  We study the dynamics of Josephson junctions with a thin ferromagnetic layer
F [superconductor-ferromagnet-insulator-ferromagnet-superconductor (SFIFS)
junctions]. In such junctions, the phase difference $\phi$ of the
superconductors and magnetization $M$ in the F layer are two dynamic parameters
coupled to each other. We derive equations describing the dynamics of these two
parameters and formulate the conditions of validity. The coupled Josephson
plasma waves and oscillations of the magnetization $M$ affect the form of the
current-voltage ($I$-$V$) characteristics in the presence of a weak magnetic
field (Fiske steps). We calculate the modified Fiske steps and show that the
magnetic degree of freedom not only changes the form of the Fiske steps but
also the overall view of the $I$-$V$ curve (new peaks related to the magnetic
resonance appear). The $I$-$V$ characteristics are shown for different lengths
of the junction including those which correspond to the current experimental
situation. We also calculate the power $P$ absorbed in the system if a
microwave radiation with an ac in-plane magnetic field is applied (magnetic
resonance). The derived formula for the power $P$ essentially differs from the
one which describes the power absorption in an isolated ferromagnetic film. In
particular, this formula describes the peaks related to the excitation of
standing plasma waves as well as the peak associated with the magnetic
resonance.
