# X-ray spectroscopy of current-induced spin-orbit torques and spin accumulation in Pt/3d transition metal bilayers

## TL;DR

This study uses x-ray spectroscopy to investigate how current-induced spin-orbit torques and spin accumulation at Pt/3d transition metal interfaces influence magnetic moments, revealing quantitative insights into spin transfer and magnetic effects.

## Contribution

It provides a quantitative, element-specific measurement of spin accumulation and magnetic moment changes at Pt/3d interfaces, with sensitivity below 10^-5 μB per atom, and explores the effects of spin currents on adjacent magnetic layers.

## Key findings

- Accumulated spins in Pt/Co cause magnetization deviation with an effective spin-Hall angle of 0.08.
- Spin and orbital magnetic moments of Co are affected equally by spin current absorption.
- Upper limits for injected spins in Pt/NM bilayers are approximately 3×10^-6 μB per atom.

## Abstract

An electric current flowing in Pt, a material with strong spin-orbit coupling, leads to spins accumulating at the interfaces by virtue of the spin Hall effect and interfacial charge-spin conversion. We measure the influence of these interfacial magnetic moments onto adjacent 3d transition metal layers by x-ray absorption spectroscopy and x-ray magnetic circular dichroism in a quantitative and element-selective way, with sensitivity below $10^{-5}~\mu_B$ per atom. In Pt(6 nm)/Co(2.5 nm), the accumulated spins cause a deviation of the Co magnetization direction, which corresponds to an effective spin-Hall angle of 0.08. The spin and orbital magnetic moments of Co are affected in equal proportion by the absorption of the spin current, showing that the transfer of orbital momentum from the recently predicted orbital Hall effect is either below our detection limit, or not directed to the 3d states of Co. For Pt/NM (NM = Ti, Cr, Cu), we find upper limits for the amount of injected spins corresponding to about $3\times 10^{-6}~\mu_B$ per atom.