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Research on Hard Magnetic Materials: Synthesis, Properties, and Applications
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Research on Hard Magnetic Materials: Synthesis, Properties, and Applications

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Physics".

Deadline for manuscript submissions: closed (20 December 2024) | Viewed by 7312

Special Issue Editors

Dr. Petra Jenuš

E-Mail Website
Guest Editor
Jožef Stefan Institute, Ljubljana, Slovenia
Interests: ferrite-based permanent magnets; bottom-up and top-down synthesis of ferrite-based materials; conventional and advanced consolidation of metallic and ceramic materials; hard-soft magnetic composites; phase, microstructure and magnetic characterization; mechanical properties
Dr. César De Julián Fernández

E-Mail Website
Guest Editor
Institute of Materials for Electronics and Magnetism (IMEM), National Research Council (CNR), Parma, Italy
Interests: nanophysics: nanoelectronics, nanophotonics, nanomagnetism; new materials: oxides, alloys, composite, organic-inorganic hybrid, nanoparticles; magnetism; permanent magnets and high anisotropy materials; characterization methods of materials

Special Issue Information

Dear Colleagues,

The Green Transition is the most important challenge of 21st-century society. Magnetic materials play a vital role in this modern transformation as being involved in most sustainable energy-transformation technologies, transport, and novel biomedical applications are key elements for improving energy efficiency, materials reduction, CO2 emission reduction and improvement of health and life quality.

This Special Issue will provide a comprehensive overview and the most recent advances in topics related to the synthesis, properties and applications of magnetic materials that participated in the Green Transition. Therefore, we invite contributions that identify novel synthesis approaches, eco-friendly and/or reduction in energy consumption, and/or improved properties of hard and/or soft magnetic materials that are precisely tailored to offer unique advantages to be used in applications for the Green Transition.

The included topics (but not limited to):

  • Permanent magnets for electric motors (electric traction, vehicles and wind generation);
  • Soft magnetic materials for motors and sensors;
  • Magnetic nanomaterials for biomedical applications, green catalysis and water purification;
  • Designed materials and applications;
  • Magnetocaloric materials for eco-friendly cooling technologies;
  • Materials for IoT and spintronics for energy efficiency improvement;
  • Recycling techniques of magnetic materials.

It is our pleasure to invite you to submit a manuscript. Full papers, communications, and reviews are all welcome.

Dr. Petra Jenuš
Dr. César De Julián Fernández
Guest Editors

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

  • magnetic materials
  • hard magnets
  • synthesis
  • magnetic properties
  • hard magnetic composites
  • green transition
  • recycling

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Published Papers (5 papers)

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Research

11 pages, 8288 KiB  
Article
Magnetic Performance and Anticorrosion Coating Stability of Thermally Demagnetized Nd-Fe-B Permanent Magnets for Reuse Applications
by Tomaž Tomše, Pierre Kubelka, Rosario Moreno López, Peter Fleissner, Laura Grau, Matej Zaplotnik and Carlo Burkhardt
Materials 2024, 17(23), 5927; https://doi.org/10.3390/ma17235927 - 4 Dec 2024
Viewed by 772
Abstract
Nd-Fe-B-type permanent magnets, containing approximately 30% critical rare-earth elements by weight, are essential components in renewable energy systems (e.g., wind turbines, hydroelectric generators) and electric vehicles. They are also critical for consumer electronics and electric motors in products like energy-efficient air conditioners and [...] Read more.
Nd-Fe-B-type permanent magnets, containing approximately 30% critical rare-earth elements by weight, are essential components in renewable energy systems (e.g., wind turbines, hydroelectric generators) and electric vehicles. They are also critical for consumer electronics and electric motors in products like energy-efficient air conditioners and home appliances. In light of advancing sustainability goals, the direct reuse of magnets from end-of-life devices offers a promising alternative to energy-intensive and costly recycling methods based on hydro- and pyrometallurgical processes, as well as modern short-loop recycling through hydrogen processing. However, Nd-Fe-B magnets must be demagnetized before they can be extracted from devices. This study explores the effects of thermal demagnetization, performed either in air or a vacuum, on the stability of anticorrosion coatings and the magnetic performance of remagnetized magnets. Corrosion tests were conducted to assess the compatibility of various coatings with thermal demagnetization, identifying those most suitable for future applications involving magnet reuse. Full article
(This article belongs to the Special Issue Research on Hard Magnetic Materials: Synthesis, Properties, and Applications)
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12 pages, 2815 KiB  
Article
Effects of Thermal Demagnetization in Air on the Microstructure and Organic Contamination of NdFeB Magnets
by Laura Grau, Rosario Moreno López, Pierre Kubelka, Fabian Burkhardt, Tomaž Tomše, Spomenka Kobe and Carlo Burkhardt
Materials 2024, 17(22), 5528; https://doi.org/10.3390/ma17225528 - 13 Nov 2024
Viewed by 807
Abstract
Demagnetization is an essential step for the demounting and safe handling of end-of-life NdFeB. Thermal demagnetization in air is a straightforward option to demount adhesive-fixed or segmented magnets. However, this process is suspected to increase the uptake of contaminants like O, C and [...] Read more.
Demagnetization is an essential step for the demounting and safe handling of end-of-life NdFeB. Thermal demagnetization in air is a straightforward option to demount adhesive-fixed or segmented magnets. However, this process is suspected to increase the uptake of contaminants like O, C and Zn from coatings and adhesives, potentially degrading the recyclate quality. This study tests the effects of thermal demagnetization in air at 400 °C for 15 to 240 min on variously coated samples with different initial oxidation levels. Furthermore, the possible reversal of the contaminant uptake is explored. Samples with low previous oxidation levels showed significant uptake in oxygen with a minimal diffusion depth, while the uptake depended on the used coating. The best protectiveness was achieved with NiCuNi with an increase in oxygen of only around 30%. Epoxy (up to ~130% O uptake) and Zn coatings (up to ~80% O uptake) disintegrated during the treatment and offered less protection but still made a difference compared to uncoated samples (up to ~220% O uptake). Samples with high initial oxidation levels show no clear tendency towards further oxygen uptake and the carbon uptake is generally low, likely due to contemporary epoxy coatings featuring a passivation underneath as a barrier layer. Zn infiltration, which carried organic debris, was observed. Short demagnetization times proved to be favorable for limiting the depth of the diffusing contaminants. Mechanical coating removal after thermal demagnetization in air can mitigate the contaminant uptake, producing clean, recyclable end-of-life material. Full article
(This article belongs to the Special Issue Research on Hard Magnetic Materials: Synthesis, Properties, and Applications)
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12 pages, 2748 KiB  
Article
Processability and Separability of Commercial Anti-Corrosion Coatings Produced by In Situ Hydrogen-Processing of Magnetic Scrap (HPMS) Recycling of NdFeB
by Laura Grau, Peter Fleissner, Spomenka Kobe and Carlo Burkhardt
Materials 2024, 17(11), 2487; https://doi.org/10.3390/ma17112487 - 21 May 2024
Cited by 5 | Viewed by 1473
Abstract
The recycling of NdFeB magnets is necessary to ensure a reliable and ethical supply of rare earth elements as critical raw materials. This has been recognized internationally, prompting the implementation of large-scale legislative measured aimed at its resolution; for example, an ambitious recycling [...] Read more.
The recycling of NdFeB magnets is necessary to ensure a reliable and ethical supply of rare earth elements as critical raw materials. This has been recognized internationally, prompting the implementation of large-scale legislative measured aimed at its resolution; for example, an ambitious recycling quote has been established in the Critical Raw Materials Act Successful recycling in sufficient quantities is challenged by product designs that do not allow the extraction and recycling of these high-performance permanent magnets without excessive effort and cost. This is particularly true for smaller motors using NdFeB magnets. Therefore, methods of recycling such arrangements with little or no dismantling are being researched. They are tested for the hydrogen-processing of magnetic scrap (HPMS) method, a short-loop mechanical recycling process. As contamination of the recycled material with residues of anti-corrosion coatings, adhesives, etc., may lead to downcycling, the separability of such residues from bulk magnets and magnet powder is explored. It is found that the hydrogen permeability, expansion volume, and the chosen coating affect the viable preparation and separation methods as recyclability-relevant design features. Full article
(This article belongs to the Special Issue Research on Hard Magnetic Materials: Synthesis, Properties, and Applications)
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11 pages, 3893 KiB  
Article
Optimizing the Sintering Conditions of (Fe,Co)1.95(P,Si) Compounds for Permanent Magnet Applications
by Jin Yiderigu, Hargen Yibole, Lingbo Bao, Lingling Bao and François Guillou
Materials 2024, 17(11), 2476; https://doi.org/10.3390/ma17112476 - 21 May 2024
Viewed by 1197
Abstract
(Fe,Co)2(P,Si) quaternary compounds combine large uniaxial magnetocrystalline anisotropy, significant saturation magnetization and tunable Curie temperature, making them attractive for permanent magnet applications. Single crystals or conventionally prepared bulk polycrystalline (Fe,Co)2(P,Si) samples do not, however, show a significant coercivity. Here, [...] Read more.
(Fe,Co)2(P,Si) quaternary compounds combine large uniaxial magnetocrystalline anisotropy, significant saturation magnetization and tunable Curie temperature, making them attractive for permanent magnet applications. Single crystals or conventionally prepared bulk polycrystalline (Fe,Co)2(P,Si) samples do not, however, show a significant coercivity. Here, after a ball-milling stage of elemental precursors, we optimize the sintering temperature and duration during the solid-state synthesis of bulk Fe1.85Co0.1P0.8Si0.2 compounds so as to obtain coercivity in bulk samples. We pay special attention to shortening the heat treatment in order to limit grain growth. Powder X-ray diffraction experiments demonstrate that a sintering of a few minutes is sufficient to form the desired Fe2P-type hexagonal structure with limited secondary-phase content (~5 wt.%). Coercivity is achieved in bulk Fe1.85Co0.1P0.8Si0.2 quaternary compounds by shortening the heat treatment. Surprisingly, the largest coercivities are observed in the samples presenting large amounts of secondary-phase content (>5 wt.%). In addition to the shape of the virgin magnetization curve, this may indicate a dominant wall-pining coercivity mechanism. Despite a tenfold improvement of the coercive fields for bulk samples, the achieved performances remain modest (HC ≈ 0.6 kOe at room temperature). These results nonetheless establish a benchmark for future developments of (Fe,Co)2(P,Si) compounds as permanent magnets. Full article
(This article belongs to the Special Issue Research on Hard Magnetic Materials: Synthesis, Properties, and Applications)
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13 pages, 2840 KiB  
Article
Short-Loop Recycling of Nd-Fe-B Permanent Magnets: A Sustainable Solution for the RE2Fe14B Matrix Phase Recovery
by Amit Mishra, Sina Khoshsima, Tomaž Tomše, Benjamin Podmiljšak, Sašo Šturm, Carlo Burkhardt and Kristina Žužek
Materials 2023, 16(19), 6565; https://doi.org/10.3390/ma16196565 - 5 Oct 2023
Cited by 3 | Viewed by 2162
Abstract
The green transition initiatives and exploitation of renewable energy sources require the sustainable development of rare earth (RE)-based permanent magnets prominent technologies like wind turbine generators and electric vehicles. The recycling of RE-based permanent magnets is necessary for the future supply of critical [...] Read more.
The green transition initiatives and exploitation of renewable energy sources require the sustainable development of rare earth (RE)-based permanent magnets prominent technologies like wind turbine generators and electric vehicles. The recycling of RE-based permanent magnets is necessary for the future supply of critical rare-earth elements. The short-loop recycling strategies to directly reprocess Nd-Fe-B magnet waste are economically attractive and practical alternatives to conventional hydro- and pyrometallurgical processes. This study focuses on the development of a procedure to extract the (Nd, Pr)2Fe14B hard-magnetic phase from sintered Nd-Fe-B magnets. The extraction is achieved through preferential chemical leaching of the secondary, RE-rich phases using 1 M citric acid. Before the acid treatment, the magnets were pulverized through hydrogen decrepitation (HD) to increase the material’s surface-to-volume ratio. The as-pulverized Nd-Fe-B powder was subsequently exposed to a 1 M citric acid solution. The effect of leaching time (5–120 min) on the phase composition and magnetic properties was studied. The results of the microstructural (SEM) and compositional (ICP-MS) analyses and the study of thermal degassing profiles revealed that the RE-rich phase is preferentially leached within 5–15 min of reaction time. Leaching of the secondary phases from the magnet’s multi-phase microstructure is governed by the negative electrochemical potential of Nd and Pr. The extraction of (Nd, Pr)2Fe14B grains by the proposed acid leaching approach is compatible with the existing hydrogen processing of magnetic scrap (HPMS) technologies. The use of mild organic acid as a leaching medium makes the leaching process environmentally friendly, as the leaching medium can be easily neutralized after the reaction is completed. Full article
(This article belongs to the Special Issue Research on Hard Magnetic Materials: Synthesis, Properties, and Applications)
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