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up to 30T稲見 俊哉; 大和田 謙二; 松田 康弘*; Ouyang, Z. W.*; 野尻 浩之*; 松村 武*; 奥山 大輔*; 村上 洋一*
Journal of Physics; Conference Series, 211, p.012010_1 - 012010_6, 2010/02
被引用回数：3 パーセンタイル：75.85(Physics, Applied)Quite recently, successive metamagnetic transitions between 16T and 28T were reported on the rare-earth tetraboride TbB. Considerable attentions have been attracted on this peculiar behavior. Recently, X-ray diffraction experiments under pulsed high magnetic field have been developed at several places. In order to examine the magnetic structures at high magnetic fields, we applied this technique to TbB. Small magnetic X-ray scattering cross section was overcome by utilizing resonance enhancement. The obtained field, polarization, and scattering angle dependence of magnetic reflections indicates that magnetic moments perpendicular to the magnetic field exist in the high-field plateau phases. This result is inconsistent with normal fractional magnetization plateau phases that posses only magnetic moments parallel or antiparallel to the field. In order to resolve this discrepancy, we propose magnetic structures that consist of Ising spins and XY spins.
松田 康弘*; Her, J. L.*; 稲見 俊哉; 大和田 謙二; Ouyang, Z. W.*; 岡田 郷子*; 野尻 浩之*; 光田 暁弘*; 和田 裕文*; 吉村 一良*; et al.
Journal of Physics; Conference Series, 190, p.012019_1 - 012019_6, 2009/11
被引用回数：7 パーセンタイル：85.24(Physics, Condensed Matter)
-edge X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectra (XAS) in several rare-earth elements have been studied in pulsed high magnetic fields up to 40 T. XMCD spectrum of Eu in EuNi
(Si
Ge
) shows a characteristic two peak structure, reflecting the valence fluctuation. However, in YbInCu, it is found that the XMCD spectrum of Yb shows only a single peak. In contrast to XMCD, two absorption bands in XAS are observed in both compounds. The intensity ratio between the two absorption bands changes significantly with increasing magnetic field in these materials, suggesting the field-induced valence change. The high magnetic field XMCD and XAS measurements have also been conducted in an antiferromagnetic heavy fermion compound CeRhSi. The Ce valence is found to be nearly trivalent and insensitive to magnetic field. The XMCD at Ce 
-edge increases rapidly around 26 T corresponding to the metamagnetic transition.
松田 康弘*; Ouyang, Z. W.*; 野尻 浩之*; 稲見 俊哉; 大和田 謙二; 鈴木 基寛*; 河村 直己*; 光田 暁弘*; 和田 裕文*
Physical Review Letters, 103(4), p.046402_1 - 046402_4, 2009/07
被引用回数：53 パーセンタイル：87.11(Physics, Multidisciplinary)価数揺動を示す二つの物質(EuNi(SiGe)とEuNiP)についてEuのL吸収端でX線磁気円二色性(XMCD)を40Tの高磁場まで測定した。磁気的な2価のEuからの主要なXMCDに加え、非磁性の3価のEuからの明瞭なXMCDが観測された。この結果はどちらの価数の5d電子は磁気的に偏極していることを示している。また、それぞれの価数での5d電子の偏極度の比は物質依存であることも示された。XMCDの起源に対する可能な説明と偏極度の比の物質依存性についての説明を伝導電子とf電子の混成の点から議論する。
稲見 俊哉; 大和田 謙二; 松田 康弘*; Ouyang, Z. W.*; 野尻 浩之*; 松村 武*; 奥山 大輔*; 村上 洋一*
Journal of the Physical Society of Japan, 78(3), p.033707_1 - 033707_4, 2009/03
被引用回数：16 パーセンタイル：65.77(Physics, Multidisciplinary)Resonant magnetic X-ray diffraction experiments on the Shastry-Sutherland lattice TbB were carried out under pulsed magnetic fields up to 30 T at 8 K. TbB exhibits a multi-step magnetization process above 16 T below about 20 K when magnetic fields are applied along the 
-axis. We examined the intensity of the 010 magnetic reflection as a function of magnetic field and found that the magnetization plateau phases are accompanied by large XY components of magnetic moments. We propose novel magnetic structures which consist of XY spins and Ising spins for the plateau phases. We also propose that energy level-crossing and its inherent degeneracy give rise to the successive met magnetic transitions in TbB.
Pt using pulsed magnetic field X-ray diffractionOuyang, Z. W.*; 松田 康弘*; 野尻 浩之*; 稲見 俊哉; 大和田 謙二; 坪田 雅己*; 左近 拓男*; 福田 敬*; 掛下 知行*
Journal of Applied Physics, 102(11), p.113917_1 - 113917_6, 2007/12
被引用回数：1 パーセンタイル：5.42(Physics, Applied)X-ray diffraction experiments in pulsed magnetic fields were performed to study the giant magnetic-field-induced strain in the martensitic phase of ordered FePt alloy. The field dependence of the arrangement of the variants (crystallographic domains) was observed directly in pulsed magnetic fields for the first time. The variants with the axis perpendicular to the magnetic field are transformed into variants with the axis nearly parallel to the magnetic field. Moreover, we found that the reorientation behaviors are different for different variants with the same crystallographic direction. The results demonstrate the crucial importance of microscopic investigation, such as X-ray diffraction analysis, of the martensitic transition. We also found that the magnetic-field-induced strain associated with the rearrangement of the variants occurs even in a very fast sweeping pulsed field of up to 1.9
10
T/s at 1 T.
の多段磁化過程に関する考察稲見 俊哉; 大和田 謙二; Ouyang, Z. W.*; 松田 康弘*; 野尻 浩之*; 松村 武*; 奥山 大輔*; 村上 洋一*
no journal, ,
正方晶希土類四硼化物RBは希土類イオンがShastry-Sutherland格子と等価な格子を組み、磁気及び四極子のフラストレーションの観点から関心を集めている。このうちTbBでは、c軸に磁場を印加すると、約30Tで飽和するまでに磁化プラトーを伴う多段の相転移をすることが磁化測定において発見され、それぞれの相でどのような磁気構造をとっているのか、また、どういう機構によるものか、興味が持たれている。われわれは、前回、パルス磁場下共鳴X線回折実験の結果から、多段転移相が
面内成分の秩序を伴うという、磁化プラトーでは異例の報告を行った。この結論を元に、強いXY型の基底状態とIsing型の励起状態というモデルを考える。このモデルは、面内異方性が無限大の場合、第1,第2,第3近接相互作用の広い範囲で、1/2プラトーを示す。さらに、フラストレーションの効果により、この磁化ステップが分裂するという計算結果を示す。
の多段磁化過程に関する考察,2稲見 俊哉; 大和田 謙二; Ouyang, Z. W.*; 松田 康弘*; 野尻 浩之*; 松村 武*; 村上 洋一*
no journal, ,
Shastry-Sutherland格子を組むTbBは基底状態がXY型の反強磁性体であるにもかかわらず、c軸に磁場を印加した場合、その磁化過程は17T以上で多段の磁化プラトーを示す。以前、強磁場下共鳴X線磁気散乱の結果を元にこの磁下過程の原因を考察したが、新たに加わった実験結果を加味して、さらに考察を進める。
稲見 俊哉; 大和田 謙二; 松田 康弘*; Ouyang, Z. W.*; 野尻 浩之*; 松村 武*; 奥山 大輔*; 村上 洋一*
no journal, ,
In the last five years, the active development of X-ray diffraction techniques under pulsed high magnetic field has enabled us to observe structural changes of crystals above 30 T. Since X-rays are also an experimental tool for detecting electronic degrees of freedom through resonant process, the development of resonant X-ray diffraction techniques under pulsed high magnetic field introduces a new microscopic probe to the high magnetic field science. After several improvements of the experimental techniques, we observed field dependence of the 100 and 500 magnetic reflections of the tetragonal rare-earth tetraboride TbB, which exhibits a number of magnetization plateaus between 16 T and 28 T. The obtained field, polarization, and scattering angle dependence indicates that magnetic moments perpendicular to the magnetic field exist in the high-field plateau phases. This result is inconsistent with normal fractional magnetization plateau phases that consist of up and down spins.
