  We study the axion in three-dimensional topological insulators with magnetic
impurities under finite temperature. We find a stable antiferromagnetic ground
state and ferromagnetic metastable state. In both magnetic states, the mass of
the axion is found to be up to eV scale and it approaches zero near the phase
boundary of the magnetic state. This result applies to both normal and
topological insulator phases, i.e., the axion mass is insensitive to the
topological states, and it will have a direct impact on the targeted mass range
of particle axion dark matter in future experiments.
