  An antiferromagnetic order breaking simultaneously the time-reversal and
space-inversion symmetries in topological insulators might give rise to
dynamical axion-like fields in the form of longitudinal spin waves. The
consequences of the associated axion-polariton state on the thermal radiation
are investigated. Planck's radiation law is shown to exhibit remarkable
anisotropic behavior as a result of the strong refraction caused by the
heat-matter interaction. A crossover scenario at low temperature is identified
and an associated regime in which the system's internal energy does not scale
with the traditional fourth power of the temperature is revealed. We show that
the polarization purity of the heat radiation and its angular distribution can
be controlled via the magnetic field, paving the way toward a
directional-tunable mechanism for thermal quanta manipulation and storage.
