Parametric oscillator based on non-linear vortex dynamics in low   resistance magnetic tunnel junctions
  Radiofrequency vortex spin-transfer oscillators based on magnetic tunnel junctions with very low resistance area product were investigated. A high power of excitations has been obtained characterized by a power spectral density containing a very sharp peak at the fundamental frequency and a series of harmonics. The observed behaviour is ascribed to the combined effect of spin transfer torque and Oersted-Amp\`ere field generated by the large applied dc-current. We furthermore show that the synchronization of a vortex oscillation by applying a ac bias current is mostly efficient when the external frequency is twice the oscillator fundamental frequency. This result is interpreted in terms of a parametric oscillator. 
S. Martin (1), N. de Mestier (1), C. Thirion (2), C. Hoarau (2), Y.   Conraux (3), C. Baraduc (1), and B. Di\'eny (1) ((1) S...
cond-mat.mes-hall