1. Address: 2401 East building Guanghua tower Email: 081019003@fudan.edu.cn081019003@fudan.edu.cn Phone: 55665244 Magnetic and spin polarized transport properties in zigzag- edged graphene nanoflakes were in- vestigated from first- principles calculations. Ferrimagnetic structure was found to be the ground state for triangular shaped graphene flakes. Magnetism is weakened by doping B or N atoms into the flakes, and it is enhanced if F atoms are doped in certain sub- lattice of the flakes. The magnetic properties can be rationalized by the behaviors of dopants as well as interactions between dopants and the host atoms. Perfect (100%) spin filtering effect was achieved for the pure or B-doped graphene flake sandwiched between two gold electrodes. The orientation of the spin current is found to be flipped if the flake is doped with N, O, or F atoms. The orientation- tunable spin filtering effect is potentially useful in practical applications. Magnetism and perfect spin filtering effect in graphene nanoflakes Wei Sheng and Zhongqin Yang Department of physics, Fudan University, Shanghai 200433, China INSERT YOUR ORGANIZATION’S LOGO HERE Perfect spin filtering effect with majority states conduction have been found for pure flakes or flakes doped with B atoms. See Fig. 2 and 3. The increase of transmission with B and N doping can be understood by the movement of the Ef due to doping: more states appear at or near Ef due to doping which can increase transmission. Structural optimization: Vienna Ab- initio Simulation Package. Non-equilibrium transport calculation: First-principle computation package MATDCAL. Self-consistent NEGF-DFT: Construct density matrix away from equilibrium via NEGF: For pure tri-GNFs, a ferrimagnetic structure is the ground state. Both B and N can reduce the net magnetic moment of the sample, while F doped in A sublattice can increase magnetism. The conductivity of the flakes can be improved significantly after doping. Perfect spin filtering effect with majority or minority states conduction is found for pure flakes and flakes doped with B or N and F atoms. Our results suggest a novel and perfect spin filtering effect whose spin conduction channel can be controlled by doping. which should be very helpful in realizing an all-carbon spin source for molecular spintronics. Since the successful experimental isolation of graphene - a single atomic layer of graphite, Graphene based materials have attracted enormous attention in the literature. Motivation Calculation 1. K. S. Novoselov et al., Science 306, 666 (2004). 2. Y. Zhang et al., Nature (London) 438, 201 (2005). 3. T. B. Martins et al., Phys. Rev. Lett. 98, 196803 (2007). CONCLUSIONS DISCUSSIONRESULTS REFERENCES Doping sites B M △ E N M △ E O M △ E F M △ E Site 13.0 2903.0 2762.0 2061.0 453 Site 23.0 2493.0 3084.0 3515.0 706 Site 33.0 2423.0 3322.0 1741.0 303 Site 43.0 2603.0 3224.0 3835.0 809 Table 1. The calculated net magnetic moments (M, in uB) for 6- GNFs with substitutional B, N, O, and F atoms doped at four different sites depicted in Fig. 1(a). Figure 4. Transmission spectrum for 6-GNFs with O and F atoms doped at the positions labeled in Fig. 1(b). ABSTRACT CONTACT Experimentally, fabrications of graphene with sizes from several tens of nanometers down to two nanometers have been achieved recently. Transmission coefficient: The current is calculated by the Landauer-Buttiker formula. Our Model: All-carbon GNR based FETs has been successfully fabricated now. Figure 5. The calculated total density of states of the three sized pure GNFs. The transmission at Ef increase substantially after B(N) doping. Figure 3. Transmission spectrum for 6-GNFs with B and N atoms doped at the positions labeled in Fig. 1(b). Figure 2. Transmission spectrum of pure 4, 6, 8- GNFs sandwiched between Au electrodes. For GNFs doped with N atom only the minority channel is conductive and the majority states are insulating. Figure 6. The DOS of the doped 6-GNF with substitutional atoms for carbon atom at different sites. Figure 1