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論文

Magnetization study on the Ising ferromagnet URhGe with high-precision angle-resolved magnetic field near the hard axis

中村 翔太*; 榊原 俊郎*; 清水 悠晴*; 橘高 俊一郎*; 河野 洋平*; 芳賀 芳範; Pospisil, J.; 山本 悦嗣

Progress in Nuclear Science and Technology (Internet), 5, p.123 - 127, 2018/11

Dc magnetization measurements have been performed on the orthorhombic Ising ferromagnet Urge. We observed a clear first-order reorientation transition with a small hysteresis and estimated the tricritical point to be around 4 K. The magnetization and the thermal expansion data indicate the presence of a characteristic temperature of about 1 K.

論文

Inelastic X-ray scattering of $$RT$$Al$$_3$$ ($$R$$ = La, Ce, $$T$$ = Cu, Au)

筒井 智嗣*; 金子 耕士; Pospisil, J.; 芳賀 芳範

Physica B; Condensed Matter, 536, p.24 - 27, 2018/05

 パーセンタイル:100(Physics, Condensed Matter)

Inelastic X-ray scattering (IXS) experiments of RTAl$$_3$$ ($$R$$ = La Ce, $$T$$ = Cu, Au) were carried out at 300 and 5.5 K. The spectra between LaCuAl$$_3$$ and CeCuAl$$_3$$ (LaAuAl$$_3$$ and CeAuAl$$_3$$) are nearly identical at both temperatures except for temperature factors such as temperature dependence of Bose factor in IXS spectra and effect on thermal expansion. This means that no evident temperature dependence of IXS spectra was observed in CeTAl$$_3$$ ($$T$$ = Cu, Au).

論文

Critical behavior of magnetization in URhAl; Quasi-two-dimensional Ising system with long-range interactions

立岩 尚之; Pospisil, J.*; 芳賀 芳範; 山本 悦嗣

Physical Review B, 97(6), p.064423_1 - 064423_10, 2018/02

 被引用回数:1 パーセンタイル:59.26(Materials Science, Multidisciplinary)

強磁性体URhAlの磁気臨界現象を研究した。自発磁化の臨界指数$$beta$$、磁化率の指数$$gamma$$、強磁性転移温度$$T_{rm C}$$における磁化の臨界指数$$delta$$を求めた。それぞれ$$beta$$=0.287$$pm$$0.005, $$gamma$$=1.47$$pm$$0.02, $$delta$$=6.08$$pm$$0.04と決定された。これらの臨界指数はWidomのスケーリング則($${delta}{,}={,}1+{,}{gamma}/{beta}$$)を満たしている。得られた結果は、二次元イジングモデルについての繰り込み群を用いた理論モデルで説明される。

論文

ScPd$$_2$$Al$$_3$$; New polymorphic phase in Al-Pd-Sc system

Pospisil, J.; 芳賀 芳範; 中島 邦久; 石川 法人; C$'i$sa$v{r}$ov$'a$, I.*; 立岩 尚之; 山本 悦嗣; 山村 朝雄*

Solid State Communications, 268, p.12 - 14, 2017/12

 パーセンタイル:100(Physics, Condensed Matter)

A new compound of the composition ScPd$$_2$$Al$$_3$$ showing polymorphism has been discovered. At room temperature, it crystalizes in the orthorhombic structure, but it transforms into a cubic phase above 1053$$^{circ}$$C. ScPd$$_2$$Al$$_3$$ exists as a very stable intermetallic phase just in the vicinity of the icosahedral quasicrystal Al$$_{54}$$Pd$$_{30}$$Sc$$_{16}$$.

論文

Magnetoresistance and Hall effect of antiferromagnetic uranium compound URhIn$$_5$$

芳賀 芳範; 松本 裕司*; Pospisil, J.; 立岩 尚之; 山本 悦嗣; 山村 朝雄*; Fisk, Z.*

Journal of Physics; Conference Series, 807(1), p.012015_1 - 012015_4, 2017/04

Transport characteristics of an antiferromagnetic uranium compound URhIn$$_5$$ are studied. The antiferromagnetic transition leads to a formation of a gap on the Fermi surface as demonstrated by a hump in the resistivity behavior as a function of temperature. Hall effect, magnetoresistance and de Haas-van Alphen study consistently demonstrate a small carrier concentration in the antiferromagnetic state suggesting that majority of the Fermi surface vanishes.

論文

Effect of pressure on magnetism of UIrGe

Pospisil, J.; 郷地 順*; 芳賀 芳範; 本多 史憲*; 上床 美也*; 立岩 尚之; 神戸 振作; 長崎 尚子*; 本間 佳哉*; 山本 悦嗣

Journal of the Physical Society of Japan, 86(4), p.044709_1 - 044709_6, 2017/04

 被引用回数:5 パーセンタイル:26.6(Physics, Multidisciplinary)

The effect of hydrostatic pressure on the electronic state of the antiferromagnet UIrGe is reported. A series of resistivity measurements up to 15 GPa demonstrated the Neel temperature decreases with increasing pressure and vanishes around 12 GPa. The transition from antiferromagnetic to paramagnetic phase appears to be of first order. A moderate increase in the effective mass was detected in the vicinity of the critical pressure.

論文

Switching of magnetic ground states across the UIr$$_{1-x}$$Rh$$_x$$Ge alloy system

Pospisil, J.; 芳賀 芳範; 神戸 振作; 徳永 陽; 立岩 尚之; 青木 大*; 本多 史憲*; 仲村 愛*; 本間 佳哉*; 山本 悦嗣; et al.

Physical Review B, 95(15), p.155138_1 - 155138_15, 2017/04

 被引用回数:6 パーセンタイル:30.1(Materials Science, Multidisciplinary)

We investigated the evolution of magnetism in UIr$$_{1-x}$$Rh$$_x$$Ge system by systematic study on high-quality single crystals. We find a field-induced first order transition in the vicinity of the critical magnetic field along the $$b$$ axis in the entire UIr$$_{1-x}$$Rh$$_x$$Ge system, including the ferromagnetic region.

論文

Properties and collapse of the ferromagnetism in UCo$$_{1-x}$$Ru$$_{x}$$Al studied in single crystals

Pospisil, J.; Opletal, P.*; Vali$v{s}$ka, M.*; 徳永 陽; Stunault, A.*; 芳賀 芳範; 立岩 尚之; Gillon, B.*; 本多 史憲*; 山村 朝雄*; et al.

Journal of the Physical Society of Japan, 85(3), p.034710_1 - 034710_10, 2016/03

 被引用回数:8 パーセンタイル:26.29(Physics, Multidisciplinary)

We have investigated the ferromagnetic (FM) phase, which suddenly develops in UCo$$_{1-x}$$Ru$$_{x}$$Al and is isolated by paramagnetic regions on both sides from the parent UCoAl and URuAl. We conclude that both criticalities are influenced by disorder. Criticality on the UCoAl side has character of a clean FM metal, while on the Ru rich side it has the character of a magnetically inhomogeneous system involving a Griffiths phase.

口頭

Magnetic phases in pseudoternary system UCo$$_{1-x}$$Ru$$_x$$Al

Pospisil, J.; 芳賀 芳範; 立岩 尚之; 山本 悦嗣

no journal, , 

UCoAl and URuAl remain paramagnetic at temperatures at least down to 30 mK. At He temperatures, UCoAl shows a metamagnetic transition at a magnetic field of 0.6 T applied along the c-axis. Despite the paramagnetism of parent compounds a huge dome of stable ferromagnetism exists over a wide concentration range of pseudoternary UCo$$_{1-x}$$Ru$$_x$$Alcompounds. For x $$>$$ 0.4, there seems to exist two ferromagnetic phases depending on temperature. We have grown three single crystals of the representative composition x = 0.56, 0.70 and 0.78, respectively, and investigated the character and temperature range of stability of the two ferromagnetic phases. A scenario will be discussed considering different coherence of the two magnetically ordered phases.

口頭

Evolution of ferromagnetism in Ru doped UCoGe studied by PND and XMCD

Pospisil, J.; 芳賀 芳範; 山本 悦嗣; 竹田 幸治; 岡根 哲夫; 山上 浩志*; Vali$v{s}$ka, M.*; Stunault, A.*; Gillon, B.*; Prokes, K.*; et al.

no journal, , 

We present that Ru substitution on the Co site in UCoGe leads to an initial sharp increase of the Curie temperature TC up to the maximum of 8.5 K for 12 of dopant. Further increase of the Ru content leads to the suppression of both the TC and spontaneous magnetic moment. Hand in hand with ferromagnetism increase suppression of superconductivity appears. Concentration dependence of the critical exponents of resistivity and heat capacity together with scaling of the TC has signs of the non-Fermi liquid (nFL) behavior around 30 of Ru. Latter performed PND and XMCD experiments assign ferromagnetism enhancement to growth of uranium orbital moment and mainly to dramatic transformation in Co sublattice. In contrast to parent UCoGe, we found parallel orientation of the U and Co moments in UCo$$_{0.96}$$Ru$$_{0.03}$$Ge and UCo$$_{0.88}$$Ru$$_{0.12}$$Ge single crystals.

口頭

アクチノイド化合物の新物質探索とその特性

芳賀 芳範; 松本 裕司*; 立岩 尚之; Pospisil, J.; 山本 悦嗣

no journal, , 

アクチノイド化合物、特にウラン化合物における新物質探索について報告する。アーク溶解、フラックス法、気相成長などにより最近得られた新物質およびその物性をまとめる。

口頭

UIrSiの単結晶育成と基礎物性

郷地 順; Pospisil, J.; 芳賀 芳範; 立岩 尚之; 山本 悦嗣

no journal, , 

UIrSiは斜方晶TiNiSi型の結晶構造を持つ。先行研究では、結晶場の影響により、80K以下で磁化率がキュリーワイス則から外れ、さらに8K以下で近藤効果による電気抵抗の増大が観測されている。今回、我々は、高純度試料について基礎物性の測定を行うことで、より詳細な情報を得ることを目的として単結晶を育成し、さらに超高真空エレクトロトランスポート法による精製を行った。講演では作製したUIrSiの結晶パラメタ及び、電気抵抗、比熱、磁化率などの測定結果について議論を行う予定である。

口頭

ウランカルコゲナイド$$beta$$-US$$_2$$単結晶$$^{33}$$S同位体濃縮

酒井 宏典; 服部 泰佑; 徳永 陽; 神戸 振作; Pospisil, J.; 立岩 尚之; 山本 悦嗣; 芳賀 芳範

no journal, , 

$$beta$$-US$$_2$$は、巨大磁気抵抗効果を示し、その機構について興味が持たれている。核磁気共鳴(NMR)法を用いてその微視的研究を行うために、安定同位体$$^{33}$$S濃縮を行った$$beta$$-US$$_2$$単結晶を育成した。当日は、その単結晶の諸物性を報告する。

口頭

Magnetocrystalline anisotropy of UIrGe compound

Pospisil, J.; 郷地 順*; 芳賀 芳範; 立岩 尚之; 山本 悦嗣; 徳永 陽; 神戸 振作

no journal, , 

UIrGe is an antiferromagnet crystallizing in the same orthorhombic structure as the ferromagnetic superconductors UCoGe and URhGe. We have studied physical properties on single crystal samples. Antifferomagnetic transition at 16.5 K was clearly observed, in consistent with the previous study. However, the results of electrical resistivity measurements obtained for our relatively high quality sample differ significantly from the previous reports, suggesting that the transport properties are significantly affected by the sample quality.

口頭

強磁性ウラン化合物URh$$_6$$X$$_4$$(X = Si, Ge)単結晶の物性

芳賀 芳範; 松本 裕司*; 中村 友紀*; Pospisil, J.; 立岩 尚之; 山本 悦嗣; 本多 史憲*; 本間 佳哉*; 青木 大*; 山村 朝雄*

no journal, , 

URh$$_6$$X$$_4$$(X = Si, Ge)は六方晶LiCo$$_{6}$$P$$_{4}$$型結晶構造をとる強磁性体である。今回、微少単結晶の育成に成功し、その物性の詳細を報告する。両者はいずれも15K付近にキュリー点を持ち、強い1軸異方性を示す。また、電子比熱係数は強磁性状態で60mJ/K$$^2$$molと、かなり増大していることがわかった。

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