Electrical Probing of Field-Driven Cascading Quantized Transitions of Skyrmion Cluster States in MnSi Nanowires

TL;DR

This study demonstrates that ultra-narrow MnSi nanowires host skyrmion clusters whose quantized changes can be detected via magnetoresistance, advancing the understanding of skyrmion behavior in confined geometries for potential memory applications.

Contribution

It provides the first experimental evidence of quantized skyrmion cluster states in nanowires with diameters comparable to a single skyrmion, supported by electrical measurements and simulations.

Findings

Quantized jumps in magnetoresistance correspond to skyrmion number changes.

Skyrmion clusters exist in nanowires with diameters near 18 nm.

Monte Carlo simulations support experimental observations.

Abstract

Magnetic skyrmions are topologically stable whirlpool-like spin textures that offer great promise as information carriers for future ultra-dense memory and logic devices1-4. To enable such applications, particular attention has been focused on the skyrmions properties in highly confined geometry such as one dimensional nanowires5-8. Hitherto it is still experimentally unclear what happens when the width of the nanowire is comparable to that of a single skyrmion. Here we report the experimental demonstration of such scheme, where magnetic field-driven skyrmion cluster (SC) states with small numbers of skyrmions were demonstrated to exist on the cross-sections of ultra-narrow single-crystal MnSi nanowires (NWs) with diameters, comparable to the skyrmion lattice constant (18 nm). In contrast to the skyrmion lattice in bulk MnSi samples, the skyrmion clusters lead to anomalous magnetoresistance (MR) behavior measured under magnetic field parallel to the NW long axis, where quantized jumps in MR are observed and directly associated with the change of the skyrmion number in the cluster, which is supported by Monte Carlo simulations. These jumps show the key difference between the clustering and crystalline states of skyrmions, and lay a solid foundation to realize skyrmion-based memory devices that the number of skyrmions can be counted via conventional electrical measurements.