Surprisingly large inverse spin Hall effect and systematic variation of spin-orbit coupling with d-orbital filling in 3d transition metals

TL;DR

This study reveals unexpectedly large spin Hall effects in 3d transition metals, driven by d-orbital filling rather than atomic number, challenging traditional views on spin-orbit coupling strength.

Contribution

It demonstrates a systematic variation of spin Hall angle with d-orbital filling in 3d metals, showing significant spin-orbit effects contrary to conventional expectations.

Findings

Cr and Ni exhibit large spin Hall angles, comparable to Pt.

Spin Hall effect in 3d metals depends on d-orbital filling, not atomic number.

Results challenge the Z4 dependence of spin-orbit coupling in light elements.

Abstract

It is generally believed that spin-orbit coupling (SOC) follows Z4 (atomic number) dependence and becomes significant only in heavy elements. Consequently, SOC in 3d transition metals should be negligible given their small Z. Using dynamic spin pumping of Y3Fe5O12-based structures, we uncover a systematic evolution of spin Hall angle with d-orbital filling in a series of 3d metals, reminiscent of behavior observed in 5d metals. In particular, Cr and Ni show very large spin Hall angle (half of that for Pt), indicating that d-orbital filling rather than Z plays a dominant role in spin Hall effect (SHE) in 3d metals. This result enriches our understanding of SHE and broadens the scope of materials available for exploring the rich phenomena enabled by SOC as well as presenting a guidepost for testing theoretical models of spin-orbit coupling in transition metals.