Robust skyrmion mediated reversal of ferromagnetic nanodots of 20 nm lateral dimension with high Ms and moderate DMI

TL;DR

This study demonstrates the formation and control of stable skyrmions in 20 nm ferromagnetic nanodots with high saturation magnetization, enabling energy-efficient data storage with voltage-controlled switching.

Contribution

It reveals that high saturation magnetization is essential for skyrmion stability in confined nanodots, challenging previous assumptions based on infinite film models.

Findings

Stable skyrmions formed in 20 nm nanodots with high Ms.

VCMA-based switching achieved with sub 1fJ/bit energy.

Skyrmion stability depends on saturation magnetization in confined geometries.

Abstract

Implementation of skyrmion based energy efficient and high-density data storage devices requires aggressive scaling of skyrmion size. Ferrimagnetic materials are considered to be a suitable platform for this purpose due to their low saturation magnetization (i.e. smaller stray field). However, we show by performing rigorous micromagnetic simulation that such scaling of skyrmion size by lowering saturation magnetization while applicable in infinite films or where the skyrmion size is very small compared to the film's lateral dimension, does not hold in confined geometries. We also found in confined geometries, where skyrmion occupies the whole volume of a nanodot, high saturation magnetization helps form stable skyrmions. Specifically, such skyrmions can be formed in 20 nm lateral dimension nanodots with high saturation magnetization (1.6-1.71 MA/m) and moderate DMI (3 mJ/m2). This result could stimulate experiments on implementation of highly dense skyrmion devices. In particular, we show that Voltage Controlled Magnetic Anisotropy (VCMA) based switching mediated by an intermediate skyrmion state can be achieved in the soft layer of a ferromagnetic p-MTJ of lateral dimensions 20 nm with sub 1fJ/bit energy in the presence of room temperature thermal noise with reasonable DMI ~3 mJ/m2.