Nanomaterials

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3 pages, 186 KiB

Open AccessEditorial

Novel Magnetic Properties in Curved Geometries

by Cristina Bran

Nanomaterials 2022, 12(7), 1175; https://doi.org/10.3390/nano12071175 - 1 Apr 2022

Viewed by 1489

Abstract

The expanding of planar magnetic structures into three dimensions (3D) creates the possibility of tuning the conventional magnetic textures or producing novel effects and functionalities by tailoring their curvature [...] Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

Research

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13 pages, 3301 KiB

Open AccessArticle

Magnetization Reversal Process and Magnetostatic Interactions in Fe₅₆Co₄₄/SiO₂/Fe₃O₄ Core/Shell Ferromagnetic Nanowires with Non-Magnetic Interlayer

by Javier García, Alejandro M. Manterola, Miguel Méndez, Jose Angel Fernández-Roldán, Víctor Vega, Silvia González and Víctor M. Prida

Nanomaterials 2021, 11(9), 2282; https://doi.org/10.3390/nano11092282 - 2 Sep 2021

Cited by 12 | Viewed by 2450

Abstract

Nowadays, numerous works regarding nanowires or nanotubes are being published, studying different combinations of materials or geometries with single or multiple layers. However, works, where both nanotube and nanowires are forming complex structures, are scarcer due to the underlying difficulties that their fabrication [...] Read more.

Nowadays, numerous works regarding nanowires or nanotubes are being published, studying different combinations of materials or geometries with single or multiple layers. However, works, where both nanotube and nanowires are forming complex structures, are scarcer due to the underlying difficulties that their fabrication and characterization entail. Among the specific applications for these nanostructures that can be used in sensing or high-density magnetic data storage devices, there are the fields of photonics or spintronics. To achieve further improvements in these research fields, a complete understanding of the magnetic properties exhibited by these nanostructures is needed, including their magnetization reversal processes and control of the magnetic domain walls. In order to gain a deeper insight into this topic, complex systems are being fabricated by altering their dimensions or composition. In this work, a successful process flow for the additive fabrication of core/shell nanowires arrays is developed. The core/shell nanostructures fabricated here consist of a magnetic nanowire nucleus (Fe₅₆Co₄₄), grown by electrodeposition and coated by a non-magnetic SiO₂ layer coaxially surrounded by a magnetic Fe₃O₄ nanotubular coating both fabricated by means of the Atomic Layer Deposition (ALD) technique. Moreover, the magnetization reversal processes of these coaxial nanostructures and the magnetostatic interactions between the two magnetic components are investigated by means of standard magnetometry and First Order Reversal Curve methodology. From this study, a two-step magnetization reversal of the core/shell bimagnetic nanostructure is inferred, which is also corroborated by the hysteresis loops of individual core/shell nanostructures measured by Kerr effect-based magnetometer. Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

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15 pages, 5308 KiB

Open AccessArticle

High-Frequency Magnetoimpedance (MI) and Stress-MI in Amorphous Microwires with Different Anisotropies

by Junaid Alam, Makhsudsho Nematov, Nikolay Yudanov, Svetlana Podgornaya and Larissa Panina

Nanomaterials 2021, 11(5), 1208; https://doi.org/10.3390/nano11051208 - 2 May 2021

Cited by 11 | Viewed by 3167

Abstract

Magnetoimpedance (MI) in Co-based microwires with an amorphous and partially crystalline state was investigated at elevated frequencies (up to several GHz), with particular attention paid to the influence of tensile stress on the MI behavior, which is called stress-MI. Two mechanisms of MI [...] Read more.

Magnetoimpedance (MI) in Co-based microwires with an amorphous and partially crystalline state was investigated at elevated frequencies (up to several GHz), with particular attention paid to the influence of tensile stress on the MI behavior, which is called stress-MI. Two mechanisms of MI sensitivity related to the DC magnetization re-orientation and AC permeability dispersion were discussed. Remarkable sensitivity of impedance changes with respect to applied tensile stress at GHz frequencies was obtained in partially crystalline wires subjected to current annealing. Increasing the annealing current enhanced the axial easy anisotropy of a magnetoelastic origin, which made it possible to increase the frequency of large stress-MI: for 90mA-annealed wire, the impedance at 2 GHz increased by about 300% when a stress of 450 MPa was applied. Potential applications included sensing elements in stretchable substrates for flexible electronics, wireless sensors, and tunable smart materials. For reliable microwave measurements, an improved SOLT (short-open-load-thru) calibration technique was developed that required specially designed strip cells as wire holders. The method made it possible to precisely measure the impedance characteristics of individual wires, which can be further employed to characterize the microwave scattering at wire inclusions used as composites fillers. Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

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16 pages, 10034 KiB

Open AccessArticle

An Indirect Method of Micromagnetic Structure Estimation in Microwires

by Iuliia Alekhina, Valeria Kolesnikova, Vladimir Rodionov, Nikolai Andreev, Larissa Panina, Valeria Rodionova and Nikolai Perov

Nanomaterials 2021, 11(2), 274; https://doi.org/10.3390/nano11020274 - 21 Jan 2021

Cited by 9 | Viewed by 2060

Abstract

The tunable magnetic properties of amorphous ferromagnetic glass-coated microwires make them suitable for a wide range of applications. Accurate knowledge of the micromagnetic structure is highly desirable since it affects almost all magnetic properties. To select an appropriate wire-sample for a specific application, [...] Read more.

The tunable magnetic properties of amorphous ferromagnetic glass-coated microwires make them suitable for a wide range of applications. Accurate knowledge of the micromagnetic structure is highly desirable since it affects almost all magnetic properties. To select an appropriate wire-sample for a specific application, a deeper understanding of the magnetization reversal process is required, because it determines the measurable response (such as induced voltage waveform and its spectrum). However, the experimental observation of micromagnetic structure of micro-scale amorphous objects has strict size limitations. In this work we proposed a novel experimental technique for evaluating the microstructural characteristics of glass-coated microwires. The cross-sectional permeability distribution in the sample was obtained from impedance measurements at different frequencies. This distribution enables estimation of the prevailing anisotropy in the local region of the wire cross-section. The results obtained were compared with the findings of magnetostatic measurements and remanent state analysis. The advantages and limitations of the methods were discussed. Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

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20 pages, 3929 KiB

Open AccessArticle

Spin Caloritronics in 3D Interconnected Nanowire Networks

by Tristan da Câmara Santa Clara Gomes, Nicolas Marchal, Flavio Abreu Araujo and Luc Piraux

Nanomaterials 2020, 10(11), 2092; https://doi.org/10.3390/nano10112092 - 22 Oct 2020

Cited by 18 | Viewed by 2674

Abstract

Recently, interconnected nanowire networks have been found suitable as flexible macroscopic spin caloritronic devices. The 3D nanowire networks are fabricated by direct electrodeposition in track-etched polymer templates with crossed nano-channels. This technique allows the fabrication of crossed nanowires consisting of both homogeneous ferromagnetic [...] Read more.

Recently, interconnected nanowire networks have been found suitable as flexible macroscopic spin caloritronic devices. The 3D nanowire networks are fabricated by direct electrodeposition in track-etched polymer templates with crossed nano-channels. This technique allows the fabrication of crossed nanowires consisting of both homogeneous ferromagnetic metals and multilayer stack with successive layers of ferromagnetic and non-magnetic metals, with controlled morphology and material composition. The networks exhibit extremely high, magnetically modulated thermoelectric power factors. Moreover, large spin-dependent Seebeck coefficients were directly extracted from experimental measurements on multilayer nanowire networks. This work provides a simple and cost-effective way to fabricate large-scale flexible and shapeable thermoelectric devices exploiting the spin degree of freedom. Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

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Review

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27 pages, 9405 KiB

Open AccessReview

Magnetic Configurations in Modulated Cylindrical Nanowires

by Cristina Bran, Jose Angel Fernandez-Roldan, Rafael P. del Real, Agustina Asenjo, Oksana Chubykalo-Fesenko and Manuel Vazquez

Nanomaterials 2021, 11(3), 600; https://doi.org/10.3390/nano11030600 - 28 Feb 2021

Cited by 28 | Viewed by 3256

Abstract

Cylindrical magnetic nanowires show great potential for 3D applications such as magnetic recording, shift registers, and logic gates, as well as in sensing architectures or biomedicine. Their cylindrical geometry leads to interesting properties of the local domain structure, leading to multifunctional responses to [...] Read more.

Cylindrical magnetic nanowires show great potential for 3D applications such as magnetic recording, shift registers, and logic gates, as well as in sensing architectures or biomedicine. Their cylindrical geometry leads to interesting properties of the local domain structure, leading to multifunctional responses to magnetic fields and electric currents, mechanical stresses, or thermal gradients. This review article is summarizing the work carried out in our group on the fabrication and magnetic characterization of cylindrical magnetic nanowires with modulated geometry and anisotropy. The nanowires are prepared by electrochemical methods allowing the fabrication of magnetic nanowires with precise control over geometry, morphology, and composition. Different routes to control the magnetization configuration and its dynamics through the geometry and magnetocrystalline anisotropy are presented. The diameter modulations change the typical single domain state present in cubic nanowires, providing the possibility to confine or pin circular domains or domain walls in each segment. The control and stabilization of domains and domain walls in cylindrical wires have been achieved in multisegmented structures by alternating magnetic segments of different magnetic properties (producing alternative anisotropy) or with non-magnetic layers. The results point out the relevance of the geometry and magnetocrystalline anisotropy to promote the occurrence of stable magnetochiral structures and provide further information for the design of cylindrical nanowires for multiple applications. Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

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19 pages, 8891 KiB

Open AccessFeature PaperReview

Focused-Electron-Beam Engineering of 3D Magnetic Nanowires

by César Magén, Javier Pablo-Navarro and José María De Teresa

Nanomaterials 2021, 11(2), 402; https://doi.org/10.3390/nano11020402 - 4 Feb 2021

Cited by 15 | Viewed by 2544

Abstract

Focused-electron-beam-induced deposition (FEBID) is the ultimate additive nanofabrication technique for the growth of 3D nanostructures. In the field of nanomagnetism and its technological applications, FEBID could be a viable solution to produce future high-density, low-power, fast nanoelectronic devices based on the domain wall [...] Read more.

Focused-electron-beam-induced deposition (FEBID) is the ultimate additive nanofabrication technique for the growth of 3D nanostructures. In the field of nanomagnetism and its technological applications, FEBID could be a viable solution to produce future high-density, low-power, fast nanoelectronic devices based on the domain wall conduit in 3D nanomagnets. While FEBID has demonstrated the flexibility to produce 3D nanostructures with almost any shape and geometry, the basic physical properties of these out-of-plane deposits are often seriously degraded from their bulk counterparts due to the presence of contaminants. This work reviews the experimental efforts to understand and control the physical processes involved in 3D FEBID growth of nanomagnets. Co and Fe FEBID straight vertical nanowires have been used as benchmark geometry to tailor their dimensions, microstructure, composition and magnetism by smartly tuning the growth parameters, post-growth purification treatments and heterostructuring. Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

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20 pages, 3720 KiB

Open AccessReview

Reversible and Non-Reversible Transformation of Magnetic Structure in Amorphous Microwires

by Alexander Chizhik, Julian Gonzalez, Arcady Zhukov, Przemyslaw Gawronski, Mihail Ipatov, Paula Corte-León, Juan Mari Blanco and Valentina Zhukova

Nanomaterials 2020, 10(8), 1450; https://doi.org/10.3390/nano10081450 - 24 Jul 2020

Cited by 4 | Viewed by 2067

Abstract

We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of [...] Read more.

We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found. Full article

(This article belongs to the Special Issue Novel Magnetic Properties in Curved Geometries)

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