Study Of Electronic Structures And Magnetic Properties For Diluted Magnetic Semiconductors Based On LiZnAs?LiZnP And LaZnAsO

As a very important functional material,the new type of dilute magnetic semiconductor has a broad application prospect.It overcomes the common drawback of charges and spin"binding" effect of tranditional DMS and realizes the separate regulation of charge and spin.In this dissertation,based on the density functional theory calculations and analysis,using CASTEP code in Materials Studio,the electronic structure and magnetic properties of LiZnAs,LiZnP and LaZnAsO based DMS are systematically studied.It provides theoretical support for new type of dilute magnetic semiconductor research.The main contents and conclusions of this paper are as follows:(1)Investigate the electronic structures and magnetic properties of Cr-doped LiZnAs system.The Cr-doped LiZnAs structures with concentration 6.25 at.%is nonmagnetic,while the system favors spin-polarized ground stated with Cr doped concentration up to 12.5 at.%.The magnetic coupling results show that Cr-doped LiZnAs exists the ferromagnetic(FM)stable state.VLi and VZn suppress the ferromagnetism in Cr-doped LiZnAs.And VAs can lead to the FM state more stability.The FM interactions in the Cr-Cr pair can be attributed to the p-d exchange interactions as Cr?-As?-Cr?.(2)Investigate the electronic structures and magnetic properties of Cr-doped LiZnP system..The results indicate that Cr-doped LiZnP structures with Cr concentration 6.25 at.%is magnetic.The magnetic coupling results show that the system exists in the FM stable state and the FM interactions in the Cr-Cr pair can be attributed to the p-d exchange interactions as Cr?-P?-Cr?.VLi act as donor,which increase the carries concentration and thus leads to the FM state more stable.Vzn has less influence on FM stability,and VP weakens FM stability of the system.(3)The electronic structures and magnetic properties for TM-doped LaZnAsO(TM=V,Cr,Mn,Fe,Co and Ni)system are studied.The results show that Ni-doped systems are nonmagnetic and V,Cr,Mn,Fe and Co-doped systems are magnetic.Further results show that Mn and V-doped systems are antiferromagnetic(AFM)stability system,while the Cr,Fe and Co-doped systems are FM stability system.Then using alkaline earth atomic AE(AE=Ca,Sr,Ba)to introduce carriers,using TM to introduce spins,and the spins and carriers in these DMSs can be contralled respectively.Then the influence of the concentration of carriers are studied.In this thesis,TM atom is used to introduce spin to provide magnetic moment,as well as vacancy or AE atom is used to provide carrier to realize the separate regulation of spin and charges.The results show that the introduction of TM atoms enables the magnetic properties of non-magnetic substrates to be displayed externally.The carrier can regulate the coupling state of magnetic atoms.The carrier concentration is not the more the better,too much carriers are detrimental to the ferromagnetic ordering,even inhibiting ferromagnetic.It requires a balance between carriers and spins to achieve the best ferromagnetic ordering.