  We examine the Casimir free energy and pressure of magnetic metal films,
which are free-standing in vacuum, sandwiched between two dielectric plates,
and deposited on either nonmagnetic or magnetic metallic plates. All
calculations are performed using both the Drude and plasma model approaches to
the Lifshitz theory. According to our results, the Casimir free energies and
pressures calculated using both theoretical approaches are significantly
different in the magnitude and sign even for thin films of several tens of
nanometers thickness. Thus, for the Ni film of 47\,nm thickness deposited on a
Fe plate the obtained magnitudes of the Casimir free energy differ by the
factor of 5866. We show that the Casimir free energy and pressure of a magnetic
film calculated using the plasma model approach do not possess the classical
limit, but exponentially fast drop to zero with increasing film thickness. If
the Drude model approach is used, the classical limit is reached for magnetic
films of about 150\,nm thickness, but the Casimir free energy remains nonzero
in the limit of ideal metal, contrary to expectations. For the plasma model
approach the Casimir free energy of a film vanishes in this case. Numerical
computations are performed for the magnetic films made of Ni, nonmagnetic
plates made of Cu and Al, and magnetic plates made of Fe using the tabulated
optical data for the complex indexes of refraction of all metals. The obtained
results can be used for a discrimination between the plasma and Drude model
approaches in the Casimir physics and in the investigation of stability of thin
films.
