Hypersonic heat-induced flows of magnons induced by femtosecond laser pulses

TL;DR

This paper demonstrates ultrafast magnonic currents induced by femtosecond laser pulses in ferrimagnetic materials, revealing ballistic magnon propagation at high velocities and implications for high-speed data processing.

Contribution

It provides the first evidence of sub-picosecond magnonic currents driven by laser-induced thermal gradients in ferrimagnets, highlighting their role in ultrafast spin dynamics.

Findings

Ballistic magnon propagation at 30 nm/ps velocity.

Magnon transport occurs on sub-picosecond timescales.

Thermal gradients induce rapid spin angular momentum transfer.

Abstract

In this work, we present evidence for the existence of a magnonic current on the sub-picosecond time-scale in a ferrimagnetic bilayer and its effect on ultrafast spin dynamics. The ferrimagnet, GdFeCo, is a material known to undergo ultrafast switching within 1-2ps after excitation with femtosecond laser pulses. Here, we show that the strong thermal gradients induced by applying femtosecond laser pulses and the presence of chemical inhomogeneities lead to local imbalances in the effective temperatures of the spins that produces a rapid transfer of spin angular momentum, which we interpret as an ultrafast spin Seebeck effect. We have quantified the typical magnon propagation in such a system. The results show ballistic magnon propagation with 30nm/ps velocities. The characteristic time scale of such magnon propagation indicates that this magnon transport can play an important role in switching, a crucial piece of understanding towards realising next generation data processing devices that operate at much higher frequencies.