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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：49.08(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 , 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 for each momentum . The width of the Lorentzian is proportional to $Q(Q^2+kappa^{2})$ with $kappa^{-1} sim 4{rm AA}$ at K. We have also found that with increasing the magnetic form factor decays faster than that of a 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

Quantum dynamics of hydrogen in the iron-based superconductor LaFeAsO $_{0.9}$ D $_{0.1}$ measured with inelastic neutron spectroscopy

山浦淳一*; 平賀晴弘*; 飯村壮史*; 村場善行*; Bang, J.*; 池内和彦*; 中村充孝; 稲村泰弘; 本田孝志*; 平石雅俊*; et al.

Physical Review B, 99(22), p.220505_1 - 220505_6, 2019/06

AA2019-0126.pdf:0.9MB

https://doi.org/10.1103/PhysRevB.99.220505

被引用回数：3 パーセンタイル：16.31(Materials Science, Multidisciplinary)

鉄系超伝導体LaFeAsO $_{0.9}$ D $_{0.1}$ の非弾性中性子散乱実験により、超伝導転移温度26K以下において、5-15meVのエネルギー領域に新しい励起が生じることを見出した。なお、この励起は母物質であるLaFeAsO $_{0.9}$ F $_{0.1}$ では現れない。14.5meVと11.1meVに現れる強い励起は水素の量子ラットリングまたはバンド運動に起因し、格子間サイトが2個以上のポテンシャル極小点を有する場合にのみ出現するものと結論付けた。

論文

Bipartite magnetic parent phases in the iron oxypnictide superconductor

平石雅俊*; 飯村壮史*; 小嶋健児*; 山浦淳一*; 平賀晴弘*; 池田一貴*; Miao, P.*; 石川喜久*; 鳥居周輝*; 宮崎正範*; et al.

Nature Physics, 10(4), p.300 - 303, 2014/04

https://doi.org/10.1038/nphys2906

被引用回数：103 パーセンタイル：95.46(Physics, Multidisciplinary)

High-temperature (high- $T_{rm c}$ ) superconductivity appears as a consequence of the carrier-doping of an undoped parent compound exhibiting antiferromagnetic order; thereby, ground-state properties of the parent compound are closely relevant to the superconducting state. On the basis of the concept, a spin-fluctuation has been addressed as an origin of pairing of the superconducting electrons in cuprates. Whereas, there is growing interest in the pairing mechanism such as an unconventional spin-fluctuation or an advanced orbital-fluctuation due to the characteristic multi-orbital system in iron-pnictides. Here, we report the discovery of an antiferromagnetic order as well as a unique structural transition in electron-overdoped LaFeAsO $_{1-x}$ H (), whereby another parent phase was uncovered, albeit heavily doped. The unprecedented two-dome superconducting phases observed in this material can be interpreted as a consequence of the carrier-doping starting from the original at and advanced at parent phases toward the intermediate region. The bipartite parent phases with distinct physical properties in the second magnetic phase provide us with an interesting example to illustrate the intimate interplay among the magnetic interaction, structural change and orbital degree of freedom in iron-pnictides.

論文

Magnetic structure and electromagnetic properties of LnCrAsO with a ZrCuSiAs-type structure (Ln = La, Ce, Pr, and Nd)

Park, S.-W.*; 溝口拓*; 樹神克明; 社本真一; 大友季哉*; 松石聡*; 神谷利夫*; 細野秀雄*

Inorganic Chemistry, 52(23), p.13363 - 13368, 2013/12

https://doi.org/10.1021/ic401487q

被引用回数：33 パーセンタイル：82.03(Chemistry, Inorganic & Nuclear)

We report the synthesis, structure, and electromagnetic properties of Cr-based layered oxyarsenides LnCrAsO (Ln = La, Ce, Pr, and Nd) with a ZrCuSiAs-type structure. All LnCrAsO samples showed metallic electronic conduction. Electron doping in LaCrAsO by Mnsubstitution for the Cr sites gave rise to a metal-insulator transition. Analysis of powder neutron diffraction data revealed that LaCrAsO had Gtype antiferromagnetic (AFM) ordering, i.e., a checkerboard-type AFM ordering in the CrAs plane and antiparallel spin coupling between the adjacent CrAs planes, at 300 K with a large spin moment of 1.57 along the c axis. The magnetic susceptibility of LaCrAsO was very small (on the order of 10 $^{-3}$ emu/mol) and showed a broad hump at 550 K. First-principles density functional theory calculations of LaCrAsO explained its crystal structure and metallic nature well, but could not replicate the antiparallel spin coupling between the CrAs layers. The electronic structure of LaCrAsO is discussed with regard to those of related compounds LaFeAsO and LaMnAsO.

論文

Switching of intra-orbital spin excitations in electron-doped iron pnictide superconductors

飯村壮史*; 松石聡*; 宮川仁*; 谷口尚*; 鈴木雄大*; 臼井秀知*; 黒木和彦*; 梶本亮一; 中村充孝; 稲村泰弘; et al.

Physical Review B, 88(6), p.060501_1 - 060501_5, 2013/08

https://doi.org/10.1103/PhysRevB.88.060501

被引用回数：26 パーセンタイル：71.33(Materials Science, Multidisciplinary)

We investigate the doping dependence of the magnetic excitations in two-superconducting-dome-system LaFeAsO $_{1-x}$ D $_{x}$ . Using inelastic neutron scattering, spin fluctuations at different wavenumbers were observed under both superconducting domes around and 0.4, but vanished at corresponding to the valley. Theoretical calculations indicate that the characteristic doping dependence of spin fluctuations is rationally explained as a consequence of the switching of the two intra-orbital nestings within Fe-3 $d_{YZ, ZX}$ and 3 $d_{X^2-Y^2}$ by electron doping. The present results imply that the multi-orbital nature plays an important role in the doping and/or material dependence of the $T_{c}$ of the iron pnictide superconductors.

論文

From antiferromagnetic insulator to ferromagnetic metal; Effect of hydrogen substitution in LaMnAsO

半那拓*; 松石聡*; 樹神克明; 大友季哉*; 社本真一; 細野秀雄*

Physical Review B, 87(2), p.020401_1 - 020401_5, 2013/01

https://doi.org/10.1103/PhysRevB.87.020401

被引用回数：35 パーセンタイル：78.6(Materials Science, Multidisciplinary)

Manganese oxyarsenide hydrides LaMnAsO $_{1-x}$ H ( = 0-0.73) were synthesized by a solid state reaction under a high pressure of 2 GPa. The hydride ions H in O $^{2-}$ sites induced an insulator-to-metal conversion and suppressed the antiferromagnetic ordering of Mn spins. Instead, ferromagnetism with negative magnetoresistance was observed. The Curie temperature and saturated moment per Mn increased with up to 264 K and 1.5 , respectively, at = 0.73. These results indicate that H donate conduction electrons to the MnAs layer, mediating a direct ferromagnetic interaction between Mn atoms.

論文

Structural analysis and superconductivity of CeFeAsO $_{1-x}$ H $_{x}$

松石聡*; 半那拓*; 村場善行*; Kim, S. W.*; Kim, J. E.*; 高田昌樹*; 社本真一; Smith, R. I.*; 細野秀雄*

Physical Review B, 85(1), p.014514_1 - 014514_6, 2012/01

https://doi.org/10.1103/PhysRevB.85.014514

被引用回数：46 パーセンタイル：84.61(Materials Science, Multidisciplinary)

LnFeAsO $_{1-x}$ H $_{x}$ (=lanthanoid)の1111型鉄系超伝導体を代表して、CeFeAsO $_{1-x}$ (D,H) $_{x}$ (=0.0-0.48)で粉末中性子回折と放射光X線回折測定を行った。これらの結果は、出発物質の水素の種類に関係なく両方の試料でH $^{-}$ イオンが酸素サイトを占めていることを強く示唆している。

論文

Hydrogen in layered iron arsenides; Indirect electron doping to induce superconductivity

半那拓*; 村場善行*; 松石聡*; 井川直樹; 樹神克明; 社本真一; 細野秀雄*

Physical Review B, 84(2), p.024521_1 - 024521_7, 2011/07

https://doi.org/10.1103/PhysRevB.84.024521

被引用回数：102 パーセンタイル：94.65(Materials Science, Multidisciplinary)

Utilizing the high stability of calcium and rare-earth hydrides, CaFeAsF $_{1-x}$ H ( = 0.0-1.0) and SmFeAsO $_{1-x}$ H ( = 0.0-0.47) have been synthesized using high pressure to form hydrogen-substituted 1111-type iron-arsenide superconductors. Neutron diffraction and density functional calculations have demonstrated that the hydrogens are incorporated as H ions occupying F sites in the blocking layer of CaFeAsF. The resulting CaFeAsO $_{1-x}$ H is nonsuperconducting, whereas, SmFeAsO $_{1-x}$ H is a superconductor, with an optimal $_{rm c}$ =55 K at 0.2. It was found that up to 40% of the O $^{2-}$ ions can be replaced by H ions, with electrons being supplied into the FeAs layer to maintain neutrality (O $^{2-}$ = H + e). When exceeded 0.2, $_{rm c}$ was reduced corresponding to an electron overdoped region.

口頭

2次元エレクトライドY $_{2}$ Cにおけるアニオン電子由来磁性

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.

no journal, ,

アニオンとして振る舞う電子を内包する結晶はエレクトライドと呼ばれる。2次元エレクトライドY $_{2}$ Cは、アニオン的な電子が[Y $_{2}$ C] $^{2+}$ レイヤー間で擬2次元電子ガスとして振る舞う層状化合物である。Y $_{2}$ Cはこのアニオン電子に由来すると考えられる特異な磁性を示しており、これまでに理論・実験の両面から探査されてきた。第一原理計算によって、Y $_{2}$ Cの電子状態はferromagnetic instabilityに近いことが指摘された。一方で、実験的にはpoly試料に対する帯磁率測定の結果、磁気秩序は2Kまで観測されず、Curie-Weiss則に従うような温度依存性が観測されるものの、Weiss温度は反強磁性を示唆する負の値となり、またその大きさもサンプルごとに大きく異なっている。本研究では、poly試料を用いた中性子非弾性散乱実験を行った。その結果、磁気秩序は先行研究と同様に観測されなかった一方で、波数Q=0 $AA$^{-1}$$ 周りに微弱ながらも明瞭な磁気励起を観測した。各波数における複素帯磁率の虚部のエネルギー依存性はローレンツ関数で表され、その線幅のQ依存性からY $_{2}$ Cはnearly ferromagnetであることが判明した。これらの結果から、Y $_{2}$ CにおけるCurie-Weiss的な帯磁率の温度依存性は、守谷理論に代表されるようなスピン揺らぎのモード結合効果によるものと考えられる。また磁気形状因子のQ依存性は、Yの4d電子のそれよりも減衰が早く、実空間で磁化密度は非局在化していることが判明した。この結果は、Y $_{2}$ Cの磁性はYの4d電子に由来するものではなく、[Y $_{2}$ C] $^{2+}$ レイヤー間に存在するアニオン電子スピンに由来することを示唆している。

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