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論文

Magnetic ordering and structural phase transitions of Nd$$_{3}$$$$T$$$$_{4}$$Sn$$_{13}$$ ($$T$$ = Rh and Ir)

下田 愛海*; 岩佐 和晃*; 桑原 慶太郎*; 佐賀山 基*; 中尾 裕則*; 石角 元志*; 大原 高志; 中尾 朗子*; 星川 晃範*; 石垣 徹*

JPS Conference Proceedings (Internet), 38, p.011091_1 - 011091_6, 2023/05

https://doi.org/10.7566/JPSCP.38.011091

Synchrotron X-ray diffraction study revealed that Nd$$_{3}$$$$T$$$$_{4}$$Sn$$_{13}$$ ($$T$$ = Rh and Ir) undergo structural phase transitions characterized by the wave vector $$q$$$$_{rm L}$$=(1/2,1/2,0). Neutron diffraction study revealed antiferromagnetic ordering below $$T$$$$_{rm N}$$ = 1.65 and 1.42 K for Nd$$_{3}$$Rh$$_{4}$$Sn$$_{13}$$ and Nd$$_{3}$$Ir$$_{4}$$Sn$$_{13}$$, respectively, which is similar to that previously reported for Nd$$_{3}$$Co$$_{4}$$Sn$$_{13}$$. These compounds show a magnetic susceptibility saturation behavior below approximately 3 K. The results indicate emergence of anomalous electronic correlation in Nd$$_{3}$$$$T$$$$_{4}$$Sn$$_{13}$$ ($$T$$ = Co, Rh, and Ir) above $$T$$$$_{rm N}$$.

論文

Quasielastic neutron scattering probing H$$^{-}$$ dynamics in the H$$^{-}$$ conductors LaH$$_{3-2x}$$O$$_{x}$$

玉造 博夢; 福井 慧賀*; 飯村 壮史*; 本田 孝志*; 多田 朋史*; 村上 洋一*; 山浦 淳一*; 倉本 義夫*; 佐賀山 基*; 山田 武*; et al.

Physical Review B, 107(18), p.184114_1 - 184114_8, 2023/05

https://doi.org/10.1103/PhysRevB.107.184114
 被引用回数：1 パーセンタイル：0.00(Materials Science, Multidisciplinary)

Using an incoherent quasi-elastic neutron scattering (QENS) technique, we investigate H$$^{-}$$ dynamics in a series of oxyhydrides LaH$$_{3-2x}$$O$$_{x}$$ that exhibit characteristic high H$$^{-}$$ conductivity. In the end member LaH$$_{3}$$ ($$x$$ = 0), two kinds of H$$^{-}$$ dynamics are identified: the jump diffusion and the localized motion. The jump length in the jump diffusion mode increases with increasing $$T$$. The localized motion is identified as a jump between the two inequivalent sites. These dynamics are corroborated by our molecular dynamical simulations. Our QENS data suggest that similar H$$^{-}$$ dynamics occurs also in oxyhydrides LaH$$_{3-2x}$$O$$_{x}$$ ($$x$$ $$neq$$ 0), whose H$$^{-}$$ concentration dependence is consistent with the previous measurement of ionic conductivity. We also discuss the possibility that LaH$$_{3-2x}$$O$$_{x}$$ is an example of H$$^{-}$$ ion conductors governed by the concerted migration mechanism. The identified H$$^{-}$$ dynamics is a key to understanding the anomalous hydrogen concentration dependence of the diffusion coefficient in lanthanum hydrides, which has been a longstanding mystery in this compound.

論文

Investigation of the phonon dispersion associated with superlattice reflections in the BiS$$_{2}$$-based superconductor LaBiS$$_{2}$$O$$_{0.5}$$F$$_{0.5}$$

玉造 博夢; 長谷川 巧*; 佐賀山 基*; 水牧 仁一朗*; 村上 洋一*; 梶谷 丈*; 東中 隆二*; 松田 達磨*; 青木 勇二*; 筒井 智嗣*

Physical Review B, 107(2), p.024303_1 - 024303_8, 2023/01

https://doi.org/10.1103/PhysRevB.107.024303
 被引用回数：1 パーセンタイル：20.07(Materials Science, Multidisciplinary)

The phonon dispersion of a BiS$$_{2}$$-based superconductor LaBiS$$_{2}$$O$$_{0.5}$$F$$_{0.5}$$ is investigated by first-principles calculations and inelastic X-ray scattering experiments. The origin of superlattice (SL) reflections arising from transverse-type lattice modulation, which were recently reported in [J. Kajitani $textit{et al}$., J. Phys. Soc. Jpn. ${bf 90}$, 103601 (2021)], is discussed in terms of lattice dynamics. Our first-principles calculations of phonon dispersion and the Fermi surfaces (FSs) demonstrate that the phonon mode corresponding to the transverse-type lattice modulation is unstable, and the propagation vector corresponding to the SL reflections is close to the FS nesting vector, which suggests that the phonon softening originates from the FS nesting. Against these calculated expectations, measured phonon dispersion in LaBiS$$_{2}$$O$$_{0.5}$$F$$_{0.5}$$ along the Z-A direction, where the SL point is located, shows no remarkable temperature dependence, and there are no steeply declining branches accompanied with a softening around the SL point. Based on these results, we discuss the two possibilities for the transverse lattice modulation in LaBiS$$_{2}$$O$$_{0.5}$$F$$_{0.5}$$: the order-disorder type structural transition and the displacive structural transition with an overdamped mode, for both of which the local structure distortion or the short range correlation within the BiS$$_{2}$$ plane would be essential.

論文

Magnetism induced by interlayer electrons in the quasi-two-dimensional electride Y$$_{2}$$C; Inelastic neutron scattering study

玉造 博夢; 村上 洋一*; 倉本 義夫*; 佐賀山 基*; 松浦 直人*; 川北 至信; 松石 聡*; 鷲尾 康仁*; 井下 猛*; 浜田 典昭*; et al.

Physical Review B, 102(22), p.224406_1 - 224406_5, 2020/12

https://doi.org/10.1103/PhysRevB.102.224406
 被引用回数：8 パーセンタイル：42.28(Materials Science, Multidisciplinary)

Magnetic excitations in layered electride Y$$_{2}$$C have been found by inelastic neutron scattering. We have observed weak but clear magnetic scattering around the wave number $$Q = 0$$, but no magnetic order down to the lowest temperature measured (7 K). The imaginary part of the dynamical susceptibility deduced is well described by the Lorentz function of energy $$E$$ for each momentum $$Q$$. The width $$mathit{Gamma}(Q)$$ of the Lorentzian is proportional to $$Q(Q^2+kappa^{2})$$ with $$kappa^{-1} sim 4{rm AA}$$ at $$T=7$$ K. We have also found that with increasing $$Q$$ the magnetic form factor decays faster than that of a $$4d$$ electron in a single Y atom, which indicates a more extended magnetic moment in Y$$_{2}$$C. These results provide experimental evidence that the itinerant magnetism in Y$$_{2}$$C originates from the anionic electrons that reside in the interlayers. The Curie-Weiss-like behavior of the magnetic susceptibility reported in Y$$_{2}$$C is ascribed to the mode coupling effects of spin fluctuations.

論文

Gapless spin liquid in a square-kagome lattice antiferromagnet

藤原 理賀*; 森田 克洋*; Mole, R.*; 満田 節生*; 遠山 貴巳*; 矢野 真一郎*; Yu, D.*; 曽田 繁利*; 桑井 智彦*; 幸田 章宏*; et al.

Nature Communications (Internet), 11, p.3429_1 - 3429_7, 2020/07

https://doi.org/10.1038/s41467-020-17235-z
 被引用回数：47 パーセンタイル：92.12(Multidisciplinary Sciences)

Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two-dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu$$_6$$AlBiO$$_4$$(SO$$_4$$)$$_5$$Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation, and inelastic neutron scattering measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state.

論文

High-field depinned phase and planar Hall effect in the skyrmion host Gd$$_2$$PdSi$$_3$$

Hirschberger, M.*; 中島 多朗*; Kriener, M.*; 車地 崇*; Spitz, L.*; Gao, S.*; 吉川 明子*; 山崎 裕一*; 佐賀山 基*; 中尾 裕則*; et al.

Physical Review B, 101(22), p.220401_1 - 220401_6, 2020/06

https://doi.org/10.1103/PhysRevB.101.220401
 被引用回数：44 パーセンタイル：90.01(Materials Science, Multidisciplinary)

For the skyrmion-hosting intermetallic Gd$$_2$$PdSi$$_3$$ with centrosymmetric hexagonal lattice and triangular net of rare earth sites, we report a thorough investigation of the magnetic phase diagram. Our work reveals a magnetic phase with an isotropic value of the critical field for all orientations, where the magnetic ordering vector ${bf q}$ is depinned from its preferred directions in the basal plane. The bulk nature of the skyrmion lattice and of other magnetic phases was evidenced by specific-heat measurements. Resistivity anisotropy, likely originating from partial gapping of the density of states along ${bf q}$ in this Ruderman-Kittel-Kasuya-Yoshida magnet, is picked up via the planar Hall effect (PHE). The PHE confirms the single-${bf q}$ nature of the magnetic order when the field is in the hexagonal plane, and allows one to detect the preferred directions of ${bf q}$. Several scenarios for the depinned phase are discussed on the basis of the data.

論文

Magnetically induced electric polarization in Ba$$_{3}$$Fe$$_{2}$$O$$_{5}$$Cl$$_{2}$$ with tunable direction in three dimensions

阿部 伸行*; 塩澤 俊介*; 松浦 慧介*; 佐賀山 基*; 中尾 朗子*; 大原 高志; 徳永 祐介*; 有馬 孝尚*

Physical Review B, 101(18), p.180407_1 - 180407_5, 2020/05

https://doi.org/10.1103/PhysRevB.101.180407
 被引用回数：2 パーセンタイル：10.49(Materials Science, Multidisciplinary)

The correlation between magnetism and electric polarization in a chiral insulating magnet Ba$$_{3}$$Fe$$_{2}$$O$$_{5}$$Cl$$_{2}$$ has been investigated. The temperature dependence of magnetic susceptibility shows an anomaly at 564 K, suggesting the onset of antiferromagnetic order of Fe$$^{3+}$$ moments. Electric polarization appears in a magnetic field below TN due to the spin-direction-dependent metal-ligand hybridization. The direction of the electric polarization can be controlled in three-dimensional space by changing the direction of an external magnetic field. This compound also shows an antiferromagnetic-to-weak-ferromagnetic transition accompanied by a structural phase transition at 140 K.

論文

Successive phase transitions in $$R_{3}$$Ir$$_{4}$$Sn$$_{13}$$ ($$R$$: La and Ce) investigated using neutron and X-ray diffraction

中里 晟也*; 岩佐 和晃*; 橋本 大輔*; 塩澤 真未*; 桑原 慶太郎*; 中尾 裕則*; 佐賀山 基*; 石角 元志*; 大原 高志; 中尾 朗子*; et al.

JPS Conference Proceedings (Internet), 30, p.011128_1 - 011128_6, 2020/03

https://doi.org/10.7566/JPSCP.30.011128

Successive phase transitions of $$R_{3}$$Ir$$_{4}$$Sn$$_{13}$$ ($$R$$: La and Ce) were studied using neutron and X-ray diffraction techniques. A semimetal Ce$$_{3}$$Ir$$_{4}$$Sn$$_{13}$$ undergoes three phase transitions: an antiferromagnetic ordering characterized by a propagation vector $$q_{rm M}$$ = (1/2, 1/2, 2/5) below 0.6 K, a structural transformation with $$q_{rm S2}$$= (1/4, 1/4, 1/4) at 2.0 K, and another structural transformation with $$q_{rm S1}$$ = (1/2, 1/2, 0) above room temperature. La$$_{3}$$Ir$$_{4}$$Sn$$_{13}$$ was confirmed to be a superconductor below 2.5 K under the $$q_{rm S1}$$ = (1/2, 1/2, 0) structure that also appears above room temperature.

論文

Gapless magnetic excitation in a heavily electron-doped antiferromagnetic phase of LaFeAsO$$_{0.5}$$D$$_{0.5}$$

玉造 博夢*; 平賀 晴弘*; 池内 和彦*; 飯村 壮史*; 村場 善行*; 中村 充孝; 佐賀山 基*; 山浦 淳一*; 村上 洋一*; 倉本 義夫*; et al.

Physical Review B, 98(17), p.174415_1 - 174415_6, 2018/11

AA2018-0436.pdf:0.85MB

https://doi.org/10.1103/PhysRevB.98.174415
 被引用回数：3 パーセンタイル：14.14(Materials Science, Multidisciplinary)

中性子非弾性散乱実験によりLaFeAsO$$_{0.5}$$D$$_{0.5}$$の第二反強磁性母相におけるギャップレス磁気励起の研究を行った。実験の結果、他の鉄系超伝導の母物質とは異なり、LaFeAsO$$_{0.5}$$D$$_{0.5}$$では磁気励起ギャップが4Kもの非常に低い温度においてもなお観測されないことを見出した。このギャップレス励起はab面内の擬等方性に起因するものと理解され、バンド計算による先行研究の結果と一致する。さらに、この相での磁気励起強度はノンドープのLaFeAsOに比べてはるかに強いこと、及び、常磁性相においてもなおLaFeAsO$$_{0.5}$$D$$_{0.5}$$の磁気励起が存在することを見出した本研究の実験結果は、本系において電子ドープが局在性を増強すると主張する最近の研究結果を強く支持する。

論文

Nanoscale ice-type structural fluctuation in spinel titanates

鳥越 秀平*; 服部 崇幸*; 樹神 克明; 本田 孝志*; 佐賀山 基*; 池田 一貴*; 大友 季哉*; 仁谷 浩明*; 阿部 仁*; 村川 寛*; et al.

Physical Review B, 98(13), p.134443_1 - 134443_7, 2018/10

https://doi.org/10.1103/PhysRevB.98.134443
 被引用回数：13 パーセンタイル：51.13(Materials Science, Multidisciplinary)

In the spinel titanate MgTi$$_2$$O$$_4$$, the tetragonal phase collapses upon substitution of a tiny amount of Mg ion at the Ti site, and the cubic phase with the geometrical frustration is resurrected. The atomic pair distribution function (PDF) and the extended X-ray absorption fine structure (EXAFS) reveal the nanoscale structural fluctuation, in which the Ti atomic displacement has the two-in two-out configuration in the cubic phase. We argue that the geometrical frustration plays an essential role in the collapse of the tetragonal phase and the resultant nanoscale ice-type structural fluctuation.

論文

Magnetic excitations in the orbital disordered phase of MnV$$_2$$O$$_4$$

松浦 慧介*; 佐賀山 基*; 上原 周*; 新居 陽一*; 梶本 亮一; 蒲沢 和也*; 池内 和彦*; Ji, S.*; 阿部 伸行*; 有馬 孝尚*

Physica B; Condensed Matter, 536, p.372 - 376, 2018/05

https://doi.org/10.1016/j.physb.2017.09.085
 被引用回数：2 パーセンタイル：9.44(Physics, Condensed Matter)

We have investigated the temperature dependence of magnetic dynamics in a spinel-type vanadium oxide MnV$$_2$$O$$_4$$ by inelastic neutron scattering. The scattering intensity of excitation around 20 meV disappears in the collinear intermediate-temperature cubic-ferrimagnetic phase, which reveals that this excitation should be peculiar to the orbital ordered phase. We have found a weakly dispersive mode emergent from a non-integer wavevector $$(1.4,1.4,0)$$ at 56 K, which lies in the cubic-ferrimagnetic phase between non-coplanar ferrimagnetic and paramagnetic phases. This indicates that the probable presence of an incommensurate instability in the simple collinear structure.

論文

Spin-orbital correlated dynamics in the spinel-type vanadium oxide MnV$$_{2}$$O$$_{4}$$

松浦 慧介*; 佐賀山 基*; 上原 周*; 新居 陽一*; 梶本 亮一; 蒲沢 和也*; 池内 和彦*; Ji, S.*; 阿部 伸行*; 有馬 孝尚*

Physical Review Letters, 119(1), p.017201_1 - 017201_6, 2017/07

https://doi.org/10.1103/PhysRevLett.119.017201
 被引用回数：16 パーセンタイル：67.63(Physics, Multidisciplinary)

We investigate the magnetic dynamics in the spinel-type vanadium oxide MnV$$_2$$O$$_4$$. Inelastic neutron scattering around 10 meV and a Heisenberg model analysis have revealed that V$$^{3+}$$ spin-wave modes exist at a lower-energy region than previously reported. The scattering around 20 meV cannot be reproduced with the spin-wave analysis. We propose that this scattering could originate from the spin-orbital coupled excitation. This scattering is most likely attributable to V$$^{3+}$$ spin-wave modes, entangled with the orbital hybridization between $$t_{2g}$$ orbitals.

論文

Magnetoelectric coupling in the honeycomb antiferromagnet Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$

Khanh, N. D.*; 阿部 伸行*; 佐賀山 基*; 中尾 朗子*; 花島 隆泰*; 鬼柳 亮嗣; 徳永 祐介*; 有馬 孝尚*

Physical Review B, 93(7), p.075117_1 - 075117_6, 2016/02

https://doi.org/10.1103/PhysRevB.93.075117
 被引用回数：111 パーセンタイル：95.30(Materials Science, Multidisciplinary)

The magnetic structure and magnetoelectric effect have been investigated for single crystals of the antiferromagnet Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$. Single-crystal neutron diffraction and magnetic susceptibility measurement have revealed that the magnetic structure is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously. Co$$^{2+}$$ magnetic moments are found to be almost lying in the basal plane, which lowers the magnetic symmetry to $$C2/c'$$ with the propagation vector $$k$$ = 0. Associated with the magnetic phase transition, a sharp anomaly in the dielectric constant and displacement current indicate the appearance of the magnetoelectric below Neel temperature TN with a large coupling constant up to 30 ps/m. The existence of off-diagonal components in a magnetoelectric tensor indicate the formation of ferrotoroidic order in Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$. Such a magnetoelectric effect can be ascribed to the reduction of symmetry caused by simple antiferromagnetic order in a honeycomb network.

論文

Large trigonal-field effect on spin-orbit coupled states in a pyrochlore iridate

植松 大介*; 佐賀山 基*; 有馬 孝尚*; 石川 洵*; 中辻 知*; 高木 英典*; 吉田 雅洋*; 水木 純一郎; 石井 賢司

Physical Review B, 92(9), p.094405_1 - 094405_6, 2015/09

https://doi.org/10.1103/PhysRevB.92.094405
 被引用回数：23 パーセンタイル：66.28(Materials Science, Multidisciplinary)

The half-filled topmost valence band of Ir$$^{4+}$$ in several iridates such as Sr$$_2$$IrO$$_4$$, IrO$$_2$$, and CaIrO$$_3$$ has been proposed to originate mainly from the spin-orbit coupled $$J_{rm eff}=1/2$$ states. In pyrochlore iridates $$R_2$$Ir$$_2$$O$$_7$$ ($$R$$: rare earth), some exotic electronic states are theoretically proposed by assuming $$J_{rm eff}=1/2$$ states. However, the octahedral coordination around Ir is trigonally distorted, which may affect the energy level scheme of Ir $$5d$$ states. Here, we report spectra of resonant elastic and inelastic X-ray scattering in Eu$$_2$$Ir$$_2$$O$$_7$$ at the Ir $$L$$ edges. A large suppression of the magnetic scattering signal at the Ir $$L_{rm II}$$ edge supports the $$J_{rm eff}=1/2$$ picture rather than the $$S=1/2$$ one. The inelastic scattering spectrum indicates that the magnitude of the trigonal field on the Ir$$^{4+}$$ states is evaluated to be comparable to the spin-orbit interaction. The energy diagram of the $$5d$$ state is proposed based on the simple cluster model.

論文

Critical competition between two distinct orbital-spin ordered states in perovskite vanadates

藤岡 淳*; 安江 俊夫*; 宮坂 茂樹*; 山崎 裕一*; 有馬 孝尚*; 佐賀山 基*; 稲見 俊哉; 石井 賢司; 十倉 好紀*

Physical Review B, 82(14), p.144425_1 - 144425_12, 2010/10

https://doi.org/10.1103/PhysRevB.82.144425
 被引用回数：54 パーセンタイル：85.54(Materials Science, Multidisciplinary)

We have investigated the spin/orbital phase diagram in the perovskite orthovanadate $$R$$VO$$_3$$ ($$R$$ = Eu, Y, Dy, and Ho) by measurements of magnetization, dielectric constant, specific heat, Raman scattering spectra, and X-ray diffraction, focusing on the interplay between the V $$3d$$ spin and the $$4f$$ moment of the $$R$$ ion. The results cannot be uniquely explained in terms of the exchange interaction between the V $$3d$$ spin and the $$R$$-ion $$4f$$ moment. By comparing this phase diagram with the spin/orbital ordering in TbVO$$_3$$, it is evident that the critical competition between the C-type spin/G-type orbital ordered phase and the G-type spin/C-type orbital ordered one depends not only on the GdFeO$$_3$$-type lattice distortion but also on the presence of the $$4f$$ moment of the $$R$$ ion. The magnetic field induced phase transition of the spin/orbital ordering is achieved concomitantly with polarizing $$R$$ $$4f$$ moments for DyVO$$_3$$ and HoVO$$_3$$. The results cannot be uniquely explained in terms of the exchange interaction between the V $$3d$$ spin and the $$R$$-ion $$4f$$ moment. The coupling of the $$R$$ $$4f$$ moment polarization with the lattice distortion tied with the orbital ordering of the V $$3d$$ sublattice may also be relevant to this field induced phase transition.

論文

Unconventional ferroelectric transition in the multiferroic compound TbMnO$$_{3}$$ revealed by the absence of an anomaly in $$c$$-polarized phonon dispersion

梶本 亮一; 佐賀山 基*; 佐々井 健蔵*; 福田 竜生; 筒井 智嗣*; 有馬 孝尚*; 廣田 和馬*; 三井 由佳利*; 吉澤 英樹*; Baron, A. Q. R.*; et al.

Physical Review Letters, 102(24), p.247602_1 - 247602_4, 2009/06

https://doi.org/10.1103/PhysRevLett.102.247602
 被引用回数：12 パーセンタイル：58.34(Physics, Multidisciplinary)

TbMnO$$_{3}$$ exhibits a spontaneous electric polarization along $$mathbf{c}$$ concomitantly with a spiral spin ordering modulated along $$mathbf{b}$$ below $$T$$$$_{rm c}$$ = 28 K. We have performed inelastic X-ray scattering measurements on a single crystal of TbMnO$$_{3}$$ to clarify whether phonon anomalies related to the ferroelectricity exist. We measured transverse modes, especially the Mn-O-Mn bending mode polarized along $$mathbf{c}$$ and propagating along $$mathbf{b}$$, which we expect is most relevant to the ferroelectricity. However, no anomaly was found in the phonon dispersion below 50 meV across $$T$$$$_{rm c}$$. The present result suggests that the mechanism of ferroelectricity in TbMnO$$_3$$ is different from that of a conventional displacive-type ferroelectric. The weak coupling between electric polarization and lattice in TbMnO$$_{3}$$ strongly suggests that the ferroelectricity is mainly derived from the spiral spin ordering.

論文

Structural transformation on the pressure-induced metal-insulator transition in PrFe$$_{4}$$4P$$_{12}$$

川名 大地*; 桑原 慶太郎*; 佐藤 正志*; 高木 正俊*; 青木 勇二*; 神木 正史*; 佐藤 英行*; 佐賀山 基*; 長壁 豊隆; 岩佐 和晃*; et al.

Journal of the Physical Society of Japan, 75(11), p.113602_1 - 113602_4, 2006/11

https://doi.org/10.1143/JPSJ.75.113602
 被引用回数：11 パーセンタイル：55.93(Physics, Multidisciplinary)

充填スクッテルダイト化合物PrFe$$_{4}$$P$$_{12}$$は常圧で金属状態であり、T$$_{A}$$=6.5K以下で非磁性秩序相を持つ。P$$_{C}$$=2.4GPaの圧力下でこの非磁性秩序相は消失し、高温下では金属状態であるが、低温下で絶縁体秩序相へと相転移する。われわれはこの物質に対し、単結晶X線回折実験を行った。その結果、P$$_{C}$$以上で、金属-絶縁体転移が生じる温度で、立方晶から斜方晶への結晶構造の転移を発見した。同時に格子定数の不連続な飛びを観測し、この圧力下での転移が一次転移であることを発見した。また、P$$_{C}$$及びT$$_{A}$$以下の非磁性秩序相で観測された(100)超格子反射が、P$$_{C}$$以上で低温下の絶縁体相で消失することを発見した。格子定数の変化や超格子ピークが消失する実験事実は、P$$_{C}$$以上で低温下の絶縁体相が(高圧下中性子回折実験で明らかにされた)反強磁性秩序相であることを考慮すると、よく説明されることがわかった。

口頭

中性子磁気散乱によるSmBaMn$$_{2}$$O$$_{6}$$の磁気構造研究

鬼柳 亮嗣; 山田 重樹*; 青木 博*; 佐賀山 基*; 茂吉 武人*; 中尾 朗子*; 有馬 孝尚*

no journal, , 

ReBaMn$$_{2}$$O$$_{6}$$で表わされるMn酸化物はAサイトが秩序化したダブルペロブスカイト型構造をとり、電荷, 軌道, スピンが競合した多彩な秩序を示す。Re=SmのSmBaMn$$_{2}$$O$$_{6}$$は380Kで電荷-軌道の秩序化、200K付近で電荷-軌道の再編と反強磁性相転移を起こす。本研究では、反強磁性相での磁気構造と、電荷-軌道の秩序化と反強磁性相発現の相関を明らかにするため、中性子磁気散乱を用いた研究を行った。測定はJ-PARC/MLFの中性子単結晶回折装置SENJUを用いて行った。測定の結果、反強磁性相の磁気秩序化に伴う磁気反射が観測され、電荷-軌道の秩序化パターンと整合する磁気秩序パターンが示唆された。また、超格子反射や磁気反射の温度変化から、反強磁性相は電荷-軌道秩序の再編が引き金となり発現していることが明らかとなった。

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中性子強吸収体SmBaMn$$_{2}$$O$$_{6}$$の結晶・磁気構造研究

鬼柳 亮嗣; 山田 重樹*; 青木 博*; 佐賀山 基*; 茂吉 武人*; 中尾 朗子*; 有馬 孝尚*

no journal, , 

RE$$_{1-x}$$AE$$_{x}$$MnO$$_{3}$$(RE=3価の希土類、AE=2価のアルカリ土類)で表されるMn酸化物は、巨大磁気抵抗に代表される様々な物性を示す物質群として盛んに研究が行われている。SmBaMn$$_{2}$$O$$_{6}$$はAサイトが秩序化したダブルペロブスカイト型構造をもち、380Kで電荷-軌道の秩序化、200K付近で電荷-軌道秩序の再編と反強磁性相転移を起こす。また、10K付近においても帯磁率に異常が観測されている。本研究では、SmBaMn$$_{2}$$O$$_{6}$$の反強磁性相や相転移の詳細を調べるため、J-PARC/MLFの単結晶装置SENJUを用いて単結晶回折実験を行った。測定の結果、中性子吸収断面積の非常に大きなSmが入っているにも関わらず、広い範囲の逆格子マップを得ることができ、180K以下で磁気超格子反射が観測された。また、超格子反射の温度変化により、200K付近の反強磁性相転移温度と電荷-軌道秩序の再編の温度はわずかに異なることが明らかとなった。

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FBRサイクル実用化戦略調査研究フェーズIIの最終とりまとめについて,1; 実用化戦略調査研究フェーズIIの目標と検討の概要

向 和夫; 丹羽 元; 佐賀山 豊; 大野 勝巳*

no journal, , 

日本原子力研究開発機構(JAEA)は、電気事業者,電中研,メーカ各社の参画を得てオールジャパン体制のもと、「FBRサイクル実用化戦略調査研究」を1999年7月から実施している。2001年度から5年計画で開始したフェーズII研究においては、フェーズIで抽出したFBR,再処理及び燃料製造の各候補概念について、成立性にかかわる要素技術開発を進めるとともに、それらの成果を取り入れた設計研究を実施した。研究の実施にあたっては、安全性,経済性,環境負荷低減性,資源有効利用性,核拡散抵抗性の5つの開発目標を設定した。フェーズIIの最終とりまとめでは、FBRシステム及び燃料サイクルシステムの各候補概念について開発目標への適合可能性と現状での技術的実現性の二つの観点から技術評価を行い、有望な候補概念を選定した。これらの有望な各概念を組合せてFBRサイクルシステムとしての有望な概念を構築し総合的な技術評価を行うとともに、多面的評価として分析的アプローチにより開発目標への目標適合度を定量的に評価した。上記の技術総括の結果から、主概念及び補完概念を選択した。さらに、FBRサイクルの実用化に向けた今後の研究開発計画を提案した。

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