Vortex dynamics in confined stratified conditions
  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. 
Farkhad G. Aliev, Juan F. Sierra, Ahmad A. Awad, Gleb N. Kakazei,   Dong-Soo Han, Sang-Koog Kim, Vitali Metlushko, Bojan Ili...