Unveiling the nonrelativistic spin current polarization in an altermagnet

TL;DR

This paper demonstrates that nonrelativistic spin currents in altermagnets like RuO2 are magnetically polarized along the Neel vector, clarifying their origin and advancing spintronics understanding.

Contribution

It provides direct experimental evidence linking the Neel vector to spin current polarization in altermagnets, using a novel measurement technique.

Findings

Nonrelativistic spin current polarization aligns with the Neel vector.

Disentangling conventional and magnetic spin Hall effects clarifies the spin current origin.

The work confirms the magnetic nature of spin currents in altermagnets.

Abstract

Spin current plays a central role in spintronics for driving exotic spin-dependent phenomena and high-performance device applications. Recently, a magnetic spin Hall effect has been discovered in spin-split antiferromagnets including noncollinear antiferromagnets and altermagnets, allowing the efficient generation of unconventional spin currents even in the absence of spin-orbit coupling. However, although such nonrelativistic spin currents are proposed to have a magnetic origin, the direct connection between the Neel vector and the spin current polarization is still missing. Here, using the altermagnetic RuO2 as a representative example, we unveil the spin current polarization by disentangling the conventional and magnetic spin Hall effects using a technique we developed based on the spin Hall magnetoresistance measurement. The results suggest that the nonrelativistic spin current hosts a polarization very close to the Neel vector. Our work offers unambiguous evidence of the magnetic origin of the nonrelativistic spin current in altermagnetic RuO2, and paves a straightforward route to understand the unconventional spin currents that are crucial in spintronics.