Abstract

Using first-principles electronic-structure calculations, we studied the structural and magnetic properties of
various hydrogen clusters, including hydrogen monomer, dimers, trimers, tetramers, and hexamers adsorbed on
a graphene surface. The magnetic behaviors of such defective systems were shown to strongly depend on the
geometrical configuration of hydrogen atoms. The stability of the structures was demonstrated to be dependent
on two important factors: the distance between hydrogen atoms and the strength of exchange couplings
between the defect-induced magnetic moments. For the magnetic structures, the electron spins populate the
quasilocalized pz-type states on specific carbon atoms. The presence of such quasilocalized pz-type states was
shown to yield relatively strong hyperfine couplings at particular carbon sites in the neighborhood of hydrogen
atoms.