Non-equilibrium self-assembly of spin-wave solitons in FePt nanoparticles

TL;DR

This paper reports the discovery of spin-wave solitons in FePt nanoparticles, formed after femtosecond laser excitation, with potential applications in THz-frequency devices due to their high-frequency spin-precession.

Contribution

It demonstrates the existence of sub-10 nm spin-wave solitons in FePt nanoparticles and characterizes their formation and properties using experimental and modeling approaches.

Findings

Spin-wave solitons form in FePt nanoparticles after femtosecond laser excitation.

The solitons exhibit a spin-precession frequency of 0.1 THz.

These structures could enable miniature THz devices.

Abstract

Magnetic nanoparticles such as FePt in the L10-phase are the bedrock of our current data storage technology. As the grains become smaller to keep up with technological demands, the superparamagnetic limit calls for materials with higher magneto-crystalline anisotropy. This in turn reduces the magnetic exchange length to just a few nanometers enabling magnetic structures to be induced within the nanoparticles. Here we describe the existence of spin-wave solitons, dynamic localized bound states of spin-wave excitations, in FePt nanoparticles. We show with time-resolved X-ray diffraction and micromagnetic modeling that spin-wave solitons of sub-10 nm sizes form out of the demagnetized state following femtosecond laser excitation. The measured soliton spin-precession frequency of 0.1 THz positions this system as a platform to develop miniature devices capable of filling the THz gap.