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論文

T-dependent nuclear hyperfine coupling at the In site in CeIrIn$$_{5}$$

神戸 振作; 酒井 宏典; 徳永 陽; 松田 達磨; 芳賀 芳範; 竹内 徹也*; 大貫 惇睦*; Walstedt, R. E.*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA009_1 - SA009_3, 2011/07

重い電子系超伝導体CeIrIn$$_5$$の単結晶試料で$$^{115}$$In-NMR測定を行った。ナイトシフトと静帯磁率の非線形な関係は中辻らによる2流体モデルでも説明できるが、温度に依存する超微細相互作用を考えても説明できる。この場合、温度依存する項はDMFTの計算による状態密度にスケールすることが確認された。また、スピン格子緩和時間は、温度依存する超微細相互作用を考えると自然に説明できる。この場合、1成分の動的帯磁率を考慮するだけでよい。静帯磁率が2成分に見える一方、動的帯磁率は1成分でも説明できるように見えることが重い電子系の2重性のひとつの現れ方と思われる。

論文

Multipole correlations of $$t_{rm 2g}$$-orbital Hubbard model with spin-orbit coupling

大西 弘明

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA141_1 - SA141_3, 2011/07

 被引用回数:2 パーセンタイル:77.51(Physics, Multidisciplinary)

We investigate multipole properties in the ground state of a $$t_{rm 2g}$$-orbital Hubbard model with the spin-orbit coupling, by exploiting numerical techniques. Here let us consider a one-dimensional chain along the $$x$$ direction with five electrons per site. Due to the spatial anisotropy of $$t_{rm 2g}$$ orbitals, $$xy$$ and $$zx$$ orbitals are active in the absence of the spin-orbit coupling. When the spin-orbit coupling is weak, spin and orbital are independent degrees of freedom at local level. With the increase of the spin-orbit coupling, the total angular momentum turns to give a good quantum state. The spin state changes from an antiferromagnetic state to a ferromagnetic state. Regarding the orbital state, the spin-orbit coupling would lead to a complex orbital state. In the presentation, we will discuss how the spin-orbital state can be understood from the viewpoint of multipole.

論文

NMR study on AmO$$_{2}$$; Comparison with UO$$_{2}$$ and NpO$$_{2}$$

徳永 陽; 西 剛史; 神戸 振作; 中田 正美; 本間 佳哉*; 酒井 宏典; 中堂 博之

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA110_1 - SA110_3, 2011/07

 被引用回数:2 パーセンタイル:77.51(Physics, Multidisciplinary)

二酸化アメリシウムにおける低温相転移の存在は1975年に帯磁率測定から初めて報告されたが、その後それを裏付ける実験結果は報告されていなかった。本研究でわれわれは二酸化アメリシウムにおいて世界初となるNMR実験を行い、相転移の存在を微視的観点から初めて明らかにした。これにより相転移が不純物相などではなく二酸化アメリシウムそのものに由来する本質的な性質であることが確認された。発表では二酸化ウラニウム及び二酸化ネプツニウムにおけるNMR実験の結果との比較を行い、二酸化アメリシウムの低温電子状態について議論を行う。

論文

Dilute La-substitutions in CeRhIn$$_5$$ studied by means of NMR/NQR techniques

酒井 宏典; 栗田 伸之*; Miclea, C. F.*; Movshovich, R.*; Lee, H.-O.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA059_1 - SA059_3, 2011/07

La希釈効果を(Ce, La)RhIn$$_5$$系において核磁気共鳴(NMR/NQR)法を用いて微視的に調べた。In(1)サイトの4$$nu_{rm Q}$$スペクトル位置から、La 5%程度の希釈によって、Ceから移送される内部磁場は減少することがわかった。これは超微細結合定数が減少したことによるものと見られる。また緩和率測定から、反強磁性秩序状態において、La希釈に伴って、Laサイトに隣接するCeモーメントが局在モーメント的に振る舞っていることがわかった。

論文

Correlation effects on antiferromagnetism in Fe pnictides

久保 勝規; Thalmeier, P.*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA121_1 - SA121_3, 2011/07

 被引用回数:7 パーセンタイル:48.23(Physics, Multidisciplinary)

We investigate the magnetism and orbital state of the ground state of a two-orbital model proposed for Fe pnictides which includes $$d_{zx}$$ and $$d_{yz}$$ orbitals of Fe ions. We apply a Hartree-Fock approximation and a variational Monte Carlo method to this model. First, we apply the Hartree-Fock approximation. The antiferromagnetic order with ordering vector $$(pi,0)$$is stabilized by the nesting between hole and electron pockets. This antiferromagnetic state accompanies ferro-orbital order, that is, the occupancies of $$d_{zx}$$ and $$d_{yz}$$ orbitals become different. Under such ferro-orbital order, the lattice should be distorted from a tetragonal to orthorhombic structure through an electron-lattice interaction. We also apply the variational Monte Carlo method to the model. We find that correlation effects reduce the ordered moment. Even for a large value of the Coulomb interaction comparable to the band width, the ordered moment can be small.

論文

Non-magnetic to magnetic transition under high pressure in narrow-gap semiconductor $$beta$$-US$$_2$$

立岩 尚之; 芳賀 芳範; 酒井 宏典; 池田 修悟*; 松田 達磨; 山本 悦嗣; 大貫 惇睦*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA103_1 - SA103_3, 2011/07

 被引用回数:2 パーセンタイル:77.51(Physics, Multidisciplinary)

ウランカルコゲナイド化合物$$beta$$-US$$_2$$の高圧下磁化測定を行った。この物質は常圧では磁気転移を示さない。過去の電気抵抗測定から2GPa以上で圧力誘起相が存在することが示唆される。本研究では高圧下磁化測定から強磁性的相転移が1GPa以上で現れることが確認され、圧力相図が決定された。$$beta$$-US$$_2$$のウラン5f電子の結晶場基底状態はsinglet stateであることを考慮すると、希土類プラセオジム化合物Pr$$_3$$Tlなどで観測される"induced-magnetic phase"が$$beta$$-US$$_2$$の圧力下で誘起されたことが示唆される。理論モデルを用いた解析結果を報告する。

論文

Specific heat and magnetization studies of the superconducting mixed state of UBe$$_{13}$$

清水 悠晴*; 池田 陽一*; 若林 琢巳*; 天谷 健一*; 芳賀 芳範; 日高 宏之*; 柳澤 達也*; 網塚 浩*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA100_1 - SA100_3, 2011/07

 被引用回数:1 パーセンタイル:87.38(Physics, Multidisciplinary)

Low-temperature specific heat and static dc magnetization measurements have been performed in the superconducting state of the heavy-fermion compound UBe$$_{13}$$. The superconducting phase diagram was obtained from these measurements. We obtained Ginzburg-Landau parameter as a function of temperature and showed that a paramagnetic effect is present down to 0.5 K.

論文

Ultrasonic measurements on the cage-structured clathrate compound U$$_3$$Pd$$_{20}$$Si$$_6$$

柳澤 達也*; 立岩 尚之; 真山 太一*; 齋藤 旬*; 日高 宏之*; 網塚 浩*; 芳賀 芳範; 根本 祐一*; 後藤 輝孝*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA105_1 - SA105_3, 2011/07

 被引用回数:3 パーセンタイル:69.23(Physics, Multidisciplinary)

Ultrasonic measurements of U$$_3$$Pd$$_{20}$$Si$$_6$$ were performed in order to investigate elastic properties of the cage-structured compound U$$_3$$Pd$$_{20}$$Si$$_6$$. At temperatures over antiferromagnetic ordering at $$T_{rm N}$$ = 19 K, neither an up-turn anomaly nor frequency dependence of the elastic constants, regarding the ultrasonic dispersion (UD), was found. A drastic change of $$C_{44}$$ mode at $$T_{rm N}$$, in particular, implies a strong magneto-elastic coupling of 5$$f$$-electrons or a possible contribution of a ferroquadrupole interaction to the antiferromagnetism in U$$_3$$Pd$$_{20}$$Si$$_6$$.

論文

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

芳賀 芳範; 青木 大*; 本間 佳哉*; 松田 達磨; 池田 修悟*; 酒井 宏典; 山本 悦嗣; 中村 彰夫; 塩川 佳伸*; 大貫 惇睦

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

 被引用回数:0 パーセンタイル:100(Physics, Multidisciplinary)

We report reinvestigation the Np-Ga binary system. We successfully obtained NpGa$$_3$$ single crystals. Detailed investigation of the crystal structure using the single-crystal X-ray diffraction has shown that the flux-grown NpGa$$_3$$ crystallizes not in cubic but in the trigonal R$$overline{3}$$m structure. It orders ferromagnetically at 70 K with the saturation moment of 1.5 $$mu_{rm B}$$/Np. It is interesting to note that the cubic NpGa$$_3$$ orders antimagnetically at similar temperature 62 and become ferromagnetic under magnetic field with the similar saturation moment 1.6 $$mu_{rm B}$$/Np. These characteristics are understood from the structural point of view.

論文

Detailed characterization of U-Co binary compounds

松田 達磨; 菅井 孝志; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA101_1 - SA101_3, 2011/07

For U-Co binary systems, at least 6 stable phases were reported previously. These systems show a variety of physical properties. U$$_6$$Co and UCo exhibit superconductivity. Furthermore, the possible crystal structural model without inversion symmetry was proposed by analyses of X-ray powder diffractions. Recently, single crystals of UCo are succeeded to grow by the Czochralski pulling method. For comparison, polycrystalline sample was also prepared by arc melting. Below 2 K, the both samples showed zero resistivity as reported earlier. We also checked the composition of these crystals by electron probe micro analyzer (EPMA) and took the pictures of scanning SEM image. We confirmed the existence of a small amount of uranium-rich 2nd phase in these crystals. Considering these results, it can be suggested that the uranium-rich 2nd phase corresponds to U$$_6$$Co.

論文

Resonant angle-resolved photoelectron spectroscopy of substitutional solid solutions of CeRu$$_2$$Si$$_2$$

岡根 哲夫; 川崎 郁斗; 保井 晃; 大河内 拓雄*; 竹田 幸治; 藤森 伸一; 斎藤 祐児; 山上 浩志; 藤森 淳; 松本 裕司*; et al.

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA060_1 - SA060_3, 2011/07

 被引用回数:1 パーセンタイル:87.38(Physics, Multidisciplinary)

Angle-resolved photoelectron spectroscopy was measured in the Ce 3$$d$$$$rightarrow$$4$$f$$ resonance energy region for the paramagnetic state of CeRu$$_2$$Si$$_2$$, Ce$$_{0.84}$$La$$_{0.16}$$Ru$$_2$$Si$$_2$$ and LaRu$$_2$$Si$$_2$$ to investigate a variation of band structures around the quantum critical point (QCP). While the results clearly demonstrate the difference of the band structures between CeRu$$_2$$Si$$_2$$ and LaRu$$_2$$Si$$_2$$, the observed band structures of CeRu$$_2$$Si$$_2$$ and Ce$$_{0.84}$$La$$_{0.16}$$Ru$$_2$$Si$$_2$$ resemble each other. The results indicate that the Ce $$4f$$ electrons in the paramagnetic state have an itinerant character in either side of the critical composition, and Ce$$_{1-x}$$La$$_{x}$$Ru$$_2$$Si$$_2$$ near QCP is similar to CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$.

論文

Possible long-periodic magnetic structure in SmPb$$_{3}$$

伊藤 孝; 髭本 亘; 二宮 和彦; Amato, A.*; 菅井 孝志; 芳賀 芳範; 鈴木 博之*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA075_1 - SA075_3, 2011/07

立方晶$$Gamma_8$$基底SmX$$_3$$(X=In, Sn, Pb)は多彩な多極子自由度を有する興味深い系である。これら一連の物質は低温において逐次転移もしくは一次転移を示し、先行する研究により多極子の関与が示唆されている。しかし、これまでに微視的な実験データの報告はなく、秩序相の詳細は明らかにされていない。われわれは微視的実験手法であるミュオンスピン回転緩和法を用いてSmX$$_3$$(X=In, Sn, Pb)の秩序相の研究を行った。零磁場における実験結果より、すべての秩序相における主要な秩序変数が磁気多極子であることが明らかになった。さらに、秩序相における磁気構造に関する知見を得た。

論文

$$^9$$Be-NMR spin-lattice relaxation rate in heavy-fermion superconductor UBe$$_{13}$$

森田 恭平*; 原 悠大*; 坂野 準哉*; 小手川 恒*; 藤 秀樹*; 芳賀 芳範; 大貫 惇睦

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA099_1 - SA099_3, 2011/07

 被引用回数:1 パーセンタイル:87.38(Physics, Multidisciplinary)

Nuclear magnetic resonance (NMR) measurements have been carried out for a single crystal UBe$$_{13}$$ superconductor. In the normal state above the superconducting transition temperature, the nuclear spin-lattice relaxation rate obey $$sqrt{T}$$, suggesting the antiferromagnetic spin fluctuation which might be responsible for the unconventional superconductivity.

論文

Magnetic-field-induced metallic state in $$beta$$-US$$_2$$

杉山 清寛*; 広瀬 雄介*; 榎 健太郎*; 池田 修悟*; 山本 悦嗣; 立岩 尚之; 芳賀 芳範; 木田 孝則*; 萩原 政幸*; 金道 浩一*; et al.

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA104_1 - SA104_3, 2011/07

 被引用回数:1 パーセンタイル:87.38(Physics, Multidisciplinary)

Magnetic and transport properties under high magnetic field were studied on a magnetic semiconductor $$beta$$-US$$_2$$. Large magnetization reaching 1.75 $$mu_{rm B}$$ has been observed at 50 T. At the same time, resistivity decreases drastically from insulating behavior at 0 T to almost metallic characteristics at 50 T. The results are discussed based on the magnetic polaron mechanism.

口頭

Resonant X-ray diffraction study on the charge ordering transitions in the mixed valent compound EuPtP

稲見 俊哉; 道村 真司; 光田 暁弘*; 和田 裕文*

no journal, , 

We report on direct observations of the charge-ordered states in the ternary rare-earth compound EuPtP by means of resonant X-ray diffraction (RXD) at the Eu $$L_3$$ absorption edge. Based on the inhomogeneous valence states obtained by M$"o$ssbauer measurements, it is proposed that two first-order transitions at $$T_1$$=246 K and $$T_2$$=200 K accompany charge ordering of the Eu valency. We first searched superlattice and forbidden reflections and found (1 1 1) and (1 1 1$$pm$$1/3) reflections at the low-temperature phase ($$T<T_2$$) and the intermediate phase ($$T_2<T<T_1$$), respectively. These reflections exhibited characteristic photon-energy dependence, and the measured energy spectra were well reproduced by assuming spatial order of the Eu valency. As a result, we conclude that three-fold and two-fold superstructures of Eu valency exist in EuPtP between $$T_1$$ and $$T_2$$and below $$T_2$$, respectively. We also considered a lattice effect as a possible mechanism of charge ordering in metallic EuPtP.

口頭

Temperature dependence of soft X-ray photoemission spectra for YbCu$$_2$$Si$$_2$$

保井 晃; 藤森 伸一; 川崎 郁斗; 岡根 哲夫; 竹田 幸治; 斎藤 祐児; 山上 浩志; 関山 明*; 摂待 力生*; 松田 達磨; et al.

no journal, , 

YbCu$$_2$$Si$$_2$$は典型的な価数揺動物質である。これまで、YbCu$$_2$$Si$$_2$$における光電子スペクトルの温度変化測定は数例あるが、それらの得られたスペクトルに対する解釈は異なっている。これまでの実験は真空紫外領域の入射光を使ったものばかりで、得られるスペクトルにはバルクのYb$$^{2+}$$ 4$$f$$ピークの低エネルギー側に表面状態に起因するピークが大きく観測されていた。バルクの電子状態の温度変化を詳細に調べるには、表面からの寄与を抑えなければならない。そこで、われわれはバルクの電子状態を調べるのに有用である軟X線光電子分光(SX-PES)実験をSPring-8のBL23SUにて行った。得られたSX-PESスペクトルにおいて、表面Yb$$^{2+}$$ピークの寄与はとても小さい。温度を上げていくとバルクのYb$$^{2+}$$ 4$$f$$ピークは高エネルギー側にシフトしていくが、Yb$$^{3+}$$多重項ピークに関してはシフトしないという結果が得られた。このような振る舞いは単サイトの不純物アンダーソンモデルでは説明できないため、YbCu$$_2$$Si$$_2$$においては、近藤格子効果が効いているものと考えられる。

口頭

Intermediate valence quasicrystals in Yb-based alloys under pressure

綿貫 徹; 川名 大地*; 町田 晃彦; Tsai, A. P.*

no journal, , 

A quasiperiodic intermediate-valence system has been demonstrated by applying pressure to an icosahedral Cd-Mg-Yb quasicrystal as well as our previous report on a Cd-Yb quasicrystal. Yb LIII-edge X-ray absorption spectroscopy experiments demonstrate that the Yb valence increases continuously upon compression from the divalent state at ambient pressure to reach a valence of 2.37 at 16.3 GPa. These Yb-based quasiperiodic intermediate-valence systems have the following two characteristic features in comparison with known other quasicrystals; (1) each quasiperiodic lattice point has a charge degree of freedom, (2) the strength of electron correlations can be controlled by pressure.

口頭

Resonant X-ray diffraction study of multipole ordering in CePd$$_3$$S$$_4$$

道村 真司; 稲見 俊哉; 松岡 英一*; 綿引 正倫*; 小野寺 秀也*

no journal, , 

Rare-earth palladium bronzes RPd$$_3$$S$$_4$$ (R = La-Yb) crystallize in a cubic structure with the space group $$P$$m-3n. Except for R = Tm, the degeneracy of the orbital degree of freedom is expected to remain in the crystalline electric field (CEF) ground states of R$$^{3+}$$ in RPd$$_3$$S$$_4$$. Accordingly, the physical properties will be different from the properties of simple magnetic ordering compounds, since mulitpole order becomes possible too. CePd$$_3$$S$$_4$$ orders ferromagnetically below T$$_{rm C}$$ = 6.3 K. It was found that the magnetic structure of CePd$$_3$$S$$_4$$ is canted with a canting angle of 51 $$^{circ}$$ by neutron powder diffraction experiments. Such structure occurs in HoB$$_2$$C$$_2$$ too, where is caused by the simultaneous occurrence of antiferroquadrupolar (AFQ) and ferromagnetic (FM) orders. This calls for investigating on the quadrupolar ordering in RPd$$_3$$S$$_4$$. We performed resonant X-ray diffraction at the Ce-$$L_3$$ absorption edge on CePd$$_3$$S$$_4$$ to study the states of quadrupolar ordering in the FM state. We observed two reflections forbidden for crystal structure, 300 and 410 reflections. Both reflections grow below T$$_{rm C}$$ and be unambiguously related to the order parameter. In the azimuthal angle dependence of 410 reflection for both $$pi$$-$$pi$$' and $$pi$$-$$sigma$$' scattering processes, the periodicals are about 180 $$^{circ}$$. The intensity of the $$pi$$-$$sigma$$' scattering process is about 20 $$%$$ of the intensity of the $$pi$$-$$pi$$' scattering process. This result suggests that an $$O_2^0$$ type - AFQ ordering coexists with FM ordering.

口頭

Neutron scattering study on rattling in filled-skutterudite compounds

金子 耕士; 松田 達磨; 木村 宏之*; 野田 幸男; 目時 直人; 門馬 綱一*; 泉 富士夫*

no journal, , 

Recently, a large-amplitude thermal vibration of a guest ion inside an oversized cage, called rattling, is considered to play a vital role for unconventional physical properties in $$cage$$ $$compounds$$. A precise single-crystal neutron diffraction and a maximum-entropy analysis are powerful method to reveal unconventional motion of rattling ions; this combination enables us a model-independent analysis to obtain an time-averaged picture of rattling motion in real space. Widely distributed anisotropic nuclear densities of $$R$$ in the Sb icosahedron cage were revealed in PrOs$$_4$$Sb$$_{12}$$, NdOs$$_4$$Sb$$_{12}$$ and PrRu$$_4$$Sb$$_{12}$$ at room temperature. Note that a substantial difference was found in a distribution of rattling ions between $$RT_4$$Sb$$_{12}$$ with $$T$$=Os and Ru. The difference between $$RT_4$$Sb$$_{12}$$ with $$T$$=Os and Ru implies that the size mismatch is not a necessary and sufficient condition for anharmonicity, and may related to the cage type in skutterudites.

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