First-principles Investigation Of 2D OsI₃ Ferromagnetic Ordering And Half-metallicity Crystal

With the rapid development of science and technology and the demand for miniaturization of electronic devices,it is urgent to develop new electronic devices with higher integration,lower power consumption,faster response speed,higher stability and storage density.Recently,a large number of two-dimensional materials have been studied in theory and experiment.It is found that 2D materials have unique electronic,magnetic and mechanical properties,and excellent physical properties make them an alternative material for new electronic devices.The ideal magnetic materials for spintronic devices should have large magnetic moment,high spin polarizability and high Curie temperature(TC.Magnetic half-metallicityity materials are considered to be promising candidates for spin injection because of their unique band structure,which are different from magnetic metals and magnetic semiconductors.One of the two spin bands shows metallicityity and the other shows semiconductor or insulator properties,which leads to the complete(100%)spin polarizability of electrons near the Fermi level,which is very important for the development of high performance spintronic devices such as spin filters.In this paper,the properties of two-dimensional intrinsic ferromagnetic half-metallicityity OsI₃ crystal materials are systematically studied by first-principles:(1)The monolayer OsI₃ crystal can form three different space groups C2//m,P3112 and R3 bulk by using the interlayer van der Waals interaction and different stacking methods.The calculated results show that the C2/m bulk phase is more stable than the R3 and P3112 space group bulk phase,and the energy is 0.03 ev/OsI₃ and 0.09 ev/OsI₃ lower than that of R3 and P3112 bulk phase,respectively.The calculated cleavage energy of C2/m bulk phase structure is 0.36J/m2,which indicates that the monolayer OsI₃ can be easily exfoliated from its bulk phase.(2)Ferromagnetic monolayer OsI₃ crystal may contain C2/m and symmetry configurations,but the energy of D3d configuration is 0.145 eV/OsI₃ higher than that of C2/m symmetry.In order to verify the dynamic stability of the structure,the phonon spectra of two configurations are calculated.It is found that there is a small virtual frequency in the phonon spectra of D3d symmetry configuration and no virtual frequency in the phonon spectra of C2/m symmetry configuration.From the point of view of energy and dynamic stability,it is proved that the ground state structure of monolayer OsI₃ is C2/m symmetry configuration.The binding energy of the ground state structure is 3.18 eV/OsI₃.Further study on the ferromagnetic stability under biaxial tension/compression showed that the OsI₃ monolayer remained ferromagnetic under biaxial strain ranging from-2%to 5%.At 300K,ab initio molecular dynamics was used to verify the stability of thermal dynamics,and the stability of energy and structure fully proved the rationality of the structure.(3)The monolayer OsI₃ is an intrinsic magnetic half-metal crystal with an indirect band gap(1.83 eV).In order to evaluate the magnetic ground state of the system,the energies of the ferromagnetic(FM)and different antiferromagnetic(AFM-Neel,AFM-zigzag,AFM-strip)configurations are compared.The results show that the energies of the ferromagnetic state are 21.51 meV,11.20 meV and 13.96 meV lower than those of AFM-Neel,AFM-zigzag and AFM-strip,respectively.We revealed that the OsI₃ monolayer has an in-plane magnetization easy axis and a magnetic anisotropy energy of up to 3.89 meV/OsI₃,which is nearly an order of magnitude higher than that of most two-dimensional magnetic materials(such as 2D monolayer OsI₃).By analyzing the electronic structure of the system(PDOS),the intrinsic mechanism of the origin of magnetic properties is fully demonstrated.(4)Based on Ising model,the Curie temperature(Tc),another important parameter of ferromagnetic materials,is evaluated more accurately by Monte Carlo simulation.The Tc of the intrinsic ferromagnetic half-metallicityity monolayer OsI₃ crystal is 35K when considering three kinds of magnetic coupling interactions.Based on the above detailed and in-depth demonstration,the excellent magnetic properties of 2D intrinsic ferromagnetic half-metal OsI₃ crystal reveal that it can be used as a candidate material for spintronics devices.