Influence of magnetic fields on ultrafast laser-induced switching dynamics in Co/Gd bilayers

TL;DR

This study investigates the ultrafast magnetization switching dynamics in Co/Gd bilayers under magnetic fields, revealing complex processes including longitudinal, precessional, and domain-wall motions, with implications for optical magnetic switching control.

Contribution

It provides the first explicit time-resolved measurements of all-optical switching dynamics in Co/Gd bilayers and analyzes the influence of magnetic fields on these processes.

Findings

Magnetization switches within several picoseconds and reverts over hundreds of picoseconds.

Switching behavior strongly depends on magnetic field strength even below one Tesla.

Multiple switching regimes, including longitudinal, precessional, and domain-wall motions, are identified.

Abstract

Recently it has been shown that not only GdFeCo alloys exhibit single-pulse helicity-independent all-optical switching (HI-AOS), but that this effect is also seen in Co/Gd bilayers. However, there have been no reports on the explicit time dynamics of the switching process in these bilayers as of yet. Furthermore, time-resolved measurements of switching of other materials are typically done with a constant applied field to reset the magnetization between consecutive pulses and thus ensure repeatable behavior. In this paper we experimentally resolve the explicit dynamics of the switching process in Co/Gd, and the influence of applied magnetic fields on the switching process. We observe that after a switch within several picoseconds, the magnetization switches back at a timescale of hundreds of picoseconds. This backswitch includes a strong dependence on the magnetic field strength even at sub-tesla fields, significantly smaller than the exchange fields that govern the switching dynamics. This surprising behaviour is explained by a combination of longitudinal switching (on a picosecond timescale), precessional switching (on a nanosecond timescale) and domain-wall motion (on a timescale of 10 ns and beyond). We discuss these different switching regimes and their relative importance using simple model calculations.