Abstract
The HyPerMag project aims to develop a new generation of rare-earth-free permanent magnets by engineering hybrid nanocomposites. We combine hard and soft magnetic phases—specifically nanostructured hexaferrites and metallic alloys—coupled via exchange or dipolar interactions. The project will focus on designing hybrid powders with tailored morphology, magnetic coupling, and optimized particle size to maximize energy product (BHmax), coercivity, and remanence. The overarching goal is to fabricate bonded and dense permanent magnets with superior performance and stability, capable of replacing AlNiCo and rare-earth-based magnets in moderate-performance technological applications, especially in a circular and sustainable economy framework. The project will demonstrate scalable, green synthesis of nanostructured hybrid materials, and produce prototypes using innovative low-temperature or high-pressure densification techniques that preserve the nanostructure. It will also provide detailed insights into the coupling mechanisms between hard and soft phases combining advanced characterization techniques like NMR, and magnetic hysteresis analysis. These results aim to open industrial applications in sectors such as e-mobility, wind energy, and household appliances, reducing dependence on critical raw materials.
Results achieved
: The HyPerMag project addressed one of the major technological challenges in the field of permanent magnets: the development of innovative rare-earth-free permanent magnets based on hybrid nanocomposites combining hard and soft magnetic phases. The project explored new synthesis strategies, advanced characterization techniques and innovative consolidation methods to develop sustainable magnetic materials with improved magnetic performances, reducing the dependence on critical raw materials. A multidisciplinary approach involving chemistry, materials science, advanced spectroscopy, microscopy and theoretical modelling enabled the optimization of several families of nanostructured magnetic materials. Different synthesis routes were developed to produce hard magnetic strontium hexaferrite nanoparticles with characteristic sizes below 100 nm and coercive fields well above the current state of the art. The project also investigated several cation-substituted hexaferrites, including Mn- and Al-doped systems, clarifying the role of chemical substitution in controlling particle size, magnetic anisotropy and coercivity. In parallel, highly magnetized Fe-, FeCo- and FeNi-based nanostructures were synthesized, providing suitable soft magnetic counterparts for the preparation of hybrid hard–soft systems. An important achievement of the project has been the successful realization of several classes of hard–soft nanocomposites and dense magnets obtained by innovative low-temperature high-pressure consolidation techniques. Although the targeted magnetic energy product could not be fully achieved, the project identified the main physical mechanisms limiting the magnetic coupling between hard and soft phases and established clear directions for future optimization. In particular, exchange-coupled oxide–oxide heterostructures demonstrated excellent magnetic coupling at the nanoscale, while scalable hard–soft composites highlighted the technological challenges associated with preserving interparticle exchange interactions during magnet fabrication. The project also provided significant advances in the fundamental understanding of magnetization reversal and magnetic interactions in ferrite nanocomposites. The combination of structural, magnetic and spectroscopic techniques clarified the respective roles of interparticle exchange interactions, dipolar coupling, magnetic anisotropy and cation substitution, providing a comprehensive picture of the mechanisms controlling magnetic reversal from isolated nanoparticles to dense hybrid magnets. A distinctive contribution of the University of Bologna (UNIBO) research unit was the development and application of zero-field Nuclear Magnetic Resonance (NMR) as a local spectroscopic probe of magnetic nanostructures and hybrid ferrite composites. Beyond the conventional characterization of magnetic materials, the project considerably extended the capabilities of NMR spectroscopy for investigating magnetic interfaces, local magnetic anisotropy and exchange-coupled nanocomposites. NMR investigations performed on single-phase strontium hexaferrites provided unique information on the occupation of the different crystallographic Fe sites and on the effects of cation substitution. In particular, studies on Mn-substituted hexaferrites clarified the oxidation state and preferential crystallographic occupation of Mn ions, resolving previous ambiguities concerning their magnetic role and explaining the evolution of the macroscopic magnetic properties with increasing Mn concentration. The UNIBO unit also developed an original methodology based on the analysis of NMR linewidths to correlate local hyperfine fields with magnetic anisotropy and magnetic coupling in ferrite nanoparticles. The contribution of UNIBO was further extended to the investigation of hybrid hard–soft ferrite heterostructures. By combining ⁵⁷Fe NMR, Mössbauer spectroscopy, high-resolution electron microscopy and atomistic simulations, the project provided the first spectroscopic identification of a distinct magnetic environment associated with the interfaces between SrFe₁₂O₁₉ and CoFe₂O₄. The systematic evolution of the NMR resonance frequencies, together with the corresponding hyperfine fields measured by Mössbauer spectroscopy, provided direct experimental evidence of interfacial superexchange interactions between the hard and soft magnetic phases, establishing a coherent microscopic description of magnetic exchange across oxide–oxide interfaces. These results demonstrate how local spectroscopic techniques can directly probe exchange coupling, complementing conventional magnetic measurements. Another important methodological achievement concerns the use of the NMR radio-frequency enhancement factor as a local probe of magnetization reversal. The project demonstrated that its dependence on composition and temperature allows one to distinguish between incoherent magnetization reversal, typical of larger hard-ferrite grains, and progressively coherent reversal in strongly exchange-coupled heterostructures. This represents a significant methodological advance, extending the applicability of NMR spectroscopy from the investigation of local hyperfine interactions to the study of collective magnetic dynamics and effective magnetic anisotropy in complex nanostructured magnetic materials. The scientific impact of the project is demonstrated by publications in leading international journals together with several additional manuscripts currently under revision or preparation, extensive participation in international conferences, the training of young researchers through doctoral theses and postdoctoral activities, and the establishment of a broad network of collaborations among CNR, the Universities of Bologna, Genoa and Ca' Foscari Venice, together with several international research institutions. Overall, HyPerMag has significantly advanced both the fundamental understanding and the technological development of rare-earth-free permanent magnetic materials. The project established new synthesis strategies for ferrite nanostructures, introduced innovative spectroscopic methodologies capable of directly probing interfacial exchange coupling, magnetic anisotropy and magnetization reversal mechanisms, and identified the key factors governing magnetic coupling in hybrid nanocomposites. These results provide a solid scientific basis for the future development of sustainable permanent magnets based on ferrite nanostructures and demonstrate that advanced local spectroscopies such as NMR can play a central role in the design and optimization of next-generation magnetic nanocomposites.Project details
Unibo Team Leader: Samuele Sanna
Unibo involved Department/s:
Dipartimento di Fisica e Astronomia "Augusto Righi"
Coordinator:
CNR - Consiglio Nazionale delle Ricerche(Italy)
Total Unibo Contribution: Euro (EUR) 30.596,00
Project Duration in months: 24
Start Date:
30/11/2023
End Date:
28/02/2026
