Ultra-low energy threshold engineering for all-optical switching of magnetization in dielectric-coated Co/Gd based synthetic-ferrimagnet

TL;DR

This study demonstrates that dielectric coatings can significantly reduce the energy required for all-optical magnetization switching in ferrimagnetic materials by enhancing light absorption through interference effects.

Contribution

It introduces a method to lower switching energy thresholds using dielectric layers, achieving an 80% reduction in energy with optimized interference.

Findings

Switching energy oscillates with dielectric layer thickness.

Threshold fluence reduced by at least 80%.

Energy per cell scales to 15 fJ for 50 nm scale.

Abstract

A femtosecond laser pulse is able to switch the magnetic state of a 3d-4f ferrimagnetic material on a pico-second time scale. Devices based on this all-optical switching (AOS) mechanism are competitive candidates for ultrafast memory applications. However, a large portion of the light energy is lost by reflection from the metal thin film as well as transmission to the substrate. In this paper, we explore the use of dielectric coatings to increase the light absorption by the magnetic metal layer based on the principle of constructive interference. We experimentally show that the switching energy oscillates with the dielectric layer thickness following the light interference profile as obtained from theoretical calculations. Furthermore, the switching threshold fluence can be reduced by at least $80\%$ to 0.6 mJ/cm$^2$ using two dielectric SiO$_2$ layers sandwiching the metal stack, which scales to 15 fJ of incident energy for a cell size of $50^2$ nm$^2$.