arXiv subjects

Yoshikazu Mizuguchi

Publications and source records attributed to Yoshikazu Mizuguchi.

At least 37 records · Page 2Linked to original sources

arXiv2024

Nonvolatile magneto-thermal switching driven by vortex trapping in commercial In-Sn solder

Magneto-thermal switching (MTS) is a key technology for efficient thermal management. Recently, large MTS with nonvolatility has been observed in Sn-Pb solders [H. Arima et al., Commun. Mater. 5, 34 (2024)] where phase separation, different superconducting transition temperature (Tc) of Sn and Pb, and magnetic-flux trapping are the causes of the nonvolatile MTS. To further understand the mechanism and to obtain the strategy for enhancing switching ratio, exploration of new phase-separated superconductors with nonvolatile MTS is needed. Here, we show that the In52-Sn48 commercial solder is a phase-separated superconducting composite with two Tc and traps vortices after field cooling. A clear signature of nonvolatile MTS was observed at T = 2.5 K. From specific heat analyses, we conclude that the vortices are mainly trapped in the lower-Tc phase (γ-phase) after field cooling, which is the evidence that vortex trapping also works on achieving nonvolatile MTS in phase-separated superconducting composites.

cond-mat.supr-con↗

arXiv2024

Large self-heating by trapped-flux reduction in Sn-Pb solders

Magnetic flux trapping in field-cooled (FC) Sn-Pb solders has been recently studied because of the observation of nonvolatile magneto-thermal switching [H. Arima et al., Commun. Mater. 5, 34 (2024)] and anomalous magnetic field-temperature (H-T) phase diagrams [T. Murakami et al., AIP Adv. 13, 125008 (2023)]. In this paper, we investigate the origin of the anomalously low specific heat (C) in Sn10-Pb90 and Sn45-Pb55 solders after FC at H = 1500 Oe. We show that the FC solders exhibit self-heating possibly caused by the flux flow during the reduction of trapped fluxes when heating the sample during the C measurements. The T dependence of T rise clearly exhibits unexpectedly large values when the low-C states are observed. In addition, the cause of the transition-like behavior in C-T of FC solders are explained by local heating during H control and flux-jump phenomena.

cond-mat.supr-con↗

arXiv2024

Influence of trapped magnetic field of Sn-Pb solders on electrical resistivity measurement: an example of superconducting transition of Sn

We examined the affection of the flux-trapped states of Sn60-Pb40 solders on superconducting properties of a Sn wire. The temperature dependence of electrical resistivity at H = 0 Oe after zero-field cooling (ZFC) showed a sharp superconducting transition at T = 3.7 K. In contrast, that after field cooling (FC) resulted in broadening of the transition. The difference between ZFC and FC data evidences critical affection of trapped fluxes at solders on superconducting states. We propose that, in electrical measurements where magnetic fields of several hundred Oe are critical, field experience should be seriously considered when using solders.

cond-mat.mtrl-sci↗

arXiv2024

Superconducting properties and electronic structure of CuAl2-type transition-metal zirconide Fe1-xNixZr2

CuAl2-type transition-metal (Tr) zirconides are superconductor family, and the Tr-site element substitution largely modifies its transition temperature (Tc). Here, we synthesized polycrystalline samples of Fe1-xNixZr2 by arc melting. From magnetic susceptibility measurements, bulk superconductivity was observed for 0.4 < x < 0.8, and the highest Tc of 2.8 K was observed for x = 0.6. Specific heat measurements were also performed, bulk superconductivity was observed for 0.4 < x < 0.8, and the highest Tc of 2.6 K was observed for x = 0.6. The obtained superconductivity phase diagram exhibits dome-shaped trend, which is similar to unconventional superconductors, where magnetic fluctuations are essential for superconductivity. In addition, from the c/a lattice constant ratio analysis, we show the possible relationship between the suppression of bulk superconductivity in the Ni-rich compositions and a collapsed tetragonal transition.

cond-mat.supr-con↗

arXiv2024

Superconducting properties of eutectic high-entropy alloy superconductor NbScTiZr

The influence of annealing on the superconducting properties of eutectic high-entropy alloy NbScTiZr was examined by measuring magnetization, electrical resistivity, and zero-field specific heat. Additionally, the extent of lattice strain was assessed via the analysis of lattice parameters and Vickers microhardness. The greatest lattice strain was inferred in the sample annealed at 400 $^{\circ}$C. Field-dependent magnetization datasets indicate enhanced flux pinning in the as-cast, 400 $^{\circ}$C annealed, and 600 $^{\circ}$C annealed samples. The superconducting parameters such as upper critical field, Ginzburg-Landau coherence length, and magnetic penetration depth do not strongly depend on the annealing temperature. However, the Maki parameter shows a peak at 400 $^{\circ}$C annealing temperature and correlates with the magnitude of lattice strain. This suggests that greater lattice strain may enhance the Maki parameter by altering the orbital-limited field through the modification of flux pinning strength. Although the influence of lattice strain is less discernible in zero-field specific heat measurements, the superconducting parameters deduced from specific heat data suggest a potential for strong-coupled superconductivity in samples heat-treated above 600 $^{\circ}$C. Our investigation underscores the substantial impact of lattice strain on the Maki parameter of eutectic HEA superconductors, primarily through the modulation of flux pinning strength.

cond-mat.supr-con↗

arXiv2024

Specific heat analyses on optical-phonon-derived uniaxial negative thermal expansion system $Tr$Zr$_{2}$ ($Tr$ = Fe and Co$_{1-x}$Ni$_{x}$)

Recently, huge uniaxial negative thermal expansion (NTE) along a $c$-axis has been observed in transition-metal ($Tr$) zirconides $Tr$Zr$_{2}$ with a tetragonal CuAl$_{2}$-type structure. In a recent study on FeZr$_{2}$ [M. Xu et al., Nat. Commun. 14, 4439 (2023)], the importance of optical phonons to the emergence of the $c$-axis NTE in FeZr$_{2}$ has been proposed. In this study, the physical properties of $Tr$Zr$_{2}$ ($Tr$ = Fe and Co$_{1-x}$Ni$_{x}$) have been studied by specific heat, sound velocity measurements, and theoretical phonon calculations to discuss the importance of optical phonons to the emergence of the $c$-axis NTE in CoZr$_{2}$ and FeZr$_{2}$. From analyses of lattice specific heat, we found that Ni substitution results in a systematic decrease in oscillator strength for the Einstein modes with 8.74 meV (CoZr$_{2}$). From phonon calculations, the low-energy optical phonon branches at the $Γ$ point were observed for CoZr$_{2}$ and FeZr$_{2}$ with $c$-axis NTE, but not in NiZr$_{2}$ with positive thermal expansion. The enhancement of phonon density of states near the above-mentioned optical phonon energy in CoZr$_{2}$ and FeZr$_{2}$ is consistent with the specific heat analyses. We propose the importance of the low-energy optical phonons to the emergence of the $c$-axis NTE in TrZr$_{2}$.

cond-mat.supr-con↗

arXiv2024

Aging Effects on Superconducting Properties of BiS2-Based Compounds: First-12-Year Restudy

Decomposition of superconductors sometimes becomes crucial when studying essential physical properties of the superconductors. For example, the cuprate superconductor YBa2Cu3O7-d decomposes by long-time air exposure. In this study, we investigate the aging effects on superconducting properties of BiS2-based superconductors Bi4O4S3 and LaO0.5F0.5BiS2, both were first synthesized in 2012, using their polycrystalline samples synthesized several years ago. We find that 12-year-old Bi4O4S3 samples exhibit bulk superconductivity with a slight degradation of the superconducting transition temperature (Tc) of 0.2 K. For a high-pressure-synthesized LaO0.5F0.5BiS2 sample, clear decrease in Tc is observed, which suggests that high-pressure strain is reduced by aging.

cond-mat.supr-con↗

arXiv2024

High entropy effect on thermoelectric properties of nonequilibrium cubic phase of AgBiSe2-2xSxTex with x = 0-0.6

Silver bismuth diselenide (AgBiSe2) has much attention as an efficient thermoelectric material due to its low thermal conductivity. However, AgBiSe2 exhibits multiple crystal structural transitions with temperature, and high thermoelectric performance was realized only in high-temperature cubic phase. We previously reported the stabilization of cubic phase in AgBiSe2-2xSxTex with x = 0.6-0.8 at room temperature by high-entropy-alloy (HEA) approach. The cubic HE-type AgBiSe0.8S0.6Te0.6 achieved a high ZT value of 0.8 at 748 K. In this paper, we succeeded in stabilizing the cubic phase in AgBiSe2-2xSxTex with x = 0-0.6 by ice-quenching method, and investigated the HE effect on the thermoelectric properties. Cubic AgBiSe2-2xSxTex exhibited n-type conductivity from 300 K to 10 K. We found that electronic conductivity was largely increased around room temperature with increasing the amount of S and Te, although carrier concentration showed almost the same values. The S and Te substitutions induced the variation of band structure, resulting in the carrier mobility enhancement. Furthermore, thermal conducutivity showed reduction tendency with increasing the amount of S and Te due to enhancement of phonon scattering. Simultaneous electronic conductivity increase and thermal conductivity reduction resulted in the systematic improvement of the ZT values for HE-type cubic AgBiSe2-2xSxTex.

cond-mat.mtrl-sci↗

arXiv2024

Vortex formation and exotic superconducting states in field-cooled Sn-Pb solders

Formation of vortices is a typical phenomenon of type-II superconductors under magnetic fields (H). In contrast, type-I superconductors do not host vortices because of their Meissner state. As rare cases, vortices have been observed in intermediate states of type-I superconductors; in addition, the recent observation of type-II superconductivity with vortices in a (originally type-I) Pb crystal film at extremely low temperature (T) under H has opened new pathway to study vortex physics. However, thermodynamic characteristics of such type-II-like superconducting states with vortices in originally type-I element superconductors have not been detected because of the lack of bulk example. In this study, we investigated superconducting states of phase-separated Sn-Pb solders using specific heat and magnetization to reveal magnetic-flux-trapping mechanisms. Here, we show that Sn islands in the Sn-Pb solders exhibit type-II-like superconducting states with vortices when the solders host extremely high magnetic fluxes after field cooling. Furthermore, with increasing T, the amount of trapped flux decreases, and the driving force of the magnetic flux changes from type-II superconducting states of Sn to supercurrent of Pb regions surrounding the Sn islands. The field-cooled Sn-Pb solders are rich in physics of bulk vortex formation and anomalously enhanced supercurrent in element (originally type-I) superconductors.

cond-mat.supr-con↗

arXiv2024

Stabilization and high thermoelectric performance of high-entropy-type cubic AgBi(S, Se, Te)2

As thermoelectric generators can convert waste heat into electricity, they play an important role in energy harvesting. The metal chalcogenide AgBiSe2 is one of the high-performance thermoelectric materials with low lattice thermal conductivity (klat), but it exhibits temperature-dependent crystal structural transitions from hexagonal to rhombohedral, and finally a cubic phase as the temperature rises. The high figure-of-merit ZT is obtained only for the high-temperature cubic phase. In this study, we utilized the high-entropy-alloy (HEA) concept for AgBiSe2 to stabilize the cubic phase throughout the entire temperature range with enhanced thermoelectric performance. We synthesized high-entropy-type AgBiSe2-2xSxTex bulk polycrystals and realized the stabilization of the cubic phase from room temperature to 800 K for x > 0.6. The ultra-low klat at of 0.30 Wm^-1K^-1 and the high peak ZT 0.9 at around 750 K were realized for cubic AgBiSe2-2xSxTex without carrier tuning. In addition, the average ZT value of x = 0.6 and 0.7 for the temperature range of 360-750 K increased to 0.38 and 0.40, respectively, which are comparable to the highest previously reported values.

cond-mat.mtrl-sci↗

arXiv2024

Spontaneous formation of Frenkel defects in high-entropy-alloys-type compound

High-entropy alloys (HEAs) are attracting attention due to their exceptional properties, such as enhanced mechanical toughness, superconducting robustness, and thermoelectric performance. Numerous HEAs have been developed for diverse applications, ranging from self-healing in fusion reactors to addressing environmental concerns with thermoelectric materials. Understanding atomic diffusion within HEA crystals is crucial for these applications. Here, this study investigates diffusion mechanisms in PbTe-based HEAs, focusing on the role of indium (In). Molecular dynamics simulations reveal that In inclusion prompts spontaneous Frenkel defect formation, notably enhancing diffusion not only of In$^+$ but also other cations. Frenkel defect formation, closely linked to alloy properties, is predominantly influenced by charge rather than cation size. This insight not only enhances comprehension of HEA diffusion mechanisms but also develops HEAs with properties such as self-healing from damage and high ion permeability, advancing the field of material science.

cond-mat.mtrl-sci↗

arXiv2023

Magnetic field hysteresis of thermal conductivity in type-I and typy-II superconductors

This study investigated the magnetic field ($H$) dependence of thermal conductivity ($κ$) in type I (Pb) and type II (Nb) superconductors. The $κ$ of Nb displayed hysteresis, showing a local minimum during increasing $H$ process but not during decreasing $H$ process. Different magnetic field dependencies were observed in Pb with varying purity: $κ$ of 3N-Pb exhibited broad hysteresis, while that of 5N-Pb showed hysteresis similar to 3N-Nb.

cond-mat.supr-con↗

arXiv2023

Observation of superconductivity and enhanced upper critical field of $η$-carbide-type oxide Zr${_\mathrm{4}}$Pd$_{\mathrm{2}}$O

We report the first observation of bulk superconductivity of a $η$-carbide-type oxide Zr$_{4}$Pd$_{2}$O. The crystal structure and the superconducting properties were studied through synchrotron X-ray diffraction, magnetization, electrical resistivity, and specific heat measurement. The superconducting transition was observed at $T_{\mathrm{c}}$ = 2.73 K. Our measurement revealed that the $η$-carbide-type oxide superconductor Zr$_{4}$Pd$_{2}$O shows an enhanced upper critical field ${μ_{\mathrm{0}}H_{\mathrm{c2}}\mathrm{(0)}}$ = 6.72 T, which violates the Pauli-Clogston limit ${μ_{\mathrm{0}}H_{\mathrm{P}}}$ = 5.29 T. On the other hand, we found that the enhanced upper critical field is absent in a Rh analogue Zr$_{4}$Rh$_{2}$O. The large ${μ_{\mathrm{0}}H_{\mathrm{c2}}\mathrm{(0)}}$ of Zr$_{4}$Pd$_{2}$O would be raised from strong spin-orbit coupling with Pd-4$d$ electrons. The discovery of new superconducting properties for Zr$_{4}$Pd$_{2}$O would shed light on the further development of $η$-carbide-type oxide superconductors.

cond-mat.supr-con↗

arXiv2023

Effect of annealing in eutectic high-entropy alloy superconductor NbScTiZr

We investigated the impact of annealing on the structural characteristics and superconducting critical temperature ($T_\mathrm{c}$) of the eutectic high-entropy alloy (HEA) superconductor NbScTiZr. The HEA manifests an eutectic microstructure composed of body-centered cubic (bcc) and hexagonal close-packed phases. Both the lattice parameters of the bcc phase and grain size of the eutectic structure exhibited pronounced sensitivity to variations in annealing temperature. The observed dependence of the lattice parameter on annealing temperature supports the possibility that lattice strain occurs at lower annealing temperatures. The as-cast sample demonstrated superconductivity at $T_\mathrm{c}$ of 7.9 K, which increased to 9 K after annealing at 800 $^{\circ}$C. However, when subjected to annealing at 1000 $^{\circ}$C, $T_\mathrm{c}$ diminishes to 8.7 K. The annealing-temperature dependence of $T_\mathrm{c}$ cannot be comprehensively elucidated based solely on the electronic density of states at the Fermi level. It is plausible that the lattice strain may influence the annealing temperature dependence of $T_\mathrm{c}$. Our results for the critical current density $J_{c}$ reveal that the self-field $J_{c}$ of the as-cast NbScTiZr at 2 K exceeds 10$^{6}$ A/cm$^{2}$.

cond-mat.supr-con↗

arXiv2023

Pressure-induced volumetric negative thermal expansion in CoZr2 superconductor

We investigate the thermal expansion and superconducting properties of a CuAl2-type (tetragonal) superconductor CoZr2 under high pressures. We perform high-pressure synchrotron X-ray diffraction in a pressure range of 2.9 GPa < P < 10.4 GPa and discover that CoZr2 exhibits volumetric negative thermal expansion under high pressures. Although the uniaxial positive thermal expansion (PTE) along the a-axis is observed under ambient pressure, that is suppressed by pressure, while the large uniaxial negative thermal expansion (NTE) along the c-axis is maintained under the pressure regime. As a result of a combination of the suppressed uniaxial PTE along the a-axis and uniaxial NTE along the c-axis, volumetric negative thermal expansion is achieved under high pressure in CoZr2. The mechanisms of volumetric NTE would be based on the flexible crystal structure caused by the soft Co-Co bond as seen in the iso-structural compound FeZr2, which exhibits uniaxial NTE along the c-axis. We also perform high-pressure electrical resistance measurements of CoZr2 to confirm the presence of superconductivity under the examined pressure regime in the range of 0.03 GPa < P < 41.9 GPa. We confirm the presence of superconductivity under all pressures and observe dome-like shape pressure dependence of superconducting transition temperature. Because of the coexistence of two phenomena, which are volumetric NTE and superconductivity, in CoZr2 under high pressure, the coexistence would be achievable under ambient pressure by tuning chemical compositions after our present observation.

cond-mat.mtrl-sci↗

arXiv2023

Observation of nonvolatile magneto-thermal switching in superconductors

Applying a magnetic field to a solid changes its thermal-transport properties. Although such magneto-thermal-transport phenomena are usually small effects, giant magneto-thermal resistance has recently been observed in spintronic materials1,2 and superconductors3,4, opening up new possibilities in thermal management technologies. However, the thermal conductivity conventionally changes only when a magnetic field is applied due to the absence of nonvolatility, which limits potential applications of thermal switching devices5,6. Here, we report the observation of nonvolatile thermal switching that changes the thermal conductivity when a magnetic field is applied and retains the value even when the field is turned off. This unconventional magneto-thermal switching, surprisingly, arises in commercial Sn-Pb solders and is realized by phase-separated superconducting states and resultant nonuniform magnetic flux distributions. This result confirms the versatility of the observed phenomenon and aids the development of active solid-state thermal management devices.

cond-mat.mtrl-sci↗

arXiv2023

Anomalous Field-Temperature Phase Diagram of Superconductivity in Sn-Pb Solder

Sn-Pb solders are superconducting materials whose Sn and Pb are perfectly phase-separated. Recently, anomalous magnetic-flux trapping in a Sn45-Pb55 solder has been revealed where the magnetic fluxes are selectively trapped in the Sn regions due to the supercurrents in the surrounding Pb regions. Here, we report on the observation of the anomalous critical field (Hc)-temperature (T) phase diagram of superconductivity in the Sn45-Pb55 solder. Although the Hc(T) for the Pb regions decreases with increasing field as in normal type-I superconductors and is consistent with the conventional trend with Hc(0) ~ 800 Oe, the Hc(T) for the Sn regions exhibits anomalous behaviors. The most noticeable trend was observed in the field-cooled (under 1500 Oe) solder. The Hc-T phase diagram for the Sn regions largely varies when the applied external field is reversed, and Tc increases with increasing field amplitude when H < 0 Oe is applied. On the basis of the flux trapping and the observed anomalous Hc-T phase diagrams, we propose that the field-robust superconductivity in the Sn regions is related to the ferromagnetically-aligned magnetic fluxes (or formation of vortices) in the Sn regions of the Sn45-Pb55 solder.

cond-mat.supr-con↗

arXiv2023

Absence of Tc-Pinning Phenomenon Under High Pressure in High-Entropy REO0.5F0.5BiS2 Layered Superconductor

Recently, robustness of superconductivity (transition temperature, Tc) under high pressures has been observed in high-entropy alloy (HEA), bcc-type Ti-Zr-Hf-Nb-Ta, and HEA-type compounds (Ag,In,Sn,Pb,Bi)Te with a NaCl-type structure. Since those materials have three-dimensional crystal structure, investigation on the pressure dependence of Tc of low-dimensional materials is needed to understand the phenomena. Here, we investigated the superconducting properties and the crystal structure of BiS2-based layered system REO0.5F0.5BiS2. Although the robustness of Tc was induced in MTe with increasing M-site configurational entropy, the increase in RE-site configurational entropy does not induce robustness of Tc under high pressures in REO0.5F0.5BiS2. The crystal structure of HEA-type REO0.5F0.5BiS2 was confirmed as monoclinic P21/m, which is the same space group as the zero-entropy counterpart LaO0.5F0.5BiS2. The results suggest that an increase in configurational entropy at blocking layers do not affect crystal structure and superconducting properties under high pressures in the BiS2-based layered system.

cond-mat.supr-con↗