▎ 摘　　要

One of the possible ways to introduce magnetism in graphene is to trap highly mobile transition metal atoms at defect sites in graphene. In this paper, based on Born-Oppenheimer molecular dynamics simulations, we investigated the self-assembly of transition metal hexamers X-6 (X = Cr, Mn, and Fe) on graphene with mono/divacancy defects and studied the fundamental electronic and magnetic properties of the resulting X-6 clusters on graphene. Interestingly, the ground state Cr-6 and Fe-6 hexamers on divacancy defects in graphene show quite small energy differences between in-plane and out-of-plane magnetism. By applying external electric fields, the easy axis of magnetization can be switched between in-plane and out-of-plane, which demonstrates potential applications in electric field-assisted magnetic recording and quantum computing.