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Permanent magnets draw their properties from a complex interplay, across multiple length scales, of the composition and distribution of their constituting phases, that act as building blocks, each with their associated intrinsic properties 1. Gaining a fundamental understanding of these interactions is hence key to decipher the origins of their magnetic performance2 and facilitate the engineering of better-performing magnets, through unlocking the design of the “perfect defects” for ultimate pinning of magnetic domains3. Here, we deployed advanced multiscale microscopy and microanalysis on a bulk Sm2(CoFeCuZr)17 pinning-type high-performance magnet with outstanding thermal and chemical stability 4. Making use of regions with different chemical compositions, we showcase how both a change in the composition and distribution of copper, along with the atomic arrangements enforce the pinning of magnetic domains, as imaged by nanoscale magnetic induction mapping. Micromagnetic simulations bridge the scales to provide an understanding of how these peculiarities of micro- and nanostructure change the hard magnetic behaviour of Sm2(CoFeCuZr)17 magnets. Unveiling the origins of the reduced coercivity allows us to propose an atomic-scale defect and chemistry manipulation strategy to define ways toward future hard magnets.

We have investigated thermal conductivities (κ) of polycrystalline Eu1–xAxTiO3 (A = Ca, Sr, Ba, 0 ≤ x ≤ 0.8) bulk materials in the temperature range of ∼ 2 K < T < 1173 K. The EuTiO3 demonstrates anomalous glass-like κ(T) behavior at low temperatures. Partial substitutions with Sr2+ and Ba2+ do not cause a significant change in the κ(T) behavior, while a κ(T) peak, which looks like a manifestation of a typical crystalline solid, appears only in the Ca-substituted samples with an orthorhombic structure when x ≥ 0.4. After excluding the magnetic effects on κ and discussing the possible phonon scattering mechanisms in depth, together with heat capacity Cp measurements and high-resolution X-Ray diffraction characterization, we find that the unusual low κ at low temperatures is attributed to resonant scattering induced by the intrinsic disordered local structure and lattice instability in EuTiO3. Due to the different lattice dynamics of ATiO3, the lattice structure of Eu1–xCaxTiO3 can be regarded as formed by a part-soft (from EuTiO3) part-rigid (from CaTiO3) sublattice. The anomalous κ(T) behavior of Eu1–xCaxTiO3 results from the combined effect of phonon transport between the normal phononic heat transport in the rigid sublattice and the strong damping of heat conduction in the soft sublattice. published

The development of new powder feedstocks using nanoparticles (NPs) has the potential to enhance the functionality of as-built parts and overcome the limitations of current additive manufacturing (AM) techniques. This study investigated the impact of magnet microparticle feedstock modification by NPs on the microstructure and functionality of Nd-Fe-B-based permanent magnets made by suction casting. This casting method is known to at least partially mimic the melting and fast solidification steps inherent to metal powder-based AM techniques such as Laser Powder Bed Fusion. Two types of NPs, Ag, and ZrB2, were used, and their effects on grain size distribution and dendritic structure were evaluated. Ag NPs resulted in smaller, more uniform grain sizes and increased functionality, but only for loadings > 0.5 monolayers. ZrB2 resulted in uniformly distributed grain sizes at much lower mass loadings, with even more compact dendritic arms. The results show that feedstock powder surface modification with low melting point metal NPs can improve the microstructure and magnetic properties of permanent magnets produced by AM and highlight the potential of using NPs to develop new powder feedstocks for AM. With this, it provides insights for future research on optimizing materials for AM processes.

The development of new powder feedstocks using nanoparticles (NPs) has the potential to enhance the functionality of as-built parts and overcome the limitations of current additive manufacturing (AM) techniques. This study investigated the impact of NP feedstock modification on the microstructure and functionality of MQP-S after suction casting. Two types of NPs, Ag, and ZrB2, were used, and their effects on grain size distribution and dendritic structure were evaluated. Ag NPs resulted in smaller, more uniform grain sizes and increased functionality, but only for loadings > 0.5 monolayers. ZrB2 resulted in uniformly distributed grain sizes at much lower mass loadings, with even more compact dendritic arms. However, no effect on functionality was observed. The results show that feedstock modification with low melting point metal NPs can improve the microstructure and magnetic properties of permanent magnets produced by AM and highlight the potential of using NPs to develop new powder feedstocks for AM. With this, it provides insights for future research on optimizing AM processes.

Powder bed fusion of metals using a laser beam (PBF-LB/M) is an established additive manufacturing (AM) method that can be used to fabricate geometrically complex NdFe-B magnets. However, the magnetic properties of Nd-Fe-B magnets manufactured by PBF-LB/M are typically inferior to conventionally produced magnets. To overcome this drawback, we modified the surface of the permanent magnet feedstock powder with 1 wt.% surfactant-free Ag nanoparticles (NPs) supporting the formation of relevant phases required for permanent magnetic performance to achieve a suitable micro- and nanostructure after AM. Our study is accompanied by finite element simulations, revealing the impact and dependency of process parameters during PBF-LB/M: a wide temperature field with a high-gradient profile in the front and on the bottom of an overheated region, implying a vast local heating/cooling rate and in-process high thermal stress. We found experimentally that the as-built part density can be affected by both the laser power and scan speed, causing a reduction in density as both parameters increase. The functionality and microstructural properties are also investigated via VSM, HR-SEM, EDX, EBSD, and exemplarily with HR-TEM-EDX and APT. Our study found that modifying MQP-S with Ag NPs increases the coercivity by approximately 20%, which we correlate to a decreased grain size. Additionally, we identified three distinct phases in the modified and unmodified samples, where Ag is primarily found in the intergranular and Nd-rich phases of the as-built parts. Overall, the study's findings contribute to the understanding of the factors that affect the quality and magnetic properties of Nd-Fe-B magnets fabricated through PBF-LB/M and provide valuable insights for further research in this area.

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

Twin defects deteriorate the magnetic properties in conventionally-fabricated L10-type and RETM12-type permanent magnets. Herein, we propose a strategy to suppress twins’ formation by decreasing the grain and/or particle sizes below a critical size Dt~300 nm, based on the stress relief mechanism resulting from the balance of volume/surface energy. Twin-free monocrystalline nanoparticles smaller than Dt were synthesized using a comprehensive spectrum of methods for preparing field-aligned polymer bonded magnet with high texture. We propose here a roadmap for selecting the best route for manufacturing high-performance rare-earth free MnAl magnets, depending on their grain/particle size. The dependence of coercivity on grain/particle sizes shows that optimal coercivity can be reached within the range of 50-200 nm, meanwhile, twin-free microstructure is realized which allows ultrahigh remanence by field induced texture. The results reported here can be applied to other twin-containing permanent magnet compounds, offering opportunities to drastically increase their texture and maximal energy products.

We are witnessing a great transition towards a society powered by renewable energies to meet the ever-stringent climate target. Hydrogen, as an energy carrier, will play a key role in building a climate-neutral society. Although liquid hydrogen is essential for hydrogen storage and transportation, liquefying hydrogen is costly with the conventional methods based on Joule-Thomas effect. As an emerging technology which is potentially more efficient, magnetocaloric hydrogen liquefaction can be a “game-changer”. In this work, we have investigated the rare-earth-based Laves phases RAl and RNi2 for magnetocaloric hydrogen liquefaction. We have noticed an unaddressed feature that the magnetocaloric effect of second-order magnetocaloric materials can become “giant” near the hydrogen boiling point. This feature indicates strong correlations, down to the boiling point of hydrogen, among the three important quantities of the magnetocaloric effect: the maximum magnetic entropy change ΔSmaxm, the maximum adiabatic temperature change ΔTmaxad , and the Curie temperature TC. Via a comprehensive literature review, we interpret the correlations for a rare-earth intermetallic series as two trends: (1) ΔSmaxm increases with decreasing TC; (2) ΔTmaxad decreases near room temperature with decreasing TC but increases at cryogenic temperatures. Moreover, we have developed a mean-field approach to describe these two trends theoretically. The dependence of ΔSmaxm and ΔTmaxad on TC revealed in this work helps researchers quickly anticipate the magnetocaloric performance of rare-earth-based compounds, guiding material design and accelerating the discoveries of magnetocaloric materials for hydrogen liquefaction.

Permanent magnets based on neodymium-iron-boron (Nd-Fe-B) alloys provide the highest performance and energy density, finding usage in many high-tech applications. Their magnetic performance relies on the intrinsic properties of the hard-magnetic Nd$_2$Fe$_{14}$B phase combined with control over the microstructure during production. In this study, a novel magnetic hardening mechanism is described in such materials based on a solid-state phase transformation. Using modified Nd-Fe-B alloys of the type Nd$_{16}$Fe$_{bal-x-y-z}$Co$_x$Mo$_y$Cu$_z$B$_7$ for the first time it is revealed how the microstructural transformation from the metastable Nd$_2$Fe$_{17}$B$_x$ phase to the hard-magnetic Nd$_2$Fe$_{14}$B phase can be thermally controlled, leading to an astonishing increase in coercivity from ≈200 kAm$^{−1}$ to almost 700 kAm$^{−1}$. Furthermore, after thermally treating a quenched sample of Nd$_{16}$Fe$_{56}$Co$_{20}$Mo$_2$Cu$_2$B$_7$, the presence of Mo leads to the formation of fine FeMo$_2$B$_2$ precipitates, in the range from micrometers down to a few nanometers. These precipitates are responsible for the refinement of the Nd$_2$Fe$_{14}$B grains and so for the high coercivity. This mechanism can be incorporated into existing manufacturing processes and can prove to be applicable to novel fabrication routes for Nd-Fe-B magnets, such as additive manufacturing