Editorial

3 pages, 179 KiB

Open AccessEditorial

Multifunctional Magnetic Nanowires and Nanotubes

by Mariana P. Proenca

Nanomaterials 2022, 12(8), 1308; https://doi.org/10.3390/nano12081308 - 11 Apr 2022

Cited by 5 | Viewed by 1245

Low-dimensional magnetic nanostructures are promising materials for applications in many different fields, for example, in medicine (for drug delivery, biomimetic devices, contrast agents in magnetic resonance imaging, hyperthermia, cell manipulation, etc [...] Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

Research

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17 pages, 5227 KiB

Open AccessArticle

Single Diameter Modulation Effects on Ni Nanowire Array Magnetization Reversal

by Luis C. C. Arzuza, Victor Vega, Victor M. Prida, Karoline O. Moura, Kleber R. Pirota and Fanny Béron

Nanomaterials 2021, 11(12), 3403; https://doi.org/10.3390/nano11123403 - 16 Dec 2021

Cited by 6 | Viewed by 2035

Abstract

Geometrically modulated magnetic nanowires are a simple yet efficient strategy to modify the magnetic domain wall propagation since a simple diameter modulation can achieve its pinning during the nanowire magnetization reversal. However, in dense systems of parallel nanowires, the stray fields arising at [...] Read more.

Geometrically modulated magnetic nanowires are a simple yet efficient strategy to modify the magnetic domain wall propagation since a simple diameter modulation can achieve its pinning during the nanowire magnetization reversal. However, in dense systems of parallel nanowires, the stray fields arising at the diameter interface can interfere with the domain wall propagation in the neighboring nanowires. Therefore, the magnetic behavior of diameter-modulated nanowire arrays can be quite complex and depending on both short and long-range interaction fields, as well as the nanowire geometric dimensions. We applied the first-order reversal curve (FORC) method to bi-segmented Ni nanowire arrays varying the wide segment (45–65 nm diameter, 2.5–10.0 μm length). The FORC results indicate a magnetic behavior modification depending on its length/diameter aspect ratio. The distributions either exhibit a strong extension along the coercivity axis or a main distribution finishing by a fork feature, whereas the extension greatly reduces in amplitude. With the help of micromagnetic simulations, we propose that a low aspect ratio stabilizes pinned domain walls at the diameter modulation during the magnetization reversal. In this case, long-range axial interaction fields nucleate a domain wall at the nanowire extremities, while short-range ones could induce a nucleation at the diameter interface. However, regardless of the wide segment aspect ratio, the magnetization reversal is governed by the local radial stray fields of the modulation near null magnetization. Our findings demonstrate the capacity of distinguishing between complex magnetic behaviors involving convoluted interaction fields. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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14 pages, 16447 KiB

Open AccessArticle

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

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

Nanomaterials 2021, 11(11), 3077; https://doi.org/10.3390/nano11113077 - 15 Nov 2021

Cited by 5 | Viewed by 1880

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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20 pages, 2724 KiB

Open AccessEditor’s ChoiceArticle

Influence of Coating and Size of Magnetic Nanoparticles on Cellular Uptake for In Vitro MRI

by Belén Cortés-Llanos, Sandra M. Ocampo, Leonor de la Cueva, Gabriel F. Calvo, Juan Belmonte-Beitia, Lucas Pérez, Gorka Salas and Ángel Ayuso-Sacido

Nanomaterials 2021, 11(11), 2888; https://doi.org/10.3390/nano11112888 - 28 Oct 2021

Cited by 13 | Viewed by 2536

Abstract

Iron oxide nanoparticles (IONPs) are suitable materials for contrast enhancement in magnetic resonance imaging (MRI). Their potential clinical applications range from diagnosis to therapy and follow-up treatments. However, a deeper understanding of the interaction between IONPs, culture media and cells is necessary for [...] Read more.

Iron oxide nanoparticles (IONPs) are suitable materials for contrast enhancement in magnetic resonance imaging (MRI). Their potential clinical applications range from diagnosis to therapy and follow-up treatments. However, a deeper understanding of the interaction between IONPs, culture media and cells is necessary for expanding the application of this technology to different types of cancer therapies. To achieve new insights of these interactions, a set of IONPs were prepared with the same inorganic core and five distinct coatings, to study their aggregation and interactions in different physiological media, as well as their cell labelling efficiency. Then, a second set of IONPs, with six different core sizes and the same coating, were used to study how the core size affects cell labelling and MRI in vitro. Here, IONPs suspended in biological media experience a partial removal of the coating and adhesion of molecules. The FBS concentration alters the labelling of all types of IONPs and hydrodynamic sizes ≥ 300 nm provide the greatest labelling using the centrifugation-mediated internalization (CMI). The best contrast for MRI results requires a core size range between 12–14 nm coated with dimercaptosuccinic acid (DMSA) producing R₂^* values of 393.7 s⁻¹ and 428.3 s⁻¹, respectively. These findings will help to bring IONPs as negative contrast agents into clinical settings. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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12 pages, 2924 KiB

Open AccessArticle

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

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

Nanomaterials 2021, 11(10), 2729; https://doi.org/10.3390/nano11102729 - 15 Oct 2021

Cited by 13 | Viewed by 1808

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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11 pages, 13125 KiB

Open AccessArticle

Scaling Up the Production of Electrodeposited Nanowires: A Roadmap towards Applications

by Claudia Fernández-González, Jesús C. Guzmán-Mínguez, Alejandra Guedeja-Marrón, Eduardo García-Martín, Michael Foerster, Miguel Ángel Niño, Lucía Aballe, Adrián Quesada, Lucas Pérez and Sandra Ruiz-Gómez

Nanomaterials 2021, 11(7), 1657; https://doi.org/10.3390/nano11071657 - 24 Jun 2021

Cited by 4 | Viewed by 2535

Abstract

The use of metallic nanowires is mostly reduced to scientific areas where a small quantity of nanostructures are needed. In order to broaden the applicability of these nanomaterials, it is necessary to establish novel synthesis protocols that provide a larger amount of nanowires [...] Read more.

The use of metallic nanowires is mostly reduced to scientific areas where a small quantity of nanostructures are needed. In order to broaden the applicability of these nanomaterials, it is necessary to establish novel synthesis protocols that provide a larger amount of nanowires than the conventional laboratory fabrication processes at a more competitive cost. In this work, we propose several modifications to the conventional electrochemical synthesis of nanowires in order to increase the production with considerably reduced production time and cost. To that end, we use a soft anodization procedure of recycled aluminum at room temperature to produce the alumina templates, followed by galvanostatic growth of CoFe nanowires. We studied their morphology, composition and magnetic configuration, and found that their properties are very similar to those obtained by conventional methods. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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19 pages, 3515 KiB

Open AccessEditor’s ChoiceArticle

Magneto-Transport in Flexible 3D Networks Made of Interconnected Magnetic Nanowires and Nanotubes

by Tristan da Câmara Santa Clara Gomes, Nicolas Marchal, Flavio Abreu Araujo, Yenni Velázquez Galván, Joaquín de la Torre Medina and Luc Piraux

Nanomaterials 2021, 11(1), 221; https://doi.org/10.3390/nano11010221 - 16 Jan 2021

Cited by 14 | Viewed by 2652

Abstract

Electrochemical deposition of interconnected nanowires and nanotubes made of ferromagnetic metals into track-etched polycarbonate templates with crossed nanochannels has been revealed suitable for the fabrication of mechanically stable three-dimensional magnetic nanostructures with large surface area. These 3D networks embedded into flexible polymer membranes [...] Read more.

Electrochemical deposition of interconnected nanowires and nanotubes made of ferromagnetic metals into track-etched polycarbonate templates with crossed nanochannels has been revealed suitable for the fabrication of mechanically stable three-dimensional magnetic nanostructures with large surface area. These 3D networks embedded into flexible polymer membranes are also planar and lightweight. This fabrication technique allows for the control of the geometric characteristics and material composition of interconnected magnetic nanowire or nanotube networks, which can be used to fine-tune their magnetic and magneto-transport properties. The magnetostatic contribution to the magnetic anisotropy of crossed nanowire networks can be easily controlled using the diameter, packing density, or angle distribution characteristics. Furthermore, the fabrication of Co and Co-rich NiCo alloy crossed nanowires with textured hcp phases leads to an additional significant magnetocrystalline contribution to the magnetic anisotropy that can either compete or add to the magnetostatic contribution. The fabrication of an interconnected nanotube network has also been demonstrated, where the hollow core and the control over the tube wall thickness add another degree of freedom to control the magnetic properties and magnetization reversal mechanisms. Finally, three-dimensional networks made of interconnected multilayered nanowire with a succession of ferromagnetic and non-magnetic layers have been successfully fabricated, leading to giant magnetoresistance responses measured in the current-perpendicular-to-plane configuration. These interconnected nanowire networks have high potential as integrated, reliable, and stable magnetic field sensors; magnetic devices for memory and logic operations; or neuromorphic computing. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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14 pages, 4330 KiB

Open AccessArticle

A Novel Design of a 3D Racetrack Memory Based on Functional Segments in Cylindrical Nanowire Arrays

by Javier Rial and Mariana P. Proenca

Nanomaterials 2020, 10(12), 2403; https://doi.org/10.3390/nano10122403 - 01 Dec 2020

Cited by 16 | Viewed by 2289

Abstract

A racetrack memory is a device where the information is stored as magnetic domains (bits) along a nanowire (track). To read and record the information, the bits are moved along the track by current pulses until they reach the reading/writing heads. In particular, [...] Read more.

A racetrack memory is a device where the information is stored as magnetic domains (bits) along a nanowire (track). To read and record the information, the bits are moved along the track by current pulses until they reach the reading/writing heads. In particular, 3D racetrack memory devices use arrays of vertically aligned wires (tracks), thus enhancing storage density. In this work, we propose a novel 3D racetrack memory configuration based on functional segments inside cylindrical nanowire arrays. The innovative idea is the integration of the writing element inside the racetrack itself, avoiding the need to implement external writing heads next to the track. The use of selective magnetic segments inside one nanowire allows the creation of writing and storage sections inside the same track, separated by chemical constraints identical to those separating the bits. Using micromagnetic simulations, our study reveals that if the writing section is composed of two segments with different coercivities, one can reverse its magnetization independently from the rest of the memory device by applying an external magnetic field. Spin-polarized current pulses then move the information bits along selected tracks, completing the writing process by pushing the new bit into the storage section of the wire. Finally, we have proven the efficacy of this system inside an array of 7 nanowires, opening the possibility to use this configuration in a 3D racetrack memory device composed of an array of thousands of nanowires produced by low-cost and high-yield template-electrodeposition methods. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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Review

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42 pages, 16350 KiB

Open AccessReview

Review of Domain Wall Dynamics Engineering in Magnetic Microwires

by Valentina Zhukova, Paula Corte-Leon, Lorena González-Legarreta, Ahmed Talaat, Juan Maria Blanco, Mihail Ipatov, Jesus Olivera and Arcady Zhukov

Nanomaterials 2020, 10(12), 2407; https://doi.org/10.3390/nano10122407 - 01 Dec 2020

Cited by 35 | Viewed by 3272

Abstract

The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, [...] Read more.

The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly affect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated. Full article

(This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes)

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