Schultz International Symposium (8th Intl. Symp. on Science of Intelligent & Sustainable Advanced Ferromagnetic and Superconducting Magnets (SISAM))

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. 
 

Intermetallic compounds of 4f and 3d elements, especially Fe and Co were intensively investigated in the 20^th century, and the roles of crystal structure, exchange and crystal field  were elucidated.  Important consequences were  rational design permanent magnets with strong uniaxial anisotropy using an appropriate light rare earth (SmCo₅, Nd₂Fe₁₄B), uniaxial ferrimagnets with compensation (TbCo₃) and cubic ferrimagnets with strong magnetostriction but no net anisotropy (Tb_0.3Dy_0.7)Fe₂. Analogous compounds with the nonmagnetic rare earth yttrium were invaluable for isolating the 3d contribution to the magnetism.  When high-quality metallic thin films began to be produced by sputtering 1970s, it was found that some 4f-3d binaries could be deposited as amorphous films which exhibited perpendicular magnetic anisotropy. Ferrimagnetic Gd-Fe-Co magneto-optic recording media with compensation point writing were an interesting, if commercially limited development [1]. Amorphous alloys with strongly anisotropic rare earth elements tend to have magnetic ground-states where the rare earth moments freeze along randomly-oriented axes, with a net magnetic moment — parallel or antiparallel to that of Fe or Co [2], and a new series of random noncollinear magnetic structures was discovered.

A revival of interest in these materials has been spurred by several developments. One is the reappraisal of transverse magnetotransport  (anomalous, spin and orbital Hall effects) in terms of real- or reciprocal-space Berry curvature. Atomic-scale simulations of atomic and magnetic structures have improved greatly in the past 50 years. Also, the observation in 2013 of ultra-fast single-pulse all-optical toggle switching in thin films of perpendicular ferrimagnetic amorphous Gd_x(FeCo)_1-x with x ≈ 0.25 opened new perspectives for magneto-optic applications, and understanding of the transient collapse of magnetization and anisotropy [3]. Proposals for using these thin films for as magnetic switches modulate an optical signal at frequencies of up 100 GHz raises the possibility of multiplexing the existing  global fibre-optic communication system and increasing its capacity by a factor of five. 

A new study of spin and orbital magnetism and magnetotransport in amorphous R­­_1-x­Co_x will be presented, which allows a reassessment of the noncollinear magnetic structures of amorphous alloys with a heavy rare earth, Th, Dy or Er and its temperature dependence and field dependence in the vicinity of the magnetic compensation point T_comp. The corresponding amorphous yttrium alloys are remarkably soft ferromagnets despite the strong random anisotropy experienced by the cobalt, which is exchange-averaged to vanishing point on account of the exchange field and extrapolated Curie temperatures in excess of 1000 K  for x ≈ 0.9. This makes the amorphous Y_1-x­Co_x alloys ideal materials with which to explore new ideas of orbital electronics, where the orbital polarization of the electrons is the key to magnetoelectronics, via the orbital Hall effect (OHE), rather than the spin polarization as in conventional spintronics [5] and effects may be are much larger. The orbital moment in random close-packed amorphous cobalt may exceed 0.5 Bohr magnetons per atom. The quantities of cobalt and rare earth metals required for the new thin-film functionality are miniscule, of order a milligram for a wafer with a trillion orbital switches 

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.

So-called “nanoglasses” are considered as non-crystalline solids which exhibit a glass-like atomic structure and contain a considerable number of internal interfaces. This metastable state of matter can be synthesized by RF magnetron thin film sputter deposition as an alternative to other methods including inert gas condensation and chemical decomposition on a nanoscale. Using sputtering targets of VIT105 and Au-based BMG as well as Fe-Sc the resulting nanostructures can be varied from monolithic amorphous to nanoglass and to columnar amorphous nanostructures at varying Argon base pressure. Remarkably, the BMG based nanoglass specimen clearly exhibit an anomaly of the specific heat typical for the glassy state. While generally glassy structures lack ductility, the nanoglass state exhibits superior mechanical properties achieving a remarkable level of plastic deformation in nanoindentation experiments. Further details, also in relation to a recent theoretical approach as well as measurements of electrical and magnetic properties will be presented and discussed.

Amorphous magnetic wires can exhibit unique magnetic properties, such as magnetic bistability [1] and/or Giant Magneto-Impedance, GMI, effect associated with excellent magnetic softness [2]. Additionally, amorphous materials are also characterized by superior mechanical and corrosion properties [3]. Such combination of physical properties makes the amorphous wires attractive for a variety of industrial applications, such as magnetic and magnetoelastic sensors or tunable metamaterials [2,4]. One of the latest trends in the development of amorphous magnetic wires is to reduce their size and expand their functionality through protective coatings. Among the most effective solutions for the production of thin amorphous magnetic wires is the so-called Taylor-Ulitovsky method, allowing the preparation of microwires with rather extended diameters range from 100 nm to 100 µm coated with an insulating, flexible and biocompatible glass coating [4]. The performance of GMI effect based sensors and devices can be significantly improved by using materials with higher GMI effect. Typically, the highest GMI ratio of about 200-300% is observed in Co-rich magnetic wires with vanishing magnetostriction coefficients, λ_s [2]. While, in carefully processed magnetic microwires, GMI ratios of up to 650% have been obtained [4]. However, the reported GMI ratios are still below the theoretically predicted 3000% [2]

Consequently, in this paper we provide our latest attempt on optimization of the magnetic softness and GMI effect in Co-rich glass-coated magnetic microwires.We studied the effect of annealing on the hysteresis loops and the GMI ratio of Co-rich microwires. Surprisingly, after conventional annealing, in most of Co-rich microwires, magnetic hardening and transformation of a linear hysteresis loop into a rectangular one with a higher coercive force are observed. However, stress-annealing allows preventing magnetic hardening and remarkably improve GMI ratio. Properly stress-annealed samples present almost unhysteretic loops with coercivity about 2 A/m and magnetic anisotropy field about 35A/m. A remarkable GMI ratio improvement up to 735% is observed after annealing of Co-rich microwires at appropriate conditions. Observed magnetic softening and GMI ratio improvement have been discussed considering the internal stresses relaxation, induced magnetic anisotropy and a change in the magnetostriction coefficient sign and values with increasing of annealing temperature.

Nowadays, magnetic resonance imaging (MRI) has become a powerful diagnostic tool in medical fields, e.g. in brain surgery, cardiovascular diseases and orthopedics. However, MRI diagnosis is inhibited by the presence of certain metallic implants in the body because they become magnetized in the intense magnetic field of the MRI instrument, which may produce image artifacts and therefore prevent exact diagnosis. To decrease the artifacts, medical alloys/devices with low magnetic susceptibility are required. Compared with stainless steel and Co–Cr alloys, which are conventional implant alloys, titanium (Ti)– and zirconium (Zr)-based alloys have lower magnetic susceptibility and are more suitable for clinical investigation using MRI than the others [1]

Metallic glasses have a great potential for small medical devices useful in dentistry (e.g. dental implants and suprastructures), osteosynthesis (e.g fracture fixation systems) and occlusive vascular diseases (e.g stents and aneurysm clips) [2-4]. Ti-, Zr- and precious metal-based bulk metallic glassess (BMGs) have been widely investigated as potential biomaterials especially for bone-related implant applications [2-3]. However, the major problem still facing the development of biomedical metallic glasses is the one of inducing amorphization without using any harmful alloying additions. We reviewed the biological safety and glass forming tendency in Ti of a series of alloying elements [2].

In the present paper we discuss the underlying processes for amorphous phase formation, mechanical and biochemical behavior as well as the biocompatibility of various Ni-free Ti- and Zr-based BMGs with potential for biomedicine. Moreover, we report the formation novel amorphous Ti-Zr-Nb-Hf-Si multi-principal element alloys with excellent corrosion stability in simulated body fluids and ultralow magnetic susceptibility, less than one-third of that of commercial biomedical Ti-based materials [4]. These alloys exhibit also higher X-ray linear attenuation coefficients relevant for interventional X-ray-based medical imaging. This two-fold advantage (lower magnetic susceptibility and higher radiopacity) allows the materials to be more precisely visualized via biomedical imaging methods, which is especially important for miniaturised implants.

Financial support through the European Commission (H2020-MSCA-ITN BIOREMIA GA 861046) is gratefully acknowledged.

Rare Earths (RE) permanent magnets are essential components for Europe's successful green and digital transition However, the entire value chain of RE magnetic materials depends on imports, which are highly vulnerable in current global supply chain models. 

To mitigate this situation, EU Regulation plans that at least 25% of the EU's annual consumption of permanent magnets should be covered by recycling capacities by 2030. Researchers in the EU H2020 project SUSMAGPRO consortium have shown that hydrogen can be used as a very efficient recycling method to extract NdFeB magnet powder from various EOL Components in the IP protected Hydrogen-based Processing of Magnet Scrap (HPMS). 

On exposure to hydrogen the sintered NdFeB magnets break down into a friable, demagnetised, hydrogenated powder containing an interstitial hydride of Nd₂Fe₁₄BH_X (10 microns) and smaller particles (< 1 micron) from the grain-boundary phase NdH_2.7. This process delivers a sustainable source of magnetic material for the production of sintered, polymer bonded and metal-injection moulded magnets [1]. 

The talk will present numerous results along the whole value chain of magnet recycling, including automatic dismantling of magnet containing products, magnets extraction, HPMS recycling, production of recycled magnets and demonstrator testing [1-5]. 

It will also discuss best practices and bottlenecks of the processes as an outlook for successful design-for-recycling of future applications. 

Magnetic wires have attracted considerable attention due to their rather attractive magnetic properties such as giant magneto-impedance (GMI) effect or magnetic bistability, potentially suitable for several prospective applications (magnetic and magnetoelastic sensors, magnetic memory and logic, electronic surveillance, etc.) [1,2]. Glass-coated magnetic microwires prepared using the Taylor-Ulitovsky technique with thin metallic nucleus (typically with diameters 0.1 to 100 μm) covered by flexible, insulating and biocompatible glass are therefore quite interesting for sensor applications [2]. This technique allows preparation of magnetic wires with amorphous or crystalline structure of metallic nucleus. In the case of glass-coated microwires the magnetoelastic anisotropy contribution becomes relevant since the preparation process involves not only the rapid quenching itself, but also simultaneous solidification of the metallic nucleus surrounded by non-magnetic glass-coating with rather different thermal expansion coefficients [3]. 

The purpose of this paper is present last results on tailoring of soft magnetic properties and GMI effect in glass-coated microwires paying special attention to achievement of high GMI effect and on optimization of domain wall dynamics.

The impact of post-processing on soft magnetic properties and the giant magnetoimpedance (GMI) effect of Fe- and Co-based glass-coated microwires is evaluated. A remarkable improvement of magnetic softness and GMI effect is observed in Fe-rich glass-coated microwires subjected to stress annealing. Annealed and stress-annealed Co-rich microwires present rectangular hysteresis loop and single and fast domain wall propagation. However, Co-based stress-annealed microwires present higher magnetoimpedance ratio. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”. Consequently, stress annealing of ferromagnetic microwires allows achievement of interesting combination of magnetic properties. 

Two aspects of magneto-optics are reviewed that have hardly be considered in the past: (i) For Magneto-optical Kerr Effect (MOKE) magnetometry it will be shown that the obtained hysteresis loops need to be interpreted very carefully as they are measured locally, determined by the internal (not applied) magnetic field and by local magnetization processes [1]. MOKE hysteresis loops are therefore in most cases significantly different from integrally measured loops on the same specimen. (ii) For wide-field MOKE microscopy numerous magneto-optical effects will be discussed that lead to intensity-based domain contrasts in the absence of analyser and compensator, which are the main optical components in conventional MOKE microscopy [2]. This includes the Transverse Kerr effect, a novel 45°-dichroic effect (Oppeneer effect), the Magnetic Linear Dichroism effect, and the Dichroic Gradient effect. All these effects require linearly polarized light for illumination. A further effect is the Magnetic Circular Dichroism effect that requires circularly polarised illumination. 

The present situation of the market and applications of rare-earths is reviewed. It is given special attention for discussing the possibility of substitution of  rare-earth magnets by other families of magnets.

Three are the main commercial applications of rare-earths: i) luminescent phosphors, ii) magnets, and iii) catalysis.

For catalysis, the cheap rare-earths as cerium and lanthanum are employed.  Luminescent phosphors are essential in many applications, as lasers and, for example, erbium is used in optical fibers. However, in spite of its relevance, erbium is not expensive as Tb and Dy. 

In LED applications, the rare-earths are used as thin films, and , thus the demand in volume  is not very significant when compared with the demand for magnets. The use of white LED (light emission diode) significantly reduced the demand for europium after 2015, but this application is still relevant. In the 1960s and up the 1980s, Europium was the most expensive rare-earth, due to extreme demand.

The rare-earth market is nowadays driven by Tb, Dy, Nd and Pr, which are employed in rare-earth iron permanent magnets of the RE2Fe14B family (RE=rare earth). For applications in high temperature, dysprosium and terbium are added, and this made the demand and price of Dy and Tb be skyrocketing.

SmCo magnets have the problem of using the expensive element cobalt. Nowadays the demand and price of cobalt increased conbseiderably due to application in rechargeable battteries, and thus, SmCo use in large scale is avoided, but they remain relevant for high temperature applications (above 150oC).

Possible alternatives for rare-earth  permanents magnets are discussed. Among the few options for replacement are the ferrite magnets (BaFe12O19 or SrFe12O19), the Alnico magnes based on shape anisotropy and maybe iron nitrogen. Economic and technical feasibility of these families of magnets are discussed.

Its is given a brief overview about recent mining projects in Brazil, which are focusing on ionic clays, with the objective of extracting the scarce and expensive elements terbium and dysprosium. 

Nanocrystalline materials have a variety of new or improved properties compared to their single crystalline counterparts [1]. Severe plastic deformation and solute segregation to grain boundaries are useful and simple methods to produce nanocrystalline materials. Examples for nanocrystalline iron doped with various solutes (carbon, nitrogen, oxygen and boron) and various concentrations are presented. The alloys were generated by ball milling iron powder with graphite, iron boride, iron nitride and iron oxide and their grain size was determined with transmission electron microscopy. Severe plastic deformation by wire drawing of Pearlite also leads to a nanocrystalline Fe-C alloy. All alloys had a grain size of about 20 nm. Results of the thermal stability of the alloys with respect to phase separation and coarsening is provided. Based on Gibbs Adsorption Isotherm the dependence of grain size on solute concentration is explained. It will be shown that Gibbs Adsorption Isotherm can be generalized [2] from surfaces and grain boundaries to all kinds of discontinuities (dislocations, vacancies etc.).

By cooling a superconductor in a magnetic field the field configuration can be permanently frozen in the material. Offering this field configuration by a continuous magnetic track allows superconducting magnetic levitation along this track. Due to the attracting and repelling forces it is passively stable without any electronic control to suspend a vehicle which can hang under the track or is standing upright. Due to this intrinsic stability, the levitation itself does not consume any energy. These are perfect conditions for a rail-bound system like Hyperloop, an individual transport with cabins for 4 to 5 passengers, requested call by call. Also mass transportation is possible. The vehicles will be levitated without friction or noise over a track constructed of rare-earth permanent magnets. In this presentation we will report on SupraTrans II, a  research and test facility for such a transport system using bulk high-temperature superconductors in the levitation and guidance system, in combination with a permanent magnetic track,  which had originally been set up at IFW Dresden and can now be visited at KIT Karlsruhe. A  vehicle for 2 passengers, equipped with linear drive propulsion, noncontact energy supply, second braking system, and various test and measurement systems is running on an 80 m long oval driveway. In the presentation, the principle of superconducting levitation by flux pinning in bulk high-temperature superconductors will be described. Based on this, an overview of the SupraTrans II research facility and future directions of superconductivity­-based magnetic levitation and bearing for automation technology, transportation, and medical treatment under enhanced gravity will be given. Also the physics behind the “Back to the Future“ superconducting hoverboard, recently presented by Lexus, will be described.

Permanent magnets (PM) are vital components of the green transition. However, the criticality of rare-earth elements (REE) [1] needed for their manufacture makes them of great strategic, geopolitical, and socio-economic importance, making it an urgent need to develop alternative REE-free magnets. The best-performing PMs are based on REEs, while lower-performance PMs use ferrites. [2] Due to the high performance of REE magnets, most modern devices employ them, as they are lighter and lead to better efficiency. Unfortunately, REEs are critical raw materials owing to their supply risk and price volatility, and also their harmful environmental impacts. [3,4] One of the main solutions focuses on improving the performance of alternative rare-earth-free or rare-earth-lean magnets co-designed with motors or generators for greater efficiency.

This study focuses on a consolidation of ferrite-based permanent magnets by means of novel Pressure-less Spark Plasma Sintering Technique (PSPS). PSPS process uses the Joule heating effect to elevate the temperature in the heating die, which is transferred to the sample via thermal radiation. The method allows very high heating rates (up to 900 °/min) and short retention times in a matter of minutes. Thus, the grain growth is suppressed. 

The starting material for the study was recycled Sr-ferrite powder obtained from the injection bonded magnets’ production waste. Processing and consolidation parameters were tailored to achieve dense magnets. The phase composition, microstructural analysis and magnetic properties of starting powders and sintered magnets were evaluated. 

Acknowledgement: This research has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 101003575 (ERA-MIN3, project GENIUS), and Slovenian national research agency (P2-0087, P2-0405, P2-0412). 

Magnetic skyrmions are topologically-protected vortex-like magnetization patterns that can exist under special conditions in noncentrosymmetric structures. They might be applicable as carriers of classical and quantum information [1]. Whereas at the macroscopic level their existence is a finite-temperature phenomenon, theory predicts skyrmions with nanometer length scales at T = 0 [2].

An appropriate model, which can exhibit the respective phase, is a two-dimensional spin-1/2 Heisenberg lattice with the Dzyaloshiskii-Moriya interaction in an external field. A promising way to find the ground and excited states of the corresponding Hamiltonian is to apply a quantum algorithm. In this manner we have mapped the model-parameters phase diagram by performing the calculations with the variational quantum eigensolver (VQE) [3]. Although, due to a limited number of the working qubits, the investigated lattices have been too small to host a full skyrmion, the results clearly indicate the relation between the parameters, required for their existence.

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.

Multicomponent alloys have attracted definitely increasing interest for the last three decades since the first synthesis of multicomponent bulk metallic glasses (BMGs) by copper mold casting in 1990. The multicomponent alloys reported to date are classified to BMGs, BMG composites, high entropy (HE) BMGs and HE alloys. When we focus on engineering applications, the most widely commercialized alloys are BMGs. Their BMGs are roughly classified into nonmagnetic Zr-based and ferromagnetic Fe-based types. The former type is typically composed of Zr-Al-Ni-Cu and Zr-Al-Ni-Cu-(Ti,Nb) systems and the latter type is Fe-Cr-(P,B,C,Si), Fe-(Cr,Nb)-P-B and Fe-(Cr,Nb)-(P,B,Si) systems. The commercialization articles have been usually produced by die casting from liquid for the Zr-based BMGs, while the Fe-based glass-type alloys have been produced by high-pressure gas atomization or ultrahigh water atomization. The former BMGs have been used as various structural materials such as casing, housing, pin spring, hinge, clinic instruments, ratch cover writing tools, precise gears, knives, optical mirrors, sporting goods and ornaments, etc., while the latter glassy powders are used to produce soft magnetic composite (SMC) by mixing with resin et al. The SMCs exhibit unique soft magnetic properties with the features of low core losses, good high-frequency permeability characteristics and high electrical resistivity in high-frequency range from 100 kHz to 5 MHz. High glass-forming ability enables the mass production of good spherical glassy powders over the whole particle size range even by low-cost water atomization process. Owing to their unique production process and good soft magnetic properties, the SMCs have been used as high performance of inductors and reactors with low core losses even in a high frequency range up to 3 MHz in various kinds of fields such as smartphone, smartwatch, tablet-type computer, notebook PC, DC/DC converter, point of load power supply, digital camera, automobile AV equipment, car navigation system and RFID sheet, etc. Thus, Zr- and Fe-based BMGs are expected to increase academic and technological interests as functional materials in recent information communication technology owing to the unique properties that cannot be obtained for ordinary crystalline structural and magnetic materials. 

The scientific and technological exploration of three-dimensional magnetic nanostructures is an emerging research field with exciting novel physical phenomena, originating from the increased complexity in spin textures, topology, and frustration in three dimensions. The concept of chirality which requires three dimensions, is essential to understand e.g., fundamental interactions in cosmology and particle physics, the evolution of life in biology, or molecular chemistry, but has recently also attracted enormous interest in the magnetism community. Tailored three-dimensional nanomagnetic structures, including in artificial spin ice systems or magnonics will enable novel applications in magnetic sensor and information processing technologies with improved energy efficiency, processing speed, functionalities, and miniaturization of future spintronic devices. 

Another approach to explore and harness the full three-dimensional space is to use curvature as a design parameter, where the local curvature impacts physical properties across multiple length scales, ranging from the macroscopic to the nanoscale at interfaces and inhomogeneities in materials with structural, chemical, electronic, and magnetic short-range order. In quantum materials, where correlations, entanglement, and topology dominate, the local curvature opens the path to novel phenomena that have recently emerged and could have a dramatic impact on future fundamental and applied studies of materials. Particularly, magnetic systems hosting non-collinear and topological states and 3D magnetic nanostructures strongly benefit from treating curvature as a new design parameter to explore prospective applications in the magnetic field and stress sensing, micro-robotics, and information processing and storage.

Exploring 3d nanomagnetism requires advances in modelling/theory, synthesis/fabrication, and state-of-the-art nanoscale characterization techniques to understand, realize and control the properties, behavior, and functionalities of these novel magnetic nanostructures.

I will summarize and review the challenges but also the opportunities ahead of us in the future exploration of nanomagnetism in three dimensions. 

This work was funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (NEMM program MSMAG).

Titanium is often used for highly complex, lightweight components especially in aviation and medical applications. Its production is particularly energy-intensive due to the high oxidation tendency, and it is six times more expensive than that of steel [1]. The machining of Titanium yields large amounts of waste in the form of chips. Conventional recycling by remelting the chips requires a lot of energy. It can be saved to a large extent by application of SPD (Severe Plastic Deformation) which uses Titanium chips as starting raw material. 

In the present work [2], the two most important Severe Plastic Deformation (SPD) methods [3]. Equal Channel Angular Pressing (ECAP) and High Pressure Torsion (HPT) - were used for recycling and/or upcycling of titanium chips. For successful consolidation, efficient cleaning of the chips was crucial. To check the quality of the consolidated materials, results of mechanical testing, texture analysis, and of optical and electron microscopy were compared with those of the bulk counterparts. Especially by measuring the torque characteristics during HPT deformation of the chips, the success of consolidation can be well demonstrated when comparing it with the torque characteristics of bulk samples. 

It is concluded that full consolidation i.e. the recycling of chips using SPD is possible at  temperatures which not only are significantly lower than those of melting but also than those of sintering while reaching the same density. However,  the chips must be prevented from mutual sliding as plastic deformation is essential for successful consolidation. Still, the enhancement of pressure and temperature remain advantageous for consolidation.

Recently, Severe Plastic Deformation (SPD, i.e. High Pressure Torsion (HPT)) has been applied not only for achieving massive samples out of Fe-based metallic glasses but also for crystallizing them [1,2], in order to increase the saturation magnetization. This paper presents the results for the magnetic properties gained by Vibrating Sample Magnetometry (VSM) of the two Fe-based metallic glasses Vitroperm Fe_73.9Cu₁Nb₃Si_15.5B_6.6 and Makino Fe_81.2Co₄Si_0.5B_9.5P₄Cu_0.8. In the Vitroperm alloy, the saturation magnetization is not affected by HPT even after high strains applied. Thermal treatment does not improve this result, only the coercivity is brought back to the value of undeformed sample. In contrast, the Makino alloy shows – after applying at least 4 turns of HPT - an increase of magnetization by 10%, and a complete removal of HPT induced increase of the coercivity related to deformation induced internal stresses. Comparing the structures reported in our recent work [3], these effects occur strictly in parallel to the crystallization observed in the Makino alloys. The results also fit to the structural investigations done for the Vitroperm alloy where no crystallization at all has been observed [3]. It can be concluded that SPD processing of soft magnetic amorphous alloys appears as a viable alternative to the addition of nanocrystallizing elements, at least unless the material specific crystal systems are too complex [3] to enable SPD induced crystallization.

The European Union has set itself the goal of achieving climate neutrality by 2050, a milestone that depends on the continent's ability to develop and implement clean energy and mobility solutions in a way that is both economically viable and environmentally sustainable. The amount of critical raw materials (CRM) needed to facilitate this energy transition is significant. In addition, industrial and household appliances will need to meet stringent energy efficiency standards to support this transition. The most energy-efficient electric motors and generators contain rare earth permanent magnets. While EU companies are world leaders in the production of electric motors, they are completely dependent on imports for the entire value chain of rare earth magnet materials. (Bernd Schaferet.al, A Report of the Rare Earth Magnets and Motors Cluster, Berlin 2021).

Rare earth elements (REEs) are essential components of these permanent magnets, which are critical for many applications that are vital to Europe's future. It is well known that REEs from China have been the main source for Europe, that supplies are uncertain, and that the Chinese production chain is generally unsustainable. At the same time, the demand for REEs for the production of new PMs is expected to double in 15 years.

In light of this data, our work focuses on the collection of EOL magnets and the sustainable recycling and reprocessing of PM from sources, concentrating on the most common and readily available source of economically recyclable electric motors: domestic appliances. We are developing new dismantling and recovery processes for PM on high-availability scrap and reprocessing lines. In HPMS (Hydrogen Processing of Magnetic Scrap)^1,2 we use an already established method of hydrogenation followed by grinding, degassing, and coating of sensitive powders. The HDDR (Hydrogenation-Disproportionation-Desorption-Regeneration)³ process has been implemented to simplify and minimize the steps in the recycling process.

Initial, ongoing pilot trials for the production of sintered and bonded magnets from recycled magnets confirm the waste-free, economic processing and future independence from unstable REE sources. For the production of sintered magnets, a new sustainable process of rapid consolidation is used, while for bonded magnets the most sensitive part to protect the reactive powders is the coating with a few monolayers of chemically bound coating precursor. In addition to magnetic measurements, various analytical techniques (SEM, HRTEM, XPS) are used to characterize the powders obtained by HPMS and HDDR processes, as well as the final magnets.

*This work is part of the “INSPIRES” project financed by EIT RawMaterials, Proposal Number 20090 (project website: https://eitrawmaterials.eu/project/inspires/).

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].

Surface energy is an essential property of condensed matter. It determines the equilibrium shape of a piece of matter and drives its interactions with the environment, for instance its wetting and adhesion properties, or even friction against another solid. Most non-metallic liquids and solid polymers are known to exhibit relatively low surface energies, in the range of few tens to few hundreds mJ/m². In contrast, metals show surface energies in the range of 1 to few J/m². For example, aluminum, copper or iron have surface energies close to 1.3, 1.8 and 2.2 J/m², respectively.

Due to the absence of translation periodicity and to their specific atomic architecture, metallic quasicrystals (QCs hereafter) present an electronic structure that differs significantly from the one of conventional metals: a marked pseudo-gap is observed at the Fermi energy [1]. The density of mobile electrons is henceforth reduced to about 10 to 20% of the one in a classical metal like Al, and the transport properties of QCs are definitely different from the ones in a periodic metal. So is also the surface energy.

This property can be assessed experimentally using single crystal specimens, but also by computational methods for periodic crystals [2]. The power of modern computers allows nowadays the study of materials with a unit cell containing several hundreds of atoms, which covers the full range of periodic metals known so far. Yet, it is still far below the range necessary to address the surface energy of QCs. The talk will review the methods used by the author [3] to overcome this difficulty and at least estimate the surface energy of few QCs such as icosahedral AlCuFe and AlPdMn in comparison to a small number of periodic crystalline materials of related composition. The meaningful low value of the surface energy found for these QCs, in the range 0.5-0.8 J/m², will be discussed in the light of applications of potential technological relevance such as reinforcement of polymer-matrix composites or friction against hard steel [4].

Entire scientific disciplines are governed by the interactions between atoms and molecules. On surfaces, forces extending into the vacuum direct the behavior of many scientifically and technologically important phenomena such as corrosion, adhesion, thin film growth, nanotribology, and surface catalysis. To advance our knowledge of the fundamentals governing these subjects, it would be useful to simultaneously map electron densities and quantify force interactions between the surface of interest and a probe with atomic resolution. When attempting to use scanning probe microscopy (SPM) towards this goal, significant limitations in both imaging and mapping persist despite their ability to image surfaces and map their properties down to the atomic level. Most commonly, SPM qualitatively records only one property at a time and at a fixed distance from the surface. To overcome these limitations, we have integrated significant extensions to existing SPM approaches, which we will shortly summarize in this talk. 

The work started in 2009, when we expanded noncontact atomic force microscopy (NC-AFM) with atomic resolution to three dimensions by adding the capability to quantify the tip-sample force fields near a surface with picometer and piconewton resolution [1, 2]. In 2013, we added electronic information through the recording of the tunneling current simultaneously with the force interaction. Using copper oxide as an example of a catalytically active surface, this allowed to study the role of surface defects as active sites [3]. With the goal of yielding information on energy barriers in on-surface chemical reactions, we further extended this approach in 2022 to gain insight into the energetics of molecular motions on surfaces, with benzene and iodobenzene as model systems. And most recently, we introduced the method to study single-molecule chemistry with the example of cobalt phthalocyanine (CoPc) molecules, which have shown great potential to favorably catalyze the formation of methanol from CO₂ and hydrogen [4, 5]. Thereby, the binding strength of the intermediate CO to the cobalt atom at the center of the CoPcs catalyst molecule has been recognized as a key descriptor affecting catalytic efficiency, with the ideal CO-Co binding strength being neither too strong nor too weak. Using a CO-terminated tip, the CO-CoPc equilibrium distances and potential energies at equilibrium distances were recovered across the molecule [6]. Currently ongoing work aims at systematically changing the substituents/side chains of the CoPc or the substrate the CoPc molecules sit on to clarify the effect of these changes on the CO-Co binding strength and eventually enable a fine tuning of the binding strength, which may open new avenues to optimize the catalytic reaction.

Recent studies of glass-forming metallic systems have revealed intriguing complexity, e.g. unusual shifts in radial distribution functions with temperature change or upon mechanical loading in the elastic or plastic regime. Nearest neighbour distances and medium-range order structural arrangements appear to change, e.g. shorten upon heating or become larger with decreasing temperature. Concomitantly, temperature changes as well as static or dynamic mechanical loading within the nominally elastic regime can trigger significant changes in glass properties, which are directly correlated with local non-reversible configurational changes due to non-affine elastic or anelastic displacements. All these findings strongly suggest that the characteristics of the atomic structure decisively determine the properties of the glass and of nanostructured materials derived from glass-forming systems.

Residual stress engineering is widely used in the design of new advanced lightweight materials. For metallic glasses the attention has been on structural changes and rejuvenation processes. High energy scanning x-ray diffraction strain mapping reveals large elastic fluctuations in metallic glasses after deformed under triaxial compression. Transmission electron microscopy proves that structural rejuvenation under room temperature deformation relates to the shear band formation that closely correlates to the underlying distribution of elastic heterogeneities. Micro-indentation hardness mapping hints at an unsymmetrical hardening/softening after compression and further reveals the competing effects of stress and structure modulation. Molecular dynamics simulations provide an atomistic understanding of the correlation between shear banding and fluctuations in the local strain/stress heterogeneity. Thus, stress engineering and elastic heterogeneity together with structure modulation is a promising approach for designing metallic glasses with enhanced ductility and strain hardening ability.

In contrast to classical ex-situ spectro-microscopic techniques, in-situ characterizations and the combined application of complementary methods on identical samples not only provide for a more comprehensive insight into the structures and phenomena of interest, but also allow to study their kinetic development under the impact of external stimuli [1-3].

The talk will present a short review of our recent endeavors along this line and will specifically report on findings on the helimagnetic Heusler compound Mn_1.4PtSn. Lorentz transmission electron microscopy (LTEM) was used to study the evolution of magnetic phases as a function of (strength and direction of) an external magnetic field. The combination of (i) real space textures as derived from LTEM with (ii) magnetic scattering patterns obtained from complementary small angle resonant X-ray scattering (REXS) and (iii) micromagnetic simulations allowed us to substantially deepen our understanding of the nature and stability of the magnetic phases in Mn_1.4PtSn as a consequence of the competing magnetic interactions at work. We could show that due to the material’s uniaxial magnetic anisotropy, a stripe domain phase derived from a chiral soliton lattice rather than the previously assumed helical phase forms the ground state of the system. The studies also reveal the occurrence a previously overlooked fan state and provide a detailed understanding as to why and how antiskyrmions are formed along a kinetic pathway that is defined through a particular sequence of to be applied external magnetic fields.

Furthermore, by measuring the anomalous Hall effect in-situ in the microscope and simultaneously with the LTEM investigations, we could show that the field-induced formation of antiskyrmions does not cause any additional contribution to the Hall effect thereby indicating the lack of any topological Hall effect in the system.

Bulk metallic glasses (BMGs) have been intensively investigated because of their special mechanical properties as amorphous materials and their unique glass transition state. However, the atomic-scale origins of their behavior have not been unequivocally clarified. To explain their properties, structural models of BMGs and their small-scale deformation behavior have been proposed but not yet confirmed due to the inability of conventional measurement approaches to characterize samples at the relevant scale. For example, local structural analysis of glasses at the atomic scale using methods such as transmission electron microscopy or neutron/x-ray scattering is challenging due to the material’s disordered nature. In contrast, scanning probe microscopes and nanoindenters possess the potential of direct nanometer-scale observation local glass structure and mechanical properties. But even with these approaches, extraction of meaningful data is challenging due to the difficulty to prepare clean, atomically flat surfaces of BMG. This is because a surface roughness of some nanometers, standard with most sample preparation techniques, may alter the results of local testing if the volumes probed are nanometer-sized as well.

In this talk, we will be reviewing our recent progress in developing novel imprinting and fabrication methods of metallic glasses that can produce both atomically flat surfaces with sub-nanometer-scale features and samples with well-defined nanometer- and micron-sized total volumes as well as their subsequent use for the study of their nanometer-scale structural and mechanical properties. Imprinting is realized via thermoplastic forming of BMGs [1,2] and, alternately, by magnetron sputtering of general metallic glasses [3]. The capability of imprinting at an atomic scale enriches the range of applications of BMGs and brings a new way to directly characterize heterogeneity, relaxation, and crystallization in BMGs [4, 5]. It also allows to study onset of yielding and the local plastic flow mechanisms of BMGs in the limit of very small activation volumes (about 1000 atoms). The experiments revealed a much higher yield stress compared to the value obtained by conventional nanoindentation testing, followed by homogeneous plastic flow [6]. These atomic-scale results are contrasted to the larger-scale model that explains plastic deformation of BMG as originating from the finite STZs activation. Finally, current work is aimed at producing large numbers (>1000) of well defined, uniform micron- or nanometer-scaled pillars that can be used to explore the deformation behavior of BMGs under compression as a function of sample volume and compression rate in a statistically relevant manner.