# All-optical Detection of Spin Hall Angle in W/CoFeB/SiO2 Heterostructures by Varying Tungsten Layer Thickness

## TL;DR

This study demonstrates an all-optical method to measure the spin Hall angle in W/CoFeB/SiO2 heterostructures, revealing a non-monotonic dependence on tungsten layer thickness and highlighting the influence of structural phase transitions.

## Contribution

It introduces an optical technique for unambiguous measurement of spin Hall angle and explores its variation with tungsten thickness in heterostructures, linking it to structural and electronic effects.

## Key findings

- Maximum SHA of about 0.4 at 3 nm W thickness
- Sharp reduction of SHA at 6 nm W thickness
- Correlation of SHA variation with W phase transition

## Abstract

The development of advanced spintronics devices hinges on the efficient generation and utilization of pure spin current. In materials with large spin-orbit coupling, the spin Hall effect may convert charge current to pure spin current and a large conversion efficiency, which is quantified by spin Hall angle (SHA), is desirable for the realization of miniaturized and energy efficient spintronic devices. Here, we report a giant SHA in beta-tungsten (\b{eta}-W) thin films in Sub/W(t)/Co20Fe60B20(3 nm)/SiO2(2 nm) heterostructures with variable W thickness. We employed an all-optical time-resolved magneto-optical Kerr effect microscope for an unambiguous determination of SHA using the principle of modulation of Gilbert damping of the adjacent ferromagnetic layer by the spin-orbit torque from the W layer. A non-monotonic variation of SHA with W layer thickness (t) is observed with a maximum of about 0.4 at about t = 3 nm, followed by a sudden reduction to a very low value at t = 6 nm. This variation of SHA with W-thickness correlates well with the thickness dependent structural phase transition and resistivity variation of W above the spin diffusion length of W, while below this length the interfacial electronic effect at W/CoFeB influences the estimation of SHA.

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Source: https://tomesphere.com/paper/1702.06258