Single-pulse all-optical switching in amorphous Dy$_x$Co$_{1-x}\text{ }$ and Tb$_x$Co$_{1-x}$

TL;DR

This paper demonstrates single-pulse all-optical magnetization switching in amorphous DyCo and TbCo thin films, revealing granular domain formation and partial re-switching behavior influenced by local anisotropy and temperature.

Contribution

It reports unusual toggle switching in DyCo and TbCo amorphous films with single femtosecond laser pulses, expanding understanding of all-optical switching mechanisms in rare-earth transition metal alloys.

Findings

Switching occurs mainly with the first pulse.

Submicron domains form at the threshold fluence.

Partial re-switching observed with subsequent pulses.

Abstract

Repeated uniform switching of the magnetization of thin films of ferrimagnetic amorphous Gd$_{x}$(FeCo)$_{1-x}$ in response to single fast laser pulses is well established. Here we report unusual toggle switching in thin films of sperimagnetic amorphous Dy$_x$Co$_{1-x}$ and Tb$_x$Co$_{1-x}$ with $\it{x} \simeq$ 0.25 irradiated with single 200 fs pulses of 800 nm laser light. The samples have strong local random anisotropy due to the non-S state rare earth. The compensation temperature of the films is $\le$ 180 K and their Curie temperature is $\simeq$ 500 K. They are mostly switched by the first pulse, and subsequent pulses lead to partial re-switching of a decreasing amount of the irradiated area, with a granular structure of submicron regions of switched and unswitched material. Individual switched domains about 700 nm in size are observed around the edge of the irradiated spots where the fluence is at the threshold for switching. Results are discussed in terms of a random anisotropy model where the ratio of local anisotropy to exchange is temperature dependent and close to the threshold for strong pinning.