Tuning Magnetic Properties Of Monolayer MoS₂ By The First-principles Calculation

Molybdenum disulfide（MoS₂）,a typical transition-metal dichalcogenide（TMD）,has attracted extensive interest in recent years due to its unique physical properties and wide applications in electronic transistors,optoelectronic devices,and sensors.Combined with the excellent electronic and optical properties of intrinsic monolayer MoS₂,the realization of tunable magnetic properties in monolayer MoS₂ is important for expanding the application in spintronic devices,and magneto-optical nanodevices,etc.Therefore,the exploration of experimentally feasible magnetic modulation of monolayer MoS₂ has attracted great attention.At present,monolayer MoS₂ can be successfully fabricated by various experi-mental methods,such as mechanical exfoliation,molecular beam epitaxy,and vapor deposition.However,there are different density vacancies（V_S）on the monolayer MoS₂ surface,which provide the opportunity to induce localized magnetism by dop-ing in MoS₂.The experimental progress of MoS₂ based van der Waals heterojunctions also provides the possibility to realize long-range ordered magnetism.In this work,we have studied the tunable magnetic properties of monolayer MoS₂ by doping and by van der Waals vertical heterojunction using first-priciples calculations.Our main works are listed as follows:（1）Tunable magnetic properties of monolayer MoS₂ by doping.Firstly,magntic properties of monolayer MoS₂ doped with light atoms of IIIA,IVA and VA have been studied.The results show that Al-,N-,P-atoms doping can induce magnetic moments in intrinsic materials,while Si-,Ge-,and As-atoms doped monolayer MoS₂ systems are non-magnetic.Moreover,the magnetic moments can be switched on and off in the range of strain from-12%to 10%.Secondly,we have studied the electronic properties of monolayer MoS₂ doped with gas molecules CO,NO,H₂O,O₂,N₂,NH₃,and CH₄and it is found that NO and N₂ doping can induce magnetic moments in MoS₂.Meanwhile,all gas molecules doped systems can realize the light absorption in the infrared region.These results indicate that doping can tune the magnetic properties of monolayer MoS₂ effectively,which is helpful for the fabrication of low dimensional spin devices and magnetic switches.（2）Tunable magnetic properties of monolayer MoS₂ by co-doping.Firstly,we have studied Ge（Si）-As co-doping effects in MoS₂.The results shown that Ge（Si）-As co-doping can induce magnetism in monolayer MoS₂,and the magnetic moment gradually disappears with the increase of the co-doping diatomic distance.And we found that the magnetic property is dependent on the interaction between the co-doped atoms.The magnetic moment decreases from 1μ_B to 0μ_B gradually as the distance between the co-doped atoms increases due to the weakening of defect-defect interaction.Secondly,Si-X co-doping causes the polarization charge of the system to transfer from the vicinity of X atom to Si atom.The results show that the interaction between Si-X weakens the orbital hybridization of X atom and the intrinsic material,and enhances the hybridization strength of the Si atom’s spin-splitting state around the Fermi level.Moreover,the biaxial strain causes the phenomenon of magnetic moment transition in the Si-X co-doped system due to the interaction between defects.Our studies not only prove that co-doping is an effective means for magnetic regulation,but also discover a new mechanism for modulating magnetic properties by the de-fect-defect interaction.（3）Non-local magnetic regulation of g-C₄N₃/MoS₂ vertical heterojunction by electric field.The results show that g-C₄N₃/MoS₂ is semi-metallic,and the magnetism is mainly concentrated in the g-C₄N₃ layer.When a positive vertical electric field is applied to g-C₄N₃/MoS₂,the layer spacing decreases with the increase of the forward electric field.At the same time,under the action of light excitation,the g-C₄N₃ layer and MoS₂ layer have the non-local electron transition in the spin up（spin down）channel,which realizes the new phenomenon of spin separation in g-C₄N₃/MoS₂ het-erojunction,and then realizes the non-local magnetic regulation in monolayer MoS₂.