  We have studied the dynamics of a spin-torque nanooscillator's (STNO) phase
locked loop (PLL) generating microwave oscillations in a broad range of
frequencies under the effect of direct current and external magnetic field.
Bifurcations in the system caused by a change in the frequency detuning of
synchronized oscillations are considered. Bands of phase locking and
synchronism are determined. The existence of a phase locking band in the
filterless PLL of STNOs basically distinguishes these oscillators from other
types of microwave generators.
