  The magnetic inertial dynamics have been investigated for one sublattice
ferromagnets. Here, we develop the magnetization dynamics in two-sublattice
ferromagnets including the intra- and inter-sublattice inertial dynamics.
First, we derive the magnetic susceptibility of such a ferromagnet. Next, by
finding the poles of the susceptibility, we calculate the precession and
nutation resonance frequencies. Our results suggest that while the resonance
frequencies show decreasing behavior with the increasing intra-sublattice
relaxation time, the effect of inter-sublattice inertial dynamics is
contrasting.
