Department of Chemistry, National University of Singapore, Singapore 117543.
J Chem Phys. 2013 Mar 28;138(12):124709. doi: 10.1063/1.4795500.
The coadsorption of hydrogen and transition metal dimers Fe2, Co2, Ni2, and FeCo on graphene is investigated using density functional theory calculations. Our work is motivated by observations that the magnetic moments of these transition metal dimers are large and that hydrogen adsorption partitions the graphene lattice into magnetic subdomains. Thus, we expect the magnetic dimers to interact strongly with the lattice. Our results show that the majority-spin direction of the lattice electronic states depends upon the dimer identity, the lattice spin polarization being in the same direction as the dimer spin polarization for Fe2 and FeCo, but opposite for Co2 and Ni2. We can understand this by examining the electronic density of states of the dimer and the lattice. We also show that coadsorption significantly increases the adsorption energies of both dimer and hydrogen leading to a more strongly-adsorbed dimer, while the bond length and magnetic moment of the upper dimer atom, the latter important for potential magnetic storage applications, are negligibly changed. Our work shows that the coadsorbed hydrogen and metal dimer interact over a long-range, this interaction being mediated by the hydrogen-induced spin-polarization of the graphene lattice. We obtain general insight into how the elemental identity of these magnetic dimers determines the spin-polarized states on the hydrogenated graphene lattice. These results could be important for potential applications of magnetic properties of decorated graphene lattices.
使用密度泛函理论计算研究了氢和过渡金属二聚体 Fe2、Co2、Ni2 和 FeCo 在石墨烯上的共吸附。我们的工作是受到以下观察结果的启发：这些过渡金属二聚体的磁矩很大，并且氢吸附将石墨烯晶格分成磁子域。因此，我们预计磁性二聚体将与晶格强烈相互作用。我们的结果表明，晶格电子态的主要自旋方向取决于二聚体的身份，晶格自旋极化与 Fe2 和 FeCo 的二聚体自旋极化方向相同，但与 Co2 和 Ni2 的相反。通过检查二聚体和晶格的电子态密度，我们可以理解这一点。我们还表明，共吸附显着增加了二聚体和氢的吸附能，导致更强烈吸附的二聚体，而上部二聚体原子的键长和磁矩（对于潜在的磁存储应用很重要）几乎没有变化。我们的工作表明，共吸附的氢和金属二聚体在长程范围内相互作用，这种相互作用是由氢诱导的石墨烯晶格的自旋极化介导的。我们获得了关于这些磁性二聚体的元素身份如何决定氢化石墨烯晶格上的自旋极化态的一般见解。这些结果对于修饰石墨烯晶格的磁性的潜在应用可能很重要。
