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Journal Articles

Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe$$_{3}$$

Chen, L.*; Mao, C.*; Chung, J.-H.*; Stone, M. B.*; Kolesnikov, A. I.*; Wang, X.*; Murai, Naoki; Gao, B.*; Delaire, O.*; Dai, P.*

Nature Communications (Internet), 13, p.4037_1 - 4037_7, 2022/07

 Times Cited Count:17 Percentile:78.95(Multidisciplinary Sciences)

Journal Articles

Faradaically selective membrane for liquid metal displacement batteries

Yin, H.*; Chung, B.*; Chen, F.*; Ouchi, Takanari*; Zhao, J.*; Tanaka, Nobuyuki; Sadoway, D. R.*

Nature Energy (Internet), 3(2), p.127 - 131, 2018/02

 Times Cited Count:63 Percentile:87.57(Energy & Fuels)

We disclose a new porous electronically conductive membrane, which achieves chemical selectivity by preferred faradaic reaction. This shift in membrane mechanism grants access to a variety of heretofore forbidden choices for positive and negative electrode metals and allows the battery to charge-discharge at high rate without degradation. Fitted with a porous membrane of TiN, a displacement cell comprising a Pb positive electrode, a Li Pb negative electrode, and LiCl-KCl eutectic electrolyte was cycled at 410$$^{circ}$$C and exhibited a coulombic efficiency of 92%. The capacity fade rate was measured to be 0.00172% per cycle, which is tantamount to retention of greater than 94% of initial capacity after 10 years. Most significant from the standpoint of scalability, we show that the faradaic membrane can be fashioned out of metal so as to be mechanically durable and therefore easily mass-produced at large scale with a thin cross-section for minimal ohmic drop in cell voltage.

Journal Articles

Validation of plasma shape reconstruction by Cauchy condition surface method in KSTAR

Miyata, Yoshiaki; Hahn, S. H.*; Suzuki, Takahiro; Ide, Shunsuke; Chung, J.*; Bak, J. G.*; Ko, W. H.*

Physics of Plasmas, 21(3), p.032502_1 - 032502_11, 2014/03

 Times Cited Count:9 Percentile:39.59(Physics, Fluids & Plasmas)

Cauchy condition surface (CCS) method is a numerical approach to reconstruct the plasma boundary precisely and calculate the quantities related to plasma shape using small number of magnetic diagnostics in real time. It has been applied to the KSTAR plasma in order to establish the plasma shape reconstruction with the high elongation of plasma shape and the large effect of eddy current flowing in the structure for the first time. Calculations have been performed to validate the plasma shape reconstruction in 2012 KSTAR experimental campaign. Comparison between the CCS calculation and non-magnetic measurements revealed that the CCS calculation can reconstruct the accurate plasma shape even with a small Ip. The application of CCS calculation to the KSTAR plasma and the validation results of the plasma shape reconstruction are reported.

Journal Articles

Spiral spin structures and origin of the magnetoelectric coupling in YMn$$_2$$O$$_5$$

Kim, J.-H.*; Lee, S.-H.*; Park, S. I.*; Kenzelmann, M.*; Harris, A. B.*; Schefer, J.*; Chung, J.-H.*; Majkrzak, C. F.*; Takeda, Masayasu; Wakimoto, Shuichi; et al.

Physical Review B, 78(24), p.245115_1 - 245115_10, 2008/12

 Times Cited Count:43 Percentile:80.96(Materials Science, Multidisciplinary)

Journal Articles

Frustrated minority spins in GeNi$$_2$$O$$_4$$

Matsuda, Masaaki; Chung, J.-H.*; Park, S.*; Sato, Taku*; Matsuno, Kenichiro*; Katori, Hiroko*; Takagi, Hidenori*; Kakurai, Kazuhisa; Kamazawa, Kazuya*; Tsunoda, Yorihiko*; et al.

Europhysics Letters, 82(3), p.37006_1 - 37006_5, 2008/05

 Times Cited Count:22 Percentile:71.50(Physics, Multidisciplinary)

Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi$$_2$$O$$_4$$ at $$T_{N1}=12.1$$ K and $$T_{N2}=11.4$$ K, respectively. Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at $$T_{N1}$$ the spins on the $$<$$111$$>$$ kagom$'e$ planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the $$<$$111$$>$$ triangular planes that separate the kagom$'e$ planes frustrated and disordered. At the lower $$T_{N2}$$, the triangular spins also order in the $$<$$111$$>$$ plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions.

Journal Articles

Spiral spin structure in the Heisenberg pyrochlore magnet CdCr$$_2$$O$$_4$$

Matsuda, Masaaki; Takeda, Masayasu; Nakamura, Mitsutaka; Kakurai, Kazuhisa; Osawa, Akira*; Leli$`e$vre-Berna, E.*; Chung, J.-H.*; Ueda, Hiroaki*; Takagi, Hidenori*; Lee, S.-H.*

Physical Review B, 75(10), p.104415_1 - 104415_6, 2007/03

 Times Cited Count:45 Percentile:81.97(Materials Science, Multidisciplinary)

A frustrated spinel CdCr$$_2$$O$$_4$$ undergoes a three-dimensional spin-Peierls transition at $$T_N$$ = 7.8 K from a cubic paramagnetic to a tetragonal N$'e$el state. The N$'e$el state has a spiral magnetic structure with a characteristic wave vector of $$(0,delta,1)$$ when the $$c$$ axis elongated. Here we report our spherical neutron polarimetry experiments to investigate the spiral spin structure in detail. Our results indicate that the spins lie in the $$ac$$ plane perpendicular to the direction of the spiral modulation. We also found that the spiral structure in the $$ac$$ plane is elliptical with the $$c$$-component larger by $$sim$$24% than the $$a$$-component, suggesting a strong coupling between the magnetic structure and structural distortion. Unpolarized neutron diffraction under an external magnetic field has also been performed. The magnetic field dependence suggests existence of magnetic anisotropy in the N$'e$el state, which is consistent with our previous inelastic studies.

Journal Articles

$$mu$$SR studies of Pu metal and the Pu-based superconductor PuCoGa$$_5$$

Heffner, R. H.; Bauer, E. D.*; Chung, B.*; Fluss, M. J.*; Higemoto, Wataru; Ito, Takashi; MacLaughlin, D. E.*; Morales, L. A.*; Morris, G. D.*; Oishi, Kazuki; et al.

Journal of the Physical Society of Japan, 75(Suppl.), p.14 - 19, 2006/08

no abstracts in English

Journal Articles

New limits on the ordered moments in $$alpha$$-Pu and Ga-stabilized $$delta$$-Pu

Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Chung, B.*; MacLaughlin, D. E.*; Shu, L.*; Anderson, J. E.*

Physica B; Condensed Matter, 374-375, p.163 - 166, 2006/03

 Times Cited Count:8 Percentile:37.57(Physics, Condensed Matter)

The $$mu$$SR measurements in pulutonium metals are reported for the first time. The ground-state properties of Pu metal is not understood clearly. We found the upper limits of the ordered moment in $$alpha$$-Pu and $$delta$$-stabilized Pu is $$<10^{-3}mu_B$$ at $$sim$$4K.

Journal Articles

Limits for ordered magnetism in Pu from muon spin rotation spectroscopy

Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Chung, B.*; McCall, S.*; MacLaughlin, D. E.*; Shu, L.*; Oishi, Kazuki; Bauer, E. D.*; Sarrao, J. L.*; et al.

Physical Review B, 73(9), p.094453_1 - 094453_5, 2006/03

 Times Cited Count:35 Percentile:77.76(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Angular distribution measurements of photo-neutron yields produced by 2.0 GeV electrons incident on thick targets

Lee, H.-S.*; Ban, Shuichi*; Sanami, Toshiya*; Takahashi, Kazutoshi*; Sato, Tatsuhiko; Shin, Kazuo*; Chung, C. W.*

Radiation Protection Dosimetry, 116(1-4), p.653 - 657, 2005/12

 Times Cited Count:5 Percentile:35.10(Environmental Sciences)

A study of differential photo-neutron yields by irradiation with 2 GeV electrons has been carried out. In this extension of a previous study in which measurements were made at an angle of 90 degrees. Relative to incident electrons, the differential photoneutron yield was obtained at two other angles, 48 and 140 degrees, to study its angular characteristics. Photo-neutron spectra were measured using a pulsed beam time-of-flight method and a BC418 plastic scintillator. The reliable range of neutron energy measurement was 8-250 MeV. The neutron spectra were measured for 10 Xo-thick Cu, Sn, W and Pb targets. The angular distribution characteristics, together with the previous results for 90, are presented in the study. The experimental results are compared with Monte Carlo calculation results. The yields predicted by MCNPX 2.5 tend to underestimate the measured ones. The same trend holds for the comparison results using the EGS4 and PICA3 codes.

Journal Articles

Large displacement of germanium atoms in crystalline Ge$$_2$$Sb$$_2$$Te$$_5$$

Shamoto, Shinichi; Yamada, Noboru*; Matsunaga, Toshiyuki*; Proffen, T.*; Richardson, J. W.*; Chung, J.-H.*; Egami, Takeshi*

Applied Physics Letters, 86(8), p.081904_1 - 081904_3, 2005/02

 Times Cited Count:50 Percentile:82.37(Physics, Applied)

Local structure of NaCl-type crystalline Ge$$_2$$Sb$$_2$$Te$$_5$$ has been studied by the atomic pair distribution function analysis of pulsed neutron powder diffraction data. We have found the large displacement of germanium atoms in this crystalline phase. Usually, such a large lattice distortion has disadvantage for the electric conductivity. The electronic band structure, however, implies that this significant distortion in addition to the lattice defect at Na site reduces only thermal conductivity, while the highly ordered tellurium atoms at Cl site keep high electric conductivity.

Journal Articles

Local structure of LiNiO$$_2$$ studied by neutron diffraction

Chung, J.-H.*; Proffen, T.*; Shamoto, Shinichi; Ghorayeb, A. M.*; Croguennec, L.*; Tian, W.*; Sales, B. C.*; Jin, R.*; Mandrus, D.*; Egami, Takeshi*

Physical Review B, 71(6), p.064410_1 - 064410_11, 2005/02

 Times Cited Count:86 Percentile:91.24(Materials Science, Multidisciplinary)

LiNiO$$_2$$ (S=1/2) forms a triangular lattice with the possible magnetic frustration, but the exact state of spin correlation has not yet been known. While there is no signature of long-range Jahn-Teller distortion, local JT distortion has been suspected. We have performed neutron diffraction and atomic pair-density function analyses up to unprecedented large distances to discover a number of unusual features, such as anomalous peak broadening, local JT distortion, sharp oxygen-oxygen distance correlations, and inverted temperature dependence of medium range correlation. These observations are best explained by local orbital ordering of Ni$$^{3+}$$ ions into three sublattices. This orbital ordering, however, cannot develop into long-range order because of the strain field it generates, and domains of about 10 nm in size are formed. Domains are susceptible to random pinning by impurities ssite disorderd resulting in the loss of structural long-range order. We suggest that this local orbital ordering is the basis for the complex magnetic properties observed in this compound.

Oral presentation

Spiral structure of a frustrated spinel CdCr$$_2$$O$$_4$$ studied by polarized neutron techniques

Matsuda, Masaaki; Osawa, Akira*; Takeda, Masayasu; Nakamura, Mitsutaka; Leli$`e$vre-Berna, E.*; Kakurai, Kazuhisa; Chung, J.-H.*; Lee, S.-H.*; Ueda, Hiroaki*; Takagi, Hidenori*

no journal, , 

no abstracts in English

Oral presentation

Demonstration of real-time plasma shape reconstruction by Cauchy Condition Surface method in KSTAR

Miyata, Yoshiaki; Hahn, S. H.*; Suzuki, Takahiro; Ide, Shunsuke; Chung, J.*; Bak, J. G.*; Ko, W. H.*

no journal, , 

The plasma shape reconstruction is essential for plasma equilibrium control and detailed physics analysis. Various methods to reconstruct a plasma shape have been developed for many tokamaks. Cauchy Condition Surface (CCS) method has reconstructed a plasma shape using the magnetic measurements in JT-60U. The CCS calculation can reconstruct the outermost magnetic surface, and calculate the eddy currents induced in the toroidal structure and the quantities related to plasma shape such as the Shafranov lambda, the safety factor and so on. In this presentation, the demonstration of real-time plasma shape reconstruction by the CCS calculation in KSTAR is discussed.

Oral presentation

Survey on experiences and needs for sharing nonproliferation-relevant information among experts within JAEA

Kawakubo, Yoko; Inoue, Naoko; Mongiello, R.*; Baldwin, G.*; Lee, N.-Y.*; Chung, J.*; Kwon, E.-H.*

no journal, , 

Japan Atomic Energy Agency (JAEA) is carrying out a project to design and establish an Information Sharing Framework (ISF) for enhancing nuclear transparency in the Asia Pacific region. This project is a cooperative effort with Sandia National Laboratories (SNL), the Korean Institute for Nuclear Nonproliferation and Control (KINAC), and Korea Atomic Energy Research Institute (KAERI). In order to design and establish the ISF as a meaningful and sustainable mechanism, it is essential to identify the needs of the potential aparticipants including their expectations and concerns. Therefore partner organizations have conducted on-line surveys and/or face-to-face interviews with the nonproliferation experts within their own organizations that were identified as primary participants of ISF. JAEA carried out several face-to-face interviews with its experts including those who are in charge of nonproliferation R&D, nuclear security implementation coordinator, and training for capacity building and infrastructure development. They were queried as to past experiences and future needs for information exchanges. The survey results indicated that there are various experiences of information sharing in each nonproliferation mission or activity, and there continues to be a need for further information sharing. Findings from the survey will be reflected to the establishment and demonstration of ISF.

Oral presentation

Development of information sharing requirements for regional nuclear transparency

Kawakubo, Yoko; Inoue, Naoko; Mongiello, R.*; Baldwin, G.*; Lee, N.-Y.*; Chung, J.*; Kwon, E.-H.*

no journal, , 

Nuclear transparency has been discussed in various contexts even within nuclear nonproliferation. Due to the wide range of the contexts, the similar discussions have been repeated. With this background, Japan Atomic Energy Agency (JAEA), US Sandia National Laboratories (SNL), Korean Institute of Nuclear Nonproliferation and Control (KINAC), and Korean Atomic Energy Research Institute (KAERI) initiated a new phase of study to develop "requirements" for information sharing framework (ISF) focusing on regional nonproliferation experts. The "requirements" in this study is defined as to implement Plan-Do-Check-Adjust (PDCA) cycle for each specific category of information to be shared. "Plan" should be made by defining seven essential elements of ISF. In "Do" stage, the participants will collect the information and initiate a sharing process. "Check" is to evaluate the effectiveness and efficiency of the ISF using the metrics and methodologies identified in "Plan". The feedback obtained from the "Check" will be reflected to the "Plan" for the second cycle, then the second cycle will be implemented. Because the nuclear transparency is a voluntary process, sustainability is a key challenge. "Requirements" were developed so that if the planning and implementation of ISF is carried out following the "requirements", ISF can automatically work in a sustainable and useful manner. This paper addresses the requirements for ISF that were developed by JAEA, SNL, KINAC, and KAERI, and demonstrates how they can work with showing the example planning.

Oral presentation

Detailed magnetic structure of a frustrated spinel CdCr$$_2$$O$$_4$$ studied by polarized neutron techniques

Matsuda, Masaaki; Osawa, Akira*; Takeda, Masayasu; Kakurai, Kazuhisa; Chung, J.-H.*; Lee, S.-H.*; Ueda, Hiroaki*; Takagi, Hidenori*

no journal, , 

CdCr$$_2$$O$$_4$$ has the spinel structure, in which geometrical frustration exists between the Cr$$^{3+}$$ moments located at the corners of the tetrahedron. It shows an incommensurate antiferromagnetic ordering below $$Trm_N$$=7.8K with a characteristic wave vector of $$Q=(0, delta, 1)$$ ($$deltasim0.09$$). We first performed a 1D polarized neutron analysis and determined that the Cr$$^{3+}$$ moments has a planer anisotropy in the $$ac$$ plane, indicating that the magnetic structure is spiral. Finally, the 3D polarized neutron analysis using a CRYOPAD on TAS-1 at JRR-3 determined that the magnetic structure is elliptical spiral in the $$ac$$ plane with ellipsoid slightly elongated along the $$c$$ axis. The origin of the structure will be discussed.

Oral presentation

Magnetic Structure of a Frustrated Spinel CdCr$$_{2}$$O$$_{4}$$

Matsuda, Masaaki; Osawa, Akira*; Takeda, Masayasu; Nakamura, Mitsutaka; Kakurai, Kazuhisa; Leli$`e$vre-Berna, E.*; Chung, J.-H.*; Lee, S.-H.*; Ueda, Hiroaki*; Takagi, Hidenori*

no journal, , 

no abstracts in English

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