Residual Ferromagnetic Regions Affecting the First-Order Phase Transition in Off-Stoichiometric Fe-Rh.

Among the magnetocaloric materials featuring first-order phase transitions (FOPT), FeRh is considered as a reference system to study the FOPT because it is a "simple" binary system with a CsCl structure exhibiting a large adiabatic temperature change. Recently, ab initio theory predicted that changes in the Fe/Rh stoichiometry in the vicinity of equiatomic composition strongly influence the FOPT characteristics. However, this theoretical prediction was not clearly verified experimentally.

Boosting Coercivity of 3D Printed Hard Magnets through Nano-Modification of the Powder Feedstock.

The demand for strong, compact permanent magnets essential for the energy transition drives innovation in magnet manufacturing. Additive manufacturing, particularly Powder Bed Fusion of metals using a laser beam (PBF-LB/M), offers potential for near-net-shaped Nd-Fe-B permanent magnets but often falls short compared to conventional methods. A less explored strategy to enhance these magnets is feedstock modification with nanoparticles.

Multicaloric Cryocooling Using Heavy Rare-Earth Free La(Fe,Si)-Based Compounds.

The transition toward a carbon-neutral society based on renewable energies goes hand in hand with the availability of energy-efficient technologies. Magnetocaloric cooling is a very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, the current reliance on highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable.

Flexible Magnetocaloric Fiber Mats for Room-Temperature Energy Applications.

Currently, magnetocaloric refrigeration technologies are emerging as ecofriendly and more energy-efficient alternatives to conventional expansion-compression systems. However, major challenges remain. A particular concern is the mechanical properties of magnetocaloric materials, namely, their fatigue under cycling and difficulty in processing and shaping.

Bulk Nanostructured Silicide Thermoelectric Materials by Reversible Hydrogen Absorption-Desorption.

The production of bulk nanostructured silicide thermoelectric materials by a reversible hydrogen absorption-desorption process is demonstrated. Here, high-pressure reactive milling under 100 bar hydrogen is used to decompose the CaSi phase into CaH and Si. Subsequent vacuum heat treatment results in hydrogen desorption and recombination of the constituents into the original phase.

Tailoring Negative Thermal Expansion via Tunable Induced Strain in La-Fe-Si-Based Multifunctional Material.

Zero thermal expansion (ZTE) composites are typically designed by combining positive thermal expansion (PTE) with negative thermal expansion (NTE) materials acting as compensators and have many diverse applications, including in high-precision instrumentation and biomedical devices. La(Fe,Si)13-based compounds display several remarkable properties, such as giant magnetocaloric effect and very large NTE at room temperature. Both are linked via strong magnetovolume coupling, which leads to sharp magnetic and volume changes occurring simultaneously across first-order phase transitions; the abrupt nature of these changes makes them unsuitable as thermal expansion compensators.

Epitaxy Induced Highly Ordered SmCo-SmCo Nanoscale Thin-Film Magnets.

Utilizing the molecular beam epitaxy technique, a nanoscale thin-film magnet of -axis-oriented SmCo and SmCo phases is stabilized. While typically in the prototype Sm(Co, Fe, Cu, Zr) pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm-Co system is shown. A detailed analysis of the extended X-ray absorption fine structure confirmed the coexistence of SmCo and SmCo phases with 65% SmCo and 35% SmCo.

Magnetoelectric Tuning of Pinning-Type Permanent Magnets through Atomic-Scale Engineering of Grain Boundaries.

Pinning-type magnets with high coercivity at high temperatures are at the core of thriving clean-energy technologies. Among these, Sm Co -based magnets are excellent candidates owing to their high-temperature stability. However, despite intensive efforts to optimize the intragranular microstructure, the coercivity currently only reaches 20-30% of the theoretical limits.

Toxicological evaluation of MnAl based permanent magnets using different in vitro models.

Due to economic, environmental and geopolitical issues, the development of permanent magnets with a composition free of rare earth elements and with acceptable magnetic properties has been considered a priority by the international community, being MnAl based alloys amongst the most promising candidates. The aim of this work was to evaluate the toxicity of powders of two forms of newly developed MnAl(C) permanent magnets through exposure experiments applying three model organisms, using as a benchmark powders of a commercial rare-earth-containing magnet (NdFeB). For this purpose, the direct exposure to the different particles suspensions as well as to magnets leachates was evaluated.

Giant voltage-induced modification of magnetism in micron-scale ferromagnetic metals by hydrogen charging.

Owing to electric-field screening, the modification of magnetic properties in ferromagnetic metals by applying small voltages is restricted to a few atomic layers at the surface of metals. Bulk metallic systems usually do not exhibit any magneto-electric effect. Here, we report that the magnetic properties of micron-scale ferromagnetic metals can be modulated substantially through electrochemically-controlled insertion and extraction of hydrogen atoms in metal structure.

Magnetic Refrigeration with Recycled Permanent Magnets and Free Rare-Earth Magnetocaloric La-Fe-Si.

Magnetic refrigeration is an upcoming technology that could be an alternative to the more than 100-year-old conventional gas-vapor compression cooling. Magnetic refrigeration might answer some of the global challenges linked with the increasing demands for readily available cooling in almost every region of the world and the global-warming potential of conventional refrigerants. Important issues to be solved are, for example, the required mass and the ecological footprint of the rare-earth permanent magnets and the magnetocaloric material, which are key parts of the magnetic cooling device.

Low-temperature synthesis of nanoscale ferromagnetic α'-MnB.

The search for tunable, size-dependent properties and unique processability has triggered the development of new synthetic routes for transition metal borides. MnB is a soft to semi-hard ferromagnetic material. This boride is now available by bottom-up, low-temperature solution chemistry.

A multicaloric cooling cycle that exploits thermal hysteresis.

The giant magnetocaloric effect, in which large thermal changes are induced in a material on the application of a magnetic field, can be used for refrigeration applications, such as the cooling of systems from a small to a relatively large scale. However, commercial uptake is limited. We propose an approach to magnetic cooling that rejects the conventional idea that the hysteresis inherent in magnetostructural phase-change materials must be minimized to maximize the reversible magnetocaloric effect.

A quantitative criterion for determining the order of magnetic phase transitions using the magnetocaloric effect.

The ideal magnetocaloric material would lay at the borderline of a first-order and a second-order phase transition. Hence, it is crucial to unambiguously determine the order of phase transitions for both applied magnetocaloric research as well as the characterization of other phase change materials. Although Ehrenfest provided a conceptually simple definition of the order of a phase transition, the known techniques for its determination based on magnetic measurements either provide erroneous results for specific cases or require extensive data analysis that depends on subjective appreciations of qualitative features of the data.

Mastering hysteresis in magnetocaloric materials.

Hysteresis is more than just an interesting oddity that occurs in materials with a first-order transition. It is a real obstacle on the path from existing laboratory-scale prototypes of magnetic refrigerators towards commercialization of this potentially disruptive cooling technology. Indeed, the reversibility of the magnetocaloric effect, being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and, therefore, it is necessary to understand the mechanisms causing hysteresis and to find solutions to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices.

Towards high-performance permanent magnets without rare earths.

Achieving a very strong magnetic anisotropy in a 3d material is a difficult, but not an impossible task. It is difficult because there is no general recipe (necessary condition) for a strong anisotropy in a band magnet. Several strategies can be pursued in this situation.

Giant magnetocaloric effect driven by structural transitions.

Magnetic cooling could be a radically different energy solution substituting conventional vapour compression refrigeration in the future. For the largest cooling effects of most potential refrigerants we need to fully exploit the different degrees of freedom such as magnetism and crystal structure. We report now for Heusler-type Ni–Mn–In–(Co) magnetic shape-memory alloys, the adiabatic temperature change ΔT(ad) = −3.

Giant rotating magnetocaloric effect in the region of spin-reorientation transition in the NdCo₅ single crystal.

We have investigated the anisotropy of the magnetocaloric effect in a NdCo₅ single crystal in a wide range of temperatures, including the spin-reorientation temperature region. In the field μ(0)H =1.3 T in the spin-reorientation region 250-310 K, we discovered a giant rotating magnetocaloric effect of ~ 1.