N°20 - 23 September 2016 - SELF-INJECTION LOCKING OF A VORTEX SPIN TORQUE OSCILLATOR BY DELAYED FEEDBACK

S. Tsunegi1,2, E. Grimaldi1, R. Lebrun1, H. Kubota2, A. Jenkins1, K. Yakushiji2, A. Fukushima2, P. Bortolotti1, J. Grollier1, S. Yuasa2 and V. Cros1
 
1Unité Mixte de Physique CNRS, Thales and Université Paris Sud, 1 Avenue Fresnel, 91767 Palaiseau, France
2Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Tsukuba, Japan
 
The self-synchronization of spin torque oscillators is investigated experimentally by re-injecting its radiofrequency (rf) current after a certain delay time. We demonstrate that the integrated power and spectral linewidth are improved for optimal delays. Moreover by varying the phase difference between the emitted power and the re-injected one, we find a clear oscillatory dependence on the phase difference with a 2π periodicity of the frequency of the oscillator as well as its power and linewidth. Such periodical behavior within the self-injection regime is well described by the general model of nonlinear auto-oscillators including not only a delayed rf current but also all spin torque forces responsible for the self-synchronization. Our results reveal new approaches for controlling the non-autonomous dynamics of spin torque oscillators, a key issue for rf spintronics applications as well as for the development of neuro-inspired spin-torque oscillators based devices.
 
Scientific Reports 6, 26849 (2016)
 Doi: 10.1038/srep26849
 
 
 
Figure 1: (a) Schematic of the delayed feedback circuit. Power Spectral Density (PSD) spectra at Idc=4.0 mA (b) without re-injection, with re-injection (c) Δt  = 37.6 ns, and (d) Δt = 38.6 ns. (d) Image plot of the PSD spectra at Idc = 4.0 mA.