First-principles Study Of ZnO Doped With Transition Metal Atoms

Diluted magnetic semiconductors(DMS)materials with magnetic and properties of semiconductor have attracted much attention.The half-metal(HM)material is widely used in spintronics devices because of its 100%spin polarization and only a single directional spin electron at its Fermi energy level.As an II-IV wide-band-gap semiconductor material,ZnO is considered to be a promising material for the preparation of magnetic materials at room temperature,due to its excellent dielectric and optical properties.Moreover,there are many reports have shown that the transition metal(TM)atoms doped ZnO system can exhibit excellent HM properties.In recent years,there are some reports on the TM atoms doping semiconductor clusters but no systematic study on Cr doping(ZnO)12 clusters.In this paper,the structural,electronic,magnetic and optical properties of TM atom doped ZnO systems as well as the structural,electronic,magnetic properties of Cr atom doped(ZnO)12 clusters are investigated by using the first-principles method.Conclusions as follows:Firstly,the structural,electronic,magnetic and optical properties of the Zn1-xNixO(x=0.00,0.25,0.50,0.75,1)systems have been investigated by using first-principles calculations.Excepting Zn0.5Ni0.5O with tetragonal structure,other Zn1-xNixO systems are cubic structure.The Zn0.25Ni0.75O,Zn0.5Ni0.5O,Zn0.75Ni0.25O and NiO systems are completely HM thus usable in spintronic devices.The magnetic moment of the Z1-xNixO systems are mainly contributed by magnetic moment of Ni atom with small contributions of parallel O and Zn atoms.Secondly,the structural,electronic and magnetic properties of the two identical TM atoms M(M=V?Cr?Mn?Fe?Co and Ni)have been investigated by using first-principles calculations.According to the distance between two identical TM atoms to consider six doping(0,i=1 to 6)configuration,finally combining the results with valence electron configuration of TM,we analyze ferromagnetic(FM)and antiferromagnetic(AFM)coupling between two identical TM atoms by using exchange and double exchange mechanism.The FM coupling between two identical M atoms under double-exchange(DE)mechanism leads to V(0,i=1-6),Cr(0,i= 1-6),Fe(0,2)and Ni(0,i=4-6)cases to be HM with integer total magnetic moments of 6,8,8 and 4?B,respectively.While the AFM coupling between two identical M atom under superexchange(SE)mechanism leads to Mn(0,i= 1-6)and Co(0,i= 1-6)cases as well as Fe(0,i?2)and Ni(0,i=1-3)cases to be nonmagnetic semiconductor as well as nonmagnetic metal,respectively.Therefore,the ZnO systems with two Fe or Ni atoms have a competition between SE and DE mechanism.Finally,the structural,electronic and magnetic properties of Cr atom doped(ZnO)12 cluster have been investigated by using first-principles calculations.Compared with the energy gap between highest occupied molecular orbital and the lowest unoccupied molecular orbital(HOMO-LUMO),the HOMO-LUMO gap of the doped clusters are smaller than that of the pure(ZnO)12 clusters.The total magnetic moment of a2 configuration is 6 ?B while the other configurations have nearly total magnetic moments 4 ?B,which may be related to the local environment around the Cr atom.The total magnetic moment of the FM state is 8 ?B and the total magnetic moment of the AFM state is 0,and the HOMO-LUMO gap of the AFM state is slightly larger than that of the FM state for all bidoped configurations(substitutional,exohedral and endohedral bidoped clusters).The magnetic coupling exhibits a competition AFM and FM coupling between two Cr atoms in bidoped configurations.The most important thing is that,in these bidoped configurations,the FM coupling state of the exohedral doped configuration is the most stable,which may be applied in future applications in spin-related nano-devices.