  The influence of magnetic dopants on the electronic and chemical environments
in topological insulators (TIs) is a key factor when considering possible
spintronic applications based on topological surface state properties. Here we
provide spectroscopic evidence for the presence of distinct chemical and
electronic behavior for surface and bulk magnetic doping of Bi2Te3. The
inclusion of Mn in the bulk of Bi2Te3 induces a genuine dilute ferromagnetic
state, with reduction of the bulk band gap as the Mn content is increased.
Deposition of Fe on the Bi2Te3 surface, on the other hand, favors the formation
of iron telluride already at coverages as low as 0.07 monolayer, as a
consequence of the reactivity of the Te-rich surface. Our results identify the
factors that need to be controlled in the realization of magnetic nanosystems
and interfaces based on TIs.
