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