Direct evidence of terahertz emission arising from anomalous Hall effect

TL;DR

This paper provides direct evidence that the anomalous Hall effect in ferromagnetic CoFeB thin films is a primary mechanism for terahertz emission, with emission optimized by material and laser parameters, and linked to skew scattering.

Contribution

It demonstrates that the anomalous Hall effect causes terahertz emission in CoFeB films and identifies skew scattering as the responsible charge carrier mechanism.

Findings

THz emission is dominated by the anomalous Hall effect.

Optimizing film thickness, orientation, and laser fluence enhances THz emission.

Skew scattering of charge carriers is responsible for the emission.

Abstract

A detailed understanding of the different mechanisms being responsible for terahertz (THz) emission in ferromagnetic (FM) materials will aid in designing efficient THz emitters. In this report, we present direct evidence of THz emission from single layer Co$_{0.4}$Fe$_{0.4}$B$_{0.2}$ (CoFeB) FM thin films. The dominant mechanism being responsible for the THz emission is the anomalous Hall effect (AHE), which is an effect of a net backflow current in the FM layer created by the spin-polarized current reflected at the interfaces of the FM layer. The THz emission from the AHE-based CoFeB emitter is optimized by varying its thickness, orientation, and pump fluence of the laser beam. Results from electrical transport measurements show that skew scattering of charge carriers is responsible for the THz emission in the CoFeB AHE-based THz emitter.