Controllable magnetic ground states in metal diiodide MI2 (M: Fe, Co, and Ni) monolayers by electric field

We investigated the controllable magnetic ground states of 1T metal diiodide MI2 (M: Fe, Co, and Ni) monolayers by applying the electric field. To do so, we utilized the generalized Bloch theorem within the density functional theory on the primitive unit cell to examine the appearance of three possible magnetic ground states, namely, ferromagnetic, spiral, and antiferromagnetic states from the specified spiral vector. We found that the ground state can be changed as the electric field increases but depends on the lattice parameter. In general, the spiral ground state exists as the electric field is taken into account, thus all these materials are prominent as multiferroics. Also, based on the competition between ferromagnetic and antiferromagnetic exchange interactions, we observed that for FeI2, the transition from the ferromagnetic exchange to the antiferromagnetic exchange happens as the electric field increases, while CoI2 and NiI2 tend to preserve their original exchange interaction. This implies that only the magnetic state in FeI2 sensitively depends on the electric field.