  We report a strain-controlled tuning of magnetism in
transition-metal-atom-decorated graphene. Our first-principles calculations
demonstrate that strain can lead to a sudden change in the magnetic
configuration of a transition metal (TM) adatom and the local atomic structure
in the sur- rounding graphene layer, which have a dramatic effect on the
effective exchange coupling between neighboring TM atoms. A strong
spin-dependent hybridization between TM d and graphene 1/4 orbital states,
derived from the orbital selection rule of the local lattice symmetry, is
responsible for the determination of the local electronic and magnetic
structure. Our results indicate that the strain can be an effective way to
control the magnetism of atomic-scale nanostructures, where the reliable
control of their magnetic states is a key step for the future spintronic
applications.
