Spin filtering in graphene junctions with Ti and Co adsorbates

Organic materials have recently demonstrated their potentiality for applications in molecular spintronics due to their electronic and magnetic properties that, for some aspects, differentiate from those of the conventional inorganic metals and semiconductors. Carbon-based structures have been investigated as possible spintronics components [1,2], exploiting the possibility of inducing and controlling magnetism in graphene. The adsorption of transition metals (TM) is one of the most appealing techniques [3,4] because it can turn graphene into a half-metal [5]. We will analyze the spin-dependent current and spin-filtering efficiency of a graphene sheet adsorbed with TM atoms (Ti and Co), from first principles. Our calculation, exploiting the Non-Equilibrium Green's Function (NEGF) formalism implemented in TranSIESTA [6], shows that the adsorption of transition metal atoms on graphene induces the opening of a gap in the transmission function in one spin channel only. Charge carriers flowing through the nanojunction in Ti@graphene and Co@graphene belong almost entirely to the minority and majority spin component, respectively. This gives rise to a spin polarization of the current of about 100%. Also the analysis of the non equilibrium electron density distribution indicates that a spin separation between the left and the right portions of the device occurs. This strong spin asymmetry suggests that transition metal adatoms have the potential of turning graphene into an efficient spin-filtering device.[6] References [1] J. Guo, J. D. Gunlycke, C. T. White, Appl. Phys. Lett. 92 163109 (2008). [2] K. Tsukagoshi, B. W. Alphenaar, H. Ago, Nature 401 572 (1999). [3] K. T. Chan, J. B. Neaton, M. L. Cohen, Phys. Rev. B 77 195434 (2008). [4] M. Manadè, F. Vi?es, F. Illas, Carbon 95 525 (2015). [5] E. del Castillo, F. Cargnoni, S. Achilli, G. Tantardini, M. I. Trioni, Surf. Sci. 634 62 (2015). [6] E. del Castillo, S. Achilli, F. Cargnoni, D. Ceresoli, R. Soave, M. I. Trioni, Chem. Phys 478 91 (2016).