Electrical characterization of the azimuthal anisotropy of $(\mathrm{Ni}_x\mathrm{Co}_{1-x})\mathrm{B}$-based ferromagnetic nanotubes

TL;DR

This study investigates the electrical and magnetic properties of Ni-Co-B ferromagnetic nanotubes with azimuthal magnetization, revealing how their anisotropy field varies with composition and wall thickness, and differs from bulk behavior.

Contribution

It provides detailed characterization of azimuthal anisotropy and magnetoresistance in Ni-Co-B nanotubes, highlighting effects of geometry and composition not observed in bulk materials.

Findings

Anisotropic magnetoresistance of 0.2-0.3% larger than bulk.

Azimuthal anisotropy field around 10mT, increasing with wall thickness and Co content.

Minimal dependence of anisotropy on tube diameter and curvature.

Abstract

We report on the structural, electric and magnetic properties of $(\mathrm{Ni}_x\mathrm{Co}_{1-x})\mathrm{B}$ ferromagnetic nanotubes, displaying azimuthal magnetization. The tubes are fabricated using electroless plating in polycarbonate porous templates, with lengths several tens of micrometers, diameters from 100nm to 500nm and wall thicknesses from 10nm to 80nm. The resistivity is $\sim 1.5\times10^{-6}\mathrm{\Omega/m}$, and the anisotropic magnetoresistance~(AMR) of 0.2-0.3%, one order of magnitude larger~(resp. smaller) than in the bulk material, which we attribute to the resistance at grain boundaries. We determined the azimuthal anisotropy field from M(H) AMR loops of single tubes contacted electrically. Its magnitude is around 10mT, and tends to increase with the tube wall thickness, as well as the Co content. However, surprisingly it does not dependent much on the diameter nor on the curvature.