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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

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

$$^{125}$$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

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

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

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:1 Percentile:65.97(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

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.

Journal Articles

A Fluorous phosphate for the effective extraction of Ln$$^{III}$$ from nitrate media; Comparison with a conventional organic phosphate

Ueda, Yuki; Kikuchi, Kei*; Tokunaga, Kohei; Sugita, Tsuyoshi; Aoyagi, Noboru; Tanaka, Kazuya; Okamura, Hiroyuki

Solvent Extraction and Ion Exchange, 39(5-6), p.491 - 511, 2021/00

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

no abstracts in English

Journal Articles

Devil's staircase transition of the electronic structures in CeSb

Kuroda, Kenta*; Arai, Yosuke*; Rezaei, N.*; Kunisada, So*; Sakuragi, Shunsuke*; Alaei, M.*; Kinoshita, Yuto*; Bareille, C.*; Noguchi, Ryo*; Nakayama, Mitsuhiro*; et al.

Nature Communications (Internet), 11, p.2888_1 - 2888_9, 2020/06

 Times Cited Count:3 Percentile:42.38(Multidisciplinary Sciences)

Journal Articles

$$^{33}$$S nuclear magnetic resonance spectra of uranium disulfide $$beta$$-US$$_2$$

Sakai, Hironori; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Ramakrishna, S. K.*; Reyes, A. P.*; Rosa, P. F. S.*; Ronning, F.*; Thompson, J. D.*; Fisk, Z.*; et al.

JPS Conference Proceedings (Internet), 30, p.011169_1 - 011169_6, 2020/03

Uranium disulfide $$beta$$-US$$_2$$ showing a semimetal-to-semiconductor crossover has been investigated by the nuclear magnetic resonance (NMR) technique for $$^{33}$$S nuclei with the nuclear spin of $$I=3/2$$. Since the natural concentration 0.76% of NMR active $$^{33}$$S nuclei is too dilute, the isotopic enrichment to $$sim$$50% has been carried out for the single crystal growth. The $$^{33}$$S NMR spectra have been successfully obtained using a single crystal of $$beta$$-US$$_2$$ with external fields along the crystallographic $$c$$ axis. The S sites assignments have been made based on these NMR spectra.

Journal Articles

$$^{125}$$Te-NMR study on a single crystal of heavy fermion superconductor UTe$$_2$$

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; Higa, Nonoka; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 88(7), p.073701_1 - 073701_4, 2019/07

 Times Cited Count:29 Percentile:95.25(Physics, Multidisciplinary)

We report $$^{125}$$Te-NMR studies on a newly discovered heavy fermion superconductor UTe$$_2$$. Using a single crystal, we have measured the $$^{125}$$Te-NMR Knight shift $$K$$ and spin-lattice relaxation rate $$1/T_1$$ for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static ($$K$$) and dynamical susceptibilities ($$1/T_1$$) in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate $$1/T_2$$, when the field is applied along the easy axis of magnetization (=$$a$$ axis). This behavior suggests the development of longitudinal magnetic fluctuations along the $$a$$ axis at very low frequencies below 20 K.

Journal Articles

Mass transport in the PdCu phase structures during hydrogen adsorption and absorption studied by XPS under hydrogen atmosphere

Tang, J.*; Yamamoto, Susumu*; Koitaya, Takanori*; Yoshigoe, Akitaka; Tokunaga, Takuma*; Mukai, Kozo*; Matsuda, Iwao*; Yoshinobu, Jun*

Applied Surface Science, 480, p.419 - 426, 2019/06

 Times Cited Count:2 Percentile:22.92(Chemistry, Physical)

Mass transports during hydrogen adsorption and absorption processes of PdCu alloys that has advantages of higher hydrogen diffusivity and economically lower-cost than the other Pd-alloys were studied. The research was made with a comparison of the well-known ordered phase of the bcc structure (the B2 phase) and a mixed phase of the fcc and B2 structures. ${it In-situ}$ ultrahigh vacuum X-ray photoelectron spectroscopy and ambient pressure X-ray photoelectron spectroscopy using synchrotron radiation were carried out to trace the chemical states of the Pd and Cu atoms as a function of temperatures. It is elucidated that the initial adsorption and absorption processes were similar in the two phases, but a hydrogen diffusion rate to the bulk was higher in the ordered phase than in the mixed one. We found the dynamics of the Pd and Cu atoms during the hydrogen adsorption/absorption processes largely depend on temperature. In the hydrogen atmosphere, the Pd atoms segregate at the surface below 373 K and Cu atoms segregate at the surface above 373 K. The present results agree well with the previous theoretical calculations and, thus, provide appropriate inputs toward developments of the hydrogen permeation materials.

Journal Articles

Magnetic and electrical properties of the ternary compound U$$_2$$Ir$$_3$$Si$$_5$$ with one-dimensional uranium zigzag chains

Li, D. X.*; Honda, Fuminori*; Miyake, Atsushi*; Homma, Yoshiya*; Haga, Yoshinori; Nakamura, Ai*; Shimizu, Yusei*; Maurya, A.*; Sato, Yoshiki*; Tokunaga, Masashi*; et al.

Physical Review B, 99(5), p.054408_1 - 054408_9, 2019/02

 Times Cited Count:2 Percentile:22.92(Materials Science, Multidisciplinary)

Journal Articles

High-field phase diagram of the heavy-fermion metal CeIn$$_3$$; Pulsed-field NMR study on single crystals up to 56 T

Tokunaga, Yo; Orlova, A.*; Bruyant, N.*; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Higa, Nonoka; et al.

Physical Review B, 99(8), p.085142_1 - 085142_5, 2019/02

 Times Cited Count:3 Percentile:33.95(Materials Science, Multidisciplinary)

The heavy-fermion antiferromagnet CeIn$$_3$$ exhibits a field-induced anomaly associated with Fermi surface reconstruction at $$H^*sim$$ 45 T, well below the antiferromagnetic (AFM) critical field that exceeds 60 T. In order to explore the origin of this anomaly, we have measured $$^{115}$$In NMR spectra in pulsed magnetic fields up to 56 T using high-quality single crystals. To within experimental resolution, we do not detect any change in the NMR spectra that could suggest a modification in either the character of the hyperfine field or the electric field gradient at In sites through $$H^*$$. This strongly suggests that the 45 T anomaly cannot be simply ascribed to a field-induced change in the magnetic structure of the AFM state.

Journal Articles

Occupation sites and valence states of Co dopants in (La, Co)-codoped M-type Sr ferrite; $$^{57}$$Fe and $$^{59}$$Co nuclear magnetic resonance studies

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ueda, Hiroaki*; Tanioku, Yasuaki*; Michioka, Chishiro*; Yoshimura, Kazuyoshi*; Takao, Kenta*; Shimoda, Aiko*; et al.

Physical Review B, 98(6), p.064403_1 - 064403_10, 2018/08

 Times Cited Count:6 Percentile:45.58(Materials Science, Multidisciplinary)

To specify preferential occupation sites of Co substituents and to clarify charge and spin states of Co ions in (La, Co)-cosubstituted hexagonal magnetoplumbite-type (M-type) Sr ferrite, $$^{57}$$Fe and $$^{59}$$Co nuclear magnetic resonance (NMR) spectra are measured under zero and external magnetic fields using powdered and single crystalline specimens. To a considerable degree, the charge compensation between La$$^{3+}$$ and Co$$^{2+}$$ works in the equal (La, Co)-codoped case, where more than half of the Co ions are considered to be present in the minority spin $$4f_1$$ sites at the center of the oxygen tetrahedra, with the $$S$$ = 3/2 state carrying a small orbital moment owing to spin-orbit interaction. The remaining small number of high-spin Co$$^{2+}$$ ($$S$$ = 3/2, $$L$$ = 1) ions with unquenched orbital moments would be distributed to the other octahedral $$12k$$, $$2a$$, and $$4f_2$$ sites.

Journal Articles

A New technique for removing strontium from seawater by coprecipitation with barite

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

Journal of Hazardous Materials, 359, p.307 - 315, 2018/07

 Times Cited Count:11 Percentile:59.27(Engineering, Environmental)

In the present study, we looked at the removal efficiency of Sr by using barite (BaSO$$_{4}$$) under various experimental conditions to develop techniques for the direct removal of Sr from seawater. The uptake of Sr by barite was found to be dependent on pH, saturation state, and [Ba$$^{2+}$$]/[SO$$_{4}$$$$^{2-}$$] ratio in initial aqueous solution, showing that most of the aqueous Sr can be removed from the aqueous solution by adjusting these parameters. However, the effects of ionic strength and competitive ions were negligible, suggesting the effectiveness of its application to removal of Sr from seawater. Batch experiments were also conducted in a seawater system, and a rather high removal efficiency of Sr from seawater (more than 90%) was achieved. Considering its high removal and retention efficiency of Sr in seawater systems, barite is a reliable material for the removal of Sr from seawater.

Journal Articles

Magnetization, specific heat, $$^{17}$$O NMR, and $$^{237}$$Np M$"o$ssbauer study of U$$_{0.15}$$Np$$_{0.85}$$O$$_2$$

Martel, L.*; Hen, A.*; Tokunaga, Yo; Kinnart, F.*; Magnani, N.*; Colineau, E.*; Griveau, J.-C.*; Caciuffo, R.*

Physical Review B, 98(1), p.014410_1 - 014410_8, 2018/07

 Times Cited Count:2 Percentile:8.26(Materials Science, Multidisciplinary)

We report a study of the magnetic and electronic properties of the U$$_{0.15}$$Np$$_{0.85}$$O$$_2$$ solid solution, based on dc- and ac- magnetisation, $$^{237}$$Np M$"o$ssbauer spectroscopy, $$^{17}$$O Nuclear Magnetic Resonance (NMR), and specific heat measurements. The compound orders antiferromagnetically at T$$_N$$ = 17 K. The different techniques reveal the complexity of this system with:(1) a spatial distribution of ordered moments, (2) a small Np ordered moment, and (3) an additional specific heat anomaly at 7.4 K, with a residual value at very low temperature and a reduced magnetic entropy. The results are compared to the end-members of the series, UO$$_2$$ and NpO$$_2$$, as well as to the other solid solutions previously reported in this system. We discuss how the properties of U$$_{0.15}$$Np$$_{0.85}$$O$$_2$$ add new input to the trend previously reported for the series, in view of the models that have been previously proposed.

Journal Articles

Easy-plane XY spin fluctuations in the cycloidal magnet UPtGe studied via field orientation-dependent $$^{195}$$Pt NMR

Tokunaga, Yo; Nakamura, Ai*; Aoki, Dai*; Shimizu, Yusei*; Homma, Yoshiya*; Honda, Fuminori*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku

Physical Review B, 98(1), p.014425_1 - 014425_5, 2018/07

 Times Cited Count:1 Percentile:8.26(Materials Science, Multidisciplinary)

$$^{195}$$Pt NMR measurements have been performed on a single crystal of the uranium-based compound UPtGe, which is the only 5f system known to possess an incommensurate helical (cycloidal) structure below TN = 50 K. Knight shift measurement confirmed the isotropic character of the static spin susceptibilities in hexagonal-like ac crystal planes of the EuAuGe-type crystal structure. The hyperfine coupling constants were also found to be isotropic in the planes. Nuclear relaxation rate measurement revealed the development of the antiferro-magnetic spin fluctuations with XY character confined to the hexagonal-like plane below 200 K. The results present a clear contrast to the Ising anisotropy of the fluctuations in ferromagnetic superconductors UCoGe and URhGe.

Journal Articles

Magnetic field induced phenomena in UIrGe in fields applied along the $$b$$ axis

Posp$'i$$v{s}$il, J.*; Haga, Yoshinori; Kohama, Yoshimitsu*; Miyake, Atsushi*; Kambe, Shinsaku; Tateiwa, Naoyuki; Vali$v{s}$ka, M.*; Proschek, P.*; Prokle$v{s}$ka, J.*; Sechovsk$'y$, V.*; et al.

Physical Review B, 98(1), p.014430_1 - 014430_7, 2018/07

 Times Cited Count:10 Percentile:63.24(Materials Science, Multidisciplinary)

Journal Articles

Odd-parity electronic multipolar ordering in URu$$_2$$Si$$_2$$; Conclusions from Si and Ru NMR measurements

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Higa, Nonoka; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*; Harima, Hisatomo*

Physical Review B, 97(23), p.235142_1 - 235142_10, 2018/06


 Times Cited Count:16 Percentile:77.41(Materials Science, Multidisciplinary)

366 (Records 1-20 displayed on this page)