Morphology control of the magnetization reversal mechanism in Co80Ni20 nanomagnets

TL;DR

This study investigates how shape and morphology influence the magnetization reversal in Co80Ni20 nanowires, revealing that head morphology and aspect ratio critically affect magnetic behavior, supported by experimental and simulation data.

Contribution

It introduces the importance of head morphology and an additional parameter t in understanding and optimizing nanomagnet behavior, expanding beyond traditional aspect ratio considerations.

Findings

Coercive field HC optimized for aspect ratio L/d > 15

Diabolo-shaped nanowires exhibit better magnetic properties than cylinders

Head morphology and thickness t significantly influence magnetization reversal

Abstract

Nanowires with very different size, shape, morphology and crystal symmetry can give rise to a wide ensemble of magnetic behaviors whose optimization determines their applications in nanomagnets. We present here an experimental work on the shape and morphological dependence of the magnetization reversal mechanism in weakly interacting Co80Ni20 hexagonal-close-packed nanowires. Non-agglomerated nanowires (with length L and diameter d) with a controlled shape going from quasi perfect cylinders to diabolos, have been studied inside their polyol solution in order to avoid any oxidation process. The coercive field HC was found to follow a standard behavior and to be optimized for an aspect ratio L/d > 15. Interestingly, an unexpected behavior was observed as function of the head morphology leading to the strange situation where a diabolo shaped nanowire is a better nanomagnet than a cylinder. This paradoxical behavior can be ascribed to the growth-competition between the aspect ratio L/d and the head morphology ratio d/D (D being the head width). Our experimental results clearly show the importance of the independent parameter (t = head thickness) that needs to be considered in addition to the shape aspect ratio (L/d) in order to fully describe the nanomagnets magnetic behavior. Micromagnetic simulations well support the experimental results and bring important insights for future optimization of the nanomagnets morphology