Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Kozai, Naofumi; Tokunaga, Kohei; Dohi, Terumi; Takahashi, Yoshio*
Journal of Environmental Chemical Engineering, 13(6), p.119612_1 - 119612_9, 2025/12
Yomogida, Takumi; Scaria, J.*; Fablet, L.*; Tokunaga, Kohei; Dei, Shuntaro; Higashi, Kotaro*; Kawamura, Naomi*; Takahashi, Yoshio*; Marsac, R.*
Chemical Communications, 61(91), p.17926 - 17929, 2025/11
This paper presents insights into the influence of magnetite stoichiometry (0 
R = Fe(II)/Fe(III) 0.5) on the surface reduction of U(VI) to U(V) and U(IV), as a key parameter controlling U redox speciation in natural settings. Although R can readily change due to the oxidation of structural Fe(II) or proton/ligand-promoted dissolution, prior studies have not quantified U(V) when assessing these effects. We employed U L
-edge HERFD-XANES spectroscopy to investigate the electronic structure of U on magnetite with varying stoichiometries and observed a peak splitting of U(V) on magnetite. Our results demonstrate the high stability of U(V) species under a wide range of conditions, and after 10 days on magnetite by the combination of MCR-ALS analysis. A key finding is that structural Fe(II), whose abundance depends on pH and redox conditions, plays a critical role for in the stabilization of U(V) on magnetite.
Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Kubo, Katsunori; Kambe, Shinsaku; Yamamoto, Etsuji; Kimata, Motoi; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; et al.
Physical Review Letters, 135(13), p.136502_1 - 136502_6, 2025/09
We investigate the effect of easy-axis metamagnetic crossover on superconductivity in UTe along the 
-axis through measurements of AC susceptibility, magnetization, and the magnetocaloric effect. In ultra-clean single crystals, we identify a field-induced phase transition within the superconducting state at 5.6 T, driven by metamagnetism. This transition leads to a high-field superconducting state, significantly increasing the upper critical field to 12 T. A sudden increase in entropy at the transition suggests a self-reconstruction of the order parameter, enabling multi-component superconducting states to adapt to external perturbations.
with 
= 2.1 K revealed by 
Te NMRMatsumura, Hiroki*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; 13 of others*
Physical Review B, 111(9), p.094507_1 - 094507_9, 2025/03
Times Cited Count：2 Percentile：77.58(Materials Science, Multidisciplinary)Nagasawa, Makoto*; Shimizu, Yusuke*; Yamaguchi, Akiko; Tokunaga, Kohei; Mukai, Hiroki*; Aoyagi, Noboru; Mei, H.; Takahashi, Yoshio*
Chemical Geology, 670, p.122431_1 - 122431_25, 2024/12
Times Cited Count：5 Percentile：82.67(Geochemistry & Geophysics)
in the early-stage sample of spin-triplet superconductor UTeKitagawa, Shunsaku*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; 11 of others*
Journal of the Physical Society of Japan, 93(12), p.123701_1 - 123701_5, 2024/11
Times Cited Count：5 Percentile：84.25(Physics, Multidisciplinary)Tanaka, Kazuya; Yamaji, Keiko*; Masuya, Hayato*; Tomita, Jumpei; Ozawa, Mayumi*; Yamasaki, Shinya*; Tokunaga, Kohei; Fukuyama, Kenjin*; Ohara, Yoshiyuki*; Maamoun, I.*; et al.
Chemosphere, 355, p.141837_1 - 141837_11, 2024/05
In this study, biogenic Mn(IV) oxide was applied to remove Ra from mine water collected from a U mill tailings pond in the Ningyo-toge center. Just 7.6 mg of biogenic Mn(IV) oxide removed more than 98% of the 
Ra from 3 L of mine water, corresponding to a distribution coefficient of 10
mL/g for Ra at pH 7. The obtained value was convincingly high for practical application of biogenic Mn(IV) oxide in water treatment.
Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Kambe, Shinsaku; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Haga, Yoshinori; et al.
Physical Review B, 109(14), p.L140502_1 - L140502_6, 2024/04
Times Cited Count：6 Percentile：76.17(Materials Science, Multidisciplinary)The normal-conducting state of the superconductor UTe is studied by entropy analysis for magnetic fields along the 
-axis, obtained from magnetization using the relation 
. We observe a strong increase in entropy with magnetic field due to metamagnetic fluctuations (spatially uniform, 
). The field dependence is well described by the Hertz-Millis-Moriya theory for quantum criticality of itinerant metamagnetism. Notably, the lower bound of the quantum-critical region coincides well with the position of the minimum in the superconducting transition temperature 
. Hence, our results suggest that fluctuations reinforce the superconductivity.
Hagihara, Koji*; Mayama, Tsuyoshi*; Yamasaki, Michiaki*; Harjo, S.; Tokunaga, Toko*; Yamamoto, Kazuki*; Sugita, Mika*; Aoyama, Kairi*; Gong, W.; Nishimoto, Soya*
International Journal of Plasticity, 173, p.103865_1 - 103865_21, 2024/02
Times Cited Count：32 Percentile：99.26(Engineering, Mechanical)Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Tokiwa, Yoshifumi; Haga, Yoshinori; Kitagawa, Shunsaku*; Ishida, Kenji*; Aoki, Dai*; Knebel, G.*; et al.
Physical Review Letters, 131(22), p.226503_1 - 226503_7, 2023/12
Times Cited Count：14 Percentile：86.17(Physics, Multidisciplinary)Tokiwa, Yoshifumi; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Yanase, Yoichi*; Haga, Yoshinori; et al.
Physical Review B, 108(14), p.144502_1 - 144502_5, 2023/10
Times Cited Count：8 Percentile：66.24(Materials Science, Multidisciplinary)The vortex dynamics in the spin-triplet superconductor, UTe, are studied by measuring the DC electrical resistivity with currents along the -axis under magnetic fields along the -axis. Surprisingly, we have discovered an island region of low critical current deep inside the superconducting (SC) state, well below the SC upper critical field, attributed to a weakening of vortex pinning. Notably, this region coincides with the recently proposed intermediate-field SC state. We discuss the possibility of nonsingular vortices in the intermediate state, where SC order parameter does not vanish entirely in the vortex cores due to the mixing of multiple SC components.
Zn
Kitazawa, Takafumi; Ikeda, Yoichi*; Sakakibara, Toshiro*; Matsuo, Akira*; Shimizu, Yusei*; Tokunaga, Yo; Haga, Yoshinori; Kindo, Koichi*; Nambu, Yusuke*; Ikeuchi, Kazuhiko*; et al.
Physical Review B, 108(8), p.085105_1 - 085105_7, 2023/08
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Kinjo, Katsuki*; Fujibayashi, Hiroki*; Matsumura, Hiroki*; Hori, Fumiya*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; et al.
Science Advances (Internet), 9(30), p.2736_1 - 2736_6, 2023/07
Times Cited Count：17 Percentile：91.30(Multidisciplinary Sciences)
Zn
Y
alloy using X-ray photoelectron spectroscopyMiyazaki, Hidetoshi*; Akatsuka, Tatsuyoshi*; Kimura, Koji*; Egusa, Daisuke*; Sato, Yohei*; Itakura, Mitsuhiro; Takagi, Yasumasa*; Yasui, Akira*; Ozawa, Kenichi*; Mase, Kazuhiko*; et al.
Materials Transactions, 64(6), p.1194 - 1198, 2023/06
Times Cited Count：1 Percentile：7.68(Materials Science, Multidisciplinary)We investigated the electronic structure of the MgZnY alloy using hard and soft X-ray photoemission spectroscopy and electronic band structure calculations to understand the mechanism of the phase stability of this material. Electronic structure of the MgZnY alloy showed a semi-metallic electronic structure with a pseudo-gap at the Fermi level. The observed electronic structure of the MgZnY alloy suggests that the presence of a pseudogap structure is responsible for phase stability.
-axis knight shift on UTe with = 2.1 KMatsumura, Hiroki*; Fujibayashi, Hiroki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; et al.
Journal of the Physical Society of Japan, 92(6), p.063701_1 - 063701_5, 2023/05
Times Cited Count：52 Percentile：98.70(Physics, Multidisciplinary)Te-NMR on the uranium-based superconductor UTeFujibayashi, Hiroki*; Kinjo, Katsuki*; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; et al.
Journal of the Physical Society of Japan, 92(5), p.053702_1 - 053702_5, 2023/05
Times Cited Count：8 Percentile：71.37(Physics, Multidisciplinary) along hard magnetic axisSakai, 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
Times Cited Count：26 Percentile：95.06(Physics, Multidisciplinary)The superconducting (SC) phase diagram in uranium ditelluride is explored under magnetic fields (
) along the hard magnetic -axis using a high-quality single crystal with 
= 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 
of 
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 , indicating an intermediate SC phase characterized by small flux pinning forces.
Maamoun, I.; Falyouna, O.*; Shariful, I. M.*; Eljamal, R.*; Bensaida, K.*; Tanaka, Kazuya; Tokunaga, Kohei; Eljamal, O.*
Advanced Materials Letters (Internet), 14(2), p.23021721_1 - 23021721_10, 2023/04
Tokunaga, Yo; Sakai, Hironori; Kitagawa, Shunsaku*; Ishida, Kenji*
Nihon Butsuri Gakkai-Shi, 78(5), p.267 - 272, 2023/04
no abstracts in English
bimetallic Ni/Fe
nanoparticles; Implications towards Tc(VII) removalMaamoun, 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 (
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) were prepared to enhance the immobilization of rhenium (Re(VII)) from aqueous solutions, as the surrogate of Tc(VII).
