Special Issue "High-Performance Nanomagnets: Alternatives to Rare-Earth-Based Magnets"

Dear Colleagues,

The ever-growing technological demand for permanent magnets has driven, since their discovery, the difficult task of improving the properties of these materials. Since the 1960s, these magnets have mainly been based on rare earth (RE) alloys. RE resources have remained scarce, and are unevenly distributed in the Earth’s crust, leading to possible RE provisioning fault and risk of raw price crisis. Additionally, their extraction has a huge impact on the local environment and severe health consequences for the neighbors of mining operations. These magnets, as alloys, are very sensitive to corrosion, and the existing recycling processes irreversibly reduce their magnetization, making the efficiency of recycling the RE from manufactured magnets insufficiently developed to change the magnet-based industry from RE mining to recycling.

In this context, the subject of reduced-RE magnets becomes crucial, and several research and development efforts are ongoing in order to improve the intrinsic anisotropy of already known RE-free ferro- or ferrimagnetic high-T_C compounds by including other anisotropy sources through domain-wall motion prevention, shape anisotropy or intergrain exchange coupling, or to produce new ferromagnetic materials exhibiting high magnetocrystalline anisotropy exploring new crystalline structures and/or new chemical compositions.

Indeed, it is now well-established that the size, thickness, and shape of nanomagnets, as well as their chemical compositions, play a vital role in determining their magnetic properties, surpassing in certain cases those of their bulk counterparts, allowing in favorable cases unexpected higher-order anisotropy terms to appear.

The recent advances in magnetic fine size- and shape-controlled particle production by chemical, physical, or mechanical routes have propelled a renewed interest in magnetic granular nanostructures, and an increasing number of studies are being conducted attempting to use these experimental strategies to design RE-free magnetic building blocks, and to assemble them while maintaining their nanostructure. As an example, the synthesis of 3D ferromagnetic metal nanowires and their assembly within polymeric matrices while controlling their alignment and their volume fraction to minimize their mutual dipolar interactions is now in progress. Magnetically contrasted 3D metal-oxide-based granular hetero-nanostructures and their flash sintering while controlling the interphase interactions in the resulting nanoconsolidates are also under focus. Research on high-entropy nanoalloys focusing on modifying their chemical formulation and nanostructure in order to address hard magnetic properties are also in progress. The possibility offered by cold-plasma implantation on nanostructures to produce various intermetallics (e.g., carbides, nitrides) with potentially hard magnetic properties also opens alternatives toward RE-free magnet processing.  

These examples are not at all exhaustive, but they highlight the diversity of approaches being considered to develop high-performance nanomagnets as alternatives to RE-based magnets. Therefore, this Special Issue invites manuscripts concerning the synthesis of nanoparticles with improved magnetic properties, their characterization, and their shaping, with a special emphasis on their application as permanent magnets. Original articles on synthesis strategies will be considered, including those on the preparation of magnetic nanohybrids and nanocomposites, shape-anisotropic nano-objects, and new compounds. Articles describing magnetic nanoparticle shaping (spark plasma sintering, ferrofluid chemistry, 3D printing, polymer embedding, etc.), including in-field processing, and the successful magnetic characterization of the resulting nanomaterials as permanent magnets will of course also be welcome.

Prof. Dr. Souad Ammar-Merah
Guest Editor

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• permanent magnets
• magnetic nanoparticles
• magnetic nanocomposites
• ferrofluids
• exchange bias
• spring magnets
• magnetic nanomaterials shaping
• in-field nanomaterial processing
• magnetic characterization