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Journal Articles

Field induced multiple superconducting phases in UTe$$_2$$ along hard magnetic axis

Sakai, Hironori; Tokiwa, Yoshifumi; Opletal, P.; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori

Physical Review Letters, 130(19), p.196002_1 - 196002_6, 2023/05

The superconducting (SC) phase diagram in uranium ditelluride is explored under magnetic fields ($$H$$) along the hard magnetic $$b$$-axis using a high-quality single crystal with $$T_{rm c}$$ = 2.1 K. Simultaneous electrical resistivity and AC magnetic susceptibility measurements discern low- and high-field SC (LFSC and HFSC, respectively) phases with contrasting field-angular dependence. Crystal quality increases the upper critical field of the LFSC phase, but the $$H^{ast}$$ of $$sim15$$ T, at which the HFSC phase appears, is always the same through the various crystals. A phase boundary signature is also observed inside the LFSC phase near $$H^{ast}$$, indicating an intermediate SC phase characterized by small flux pinning forces.

Journal Articles

Improved immobilization of Re(VII) from aqueous solutions $$via$$ bimetallic Ni/Fe$$^{0}$$ nanoparticles; Implications towards Tc(VII) removal

Maamoun, I.; Tokunaga, Kohei; Dohi, Terumi; Kanno, Futoshi*; Falyouna, O.*; Eljamal, O.*; Tanaka, Kazuya

Frontiers in Nuclear Engineering (Internet), 2, p.1142823_1 - 1142823_17, 2023/03

Recently, the rapid development of nuclear power technologies and the continuous energy demand around the world exhibited massive amounts of contaminated water with radionuclides. Technetium-99 ($$^{99}$$Tc) is one of the long-lived radionuclides with a highly mobile anionic form (Tc(VII)) in aqueous solutions. Hence, the rapid and efficient Tc(VII) removal from radioactive water has emerged as a challenging issue. In this work, bimetallic nickel/iron nanoparticles (Ni/Fe$$^{0}$$) were prepared to enhance the immobilization of rhenium (Re(VII)) from aqueous solutions, as the surrogate of Tc(VII).

Journal Articles

Ferromagnetic crossover within the ferromagnetic order of U$$_{7}$$Te$$_{12}$$

Opletal, P.; Sakai, Hironori; Haga, Yoshinori; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Kambe, Shinsaku; Tokunaga, Yo

Journal of the Physical Society of Japan, 92(3), p.034704_1 - 034704_5, 2023/03

 Times Cited Count:0 Percentile:0.02(Physics, Multidisciplinary)

We investigate the physical properties of a single crystal of uranium telluride U$$_{7}$$Te$$_{12}$$. We have confirmed that U$$_{7}$$Te$$_{12}$$ crystallizes in the hexagonal structure with three nonequivalent crystallographic uranium sites. The paramagnetic moments are estimated to be approximately 1 $$mu_{B}$$ per the uranium site, assuming a uniform moment on all the sites. A ferromagnetic phase transition occurs at $$T_{rm C}$$= 48 K, where the in-plane magnetization increases sharply, whereas the out of-plane component does not increase significantly. With decreasing temperature further below $$T_{rm C}$$ under field-cooling conditions, the out-of-plane component increases rapidly around T$$^{star}$$= 26 K. In contrast, the in-plane component hardly changes at T$$^{star}$$. Specific heat measurement indicates no $$lambda$$-type anomaly around T$$^{star}$$, so this is a cross-over suggesting a reorientation of the ordering moments or successive magnetic ordering on the part of the multiple uranium sites.

Journal Articles

An Answer after 50 Years

Tokunaga, Yo

JPSJ News and Comments (Internet), 19, p.20_1 - 20_2, 2022/12

Journal Articles

Nested antiferromagnetic spin fluctuations and non-Fermi-liquid behavior in electron-doped CeCo$$_{1-x}$$Ni$$_{x}$$In$$_5$$

Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Zhu, J.-X.*; Ronning, F.*; Thompson, J. D.*; Kotegawa, Hisashi*; To, Hideki*; Suzuki, Kohei*; Oshima, Yoshiki*; et al.

Physical Review B, 106(23), p.235152_1 - 235152_8, 2022/12

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

We investigate the electronic state of Ni-substituted CeCo$$_{1-x}$$Ni$$_x$$In$$_5$$ by nuclear quadrupole and magnetic resonance (NQR/NMR) techniques. The heavy fermion superconductivity below $$T_{rm c} = 2.3$$ K for $$x = 0$$ is suppressed by Ni substitutions, and $$T_{rm c}$$ reaches zero for $$x = 0.25$$. The $$^{115}$$In NQR spectra for $$x = 0.125$$ and 0.25 can be explained by simulating the electrical field gradient that is calculated for a virtual supercell with density functional theory. The spin-lattice relaxation rate $$1/T_1$$ indicates that Ni substitution weakens antiferromagnetic correlations that are not localized near the substituent but instead are uniform in space. The temperature ($$T$$) dependence of $$(T_1T)^{-1}$$ for $$x = 0.25$$ shows a maximum around $$T_{rm g} = 2$$ K and $$(T_1T)^{-1}$$ decreases toward almost zero when temperature is further reduced as if a gap might be opening in the magnetic excitation spectrum; however, the magnetic specific heat and the static magnetic susceptibility evolve smoothly through $$T_{rm g}$$ with a $$-ln T$$ dependence. The peculiar T dependence of $$(T_1T)^{-1}$$ and non-Fermi-liquid specific heat and susceptibility can be interpreted in a unified way by assuming nested antiferromagnetic spin fluctuations in a quasi-two-dimensional electronic system.

Journal Articles

Single crystal growth of superconducting UTe$$_2$$ by molten salt flux method

Sakai, Hironori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Tokunaga, Yo; Kambe, Shinsaku; Haga, Yoshinori

Physical Review Materials (Internet), 6(7), p.073401_1 - 073401_10, 2022/07

 Times Cited Count:3 Percentile:74.68(Materials Science, Multidisciplinary)

The molten salt flux method is applied as a new synthetic route for the single crystals of the spin-triplet superconductor UTe$$_2$$. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at $$T_{rm c}=2.1$$ K, which is the highest $$T_{rm c}$$ reported for this compound. The obtained crystals show a remarkably large residual resistivity ratio with respect to the room temperature value and a small residual electronic contribution in specific heat well below $$T_{rm c}$$. These results indicate that the increase of $$T_{rm c}$$ in UTe$$_2$$ can be achieved by reducing the disorder associated with uranium vacancies. The excess uranium in the molten salt acts as a reducing agent, preventing tetravalent uranium from becoming pentavalent and suppressing creation of uranium vacancies. At the same time, the relatively low growth temperature can suppress Te volatilization.

Journal Articles

Unconventional superconductivity in UTe$$_2$$

Aoki, Dai*; Brison, J.-P.*; Flouquet, J.*; Ishida, Kenji*; Knebel, G.*; Tokunaga, Yo; Yanase, Yoichi*

Journal of Physics; Condensed Matter, 34(24), p.243002_1 - 243002_41, 2022/06

 Times Cited Count:24 Percentile:92.97(Physics, Condensed Matter)

Journal Articles

Urea-introduced ionic liquid for the effective extraction of Pt(IV) and Pd(II) ions

Ueda, Yuki; Eguchi, Ayano; Tokunaga, Kohei; Kikuchi, Kei*; Sugita, Tsuyoshi; Okamura, Hiroyuki; Naganawa, Hirochika

Industrial & Engineering Chemistry Research, 61(19), p.6640 - 6649, 2022/05

 Times Cited Count:0 Percentile:0(Engineering, Chemical)

no abstracts in English

Journal Articles

Effect of uranium deficiency on normal and superconducting properties in unconventional superconductor UTe$$_2$$

Haga, Yoshinori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori

Journal of Physics; Condensed Matter, 34(17), p.175601_1 - 175601_7, 2022/04

 Times Cited Count:8 Percentile:91.19(Physics, Condensed Matter)

Journal Articles

Multipole polaron in the devil's staircase of CeSb

Arai, Yosuke*; Kuroda, Kenta*; Nomoto, Takuya*; Tin, Z. H.*; Sakuragi, Shunsuke*; Bareille, C.*; Akebi, Shuntaro*; Kurokawa, Kifu*; Kinoshita, Yuto*; Zhang, W.-L.*; et al.

Nature Materials, 21(4), p.410 - 415, 2022/04

 Times Cited Count:4 Percentile:85.24(Chemistry, Physical)

Journal Articles

Drastic change in magnetic anisotropy of UTe$$_2$$ under pressure revealed by $$^{125}$$Te-NMR

Kinjo, Katsuki*; Fujibayashi, Hiroki*; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; et al.

Physical Review B, 105(14), p.L140502_1 - L140502_5, 2022/04

 Times Cited Count:3 Percentile:78.61(Materials Science, Multidisciplinary)

Journal Articles

Slow electronic dynamics in the paramagnetic state of UTe$$_2$$

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Haga, Yoshinori; Tokiwa, Yoshifumi; Opletal, P.; Fujibayashi, Hiroyuki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; et al.

Journal of the Physical Society of Japan, 91(2), p.023707_1 - 023707_5, 2022/02

 Times Cited Count:8 Percentile:94.37(Physics, Multidisciplinary)

$$^{125}$$Te NMR experiments in field ($$H$$) applied along the easy magnetization axis (the $$a$$-axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe$$_2$$. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 30$$-$$40 K, where the spin susceptibility along the hard magnetization axis (the $$b$$-axis) shows a broad maximum. The experiments also imply that tiny amounts of disorder or defects locally disturb the long-range electronic correlations and develop an inhomogeneous electronic state at low temperatures, leading to a low temperature upturn observed in the bulk-susceptibility in $$H|a$$. We suggest that UTe$$_2$$ would be located on the paramagnetic side near an electronic phase boundary, where either the magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations.

Journal Articles

Coexistence of magnetoelectric and antiferroelectric-like orders in Mn$$_{3}$$Ta$$_{2}$$O$$_{8}$$

Kimura, Kenta*; Yagi, Naoki*; Hasegawa, Shunsuke*; Hagihara, Masato; Miyake, Atsushi*; Tokunaga, Masashi*; Cao, H.*; Masuda, Takatsugu*; Kimura, Tsuyoshi*

Inorganic Chemistry, 60(20), p.15078 - 15084, 2021/10

 Times Cited Count:0 Percentile:0.01(Chemistry, Inorganic & Nuclear)

Journal Articles

Nanoscale heterogeneity induced by nonmagnetic Zn dopants in the quantum critical metal CeCoIn$$_5$$; $$^{115}$$In NQR/NMR and $$^{59}$$Co NMR study

Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Zhu, J.-X.*; Ronning, F.*; Thompson, J. D.*; Ramakrishna, S. K.*; Reyes, A. P.*; Suzuki, Kohei*; Oshima, Yoshiki*; et al.

Physical Review B, 104(8), p.085106_1 - 085106_12, 2021/08

 Times Cited Count:2 Percentile:28.94(Materials Science, Multidisciplinary)

Antiferromagnetism in a prototypical quantum critical metal CeCoIn$$_5$$ is known to be induced by slight substitutions of non-magnetic Zn atoms for In. In nominally 7% Zn substituted CeCoIn$$_5$$, an antiferromagnetic (AFM) state coexists with heavy fermion superconductivity. Heterogeneity of the electronic states is investigated in Zn doped CeCoIn$$_5$$ by means of nuclear quadrupole and magnetic resonances (NQR and NMR). Site-dependent NQR relaxation rates $$1/T_1$$ indicate that the AFM state is locally nucleated around Zn substituents in the matrix of a heavy fermion state, and percolates through the bulk at the AFM transition temperature $$T_{rm N}$$. At lower temperatures, an anisotropic superconducting (SC) gap below the SC transition temperature $$T_{rm c}$$, and the SC state permeates through the AFM regions via a SC proximity effect. Applying an external magnetic field induces a spin-flop transition near 5 T, reducing the volume of the AFM regions. Consequently, a short ranged inhomogeneous AFM state survives and coexists with a paramagnetic Fermi liquid state at high fields.

Journal Articles

Anisotropic physical properties of layered antiferromagnet U$$_2$$Pt$$_6$$Ga$$_{15}$$

Matsumoto, Yuji*; Haga, Yoshinori; Yamamoto, Etsuji; Takeuchi, Tetsuya*; Miyake, Atsushi*; Tokunaga, Masashi*

Journal of the Physical Society of Japan, 90(7), p.074707_1 - 074707_6, 2021/07

 Times Cited Count:0 Percentile:0(Physics, Multidisciplinary)

Journal Articles

Critical slowing-down and field-dependent paramagnetic fluctuations in the skyrmion host EuPtSi; $$mu$$SR and NMR studies

Higa, Nonoka*; Ito, Takashi; Yogi, Mamoru*; Hattori, Taisuke; Sakai, Hironori; Kambe, Shinsaku; Guguchia, Z.*; Higemoto, Wataru; Nakashima, Miho*; Homma, Yoshiya*; et al.

Physical Review B, 104(4), p.045145_1 - 045145_7, 2021/07

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

Journal Articles

Inhomogeneous superconducting state probed by $$^{125}$$Te NMR on UTe$$_2$$

Nakamine, Genki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; Homma, Yoshiya*; et al.

Journal of the Physical Society of Japan, 90(6), p.064709_1 - 064709_7, 2021/06

 Times Cited Count:12 Percentile:86.17(Physics, Multidisciplinary)

Journal Articles

Effective removal of iodate by coprecipitation with barite; Behavior and mechanism

Tokunaga, Kohei; Takahashi, Yoshio*; Tanaka, Kazuya; Kozai, Naofumi

Chemosphere, 266, p.129104_1 - 129104_10, 2021/03

 Times Cited Count:4 Percentile:43.67(Environmental Sciences)

Radioactive iodine ($$^{129}$$I) is of great concern owing to its high mobility in the environment and long-term radiotoxicity, but there is a lack of effective techniques for removing iodate (IO$$_{3}$$$$^{-}$$) from aqueous solution. The aim of this study is to develop a new technique for removing radioactive iodate from contaminated solution by using barite (BaSO$$_{4}$$). In the present study, we examined the coprecipitation mechanism of iodate by barite at the molecular level for determining optimum conditions for iodate removal. The results showed that iodate was effectively removed from aqueous solution by coprecipitation, even in the presence of competitive anions in solution. Comparing our method with previous studies, iodate removal efficiency by barite was determined to be about two orders of magnitude greater than that by hydrotalcite-like layered double hydroxide at Cl$$^{-}$$ concentration of 10 mmol L$$^{-1}$$. Extended X-ray absorption fine structure (EXAFS) analysis indicated that incorporated iodate was strongly bound in the crystal lattice of barite by substituting the sulfate site in the structure when the iodine concentration was low. The charge compensation problem from the IO$$_{3}$$$$^{-}$$ substitution in SO$$_{4}$$$$^{2-}$$ site is achieved by the substitution of Na$$^{+}$$-IO$$_{3}$$$$^{-}$$ pairs at the nearest Ba$$^{2+}$$ site. Therefore, considering high removal efficiency and strong binding of iodate in barite, coprecipitation with barite is a promising material for removing radioactive iodate from various aqueous solutions contaminated with iodate.

Journal Articles

Anisotropic response of spin susceptibility in the superconducting state of UTe$$_2$$ probed with $$^{125}$$Te-NMR measurement

Nakamine, Genki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; Homma, Yoshiya*; et al.

Physical Review B, 103(10), p.L100503_1 - L100503_5, 2021/03

 Times Cited Count:20 Percentile:91.69(Materials Science, Multidisciplinary)

Journal Articles

Universal scaling behavior under pressure in the heavy-fermion antiferromagnet CeRh$$_2$$Si$$_2$$; $$^{29}$$Si NMR study

Sakai, Hironori; Matsumoto, Yuji*; Haga, Yoshinori; Tokunaga, Yo; Kambe, Shinsaku

Physical Review B, 103(8), p.085114_1 - 085114_8, 2021/02

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

The microscopic origin of a magnetic phase diagram under pressure in a heavy fermion antiferromagnet CeRh$$_2$$Si$$_2$$ was investigated using the $$^{29}$$Si nuclear magnetic resonance (NMR) technique. We investigated the temperature and pressure dependencies of $$q$$-independent local fluctuations caused by the single-site Kondo effect. A universal scaling behavior observed on the energy scale of the local fluctuations in an entire pressure region demonstrates that a characteristic energy scale $$T_0$$ of Kondo interactions monotonically increases by applying pressure without a critical anomaly around the quantum critical pressure $$P_{rm c}$$ of antiferromagnetism. Our NMR result agrees with the Doniach picture of the heavy-fermion phase diagram, where the progressive delocalization of the $$f$$-electrons occurs across $$P_{rm c}$$, accompanied by the development of antiferromagnetic correlations among the $$f$$-electrons.

405 (Records 1-20 displayed on this page)