1. Chemical ordering and non-linear magnetic behavior : enhancing magnetocaloric effect in FeMnNiGeSi high-entropy materialsVincent Fournée, G. Lengaigne, Pascal Boulet, Sorour Semsari Parapari, Sergej Ražnjević, Sašo Šturm, Franca Albertini, 2026, izvirni znanstveni članek Povzetek: High-entropy alloys (HEAs) offer opportunities to discover new functional materials with combination of properties not reached in other classes of materials. Here we report a detailed investigation of the structure, magnetic and magnetocaloric properties of some high entropy materials in the FeMnNiGeSi quinary system. Our findings indicate the persistence of partial chemical ordering, with transition metal atoms and metalloids preferentially occupying specific crystallographic sites. This ordering is further supported by ab initio total energy calculation. In turn, the magnetic moment - carried out mainly by Fe and Mn - exhibits a strong dependence on the crystallographic sites occupied by these magnetic atoms. By exploring the chemical landscape, we observed highly non-linear magnetic behavior upon Mn doping, resulting in an isothermal entropy change (ΔSm) as high as 35 Jkg−1K−1 in 5 T, while the transition temperature can be tuned in the range from 160 to 263 K, approaching room temperature. These outstanding performances suggest that rare-earth free high entropy materials can rival conventional magnetocaloric materials. Additionally, we find that the first-order magnetostructural transition can evolve into a second-order magnetic transition through chemical tuning. This opens the possibility of discovering similar materials near the boundary between first- and second-order transitions, with vanishing hysteresis - potentially addressing their mechanical instability issue.
Ključne besede: high-entropy alloys, magnetocaloric properties
Objavljeno v DiRROS: 04.06.2026; Ogledov: 103; Prenosov: 94
 Celotno besedilo (6,90 MB)
Gradivo ima več datotek! Več... |
2. Oscillating topological charge for skyrmion-based spin-transfer torque nano-oscillatorVinko Sršan, Matej Komelj, Sašo Šturm, 2026, izvirni znanstveni članek Povzetek: Magnetic skyrmions are considered as promising candidates for next generation information carriers. In cubic chiral magnets with bulk Dzyaloshinskii–Moriya interaction, skyrmions trivially extend into the third dimension forming so-called skyrmion string. The third dimension of skyrmion strings introduces an additional degree of freedom that can be utilized in skyrmion-based applications. An example of such application is spin-torque oscillator based on skyrmion breathing, gyrotropic motion and skyrmion deformation mechanisms. Expanding these mechanisms, we propose design of spin-torque oscillator based on topological charge oscillation in confined geometry where skyrmion string breathing, gyrotropic motion and skyrmion-edge interactions are coupled. Micromagnetic calculations were employed to demonstrate topological charge oscillation as a function of model geometries. It is shown that only a small subset of material geometries is suitable to obtain topological charge oscillations, indicating that precise engineering of geometry would be required to realize such a device. Findings presented in this work contribute to a better understanding of a skyrmion string dynamical phenomena, which offer additional route in designing spin-torque oscillators.
Ključne besede: magnetic skyrmions, skyrmion strings, micromagnetics, spin torque nano-oscillator
Objavljeno v DiRROS: 28.05.2026; Ogledov: 95; Prenosov: 84
Celotno besedilo (2,52 MB)
Gradivo ima več datotek! Več... |
3. Anisotropy limitations in additive manufacturing with material extrusionBenjamin Podmiljšak, Matej Komelj, Anubhav Vishwakarma, Petra Jenuš, Sašo Šturm, Kristina Žužek Rožman, 2026, izvirni znanstveni članek Povzetek: Achieving anisotropy in additively manufactured composites is essential for high-performance functional materials but remains challenging in fused filament fabrication (FFF). This study investigates a field-assisted FFF approach using strontium hexaferrite (SrFe12O19)–polyphenylene sulfide (PPS) composites, in which particle alignment is induced by processing on top of a high-strength neodymium–iron–boron (Nd–Fe–B) magnet. Two configurations were compared: (i) a continuous setup, where the growing printed material remains in direct contact with the magnet and can act as a flux-guiding core, and (ii) a spacer-based setup, where non-magnetic spacers separate the print from the field source. Structural, functional (magnetic) measurements and finite element simulations (FEMM) were used to quantify the evolution of anisotropy as a function of build height. In the continuous configuration, particle alignment—and thus macroscopic anisotropy—remains high up to about 20 mm, with 0.90, and then gradually declines while still being detectable at 57.5 mm. Spacer-printed samples lose anisotropy much earlier, with approaching isotropic values (∼0.5) beyond 20–25 mm. Simulations reproduce these trends and show that previously deposited material acts as a flux-guiding path, sustaining a predominantly uniaxial field with height. The results define practical limits for static-field alignment in material-extrusion processing and provide geometry-dependent design rules for scalable fabrication of anisotropic ceramic–polymer composites. The findings are relevant for materials and process design in applications where controlled anisotropy is required over centimetre-scale dimensions.
Objavljeno v DiRROS: 11.02.2026; Ogledov: 569; Prenosov: 275
Celotno besedilo (8,61 MB)
Gradivo ima več datotek! Več... |
4. Transmission electron microscopy analysis of shock veins in the meteorite JeseniceBojan Ambrožič, Sašo Šturm, Mirijam Vrabec, 2025, izvirni znanstveni članek Povzetek: Meteorite Jesenice is a weakly (S3) shocked ordinary chondrite from Slovenia. The shock event was violent enough to cause localized partial melting of the meteorite and the formation of shock veins. Inside the shock veins, metal-sulfide globules were found, which provided evidence for a post-shock cooling rate of 2.2·105 Ks–1 – 7.4·103 Ks–1. From the mineral paragenesis of the shock veins, shock pressure and peak shock temperature were deduced as 2.5–15 GPa and 1500–2150 °C, respectively. We provide evidence that shock veins were formed via a shear and friction mechanism. Furthermore, the confirmed presence of ordered FeNi metal (tetrataenite) found in the matrix indicates that the shock occurred in the parent body of the meteorite Jesenice.
Ključne besede: chondrite, shock stage, shock veins, metal-sulfide globules, tetrataenite, transmission electron microscopy
Objavljeno v DiRROS: 24.12.2025; Ogledov: 966; Prenosov: 216
Celotno besedilo (2,81 MB) |
5. Unravelling the intricacies of micro-nonuniform heating in field-assisted sintering of multiphase metallic microstructuresTomaž Tomše, Benjamin Podmiljšak, Lavinia Scherf, Reto Kessler, Spomenka Kobe, Andraž Kocjan, Sašo Šturm, Kristina Žužek Rožman, 2024, izvirni znanstveni članek Povzetek: 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 contacts due to the Joule effect. However, recent theoretical modelling studies suggest that the very fast diffusion of heat within the micron-sized particles prevents the overheating, thereby challenging the conventional understanding of FAST-related heating effects. To provide a new experimental perspective on the local overheating and underscore its pivotal role in controlling the microstructure formation, we have studied the phase transformations in a Nd-Fe-B-type multiphase metallic powder during FAST. The formation of the α-Fe phase, following the peritectic decomposition of the Nd2Fe14B matrix phase expected at ≈1180 ◦C (TPER), was observed for FAST temperatures (TFAST) below TPER. A correlation between the electric current and the final phase composition, which can only be explained by considering the local overheating effect, was established. We showed that the formation of the α-Fe phase at TFAST < TPER can be mitigated by (i) decreasing the electric current through the sample, which is achieved by lowering the heating rate from 100 to 10 ◦C/min or by using electrically highly conductive pressing tools (WC) and a non-conductive coating (BN), or by (ii) interparticle necking achieved through a thermal pre-treatment of the powder compact that decreases the overall resistance. Our findings emphasize the criticality of the electric current modulation to minimize any undesired phase transformation, paving the way for future developments in rapid, FAST-based strategies aimed at refining the microstructures and tailoring the properties of multiphase metallic materials
Objavljeno v DiRROS: 28.03.2025; Ogledov: 984; Prenosov: 328
Celotno besedilo (4,68 MB) |
6. A rapid thermal-radiation-assisted sintering strategy for Nd-Fe-B-type magnetsTomaž Tomše, Aljaž Iveković, Andraž Kocjan, Sašo Šturm, Kristina Žužek Rožman, 2024, izvirni znanstveni članek Povzetek: The green transition has spiked demand for high-performance sintered Nd-Fe-B permanent magnets, necessitating advanced powder consolidation technologies to enhance production efficiency. This study explores the rapid sintering methodology for an Nd-Fe-B powder using a radiation-assisted sintering approach. The case study material is an industrially used powder, prepared through strip-casting, hydrogen decrepitation, and jet milling, with a mean particle size of 5.5 µm. The powder is sintered to full density in a modified Spark Plasma Sintering furnace, achieving pressureless conditions and eliminating electrical currents in the sample to preserve grain alignment and prevent decomposition of the hard-magnetic phase. Fully-dense samples are obtained with heating rates ranging from 10 to 200 °C/min and up to 5 minutes of dwell time at 1100 °C. Rapid heating results in grain size and microstructure comparable to conventionally sintered magnets prepared from the same powder, without compromising magnetic performance after post-sinter annealing at 520 °C for 120 minutes. This sintering method contributes to a novel strategy for optimizing magnet production by utilizing efficient thermal-radiation heat transfer. The combination of rapid heating and pressureless sintering drastically reduces heat-up and dwell times, providing a fundamental advantage over slow conventional sintering.
Ključne besede: rapid sintering, finite-element modeling
Objavljeno v DiRROS: 28.03.2025; Ogledov: 1551; Prenosov: 359
Celotno besedilo (2,89 MB) |
7. IoT electrochemical sensor with integrated ▫$Ni(OH)_2–Ni$▫ nanowires for detecting formaldehyde in tap waterŠpela Trafela, Abhilash Krishnamurthy, Kristina Žagar, Urška Kavčič, Igor Karlovits, Beno Klopčič, Sašo Šturm, Kristina Žužek Rožman, 2023, izvirni znanstveni članek Povzetek: Simple, low-cost methods for sensing volatile organic compounds that leave no trace and do not have a detrimental effect on the environment are able to protect communities from the impacts of contaminants in water supplies. This paper reports the development of a portable, autonomous, Internet of Things (IoT) electrochemical sensor for detecting formaldehyde in tap water. The sensor is assembled from electronics, i.e., a custom-designed sensor platform and developed HCHO detection system based on Ni(OH)2–Ni nanowires (NWs) and synthetic-paper-based, screen-printed electrodes (pSPEs). The sensor platform, consisting of the IoT technology, a Wi-Fi communication system, and a miniaturized potentiostat can be easily connected to the Ni(OH)2–Ni NWs and pSPEs via a three-terminal electrode. The custom-made sensor, which has a detection capability of 0.8 µM/24 ppb, was tested for an amperometric determination of the HCHO in deionized (DI) and tap-water-based alkaline electrolytes. This promising concept of an electrochemical IoT sensor that is easy to operate, rapid, and affordable (it is considerably cheaper than any lab-grade potentiostat) could lead to the straightforward detection of HCHO in tap water.
Ključne besede: formaldehyde, electrochemical sensor, nickel, tap water
Objavljeno v DiRROS: 06.06.2023; Ogledov: 1934; Prenosov: 1536
Celotno besedilo (2,65 MB)
Gradivo ima več datotek! Več... |
8. |
9. |
