Embedding transition-metal atoms in graphene: structure, bonding, and magnetism.

We present a density-functional-theory study of transition-metal atoms (Sc-Zn, Pt, and Au) embedded in single and double vacancies (SV and DV) in a graphene sheet. We show that for most metals, the bonding is strong and the metal-vacancy complexes exhibit interesting magnetic behavior. In particular, an Fe atom on a SV is not magnetic, while the Fe@DV complex has a high magnetic moment. Surprisingly, Au and Cu atoms at SV are magnetic. Both bond strengths and magnetic moments can be understood within a simple local-orbital picture, involving carbon sp(2) hybrids and the metal spd orbitals. We further calculate the barriers for impurity-atom migration, and they agree well with available experimental data. We discuss the experimental realization of such systems in the context of spintronics and nanocatalysis.

Irradiation-induced magnetism in graphite: a density functional study.

Recent experiments indicate that proton irradiation triggers ferromagnetism in originally nonmagnetic graphite samples while He ion bombardment has a much smaller effect. To understand the origin of irradiation-induced magnetism, we have performed spin-polarized density functional theory calculations of the magnetic properties of the defects which are most likely to appear under irradiation vacancies and vacancy-hydrogen complexes. Both defects are magnetic, but as for the latter we find that H adsorption on one of the vacancy dangling bonds gives rise to a magnetic moment double that of the naked vacancy. We show that for small irradiation doses vacancy-hydrogen complexes result in a macroscopic magnetic signal which agrees well with the experimental values.

Magnetic properties and diffusion of adatoms on a graphene sheet.

We use ab initio methods to calculate the properties of adatom defects on a graphite surface. By applying a full spin-polarized description to the system we demonstrate that these defects have a magnetic moment of about 0.5micro(B) and also calculate its role in diffusion over the surface. The magnetic nature of these intrinsic carbon defects suggests that it is important to understand their role in the recently observed magnetism in pure carbon systems.