  The core of the vortex in the Neel order parameter for an easy-plane
antiferromagnet on honeycomb lattice is demonstrated to bind two zero-energy
states. Remarkably, a single electron occupying this mid-gap band has its spin
fragmented between the two sublattices: Whereas it yields a vanishing total
magnetization it shows a finite Neel order, orthogonal to the one of the
assumed background. The requisite easy-plane anisotropy may be introduced by a
magnetic field parallel to the graphene layer, for example. The results are
relevant for spin-1/2 fermions on graphene's or optical honeycomb lattice, in
the strongly interacting regime.
