  Vortex based spin torque nano oscillators (STVOs) can present more complex
dynamics than the spin torque induced gyrotropic (G) motion of the vortex core.
The respective dynamic modes and the transition between them can be controlled
by experimental parameters such as the applied dc current. An interesting
behavior is the stochastic transition from the G- to a dynamic C-state
occurring for large current densities. Moreover, the C-state oscillations
exhibit a constant active magnetic volume. We present noise measurements in the
different dynamic states that allow accessing specific properties of the
stochastic transition, such as the characteristic state transition frequency.
Furthermore,we confirm, as theoretically predicted, an increase of flicker
noise with $I_{dc}^2$ when the oscillation volume remains constant with the
current. These results bring insight into the potential optimization of noise
properties sought for many potential rf applications with spin torque
oscillators. Furthermore, the investigated stochastic characteristics open up
new potentialities, for instance in the emerging field of neuromorphic
computing schemes.
