Giant voltage-controlled modulation of spin Hall nano-oscillator damping

Himanshu Fulara,Shun Kanai,Roman Khymyn,Hideo Ohno,Mohammad Zahedinejad,Johan Åkerman,Mykola Dvornik,Shunsuke Fukami

doi:10.1038/s41467-020-17833-x

Abstract

Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for microwave signal generation and oscillator-based neuromorphic computing combining nano-scale footprint, fast and ultra-wide microwave frequency tunability, CMOS compatibility, and strong non-linear properties providing robust large-scale mutual synchronization in chains and two-dimensional arrays. While SHNOs can be tuned via magnetic fields and the drive current, neither approach is conducive to individual SHNO control in large arrays. Here, we demonstrate electrically gated W/CoFeB/MgO nano-constrictions in which the voltage-dependent perpendicular magnetic anisotropy tunes the frequency and, thanks to nano-constriction geometry, drastically modifies the spin-wave localization in the constriction region resulting in a giant 42% variation of the effective damping over four volts. As a consequence, the SHNO threshold current can be strongly tuned. Our demonstration adds key functionality to nano-constriction SHNOs and paves the way for energy-efficient control of individual oscillators in SHNO chains and arrays for neuromorphic computing.

Highlights

Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for microwave signal generation and oscillator-based neuromorphic computing combining nano-scale footprint, fast and ultra-wide microwave frequency tunability, CMOS compatibility, and strong nonlinear properties providing robust large-scale mutual synchronization in chains and twodimensional arrays
The β-phase of W is known to produce large SOT13,31,32 and the thinner CoFeB exposed to MgO layer facilitates the perpendicular magnetic anisotropy (PMA) in the CoFeB layer[33]
There are in general two types of Voltage-controlled magnetic anisotropy (VCMA) effects reported in the literature to tailor the magnetic properties of FM thin films

Summary

Introduction

Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for microwave signal generation and oscillator-based neuromorphic computing combining nano-scale footprint, fast and ultra-wide microwave frequency tunability, CMOS compatibility, and strong nonlinear properties providing robust large-scale mutual synchronization in chains and twodimensional arrays. Our demonstration adds key functionality to nano-constriction SHNOs and paves the way for energy-efficient control of individual oscillators in SHNO chains and arrays for neuromorphic computing. We demonstrate how VCMA can provide strong individual control of the threshold current and the auto-oscillation frequency of nanoconstriction based W(5 nm)/ðCo0:75Fe0:25Þ75B25(1.7 nm)/MgO(2 nm)/AlOx(2 nm) SHNOs with relatively strong interfacial perpendicular magnetic anisotropy (PMA)[9]. When the coupling to the surrounding spin waves increases, the auto-oscillating mode experiences an increasing load due to radiation of magnons into the magnetic leads, which is experimentally observed as strongly increased effective damping in the ST-FMR measurements and an increased threshold current of the SHNOs. The increased frequency tunability and the possibility to turn individual oscillators on/off within a large network will allow for recently suggested oscillator computing approaches to be implemented using voltage-controlled SHNOs

Methods

Results

Conclusion