  The spin-momentum locking of topological states offers an ideal platform to
explore novel magneto-electric effects. These intimately depend on the ability
to manipulate the spin texture in a controlled way. Here, we combine scanning
tunneling microscopy with single atoms deposition to map the evolution of
topological states under the influence of different magnetic perturbations. We
obtain signatures of Dirac fermion-mediated magnetic order for extremely dilute
adatoms concentrations. This striking observation is found to critically depend
on the single adatoms magnetic anisotropy and the position of the Fermi level.
Our findings open new perspectives in spin engineering topological states at
the atomic scale and pave the way to explore novel spin-related topological
phenomena with promising potential for applications.
