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Np and 
Am gamma ray regionsFukuda, Tatsuo; Kobata, Masaaki; Shobu, Takahisa; Yoshii, Kenji; Kamiya, Junichiro; Iwamoto, Yosuke; Makino, Takahiro*; Yamazaki, Yuichi*; Oshima, Takeshi*; Shirai, Yasuhiro*; et al.
Journal of Applied Physics, 132(24), p.245102_1 - 245102_8, 2022/12
Times Cited Count：1 Percentile：17.38(Physics, Applied)Direct energy conversion has been investigated using Ni/SiC Schottky junctions with the irradiation of monochromatized synchrotron X-rays simulating the gamma rays of Np (30 keV) and Am (60 keV). From current-voltage measurements, electrical energies were obtained for both kinds of gamma rays. The energy conversion efficiencies were found to reach up to 
1.6%, which is comparable to those of a few other semiconducting systems reported thus far. This result shows a possibility of energy recovery from nuclear wastes using the present system, judging from the radiation tolerant nature of SiC. Also, we found different conversion efficiencies between the two samples. This could be understandable from hard X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements, suggesting the formation of Ni-Si compounds at the interface in the sample with a poor performance. Hence, such combined measurements are useful to provide information that cannot be obtained by electrical measurements alone.
Fe
O
/Pt heterostructuresIeda, Junichi; Okayasu, Satoru; Harii, Kazuya*; Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Ishida, Masahiko*; Saito, Eiji
IEEE Transactions on Magnetics, 58(8), p.1301106_1 - 1301106_6, 2022/08
Times Cited Count：1 Percentile：22.45(Engineering, Electrical & Electronic)The combination of spin-driven thermoelectric (STE) devices based on spin Seebeck effect (SSE), and radioactive isotopes as heat sources, has potential as a next-generation method of power generation in applications such as power supplies for space probes. However, there has been very limited knowledge available indicating the irradiation tolerance of spin thermoelectric devices. Through analysis using a heavy ion-beam accelerator and the hard X-ray photoemission spectroscopy (HAXPES) measurements, we show that a prototypical STE device based on YFeO/Pt heterostructures has tolerance to irradiation of high-energy heavy-ion beams. We used 320 MeV gold ion beams modeling cumulative damages due to fission products emitted from the surface of spent nuclear fuels. By varying the dose level, we confirmed that the thermoelectric and magnetic properties of the SSE elements are not affected by the ion-irradiation dose up to 
ions/cm
fluence and that the SSE signal is extinguished around 
ions/cm, in which the ion tracks almost fully cover the sample surface. In addition, the HAXPES measurements were performed to understand the effects at the interface of YFeO/Pt. The HAXPES measurements suggest that the chemical reaction that diminishes the SSE signals is enhanced with the increase of the irradiation dose. We share the current understandings of the damage analysis in YFeO/Pt for developing better STE devices applicable to harsh environmental usages.
O
with electrochemical Li
intercalationMurase, Satoshi*; Yoshikawa, Yumi*; Fujiwara, Kosuke*; Fukada, Yukimasa*; Teranishi, Takashi*; Kano, Jun*; Fujii, Tatsuo*; Inada, Yasuhiro*; Katayama, Misaki*; Yoshii, Kenji; et al.
Journal of Physics and Chemistry of Solids, 162, p.110468_1 - 110468_6, 2022/03
Times Cited Count：0 Percentile：0(Chemistry, Multidisciplinary)We report a trial of the valence control for mixed valence iron triangular oxide YbFeO in order to develop an effective technique to control the frustration of charges in strongly correlated electron systems. The electro-chemical doping of Li into YbFeO was examined on the cell type sample similar to the Li-ion secondary battery cell. Systematic change of the lattice constant, Fe-Fe and Fe-Yb distance were observed with Li doping. Maximum value of the doping was over 300 mAh/g. An EXAFS experiment indicated that Li positioned between Yb octahedron layer (U-layer) and Fe-bipyramidal layer (W-layer). However, detailed change of iron valence state of YbFeO was not clearly observed because of the superimpose of the signal from iron metal nano particles in XANES observation. The results indicate that the electrochemical method might be one of the potential technique to control the frustration of charges in YbFeO.
Kosugi, Yoshihisa*; Goto, Matato*; Tan, Z.*; Kan, Daisuke*; Isobe, Masahiko*; Yoshii, Kenji; Mizumaki, Masaichiro*; Fujita, Asaya*; Takagi, Hidenori*; Shimakawa, Yuichi*
Scientific Reports (Internet), 11(1), p.12682_1 - 12682_8, 2021/06
Times Cited Count：5 Percentile：44.86(Multidisciplinary Sciences)Caloric effects of solids provide more efficient and environment-friendly innovative refrigeration systems compared to the widely-used conventional vapor compressive cooling systems. Exploring novel caloric materials is challenging but critically important in developing future technologies. Here we discovered that the quadruple perovskite structure ferrimagnet BiCu
CrO shows a large multicaloric effect at the first-order charge transition occurred around 190 K. Large latent heat and the corresponding isothermal entropy changes 28.2 J K
kg can be fully utilized by applying both magnetic fields (magnetocaloric effect) and pressure (barocaloric effect). Adiabatic temperature changes reach 3.9 K for the 50 kOe magnetic field and 4.8 K for the 4.9 kbar pressure, and thus highly efficient thermal controls are achieved by multiple ways.
FeO
with distributed equivalent circuit modelFukada, Yukimasa*; Fukuyama, Ryota*; Fujiwara, Kosuke*; Yoshii, Kenji; Shigematsu, Kei*; Azuma, Masaki*; Ikeda, Naoshi*
Journal of the Physical Society of Japan, 90(2), p.024710_1 - 024710_6, 2021/02
Times Cited Count：2 Percentile：30.35(Physics, Multidisciplinary)We report an analysis of the dielectric glasslike state of the spin- and charge-ordered system LuFeO, which has structural and physical properties analogous to those of the electronic ferroelectrics 
FeO (: rare earth). Aging and memory effects of resistivity were found in the electric impedance response. We performed a numerical analysis with equivalent electric circuits that have a logarithmic Gaussian distribution of resistance and capacitance. The distribution parameters well explained the glassy nature of the electric and dielectric properties between 100 and 200 K and the distribution variations of charge- and magnetic-ordered domains underlying the glass nature.
O (R: Y, Lu) investigated by transmission electron microscopyHoribe, Yoichi*; Mori, Shigeo*; Ikeda, Naoshi*; Yoshii, Kenji; Maeno, Hiroshi*; Murakami, Yasukazu*
Ferroelectrics, 584(1), p.20 - 30, 2021/00
Times Cited Count：1 Percentile：7.92(Materials Science, Multidisciplinary)Temperature dependence of charge-ordered crystal structures and domain structures in RFeO (R: Y and Lu) was investigated by energy-filtered transmission electron microscopy, combined with conventional transmission electron microscopy. The presence of three-dimensional to two-dimensional charge ordering transition were observed in both RFeO on heating. Furthermore, real-space images obtained with the energy-filtered transmission electron microscopy revealed that YRFeO has less anisotropic nanometer-scale charge-ordered domains than LuRFeO. These findings in RFeO indicate the importance of the interchange interactions between Fe-O bilayers in addition to those within bilayers in the structural phase transitions associated with charge ordering in this system.
Okayasu, Satoru; Harii, Kazuya*; Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Ishida, Masahiko*; Ieda, Junichi; Saito, Eiji
Journal of Applied Physics, 128(8), p.083902_1 - 083902_7, 2020/08
Times Cited Count：3 Percentile：19.49(Physics, Applied)Fe
OKobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Kawasaki, Ikuto; Okane, Tetsuo; Yamagami, Hiroshi; Yaita, Tsuyoshi; Harii, Kazuya; Ieda, Junichi; Okayasu, Satoru; et al.
JPS Conference Proceedings (Internet), 30, p.011192_1 - 011192_6, 2020/03
High energy X-ray photoelectron spectroscopy (HAXPES) measurements were carried out for the Spin Seebeck system Pt/YFeO(YIG). This system was found to show anomalous Hall effect, possible due to the formation of intermetallic compounds between Fe
and Pt. To reveal this possibility, we have measured the Fe 1s photoelectron peaks by using HAXPES. It was found that the Fe ions consist of Fe in YIG and metallic Fe. The formation of the metallic state is consistent with the proposed origin of the anomalous Hall effect. Other spectra such as Pt 4f will be presented at the conference.
SNomura, Takuji*; Yamamoto, Yuji*; Yoshii, Kenji
Journal of the Physical Society of Japan, 89(2), p.024704_1 - 024704_10, 2020/02
Times Cited Count：0 Percentile：0(Physics, Multidisciplinary)We report a mean-field theoretical study of a triangular magnet NiGaS. Using the localized Wannier functions obtained from a band calculation, the most stable magnetic state was found to be spiral with the incommensurate structure, consistent with the result from neutron diffraction. The Ni-site Coulomb interaction was not strong (U about 2 eV). The spin value at the Ni site was also not so large about 1.1 mb. These results mean that the hybridization between Ni and S may play an important role. The dynamical spin correlation function was found to in accord with the results from neutron scattering.
Sr
CoO (0
0.5)Matsumura, Daiju; Tsuji, Takuya; Yoshii, Kenji
Materials Chemistry and Physics, 238, p.121885_1 - 121885_5, 2019/12
Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)We have conducted X-ray absorption spectroscopy study for perovskite cobaltite PrSrCoO (00.5) to understand Sr doping effect and magnetocaloric measurement for Pr
SrCoO to reveal the origin of magnetic anomaly at around 110 K. The extended X-ray absorption fine structure (EXAFS) measurements at the Co 
-edge suggest that the average valence value of Co ions increases, the interatomic distance of Co-O bonding decreases, and the local distortion of CoO
octahedron increases as Sr is doped in PrCoO. The interatomic distance of Co-O bonding shrinks more greatly for the larger doping region. No temperature dependent electronic and structural changes were observed from Co -edge X-ray absorption spectra in the whole thermal range studied (17-300 K). The magnetocaloric effect of PrSrCoO indicates the change of magnetic structure at 110 K.
Yoshii, Kenji; Ikeda, Naoshi*
Journal of Alloys and Compounds, 804, p.364 - 369, 2019/10
Times Cited Count：11 Percentile：54.33(Chemistry, Physical)Dielectric and magnetocaloric measurements are carried out for the chromite TmCrO. This oxide was reported to be multiferroic below the N
el temperature (
) of 125 K, likely due to a structural transformation. The dielectric response shows large dielectric constants below 300 K. However, from the analyses of loss tangent, AC conductivity and dielectric modulus, this behavior is rooted in hopping of charge carriers rather than electric dipoles, as proposed for some other chromites. No dielectric anomaly is found at . The magnetocaloric effect shows that the magnetic transitions at as well as the spin reorientation temperature are of a second order. This result strongly suggests the absence of magnetostructural transition at in accord with no observation of ferroelectric transition at this temperature.
CrO (=LaPr, Gd, and Tm); Reinvestigation of magnetization reversalYoshii, Kenji
Journal of Applied Physics, 126(12), p.123904_1 - 123904_8, 2019/09
Times Cited Count：11 Percentile：53.18(Physics, Applied)We have reinvestigated the magnetization reversal in perovskites LaPrCrO, GdCrO, and TmCrO and show that spin rotation or reorientation plays a key role in this property. The magnetization measurements on all systems show the appearance and disappearance of the reversal are commonly depend on a strength of a Zeeman energy at the rare earth site in analogy with spin rotation in GdCrO and TmCrO, denoted at the spin reorientation. Magnetic susceptibility measurements point to either superparamagnetic or single-molecule-magnet-like glassy behavior in all three systems, which is likely linked to a rotation of the R-Cr coupling, as seen from magnetocalorimetry (
= LaPr, Gd, and Tm). We also present a characteristic magnetization switching by rotating the R moments with the aid of large Zeeman energies.
Kim, J.*; Yamanaka, Satoru*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Takeda, Masatoshi*; et al.
Advanced Sustainable Systems (Internet), 2(11), p.1800067_1 - 1800067_8, 2018/11
Times Cited Count：7 Percentile：27.76(Green & Sustainable Science & Technology)Kim, J.*; Yamanaka, Satoru*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Takeda, Masatoshi*; et al.
Ferroelectrics, 512(1), p.92 - 99, 2017/08
Times Cited Count：14 Percentile：56.08(Materials Science, Multidisciplinary) in the liquid nitrogen and natural gas temperature regionsYoshii, Kenji; Hayashi, Naoaki*; Mizumaki, Masaichiro*; Takano, Mikio*
AIP Advances (Internet), 7(4), p.045117_1 - 045117_6, 2017/04
Times Cited Count：6 Percentile：29.59(Nanoscience & Nanotechnology)We have investigated the magnetocaloric effect (MCE) of BaSrFe
O (x
0.2), a series of cubic perovskites showing a field-induced transition from helical antiferromagnetism to ferromagnetism. The maximum magnetic entropy change (-
S
) at 50 kOe varies from 5.8 J kgK (x=0) to 4.9 J kgK (x=0.2), while the refrigerant capacity remains almost the same at 165 J kg. Interestingly, the temperature of -S decreases from 116 K to 77 K with increasing x, providing this series of rare-earth-free oxides with potential as a magnetic refrigerant for the liquefaction of nitrogen and natural gas.
Yamanaka, Satoru*; Kim, J.*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Yamada, Noboru*; et al.
Advanced Sustainable Systems (Internet), 1(3-4), p.1600020_1 - 1600020_6, 2017/04
no abstracts in English
CrO (=La and Pr)Yoshii, Kenji; Ikeda, Naoshi*; Shimojo, Yutaka; Ishii, Yoshinobu*
Materials Chemistry and Physics, 190, p.96 - 101, 2017/04
Times Cited Count：15 Percentile：48.52(Materials Science, Multidisciplinary)Magnetic and dielectric properties have been studied for LaCrO, PrCrO, and their solid solution LaPrCrO, belonging to a family of ferroelectricorthochromite series 
CrO (: rare earths). The magnetic measurements confirm that the material shows canted antiferromagnetic ordering at 240-288 K. Neutron diffraction patterns could be fitted with the centrosymmetric 
, which is different from the non-centrosymmetric structure proposed for the ferroelectric phase of NdCrO. The large dielectric constants are likely due to the hopping of charge carriers as proposed previously for other chromites.
Fujita, Yuji; Yoshii, Kenji
Denki Hyoron, 101(2), p.43 - 58, 2016/02
Japan Atomic Energy Agency (JAEA) is conducting many kinds of research activities, including fundamental and applied researches, and project studies to create novel technologies and industries. In particular, the activities are mainly focused on the R&D studies for recovery from the Fukushima Daiichi Nuclear NPS accident, safety researches, the development of fast reactor cycles, and high-level radioactive waste disposal. This article gives reviews on current status of the researches of JAEA in this fiscal year.
Torigoe, Shuhei*; Ishimoto, Yutaro*; Aoishi, Yuhei*; Murakawa, Hiroshi*; Matsumura, Daiju; Yoshii, Kenji; Yoneda, Yasuhiro; Nishihata, Yasuo; Kodama, Katsuaki; Tomiyasu, Keisuke*; et al.
Physical Review B, 93(8), p.085109_1 - 085109_5, 2016/02
Times Cited Count：5 Percentile：25.9(Materials Science, Multidisciplinary)Kim, Y.*; Kim, J.*; Yamanaka, Satoru*; Nakajima, Akira*; Ogawa, Takashi*; Serizawa, Takeshi*; Tanaka, Hirohisa*; Baba, Masaaki*; Fukuda, Tatsuo; Yoshii, Kenji; et al.
Advanced Energy Materials, 5(13), p.1401942_1 - 1401942_6, 2015/07
Times Cited Count：18 Percentile：60.39(Chemistry, Physical)An innovative electro-thermodynamic cycle based on temporal temperature variations using pyroelectric effect has been presented. Practical energy is successfully generated in both 
synchrotron X-ray diffraction measurements under controlled conditions and 
real engine dynamometer experiments. The main generating origin is revealed as a combination of a crystal structure change and dipole change phenomenon corresponds to the temperature variation. In particular, the electric field induced 180
domain switching extremely improves generating power, and the true energy breakeven with temperature variation is firstly achieved.
