Mechanical, Electronic, and Magnetic Properties of NiX₂ (X = Cl, Br, I) Layers

Abstract

Since the recent experimental discovery of the CrI 3 and CrGeTe 3 monolayers, van der Waals (vdW) layered transition metal compounds have been recognized as promising candidates to realize 2D ferromagnetic (FM) semiconductors. However, until now, only limited compounds have been proposed to be ferromagnetic semiconductors. Here, on the basis of first-principles calculations, we report that the monolayer, Janus monolayer, and bilayer of NiX 2 (X = Cl, Br, I) are intrinsic 2D FM semiconductors. Our results show that exfoliation energy of the NiX 2 monolayer is smaller than that of graphene, and all studied NiX 2 layers show semiconducting band gaps. The predicted Curie temperature values for NiX 2 (X = Cl, Br, I) monolayers ranged from 120 to 170 K with Monte Carlo simulations. For the Janus monolayer, we found that the spin interaction shows a very strong magnetoelectric coupling under an external electric field. Furthermore, for the bilayer of NiX 2 , our results show that the interlayer coupling is quite weak, indicating the possibility of tuning the magnetic coupling through external manipulations.

Tunable spin-polarized band gap in Si2/NiI2 vdW heterostructure

“…The SOC effects in the ground states of metal dihalide systems (layer and bulk) have been recently studied by A. S. Botana and M. R. Norman using state of the art electronic structure calculations. 43 Our results agree with previous calculations, 29,32,43,48 and we also observe that the SOC effects are small. As we will discuss in the next subsection, the properties of the silicene/NiI 2 vdW heterostructure are mainly ruled by cohesive forces and spinpolarized charge transfer.…”

“…These values are in good agreement with previous calculations. 29,30,32 The magnetic structure of the bulk NiI 2 was determined by neutron diffraction, with spins ordered ferromagnetically in each Ni 2+ ion and a magnetic moment of 1.6 m B (ref. 42), and for a single layer the calculated magnetic moment is 2 m B .…”

“…From our analytical calculations, T C is found to be 136.52 K, which is close to the value obtained from Monte Carlo simulations. 30,32 For the NiI 2 bulk system, the electronic band structure calculation yielded fully occupied 5p-iodine and partially lled 3d-nickel sub-bands, 45 with the system being a Mott insulator. 46 This was conrmed by photoconductivity measurements showing an indirect transition and an energy band gap of 1.8 eV.…”

“…29,30 Bulk metal dihalides have a natural layered structure and theoretical investigations show that layers can potentially be extracted using exfoliation techniques. 31,32 Nickel iodide (NiI 2 ) consists of strongly bonded triple ions (I À , Ni 2+ and I À ) in a hexagonal lattice with a trigonal structure. The layers weakly interact with each other via cohesive forces (vdW interactions).…”

Strain-induced phase transition in CrI3 bilayers

“…The Ising model is widely used to describe the magnetic coupling of low-dimensional magnetic systems [42][43][44] . Herein, we numerically solve the Ising model to calculate the Curie temperature T C .…”