimensional materials provides a unique opportunity to control their electrical¹ and optical² properties as well as to drive the electronic phase transitions³ by electrostatic doping. The discovery of two-dimensional magnetic materials^4-10 has opened up the prospect of the electrical control of magnetism and the realization of new functional devices¹¹. A recent experiment based on the linear magneto-electric effect has demonstrated control of the magnetic order in bilayer CrI₃ by electric fields¹². However, this approach is limited to non-centrosymmetric materials^11,13-16 magnetically biased near the antiferromagnet-ferromagnet transition. Here, we demonstrate control of the magnetic properties of both monolayer and bilayer CrI₃ by electrostatic doping using CrI₃-graphene vertical heterostructures. In monolayer CrI₃, doping significantly modifies the saturation magnetization, coercive force and Curie temperature, showing strengthened/weakened magnetic order with hole/electron doping. Remarkably, in bilayer CrI₃, the electron doping above ~2.5 × 10¹³ cm^-2 induces a transition from an antiferromagnetic to a ferromagnetic ground state in the absence of a magnetic field. The result reveals a strongly doping-dependent interlayer exchange coupling, which enables robust switching of magnetization in bilayer CrI₃ by small gate voltages.