Effects Of Defects On Geometric Structure, Electronic And Magnetic Properties Of Monolayer MoSi₂N₄

Synthesizing two-dimensional(2D)van der Waals(vd W)materials without known 3D layered parents would provide a huge opportunity for engineering materials with new attribute and functionality.The experimentally fabricated recently Mo Si₂N₄compound that represents a milestone in development of 2D materials,a novel synthetic2D vd W layered material,are attracting great interest in the optoelectronics,valleytronics,spintronics,etc.Despite an increasing theoretical exploration toward Mo Si₂N₄ monolayer recently,to date the effect of defect on its physical properties has not yet been investigated.Besides,such work is significant to understand the natures of Mo Si₂N₄ compound and develop its practical application further.In this paper,the effect of four types of defects(O_Nout,O_Nin,V_Nout and V_Nin)on the structural,electronic and magnetic properties of Mo Si₂N₄ monolayer was investigated using first-principles calculations based on density functional theory.The calculated results reveal that all the four types of defects lead to structural distortions around the O-dopant or N-vacancy,and thereby change the lattice parameter and monolayer height.Specifically,O_Nout or O_Nin increases the lattice parameter,but V_Nout or V_Nin is on the contrary.O_Nout or V_Noutincreases the monolayer height,whereas the height decreases for O_Nin or V_Nin.Each of the four types of defects has a fundamental effect on the electronic properties of Mo Si₂N₄ monolayer,which can induce a transition from semiconductor to metal.Moreover,all the O_Nout,O_Nin and V_Nin have a marginal effect on the spin-orbit coupling in Mo Si₂N₄ monolayer.O_Nout or V_Nout has no effect on the magnetic properties of Mo Si₂N₄ monolayer,whereas O_Nin or V_Nin plays an essential role in the occurrence of a transition from non-magnetism to ferrimagnetism in Mo Si₂N₄ monolayer.The effect of biaxial strain on the magnetic properties of the two systems with O_Nin and V_Nin was subsequently investigated.It is found that the total magnetic moments are less sensitive to biaxial strain whereas the local magnetic moments residing on the Mo atoms are increased for the two systems with O_Nin and V_Nin,as strain increases from-3%to 10%and from-9%to 10%,respectively.Furthermore,the magnetic phase transitions between ferrimagnetic and paramagnetic states were found to occur around-4%strain and within the strain range of-10%?-9%for the two systems with O_Nin and V_Nin,respectively.This study may provide a guidance for the application of Mo Si₂N₄monolayer in the spintronic and 2D magnetic materials.