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Advances in Superconductive and Magnetic Nanomaterials

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A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 June 2018) | Viewed by 28226

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Prof. Dr. Jose Maria De Teresa

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Instituto de Nanociencia y Materiales de Aragón, CSIC-Universidad de Zaragoza, Facultad de Ciencias, 50009 Zaragoza, Spain
Interests: advanced nanolithography techniques by focused ion and electron beams; nano-magnetism and spintronics; nano-superconductivity; new materials (graphene, topological materials, etc.)
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Special Issue Information

Dear Colleagues,

Magnetic and superconductive materials currently have great impact in our daily lives: It is difficult to imagine our current life without motors or magnetic resonance imaging. In the last 25 years, nanotechnology has opened up new perspectives in the development of magnetic and superconducting materials and corresponding new applications. Successful stories can be mentioned in fields such as magnetic data storage, magnetic hyperthermia in biomedicine, quantum computation, advanced sensors, etc. All these new developments call for magnetic or superconducting advanced materials with dimensions tailored to the nanoscale. Enormous efforts have been made to improve the functionality of these nanomaterials, either by optimizing their compositions or their dimensions or the device concepts themselves.

The present Special Issue aims to collect representative work of the latest advances in superconductive and magnetic nanomaterials and their applications. In particular, contributions are expected on the following topics:

Magnetic nanomaterials: magnetic thin films and multilayers, magnetic nanowires, nanotubes and nanoparticles, 3D magnetic nano-objects, nanopatterning of magnetic materials, spintronic effects, interface-driven magnetic phenomena, multiferroic nanomaterials, domain-wall conduits, micromagnetic simulations, magnetic exchange bias, magnetic skyrmions, magnetic microscopy and imaging, and magnetic nano-devices.

Superconducting nanomaterials: superconducting nanowires and films, nanopatterned superconductors, superconducting nanocontacts, nano-SQUIDs, vortex in nanostructured superconductors, vortex dynamics and pinning, vortex imaging, interface superconductivity, quantum behaviour in low-dimensional superconductors, mesoscopic superconductivity, superconductor qubits, superconducting nano-devices, etc.

Hybrid devices including magnetic and superconducting nanomaterials: proximity effects, coexistence of magnetism and superconductivity, superconductor vortex pinning with magnetic nanomaterials, Andreev reflection, hybrid magnetic-superconductor sensors, etc.

It is my pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Jose Maria De Teresa
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Nanostructured magnetic materials
Nanostructured superconductors
Magnetic, superconducting or hybrid nano-devices

Published Papers (6 papers)

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Research

16 pages, 4575 KiB

Open AccessFeature PaperArticle

Magnetic Characterization of Direct-Write Free-Form Building Blocks for Artificial Magnetic 3D Lattices

by Mohanad K. I. Al Mamoori, Lukas Keller, Jonathan Pieper, Sven Barth, Robert Winkler, Harald Plank, Jens Müller and Michael Huth

Materials 2018, 11(2), 289; https://doi.org/10.3390/ma11020289 - 12 Feb 2018

Cited by 36 | Viewed by 5065

Abstract

Three-dimensional (3D) nanomagnetism, where spin configurations extend into the vertical direction of a substrate plane allow for more complex, hierarchical systems and the design of novel magnetic effects. As an important step towards this goal, we have recently demonstrated the direct-write fabrication of freestanding ferromagnetic 3D nano-architectures of ferromagnetic CoFe in shapes of nano-tree and nano-cube structures by means of focused electron beam induced deposition. Here, we present a comprehensive characterization of the magnetic properties of these structures by local stray-field measurements using a high-resolution micro-Hall magnetometer. Measurements in a wide range of temperatures and different angles of the externally applied magnetic field with respect to the surface plane of the sensor are supported by corresponding micromagnetic simulations, which explain the overall switching behavior of in part rather complex magnetization configurations remarkably well. In particular, the simulations yield coercive and switching fields that are in good quantitative correspondence with the measured coercive and switching fields assuming a bulk metal content of 100 at % consisting of bcc Co

_{3}

Fe. We show that thermally-unstable magnetization states can be repetitively prepared and their lifetime controlled at will, a prerequisite to realizing dynamic and thermally-active magnetic configurations if the building blocks are to be used in lattice structures. Full article

(This article belongs to the Special Issue Advances in Superconductive and Magnetic Nanomaterials)

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23 pages, 8516 KiB

Open AccessFeature PaperArticle

Modulation of Magnetic Properties at the Nanometer Scale in Continuously Graded Ferromagnets

by Lorenzo Fallarino, Patricia Riego, Brian J. Kirby, Casey W. Miller and Andreas Berger

Materials 2018, 11(2), 251; https://doi.org/10.3390/ma11020251 - 06 Feb 2018

Cited by 16 | Viewed by 4186

Abstract

Ferromagnetic alloy materials with designed composition depth profiles provide an efficient route for the control of magnetism at the nanometer length scale. In this regard, cobalt-chromium and cobalt-ruthenium alloys constitute powerful model systems. They exhibit easy-to-tune magnetic properties such as saturation magnetization M_S and Curie temperature T_C while preserving their crystalline structure over a wide composition range. In order to demonstrate this materials design potential, we have grown a series of graded Co_1−xCr_x and Co_1−wRu_w (10

\bar{1}

0) epitaxial thin films, with x and w following predefined concentration profiles. Structural analysis measurements verify the epitaxial nature and crystallographic quality of our entire sample sets, which were designed to exhibit in-plane c-axis orientation and thus a magnetic in-plane easy axis to achieve suppression of magnetostatic domain generation. Temperature and field-dependent magnetic depth profiles have been measured by means of polarized neutron reflectometry. In both investigated structures, T_C and M_S are found to vary as a function of depth in accordance with the predefined compositional depth profiles. Our Co_1−wRu_w sample structures, which exhibit very steep material gradients, allow us to determine the localization limit for compositionally graded materials, which we find to be of the order of 1 nm. The Co_1−xCr_x systems show the expected U-shaped T_C and M_S depth profiles, for which these specific samples were designed. The corresponding temperature dependent magnetization profile is then utilized to control the coupling along the film depth, which even allows for a sharp onset of decoupling of top and bottom sample parts at elevated temperatures. Full article

(This article belongs to the Special Issue Advances in Superconductive and Magnetic Nanomaterials)

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10 pages, 4007 KiB

Open AccessFeature PaperArticle

Vortex Lattice Instabilities in YBa₂Cu₃O_7-x Nanowires

by Víctor Rouco, Davide Massarotti, Daniela Stornaiuolo, Gian Paolo Papari, Xavier Obradors, Teresa Puig, Francesco Tafuri and Anna Palau

Materials 2018, 11(2), 211; https://doi.org/10.3390/ma11020211 - 30 Jan 2018

Cited by 12 | Viewed by 4094

Abstract

High-resolution focused ion beam lithography has been used to fabricate YBa₂Cu₃O_7-x (YBCO) wires with nanometric lateral dimensions. In the present work, we investigate Flux-flow instabilities in nanowires of different widths, showing sudden voltage switching jumps from the superconducting to the normal state. We present an extensive study on the temperature and field dependence of the switching characteristics which reveal that voltage jumps become less abrupt as the temperature increases, and disappear at the vortex-liquid state. On the contrary, the current distribution at the critical point becomes narrower at high temperatures. Sharp voltage switchings very close to the critical current density can be obtained by reducing the width of the nanowires, making them very appealing for practical applications. Full article

(This article belongs to the Special Issue Advances in Superconductive and Magnetic Nanomaterials)

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11 pages, 1885 KiB

Open AccessFeature PaperArticle

Magnetization Reversal Modes in Short Nanotubes with Chiral Vortex Domain Walls

by Ai Ping Chen, Julian Gonzalez and Konstantin Guslienko

Materials 2018, 11(1), 101; https://doi.org/10.3390/ma11010101 - 10 Jan 2018

Cited by 5 | Viewed by 3400

Abstract

Micromagnetic simulations of magnetization reversal were performed for magnetic nanotubes of a finite length, L, equal to 1 and 2 μm, 50 and 100 nm radii, R, and uniaxial anisotropy with “easy axis” parallel to the tube length. I.e., we considered relatively short nanotubes with the aspect ratio L/R in the range 10–40. The non-uniform curling magnetization states on both ends of the nanotubes can be treated as vortex domain walls (DW). The domain wall length, L_c, depends on the tube geometric parameters and the anisotropy constant K_u, and determines the magnetization reversal mode, as well as the switching field value. For nanotubes with relative small values of L_c (L_c/L < 0.2) the magnetization reversal process is characterized by flipping of the magnetization in the middle uniform state. Whereas, for relative large values of L_c, in the reverse magnetic field, coupling of two vortex domain walls with opposite magnetization rotation directions results in the formation of a specific narrow Néel type DW in the middle of the nanotube. The nanotube magnetization suddenly aligns to the applied field at the switching field, collapsing the central DW. Full article

(This article belongs to the Special Issue Advances in Superconductive and Magnetic Nanomaterials)

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9670 KiB

Open AccessFeature PaperArticle

Structurally Oriented Nano-Sheets in Co Thin Films: Changing Their Anisotropic Physical Properties by Thermally-Induced Relaxation

by José Vergara, Cristina Favieres, César Magén, José María De Teresa, Manuel Ricardo Ibarra and Vicente Madurga

Materials 2017, 10(12), 1390; https://doi.org/10.3390/ma10121390 - 05 Dec 2017

Cited by 5 | Viewed by 4029

Abstract

We show how nanocrystalline Co films formed by separated oblique nano-sheets display anisotropy in their resistivity, magnetization process, surface nano-morphology and optical transmission. After performing a heat treatment at 270 °C, these anisotropies decrease. This loss has been monitored measuring the resistivity as a function of temperature. The resistivity measured parallel to the direction of the nano-sheets has been constant up to 270 °C, but it decreases when measured perpendicular to the nano-sheets. This suggests the existence of a structural relaxation, which produces the change of the Co nano-sheets during annealing. The changes in the nano-morphology and the local chemical composition of the films at the nanoscale after heating above 270 °C have been analysed by scanning transmission electron microscopy (STEM). Thus, an approach and coalescence of the nano-sheets have been directly visualized. The spectrum of activation energies of this structural relaxation has indicated that the coalescence of the nano-sheets has taken place between 1.2 and 1.7 eV. In addition, an increase in the size of the nano-crystals has occurred in the samples annealed at 400 °C. This study may be relevant for the application in devices working, for example, in the GHz range and to achieve the retention of the anisotropy of these films at higher temperatures. Full article

(This article belongs to the Special Issue Advances in Superconductive and Magnetic Nanomaterials)

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2665 KiB

Open AccessArticle

Magnetic Hysteresis in Nanocomposite Films Consisting of a Ferromagnetic AuCo Alloy and Ultrafine Co Particles

by Federico Chinni, Federico Spizzo, Federico Montoncello, Valentina Mattarello, Chiara Maurizio, Giovanni Mattei and Lucia Del Bianco

Materials 2017, 10(7), 717; https://doi.org/10.3390/ma10070717 - 28 Jun 2017

Cited by 13 | Viewed by 6786

Abstract

One fundamental requirement in the search for novel magnetic materials is the possibility of predicting and controlling their magnetic anisotropy and hence the overall hysteretic behavior. We have studied the magnetism of Au:Co films (~30 nm thick) with concentration ratios of 2:1, 1:1, and 1:2, grown by magnetron sputtering co-deposition on natively oxidized Si substrates. They consist of a AuCo ferromagnetic alloy in which segregated ultrafine Co particles are dispersed (the fractions of Co in the AuCo alloy and of segregated Co increase with decreasing the Au:Co ratio). We have observed an unexpected hysteretic behavior characterized by in-plane anisotropy and crossed branches in the loops measured along the hard magnetization direction. To elucidate this phenomenon, micromagnetic calculations have been performed for a simplified system composed of two exchange-coupled phases: a AuCo matrix surrounding a Co cluster, which represents an aggregate of particles. The hysteretic features are qualitatively well reproduced provided that the two phases have almost orthogonal anisotropy axes. This requirement can be plausibly fulfilled assuming a dominant magnetoelastic character of the anisotropy in both phases. The achieved conclusions expand the fundamental knowledge on nanocomposite magnetic materials, offering general guidelines for tuning the hysteretic properties of future engineered systems. Full article

(This article belongs to the Special Issue Advances in Superconductive and Magnetic Nanomaterials)

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