Characteristic Study On Co,Mn Doped ZnO-based Diluted Magnetic Semiconductors

Spintronic devices can increase the speed of information processing substantially,because of the advantages of small volume,high speed and nonvolatile.As the key material in spintronic devices,diluted magnetic semiconductor(DMS)has raised great attention among the researchers in electronics,physics and material science.ZnO based DMS has the advantages of stable property,abundant resource and the realization of high doping concentration.It has many outstanding properties in the areas of optics,electricity and magnetics.Therefore,ZnO based DMS has become a critical area in the study of DMS.Until now,the theoretical and experimental research has achieved certain progress.However,there are still some problems needed to be solved.For instance,the experiments lack repeatability,the Curie temperature is lower than room temperature and the origin of magnetic mechanism is controversial.Based on this background,to seek the ZnO based DMS with high Curie temperature and investigate the origin of ZnO based DMS,this paper studies the magnetism and electronic properties of Co,Mn doped ZnO.First-principle studies is used basing on density functional theory(DFT).Besides that,this paper also discusses the effect of doping defects and nonmetallic elements into Co-Mn co-doped ZnO.The followings give the main results of this paper:(1)After building a 2×2×2 ZnO supercell,five different configurations of Co doped ZnO and Mn doped ZnO has been studied,at the doping concentration of 12.5%.The calculation results indicate that neither Co doped ZnO nor Mn doped ZnO shows room temperature ferromagnetism.The magnetic stability of the system depends on the doping position of the dopants.The magnetic stability of Co doped ZnO changes as different configurations,while Mn doped ZnO shows antiferromagnetic state in all configurations.From the point of energy,Co doped ZnO and Mn doped ZnO tend to compact configurations.This means the energy of the system has a downward trend as the position of the dopants getting closed.(2)Based on the result of Co doped ZnO and Mn doped ZnO,this paper build a Co-Mn co-doped ZnO model in a compact configuration.The calculation and analytic result shows that the systems become stable ferromagnetism after the co-doping of the two metallic elements.In addition,it has the Curie temperature higher than room temperature.Therefore,Co-Mn co-doped ZnO is an ideal DMS material.The analysis of electronic structure shows that the origin of the ferromagnetism probably comes from the exchange interaction between the 3d electrons in Co,Mn.The 2p electron in the neighbouring O atoms carries this interaction.(3)To study the effects of the common defects and impurities in ZnO based DMS,this paper studies several kinds of properties of Co-Mn co-doped ZnO.The results show that after doping O vacancy,C and N elements into Co-Mn co-doped ZnO,the systems become antiferromagnetism,instead of the ferromagnetism before.Consequently,the preparation experiment of Co-Mn co-doped ZnO DMS should avoid such dopants.The doping of Zn vacancy improves the magnetic moment of Co-Mn co-doped ZnO,especially to the neighbouring O atoms.However,the magnetic moment of Mn is slightly weakened because of Zn vacancy.The spin splitting of the system mainly comes from the hybridization of Co-3d and Mn-3d.Besides that,the spin splitting of O-2p is greatly strengthened as a result of introducing Zn vacancy.