Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current

M Tarequzzaman,T Böhnert,R Ferreira,J Borme,M Decker,A S Jenkins,J D Costa,C H Back,B Lacoste,P P Freitas,S Serrano-Guisan,E Paz

doi:10.1038/s42005-019-0119-7

Abstract

Spin-transfer torque nano-oscillators (STNO) are important candidates for several applications based on ultra-tunable microwave generation and detection. The microwave dynamics in these STNOs are induced by spin currents that are typically generated either by spin polarization in an adjacent ferromagnetic layer or through the spin Hall effect. In this paper, a 3-terminal STNO based on a magnetic tunnel junction is excited by both of these spin injection mechanisms. The combination of these two mechanisms excites the free layer into dynamic regimes beyond what can be achieved by each excitation mechanism individually, resulting in enhanced output powers, a key figures of merit for device performance. The system response can be coherently quantified as a function of the total injected spin current density. The experimental data shows an excellent consistency with this simple model and a critical spin current density of 4.52 ± 0.18 × 109ħ/2 e−1 Am−2.

Highlights

Spin-transfer torque nano-oscillators (STNO) are important candidates for several applications based on ultra-tunable microwave generation and detection
Spin torque nano-oscillators (STNOs) based on the spintransfer torque (STT) associated with net spin currents are important candidates for several applications including frequency signal generation[1], signal modulation[2], spin wave generation[3], neuromorphic computing[4] and ultra-tunable microwave generators[5,6,7,8]. Such devices are conventionally manufactured from spin valve or magnetic tunnel junction (MTJ) stacks nanofabricated in different geometries, including nanocontacts[9,10,11] and nanopillars[12,13,14]
Μ0 is the permeability of free space, ħ is the reduced Planck constant, Ms is the free layer saturation magnetization, α is the Gilbert damping constant, t is the thickness of the free layer, Happ is the applied field along easy axis, Jctu;cnrniteling is the critical tunneling current density and η is the spin injection efficiency associated with the injection of the spin-polarized tunneling current from the reference layer into the free layer

Summary

Introduction

Spin-transfer torque nano-oscillators (STNO) are important candidates for several applications based on ultra-tunable microwave generation and detection. Spin torque nano-oscillators (STNOs) based on the spintransfer torque (STT) associated with net spin currents are important candidates for several applications including frequency signal generation[1], signal modulation[2], spin wave generation[3], neuromorphic computing[4] and ultra-tunable microwave generators[5,6,7,8]. Such devices are conventionally manufactured from spin valve or magnetic tunnel junction (MTJ) stacks nanofabricated in different geometries, including nanocontacts[9,10,11] and nanopillars[12,13,14]. Realizing nano-oscillators from stacks incorporating ultra-thin tunnel barriers is required in order to increase the maximum current sustained by the devices, but as the MgO becomes thinner the tunnel magnetoresistance (TMR) and p tend to decrease

Methods

Results

Conclusion