  The mutual interaction between the different eigenmodes of a spin-torque
oscillator can lead to a large variety of physical mechanisms from mode hopping
to multi-mode generation, that usually reduce their performances as
radio-frequency devices. To tackle this issue for the future applications, we
investigate the properties of a model spin-torque oscillator that is composed
of two coupled vortices with one vortex in each of the two magnetic layers of
the oscillator. In such double-vortex system, the remarkable properties of
energy transfer between the coupled modes, one being excited by spin transfer
torque while the second one being damped, result into an alteration of the
damping parameters. As a consequence, the oscillator nonlinear behavior is
concomitantly drastically impacted. This efficient coupling mechanism, driven
mainly by the dynamic dipolar field generated by the spin transfer torque
induced motion of the vortices, gives rise to an unexpected dynamical regime of
self-resonance excitation. These results show that mode coupling can be
leveraged for controlling the synchronization process as well as the frequency
tunability of spin-torque oscillators.
