  In the present study, we investigate a dynamical mode beyond the gyrotropic
(G) motion of a magnetic vortex core in a confined magnetic disk of a
nano-pillar spin torque nano oscillator. It is characterized by the in-plane
circular precession associated to a C-shaped magnetization distribution. We
show a transition between G and C-state mode which is found to be purely
stochastic in a current-controllable range. Supporting our experimental
findings with micromagnetic simulations, we believe that the results provide
novel opportunities for the dynamic and stochastic control of STOs, which could
be interesting to be implemented for example in neuromorphic networks.
