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The concept of topology has dramatically expanded the landscape of magnetism, leading to the discovery of numerous magnetic textures with intriguing topological properties. A magnetic skyrmion is an emergent topological magnetic texture with a string-like structure in three dimensions and a disk-like structure in one and two dimensions. Skyrmions in zero dimensions have remained elusive owing to challenges from many competing orders. Herein, by integrating electron holography and micromagnetic simulations, we uncover the real-space magnetic configurations of a novel skyrmionic vortex structure confined in a B20-type FeGe tetrahedral nanoparticle. This texture shows excellent robustness against temperature without applying a magnetic field; an isolated skyrmionic vortex forms at the ground state. These findings shed light on zero-dimensional geometrical confinement as a route to engineer and manipulate individual skyrmionic metastructures.

Since the introduction of biomaterials, infection has been a serious problem in clinical operations. Although several studies have introduced hybrid materials of calcium phosphate and Ag0 nanoparticles (NPs) that exhibit antibacterial activity, released Ag+ ions and Ag0 NPs are highly cytotoxic and the materials require complex fabrication techniques such as laser irradiation. In this study, we introduce a simple one-pot synthesis method based on crystal-engineering techniques to prepare Ag+-substituted octacalcium phosphate (OCP-Ag) powder that simultaneously exhibits antibacterial activity, little change in color, and low cytotoxicity, thereby overcoming the shortcomings of calcium phosphate as a biomaterial. We used AgNO3-containing (NH4)2HPO4 aqueous solutions as reaction solutions in which Ag+ forms soluble complex [Ag(NH3)2]+ ions that are stable at Ag+ concentrations less than ∼30 mmol/L. Hydrolysis of soluble calcium phosphate in this solution led to pure OCP-Ag when the Ag+ concentration was less than ∼30 mmol/L. Crystallographic analysis showed that Ag+ substituted at the P5 PO4-conjugated sites and was uniformly distributed. When the concentration of Ag+ in the reaction solution was varied, the Ag+ content of the OCP-Ag could be controlled. The obtained OCP-Ag exhibited little color change or Ag+ release when immersed in various media; however, it exhibited contact antibacterial ability toward resident oral bacteria. The prepared OCP-Ag showed no substantial cytotoxicity toward undifferentiated and differentiated MC3T3-E1 cells in assays. Notably, when the Ag+ content in OCP-Ag was optimized (Ag: ∼1 at %), it simultaneously exhibited contact antibacterial ability, little color change, and low cytotoxicity.

We performed compression tests at low temperatures under various strain rates for Ni-rich Ti-Ni alloys. Thermal activation theory for the habit plane motion with a thermal activation energy of ~0.5 eV successfully reproduced both the examined temperature and strain-rate dependences of the transformation stress hysteresis. This indicates that the thermal activation process of the habit plane motion underlies the dramatic increase in the transformation hysteresis at lower temperatures in this system. These findings are critical to elucidate the physical impact of the thermal activation nature on the transformation hysteresis and to consider the feasibility of low-temperature operation of shape-memory functions.

All-solid-state lithium-ion batteries (ASSLIBs) with oxide-based solid electrolytes are a promising candidate for next generation of rechargeable batteries, due to their reliability and high-energy density. The formation of well-defined electrode/solid electrolyte interfaces with an excellent ionic conductivity by co-sintering is one of the key challenges to develop oxide-based ASSLIBs.1 Electrode materials and solid electrolytes often react with each other to form a resistive substance at their interface during co-sintering.2-4 Thus, optimization of the co-sintering conditions is important to control the interfacial structure which governs the ionic conductivity. However, the effect of the interfacial structure on the ionic conductivity remains unclear. In this study, we co-sintered the composites of LiCoPO4 (LCP) electrode material and Li1.3Al0.3Ti1.7(PO4)3 (LATP) oxide-based solid electrolyte and investigated the interfacial structure by using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and scanning transmission electron microscopy combined with electron energy loss spectroscopy and an energy-dispersive X-ray spectroscopy (STEM-EELS/EDX). Figure 1(a) shows the XRD patterns of the LCP/LATP composites before and after sintering at 800°C. The diffraction patterns are almost identical to each other and all the diffraction peaks are attributed to the LCP and LATP with an exception of AlPO4 impurity. However, the Co K-edge XANES is slightly changed after sintering as shown in Figure 1(b). These results suggest that a small amount of LCP and LATP react with each other. Figure 1(c) shows a typical STEM image of the LCP/LATP composites after sintering at 800°C. According to EDX analysis, light and dark gray domains correspond to LCP and LATP, respectively. Apart from LCP and LATP, there are two types of LCP/LATP interfaces: interface A and B. Line profile STEM-EELS/EDX analysis revealed that LCP and LATP directly bound to each other at the interface A. On the other hand, a thermally reacted thin layer, possibly cobalt oxide (CoO) and/or cobalt phosphide (Co2P), is formed at interface B. The effect of such thermally reacted interlayer on the ionic conductivity will be discussed in detail. References: R. Chen, Q. Li, X. Yu, L. Chen and H. Li, Chemical Reviews, 2020, 120, 6820-6877. M. Gellert, E. Dashjav, D. Grüner, Q. Ma and F. Tietz, Ionics, 2017, 24, 1001-1006. C.-Y. Yu, J. Choi, V. Anandan and J.-H. Kim, The Journal of Physical Chemistry C, 2020, 124, 14963-14971. L. Miara, A. Windmuller, C. L. Tsai, W. D. Richards, Q. Ma, S. Uhlenbruck, O. Guillon and G. Ceder, ACS Applied Materials and Interfaces, 2016, 8, 26842-26850. Figure 1

Magnetic skyrmions are topological spin textures that have shown promise for future nonvolatile memory devices. Herein, we report on the stability of magnetic skyrmions in alloyed cubic B20 Fe1–xCo...

Fraunhofer electron holography using an asymmetric double slit was realized. A Fraunhofer diffraction wave from the wider slit was recorded in a hologram interfered with a plane wave from the narrower slit. The phase distribution of the diffraction wave was succeeded in reconstructing as a step pattern of π radians., Electron holography in Fraunhofer region was realized by using an asymmetric double slit. A Fraunhofer diffraction wave from a wider slit worked as an objective wave interfered with a plane wave from a narrower slit as a reference wave under the pre-Fraunhofer condition and recorded as a hologram. Here, the pre-Fraunhofer condition means that the following conditions are simultaneously satisfied: single-slit observations are performed under the Fraunhofer condition and the double-slit observations are performed under the Fresnel condition. Amplitude and phase distributions of the Fraunhofer diffraction wave were reconstructed from the hologram by the Fourier transform reconstruction method. The reconstructed amplitude and phase images corresponded to Fraunhofer diffraction patterns; in particular, the phase steps of π at each band pattern in the phase image were confirmed. We hope that the developed Fraunhofer electron holography can be extended to a direct phase detection method in the reciprocal space.

Phase equilibria among the η-Fe2Al5 phase and its higher-ordered phases with the η framework structure were determined experimentally. The solubility range of the η phase at elevated temperature does not differ remarkably from that in previous studies, but this phase is found to undergo complicated phase transformations upon cooling. Four phases are present, namely η’, η”, η”’ and ηm, with higher-order atomic orderings in the c-axis chain sites of the orthorhombic crystal structure of the parent η phase. The η” and η”’ phases form on the Al-poor and Al-rich sides, respectively, in equilibrium with the ζ-FeAl2 phase below ~415°C and θ-Fe4Al13 phase below ~405°C. The η’ and ηm phases become stable below 312°C and 343°C with the peritectoid reactions η’ → ηm + η”’ and ηm → η + η”, respectively. The η phase is not stable below 331°C with the eutectoid reaction of ηm + η”’ → η. On the basis of these findings, we unraveled the phase equilibria among the η-Fe2Al5 phase and its higher-ordered phases with the η framework structure., Graphical abstract

Silica is not only a biocompatible trace element but also an essential element for bone formation and metabolism. Therefore, it is often doped into bioceramics such as calcium phosphate and calcium carbonate for enhancing biomaterial ability. Heretofore, organic silica materials are employed as silica sources, but the residual organic matter is a significant drawback in biomaterial applications. Therefore, in this study, we introduce a one-pot inorganic synthesis method for the formation of silica-doped octacalcium phosphate (OCP) using Na2SiO3 as the silica source. Silica was intercalated into the OCP unit lattice, replacing its hydrous layer structure, and then a layer-by-layer structure of apatite and silica was formed. Furthermore, by immersing the fabricated silica-doped OCP into suitable solutions, both silica-doped hydroxyapatite and carbonate apatite were fabricated through a one-step inorganic processes.

Ferromagnetic exchange stiffness is a key to describe the robustness of a ferromagnetic interaction. Because the experimental determination of the exchange stiffness constant $A$ continues to be elusive, especially at elevated temperatures, micromagnetic insights on the impact of thermal fluctuations on the ferromagnetic spin order have remained less tractable. In this study, the temperature dependence of $A$ is experimentally determined for a $\mathrm{N}{\mathrm{i}}_{2}\mathrm{M}{\mathrm{n}}_{0.8}\mathrm{I}{\mathrm{n}}_{1.2}$ single crystal by measuring the ${180}^{\ensuremath{\circ}}$ domain-wall width using off-axis electron holography and magnetocrystalline anisotropy. The theoretically expected power-law scaling with magnetization for $A$ is shown to be applicable only in the low-temperature region (approximately half of the Curie temperature), and $A$ starts to follow the power law with a significantly larger scaling exponent in the higher-temperature region. The decremental trends in the domain-wall width and the exchange length at elevated temperature seem to be attributed to this temperature dependence of $A$.

Electron holography is used to visualize the electromagnetic field inside and outside a sample with high resolution. However, for analysis of nanocrystalline materials, difficulties related to electron diffraction are expected to arise due to the random orientation of the nanocrystallites. Here we present a procedure to extract magnetic field information from holograms and reduce the effect of electron diffraction by paying attention to the contrast of bright-field images. As a demonstration, the difference in the intensity of the magnetic flux between the Fe-Si-B-P-Cu amorphous matrix and Fe-rich body-centered cubic (bcc) nanocrystallites is detected with this procedure.

The magnetism of grain boundary (GB) phases in the Nd-rich Ga-doped Nd-Fe-B sintered magnet that shows unusually high improvement in coercivity by post-sinter optimal heat treatment was studied using electron holography. Transmission electron microscopy observations identified three types of GB phases with distinct structures, i.e., Ia 3 ¯ -type, amorphous-type, and Nd6(Fe,Ga)14-type. The magnetic flux densities of these three GB phases were systematically analyzed by measuring the phase shifts of incident electrons, and all of these GB phases are concluded to be nonferromagnetic. Unlike the standard commercial sintered magnets, this study has shown that the Nd2Fe14B grains in the optimally heat treated Nd-rich Ga-doped sintered magnet are exchange decoupled by the formation of the three types of nonferromagnetic GB phases. The observations provide useful information for GB engineering of Nd-Fe-B sintered magnets, which is key for further improvements of their coercivities without relying on grain size refinement.

To utilize magnetic skyrmions, nanoscale vortex-like magnetic structures, experimental elucidation of their dynamics against current application in various circumstances such as in confined structure and mixture of different magnetic phases is indispensable. Here, we investigate the current-induced dynamics of the coexistence state of magnetic skyrmions and helical magnetic structure in a thin plate of B20-type helimagnet FeGe in terms of in situ real-space observation using Lorentz transmission electron microscopy. Current pulses with various heights and widths were applied, and the change of the magnetic domain distribution was analyzed using a machine-learning technique. The observed average driving direction of the two-magnetic-state domain boundary is opposite to the applied electric current, indicating ferromagnetic s-d exchange coupling in the spin-transfer torque mechanism. The evaluated driving distance tends to increase with increasing the pulse duration time, current density (>1 × 109 A/m2), an...

Advanced electron microscopy technologies have made it possible to perform precise double-slit interference experiments. We used a 1.2-MV field emission electron microscope providing coherent electron waves and a direct detection camera system enabling single-electron detections at a sub-second exposure time. We developed a method to perform the interference experiment by using an asymmetric double-slit fabricated by a focused ion beam instrument and by operating the microscope under a “pre-Fraunhofer” condition, different from the Fraunhofer condition of conventional double-slit experiments. Here, pre-Fraunhofer condition means that each single-slit observation was performed under the Fraunhofer condition, while the double-slit observations were performed under the Fresnel condition. The interference experiments with each single slit and with the asymmetric double slit were carried out under two different electron dose conditions: high-dose for calculation of electron probability distribution and low-dose for each single electron distribution. Finally, we exemplified the distribution of single electrons by color-coding according to the above three types of experiments as a composite image.

Many issues concerning the transformation behaviors in the Ni-rich Ti-Ni system remain unresolved, such as the isothermal nature of the B19′-martensitic and R-phase transformations and the precursor phenomena in the B2-parent phase. To clarify the origins of these behaviors, we investigated the transformation latent heat, specific heat, and superelastic behaviors of several Ni-rich Ti-Ni alloys in terms of the entropy change. An anomalous, very wide hump in the specific heat was detected for the B2-parent phase, which can likely be attributed to the precursor phenomenon in the B2-parent phase. In the critical region where the anomalous hump intersects the B19′-martensitic transformation, some evidences of the R-phase transformation were observed, such as a tweed-like microstructure and a specific heat peak with first-order-transformation characteristics. These findings suggest a strong relationship between the R phase and the precursor state in the B2-parent phase.

The microstructure in a Mn 55.2 Ga 19.0 Cu 25.8 alloy that exhibits both martensitic and diffusional phase transformations was examined by electron microscopy, and the potential effects of these transformations on the large coercivity (~ 2 T) were discussed. The alloy showed a cellular microstructure, composed of a cuboidal matrix enveloped by a boundary phase, and superposed on well-defined martensite plates. Since the boundary phase is enriched by the non-magnetic element Cu, it may serve as magnetic isolation for the matrix region with a face centered tetragonal lattice formed by the martensitic transformation, or offer potential pinning sites for magnetic domain walls.

The atomic arrangement and microsegregation in the vicinity of thermally induced antiphase boundaries in a Ni 50 Mn 20 In 30 Heusler alloy are investigated through multislice simulations, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction pattern Rietveld analysis, energy-dispersive X-ray spectroscopy, and modified Bragg–Williams–Gorsky calculations. Intensity analysis of atomic-resolution HAADF-STEM images revealed that a 180° geometrical phase shift occurred across the antiphase boundaries, accompanied by a decay in the degree of atomic order and an enrichment of In. Energy-dispersive (X-ray) spectroscopy analysis revealed an In enrichment as high as 2.7 at.% at the center of the antiphase boundaries, comparable to that (1.0–1.8 at.%) suggested by the parallel tangent law for the Gibbs energy curves of the L 2 1 and B 2 phases using the modified Bragg–Williams–Gorsky calculation. This suggests that microsegregation occurs at the antiphase boundaries and can be understood basically within the framework of the local thermodynamic equilibrium.

Magnetic skyrmions are topological spin textures that have shown promise for future nonvolatile memory devices. Herein, we report on the stability of magnetic skyrmions in alloyed cubic B20 Fe

This work demonstrates a new technique to derive the magnetic exchange stiffness, A, using a measurement of the Bloch-type 180° domain wall width. Because this method is static and free from external fields, it enables the derivation of A over almost the entire temperature range up to near the Curie temperature, T C, which is difficult for existing techniques. With this technique, the temperature dependence of A for iron and nickel was assessed. Furthermore, after a systematic comparison of existing scaling functions, a promising scaling of A was demonstrated.

High strength has always been pursued in binary Al–Mg and 5xxx series Al alloys. However, these alloys usually provide medium strength due to lack of multiple strengthening methods. Here, this study reports on multiple strengthening effects existing in a binary ultrafine-grained (UFG) Al-7.5at.%Mg alloy prepared by mechanical alloying and hot extrusion. Different strengthening mechanisms, in particular, dispersoid strengthening and stacking fault strengthening, are analyzed and evaluated in terms of their respective contribution to the 511 MPa yield strength of the alloy. The strengthening analysis proves that the concurrent generation of nanoscale dispersoids and stacking faults (SFs) can be used as a new microstructural design in developing novel Al–Mg-based alloys with higher strength and enhanced ductility.

Hole free phase plate (HFPP) imaging provides a convenient way to enhance phase contrast in a TEM [1]. HFPP imaging applications range from biology to magnetic materials, but quantitative image interpretation has not been possible so far [1,2,3]. Here we present a detailed study of HFPP images of a FIB-fabricated phase grating that allows us to study how the HFPP modifies the phase relationship between direct and diffracted beams., M & M 2018: Microscopy & Microanalysis 2018 Meeting, August 5-9, Baltimore, Maryland

For Ni-rich Ti–Ni alloys, physical properties such as specific heat and electric resistance were systematically investigated. The B2/B19′ martensitic transformation temperatures ranging from 180 to 373 K were determined for Ni contents of 49.98–51.09 %, and a sudden disappearance of martensitic transformation was confirmed for Ni contents greater than 51.23 %, which has also been well reported in the literatures. The entropy change was also evaluated from differential scanning calorimeter measurement, and it was clarified that the entropy change plotted to T 0 temperature shows an S-shaped curve, starting to drastically decrease at about 300 K. Thermodynamic approaches were then carried out attempting to determine the reason for the disappearance of transformation. The entropy change estimated from direct measurements of specific heats for 51.75 Ni (B2) and 50.92 Ni (B19′) was found to be more consistent with the experimental data, rather than the calculated curve based on the Debye model for vibration specific heat. It was proposed that the equilibrium between the parent and martensite phases obeys the Clausius–Clapeyron relationship in the composition–temperature system. Using the constructed composition–temperature diagram, the disappearance of martensitic transformation in the Ti–Ni system can be well understood as being due to the drastic increase of hysteresis at low temperature.

Nanometre-scale magnetic field distributions in materials such as those at oxide interfaces, in thin layers of spintronics devices, and at boundaries in magnets have become important research targets in materials science and applied physics. Electron holography has advantages in nanometric magnetic field observations, and the realization of aberration correctors has improved its spatial resolution. Here we show the subnanometre magnetic field observations inside a sample at 0.67-nm resolution achieved by an aberration-corrected 1.2-MV holography electron microscope with a pulse magnetization system. A magnetization reduction due to intermixing in a CoFeB/Ta multilayer is analyzed by observing magnetic field and electrostatic potential distributions simultaneously. Our results demonstrate that high-voltage electron holography can be widely applied to pin-point magnetization analysis with structural and composition information in physics, chemistry, and materials science.

Charging of a SiO2 particle induced by electron illumination was investigated by changing the illuminated area of the particle and its support film through control of the position of the mask plate inserted in a transmission electron microscope illumination system. The electric fields around the charged SiO2 particle were analyzed using electron holography. The amount of charge was evaluated quantitatively by comparing the reconstructed phase images with the simulated phase images. When the support film was not covered against the incident electron beam, secondary electrons emitted from the conductive support film were attracted to the charged particle, resulting in particle discharge. In contrast, when the support film was completely covered, secondary electrons were not emitted from the film, so that the particle remained positively charged.

For polycrystalline Ti-51.8Ni (at.%) specimens annealed at 473 and 943 K, the microstructures at room temperature were observed by transmission electron microscopy and the stress-induced transformation behaviors at low temperatures were investigated by compressive test. The precipitation of Ti3Ni4 was confirmed in the both annealed specimens, where the precipitates at 943 K had a lenticular shape in micrometer size, and those at 473 K seemed to be clusters in nanometer size. Superelasticity with almost complete shape recovery was detected at temperatures below 200 K for all the annealed specimens. In comparison to the as-homogenized specimen, although the temperature dependence on the stress hysteresis only slightly changed in each annealing condition, the equilibrium stresses in the specimen annealed at 473 and 943 K apparently increased and decreased, respectively.

The microstructure and magnetic properties of cubic- and tetragonal-La(Fe 1− x Si x ) 13 compounds were systematically investigated. Obtained XRD patterns revealed that a semi-ordered tetragonal-La(Fe 1− x Si x ) 13 phase (termed the τ 2 ′ phase in this work) appears due to quenching from the Si-rich concentration range of the cubic-La(Fe 1− x Si x ) 13 ( τ 1 ) single phase region, whose tetragonality, namely the ratio of short and long axes, is lower than that of the known tetragonal Ce 2 Ni 17 Si 9 -type La(Fe 1− x Si x ) 13 ( τ 2 ) phase. It was also found that the τ 2 ′ phase has not only periodically configurated twin boundaries as a microstructural feature but also unique concentration dependence of magnetic properties, i.e., Curie temperature and spontaneous magnetization drastically decrease with increasing Si concentration.

Understanding magnetic degradation in interface regions is important for materials science and technologies. An essential problem is the significant depression of ferromagnetism observed in an antiphase boundary (APB), which induces material functionalities/anomalies such as pinning of magnetic domain walls, etc. However, magnetization analysis on APB remains challenging due to the difficulty of collecting magnetic information from such a nanometer-scale interface region. We here use electron holography in order to obtain magnetic information from the narrow APB region in a Heusler alloy Ni 50 Mn 25 Al 12.5 Ga 12.5 . The magnetic flux density in APB (∼5.6 nm in breadth) was determined at 0.04 T, and was only 12% of the value for the APB-free matrix. This magnetic depression could be explained by atomic disordering in the APB region, ascertained by high-resolution atomic-column imaging. It is expected that our microscopic approach can be used to understand anomalous interface magnetism observed in various magnetic compounds and/or spin devices.

The Effect of Microalloying Elements and Compounds, such as Be, B, C, P, S, Ti, V, Cu, Zn, in, BN, VN, Mn3N, LaN, MnS and Ti4C2S2, Ranging in Amount from 0.005 to 0.2 at.%, on the α-Fe + FeLaSi Two-Phase Microstructure of a La(Fe0.89Si0.11)13 as-Melted Specimen Was Investigated. The Addition of Mn3N Was Found to Contribute to α-Fe Grain Refinement to a Certain Extent, but to Harm the Uniform Growth of the τ1 Phase in the Stage of Subsequent Annealing.

The isothermal section of the phase diagrams at 1173, 1373 and 1573 K and vertical section phase diagrams in La(Fe 1− x Si x ) 13 (0.07≦ x ≦0.40) and Fe 95 Si 5 –La 33.3 Fe 33.3 Si 33.3 (at. %) sections were experimentally determined mainly using X-ray diffractometer (XRD), electron probe microanalyzer (EPMA) and differential scanning calorimeter (DSC). The obtained phase diagrams showed that six ternary intermetallic compounds (IMCs), including the cubic NaZn 13 -type La(Fe 1− x Si x ) 13 phase (τ 1 ) and the tetragonal Ce 2 Ni 17 Si 9 -type La(Fe 1− x Si x ) 13 phase (τ 2 ), exist at temperatures over 1173 K at least and that most of the ternary phases, except the τ 1 and τ 2 phases, have only small solubility ranges from their stoichiometric compositions. It was also found that the τ 1 and τ 2 phases form by the following peritectic reactions: αFe (or L FeSi ) + L La + LaFe 2 Si 2 → τ 1 at about 1665 K and τ 1 + L FeSi + LaFe 2 Si 2 → τ 2 at about 1623 K, respectively.

Phase transformations in the β (B2) phase of Co–21 and –23 at.% Al alloys were examined using transmission electron microscopy, energy dispersive X-ray spectroscopy and differential scanning calorimetry. The microstructures obtained from as-quenched specimens were found to be strongly affected by the quenching condition. While relatively thick sheet-specimens with a lower quenching rate showed bainitic plate precipitates with a fcc structure, a martensite-like structure was observed by optical microscopy in relatively thin specimens with a higher quenching rate. Regardless of the quenching condition, a spinodal-like microstructure composed of A2 and B2 phases was also detected and the A2 phase changed to a metastable hcp phase during further aging.

Shape-memory alloys suitable for low-temperature environments are crucially lacking despite their potential applications for aerospace engineering, superconducting technologies, and liquefied-gas-storage technologies. Even for benchmark shape-memory alloys such as Ti–Ni and Ni-based Heusler alloys, superelasticity becomes appreciably difficult to achieve upon cooling because of a drastic increase in stress hysteresis. Here, we report a superelastic strain of more than 7% for a Cu–Al–Mn shape-memory alloy down to 4.2 K with stress hysteresis as small as that at ambient temperature. Furthermore, the transformation entropy change remains as large as that at ambient temperature down to ~50 K. Consequently, an excellent elastocaloric cooling property is simultaneously obtained even at cryogenic temperatures, at which existing shape-memory alloys lose this property because of decreased entropy change and increased stress hysteresis. The developed cryogenic superelastic alloy shows excellent potential as a new class of material combining superelastic properties with sufficiently small dissipated energy and persistent elastocaloric cooling ability even in cryogenic environments. An alloy that recreates its shape even after being warped at cryogenic temperatures can benefit advanced cooling technology. Certain copper-based composites are promising for an environmentally friendly refrigeration method, called elastocaloric cooling, which uses shape-memory effects to extract heat from a system and hence lower its temperature. Kodai Niitsu and colleagues from Tohoku University in Japan now report a means to expand the working temperatures of elastocaloric alloys to near absolute-zero temperatures, which are normally too brittle for metals. By melting and hot-rolling a mix of copper, aluminum and manganese atoms into thin plates, the researchers produced a material with sufficient compatibility between the parent and deformed phases to produce a 7% recoverable transformation strain at 4.2 degrees kelvin. This shape shifting at extremely low temperatures has potential for cooling superconductors and maintaining liquefied gases. Superelastic alloys suitable for low-temperature environments are crucially lacking. Here, we report an excellent superelastic (rubber-like) strain of more than 7% at 4.2 K using a Cu–Al–Mn shape-memory alloy. This alloy also possesses a small stress hysteresis of less than 30 MPa down to 4.2 K, resulting in particularly persistent elastocaloric cooling ability in the low-temperature region. The present Cu–Al–Mn alloy will have significant engineering impact, especially in the fields of aerospace engineering, superconducting technologies, and liquefied-gas-storage technologies, as a new class of materials combining superelastic properties and persistent elastocaloric cooling properties even at cryogenic environments.

Oxidation resistance and tribological properties of SHS-produced chromium sulfide have been explored. The material was oxidized up to 5 to 7 μm thick from its surface upon heat treatment at 1000°C for a short time. It also exhibited a unique compositional change in sulfur and chromium at the interface between matrix and oxide layer formed during heat treatment. Meanwhile, the synthesized material showed the coefficient of kinetic friction of below 0.18, which is an acceptable value for a solid lubricant. Although the friction coefficient of CrS was initially low, it was found to grow upon high-temperature oxidation of the CrS surface. This fluctuation in the tribological property seems to depend on both the crystal structures of chromium sulfide and chromium oxide and of the interface between the oxide and matrix.