Large microwave generation from d.c. driven magnetic vortex oscillators in magnetic tunnel junctions A. Dussaux, 1 B. Georges, 1 J. Grollier, 1 V. Cros, 1 A. V. Khvalkovskiy, 1, 2 A. Fukushima, 3 M. Konoto, 3 H. Kubota, 3 K. Yakushiji, 3 S. Yuasa, 3 K.A. Zvezdin, 2, 4 K. Ando, 3 and A. Fert 1 Spin polarized current can excite the magnetization of a ferromagnet through the transfer of spin angular momentum to the local spin system. This pure spin-related transport phenomena leads to alluring possibilities for the achievement of a nanometer scale, CMOS compatible and tunable microwave generator operating at low bias for future wireless communications. Microwave emission generated by the persitent motion of magnetic vortices induced by spin transfer effect seems to be a unique manner to reach appropriate spectral linewidth. However, in metallic systems, where such vortex oscillations have been observed, the resulting microwave power is much too small. Here we present experimental evidences of spin-transfer induced core vortex precessions in MgO- based magnetic tunnel junctions with similar good spectral quality but an emitted power at least one order of magnitude stronger. More importantly, unlike to others spin transfer excitations, the thorough comparison between experimental results and models provide a clear textbook illustration of the mechanisms of vortex precessions induced by spin transfer. 1 Abstract arXiv:1001.4933v1 [cond-mat.mtrl-sci] 27 Jan 2010 $^{1}$Unit´ e Mixte de Physique CNRS/Thales and Universit´ e Paris Sud 11, 1 ave A. Fresnel, 91767 Palaiseau, France $^{2}$A.M. Prokhorov General Physics Institute of RAS, Vavilova str. 38, 119991 Moscow, Russia $^{3}$National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan $^{4}$Istituto P.M. s.r.l., via Cernaia 24, 10122 Torino, Italy