Laser induced THz emission from femtosecond photocurrents in Co/ZnO/Pt and Co/Cu/Pt multilayers

TL;DR

This study investigates how ultrafast laser pulses generate and control spin and charge photocurrents in Co/X/Pt multilayers, revealing the influence of interlayer materials and thickness on THz emission and interfacial spin dynamics.

Contribution

It provides new insights into the role of Cu and ZnO interlayers in modulating laser-induced photocurrents in magnetic heterostructures, highlighting interfacial effects.

Findings

Interlayer material affects THz emission strength.

Photocurrent direction can be controlled by laser helicity.

Interlayer thickness influences spin diffusion and torque.

Abstract

The ultrashort laser excitation of Co/Pt magnetic heterostructures can effectively generate spin and charge currents at the interfaces between magnetic and nonmagnetic layers. The direction of these photocurrents can be controlled by the helicity of the circularly polarized laser light and an external magnetic field. Here, we employ THz time-domain spectroscopy to investigate further the role of interfaces in these photo-galvanic phenomena. In particular, the effects of either Cu or ZnO interlayers on the photocurrents in Co/X/Pt (X = Cu, ZnO) have been studied by varying the thickness of the interlayers up to 5 nm. The results are discussed in terms of spin-diffusion phenomena and interfacial spin-orbit torque.