Achieving a climate-neutral and circular economy by 2050 is a significant goal for Europe, emphasising innovation in clean energy and e-mobility. A major role in this transformation have permanent magnets (PM), vital in electric vehicles and renewable energy technologies. Despite their specialised market, they have a strategic impact on the EU's mobility sector and its dependence on imports. Given their critical role in numerous industrial and consumer applications, there is a pressing need for innovative approaches in their production and recycling.
For over 30 years, our research group at the Jožef Stefan Institute has led research and innovations in PMs, focusing on enhancing magnetic properties and efficient use of critical material resources. The most recent activities towards these goals are commonly referred to as grain-boundary engineering, focused on manipulating the non-magnetic two-dimensional-like grain boundary regions between the magnetic matrix grains to enhance the overall coercivity of the entire magnet. Simultaneously, we have explored various recycling and reprocessing strategies to enable the sustainable reuse of magnet waste into new functional magnets with only a little or negligible loss of overall magnetic performance. 
In this presentation, we will discuss several case studies illustrating how atomic-level structural and chemical analysis enhances our understanding of key physical and chemical mechanisms, which are essential for optimising magnetic performance and developing effective recycling strategies. For that purpose, we employed Advanced Transmission Electron Microscopy along with specialised analytical techniques such as Electron Energy-Loss Spectroscopy and Electron Holography, which provides quantitative magnetic characterisation at nanometer resolution. Among other findings, we will highlight how various grain-boundary structural refinement strategies during spark plasma sintering (SPS) influence the coercivity of Nd–Fe–B bulk magnets [1,2]. Additionally, we will discuss innovative electrochemical recycling techniques for sintered Nd–Fe–B PMs [3,4]. These techniques, which include direct recovery of the matrix phase and pure metal winning, are still emerging but have already shown promising results in our studies. 
 

Achieving a climate-neutral and circular economy by 2050 is a significant goal for Europe, emphasising innovation in clean energy and e-mobility. A major role in this transformation have permanent magnets (PM), vital in electric vehicles and renewable energy technologies. Despite their specialised market, they have a strategic impact on the EU's mobility sector and its dependence on imports. Given their critical role in numerous industrial and consumer applications, there is a pressing need for innovative approaches in their production and recycling.
For over 30 years, our research group at the Jožef Stefan Institute has led research and innovations in PMs, focusing on enhancing magnetic properties and efficient use of critical material resources. The most recent activities towards these goals are commonly referred to as grain-boundary engineering, focused on manipulating the non-magnetic two-dimensional-like grain boundary regions between the magnetic matrix grains to enhance the overall coercivity of the entire magnet. Simultaneously, we have explored various recycling and reprocessing strategies to enable the sustainable reuse of magnet waste into new functional magnets with only a little or negligible loss of overall magnetic performance. 
In this presentation, we will discuss several case studies illustrating how atomic-level structural and chemical analysis enhances our understanding of key physical and chemical mechanisms, which are essential for optimising magnetic performance and developing effective recycling strategies. For that purpose, we employed Advanced Transmission Electron Microscopy along with specialised analytical techniques such as Electron Energy-Loss Spectroscopy and Electron Holography, which provides quantitative magnetic characterisation at nanometer resolution. Among other findings, we will highlight how various grain-boundary structural refinement strategies during spark plasma sintering (SPS) influence the coercivity of Nd–Fe–B bulk magnets [1,2]. Additionally, we will discuss innovative electrochemical recycling techniques for sintered Nd–Fe–B PMs [3,4]. These techniques, which include direct recovery of the matrix phase and pure metal winning, are still emerging but have already shown promising results in our studies. 

Advancements in e-mobility and green power generation are crucial for fulfilling the Green Deal's objectives of creating a low-carbon society. Central to this goal are high-performing permanent magnets, such as Nd-Fe-B and Sm-Co, essential components in electric motors and generators. Consequently, intensive research into these magnets is critical to enhance their performance. However, a significant challenge is the scarce availability of these rare earth elements, designated as essential raw materials by the EU. Therefore, comprehensive approaches in resource-efficient processing, reprocessing, and recycling of these magnets are vital for the future development of permanent magnets. We are dedicated to researching and improving the viability of reprocessing and recycling Nd-Fe-B and other permanent magnets. Techniques such as electrochemical separation via anodic oxidation have successfully recycled Nd-Fe-B scrap into Nd₂Fe₁₄B matrix phase grains or break them down into rare earth-based precursors [1]. Moreover, Sm-Co permanent magnets have also shown promising recyclability through electrochemical methods [2]. Progress in scaling up recycling methods for Nd-Fe-B has been achieved through selective electrochemical and chemical approaches [3-4]. These innovative recycling and upcycling techniques pave the way for completely reengineering Nd-Fe-B magnets from the ground up, offering a break from traditional methods and potential enhancements in magnet performance metrics like energy products. Our current research also explores rapid consolidation methods, such as spark plasma sintering, which promise to advance Nd-Fe-B magnet development further [4].

In this study, we explore the challenge of creating anisotropic permanent magnets through the process of additive manufacturing, specifically using material extrusion (MEX). Typically, the production of anisotropic magnets requires the application of an external magnetic field, with the most cost-effective approach being the utilization of permanent magnets in a specific orientation to align the particles. However, when employing a filament-based 3D printer or material extruder, generating an adequate magnetic field presents certain difficulties. The simplest method involves printing directly atop a permanent magnet, as shown in previous studies. [1] However, this approach restricts the magnet's height due to the diminishing magnetic field with distance, eventually leading to a point where particle orientation ceases. Contrary to predictions, our observations revealed that the printed magnet not only sustains but also extends the magnetic field of the underlying permanent magnet. This results in a greater degree of anisotropy at distances further from the magnetic field source than initially anticipated. This discovery opens up new possibilities for more intricate designs, circumventing the limitations imposed by space constraints for permanent magnet placement by leveraging the magnetic field extension provided by the previously printed magnet.

The green transition drives the advancement of sustainable energy conversion technologies. Nd-Fe-B permanent magnets are crucial components of energy-efficient electric motors and generator systems. Presently, state-of-the-art magnets, boasting maximum energy products as high as 450 kJ/m³, are produced through powder metallurgy routes. However, conventional sintering is energy-intensive and offers limited control over microstructure formation and the final magnet's geometry.

Rapid powder consolidation techniques, like Spark Plasma Sintering (SPS), present notable advantages over conventional methods. They offer faster and more energy-efficient sintering processes, lower sintering temperatures, and the potential for net-shape manufacture, promising a new generation of Nd-Fe-B magnets with improved functionalities. Yet, due to the strong structure-properties dependence, consolidation of microcrystalline Nd-Fe-B-type powders via SPS proved challenging. Localized overheating at particle-particle contacts, owing to the Joule effect, can disrupt the delicate phase composition of the material, resulting in a drastic loss of hard-magnetic performance [1, 2]. 

Through careful optimization of heating conditions and the introduction of novel concepts in processing multiphase metallic systems like Nd-Fe-B, our research has been focused on developing alternative sintering strategies for the manufacture of Nd-Fe-B magnets. Fast sintering cycles have been employed to enhance the material's high-temperature performance by suppressing grain growth during densification. We will show that rapid sintering can reduce the energy consumption required to densify an Nd-Fe-B-type powder by an order of magnitude compared to slow conventional sintering. The new powder consolidation paradigms are applicable for processing both fresh and recycled powders, offering great potential for reengineering the magnet's microstructure, and having implications for future industrial processes.

The green transition drives the advancement of sustainable energy conversion technologies. Nd-Fe-B permanent magnets are crucial components of energy-efficient electric motors and generator systems. Presently, state-of-the-art magnets, boasting maximum energy products as high as 450 kJ/m³, are produced through powder metallurgy routes. However, conventional sintering is energy-intensive and offers limited control over microstructure formation and the final magnet's geometry.

Rapid powder consolidation techniques, like Spark Plasma Sintering (SPS), present notable advantages over conventional methods. They offer faster and more energy-efficient sintering processes, lower sintering temperatures, and the potential for net-shape manufacture, promising a new generation of Nd-Fe-B magnets with improved functionalities. Yet, due to the strong structure-properties dependence, consolidation of microcrystalline Nd-Fe-B-type powders via SPS proved challenging. Localized overheating at particle-particle contacts, owing to the Joule effect, can disrupt the delicate phase composition of the material, resulting in a drastic loss of hard-magnetic performance [1, 2]. 

Through careful optimization of heating conditions and the introduction of novel concepts in processing multiphase metallic systems like Nd-Fe-B, our research has been focused on developing alternative sintering strategies for the manufacture of Nd-Fe-B magnets. Fast sintering cycles have been employed to enhance the material's high-temperature performance by suppressing grain growth during densification. We will show that rapid sintering can reduce the energy consumption required to densify an Nd-Fe-B-type powder by an order of magnitude compared to slow conventional sintering. The new powder consolidation paradigms are applicable for processing both fresh and recycled powders, offering great potential for reengineering the magnet's microstructure, and having implications for future industrial processes.