Spomenka Kobe

Jožef Stefan Institute | IJS · Department of Nanostructured Materials

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 r...

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 M...

Micro-nonuniform heating in the field-assisted sintering (FAST) of electrically conductive powders has been a topic of discussion in the materials science community. Microstructural specifics, such as neck formation at low consolidation temperatures and density variations, have previously been ascribed to local overheating at the particle-particle...

In this review article, we focus on the relationship between permanent magnets and the electric motor, as this relationship has not been covered in a review paper before. With the increasing focus on battery research, other parts of the electric system have been neglected. To make electrification a smooth transition, as has been promised by governi...

Recycling of NdFeB magnets is necessary to ensure a reliable and ethical supply of the rare earth elements as critical raw materials. Successful recycling in adequate 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 parti...

Within this work, we demonstrate in-situ alignment of the easy axis single-crystal magnetic particles inside a polymer matrix using fused filament fabrication. Two different magnetic materials are investigated: (i) Strontium hexaferrite inside a PA6 matrix, fill grade: 49 vol% and (ii) Samarium iron nitride inside a PA12 matrix, fill grade: 44 vol%...

The rare earths are some of the most critical raw materials, yet electromobility and green energy strongly rely on Rare Earth Permanent Magnets (REPM). To secure the supply and improve the ecological footprint of REPM, a hydrogen-aided powder-metallurgical reprocessing route was successfully established and continues to be improved. A remaining obs...

Within this work, we demonstrate in-situ easy-axis alignment of single-crystal magnetic particles inside a polymer matrix using fused filament fabrication. Two different magnetic materials are investigated: (i) Strontium hexaferrite inside a PA6 matrix, fill grade: 49 vol% and (ii) Samarium iron nitride inside a PA12 matrix, fill grade: 44 vol%. In...

Various anti-corrosion coatings used on commercially available NdFeB-type magnets were comparatively examined for their durability and suitability for magnet reprocessing by hydrogen-assisted recycling (HPMS). Layer thickness and structure were determined by systematic microstructural analysis, and a standardized corrosion test was used to assess t...

This work has demonstrated that a high coercivity of 2.5 T can be achieved in a 5.6-mm-thick Nd-Fe-B anisotropic magnet by applying the two-step diffusion process using Nd50Dy30Cu20 and Nd80Cu20 eutectic alloys to a Dy-free Nd-Fe-B hot-deformed magnet. This is in contrast to the fact that about 5 wt.% Dy was needed to reach this coercivity level in...

In this work, we present a newly developed, economically efficient method for processing rare-earth Nd-Fe-B magnets based on spark plasma sintering. It makes us possible to retain the technologically essential properties of the produced magnet by consuming about 30% of the energy as compared to the conventional SPS process. A magnet with anisotropi...

The magnetic properties of an Nd-Fe-B-type permanent magnet depend on the microstructure and the chemistry of the material. To compensate for unfavorable microstructural features, such as micron-sized grains of the hard-magnetic phase, the intrinsic coercivity is often enhanced by the addition of heavy-rare-earth elements, but these additions also...

We propose a dominant core-shell formation mechanism for grain-boundary-diffusion-processed (GBDP), Tb-treated, Nd2Fe14B sintered magnets. A depth-sensitive analysis of Tb-treated samples, relative to a non-GBDP Nd2Fe14B magnet, showed a 30% increase of the coercivity in the central part of the magnet. A structure-chemistry-magnetic-property analys...

Availability of magnetic materials is most crucial for modern Europe, as they are integral to energy conversion across the renewable energy and electric mobility sectors. Unfortunately, there is still no circular economy to reuse and capture value for these types of materials. With the prediction that the need for NdFeB Rare Earth (RE) magnets will...

Fully dense spark plasma sintered recycled and fresh HDDR Nd-Fe-B nanocrystalline bulk magnets were processed by surface grain boundary diffusion (GBD) treatment to further augment the coercivity and investigate the underlying diffusion mechanism. The fully dense SPS processed HDDR based magnets were placed in a crucible with varying the eutectic a...

We have produced hot-deformed Nd-Fe-B magnets from commercial (MQU-F) Nd-Fe-B ribbons. The spark-plasma-sintering technique was used to deform the samples under low pressures of 40 MPa. The initial stages of the hot-deformation process were investigated in terms of microstructures and magnetic properties. Hot-deformed magnets with different deforma...

Sintered Nd-Fe-B permanent magnets are the first choice for electro-mechanical devices that rely on hard-magnetic materials to provide strong magnetic fields in a variety of operating conditions. However, the limitations of conventional powder-metallurgy methods regarding the complexity of the magnet’s geometry restrict the design freedom for elect...

The low-pressure hot-deformation methodology was applied to reprocess the nanocrystalline hydrogenation-disproportionation-desorption-recombination (HDDR) Nd-Fe-B powders from end-of-life (EOL) permanent magnets' waste to determine the mechanism of texture development and the resultant improvement in remanence (and BH max) in the recycled material....

The possibility of producing polymer-bonded magnets with the aid of additive processes, such as 3D printing, opens up a multitude of new areas of application. Almost any structures and prototypes can be produced cost-effectively in small quantities. Extending the 3D printing process allows the manufacturing of anisotropic magnetic structures by ali...

The possibility of producing polymer-bonded magnets with the aid of additive processes, such as 3D printing, opens up a multitude of new areas of application. Almost any structures and prototypes can be produced cost-effectively in small quantities. Extending the 3D printing process allows the manufacturing of anisotropic magnetic structures by ali...

Magnetic remanence (Br) and coercivity (Hc) of hard magnets play a crucial role in electro-mechanical devices like electrical motors or generators. Elevated remanence ensures high efficiency of the device, and large coercivity protects the magnet from demagnetization. Usually, the increase of one comes at the cost of the other, such that the materi...

The magnetic properties of the recycled hydrogenation disproportionation desorption recombination (HDDR) Nd-Fe-B powder, doped with a low weight fraction of DyF 3 nanoparticles, were investigated. Spark plasma sintering (SPS) was used to consolidate the recycled Nd-Fe-B powder blends containing 1, 2, and 5 wt.% of DyF 3 grounded powder. Different p...

The dependence of the magnetic properties on the particle size of recycled HDDR Nd-Fe-B powders were investigated, with the aim to assess the reprocessing potential of the end-of-life scrap magnets via spark plasma sintering (SPS). The as received recycled HDDR powder had coercivity (HCi) = 830 kA/m and particles in the range from 30 – 700 µm (aver...

The goal of this study was to justify the reprocessing of recycled HDDR Nd-Fe-B powders with spark plasma sintering (SPS) and to investigate the dependence of the final magnetic properties on SPS and thermal treatment. The initial recycled HDDR powder of the composition Nd13.4Dy0.6Fe78.6B6.1Nb0.4Al0.7 with 4760 ppm O2 content, coercivity (HCi) = 83...

An Al–Mn alloy with additions of copper, magnesium, and silicon was prepared and cast into a copper mold. It contains in situ-formed icosahedral quasicrystals (iQCs), as confirmed by electron backscatter diffraction. The aim of this work is to present the mechanical and corrosion properties of this alloy and compare its properties with some convent...

A detailed magnetic study of separated Fe–Pt NPs and Fe–Pt clusters was performed to predict their optimal size and morphology for the maximum saturation magnetization, a factor that is known to influence the performance of a magnetic-resonance-imaging (MRI) contrast agent. Excellent stability and biocompatibility of the nanoparticle suspension was...

Metal-bonded magnets based on the nanocrystalline YCo4.8Fe0.2 powder were produced by hot-compaction using a spark plasma-sintering device. Zn and Zn/Al metallic binders with a melting temperature close to 420 °C were employed to fabricate dense cylindrical magnets. Two different pressures were used for compaction. The higher pressure of 400 MPa pr...

Iron and copper are immiscible elements, but can be combined in the presence of a third element such as aluminium or cerium. We varied the additions of immiscible Fe and Cu (ratio y) in the stoichiometric Al20.5Ce41.5(FeyCu1 − y)38 alloys in order to trace their impact on the structure, microstructure, thermal properties and magnetism. By powder X-...

Different grades of Nd-Fe-B permanent magnets are available on the market today and their magnetic properties highly depend on the microstructure, which is controlled by the chemical composition of the alloy and the magnets’ manufacturing route. Gas atomization is a rapid solidification technique that is seldom used for the production of Nd-Fe-B ma...

We have produced an innovative, theranostic material based on FePt/SiO2/Au hybrid nanoparticles (NPs) for both, photo-thermal therapy and magnetic resonance imaging (MRI). Furthermore, a new synthesis approach, i.e., Au double seeding, for the preparation of the Au nanoshells around the FePt/SiO2 cores, is proposed. The photo-thermal and the MRI re...

We prepared three Al–Mn-based alloys with different copper, magnesium and silicon contents by casting into cylindrical copper molds. All the alloys exhibited primary metastable quasicrystals (QCs). In order to confirm the presence of either primary decagonal QCs (dQCs) or icosahedral QCs (iQCs) and to determine their compositions, the castings were...

We report on synthesis and characterization of a novel group of compounds based on copper, gadolinium, and calcium. Cu-Ca and Cu-Gd binaries were previously studied while Ca and Gd are known to be immiscible themselves. The effects of substituting Gd with Ca in Cu 5 Gd 1−í µí±¥ Ca í µí±¥ compounds (0 ≤ í µí±¥ ≤ 1) were studied by investigating the...

We studied the effects of substituting gadolinium in the compound Cu5Gd with Ca by investigating the phase stability and crystal structure of the resulting new compounds. For rapidly quenched materials produced by melt spinning, the crystal structure was always hexagonal P6/mmm, irrespective of the Ca addition (x) in alloys with the formula Cu5Gd1-...

We report on the effect of loading factor and pressure on the density and the magnetic properties of Zn-bonded Nd–Fe–B magnets produced by pulsed-electric-current sintering (PECS). The idea behind this study is to fabricate bonded magnets with a metallic binder in order for the bonded magnet to operate at temperatures higher than 180 °C: the curren...

The present work describes the formation of amorphous alloys in the (Al1−xCex)62Cu25Fe13 quaternary system (0 ≤ x ≤ 1). When the amount of Ce falls in the range 0.67 ≤ x ≤ 0.83, the alloys obtained exhibit a completely amorphous structure confirmed by powder X-ray diffraction. Otherwise, at compositions x = 0.5, 0.58, 0.92 and 1, a primary crystall...

Using a grain-boundary diffusion process (GBDP) involving the electrophoretic deposition (EPD) of submicron TbF3 powder, we substantially increased the coercivity of sintered Nd-Fe-B permanent magnets. The experiments used magnets with low heavy-rare-earth (HRE) content (HRE = 1.2 wt%) and a coercivity of 790 kA/m (at 75 °C). After experiencing opt...

In this report, Co–Pt nanowires (NWs) were produced via potentiostatic electrodeposition into commonly used commercial ordered-alumina and disordered-polycarbonate membranes with similar pore diameters (≈200 nm). The pore diameter of the membranes and the deposition conditions were chosen such that the Co–Pt NWs fabricated into both membranes had a...

Several Cu-Gd-Ca alloys were prepared by arc-melting and melt-spinning in order to find quasicrystals or complex approximants. Up to date no complex structure was identified in our Cu-Gd-Ca samples, but we rather report on novel high temperature phases, which serve as a framework for ternary phase diagram. To the best of our knowledge we are the fi...

This is a draft of a paper, which describes the mechanism of coercivity improvement of MQ-II-type permanent magnets by the reaction between DyF3 and Nd2Fe14B, diffusion of Dy and formation of (Nd,Dy)2Fe14B phase..

Ferrite‐based, hard‐soft magnetic nanocomposites with the composition (100%−x)SrFe12O19–xCoFe2O4, where x = 5, 10, and 15 wt%, were prepared by mixing the constituent powders, followed by spark plasma sintering. In order to control the particle size of the constituent materials, the SrFe12O19 and CoFe2O4 powders were synthesized using the hydrother...

The value of the magnetization has a strong influence on the performance of nanoparticles that act as the contrast agent material for MRI. In this article, we describe processing routes for the synthesis of FePt nanoparticles of different sizes, which, as a result, exhibit different magnetization values. “Single-core” FePt nanoparticles of differen...

Using electrodeposition into anodic aluminium oxide (AAO) membranes we have successfully fabricated near-equiatomic Fe48+3Pd52+3 nanowires (NWs) with diameters of ≈ 200 nm and lengths of ≈ 3.5 um. XRD and TEM/SAED analyses revealed that the as-deposited NWs are isotropic and polycrystalline with an average crystal size of 5 nm and have an fcc cryst...

This study reports on the selective adsorption of whole plasma proteins on hydrothermally (HT) grown TiO2-anatase coatings and its dependence on the three main surface properties: surface charge, wettability and roughness. The influence of the photo-activation of TiO2 by UV irradiation as also evaluated. Even though the protein adhesion onto Ti-bas...

Near equiatomic Fe52±3Pd48±3 nanowires (NWs) with the length of 3.5 $mu text{m}$ and diameter of $approx 200$ nm were potentiostatically deposited at −1.1 V for 900 s into a porous anodic aluminum oxide template. Cylindrical NWs with a consistent composition along their length were obtained after introducing two additional steps prior to the electr...

Despite the increasing number of successful treatments for cancer, new forms of therapy are urgently required in order to combat the disease. In this investigation, we have produced an innovative material based on FePt/SiO 2 /Au hybrid nanoparticles that exhibit a combination of photothermal and magnetic properties as a basis for a local hypothermi...

The rare-earth crisis, which peaked in the summer of 2011 with the prices of both light and heavy rare earths soaring to unprecedented levels, brought about the widespread realization that the long-term availability and price stability of rare earths could not be guaranteed. This triggered a rapid response from manufacturers involved in rare earths...

It is known that the "race for the surface" determining the in vivo response is strictly connected to the physico-chemical properties of the material, especially at its surface. Accordingly, the study of surface roughness, charge and wettability is fundamental to predict the bio-response to the implant. In this work, streaming potential was chosen...

This manuscript presents our patent for a more effective magnetocaloric material based on Gd5Si2Ge2 as well as its method of production. The material has high refrigeration capacities and, with modifications to its composition, it is possible to control the temperature at which its magnetocaloric effect is the largest. This effect was achieved by m...

Even though Ti-based implants are the most used materials for hard tissue replacement, they may present lack of osseointegration on the long term, due to their inertness. Hydrothermal treatment (HT) is a useful technique for the synthesis of firmly attached, highly crystalline coatings made of anatase titanium dioxide (TiO2), providing favorable na...

This study examines bacterial adhesion on titanium-substrates used for bone implants. Adhesion is the most critical phase of bacterial colonization on medical devices. The surface of titanium was modified by hydrothermal treatment (HT) to synthesize nanostructured TiO2-anatase coatings, which were previously proven to improve corrosion resistance,...

We have fabricated Co–Pt cylindrical nanostructures comprised of a pair of nanotube and nanowire segments via direct electroplating into anodic alumina (AAO) membranes. The fabrication of such nanostructures is possible due to the penetration of sputtered gold (Au) nanoparticles inside the template, which serve as nucleation spots. The current tran...

We report on the influence of the magnetocrystalline anisotropy on the easy magnetization axis, magnetization reversal and magnetic domain configurations of electrodeposited Co-Pt nanowires with length of 4-6 μm and a diameter of 250 nm. The transmission electron microscopy and the X-ray diffractions revealed that the nanowires are composed of an i...

Fe–Pd nanowires were synthesised in anodic alumina templates by applying both potentiostatic and pulsed electrodeposition regimes. When using potentiostatic deposition, only fragmented nanowireswere obtained; however, the use of pulse deposition was shown to be effective for producing solid nanowires. In order to achieve this, different on-times fo...

We have studied the influence of Ni on the magnetocaloric effect (MCE) in Nanoperm-type amorphous materials by investigating a series of Fe84−xNixZr6B10 alloys with x = 0, 2, 4 and 6. As expected, the Curie temperature increased with the amount of Ni from 427 K for x = 0 to 482 K for x = 6. The maximum magnetic entropy change (ΔSMpk) for an applied...

The paper reports on the photoinduced properties of hydrothermally treated (HT) titanium used for bone implants. The anatase coatings composed of 30–100 nm anatase crystals exhibited high photocatalytic activity and good photo-induced wettability, reaching a superhydrophilic state, despite the larger crystal dimensions than the previously reported...