Different spin relaxation property observed in linearly and circularly polarized laser induced terahertz emission from Bi/Co bilayer

TL;DR

This study compares spin relaxation properties in Bi/Co bilayers by analyzing THz emissions induced by different spin current generation mechanisms, revealing distinct thickness dependencies linked to different relaxation behaviors.

Contribution

It provides the first direct comparison of spin relaxation properties in Bi/Co bilayers using two different THz emission mechanisms, highlighting their distinct thickness-dependent behaviors.

Findings

Different Bi thickness dependence of THz emission intensity and bandwidth.

Spin relaxation properties differ for spin currents induced by demagnetization and photo-spin conversion.

Distinct mechanisms reveal different spin relaxation dynamics in Bi layers.

Abstract

Recently, helicity-dependent photocurrent was reported in Bi single thin fi lms. It is proposed that the origin of this photocurrent is the combination of photo-spin conversion and spin-charge conversion effects in Bi and efficient spin conversion in Bi is expected. In this study, we measured two types of terahertz (THz) emissions from Bi/Co bilayer films induced by spin current generation using laser-induced demagnetization of the Co layer and photo-spin conversion effect in the Bi layer to investigate the spin current induced by the two mechanisms simultaneously. We clearly observed diff erent Bi thickness dependence of peak intensity and that of bandwidth for THz spin current in two experiments, i.e., spin current induced by demagnetization of Co and that by photo-spin conversion in Bi. The different Bi thickness dependence of spin current intensity and bandwidth in two experiments is caused by different spin relaxation properties of optically excited spin currents in Bi layers.