Non-Adlerian phase slip and non stationary synchronization of spin-torque oscillators to a microwave source

The nonautonomous dynamics of spin-torque oscillators in presence of both microwave current and field at the same frequency can exhibit complex non-isochronous effects. A non-stationary mode hopping between quasi-periodic mode (frequency pulling) and periodic mode (phase locking), and a deterministic phase slip characterized by an oscillatory synchronization transient (non-Adlerian phase slip) after the phase jump of ±2p have been predicted. In the latter effect, a wavelet based analysis reveals that in the positive and negative phase jump the synchronization transient occurs at the frequency of the higher and lower sideband frequency respectively. The non-Adlerian phase slip effect, even if discovered in STOs, is a general property of non-autonomous behavior valid to any non-isochronous auto-oscillator in regime of moderate and large force locking.