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2025-07-18: New CRC/TRR 270 HoMMage publication: Nanocrystalline CoMnFeNiGa high entropy alloys: Room temperature ferromagnetism bridging the gap from Bulk to Nano
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This study demonstrates a scalable and unique processing strategy for tailoring the structure, microstructure and magnetic properties of CoMnFeNiGa HEAs across different length scales — micropowder, bulk, and NPs. The high energy ball milling (HEBM) enables the incorporation of low-melting Ga into a stable, single-phase FCC nanocrystalline HEA matrix. Subsequent spark plasma sintering (SPS) induces partial FCC→BCC transformation and nanoscale compositional segregation, producing dual-phase HEA bulk with enhanced magnetic performance. Microparticle laser fragmentation in liquid (MP-LFL) emerges as a robust synthesis platform for producing compositionally complex NPs in a single step directly from the HEBM microparticles. Metal-liquid interactions critically determine the NP morphology (spheres and platelets) and subsequent phase structure, offering promising avenues for solvent-dependent phase control while retaining multi-elemental stoichiometry. Despite structural complexity, all forms exhibit RT ferromagnetism, with magnetic behavior governed by processing-induced variations in phase composition, crystallite size, and microstrain. A rapid thermal treatment (30 s) at 1000 K led to significant improvements in magnetic properties across all forms, driven by phase transformations and microstructural modification. This study provides a new pathway to engineer soft ferromagnetic HEAs with tailored properties by controlling phase composition, crystallite size, nanoscale chemical segregation, and processing-induced microstructure through synthesis and subsequent heat treatment.
For details see here.
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2025-07-01: New publication: Amorphization of laser-fabricated ignoble high-entropy alloy nanoparticles and its impact on surface composition and electrochemistry
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This study presents a green and scalable approach for synthesizing ignoble high-entropy alloy (HEA) nanoparticles using Laser Synthesis and Processing of Colloids (LSPC) in ethanol, developed through a collaboration within the Transregio CRC/TRR 270 HoMMage. By employing laser ablation in liquids (LAL) with nanosecond and picosecond pulses, phase-selective synthesis of CrMnFeCoNi and CrFeCoNiCu nanoparticles was achieved. The internal structure — amorphous or crystalline — was controlled by pulse duration, with amorphization favored in Cu-containing systems due to enhanced carbon incorporation from laser-induced solvent decomposition.
The underlying mechanism combines thermal kinetics and in situ reaction chemistry. The concept was successfully extended to microparticle laser fragmentation in liquids (MP-LFL), confirming its scalability and effectiveness. Electrochemical analysis showed that surface composition, especially the substitution of Mn with Cu, had a stronger influence on oxygen evolution reaction (OER) performance than structural phase alone. Amorphous CrMnFeCoNi nanoparticles exhibited the highest catalytic activity and durability, demonstrating the potential of LSPC for designing functional HEA nanomaterials through combined structural and compositional tuning.
For details see here.
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2025-06-25: Decomposition of Ni50Mn45In5: A Transmission Electron Microscopy study
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In an international collaboration with Prof. Zi-An Li (Guangxi University) and his group we studied the microstructural changes during thermal treatment up to 750 K. Both ex situ and in situ TEM experiments reveal similar trends in the processes of alloy decomposition and nanoprecipitation, But the influence of sample thickness and vacuum conditions during in situ TEM heating must be considered. Additionally, we establish a relationship between the magnetic properties of the dual-phase system, consisting of antiferromagnetic L10–NiMn matrix and ferromagnetic L21–Ni2MnIn nanoprecipitates and the microstructural features. Our findings may provide insights that can be applied to other Ni–Mn-based alloys and potentially to a broader range of materials, offering a framework for understanding alloy decomposition, nanoprecipitation, and their impact on magnetic properties. For details see here.
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2025-06-12: Rare-Earth-free materials: An alternative for current magnetocaloric alloys
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In a collaboration within the Transregio TRR270 we prepared and studied rare-earth-free compositionally complex alloys (CCAs) with magnetic phase
transitions, spanning from bulk materials to nanoparticles. Magnetic phase transitions at the Curie temperature are essential for applications like magnetocaloric refrigeration, magnetic sensors, and actuators, but the reliance on costly, scarce rare-earth materials limits sustainability. Specifically, we investigated Mn22.3Fe22.2Ni22.2Ge16.65Si16.65 (Ge-based CCA) and Mn0.5Fe0.5NiSi0.93Al0.07 (Al-based CCA). Magnetization measurements confirm a ferromagnetic-to-paramagnetic phase transition in bulk alloys, with Tc = 179 K for Ge-based CCA and Tc = 263 K for Al-based CCA. At the nanoscale, both Ge- and Al-based NPs exhibit superparamagnetic behaviour, with blocking temperatures of TB ≈ 120 K for Ge-based NPs (xc = 13.4 ± 15.5 nm, average particle size) and TB ≈ 100 K for Al-based NPs (xc = 18.4 ± 9.1 nm, average particle size). Our results indicate that the Al-based CCA is a promising, cost-effective alternative to Ge-based CCA at the nanoscale, providing an economically viable and cost-effective alternative for nanoscale-based applications. Details see here
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2025-05-16: Magnetocrystalline anisotropy of the MAB phase Fe$_2$AlB$_2$
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Within the collaborative research center HoMMage (CRC/TRR 270), we determined the temperature dependence of the magnetocrystalline anisotropy of Fe2AlB2 for the first time. Fe2AlB2 belongs to the group of the MAB phases and is a promising candidate for magnetocaloric applications due to low costs and its magnetic transition close to ambient temperature.
See the publication in
Physical Review Materials
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2025-05-01: Visit of Prof. Preeti Bhobe
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We are happy to announce the visit of Prof. Preeti Bhobe (Indian Institute of Technology Indore, India) within the UDE International Guest Lecturer Programme. She specializes on studying different functional materials using X-ray absorption fine structure (XAFS) spectroscopy and will give three lectures on functional materials like Half-metals and topological states in Heuslers, and Magneto-transport in 2D Chalcogenides and Kagome lattices.
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