  We deal with Dirac operators with external homogeneous magnetic fields.
Hardy-type inequalities related to these operators are investigated: for a
suitable class of transversal magnetic fields, we prove a Hardy inequality with
the same best constant as in the free case. This leaves naturally open an
interesting question whether there exist magnetic fields for which a Hardy
inequality with a better constant than the usual one, in connection with the
well known diamagnetic phenomenon arising in non-relativistic models.
