2-Dimensional Nuclear Magnetism of Adsorbed ^3He Thin Films

吸附^3He薄膜的二维核磁性

• 批准号: 05452048
• 负责人: FUKUYAMA Hiroshi
• 金额: $ 4.74万
• 依托单位: University of Tsukuba
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1993
• 资助国家: 日本
• 起止时间: 1993 至 1994
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-05452048/
• 关键词: Low Dimension Quantum Spin System; Quantum Solid; Exchange Interaction; Ultra-low Temperature Physics; Nuclear Magnetic Resonance; Heat Capacity

1.NMR ExperimentsContinuous wave NMR was used to study pure ^3He films at coverage from below 2nd layr completion to above the ferromagnetic peak coverage at -2.5 layrs. The films were adsorbed on Grafoil and were cooled to temperatures as low as 0.075mK.The first layr magnetization followed Curie law very well, with a Weiss constant of less than 0.01mK.We measured the ferromagnetic 2nd layr magnetization to temperatures far below the exchange energy (J) as a function of coverage. Preliminary analysis indicated that J did not vary strongly with coverage, and that the zero temperature 2nd layr magnetization was linear in 2nd layr density. Both of these properties are consistent with there being two phases in coexistence., only one of which is ferromagnetic.2.Hear Capacity MeasurementsWe have measured heat capacities of ^3He thin films adsorbed on Grafoil at temperatures between 0.3 and 60mK for areal densities where the 2nd layr solid ^3He shows antiferromagnetism.. The measured heat capacities do not seem to agree qualitatively with previous measurements by Graywall. Our data show rounded maxima at about 2mK and 1/T^2 behavior at high temperatures, while he observed rather sharp peaks at 2.5mK and 1/T behavior at high temperatures. Although our data agree semi-quantitatively with theoretical calculations for the spin-1/2 Heisenberg antiferromagnet on the triangular lattice studied by Elstner et al., the magnitude of measured heat capacities is smaller than the theoretical one by 30% at any fixed temperature. Nuclear spin entropy calculated from our data decreases by 0.6Rln2 from the infinite temperature to 1mK.The "missing entropy" seems to reach about 0.4ln2.

1.核磁共振实验连续波核磁共振被用来研究纯^3He薄膜，其覆盖范围从第2层以下到-2.5层的铁磁峰以上。将薄膜吸附在Grafoil上，冷却至0.075mK，第一层磁化强度符合居里定律，韦斯常数小于0.01mK，第二层磁化强度在远低于交换能J的温度下随覆盖率的变化。初步分析表明，J随覆盖率变化不大，零温第二层磁化强度与第二层密度呈线性关系。这两种性质都与共存的两相相一致。2.热容测量我们测量了吸附在石墨箔上的^3He薄膜在0.3 ~ 60 mK温度范围内的热容，其面密度为第二层固体^3He显示反铁磁性。测得的热容似乎不同意定性与以前的测量Graywall。我们的数据显示，在高温下，在约2 mK和1/T^2的行为下出现了四舍五入的最大值，而他在高温下观察到了在2.5mK和1/T的行为下出现了相当尖锐的峰值。虽然我们的数据与Elstner等人研究的三角晶格上自旋为1/2的海森堡反铁磁体的理论计算半定量地一致，在任何固定温度下，测得的热容值比理论值小30%。从无限温度到1 mK，计算的核自旋熵减少了0.6Rln ~ 2，“丢失熵”约为0.4ln ~ 2.

项目成果

P.Schiffer: "Magnetization of ^3He on Grafoil in the Low-Temperature Limit" Physcal Review Letters.71. 1403-1406 (1993)

P.Schiffer：“低温极限下 Grafoil 上 ^3He 的磁化”物理评论快报.71。

P.Schiffer: "Low Temperature Magnetization of ^3He Films" Journal of Low Temperature Physics. 94. 489-513 (1994)

P.Schiffer：“^3He 薄膜的低温磁化”《低温物理学杂志》。

P.Schiffer: "Low Temperature Magnetization of ^3He Films" Journal of Low Temperature Physics. Vol.94. 489-684 (1994)

P.Schiffer：“^3He 薄膜的低温磁化”《低温物理学杂志》。

Tohru Okamoto: "Direct Demagnetization Cooling of High-Density Solid ^3He" Physcal Review Letters. 72. 868-871 (1994)

Tohru Okamoto：“高密度固体的直接退磁冷却^3He”物理评论快报。

Hiroshi Fukuyama: "Low Temperature Magnetization of Pure ^3He Films on Grafoil" Physica B. 194-196. 683-684 (1994)

Hiroshi Fukuyama：“Grafoil 上纯 ^3He 薄膜的低温磁化”Physica B. 194-196。