Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling

TL;DR

This study demonstrates that electromagnetic energy-funneling nanoantennas can significantly reduce demagnetization in ferrimagnetic films, paving the way for nanoscale ultrafast all-optical magnetic switching.

Contribution

It introduces the use of resonant plasmon nanoantennas to control and reduce demagnetization at the nanoscale in ferrimagnetic alloys, enabling potential ultrafast magnetic switching.

Findings

Resonant nanoantennas reduce demagnetization response by up to three times.

Electromagnetic simulations support energy-funneling into the magnetic film.

First step towards nanoscale ultrafast all-optical magnetization switching.

Abstract

The quest to improve density, speed and energy efficiency of magnetic memory storage has led to exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy-funneling plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film. We demonstrate how Ag nanoring-shaped antennas under resonant optical femtosecond pumping reduce the overall magneto-optical response due to demagnetization in the underlying films up to three times compared to non-resonant illumination. We attribute such substantial reduction to the nanoscale confinement of the demagnetization process. This is qualitatively supported by the electromagnetic simulations that strongly evidence the optical energy-funneling to the nanoscale from the nanoantennas into the ferrimagnetic film. This is the first and defining step for reaching deterministic ultrafast all-optical magnetization switching at the nanoscale in such systems, opening a route to develop nanoscale ultrafast magneto-optics.