Decoherence and mode-hopping in a magnetic tunnel junction-based   spin-torque oscillator
  We discuss the coherence of magnetic oscillations in a magnetic tunnel junction-based spin-torque oscillator as a function of external field angle. Time-frequency analysis shows mode-hopping between distinct oscillator modes, which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert equation, analogous to mode-hopping observed in semiconductor ring lasers. These couplings and therefore mode-hopping are minimized near the current threshold for antiparallel (AP) alignment of free layer with reference layer magnetization. Away from the AP alignment, mode-hopping limits oscillator coherence. 
P. K. Muduli, O. G. Heinonen, and J. {\AA}kerman
cond-mat.mtrl-sci cond-mat.mes-hall cond-mat.other