Magnetic Doping And Spin Manipulation Of Two-dimensional Semiconducting Nano Materials From First-principles Study

Two-dimensional semiconductor such as graphyne(GY), Graphdiyne(GDY) andBN sheet show attractive potential in future nanoelectronics due to their uniqueelectronic properties. Transition-Metal(TM) doping can effectively manipulate theelectronic structure and magnetic property of the systems. Such magneticmanipulation can promote the application of these two dimensional syatems inspintronics. In present work, useing first-principles method plus self-consistentHubbard U approach, we systematilly study the manipulation effect of3d transitionmetal on the two dimensional systems. Our studies provide theoretical evidence of thepotential of the two dimensional systems in spintronics. The main results andconclusions can be summarized as follows:(1)3d TM adsorption on the electronic and magnetic properties of GY and GDY.We find that electronic structures of TM-GDY/GY are sensitive to the value ofthe on-site Coulomb energy of the TM3d orbital. Using DFT+U method is crucial toaccurately account for the electron correlation in these materials. By using linearresponse method, we obtain the Ueffvalue for all TM adatoms. We find that theadsorption of TM atom not only efficiently modulates the electronic structures ofGDY/GY system but also introduces excellent magnetic properties, such as spinpolarized half semiconductor. Such modulation originates from the charge transferbetween TM adatom and GDY/GY sheet as well as the electron redistribution of theTM intra-atomic s, p, and d orbitals. Our results indicate that the TM adsorbedGDY/GY are excellent candidates for spintronics;(2) Magnetic Exchange Coupling and Anisotropy of3d Transition Metal Nanowireson GY.Applying two-dimensional monolayer materials in nanoelectronics andspintronics is hindered by the lack of ordered and separately distributed spinstructures. We investigate the electronic and magnetic properties of one-dimensionalzigzag and armchair3d transition metal (TM) nanowires on GY. The3d TMnanowires are favorably formed on graphyne (GY) surfaces. TM atoms separately andregularly embed within GY, achieving long-range magnetic spin ordering. TMexchange coupling of the zigzag and armchair nanowires is mediated by sp-hybridizedcarbon, and results in long-range magnetic order and magnetic anisotropy due to the super-exchange interaction of the TM atoms. These results indicate that GY is thechoice template to realize ordered and separately distributed spin structures forspintronics.(3) Spin Switch of Transition-Metal Doped Boron Nitride Sheet through H/FChemical DecorationThe effects of H/F chemical decoration on the spin switch of single TM dopedboron nitride (BN) sheet are systematically studied using DFT+U method. It is foundthat the ground spin state of TM embedded in BN sheet is sensitive to the value of theon-site Coulomb energy. Interestingly, we find that the spin of Fe-BN system isswitched from spin ON (S=5/2) to spin OFF (S=0) for H decoration, and from spin high (S=2) to spin low(S=1/2) for H decorated Mn-BN and F decoratedCo-BN system. Such spin state switching opens a new route to realize the applicationsof TM doped BN in spintronics and quantum information.(4) Two-dimensional antiferromagnet half-semiconductor and spin gaplesssemiconductors with zero magnetic moments.We propose a concept of half semiconductor antiferromagnets in which fullyspin polarized valence and conduction bands belong to the same spin channel withcompletely compensated spontaneous magnetization. Using DFT+U, we find a viableapproach to achieve the half semiconductor antiferromagnets through the transitionmetal (TM) Fe and Cr codoped boron nitride (BN) sheet. Moreover, spin gaplesssemiconductor antiferromagnets with zero magnetic moment are also achieved in suchsystems.