W thickness dependence of spin Hall effect for (W/Hf)-multilayer electrode/CoFeB/MgO systems with flat and highly (100) oriented MgO layer

Yoshiaki Saito,Nobuki Tezuka,Shoji Ikeda,Tetsuo Endoh

doi:10.1063/9.0000011

Abstract

We investigated spin-Hall effect (SHE) and degree of MgO (100) orientation in artificially synthesized (W/Hf)-multilayer/CoFeB/MgO systems with various W thicknesses. We found that the artificially synthesized multilayer systems can enhance the spin-Hall effect and control the value of spin diffusion length. We observed a maximum magnitude in both spin-Hall angle and spin-Hall conductivity as a function of W thickness in W/Hf-multilayer systems, and found that the values of spin-Hall conductivity are larger than that for β-phase W. In addition, a more highly oriented MgO (100) texture on CoFeB is obtained for (W/Hf)-multilayer systems prepared under low-Ar-pressure condition, which would be suitable for preparation of magnetic tunnel junctions with high tunnel magnetoresistance properties on (W/Hf)-multilayer heavy metal electrode. These results suggest that the artificially synthesized multilayer system is one of the avenues for realizing spin devices using spin-orbit torque.

Highlights

INTRODUCTIONScitation.org/journal/adv β-phase W (β-W) has a relatively large ∣θSH∣ of approximately 0.2 - 0.3, β-W have a very high ρxx. The magnitude of ∣θSH∣ for both intrinsic and extrinsic (side jump mechanism) terms is proportional to the magnitude of ρxx value (∣θSH∣ ∼ σSH ρxx27,28), where σSH is spin Hall conductivity
Current-induced spin-orbit torque (SOT) originating from the spin-Hall effect (SHE) in heavy metal/ferromagnet (HM/FM) systems has attracted attention due to their potential for application to SOT magnetoresistive random access memory (SOT-MRAM), skyrmion and domain wall devices.1–18 Study of HM materials as well as HM/FM interfaces with larger spin-orbit coupling is being actively carried out because of allowing a larger amount of spin current (Js) to be generated for manipulating the nano magneto when flowing the write charge current (JC) through the HM layers
We observed that large magnitude of σSH and enhancement of perpendicular magnetic anisotropy in (W/Hf)-multilayer/CoFeB/MgO systems with tW = tHf = 0.35 nm and 0.7 nm compare to β-phase W (β-W)/CoFeB/MgO system

Summary

INTRODUCTION

Scitation.org/journal/adv β-phase W (β-W) has a relatively large ∣θSH∣ of approximately 0.2 - 0.3, β-W have a very high ρxx. The magnitude of ∣θSH∣ for both intrinsic and extrinsic (side jump mechanism) terms is proportional to the magnitude of ρxx value (∣θSH∣ ∼ σSH ρxx27,28), where σSH is spin Hall conductivity. Increase in the magnitude of σSH is important from the application point of view.. We observed that large magnitude of σSH and enhancement of perpendicular magnetic anisotropy in (W (tW)/Hf (tHf))-multilayer/CoFeB/MgO systems with tW = tHf = 0.35 nm and 0.7 nm compare to β-W/CoFeB/MgO system.. We found magnitude of σSH for (W (0.7)/Hf (0.7))-multilayer system is larger than that for (W (0.35)/Hf (0.35))-multilayer system. When the film thickness ratio between W and Hf is optimized, further increase of σSH is expected in the (W/Hf)-multilayer system. We investigated W thickness dependence of σSH, θSH, ρxx and spin diffusion length (λS) in amorphous (W (tW)/Hf (0.35))-multilayer/CoFeB/MgO systems with various tW and evaluated the degree of MgO (100) orientation on the (W/Hf)-multilayer HM electrode

EXPERIMENTS

RESULTS

CONCLUSIONS