Narrow Segment Driven Multistep Magnetization Reversal Process in Sharp Diameter Modulated Fe67Co33 Nanowires.

Javier García,Manuel Vázquez,Cristina Bran,Víctor M Prida,Silvia González,Jose A Fernández-Roldán,Miguel Méndez,Roque González,Víctor Vega

doi:10.3390/nano11113077

Javier García, Manuel Vázquez + Show 7 more

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https://doi.org/10.3390/nano11113077

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Abstract

Magnetic nanomaterials are of great interest due to their potential use in data storage, biotechnology, or spintronic based devices, among others. The control of magnetism at such scale entails complexing the nanostructures by tuning their composition, shape, sizes, or even several of these properties at the same time, in order to search for new phenomena or optimize their performance. An interesting pathway to affect the dynamics of the magnetization reversal in ferromagnetic nanostructures is to introduce geometrical modulations to act as nucleation or pinning centers for the magnetic domain walls. Considering the case of 3D magnetic nanowires, the modulation of the diameter across their length can produce such effect as long as the segment diameter transition is sharp enough. In this work, diameter modulated Fe67Co33 ferromagnetic nanowires have been grown into the prepatterned diameter modulated nanopores of anodized Al2O3 membranes. Their morphological and compositional characterization was carried out by electron-based microscopy, while their magnetic behavior has been measured on both the nanowire array as well as for individual bisegmented nanowires after being released from the alumina template. The magnetic hysteresis loops, together with the evaluation of First Order Reversal Curve diagrams, point out that the magnetization reversal of the bisegmented FeCo nanowires is carried out in two steps. These two stages are interpreted by micromagnetic modeling, where a shell of the wide segment reverses its magnetization first, followed by the reversal of its core together with the narrow segment of the nanowire at once.

Highlights

Nowadays, technology is pushing forward, increasing efforts in the scientific community to deeply understand and control nature at lower scales
In order to determine the magnetization reversal mechanism of the bisegmented diameter modulated FeCo nanowires, we have modelled the hysteresis loop and the magnetization reversal process in an individual bisegmented FeCo nanowire made of two cylindrical segments with 2 microns in total length, and with 100 and 200 nm in diameter for the narrow and wide segments, respectively, via micromagnetic modelling with MuMax3 [47]
Macroscopic magnetometry, as well as First Order Reversal Curve (FORC) analysis, have pointed out the coexistence of two different magnetization reversal contributions which can be associated to the narrow and wide segment

Summary

Introduction

Technology is pushing forward, increasing efforts in the scientific community to deeply understand and control nature at lower scales. The application concepts often require 3D nano-architectures, which implies a collective magnetic behavior, including magnetostatic or exchange interactions, among nanowires or layers [13,14,15,16] In such case, techniques such as vibrating sample magnetometry (VSM) or superconducting quantum interference devices (SQUID) help to obtain a wider picture of the collective magnetic behavior of the nanostructured system. Techniques such as vibrating sample magnetometry (VSM) or superconducting quantum interference devices (SQUID) help to obtain a wider picture of the collective magnetic behavior of the nanostructured system In both cases, the progress in the field of nanomagnetism has the effect of bringing increasingly complex structures, such as core-shell or compositional and geometrical modulated nanowires, into focus [17,18,19,20,21,22,23,24,25,26]

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