Femtosecond Photocurrents at the Pt/FeRh Interface

TL;DR

This study investigates femtosecond laser-induced photocurrents at the FeRh/Pt interface, revealing ultrafast spin dynamics and inverse spin-orbit effects that generate THz emission, advancing understanding of ultrafast spintronic phenomena.

Contribution

It demonstrates the mechanisms of ultrafast photocurrent generation at the FeRh/Pt interface, including spin pumping and inverse spin-orbit torque, under various experimental conditions.

Findings

Photocurrent emission is driven by ultrafast demagnetization of FeRh.

Vertical spin pumping is polarization-independent.

Inverse spin-orbit torque depends on circular polarization of light.

Abstract

Femtosecond laser excitation of FeRh/Pt bilayers launches an ultrafast pulse of electric photocurrent in the Pt-layer and thus results in emission of electromagnetic radiation in the THz spectral range. Analysis of the THz emission as a function of polarization of the femtosecond laser pulse, external magnetic field, sample temperature and sample orientation shows that photocurrent can emerge due to vertical spin pumping and photo-induced inverse spin-orbit torque at the FeRh/Pt interface. The vertical spin pumping from FeRh to Pt does not depend on the polarization of light and originates from ultrafast laser-induced demagnetization of the ferromagnetic phase of FeRh. The photo-induced inverse spin-orbit torque at the FeRh/Pt interface can be described in terms of a helicity-dependent effect of circularly polarized light on the magnetization of the ferromagnetic FeRh and subsequent generation of a photocurrent.