Kristina Žužek Rožman

• Professor
• Group Leader at Jožef Stefan Institute

In recent decades rare-earth-element Nd-Fe-B permanent magnets have significantly shaped the global technological landscape. These magnets can be found in crucial technologies such as motors, generators, electric cars, wind turbines and an expansive range of consumer electronics1,2. The European magnet industry faces a myriad of challenges that mus...

In recent decades rare-earth-element Nd-Fe-B permanent magnets have significantly shaped the global technological landscape. These magnets can be found in crucial technologies such as motors, generators, electric cars, wind turbines and an expansive range of consumer electronics1,2. The European magnet industry faces a myriad of challenges that mus...

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...

Ammonia (NH3) present in biological fluids is biomarker for several disease states. In this work the well-known interaction between polyaniline (PANI) and NH3 was used for the fabrication of an amperometric sensory platform to detect aqueous NH3 at neutral i.e. biological pH. Understanding PANI's electrochemical synthesis and redox behaviour in aci...

The investigation of the nucleation and dissolution of gold nanoparticles on a glassy carbon substrate with Scanning Electrochemical Cell Microscopy (SECCM) combined with in-situ electrochemical TEM (EC-TEM) revealed the subtle influence of the local properties of the substrate on the electrochemical processes. Conducting hundreds of locally-resolv...

The consumption of critical raw materials, especially those in permanent magnets of Nd–Fe–B and Sm–Co-type, has significantly grown in the past decade. With predictions on further electrification growing exponentially the demand for these materials will even increase. This implies that efforts in assuring sustainability must involve recycling from...

Despite medical advances, skin-associated disorders continue to pose a unique challenge to physicians worldwide. Skin cancer is one of the most common forms of cancer, with more than one million new cases reported each year. Currently, surgical excision is its primary treatment; however, this can be impractical or even contradictory in certain situ...

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 use of screen-printed electrodes in different monitoring applications, e.g., polluted water, biotechnology, agriculture, industrial process control, and other applications, are continuously being developed. New cheap and open-source potentiostats have been recently emerging, in addition to the commercial and proprietary solutions on the market....

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...

The main challenge with electrocatalysis is finding low-cost electrocatalysts that can work efficiently to oxidize the HCHO. Here, we propose a mechanism for the voltammetric formation of a highly active, structurally disordered β-Ni(OH)2/β-NiOOH redox pair on the surface of electrodeposited Ni thin films to achieve an extraordinary catalytic perfo...

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...

Our contribution focuses on a correlative study of polyaniline (PANI) electropolymerisation and UV/VIS spectroscopy. PANI was prepared via electro-oxidation using a potentiodynamic method on commercial gold screen-printed electrodes (Au-SPE). By using an in-situ spectroelectrochemical method, the development of the polymer was observed from monomer...

Polyaniline (PANI) is a conducting polymer, widely used in gas-sensing applications. Due to its classification as a semiconductor, PANI is also used to detect reducing ammonia gas (NH3), which is a well-known and studied topic. However, easier, cheaper and more straightforward procedures for sensor fabrication are still the subject of much research...

In present work, we report on the enhanced electrocatalytic activity of formaldehyde oxidation in alkaline media for modified Ni nanowires (NWs)-based electrodes. Electrochemically deposited Ni NWs composed of metallic Ni and surface NiO were modified in KOH via cyclic voltammetry using different scan rates (10, 200 and 400 mV s⁻¹) in order to tran...

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...

Three phases can be distinguished in Nd‒Fe‒B permanent magnets: a Nd2Fe14B matrix grain phase, a Nd-rich grain boundary phase and a Nd-oxide phases. Common reaction models for leaching, such as the shrinking-particle model, cannot simply be applied to composite Nd‒Fe‒B permanent magnets because of the different chemical reactivities of the crystall...

The electrochemical polymerization of polyaniline (PANI) was studied using correlative measurements of electrochemistry and UV–vis spectroscopy, i.e., spectroelectrochemistry. The electropolymerization of PANI was performed in an acidic medium (1 M HCl) containing 0.1 M aniline with cyclic voltammetry (CV) in a potential window from −0.3 to 1 V and...

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 BHmax) in the recycled material....

A closed loop of recovering rare-earth elements and transition metals from Nd–Fe–B magnets with the total re-use of the electrolyte using a facile electrolysis-selective precipitation procedure.

Recycling of end‐of‐life Nd–Fe–B magnets is an important strategy for reducing the environmental dangers associated with rare‐earth mining and overcoming the supply risks associated with the rare‐earth elements. In this study, a novel concept for recycling of sintered Nd–Fe–B magnets by directly recovering the matrix Nd2Fe14B grains is presented. T...

A Ni nanowires-based electrodes for formaldehyde (HCHO) detection were fabricated via a template-assisted electrodeposition. The as-deposited Ni nanowires (NWs) were characterized by scanning electron microscope (SEM). In order to form an active redox couple of Ni(OH)2/NiOOH on the surface of nanowires, the Ni NWs were electrochemically modified in...

With Liquid-Cell Transmission Electron Microscopy (LCTEM) we can observe the kinetic processes taking place in nanoscale materials that are in a solvated environment. However, the beam-driven solvent radiolysis, which results from the microscope's high-energy electron beam, can dramatically influence the dynamics of the system. Recent research sugg...

The magnetic properties of the recycled hydrogenation disproportionation desorption recombination (HDDR) Nd-Fe-B powder, doped with a low weight fraction of DyF3 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 DyF3 grounded powder. Different pos...

The Cover Feature demonstrates the induced deposition of rare earth element (REE) catalyzed by the activated‐state transition metal (TM).More information can be found in the Article by X. Xu et al.

Rare earth element (REE)‐based metals and alloys are generally synthesized by molten‐salt electrolysis which is an energy‐intensive approach. Previous attempts to deposit alloys of rare earths from solutions at mild temperatures have met with little success. Excitingly, in this investigation we were able to electrodeposit Nd–Fe from the 1‐ethyl‐3‐m...

Highly ordered, Ni(OH) 2 [sbnd]Ni-nanowire-based receptor elements were electrochemically fabricated and tested for formaldehyde (HCHO) detection by monitoring their oxidation ability in alkaline media. In order to normalize the electrochemical output currents, the Ni nanowires' electrochemically active surface area was assessed using an oxalate-ba...

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...

In-Situ Observation of the Reversible Electrochemical Deposition of Fe in a Transmission Electron Microscope - Volume 24 Supplement - U. Wolff, B. Ambrozic, K. Zuzek Rozman, K. Leistner, K. Nielsch, S. Sturm

Composition evolution and structural properties of Fe-Co-Ni thin films have been studied by transmission electron microscopy along the growth direction. The samples were electrodeposited with constant current from stagnant solution. The samples were of uneven composition, exhibiting two major modes of composition change: a near-substrate compositio...

Spark plasma sintering (SPS) technique is applied in combination with hydrogen decrepitation process for the recycling of SmCo5 magnets. The SmCo5 magnets for recycling were first decrepitated by hydrogen gas of a pressure of 4 bar for 3 hours to produce decrepitated powder. This powder was then used to prepare isotropic sintered magnets using the...

The spark plasma sintering (SPS) technique is applied in combination with the hydrogen decrepitation process for the recycling of SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> magnets. The SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"...

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...

The aim of the study is to investigate the relationship between the physico‐chemical properties of superparamagnetic iron oxide nanoparticles (SPIONs) and their cytotoxicity profile in light of their potential biomedical application as nanocarriers for pancreatic cancer treatment. Two types of SPIONs were tested: magnetite nanoparticles (Fe3O4 NPs)...

Fe69±3Pd31±3 nanowires (NWs) with lengths of a few microns and diameters of 200 nm were synthesized via template-assisted pulsed electrodeposition into alumina-based templates. The as-deposited Fe69±3Pd31±3 NWs exhibited α-Fe (bcc-solid solution of Fe, Pd) nanocrystalline structure as seen from the x-ray diffraction (XRD), that got confirmed by tra...

p class="PaperAbstract">It is shown in this overview that modern composition depth profiling methods like secondary neutral mass spectroscopy (SNMS) and glow-discharge – time-of-flight mass spectrometry (GD-ToFMS) can be used to gain highly specific composition depth profile information on electrodeposited alloys. In some cases, cross-sectional tra...

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...

– For the past several years, different strategies have been developed to design and fabricate Au/TiO2 nanostructures for solar-light-driven applications. Owing to the localized surface plasmon resonance properties of Au, Au/TiO2 nanostructures display extraordinary features including enhanced visible light harvesting, hot electron injection, and S...

Stable suspensions of spherical 10–15 nm superparamagnetic iron oxide nanoparticles (SPIONs) have been synthetized by co-precipitation, stabilized with citric acid, surface functionalized with aminopropyltriethoxysilane (APTES) and finally decorated with ultra-small gold nanoparticles (GNPs) by in situ reduction of a soluble gold salt (HAuCl4), obt...

Introduction Nanomedical approaches in cancer treatment have the potential to enhance the effectiveness of localized therapy while minimizing side effects on the surrounding healthy tissue. The aim of our study was the development of a novel hybrid nanoparticles (hNPs) based on magnetic core (FePt) and photothermaly active shell (SiO 2 /Au) for tar...

Yttria, a host for heavy rare earth elements, is an important up‐conversion material, able to convert lower energy near‐infrared light into higher energy visible light, opening the avenue for a wide spectrum of applications from laser technology, photovoltaics to theranostics [1,2]. The efficient use of yttria in the form of nanoparticles (NPs) is...

Yttrium oxide (Y2O3) nanoparticles (NPs) as a host for heavy rare earth elements (Yb3+, Eu3+) have shown to be an efficient up‐conversion phosphor material with a great potential ranging from therapy and sensing for drug delivery to photovoltaic applications [1]. In order to achieve desired morphology and size distribution of Y2O3 NPs the nucleatio...

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...

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...

Elongated magnetic nanostructures, that is, magnetic nanowires, can be activated, controlled and manipulated remotely with the application of modest external magnetic fields. With their size and shape being experimentally set and controlled within a range of a few nm to several hundred nm, this puts them in a similar size category to biological ent...

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...

The first one-step synthesis of dumbbell-like gold-iron oxide nanoparticles has been reported here. Surface functionalization with a biocompatible chitosan matrix allowed us to obtain a novel targetable diagnostic and therapeutic tool.

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...

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...

Using template-assisted electrodeposition in partially Au-covered polycarbonate templates, we have successfully deposited equiatomic Co–Pt nanotubes with an external radius R of 100 nm, lengths L of 800–2000 nm and tube-wall thicknesses of 70 nm. By applying different characterization methods – vibrating-sample magnetometry and combined atomic and...

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...

The urothelium forms the blood-urine barrier, which depends on the complex organization of transmembrane proteins, uroplakins, in the apical plasma membrane of umbrella cells. Uroplakins compose 16 nm intramembrane particles, which are assembled into urothelial plaques. Here we present an integrated survey on the molecular ultrastructure of urothel...

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 report on the influence of the mag-netocrystalline anisotropy on the easy magnetization axis, magnetization reversal and magnetic domain configurations of electrodeposited Co–Pt nanowires with lengths in the range of 4–6 lm and a diameter of 250 nm. The transmission electron microscopy and the X-ray diffractions revealed that the nanowires are c...

We have investigated the effect of the microstructure on the magnetic properties of Co-Pt nanowires (NWs) with diameters of 15, 50, and 80 nm. These Co-Pt NWs were fabricated by using polycarbonate membranes with different pore diameters via direct electrodeposition. A detailed transmission-electron-microscopy analysis revealed that the Co-Pt NWs t...

We report on nitrogen-filled hollow Co-Pt nanospheres produced via pulsed-laser ablation in ambient nitrogen gas. The resulting nanospheres are characterized by a single-crystalline face-centred cubic Co55 +/- 3Pt45 +/- 3 shell and a void filled with molecular nitrogen, typically occupying the sphere's central region. The average diameter of the sp...

Fe-Pd thin films with various compositions and thicknesses were produced with electrodeposition using the constant potentials from -1.0 to -1.3 V. The FEGSEM and AFM analyses revealed a smooth, nanostructured surface morphology of the films, with more granular features appearing at more negative potentials. The high-resolution FEGSEM images of the...

Copper sulfide (CuS)-based thin films with different thickness have been prepared by thermal co-evaporation of the elemental constituents. Morphological and microstructural properties were shown to vary with film thickness. Optical properties of films encapsulated in a double-glazed configuration and containing an air gap have been measured. Encaps...

In a novel process to enhance the coercivity we have electrophoretically deposited DyF3 powder onto the surface of an as-sintered Nd–Fe–B magnet as the initial step in the grain-boundary diffusion process. After a conventional heat treatment at 850 and 500 °C the coercivities were higher than in the case of simple dipping after a typical 10 h, with...

Fe–Pd-based tubular nanostructures were prepared by direct electrodeposition into track-etched polycarbonate templates. The characterization of the electrodeposition process showed that the complexing of Pd and Fe is necessary for the co-deposition of both metals. In the as-deposited nanotubes, which exhibited an overall composition of Fe70Pd30 as...

Near-equiatomic Fe–Pd-based nanotubes with diameters of 200nm and lengths of 1μm were directly electrodeposited from a single electrolyte into polycarbonate templates. The as-deposited Fe50Pd50 nanotubes were then characterized compositionally, structurally and magnetically. The as-deposited Fe50Pd50 tubes had an fcc crystal structure and were magn...

SmFe based alloys interstitially modified with nitrogen are potential candidates for high energy permanent magnets. In order to obtain the optimum properties a thorough understanding of the starting material and processing parameters is required. The microstructures of two cast alloys of composition Sm13.8Fe82.2Ta4.0 and Sm13.7Fe86.3 were carefully...

Sm-Fe-Ta-N-O nanospheres were synthesized by pulsed-laser deposition from a Sm(13.8)Fe(82.2)Ta(4.0) target in a nitrogen atmosphere. Three structurally and compositionally distinct types were identified: amorphous, core-shell and hollow nanospheres. Amorphous spheres were compositionally homogeneous and completely oxidized. The core-shell spheres w...

Equiatomic Fe–Pd thin films with thicknesses of 200 nm were deposited from a single electrolyte onto glass-based, Au-coated substrates using the electrodeposition method. The as-deposited films were annealed at temperatures from 400 to 600 ° C for 1 h in Ar +7 % H ₂ . The phase formation, microstructure and the magnetic properties were a...

In this investigation commercial magnets based on ( Nd , Dy )₁₄( Fe , Co )₇₉ B ₇ were prepared by a conventional powder-metallurgy route with a degree of alignment equal to ∼90 % and then exposed to hydrogen at a pressure of 1 bar. The magnets, in the form of cylinders, were observed to decrepitate exclusively from...

Near-equiatomic Co–Pt thin films with thicknesses of 520nm were deposited from a single electrolyte onto glass-based Au-coated substrates using the electrodeposition method. The as-deposited Co–Pt-based films were annealed at temperatures from 500ºC to 700ºC for 1h. The phase formation, microstructure and the magnetic properties were analyzed. It w...

Quantitative electron-probe microanalysis (EPMA) with energy-dispersive (EDS) and wavelength-dispersive (WDS) X-ray spectroscopy was performed to determine the chemical composition of Co–Pt ferromagnetic thin films. The conventional “bulk” EPMA approach was applied and tested in detail by using several analytical set-ups with different combinations...

Co-Pt nanostructures having a tubular geometry, a diameter of 200 nm and a length of 2 mum were produced via direct electroplating into polycarbonate-based templates. The nanotube-formation mechanism was explained using the relative rates of deposition and the diffusion of the metal ions. The as-deposited Co-Pt nanotubes are magnetically soft, with...

Co–Pt-based tubular nanostructures were prepared by direct plating into track-etched polycarbonate templates from a single electrolyte containing a Pt-p-salt and Co-sulphamate. These tubular nanostructures, with a diameter of 200nm and lengths up to 5μm, were obtained with potentiostatic depositions at potentials of −1.9V to −2.5V, measured against...

PLD (pulsed laser deposition) is an attractive technique to fabricate thin films with a stoichiometry reflecting that of the target material. Conventional PLD instruments are more or less black boxes in which PLD is performed virtually "blind", i.e. without having great control on the important PLD parameters. In this preliminary study, for the fir...

We have investigated samples of Gd 5 Ge 2 Si X−2 Fe X , where X = 0, 0.125, 0.25, and 0.5, and Gd 5 Si 2 Ge Y−2 Fe Y , where Y = 0, 0.06, 0.25, and 0.5, using magnetic measurements and high-resolution transmission electron microscopy. We found that the Y = 0.25 sample, with Fe substituting for Ge, reduced the hysteresis losses practically to zero;...

Gd5Si2Ge2-based alloys can exhibit a giant magnetocaloric effect (GMCE); this gives them the potential for use in cooling technologies. It has also been reported that a small addition of iron reduces the hysteresis losses in Gd5Si2Ge2-based alloys, thus increasing the net refrigerating capacity. In this investigation, we have been the first to look...

Magnetocaloric Gd₅Si₂Ge₂-based alloys exhibit a well-documented giant magnetocaloric effect at around room temperature. However, as candidate materials for real-world refrigeration devices, they suffer from a number of problems, one of which is large hysteresis losses while cycling in and out of the magnetic field....