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

The nonautonomous dynamics of spin-torque oscillators in the presence of both microwave current and field at the same frequency can exhibit complex nonisochronous effects. A nonstationary mode hopping between quasiperiodic 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 +/- 2 pi were 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 nonautonomous behavior valid to any nonisochronous auto-oscillator in regime of moderate and large force locking.