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Journal Articles

Measurement of ion beam induced current in quantum dot solar cells

Nakamura, Tetsuya*; Imaizumi, Mitsuru*; Sato, Shinichiro; Sugaya, Takeyoshi*; Mochizuki, Toru*; Okano, Yoshinobu*; Oshima, Takeshi

Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.73 - 76, 2015/11

The radiation effect on GaAs p-i-n solar cells with quantum dot (QD) in the i-layer was investigated. In a previous work, we particularly noted the degradation of fill-factor (FF) for the QD cells. In this work, to clarify the reason of the FF degradation in QD cells, generation current due to low-energy proton irradiation, which we call ion beam induced current (IBIC), was observed to characterize behavior of the generated minority carrier by the protons in the depletion region where QDs are located. The energy of protons was adjusted to damage the depletion region, and decrease of generation current was measured during the proton irradiation. The results suggest that the serious degradation of FF is caused by a decrease of the carrier collection efficiency in the depletion region due to proton damage.

Journal Articles

Corrosion evaluation of uranyl nitrate solution evaporator and denitrator in Tokai Reprocessing Plant

Yamanaka, Atsushi; Hashimoto, Kowa; Uchida, Toyomi; Shirato, Yoji; Isozaki, Toshihiko; Nakamura, Yoshinobu

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 6 Pages, 2011/12

The Tokai Reprocessing Plant (TRP) adopted the PUREX method in 1977 and has reprocessed spent nuclear fuel of 1140 tHM (tons of heavy metals) since then. The reprocessing equipment suffers from various corrosion phenomena because of high nitric acidity, solution ion concentrations, such as uranium, plutonium, and fission products, and temperature. Therefore, considering corrosion performance in such a severe environment, stainless steels, titanium steel, and so forth were employed as corrosion resistant materials. The severity of the corrosive environment depends on the nitric acid concentration and the temperature of the solution, and uranium in the solution reportedly does not significantly affect the corrosion of stainless steels and controls the corrosion rates of titanium steel. The TRP equipment that handles uranyl nitrate solution operates at a low nitric acid concentration and has not experienced corrosion problems until now. However, there is a report that corrosion rates of some stainless steels increase in proportion to rising uranium concentrations. The equipment that handles the uranyl nitrate solution in the TRP includes the evaporators, which concentrate uranyl nitrate to a maximum concentration of about 1000 gU/L (grams of uranium per liter), and the denitrator, where uranyl nitrate is converted to UO$$_{3}$$ powder at about 320$$^{circ}$$C. These equipments are therefore required to grasp the degree of the progress of corrosion to handle high-temperature and high-concentration uranyl nitrate. The evaluation of this equipment on the basis of thickness measurement confirmed only minor corrosion and indicated that the equipment would be fully adequate for future operation.

Journal Articles

Crystal structure and physical properties of trigonal NpGa$$_3$$ and Np$$_{3}$$Ga$$_{11}$$

Haga, Yoshinori; Aoki, Dai*; Homma, Yoshiya*; Matsuda, Tatsuma; Ikeda, Shugo*; Sakai, Hironori; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Onuki, Yoshichika

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA109_1 - SA109_3, 2011/07

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

Journal Articles

Magnetic and dielectric study of R$$_{0.5}$$Sr$$_{0.5}$$MnO$$_{3}$$ (R = Gd, Tb and Dy)

Yoshii, Kenji; Hiramitsu, Yusuke*; Okajima, Yuka*; Yoneda, Yasuhiro; Nishihata, Yasuo; Mizuki, Junichiro; Nakamura, Akio; Shimojo, Yutaka; Ishii, Yoshinobu*; Morii, Yukio; et al.

Materials Research Bulletin, 45(11), p.1574 - 1580, 2010/10

 Times Cited Count:12 Percentile:39.23(Materials Science, Multidisciplinary)

Magnetic and dielectric properties of perovskite manganites R$$_{0.5}$$Sr$$_{0.5}$$MnO$$_{3}$$ (R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at Tg about 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R$$^{3+}$$ and Sr$$^{3+}$$ settled randomly at the same crystallographic site. Dielectric constants for each material were about 1000-10000 between about 50 K and 300 K and showed broad maximums above Tg. Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R/Sr site. The tan$$delta$$ and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons.

Journal Articles

Possible existence of magnetic polaron in nearly ferromagnetic semiconductor $$beta$$-US$$_2$$

Ikeda, Shugo*; Sakai, Hironori; Tateiwa, Naoyuki; Matsuda, Tatsuma; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Ota, Yuki*; et al.

Journal of the Physical Society of Japan, 78(11), p.114704_1 - 114704_10, 2009/11

 Times Cited Count:11 Percentile:55.93(Physics, Multidisciplinary)

Journal Articles

Element and orbital-specific observation of two-step magnetic transition in NpNiGa$$_5$$; X-ray magnetic circular dichroism study

Okane, Tetsuo; Okochi, Takuo*; Inami, Toshiya; Takeda, Yukiharu; Fujimori, Shinichi; Kawamura, Naomi*; Suzuki, Motohiro*; Tsutsui, Satoshi*; Yamagami, Hiroshi; Fujimori, Atsushi; et al.

Physical Review B, 80(10), p.104419_1 - 104419_7, 2009/09

 Times Cited Count:6 Percentile:30.58(Materials Science, Multidisciplinary)

Journal Articles

Hyperfine interactions in the itinerant system UFeGa$$_{5}$$

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Chudo, Hiroyuki; Yasuoka, Hiroshi; Matsuda, Tatsuma; Haga, Yoshinori; Ikeda, Shugo; Nakamura, Akio; Yamamoto, Etsuji; et al.

Journal of Nuclear Materials, 385(1), p.1 - 3, 2009/03

 Times Cited Count:1 Percentile:10.64(Materials Science, Multidisciplinary)

In 5f-electron systems, exotic magnetism and unconventional superconductivity appear at low temperatures owing to strong electron correlations and orbital degeneracy. For example, we have investigated the unconventional superconducting states of recently synthesized NpPd$$_5$$Al$$_2$$ ($$T_c$$=5K) and PuRhGa$$_5$$ ($$T_c$$=9K) in terms of both macroscopic (staticsusceptibility, specific heat, resistivity) and microscopic (NMR) probes. The relation between magnetic fluctuations and unconventional superconductivity in f-electron systems is also discussed. Another exciting topic concerns the series AnO$$_2$$ (An; U, Np, Pu, Am). Besides the importance of AnO$$_2$$ as a nuclear fuel, the magnetic properties of these compounds at low temperatures are particularly interesting. On the basis of $$^{17}$$O-NMR studies, multipolar ordered states have been identified in UO$$_2$$ (dipolar + quadrupolar ordering) and NpO$$_2$$ (quadrupolar + octupolar ordering), in contrast with the non-magnetic ground state of PuO$$_2$$.

Journal Articles

Crystal structure and magnetic properties of the new ternary actinide compounds AnPd$$_5$$Al$$_2$$ (An = U, Np)

Haga, Yoshinori; Aoki, Dai*; Homma, Yoshiya*; Ikeda, Shugo; Matsuda, Tatsuma; Yamamoto, Etsuji; Sakai, Hironori; Tateiwa, Naoyuki; Dung, N. D.*; Nakamura, Akio; et al.

Journal of Alloys and Compounds, 464(1-2), p.47 - 50, 2008/09

 Times Cited Count:19 Percentile:68.64(Chemistry, Physical)

Journal Articles

NMR investigation of quadrupole order parameter in actinide dioxides

Tokunaga, Yo; Homma, Yoshiya*; Kambe, Shinsaku; Aoki, Dai*; Sakai, Hironori; Chudo, Hiroyuki; Ikushima, Kenji*; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; et al.

Journal of Optoelectronics and Advanced Materials, 10(7), p.1663 - 1665, 2008/07

Multipolar degrees of freedom characteristic of $$f$$-electrons bring rich and complex physics to rare-earth and actinide compounds. In the present work, we demonstrate that microscopic investigation of multipole order parameters is also possible by means of NMR through the hyperfine interactions. Our $$^{17}$$O NMR study performed on a single crystal of NpO$$_2$$ provide definitive support for the proposed longitudinal triple-$$q$$ type antiferro-octupolar ordering below $$T_0=$$26 K. We shall also provide our $$^{17}$$O NMR results on UO$$_2$$ and PuO$$_2$$. The microscopic NMR clearly indicates the different nature of the magnetic ground states among three actinide dioxides.

Journal Articles

Pressure effect on paramagnet $$beta$$-US$$_2$$

Ikeda, Shugo; Sakai, Hironori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Nakamura, Akio; Yamamoto, Etsuji; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Hedo, Masato*; et al.

Physica B; Condensed Matter, 403(5-9), p.893 - 894, 2008/04

 Times Cited Count:6 Percentile:31.29(Physics, Condensed Matter)

Single crystals of paramagnetic semiconductor $$beta$$-US$$_2$$ with the orthorhombic ($textit{Pnma}$) crystal structure were grown by chemical transport method. We measured the electrical resistivity $$rho$$ under high pressure, and magnetization. With increasing pressure, the temperature dependence of $$rho$$ approaches to semimetallic behavior and a kink anomaly appears at $$T_{rm a}$$.$$T_{rm a}$$ shifts to higher temperature with increasing pressure. From the comparison with ferromagnetic semimetal UTeS having the same crystal structure, it seems that $$T_{rm a}$$ is a ferromagnetic transition.

Journal Articles

$$^{31}$$P-NMR study of the neptunium-based filled-skutterudite NpFe$$_4$$P$$_{12}$$

Tokunaga, Yo; Aoki, Dai*; Homma, Yoshiya*; Sakai, Hironori; Chudo, Hiroyuki; Kambe, Shinsaku; Matsuda, Tatsuma; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 77(Suppl.A), p.211 - 213, 2008/00

 Times Cited Count:3 Percentile:28.46(Physics, Multidisciplinary)

$$^{31}$$P-NMR measurements have been performed on a single crystal of NpFe$$_4$$P$$_{12}$$ which is the first crystallized transuranium filled-skutterudite compound. The field-orientation dependence of the hyperfine interaction has been measured using the single crystal, and the results compared with those obtained previously in isostructural compounds UFe$$_4$$P$$_{12}$$ and PrFe$$_4$$P$$_{12}$$. We have also measured the field and temperature dependence of the nuclear spin-lattice relaxation rate in several fields between 1.8 and 8 T at temperatures between 4.2 and 300 K. The results are discussed on the basis of a localized picture for the 5f electrons.

Journal Articles

Pressure effect on ferromagnet UTeS

Ikeda, Shugo*; Sakai, Hironori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Aoki, Dai*; Homma, Yoshiya*; Nakamura, Akio; Yamamoto, Etsuji; Shiokawa, Yoshinobu*; Hedo, Masato*; et al.

Journal of the Physical Society of Japan, 77(Suppl.A), p.359 - 361, 2008/00

 Times Cited Count:1 Percentile:11.98(Physics, Multidisciplinary)

The ferromagnet UTeS was studied by measurement the resistivity under high pressure. The Curie temperature $$T_{rm C}$$ rapidly increases from 87 K to 166 Kat 8 GPa. The result suggests that there is a correlation between the electrical conductivity and magnetic transition temperature, implying the strong hybridization.

Journal Articles

Heavy fermion superconductivity with the strong Pauli paramagnetic effect on NpPd$$_5$$Al$$_2$$

Aoki, Dai*; Haga, Yoshinori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Ikeda, Shugo*; Homma, Yoshiya*; Sakai, Hironori; Shiokawa, Yoshinobu*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 77(Suppl.A), p.159 - 164, 2008/00

 Times Cited Count:3 Percentile:28.46(Physics, Multidisciplinary)

Superconducting properties are investigated on the new neptunium-based superconductor NpPd$$_5$$Al$$_2$$. The large electronic specific heat, anisotropy of magnetic as well as superconducting properties and strong paramagnetic effect implies spin-singlet pairing with anisotropic superconducting gap.

Journal Articles

Ga NQR relaxation rates in superconductor PuRhGa$$_5$$

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of Physics and Chemistry of Solids, 68(11), p.2103 - 2106, 2007/11

 Times Cited Count:1 Percentile:7.27(Chemistry, Multidisciplinary)

A lot of attention is currently focused on Pu-based superconductors. These systems have relatively high superconducting (SC) transition temperatures, ${it i.e.,}$ $$T_{rm c}simeq$$ 18 K for PuCoGa$$_{5}$$ and $$T_{rm c}simeq$$ 9 K for PuRhGa$$_{5}$$. Both compounds crystallize in the tetragonal HoCoGa$$_{5}$$ (115) structure, which is well known for the heavy-fermion SC systems Ce$$T$$In$$_{5}$$ ($$T$$=Co, Rh, Ir)with $$T_{rm c} sim$$ 2 K at most. Recently, NMR and NQR experiments have been reported for PuCoGa$$_{5}$$ by Curro et al. and for PuRhGa$$_{5}$$ by our group. In both cases, measurements of $$1/T_{1}$$ using NQR have revealed that the Pu115 superconductors show unconventional superconductivity with an anisotropic gap. Now we have measured the more detailed data of $$1/T_{1}$$ for NQR lines in PuRhGa$$_5$$, especially focusing on the low-lying magnetic excitation in the normal state. From the viewpoint of spin-fluctuations, we will discuss the difference between PuRhGa$$_{5}$$ and PuCoGa$$_{5}$$ and between superconducting Pu115 and non-superconducting An115 series.

Journal Articles

$$^{17}$$O NMR spin-lattice relaxation in NpO$$_2$$; Field-dependent cross-relaxation process driven by $$^{237}$$Np spins

Tokunaga, Yo; Walstedt, R. E.*; Homma, Yoshiya*; Aoki, Dai*; Kambe, Shinsaku; Sakai, Hironori; Fujimoto, Tatsuya; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of Physics and Chemistry of Solids, 68(11), p.2016 - 2019, 2007/11

 Times Cited Count:2 Percentile:12.99(Chemistry, Multidisciplinary)

In this paper, we report a comprehensive study of $$^{17}$$O nuclear spin-lattice relaxation in NpO$$_2$$ for a wide range of fields and temperatures. In both the paramagnetic and ordered-state regions, a strong, field-dependent $$^{237}$$Np -$$^{17}$$O nuclei cross-relaxation process is observed in addition to the expected background rate. The cross relaxation process, driven by the $$^{237}$$Np spins, is conveyed to the $$^{17}$$O via a greatly enhanced indirect nuclear spin-spin coupling which is described and reported here for the first time. The magnitude and temperature dependence of the indirect coupling are in reasonable accord with a simple theoretical model. The magnitude and temperature dependence of the $$^{237}$$Np $$T_1$$ process are also deduced from the data obtained.

Journal Articles

Magnetic and dielectric properties of Tb$$_{0.5}$$Ca$$_{0.5}$$MnO$$_{3}$$

Hiramitsu, Yusuke*; Yoshii, Kenji; Yoneda, Yasuhiro; Mizuki, Junichiro; Nakamura, Akio; Shimojo, Yutaka; Ishii, Yoshinobu*; Morii, Yukio; Ikeda, Naoshi*

Japanese Journal of Applied Physics, Part 1, 46(10B), p.7171 - 7174, 2007/10

 Times Cited Count:15 Percentile:52.56(Physics, Applied)

Magnetic and dielectric properties of a perivskite manganite Tb$$_{0.5}$$Ca$$_{0.5}$$MnO$$_{3}$$ were investigated. Magnetic measurements showed three characteristic temperatures, originating from charge ordering (300 K), antiferromagnetic ordering (120 K) and a transition to a glassy state (50 K). The coexistence of the charge and antiferromagnetic ordering was consistent with the result of powder neutron diffraction. AC dielectric measurements showed large dielectric constants of about 5000 at around room temperature. A temperature dependence of the dielectric constant changed just below the charge-ordering temperature. From the analysis of tan$$delta$$;, the activation energy for a domain-boundary motion was calculated to be about 0.09 eV. These results strongly suggest that the dielectric properties of this material are governed by the ordering and transfer of the Mn-3d charges.

Journal Articles

NMR studies of actinide dioxides

Tokunaga, Yo; Sakai, Hironori; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.*; Ikushima, Kenji*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Haga, Yoshinori; et al.

Journal of Alloys and Compounds, 444-445, p.241 - 245, 2007/10

 Times Cited Count:16 Percentile:66.16(Chemistry, Physical)

In this paper, we present our recent NMR works on Neptunium and Plutonium compounds. In order to elucidate the nature of the exotic multipolar ordered phase of NpO$$_2$$, we have initiated the first NMR measurements on this system. We have shown that direct observation of multipole order parameters is possible by means of NMR. Our NMR results provide further insight into the microscopic nature of multipole phase transitions in f-electron systems. We have also performed $$^{69,71}$$Ga NMR/NQR studies on a single crystal of PuRhGa$$_5$$. From the temperature dependence of the spin-lattice relaxation rate ($$1/T_1$$), we have found that PuRhGa$$_5$$ is an unconventional superconductor having an anisotropic superconducting (SC) gap 2$$Delta(0)$$=5$$K_BT_c$$. Furthermore, we have confirmed the Knight shift to be decreased below $$T_c$$. This gives strong evidence for spin singlet SC pairing.

Journal Articles

Single crystal growth, superconductivity and Fermi surface study of plutonium compounds

Haga, Yoshinori; Aoki, Dai*; Yamagami, Hiroshi*; Matsuda, Tatsuma; Nakajima, Kunihisa; Arai, Yasuo; Yamamoto, Etsuji; Nakamura, Akio; Homma, Yoshiya*; Shiokawa, Yoshinobu*; et al.

Journal of Alloys and Compounds, 444-445, p.114 - 118, 2007/10

 Times Cited Count:3 Percentile:28.86(Chemistry, Physical)

We report the first dHvA study in plutonium compound PuIn$$_3$$ with the cubic AuCu$$_3$$ type structure, which can be regarded as a reference compound of PuCoGa$$_5$$. The result of the angular dependence of the dHvA frequency, which corresponds to the extremal cross section of the Fermi surface perpendicular to the field direction, was analyzed by the band calculations. The experimental data agree well with the theory, indicating that the 5f electrons can be treated as itinerant ones. The experimental dHvA study for plutonium-based superconductors such as PuCoGa$$_5$$ are also desired but more challenging because the superconducting mixed state extremely weaken the dHvA amplitude.

Journal Articles

Anisotropic superconductivity in NpPd$$_5$$Al$$_2$$ in the vicinity of the heavy fermion formation

Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Haga, Yoshinori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Ikeda, Shugo; Sakai, Hironori; Yamamoto, Etsuji; Nakamura, Akio; et al.

Kotai Butsuri, 42(9), p.569 - 580, 2007/09

The first neptunium superconductor was discovered in NpPd$$_5$$Al$$_2$$. Unconventional superconductivity of NpPd$$_5$$Al$$_2$$ is realized before onset of the heavy fermion state, which is compared with superconducting properties of CeCoIn$$_5$$ and PuRhGa$$_5$$ (PuCoGa$$_5$$).

Journal Articles

Electrical and magnetic properties of an ising-type ferromagnet NpSb$$_2$$

Homma, Yoshiya*; Aoki, Dai*; Haga, Yoshinori; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Onuki, Yoshichika

Journal of the Physical Society of Japan, 76(7), p.074715_1 - 074715_6, 2007/07

 Times Cited Count:1 Percentile:11.22(Physics, Multidisciplinary)

104 (Records 1-20 displayed on this page)