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.
@article{arxiv.1107.0867,
title = {Parametric oscillator based on non-linear vortex dynamics in low resistance magnetic tunnel junctions},
author = {S. Martin and N. de Mestier and C. Thirion and C. Hoarau and Y. Conraux and C. Baraduc and B. Diény},
journal= {arXiv preprint arXiv:1107.0867},
year = {2013}
}