Controlling phase transition in monolayer metal diiodides XI$_{2}$ (X: Fe, Co, and Ni) by carrier doping

TL;DR

This study uses first-principles calculations to explore and control the magnetic ground states of monolayer metal diiodides, revealing doping-induced phase transitions and potential for spintronic applications.

Contribution

It demonstrates how carrier doping can manipulate phase transitions in monolayer metal diiodides, identifying promising multiferroic states and magnetic behaviors.

Findings

FeI2 is ferromagnetic in ground state

CoI2 and NiI2 favor spiral states as ground states

Doping induces phase transitions in NiI2

Abstract

We applied the generalized Bloch theorem to verify the ground state (most stable state) in monolayer metal diiodides 1T-XI$_{2}$ (X: Fe, Co, and Ni), a family of metal dihalides, using the first-principles calculations. The ground state, which can be ferromagnetic, antiferromagnetic, or spiral state, was specified by a wavevector in the primitive unit cell. While the ground state of FeI$_{2}$ is ferromagnetic, the spiral state becomes the ground state for CoI$_{2}$ and NiI$_{2}$. Since the multiferroic behavior in the metal dihalide can be preserved by the spiral structure, we believe that CoI$_{2}$ and NiI$_{2}$ are promising multiferroic materials in the most stable state. When the lattice parameter increases, we also show that the ground state of NiI$_{2}$ changes to a ferromagnetic state while others still keep their initial ground states. For the last discussion, we revealed the phase transition manipulated by hole-electron doping due to the spin-spin competition between the ferromagnetic superexchange and the antiferromagnetic direct exchange. These results convince us that metal diiodides have many benefits for future spintronic devices.