Recent Publications

Elton J Santos

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  1. Title: First-principles study of substitutional metal impurities in graphene: structural, electronic and magnetic properties

    Author(s): Santos E.J.G., Ayuela A., D Sánchez-Portal D.

    New Journal of Physics, 12, pp. 053012- (May 2010)

    doi: 10.1088/1367-2630/12/5/053012

    We present a theoretical study using density functional calculations of the structural, electronic and magnetic properties of 3d transition metal, noble metal and Zn atoms interacting with carbon monovacancies in graphene. We pay special attention to the electronic and magnetic properties of these substitutional impurities and find that they can be fully understood using a simple model based on the hybridization between the states of the metal atom, particularly the d shell, and the defect levels associated with an unreconstructed D3h carbon vacancy. We identify three different regimes associated with the occupation of different carbon–metal hybridized electronic levels: (i) bonding states are completely filled for Sc and Ti, and these impurities are non-magnetic; (ii) the non-bonding d shell is partially occupied for V, Cr and Mn and, correspondingly, these impurities present large and localized spin moments; (iii) antibonding states with increasing carbon character are progressively filled for Co, Ni, the noble metals and Zn. The spin moments of these impurities oscillate between 0 and 1μB and are increasingly delocalized. The substitutional Zn suffers a Jahn–Teller-like distortion from the C3v symmetry and, as a consequence, has a zero spin moment. Fe occupies a distinct position at the border between regimes (ii) and (iii) and shows a more complex behavior: while it is non-magnetic at the level of generalized gradient approximation (GGA) calculations, its spin moment can be switched on using GGA+U calculations with moderate values of the U parameter.

  2. Title: Magnetism of substitutional Co impurities in graphene: Realization of single π vacancies

    Author(s): Santos E.J.G., Sánchez-Portal D., Ayuela A.

    Physical Review B, 81, No. 12, pp. 125433- (26 March 2010)

    doi: 10.1103/PhysRevB.81.125433

    We report ab initio calculations of the structural, electronic, and magnetic properties of a graphene monolayer substitutionally doped with Co (Cosub) atoms. These calculations are done within density-functional theory using the generalized gradient approximation. We focus in Co because among traditional ferromagnetic elements (Fe, Co, and Ni), only Cosub atoms induce spin polarization in graphene. Our results show the complex magnetism of Co substitutional impurities in graphene, which is mapped into simple models such as the π-vacancy and Heisenberg model. The links established in our work can be used to bring into contact the engineering of nanostructures with the results of π models in defective graphene. In principle, the structures considered here can be fabricated using electron irradiation to create defects and depositing Co at the same time.