Periodic chiral magnetic domains in single-crystal nickel nanowires

TL;DR

This study combines experimental and computational methods to reveal a periodic chiral vortex domain pattern in single-crystal nickel nanowires, driven by cubic anisotropy and strain effects, with potential topological stability.

Contribution

It demonstrates the existence of a stable, periodic vortex domain structure in Ni nanowires and elucidates the influence of anisotropy and strain on vortex formation, advancing understanding of magnetic domain configurations.

Findings

Periodic vortex domains with 250 nm period observed experimentally.

Micromagnetic simulations confirm vortex stability and periodicity.

Material properties and strain significantly affect vortex formation and stability.

Abstract

We report on experimental and computational investigations of the domain structure of ~0.2 x 0.2 x 8 {\mu}m single-crystal Ni nanowires (NWs). The Ni NWs were grown by a thermal chemical vapor deposition technique that results in highly-oriented single-crystal structures on amorphous SiOx coated Si substrates. Magnetoresistance measurements of the Ni NWs suggest the average magnetization points largely off the NW long axis at zero field. X-ray photoemission electron microscopy images show a well-defined periodic magnetization pattern along the surface of the nanowires with a period of {\lambda} = 250 nm. Finite element micromagnetic simulations reveal that an oscillatory magnetization configuration with a period closely matching experimental observation ({\lambda} = 240 nm) is obtainable at remanence. This magnetization configuration involves a periodic array of alternating chirality vortex domains distributed along the length of the NW. Vortex formation is attributable to the cubic anisotropy of the single crystal Ni NW system and its reduced structural dimensions. The periodic alternating chirality vortex state is a topologically protected metastable state, analogous to an array of 360{\deg} domain walls in a thin strip. Simulations show that other remanent states are also possible, depending on the field history. Effects of material properties and strain on the vortex pattern are investigated. It is shown that at reduced cubic anisotropy vortices are no longer stable, while negative uniaxial anisotropy and magnetoelastic effects in the presence of compressive biaxial strain contribute to vortex formation.