  We report on linear spin dynamics in the vortex state of the Permalloy dots
subjected to stratified (magnetic) field. We demonstrate experimentally and by
simulations the existence of two distinct dynamic regimes corresponding to the
vortex stable and metastable states. Breaking cylindrical symmetry leads to
unexpected eigenmodes frequency splitting in the stable state and appearance of
new eigenmodes in the metastable state above the vortex nucleation field.
Dynamic response in the metastable state strongly depends on relative
orientation of the external rf pumping and the bias magnetic fields. These
findings may be relevant for different vortex states in confined and stratified
conditions.
