Long lifetimes of nanoscale skyrmions in lithium-decorated van der Waals ferromagnet Fe$_3$GeTe$_2$

TL;DR

This study predicts the formation of long-lived nanoscale skyrmions in lithium-decorated monolayer Fe$_3$GeTe$_2$, demonstrating large energy barriers and stability at low temperatures, advancing potential applications in 2D spintronics.

Contribution

It introduces a feasible method to induce large DMI in 2D magnets via lithium decoration, enabling stable nanoscale skyrmions with long lifetimes.

Findings

Nanoscale skyrmions form in lithium-decorated Fe$_3$GeTe$_2$ under small magnetic fields.

Skyrmions exhibit energy barriers over 300 meV, comparable to heavy-metal interfaces.

Metastable skyrmions can last over an hour at temperatures up to 75 K.

Abstract

The Dzyaloshinskii-Moriya interaction (DMI), which originates from spin-orbit coupling and relies on broken inversion symmetry, is recognized as a key ingredient in forming magnetic skyrmions. However, most 2D magnets exhibit inversion symmetry; therefore, the DMI is suppressed. Here, we propose a strategy to induce large DMI via lithium absorption on the surface of 2D magnets -- an experimentally feasible approach. Using first-principles and atomistic spin simulations, we predict the formation of nanoscale skyrmions in lithium-decorated monolayer Fe$_3$GeTe$_2$ by imposing small out-of-plane magnetic fields ($B_z$). Notably, we find very large skyrmion energy barriers of more than 300 meV at $B_z = 0.4$ T, comparable to those observed in ferromagnet/heavy-metal interfaces. The origin of these unique skyrmions is attributed to the competition between strong DMI, exchange frustration, and small magnetocrystalline anisotropy energy. We further show that the lifetimes of metastable skyrmions exceed one hour for temperatures up to 75 K.