Controlled co-excitation of direct and indirect ultrafast demagnetization in Co/Pd multilayer with large perpendicular magnetic anisotropy

TL;DR

This study demonstrates controlled simultaneous excitation of direct and indirect ultrafast demagnetization mechanisms in Co/Pd multilayers, revealing how fluence, thickness, and wavelength influence demagnetization dynamics and advancing understanding of the process.

Contribution

It introduces the first experimental demonstration of simultaneous control over direct and indirect demagnetization mechanisms in multilayer systems.

Findings

Demonstrated control of demagnetization time from ~350 fs to ~750 fs.

Showed modulation of indirect excitation via heat current and pump wavelength.

Confirmed the combined role of direct and indirect processes in ultrafast demagnetization.

Abstract

Ever since its discovery in 1996, ultrafast demagnetization has ignited immense research interest due to its scientific rigor and technological potential. A flurry of recent theoretical and experimental investigations has proposed direct and indirect excitation processes in separate systems. However, it still lacks a unified mechanism and remains highly debatable. Here, for the first time, we demonstrate that instead of either direct or indirect interaction, simultaneous and controlled excitation of both direct and indirect mechanisms of demagnetization are possible in a multilayers composed of repeated Co/Pd bi-layers. Moreover, we were able to modulate demagnetization time (from ~350 fs to ~750 fs) by fluence and thickness dependent indirect excitation due to heat current flowing vertically downward from top layers, which is combined with an altogether different scenario of direct irradiation. Finally, by regulating the pump wavelength we could effectively control the contribution of indirect process, which gives a confirmation to our understanding of the ultrafast demagnetization process.