  We investigate the synchronization phenomenon between two Spin-transfer
Torque Nano-Oscillators (STNOs) of different frequencies in two pillar systems
under vortex configuration detunings or driving frequencies. The oscillators'
mutual synchronization occurs through magnetic dipolar interaction. Our
micromagnetic simulations show that an amplitude fluctuation referred to as
$\Gamma_p$ has a significant impact on determining the synchronization
frequency. The evolution of frequency and amplitude fluctuation rate in two
different oscillator sizes versus external perpendicular field are compared and
discussed. Our results reveal that the oscillator with lower $\Gamma_p$,
referred to as the "Leader" oscillator, leads the synchronization process. As
such, the "follower" oscillator adjusts its frequency as to that of the
"Leader", thus achieving synchronization. We believe that taking $\Gamma_p$
into consideration can help in controlling synchronization frequencies in
future building blocks of any network multi-array spintronics' devices.
