ィイD1235ィエD1U NMR Study of Uranium Oxides

D1235 铀氧化物的 D1U NMR 研究

• 批准号: 10440105
• 负责人: UEDA Yutaka
• 金额: $ 8.51万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1998
• 资助国家: 日本
• 起止时间: 1998 至 1999
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10440105/
• 关键词: ィイD1235ィエD1U NMR; UOィイD22ィエD2; Cooperative Jahn-Teller Distortion; Spin-Echo Oscillation; ィイD1171ィエD1Yb NMR; YbBィイD212ィエD2; Kondo Semiconductor; ^<235>U核磁気共鳴; アーンテラー歪み; 核磁気共鳴法; NMR; ウラン化合物; 四重極秩序; 反強磁性体

The purpose for this study is the observation of actinide and rare earth NMR and the acquisition of typical examples with respect to the interaction between actinide or rare earth nucleus and electrons. This will be the starting point of our goal. The actinide and rare earth NMR is, however, very difficult to observe the signals because of poor natural abundance or too short relaxation time. We have tried detecting actinide and rare earth NMR signals in some materials. As the result, we succeed in the observation of ィイD1235ィエD1U and ィイD1171ィエD1Yb NMR in UOィイD22ィエD2 and YbBィイD212ィエD2, respectively. In the following, each summary is presented.Seven ィイD1235ィエD1U resonance lines with a sharp line width have been observed in a 93% ィイD1235ィエD1U-ehriehed UOィイD22ィエD2 sample below 4.2 K and at zero magnetic field. This, is the first NMR observation for magnetic actinide ions. The hyperfine field at the U sites is evaluated as 252.3 ± 0.5 T, which is considered as the orbital field due to 5f-ele … More ctrons of the ィイD13ィエD1HィイD24ィエD2 state. Most interesting feature is that the electric quadrupole interaction at the ィイD1235ィエD1U sites is clearly observed in the antiferromagnetic state. In the strong LS coupling systems, an electric quadrupole interaction normally exists even in the cubic crystalline field if magnetic ordering is present, because the spatial alignment of the magnetic moments requires that of the orbital momentum and causes an axially symmetric charge distribution around the nucleus. In fact, the ィイD1235ィエD1U NMR spectrum indicates the axially symmetric electric field gradient (EFG) at the U sites. In addition, we quantitatively confirmed that the EFG is attributed to the reduction of symmetry of the 5f-wave function due to magnetic ordering.The ィイD117ィエD1O NMR experiments were also performed to investigate the magnetic structure. The oscillation phenomenon due to the quadrupole splitting in the spin-echo decay is observed in the antiferromagnetic state. This clearly shows the Jahn-Teller distortion below TN. As the result, we conclude that a non-collinear 3q-strucure is most likely of the magnetic structures proposed by the neutron scattering experiments. It is very interesting that the EFG at the ィイD1235ィエD1U sites reflects the change of the 5f-wave function, that is, quadrupole ordering, while the EFG at the ィイD117ィエD1O sites reflects the change of the lattice, that is, the cooperative Jahn-Teller transition.The ィイD1171ィエD1Yb NMR signal is observed below 10K in the single crystal of the Kondo semiconductor, YbBィイD212ィエD2, with the large shift of 66%. The hyperfine coupling constant is in good agreement with the orbital one calculated for a free YbィイD13+ィエD1 ion, indicating that the magnetic susceptibility at the low temperature limit is the Van-Vleck contribution within the J=7/2 multiplet. The nuclear spin-lattice relaxation rate at the YB site shows an activated temperature dependence below 15 K with the activation energy of 87 K, which, however, is completely different from the behavior at the B sites. The site-dependence may give us clue to reveal low energy excitations in the Kondo semiconductors. Less

这项研究的目的是观察鳗系元素和稀土元素的核磁共振，并获得有关元素元素或稀土元素核与电子相互作用的典型例子。这将是我们目标的起点。然而，由于天然丰度较低或弛豫时间太短，榄系元素和稀土元素的核磁共振很难观察到信号。我们已经尝试在一些材料中检测到了鳗系元素和稀土元素的核磁共振信号。结果，我们成功地观察到ィイD1235ィエD1U和ィイD1171ィエD1Yb核磁共振分别在UOィイD22ィエD2和YbBィイD212ィエD2中。在4.2K和零磁场下，在93%ィイD1235ィエD1U-UOィエD22 D2样品中观察到7条具有尖锐线宽的ィエD1235ィイD1U共振线。这是第一次对有磁性的榄系元素离子进行核磁共振观测。U位的超精细场为252.3±0.5T，被认为是5f-Ele…产生的轨道场ィイD13ィエD1HィイD24ィエD2状态的更多控制。最有趣的特征是，在反铁磁态下，可以清楚地观察到ィイD1235ィエD1U位的电四极相互作用。在强LS耦合系统中，即使在立方晶场中，如果存在磁有序，通常也存在电四极相互作用，因为磁矩的空间排列需要轨道动量的空间排列，并导致围绕原子核的轴对称电荷分布。事实上，ィイD1235ィエD1U核磁共振谱表明U位存在轴对称的电场梯度。此外，我们还定量地证实了EFG是由于磁有序导致5f波函数对称性降低所致。ィイD117ィエD1O核磁共振实验也用来研究其磁结构。在反铁磁态观察到自旋-回波衰变中的四极分裂引起的振荡现象。这清楚地显示了Tn以下的Jahn-Teller扭曲。因此，我们得出结论，非共线3Q结构是中子散射实验提出的最有可能的磁性结构。有趣的是，ィイD1235ィエD1U位的EFG反映了5f波函数的变化，即四极有序，而ィイD117ィエD10位的EFG反映了晶格的变化，即合作的Jahn-Teller转变。在近藤半导体ィイD1171ィエD1Yb D1Yb单晶中，在10K以下观察到ィイD212ィエD2的核磁共振信号，其位移为66%。超精细耦合常数与自由YbィイD13+ィエD1离子的轨道耦合常数符合得很好，表明低温磁化率是J=7/2多重态的Van-Vleck贡献。YB位的核自旋-晶格驰豫速率在15K以下表现出激活温度依赖性，激活能为87K，这与B位的行为完全不同。这种位置依赖性可能给我们提供线索来揭示近藤半导体中的低能激发。较少

项目成果

S.Tsutsui: "Nuclear Magnetic Moment of the First Excited State(I=2^+) of 238U"Journal of Physical Society of Japan. 67. 2641-2644 (1998)

S.Tsutsui：“238U的第一激发态(I=2^)的核磁矩”日本物理学会杂志。

Kenji Ikushima: "Scaling behavior in the Ce-Kondo semiconductor : NQR/NMR measurements of CeRhSb and CeNiSn under high pressure"Physica Review B. 60. 14537-14540 (1999)

Kenji Ikushima：“Ce-Kondo 半导体中的结垢行为：高压下 CeRhSb 和 CeNiSn 的 NQR/NMR 测量”Physica Review B. 60. 14537-14540 (1999)

K. Ikushima, H. Yasuoka, S. Tsutsui, M. Saeki, S. Nasu and M.: "Date Observation of ィイD1235ィエD1U NMR in the Antiferromagnetic State of UOィイD22ィエD2"J. Phys. Soc. Jpn.. 67-1. 65 (1998)

K. Ikushima、H. Yasuoka、S. Tsutsui、M. Saeki、S. Nasu 和 M.：“UOD22D2 反铁磁状态下的 D1235D1U NMR 的日期观察”Jpn.67-1。 (1998)

Kenji Ikushima: "^<171>Yb NMR in the Kondo Semiconductor YbB_<12>"Physica B. (in press). (2000)

Kenji Ikushima：“Kondo Semiconductor YbB_<12> 中的 ^<171>Yb NMR”Physica B.（出版中）。