Magneto-electronics Properties Of Net-Y Nanoribbons And Magnetism In CrI₃/SiC Van Der Waals Heterostructures

With the size of electronics devices approaching physical limitation,nanoelectronics has attracted great attention.A bloom of research activities in the field of nanomaterial and nanoelectronics have been witnessed after graphene was successful fabricated.Due to the exceptional electronic properties,it has been intensely studied in the condensed matter physics and material field.It suggests that carbon will play a crucial role in the progress of nanoelectronics and replacing silicon to become dominant materials for the next generation devices.However,graphene is a zero band-gap semi-metal,it can not achieve the function of"off" in field-effect transistors(FETs),severely limiting its applications in nanoelectronics devices.Fortunately,inspired by graphene,a variety of two dimension(2D)materials have been predicted theoretically and synthesized in experiments.This work is conducted by the first-principles method which based on the density functional theory(DFT),studies magneto-electronic properties of nanoribbons derived from a novel planar 2D carbon allotrope net-Y and investigates magnetism in CrI3/SiC van der Waals Heterostructures.In the first chapter,we represent the discovery and research background of novel 2D materials such as graphene or graphene-like,including h-BN monolayer,silicene,carbon allotrope net-Y and typically focused on CrI3.In the second chapter,intrinsic net-Y nanoribbons were investigated,special attention will be given to the structure stability,electronic and transport properties,especially on the physical field coupling effects of electronic behaviors.The very high stability is predicted for various types of nanoribbons by the calculated binding energy and molecular dynamics simulation.Different edge-shape and widths have a significant influence on their electronic properties.Armchair nanoribbons are always semiconductors.After hydrogen termination,some metallic nanoribbons can become semiconductors or quasi-metals with massless Dirac-fermion behavior.In particular,the electronic properties of ribbons can be effectively modulated by applying strain and electric field.The band gap size and the transition from indirect to direct band gap can be realized upon strain or electric field.These flexibly tunable electronic properties for nanoribbons expand their applications in nanoelectronics and optoelectronics.In the third chapter,we report theoretical investigations on structural stability and magneto-electronic properties,focusing on electric-magnetic and mechano-magnetic coupling effects,for the net-Y armchair nanoribbons doped with low-concentration transition metal(TM)atoms(Mn,Ni,Fe,Co,V).The calculated binding energy and molecular dynamics simulation display that all the ribbons have a higher stability.Particularly,these ribbons present rich magnetic features and different TM atom doping can make an intrinsic non-magnetic semiconducting ribbon converted to a bipolar magnetic semiconductor(BMS),a half metal(HM),or a spin-degenerate magnetic semiconductor(MSC).Their magnetism is flexibly tunable by applying a transverse electric field or stretched strain.For example,a low electric field can regulate the ribbon into the HM phase,and the mechanic strain can realize a continuous magnetic phase transition among BMS,magnetic metal(MS),MSC,HM,and half semiconductor(HSC).These findings suggest that the TM-doped net-Y ribbon possesses a favorable and flexible tunable magnetism,which might have wide potential in applications for developing magnetic nano-devices.At the last chapter,this research pays attention to the magnetism of CrI3/SiC van der Waals(vdW)heterojunction.Due to the monolayer of CrI3 possess long-range ferromagnetic(FM)order,it is desirable in applications.However,the Curie temperature(Tc)of this monolayer is low(-45K)for practical purpose.We prompt the magnetic moments(MM)and Tc of this vdW heterojunction and managed to further enhance the magnetism by applying mechanic strain or electric filed.The results show that when a heterojunction was composited,the Tc increased as well as induced magnetism in SiC monolayer.Moreover,as the interlayer gap decreases,the MM of both two layers increase and the Tc enhanced further.Besides,by applying electric filed,the total magnetic moment changed to a higher values and in a specific range the object maintains a half metal behavior.The results provide a new method for expanding 2D magnets.This discovery has great potential for flexible and practical magnetoelectronic devices.