A5015124424- Magnetic and transport properties of perovskites and related materials
- Shape Memory Alloy Transformations
- Magnetic Properties of Alloys
- Heusler alloys: electronic and magnetic properties
- Thermal Expansion and Ionic Conductivity
- Intermetallics and Advanced Alloy Properties
- Hydrogen Storage and Materials
- Metallurgical and Alloy Processes
- Advanced Thermoelectric Materials and Devices
- Catalysis and Oxidation Reactions
- MXene and MAX Phase Materials
- 2D Materials and Applications
- Rare-earth and actinide compounds
- Ferroelectric and Piezoelectric Materials
- Ferroelectric and Negative Capacitance Devices
- Brake Systems and Friction Analysis
Technical University of Darmstadt
2020-2025
University of Duisburg-Essen
2022
Ni-Mn-based Heusler alloys, in particular all-d-metal Ni(-Co)-Mn-Ti, are highly promising materials for energy-efficient solid-state refrigeration as large multicaloric effects can be achieved across their magnetostructural martensitic transformation. However, no comprehensive study on the crucially important transition entropy change $\Delta s_t$ exists so far Ni(-Co)-Mn-Ti. Here, we present a systematic analyzing composition and temperature dependence of s_t$. Our results reveal...
The transition toward a carbon-neutral society based on renewable energies goes hand in with the availability of energy-efficient technologies. Magnetocaloric cooling is very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, current reliance highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable. Here, we aim mitigate limitation through utilization multicaloric concept, which...
The multicaloric effect is described by a temperature or entropy change of material triggered external stimuli applied removed simultaneously sequentially. prerequisite for this exhibiting multiple ferroic states. However, direct measurements the are rarely reported. Now, reason, we built measurement device allowing to determine adiabatic in pulsed magnetic fields and, simultaneously, under influence uniaxial load. We selected all-d-metal Heusler alloy Ni–Mn–Ti–Co our first test because its...
The chemical composition variety of MAX phases is rapidly evolving in many different directions, especially with the synthesis carbides that contain two or more metals on M-site these layered solids. However, nitride and carbonitride are still underrepresented, only a few members have been reported for most part barely characterized, particularly terms magnetic electronic properties. Here, we demonstrate simple effective route, as well comprehensive characterization three phases, (i) V2GeC,...
Maximizing the performance of magnetic refrigerators and thermomagnetic energy harvesters is imperative for their successful implementation can be done by maximizing operation frequency. One features delimiting frequency efficiency such devices phase transition kinetics magnetocaloric/thermomagnetic active material. While previous studies have described component governing magnetovolume in La(Fe,Si)13 giant magnetocaloric materials, a comprehensive description its structural has yet to...
We determined the temperature dependence of first-order magnetocrystalline anisotropy constants orthorhombic ferromagnetic MAB-phase <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Fe</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>AlB</a:mi><a:mn>2</a:mn></a:msub></a:mrow></a:math>. For this we prepared <b:math...
Abstract The magnetocaloric effect (MCE) offers a promising alternative for environmentally friendly cooling technologies, particularly at cryogenic temperatures. However, overestimating material capabilities can lead to misguided research efforts and hinder technological progress. Metamagnetic materials undergoing transition from an antiferromagnetic ferromagnetic state are often predicted exhibit strong inverse MCE temperatures based on magnetization measurements. This assumption is...
Zero thermal expansion (ZTE) composites are typically designed by combining positive (PTE) with negative (NTE) materials acting as compensators and have many diverse applications, including in high-precision instrumentation biomedical devices. La(Fe1–x,Six)13-based compounds display several remarkable properties, such giant magnetocaloric effect very large NTE at room temperature. Both linked via strong magnetovolume coupling, which leads to sharp magnetic volume changes occurring...
Reactive single-step hot-pressing at 1473 K and 35 MPa for 4 h produces dense, bulk, near single-phase, low-cost low-criticality Fe$_2$Al$_{1.15}$B$_2$ Fe$_2$Al$_{1.1}$B$_2$Ge$_{0.05}$Ga$_{0.05}$ MAB samples, showing a second-order magnetic phase transition with favorable magnetocaloric properties around room temperature. The as well can be tailored upon Ge Ga doping, leading to an increase of Curie temperature $T_C$ spontaneous magnetization $m_S$. maximum isothermal entropy change $\Delta...
Chemical ordering in NiMn-based Heusler alloys with magnetostructural phase transition is crucial for understanding the physics of transition. In new field all-d-metal Ni(Co)MnTi alloys, experimental determination chemical order challenging due to low difference scattering power different elements. Here, we report a combined approach neutron and x-ray diffraction an analysis show that no Heusler-typical L21 between Ti Mn present. Furthermore, Co Ni atoms do not exhibit among them; however,...
We have performed a combined experimental and theoretical investigation of the vibrational properties ${\mathrm{Ni}}_{2}\mathrm{Mn}\mathrm{Sn}$ Heusler alloys. Sn-partial density states (VDOS) $^{119}\mathrm{Sn}$ was measured by nuclear resonant inelastic x-ray scattering at temperatures 15 300 K, while magnetism local environment Sn resolved M\"ossbauer spectroscopy. Using functional theory, we associate peaks in VDOS with particular features element-resolved phonon dispersion...
Among the magnetocaloric materials featuring first-order phase transitions (FOPT), FeRh is considered as a reference system to study FOPT because it "simple" binary with CsCl structure exhibiting large adiabatic temperature change. Recently, ab initio theory predicted that changes in Fe/Rh stoichiometry vicinity of equiatomic composition strongly influence characteristics. However, this theoretical prediction was not clearly verified experimentally. Here, we investigated dependence...
La-Fe-Si-based alloys represent a promising material class for magnetocaloric cooling at ambient temperatures, but contain highly oxophilic elements and are chemically sensitive, which impairs their continued operation in aqueous heat exchange media. The development of protection strategies ensuring long-term stability necessitates comprehensive understanding the material’s corrosion characteristics. present work focuses on such an assessment hydrogenated La(FeMnSi) 13 containing α-Fe to...