The spin Hall effect as a probe of nonlinear spin fluctuations

TL;DR

This paper reveals an anomaly in the inverse spin Hall effect near Curie temperatures in NiPd alloys, explained by second-order nonlinear spin fluctuations, suggesting a new method to detect tiny magnetic moments.

Contribution

It extends Kondo's model to explain the spin Hall effect anomaly as arising from nonlinear spin fluctuations, highlighting a fundamental symmetry difference from the anomalous Hall effect.

Findings

Observed shape-independent anomaly in inverse spin Hall effect near Curie temperature.

Attributed the anomaly to second-order nonlinear spin fluctuations of Ni moments.

Proposed a new application for detecting minuscule magnetic moments.

Abstract

The spin Hall effect and its inverse play key roles in spintronic devices since they allow conversion of charge currents to and from spin currents. The conversion efficiency strongly depends on material details, such as the electronic band structure and the nature of impurities. Here we show an anomaly in the inverse spin Hall effect in weak ferromagnetic NiPd alloys near their Curie temperatures with a shape independent of material details, such as Ni concentrations. By extending Kondo's model for the anomalous Hall effect, we explain the observed anomaly as originating from the second-order nonlinear spin fluctuation of Ni moments. This brings to light an essential symmetry difference between the spin Hall effect and the anomalous Hall effect which reflects the first order nonlinear fluctuations of local moments. Our finding opens up a new application of the spin Hall effect, by which a minuscule magnetic moment can be detected.