Critical enhancement of the spin Hall effect by spin fluctuations

TL;DR

This paper presents a microscopic theory showing that spin fluctuations near magnetic transition temperatures can significantly enhance the spin Hall effect in magnetic metals, with distinct behaviors in ferromagnetic and antiferromagnetic cases.

Contribution

It introduces a theoretical framework explaining how spin fluctuations enhance the spin Hall effect in magnetic metals near their transition temperatures.

Findings

Spin Hall conductivity is significantly enhanced by spin fluctuations near magnetic transitions.

Pure spin Hall effect persists in antiferromagnetic metals across all temperatures.

In ferromagnetic metals, the spin Hall effect is replaced by the anomalous Hall effect below the transition.

Abstract

The spin Hall (SH) effect, the conversion of the electric current to the spin current along the transverse direction, relies on the relativistic spin-orbit coupling (SOC). Here, we develop a microscopic theory on the mechanisms of the SH effect in magnetic metals, where itinerant electrons are coupled with localized magnetic moments via the Hund exchange interaction and the SOC. Both antiferromagnetic metals and ferromagnetic metals are considered. It is shown that the SH conductivity can be significantly enhanced by the spin fluctuation when approaching the magnetic transition temperature of both cases. For antiferromagnetic metals, the pure SH effect appears in the entire temperature range, while for ferromagnetic metals, the pure SH effect is expected to be replaced by the anomalous Hall effect below the transition temperature. We discuss possible experimental realizations and the effect of the quantum criticality when the antiferromagnetic transition temperature is tuned to zero temperature.