  We investigate the Casimir effect at finite temperature for a charged scalar
field in the presence of an external uniform and constant magnetic field,
perpendicular to the Casimir plates. We have used a boundary condition
characterized by a deformation parameter $\theta$; for $\theta=0$ we have a
periodic condition and for $\theta=\pi$, an antiperiodic one, for intermediate
values, we have a deformation. The temperature was introduced using the
imaginary time formalism and both the lagrangian and free energy were obtained
from Schwinger proper time method for computing the effective action. We also
computed the permeability and its asymptotic expressions for low and high
temperatures.
