Synchronization of spin Hall nano-oscillators to external microwave signals

Abstract

Recently, a novel type of spin-torque nano-oscillators driven by pure spin current generated via the spin Hall effect was demonstrated. Here we report the study of the effects of external microwave signals on these oscillators. Our results show that they can be efficiently synchronized by applying a microwave signal at approximately twice the frequency of the auto-oscillation, which opens additional possibilities for the development of novel spintronic devices. We find that the synchronization exhibits a threshold determined by magnetic fluctuations pumped above their thermal level by the spin current, and is significantly influenced by the nonlinear self-localized nature of the auto-oscillatory mode.

Kinetic theory of spin-polarized systems in electric and magnetic fields with spin-orbit coupling. II. RPA response functions and collective modes

“…The Zeeman field is reported to trigger a transition from a charge density wave to a spin density wave 34 . Quite promising for technological applications turns out the possibility to create magnetic nanooscillations by pure spin currents 35 . The spin current can be converted into a terahertz electromagnetic pulse due to the inverse spin Hall effect 36 .…”

Spin Torque Study of the Spin Hall Conductivity and Spin Diffusion Length in Platinum Thin Films with Varying Resistivity

“…The spin Hall effect (SHE) [1][2][3], in which a transverse spin current density SHE j is induced by a longitudinal charge current density e j and whose strength is characterized by the spin Hall ratio SH SHE (2 / ) / e e j j θ ≡ h , has recently drawn much attention because of its promise for spintronics applications [4][5][6][7][8][9][10][11][12][13]. Mechanisms which might give rise to the SHE [14,15] include the intrinsic SHE [1,16], side-jump scattering [17] and skew scattering [18].…”

Low operational current spin Hall nano-oscillators based on NiFe/W bilayers

“…To date, most SHNOs have been based on NiFe/ Pt, 2,[13][14][15][16][17][18][19][20] YIG/Pt, 21,22 and CoFeB/Pt, 23 with SOT produced by a Pt layer. Many other heavy metals, such as W, 10,11 IrCu, 24,25 and CuBi, 26 have however been investigated, revealing that the so-called spin Hall angle (h SH ), which describes the charge current to spin current conversion efficiency, can exceed that of Pt.…”

“…We find a large negative value of h SH ¼ À0.385 and a corresponding dramatic reduction of the SHNO threshold current by over 60% compared to Pt-based SHNOs. 2,[13][14][15][16][17][18][19][21][22][23] All thin films were deposited at room temperature on cplane sapphire substrates using magnetron sputtering in a 2.5 mTorr Ar atmosphere, in an ultra-high vacuum (base pressure below 1 Â 10 À8 mTorr) AJA Orion 8 sputtering system. First we carried out a detailed study of the thickness dependence of the W film resistivity in films deposited at a rate of 0.07 Å /s.…”