arXiv subjects

Yoshihiko Takano

Publications and source records attributed to Yoshihiko Takano.

At least 73 records · Page 4Linked to original sources

arXiv2020

Effect of Dy substitution in the giant magnetocaloric properties of HoB$_{2}$

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}$) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |$Δ\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 |$Δ\textit{S}_{M}$|, 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.

cond-mat.mtrl-sci↗

arXiv2020

Demonstration of Electric Double Layer Gating under High Pressure by the Development of Field-Effect Diamond Anvil Cell

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).

cond-mat.mtrl-sci↗

arXiv2020

Machine Learning Guided Discovery of Gigantic Magnetocaloric Effect in HoB$_{2}$ Near Hydrogen Liquefaction Temperature

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.

cond-mat.mtrl-sci↗

arXiv2020

Magnetic entropy change of ErAl2 magnetocaloric wires fabricated by a powder-in-tube method

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.

cond-mat.mtrl-sci↗

arXiv2019

Growth of superconducting Sm(O,F)BiS2 single crystals

Superconducting Sm(O,F)BiS2 single crystals were successfully grown using KI-KCl flux. The obtained single crystals were flat-shaped and their size was 500um. The structure and composition of the obtained single crystals were obtained using X-ray diffraction and X-ray spectroscopy. The lattice constants of the obtained Sm(O,F)BiS2 single crystals were evaluated to be a = 3.9672(4) A and c = 13.417(6) A, while their F/(O + F) molar ratio was approximately 0.17. The superconducting transition temperature of the obtained Sm(O,F)BiS2 single crystals was 4.8 K. This was different from the reported Sm(O,F)BiS2 with no superconducting transition above 2 K. The superconducting anisotropies of the upper critical field and effective mass model of the obtained Sm(O,F)BiS2 single crystals were estimated to be approximately 26 and 10, respectively.

cond-mat.supr-con↗

arXiv2019

Crystal Size Improvement of Bi-based Superconducting Whiskers under Stress-controlled Condition

Using stress-controlled amorphous precursors, we have successfully grown large $Bi_{2}$$Sr_{2}$$Ca_{\textit{n}-1}$$Cu_{\textit{n}}$$O_{\textit{y}}$ (Bi-based) high-transition temperature superconducting whiskers. Especially, under a high compressive stress attained by 1 GPa pelletizing, the crystal size of a whisker was significantly enhanced up to 9.5 mm length (growth period: 96 h) which is 2.4 times larger than that of the conventional amorphous-precursors method. In addition, by using the stress-controlled precursors, the number of the obtained Bi-based whiskers were also increased by a factor of 1.8.

cond-mat.supr-con↗

arXiv2019

Pressure-induced superconductivity in layered pnictogen diselenide NdO$_{0.8}$F$_{0.2}$Sb$_{1-x}$Bi$_x$Se$_2$ (x = 0.3 and 0.7)

Polycrystalline samples of layered pnictogen diselenide NdO0.8F0.2Sb1-xBixSe2 (x = 0 to 0.8) were successfully synthesized by solid-state reactions. Electrical resistivity in the synthesized samples was systematically decreased with an increase in Bi content x. Crystal structure analysis using synchrotron X-ray diffraction suggests that insulator to metal transition upon Bi doping correlates with anomalous change in c-axis length and/or corrugation in conducting layer. The emergence of superconductivity under high pressure is demonstrated using diamond anvil cell (DAC) with boron-doped diamond electrodes, for x = 0.3 and 0.7 as the representative samples. For Sb-rich one (x = 0.3), we observed a superconducting transition with Tconset = 5.3 K at 50 GPa, which is the first-ever report of the superconductivity in layered SbCh2-based (Ch: chalcogen) compounds. The Tconset of x = 0.3 increased with increasing pressure and reached 7.9 K at 70.8 GPa, followed by the gradual decrease in Tc up to 90 GPa. For Bi-rich one (x = 0.7), a superconducting transition with Tconset = 5.9 K was observed at 43.5 GPa, which is the almost comparable to that of x = 0.3; besides, upper critical field (Hc2) is evaluated to be ~10 T for x = 0.7, which is higher than that of x = 0.3 (Hc2 = 6.7 T at 50 GPa).

cond-mat.supr-con↗

arXiv2019

Crystal Growth of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ Whiskers from Pulverized Amorphous Precursors

High-transition temperature superconducting whiskers of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ were successfully grown from pulverized amorphous precursors. The obtained whiskers revealed a typical composition and diffraction patterns of a superconducting Bi-2212 phase. The whiskers from tiny precursors exhibit a spiral feature, suggesting a contribution from the growth mechanism of both vapor-liquid-solid and compressive stress models. The proposed method provides longer whiskers against the growth period, compared with that from conventional root-growth method.

cond-mat.supr-con↗

arXiv2019

Direct Patterning of Boron-doped Amorphous Carbon Using Focused Ion Beam-assisted Chemical Vapor Deposition

The deposition of boron-doped amorphous carbon thin films on SiO2 substrate was achieved via a focused ion beam-assisted chemical vapor deposition of triphenyl borane (C18H15B) and triphenyl borate (C18H15BO3). The existence of boron in the deposited film from triphenyl borane, with a precursor temperature of 90 °C, was confirmed by a core level X-ray photoelectron spectroscopy analysis. The film exhibited a semiconducting behavior with a band gap of 285 meV. Although the band gap was decreased to 197 meV after an annealing process, the film was still semiconductor. Additionally, a drastic reduction of the resistance on the deposited film by applying pressures was observed from an in-situ electrical transport measurements using a diamond anvil cell.

cond-mat.mtrl-sci↗

arXiv2019

Mask-less Patterning of Gallium-irradiated Superconducting Silicon Using Focused Ion Beam

A direct patterning technique of gallium-irradiated superconducting silicon has been established by focused gallium-ion beam without any mask-based lithography process. The electrical transport measurements for line and square shaped patterns of gallium-irradiated silicon were carried out under self-field and magnetic field up to 7 T. Sharp superconducting transitions were observed in both patterns at temperature of 7 K. The line pattern exhibited a signature of higher onset temperature above 10 K. A critical dose amount to obtain the superconducting gallium-irradiated silicon was investigated by the fabrication of various samples with different doses. This technique can be used as a simple fabrication method for superconducting device.

physics.app-ph↗

arXiv2019

Pressure-induced superconductivity in SnSb2Te4

We report the discovery of a new superconductor from phase change materials SnSb2Te4. Single crystals of SnSb2Te4 were grown using a conventional melting-growth method. The sample resistance under pressure was measured using an originally designed diamond anvil cell with boron-doped diamond electrodes. The pressure dependence of the resistance has been measured up to 32.6 GPa. The superconducting transition of SnSb2Te4 appeared at 2.1 K(Tconset) under 8.1 GPa, which was further increased with applied pressure to a maximum onset transition temperature 7.4K under 32.6 GPa.

cond-mat.mtrl-sci↗

arXiv2019

Growth and characterization of (La,Ce)OBiS2 single crystals

(La,Ce)OBiS2 single crystals are successfully grown using CsCl flux. The obtained single crystals have a plate-like shape with a size of 0.5-2.0 mm and a well-developed ab-plane. The thickness of the crystals increases with a decrease in the Ce content. The (La,Ce)OBiS2 single crystals exhibit superconducting properties. Moreover, the superconducting transition temperature increases with an increase in the Ce content. The obtained (La,Ce)OBiS2 single crystals exhibit a tetragonal structure and the valence state of Ce in the crystals is determined to be mixed with Ce3+ and Ce4+ based on X-ray absorption fine structure spectroscopy.

physics.app-ph↗

arXiv2019

Growth and transport properties under high pressure of PrOBiS2 single crystals

PrOBiS2 single crystals were successfully grown using a KCl flux. The obtained crystals had a plate-like shape with a typical size of 0.5-1.0 mm and well-developed ab-plane. The Pr valence of the grown crystals, as determined by an X-ray absorption fine structure spectroscopy analysis, was almost trivalent. The PrOBiS2 single crystals did not exhibit superconductivity down to 0.25 K. The transport properties under high pressures up to 50 GPa ensured semiconducting behavior for 2-300 K using a diamond anvil cell.

cond-mat.supr-con↗

arXiv2019

Fabrication of Superconducting YBa2Cu4O8 Film via Coprecipitation

We have successfully synthesized the c-axis oriented YBa2Cu4O8 (Y-124) film on a SrTiO3 (1 0 0) substrate via a coprecipitation and a dip-coating method. The precipitations including Y, Ba and Cu ions were obtained using their metal nitrates solution and the aqueous solution of sodium hydroxide and oxalic acid. Superconducting transition of the synthesized film was observed at 64-70 K corresponding to bulk Y-124 in the magnetization and resistance measurement. The developed method is suitable to synthesize superconducting Y-124 films for technological applications.

cond-mat.supr-con↗

arXiv2019

Pressure Effect in Bi-2212 and Bi-2223 Cuprate Superconductor

We report the pressure effect in Bi2Sr2Ca2Cu3O10+δ (Bi-2223) single crystal with a small amount of intergrowth of Bi2Sr2CaCu2O8+δ (Bi-2212). Their superconducting transition temperatures Tcs showed a domelike shape as a function of pressure, which showed a good agreement with the general relation between the carrier concentration and Tc. Our experimental results indicate that high pressure can induce effective carrier doping into the multilayered high-Tc cuprate superconductor

cond-mat.supr-con↗

arXiv2019

Synthesis of Hg-based cuprate superconductors $HgBa_{2}Ca_{n-1}Cu_{n}O_{2(n+1)+δ}$ by CsCl flux additional method

We have succeeded in the synthesis of Re-doped $HgBa_{2}Ca_{n-1}Cu_{n}O_{2(n+1)+δ}$ quickly by a sealed tube technique with a bit of CsCl flux. Powder X-ray diffraction measurement revealed that the single phases of Re-doped $HgBa_{2}CuO_{4+δ}$ (Hg1201), $HgBa_{2}CaCu_{2}O_{6+δ}$ (Hg1212), and $HgBa_{2}Ca_{2}Cu_{3}O_{8+δ}$ (Hg1223) formed in 4 h. The sample grains exhibited plate-like crystals with the sizes of 20$\times$20$\times$1 $μm^{3}$ and the chemical compositions of Hg1201, Hg1212, and Hg1223. The superconducting transitions were observed at 25 K for Hg1201, 122 for Hg1212, and 133 K for Hg1223 in the magnetic susceptibility. These results indicate that the developed method is useful for the fabrication of Hg-based superconducting wires.

cond-mat.supr-con↗

arXiv2019

Data-driven Exploration of Pressure-Induced Superconductivity in AgIn$_{5}$Se$_{8}$

Candidates compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by a high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on AgIn$_{5}$Se$_{8}$ which has high density of state near the Fermi level. AgIn$_{5}$Se$_{8}$ was successfully synthesized as single crystals using a melt and slow cooling method. The single-crystal X-ray diffraction analysis revealed the obtained crystal is high quality without deficiencies. The valence states in AgIn$_{5}$Se$_{8}$ were determined to be Ag1+, In3+ and Se2- in accordance with a formal charge by the core level X-ray photoelectron spectroscopy analysis. The electrical resistance was evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. Although the sample was insulator with a resistance of above 40 MΩ at ambient pressure, the resistance markedly decreased with increase of the pressure, and a pressure-induced superconducting transition was discovered at 3.4 K under 52.5 GPa. The transition temperature increased up to 3.7 K under further pressure of 74.0 GPa.

cond-mat.supr-con↗

arXiv2019

Pressure-induced Superconductivity in Tin Sulfide

Tin sulfide (SnS) was successfully synthesized in single crystals by a melt and slow-cooling method. The obtained sample was characterized by an X-ray diffraction, an energy dispersive spectrometry, and an X-ray photoelectron spectroscopy. Electrical transport properties in SnS were investigated under high pressure using a diamond anvil cell with boron-doped metallic diamond electrodes and undoped diamond insulating layer. We successfully observed an insulator to metal transition from 12.5 GPa and pressure-induced superconductivity at 5.8 K under 47.8 GPa as predicted by a theoretical calculation.

cond-mat.supr-con↗