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We investigate the magnetic, thermal, and magnetocaloric properties of the intermetallic HoAl$_{3}$ compounds with two different crystal structures. The room-temperature equilibrium trigonal phase HoAl$_{3}$ undergoes an antiferromagnetic (AFM) transition at the Neel temperature $T^{\rm tri}_{\rm N} =$ 9.8 K. The AFM ordering of the compound is strong against the magnetic field, so that inverse magnetocaloric effect (MCE) is found even under a magnetic field change of 0-50 kOe. The high-pressure cubic phase HoAl3, prepared by a rapid-solidification process, is antiferromagnetically ordered below $T^{\rm cub}_{\rm N} =$ 15 K. Magnetic and specific heat measurements reveal that this long-range AFM state becomes unstable as the temperature drops and then it is replaced by a magnetic glassy state below a spin freezing temperature $T_{\rm f} =$ 11 K. The successive changes in magnetic state result in complicated temperature and field dependence of the MCE at low temperatures., Journal of Magnetism and Magnetic Materials Accepted

A growing number of papers are published in the area of superconducting materials science. However, novel text and data mining (TDM) processes are still needed to efficiently access and exploit this accumulated knowledge, paving the way towards data-driven materials design. Herein, we present SuperMat (Superconductor Materials), an annotated corpus of linked data derived from scientific publications on superconductors, which comprises 142 articles, 16052 entities, and 1398 links that are characterised into six categories: the names, classes, and properties of materials; links to their respective superconducting critical temperature (Tc); and parametric conditions such as applied pressure or measurement methods. The construction of SuperMat resulted from a fruitful collaboration between computer scientists and material scientists, and its high quality is ensured through validation by domain experts. The quality of the annotation guidelines was ensured by satisfactory Inter Annotator Agreement (IAA) between the annotators and the domain experts. SuperMat includes the dataset, annotation guidelines, and annotation support tools that use automatic suggestions to help minimise human errors., Luca Foppiano, Sae Dieb, Akira Suzuki, Pedro Baptista de Castro, Suguru Iwasaki, et al.. SuperMat: Construction of a linked annotated dataset from superconductors-related publications. 2021. ⟨hal-03101177v3⟩

We have investigated the local structure of BiS2-based layered materials by Bi L3-edge extended X-ray absorption fine structure (EXAFS) measurements performed on single crystal samples with polarization of the X-ray beam parallel to the BiS2 plane. The results confirm highly instable nature of BiS2 layer, characterized by ferroelectric like distortions. The distortion amplitude, determined by the separation between the two in-plane (Bi-S1) bonds, is found to be highest in LaO0.77F0.23BiS2 with ΔR∼0.26 Å and lowest in NdO0.71F0.29BiS2 with ΔR∼0.13 Å. Among the systems with intrinsic doping, CeOBiS2 shows smaller distortion (ΔR∼0.15 Å) than PrOBiS2 (ΔR∼0.18 Å) while the highest distortion appears for EuFBiS2 revealing ΔR∼0.22 Å. It appears that the distortion amplitude is controlled by the nature of the RE(O,F) spacer layer in the RE(O,F)BiS2 structure. The X-ray absorption near edge structure (XANES) spectra, probing the local geometry, shows a spectral weight transfer that evolves systematically with the distortion amplitude in the BiS2-layer. The results provide a quantitative measurements of the local distortions in the instable BiS2-layer with direct implication on the physical properties of these materials.

Processing magnetocaloric materials into magnetic refrigerant particles is an essential issue in developing high-performance magnetic refrigerators. Here, we succeed in stably producing magnetocaloric particles of the promising material HoAl2 by a newly devised method based on electrode induction melting gas atomization process. The particle size range is on the order of submillimeter, which is suitable for practical refrigeration systems. The resulting particles with less contamination have good morphological, magnetic, and magnetocaloric properties: (i) almost spherical shapes with few internal pores, (ii) a sharp ferromagnetic transition around 30 K, and (iii) a large magnetocaloric effect comparable to the bulk counterpart. These features suggest the HoAl$_{2}$ gas-atomized particles have the potential of use as a magnetic refrigerant. The presented method can be applied not only to HoAl2 but also to other brittle magnetocaloric materials with high melting points, facilitating the production of various magnetic refrigerants needed to develop magnetic refrigerators for hydrogen liquefaction.

The superconducting transition temperature, $T_{\rm{c}}$, of FeSe can be significantly enhanced several-fold by applying pressure, electron doping, intercalating spacing layer, and reducing dimensionality. Various ordered electronic phases, such as nematicity and spin density waves, have also been observed accompanying high-$T_{\rm{c}}$ superconductivity. Investigation on the evolution of the electronic structure with $T_{\rm{c}}$ is essential to understanding electronic behavior and high-$T_{\rm{c}}$ superconductivity in FeSe and its derived superconductors. In this report, we have found a series of discrete superconducting phases, with a maximum $T_{\rm{c}}$ up to 44 K, in H$^+$-intercalated FeSe single crystals using an ionic liquid gating method. Accompanied with the increase of $T_{\rm{c}}$, suppression of the nematic phase and evolution from non-Fermi-liquid to Fermi-liquid behavior was observed. An abrupt change in the Fermi surface topology was proposed to explain the discrete superconducting phases. A band structure that favors the high-$T_{\rm{c}}$ superconducting phase was also revealed., 23 pages, 8 figures

Recently, a massive magnetocaloric effect near the liquefaction temperature of hydrogen has been reported in the ferromagnetic material HoB$_{2}$. Here we investigate the effects of Dy substitution in the magnetocaloric properties of Ho$_{1-x}$Dy$_{x}$B$_{2}$ alloys ($\textit{x}$ = 0, 0.3, 0.5, 0.7, 1.0). We find that the Curie temperature ($\textit{T}$$_{C}$) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |$\Delta \textit{S}_{M}$| at $\textit{T}$ = $\textit{T}_{C}$ decreases from 0.35 to 0.15 J cm$^{-3}$ K$^{-1}$ for a field change of 5 T. Due to the presence of two magnetic transitions in these alloys, despite the change in the peak magnitude of |$\Delta \textit{S}_{M}$|, the refrigerant capacity ($\textit{RC}$) and refrigerant cooling power ($\textit{RCP}$) remains almost constant in all doping range, which as large as 5.5 J cm$^{-3}$ and 7.0 J cm$^{-3}$ for a field change of 5 T. These results imply that this series of alloys could be an exciting candidate for magnetic refrigeration in the temperature range between 10-50 K., Comment: 19 pages, 5 figures, 2 tables

We fabricate gas-atomized particles by inductively melting electrode rods of HoB2-x (x = -0.3, 0, 0.3, and 1.0) and investigate the effect of non-stoichiometry on the phase fraction, microstructure, and physical properties. Shifting the stoichiometric ratio of the electrode rod to the B (Ho)-rich side increases HoB4 (Ho) phase in the resulting atomized particles. Even if the atomized particles contain 15-20 weight percent (wt.%) of the impurity phase, the influence of which on the physical properties is less severe: the maximum value of the magnetic entropy change is only reduced by 10% compared to HoB2.0 particles. We further find that the ductile Ho phase exists so as to fill the space between the brittle HoB2 phases in the atomized particles, which may be beneficial to the mechanical properties of the particles. Our findings suggest that it would be better to use the Ho-rich electrode rods than the stoichiometric ones to produce HoB2-x particles with more suitable properties as a magnetic refrigerant for magnetic refrigeration systems.

We studied Gr\"uneisen parameter ({\gamma}G) to investigate lattice anharmonicity in a layered BiS2-based superconductor system REO1-xFxBiS2 (RE = La, Ce, Pr, Nd), where in-plane chemical pressure was tuned by substituting the RE elements. With increasing in-plane chemical pressure, bulk modulus remarkably increases, and a high {\gamma}G is observed for RE = Nd. The dependence of {\gamma}G on in-plane chemical pressure exhibits a good correlation with Tc, and a higher Tc is achieved when {\gamma}G is large for RE = Nd. In addition, {\gamma}G shows a slight decrease by a decrease of F concentration (x) in REO1-xFxBiS2. Our results show that the anharmonic vibration of Bi along the c-axis is present in REO1-xFxBiS2, and the enhancement of the anharmonicity is positively linked to superconducting Tc and pairing mechanisms., Comment: 15 pages, 5 figures

Processing magnetocaloric materials into magnetic refrigerants with appropriate shapes is essential for the development of magnetic refrigeration systems. In this context, the impact of processing on the physical properties of magnetocaloric materials is one of the important issues. Here, we investigate the crystallographic, magnetic, and magnetocaloric properties of gas-atomized particles of the intermetallic compound ErCo$_{2}$, a giant magnetocaloric material for low-temperature applications. The results demonstrate that the physical properties of ErCo$_{2}$ are significantly changed by atomization and subsequent thermal annealing. In the as-atomized particles, the magnetic transition temperature increases from 34 to 56 K and the phase transition changes from first order to second order. The thermal annealing shifts the transition temperature back to the original one and restores the first-order phase transition characteristic. The changes in magnetic properties are closely related to those in crystallographic properties, suggesting the importance of the magneto-structural coupling. The magnetic entropy change $-\Delta S_{M}$ of the particles can be tuned in size, shape, and peak temperature depending on the annealing conditions. The peak value of $-\Delta S_{M}$ varies in the range of 9--33 J kg$^{-1}$ K$^{-1}$ for a magnetic field change of 0--5 T. All the ErCo$_{2}$ atomized particles have magnetocaloric properties comparable or superior to other promising candidates for low-temperature magnetic refrigerants., Comment: Journal of Alloys and Compounds (in press)

For performing successful measurements within limited experimental time, efficient use of preliminary data plays a crucial role. This work shows that a simple feedforward type neural networks approach for learning preliminary experimental data can provide quick access to simulate the experiment within the learned range. The approach is especially beneficial for physical properties measurements with scanning on multiple axes, where derivative or integration of data are required to obtain the objective quantity. Due to its simplicity, the learning process is fast enough for the users to perform learning and simulation on-the-fly by using a combination of open-source optimization techniques and deep-learning libraries. Here such a tool for augmenting the experimental data is proposed, aiming to help researchers to decide the most suitable experimental conditions before performing costly experiments in real. Furthermore, this tool can also be used from the perspective of taking advantage of reutilizing and repurposing previously published data, accelerating data-driven exploration of functional materials., Comment: 19 pages, 5 figures + 7 pages of Supporting Information

High-pressure techniques open exploration of functional materials in broad research fields. An established diamond anvil cell with a boron-doped diamond heater and transport measurement terminals has performed the high-pressure synthesis of a cubic Sn$_{3}$S$_{4}$ superconductor. X-ray diffraction and Raman spectroscopy reveal that the Sn$_{3}$S$_{4}$ phase is stable in the pressure range of P>5 GPa in a decompression process. Transport measurement terminals in the diamond anvil cell detect a metallic nature and superconductivity in the synthesized Sn$_{3}$S$_{4}$ with a maximum onset transition temperature of 13.3 K at 5.6 GPa. The observed pressure-T$_{c}$ relationship is consistent with that from the first-principles calculation. The observation of superconductivity in Sn$_{3}$S$_{4}$ opens further materials exploration under high temperature and pressure conditions.

The processing of promising magnetocaloric materials into spheres is one of the important issues on developing high-performance magnetic refrigeration systems. In the present study, we achieved in producing spherical particles of a giant magnetocaloric compound HoB2 by a crucible-free gas atomization process, despite its high melting point of 2350 C. The particle size distribution ranges from 100 to 710 micrometers centered at 212-355 micrometers with the highest yield of 14-20wt% of total melted electrode, which is suitable for magnetic refrigeration systems. The majority of the resulting particles are mostly spherical with no contamination during the processing, while unique microstructures are observed on the surface and inside. These spherical particles exhibit sharp magnetic transitions and huge magnetic entropy change of 0.34 J cm^{-3} K^{-1} for a magnetic field change of 5 T at 15.5 K. The high sphericality and the high magnetocaloric performance suggest that the HoB2 gas-atomized particles have good potential as magnetic refrigerants for use in magnetic refrigerators for hydrogen liquefaction., Comment: 6pages(double column), 6 figures

Diamond has two crystallographically inequivalent sites in the unit cell. In doped diamond, dopant occupation in the two sites is expected to be equal. Nevertheless, preferential dopant occupation during growth under nonequilibrium conditions is of fundamental importance, for example, to enhance the properties of nitrogen-vacancy (N-V) centers; therefore, this is a promising candidate for a qubit. However, the lack of suitable experimental techniques has made it difficult to study the crystal- and chemical-site-resolved local structures of dopants. Here, we confirm the identity of two chemical sites with asymmetric dopant incorporation in the diamond structure, via the photoelectron holography (PEH) of heavily phosphorus (P)-doped diamond prepared by chemical vapor deposition. One is substitutionally incorporated P with preferential site occupations and the other can be attributed to a PV split vacancy complex with preferential orientation. The present study shows that PEH is a valuable technique to study the local structures around dopants with a resolution of crystallographically inequivalent but energetically equivalent sites/orientations. Such information provides strategies to improve the properties of dopant related-complexes in which alignment is crucial for sensing of magnetic field or quantum spin register using N-V centers in diamond.

Analysis of XRD diffraction patterns is one of the keystones of materials science and materials research. With the advancement of data-driven methods for materials design, candidate materials can be quickly screened for the study of a desired physical property. Efficient methods to automatically analyze and identify phases present in a given pattern, are paramount for the success of this new paradigm. To aid this process, the open source python package Xray Estimation and Refinement Using Similarity (XERUS) for semi-automatic/automatic phase identification is presented. XERUS takes advantages of open crystal structure databases, not relying on proprietary databases, to obtain crystal structures on the fly, being then chemical space agnostic. By wrapping around GSASII, it can automatically simulate patterns and calculate similarity measures used for phase identification. Our approach is simple and quick but also applicable to multiphase identification, by coupling the similarity calculations with quick refinements followed by an iterative peak removal process. XERUS is shown in action in four different experimental datasets and also it is benchmarked against a recently proposed deep learning method for a mixture dataset covering the Li-Mn-O-F chemical space. XERUS will be freely available on https://www.github.com/pedrobcst/Xerus/

Recently, ammonia-thermal reaction has been used for molecular intercalation in layered FeSe, resulting a new Lix(NH3)yFe2Se2 superconductor with Tc ~ 45 K. Here, we have used temperature dependent extended x-ray absorption fine structure (EXAFS) to investigate local atomic displacements in single crystals of this new superconductor. Using polarized EXAFS at Fe K-edge we have obtained direct information on the local Fe-Se and Fe-Fe bondlengths and corresponding mean square relative displacements (MSRD). We find that the Se-height in the intercalated system is lower than the one in the binary FeSe, suggesting compressed FeSe4 tetrahedron in the title system. Incidentally, there is hardly any effect of the intercalation on the bondlengths characteristics, revealed by the Einstein temperatures, that are similar to those found in the binary FeSe. Therefore, the molecular intercalation induces an effective compression and decouples the FeSe slabs. Furthermore, the results reveal an anomalous change in the atomic correlations across Tc, appearing as a clear decrease in the MSRD, indicating hardening of the local lattice mode. Similar response of the local lattice has been found in other families of superconductors, e.g., A15-type and cuprates superconductors. This observation suggests that local atomic correlations should have some direct correlation with the superconductivity.

The ${\mathrm{BiS}}_{2}$-based layered materials are characterized by a highly susceptible physical state, revealing a large response to external conditions. A particular case is the ${\mathrm{EuFBiS}}_{2}$ compound, showing a superconducting transition temperature ${T}_{c}\ensuremath{\sim}0.3$ K at ambient pressure. Upon increasing external pressure, ${T}_{c}$ goes through a large amplification, accompanied by a structural phase transition (SPT) from tetragonal to monoclinic symmetry. Here, we use a combination of Eu ${\phantom{\rule{4pt}{0ex}}L}_{3}$ - edge x-ray absorption spectroscopy and synchrotron x-ray diffraction to unveil the evolution of the Eu valence and lattice symmetry under high pressure. We find that the average Eu valence increases gradually with pressure, exhibiting a pressure plateau near the SPT, at which the ${T}_{c}$ increases sharply. Since in ${\mathrm{EuFBiS}}_{2}$ the charge carriers are introduced via self-doping induced by the mixed valence of the Eu ions, our findings clearly indicate that the role of the charge doping is marginal in the ${T}_{c}$ enhancement. On the other hand, the structural distortions, taking place at the SPT, play a central role in enhancing the superconducting properties of the ${\mathrm{EuFBiS}}_{2}$ system.

Magnetic refrigeration exploits the magnetocaloric effect which is the entropy change upon application and removal of magnetic fields in materials, providing an alternate path for refrigeration other than the conventional gas cycles. While intensive research has uncovered a vast number of magnetic materials which exhibits large magnetocaloric effect, these properties for a large number of compounds still remain unknown. To explore new functional materials in this unknown space, machine learning is used as a guide for selecting materials which could exhibit large magnetocaloric effect. By this approach, HoB$_{2}$ is singled out, synthesized and its magnetocaloric properties are evaluated, leading to the experimental discovery of gigantic magnetic entropy change 40.1 J kg$^{-1}$ K$^{-1}$ (0.35 J cm$^{-3}$ K$^{-1}$) for a field change of 5 T in the vicinity of a ferromagnetic second-order phase transition with a Curie temperature of 15 K. This is the highest value reported so far, to our knowledge, near the hydrogen liquefaction temperature thus it is a highly suitable material for hydrogen liquefaction and low temperature magnetic cooling applications., 12 pages including 3 figures and 1 table + 11 pages of supplementary information. Published version available at: https://rdcu.be/b36ep

We have developed an approach to control the carrier density in various material under high pressure by the combination of an electric double layer transistor (EDLT) with a diamond anvil cell (DAC). In this study, this EDLT-DAC was applied to a Bi thin film, and here we report the field-effect under high pressure in the material. Our EDLT-DAC is a promising device for exploring unknown physical phenomena such as high transition-temperature superconductivity (HTS)., 10 pages, 4 figures

We report the fabrication of ErAl2 magnetocaloric wires by a powder-in-tube method (PIT) and the evaluation of magnetic entropy change through magnetization measurements. The magnetic entropy change of ErAl2 PIT wires exhibits similar behavior to the bulk counterpart, while its magnitude is reduced by the decrease in the volume fraction of ErAl2 due to the surrounding non-magnetic sheaths. We find that another effect reduces the magnetic entropy change of the ErAl2 PIT wires around the Curie temperature, and discuss its possible origin in terms of a correlation between magnetic properties of ErAl2 and mechanical properties of sheath material., Comment: This is the version of the article before peer review or editing, as submitted by an author to {insert name of Journal}. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at {https://dx.doi.org/10.1088/1361-6463/ab5c71}

Since the first observation of the metal-to-insulator transition (MIT), VO2 has attracted substantial attention in terms of whether this transition is impelled by electron–phonon interaction (Peierls transition) or electron–electron interaction. Regarding Peierls transition, it has been theoretically predicted that the Fermi surface (FS) cross-section exhibits certain nesting features for a metallic phase of VO2. Various experimental studies related to the nesting feature have been reported. Nevertheless, there is no experimental result on FS topology. In this work, we determine the FS topology of the metallic phase of VO2 through studies of VO2 epitaxial thin films on TiO2(001) substrates, using synchrotron radiation angle-resolved photoemission spectroscopy (ARPES). Three electron pockets around Γ are observed in band structures along the Γ–X direction. These three bands form electron surfaces around Γ in the ΓXRZ plane. Furthermore, the lowest energy band FS exhibits the nesting feature corresponding to a nesting vector $$\overrightarrow{q}$$ q → = ΓR, as predicted by the calculation. Our results strongly indicate the formation of the charge-density wave with $$\overrightarrow{q}$$ q → = ΓR and thus, the importance of Peierls transition for the mechanism of the MIT in VO2.

Recently CeOBiS2 system without any fluorine doping is found to show superconductivity posing question on its origin. Using space resolved ARPES we have found a metallic phase embedded in the morphological defects and at the sample edges of stoichiometric CeOBiS2. While bulk of the sample is semiconducting, the embedded metallic phase is characterized by the usual electron pocket at X point, similar to the Fermi surface of doped BiS2-based superconductors. Typical size of the observed metallic domain is larger than the superconducting correlation length of the system suggesting that the observed superconductivity in undoped CeOBiS2 might be due to this embedded metallic phase at the defects. The results also suggest a possible way to develop new systems by manipulation of the defects in these chalcogenides with structural instability.

Layered ternary transition-metal chalcogenides have been focused as a vein of exploration for superconductors. In this study, TiGeTe6 single crystals were synthesized and characterized by structural and valence state analyses and electrical transport measurements. The transport properties were measured under various pressures up to 71 GPa. The activation energy gets smaller as the applied pressure increases, and a signature of a pressure-induced metallization was observed under around 8.4 GPa. Under 13 GPa, pressure-induced superconductivity was discovered in this compound for the first time, with successive drops at 3 K and 6 K in the resistance, indicating the presence of multiple superconducting transitions. The superconducting transition temperature kept increasing as we further applied the pressure to the TiGeTe6 single crystal in the performed pressure range, reaching as high as 8.1 K under 71 GPa.

We have investigated the electronic states and spin polarization of half-metallic ferromagnet CrO$_2$ (100) epitaxial films by bulk-sensitive spin-resolved photoemission spectroscopy with a focus on non-quasiparticle (NQP) states derived from electron-magnon interactions. We found that the averaged values of the spin polarization are approximately 100% and 40% at 40 K and 300 K, respectively. This is consistent with the previously reported result [H. Fujiwara et al., Appl. Phys. Lett. 106, 202404 (2015).]. At 100 K, peculiar spin depolarization was observed at the Fermi level ($E_{F}$), which is supported by theoretical calculations predicting NQP states. This suggests the possible appearance of NQP states in CrO$_2$. We also compare the temperature dependence of our spin polarizations with that of the magnetization., Comment: 8 pages, 3 figures, VUVX 2016

Spectroscopic techniques, including photoelectron spectroscopy, diffuse reflectance, and x-ray absorption, are used to investigate the electronic structure and the local structure of LaOBiS$_{2-x}$Se$_x$ thermoelectric material. It is found that Se substitution effectively suppresses local distortion, that can be responsible for the increased carrier mobility together with a change in the electronic structure. The results suggest a possible way to control thermoelectric properties by tuning of the local crystal structure of these materials., Comment: 6 pages, 4 figures, 1 table, J. Appl. Phys. (in press)

Electron-doped TiNCl is a superconductor, for which exotic mechanisms of the superconductivity have been discussed. However, difficulty in preparing large single-phase samples has prevented the direct observation of its electronic structure and how that changes with electron doping. In this study, micro-photoemission spectroscopy ({\mu}-PES) was used to reveal the electronic structures of TiNCl and Na-intercalated TiNCl (Na-TiNCl). Comparison of Ti 2p core-level spectra shows the enhancement of a spectral feature in Na-TiNCl that suggests an increase in its metallic character. This indicates the introduction of electron carriers to the TiNCl layers. Although the overall valence band electronic structure of parent TiNCl could be reproduced by first-principle calculations, that of Na-TiNCl showed a marked deviation from the rigid band model near the Fermi level (EF). The spectral shape observed near EF of Na-TiNCl was found to be similar to a result in early transition metal oxides that has been attributed to the effect of strong electron correlation. The present study also demonstrated the usefulness of {\mu}-PES to obtain reliable electronic structure data for samples that are difficult to make at large sizes., Comment: 14 page, 5 figures

Stoichiometric ${\mathrm{EuFBiS}}_{2}$ with mixed valent Eu shows self-doped superconductivity at low temperatures due to the Eu-to-Bi charge transfer. The metallic/nonmetallic bistability of the ${\mathrm{BiS}}_{2}$ layer can couple with the valence fluctuation of Eu and provide a highly susceptible electronic state. Here, we report space-resolved photoemission measurements on ${\mathrm{EuFBiS}}_{2}$ revealing an inhomogeneous charge distribution with the coexistence of metallic and nonmetallic phases at mesoscopic length scales. Angle-resolved photoemission measurements using a submicron beam size have confirmed a clear Fermi surface around the zone boundaries in the metallic region, typically observed in a doped system, while it can be hardly seen in the nonmetallic region. Density functional theory calculations suggest that the out-of-plane S atom position in the structure is one of the important factors for the self-doping in this material.

To optimize the giant magnetocaloric properties of HoB2, we synthesized and characterized the magnetocaloric properties of Ho1-xGdxB2 (0.1 ≤ x ≤ 0.4) alloys. We found out that Gd enters stoichiometrically and randomly into the Ho site, leading to a Vegard-type structural change. The addition of spherical S7/2 Gd3+ moments prompts an enhancement in Curie temperature from 15 K to 30 K (at x = 0.4), a reduction in peak value of the magnetic entropy change, from 0.35 (40.1) to 0.17 (20.2) J cm−3 K−1 (J kg−1 K−1), and a broadening of the magnetic entropy change curves. The overall influence is a relatively high refrigerant capacity and relative cooling power, peaking at 6.07 (711) and 7.68 (899) J cm−3 (J kg−1) for x = 0.2, and an extension of the thermal working range to higher temperatures. Unlike Ho1−xDyxB2 alloys, the Gd substituted samples show no magnetic hysteresis. Furthermore, scaling analysis of the entropy curves suggests a second-order phase transition for the ferromagnetic transition in these alloys. Thus, Ho1-xGdxB2 alloys are potential candidates for cryogenic refrigeration applications.

Cuprate superconductor Bi2Sr2CaCu2O8+δ (BSCCO) has been a promising candidate of a coherent, continuous, and compact THz light source owing to its intrinsic Josephson junction (IJJ) inside the crystal structure. In this paper, we utilized BSCCO cross-whisker (CW) junctions to produce THz emitter device using the whisker crystals which can be easily obtained compared with single crystals. As a result, we have successfully observed the emission from the CW IJJ at the frequency of ∼0.7 THz, which is the first observation of a THz emission from whiskers to our knowledge. Our findings would enlarge the applicability of BSCCO superconductors for compact THz emission sources.

We performed soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements at Fe L2,3-edges and Ce M4,5-edges on Ce2Fe14B at 300 K. The valence and total atomic moment of Ce in Ce2Fe14B were determined to be ∼+3.12 and ∼0.100 μ B, respectively, which mainly stem from a large portion of the well-localized 4f 1 configurations. Besides, the individual orbital and spin moments of Ce in Ce2Fe14B as well as those of Fe were determined for the first time with consideration of the magnetic dipole term.

TaO2 thin films were prepared using rutile-type NbO2 template layers on Al2O3(0001) substrates by a pulsed laser deposition technique. The structural and electronic properties of the films were characterized by performing four-circle X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) measurements. Four-circle XRD measurements revealed the formation and epitaxial growth of (100)-oriented tetragonal TaO2 on the NbO2 template layers. On the other hand, XPS measurements showed two kinds of valence states, namely Ta4 + and Ta5 + in the surface region of the film. The results from the XRD and XPS measurements suggest that the film is composed of epitaxially grown TaO2 with an amorphous Ta2O5 surface layer. It is found from control experiments that the NbO2 template layers play an important role in inducing the crystallization of the TaO2 films and promoting the formation of Ta4 + in the films deposited thereon. The results indicate the effectiveness of the NbO2 template layers for the formation of TaO2 thin films. Our work presents a promising method for the preparation of TaO2 thin films and provides a starting point for further research on TaO2.

We report the adiabatic temperature change in ErAl2 magnetocaloric wires fabricated by a powder-in-tube (PIT) process. The adiabatic temperature change of the PIT wires is found to be determined by not only the volume fraction of ErAl2 core but also the magnitude relationship between the specific heat of the ErAl2 core and the metal sheath. We propose a quantitative analysis method for calculating the temperature and core volume fraction dependence of adiabatic temperature change in the PIT wire, whose formula is applicable to also various magnetocaloric composites, useful to estimate the magnetocaloric response prior to fabrication., Comment: 14 pages, 5 figures

A diamond anvil cell (DAC) has become an effective tool for investigating physical phenomena that occur at extremely high pressure, such as high-transition temperature superconductivity. Electrical transport measurements, which are used to characterize one of the most important properties of superconducting materials, are difficult to perform using conventional DACs. The available sample space in conventional DACs is very small and there is an added risk of electrode deformation under extreme operating conditions. To overcome these limitations, we herein report the fabrication of a boron-doped diamond microelectrode and undoped diamond insulation on a beveled culet surface of a diamond anvil. Using the newly developed DAC, we have performed in-situ electrical transport measurements on sulfur hydride H2S, which is a well-known precursor of the pressure-induced, high-transition temperature superconducting sulfur hydride, H3S. These measurements conducted under high pressures up to 192 GPa, indicated the presence of a multi-step superconducting transition, which we have attributed to elemental sulfur and possibly HS2.

We investigate the influence of lattice strain in the c-axis direction on spinodal decomposition in rutile TiO2-VO2 films on TiO2(100) substrates. The [100]-oriented Ti0.4V0.6O2 (TVO) solid-solution films are fabricated on rutile TiO2(100) substrates using a pulsed laser deposition with a KrF excimer laser, and are annealed inside the spinodal region. X-ray diffraction and scanning transmission electron microscopy are employed for characterization. Consequently, the in-plane tensile strain in the c-axis direction promotes the Ti-V interdiffusion in TVO/TiO2(100) under thermal annealing. In contrast, relaxation of the tensile strain results in the occurrence of spinodal decomposition along the c-axis direction in the film. These results indicate that the relaxation of the tensile strain in the c-axis direction is critically important for enabling spinodal decomposition in TVO/TiO2(100). Our work helps deepen the understanding of spinodal decomposition in the TVO film and provides information on achieving novel nanostructures via spinodal decomposition in TVO/TiO2(100).

Using high-resolution spin-resolved photoemission spectroscopy, we observed a thermal spin depolarization to which all spin-polarized electrons contribute. Furthermore we observed a distinct minority spin state near the Fermi level and a corresponding depolarization that seldom contributes to demagnetization. The origin of this depolarization has been identified as the many-body effect characteristics of half-metallic ferromagnets. Our investigation opens an experimental field of itinerant ferromagnetic physics focusing on phenomena with sub-meV energy scale., 19 pages, 10 figures

The local structures of 122-type paradium arsenides, namely BaPd2As2 and SrPd2As2, are examined by As K-edge extended x-ray absorption fine structure measurements to find a possible correlation between the variation of their superconducting transition temperature and the local structure. The local atomic distances are found to be consistent with average distances measured by diffraction techniques. The temperature dependence of mean square relative displacements reveal that, while BaPd2As2 is characterized by a local As-Pd soft mode, albeit with larger atomic disorder, SrPd2As2 shows anomalous As-Pd correlations with a kink at similar to 160 K due to hardening by raising temperature. We have discussed implications of these results and possible mechanisms of differing superconducting transition temperature in relation with the structural instability.

The temperature dependence of the resistivity (ρ) of Ag-doped Bi2Se3 (AgxBi2−xSe3) shows insulating behavior above 35 K, but below 35 K, ρ suddenly decreases with decreasing temperature, in contrast to the metallic behavior for non-doped Bi2Se3 at 1.5–300 K. This significant change in transport properties from metallic behavior clearly shows that the Ag doping of Bi2Se3 can effectively tune the Fermi level downward. The Hall effect measurement shows that carrier is still electron in AgxBi2−xSe3 and the electron density changes with temperature to reasonably explain the transport properties. Furthermore, the positive gating of AgxBi2−xSe3 provides metallic behavior that is similar to that of non-doped Bi2Se3, indicating a successful upward tuning of the Fermi level.

The local structure of correlated spin-orbit insulator Sr$_{2-x}$M$_x$IrO$_4$ (M = K, La) has been investigated by Ir L$_3$-edge extended x-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the N\'eel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating possibility of a nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed., Comment: Main text: 6 pages, 4 figures, Supplemental information: 2 pages, 2 figures

The electronic structure of the lightly electron-doped correlated spin-orbit insulator Sr2IrO4 has been studied by angle-resolved photoelectron spectroscopy. We have observed the coexistence of a lower Hubbard band and an in-gap band; the momentum dependence of the latter traces that of the band calculations without on-site Coulomb repulsion. The in-gap state remained anisotropically gapped in all observed momentum areas, forming a remnant Fermi-surface state, evolving towards the Fermi energy by carrier doping. These experimental results show a striking similarity with those observed in deeply underdoped cuprates, suggesting the common nature of the nodal liquid states observed in both compounds.

We use soft x-ray photoemission spectroscopy (SXPES) to investigate Ce 4f electronic states of a new BiS2 layered superconductor CeO1-xFxBiS2, for polycrystalline and single-crystal samples. The Ce 3d spectrum of the single crystal of nominal composition x = 0.7 has no f(0) component and the spectral shape closely resembles the ones observed for Ce trivalent insulating compounds, strongly implying that the CeO layer is still in an insulating state even after the F doping. The Ce 3d-4f resonant SXPES for both polycrystalline and single-crystal samples shows that the prominent peak is located around 1 eV below the Fermi level (E-F) with negligible spectral intensity at EF. The F-concentration dependence of the valence band spectra for single crystals shows the increases of the degeneracy in energy levels and of the interaction between Ce 4f and S 3p states. These results give insight into the nature of the CeO1-xFx layer and the microscopic coexistence of magnetism and superconductivity in CeO1-xFxBiS2.

We have studied the electronic structure of ${\mathrm{Eu}}_{3}{\mathrm{F}}_{4}{\mathrm{Bi}}_{2}{\mathrm{S}}_{4}$ using a combination of Eu ${L}_{3}$-edge x-ray absorption spectroscopy (XAS) and space-resolved angle-resolved photoemission spectroscopy (ARPES). From the Eu ${L}_{3}$-edge XAS, we have found that the Eu in this system is in mixed valence state with coexistence of ${\mathrm{Eu}}^{2+}/{\mathrm{Eu}}^{3+}$. The bulk charge doping was estimated to be $\ensuremath{\sim}0.3$ per Bi site in ${\mathrm{Eu}}_{3}{\mathrm{F}}_{4}{\mathrm{Bi}}_{2}{\mathrm{S}}_{4}$, which corresponds to the nominal $x$ in a typical RE${\mathrm{O}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}{\mathrm{BiS}}_{2}$ system (RE: rare-earth elements). From the space-resolved ARPES, we have ruled out the possibility of any microscale phase separation of Eu valence in the system. Using a microfocused beam we have observed the band structure as well as the Fermi surface that appeared similar to other compounds of this family with disconnected rectangular electronlike pockets around the $X$ point. The Luttinger volume analysis gives the effective carrier to be 0.23 electrons per Bi site in ${\mathrm{Eu}}_{3}{\mathrm{F}}_{4}{\mathrm{Bi}}_{2}{\mathrm{S}}_{4}$, indicating that the system is likely to be in the underdoped region of its superconducting phase diagram.

We report syntheses of new superconducting metal-doped MoSe2 materials (MxMoSe2). The superconducting MxMoSe2 samples were prepared using a liquid NH3 technique and can be represented as ‘(NH3)yMxMoSe2’. The Tcs of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH3)yNaxMoSe2 were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe2 layers. The x-independence of c was observed in (NH3)yNaxMoSe2, indicating the formation of a stoichiometric compound in the entire x range, which is consistent with the x-independence of Tc. A metallic edge of the Fermi level was observed in the photoemission spectrum at 30 K, demonstrating its metallic character in the normal state. Doping of MoSe2 with Li and K also yielded superconductivity. Thus, MoSe2 is a promising material for designing new superconductors, as are other transition metal dichalcogenides.