The Magnetic Properties of Fe/Cu Multilayered Nanowires: The Role of the Number of Fe Layers and Their Thickness.

Sofia Caspani,Suellen Moraes,Cláudia Nunes,David Navas,Célia T Sousa,Ricardo Magalhães,Mariana P Proenca,João Pedro Araújo

doi:10.3390/nano11102729

Sofia Caspani, Suellen Moraes + Show 6 more

Open Access

https://doi.org/10.3390/nano11102729

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Abstract

Multi-segmented bilayered Fe/Cu nanowires have been fabricated through the electrodeposition in porous anodic alumina membranes. We have assessed, with the support of micromagnetic simulations, the dependence of fabricated nanostructures’ magnetic properties either on the number of Fe/Cu bilayers or on the length of the magnetic layers, by fixing both the nonmagnetic segment length and the wire diameter. The magnetic reversal, in the segmented Fe nanowires (NWs) with a 300 nm length, occurs through the nucleation and propagation of a vortex domain wall (V-DW) from the extremities of each segment. By increasing the number of bilayers, the coercive field progressively increases due to the small magnetostatic coupling between Fe segments, but the coercivity found in an Fe continuous nanowire is not reached, since the interactions between layers is limited by the Cu separation. On the other hand, Fe segments 30 nm in length have exhibited a vortex configuration, with around 60% of the magnetization pointing parallel to the wires’ long axis, which is equivalent to an isolated Fe nanodisc. By increasing the Fe segment length, a magnetic reversal occurred through the nucleation and propagation of a V-DW from the extremities of each segment, similar to what happens in a long cylindrical Fe nanowire. The particular case of the Fe/Cu bilayered nanowires with Fe segments 20 nm in length revealed a magnetization oriented in opposite directions, forming a synthetic antiferromagnetic system with coercivity and remanence values close to zero.

Highlights

Considerable interest has arisen recently in studying 1D nanostructures, such as nanowires, nanopillars, and nanorods, owing to their potential applications [1,2]
Cylindrical NWs have been suggested as key elements for the development and understanding of a new research field known as magnetism in curved geometries [7]
We have investigated the changes in the magnetic behavior of multi-segmented Fe/Cu NWs resulting from varying the number of bilayers from 1 to 20, for fixed Fe and Cu lengths, or changing the length of the magnetic layer for two Cu layer lengths (60 and 120 nm)

Summary

Introduction

Considerable interest has arisen recently in studying 1D nanostructures, such as nanowires, nanopillars, and nanorods, owing to their potential applications [1,2]. The term nanowires (NWs) describes wires with a large length-to-diameter ratio, i.e., aspect ratio. Some of their remarkable properties arise from having a high density of electronic states, diameter-dependent band gaps, an enhanced surface scattering of electrons and photons, and high surface-to-volume ratios [3,4,5]. These properties lead to a unique electrical, optical, and magnetic behavior, making them suitable for many industrial and medical applications [2,6]. It was recently demonstrated that the curved geometry of NWs can lead to novel and non-trivial magnetic phenomena, such as the formation of skyrmion magnetic configurations [8,9] and Bloch-point domain walls [10,11]

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