  The magnetized relativistic Fermi and Bose gases are studied at finite
temperature and density.In the case of the Fermi gas, the contribution to the
magnetization from the vacuum becomes dominant for high magnetic fields, when
the thermal contribution saturates.
  In the case of the charged Bose gas, the (paramagnetic) vacuum--magnetization
becomes dominant when the gas changes from a diamagnetic to a paramagnetic
behaviour. We furthermore find that the scalar--QED effective coupling constant
for a weak non--zero external magnetic field is a decreasing function of the
temperature.

High Energy Physics - Phenomenology;High Energy Physics - Theory