Magnetic Domain Structure and Anisotropic Thermal Conductivity

磁畴结构和各向异性导热率

基本信息

批准号：
15340117
负责人：
SASAKI Yutaka
金额：
$ 10.69万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-15340117/
关键词：
Nucler Ordered Solid ^3He antiferromagnetism magnetic domain structure Magnetic Resonace Imaging magnetic domain wall memory effect micro Kelvin MRI 自由誘導減衰

项目摘要

We have completed a construction of new refrigerator for ultra low temperature MRI and variable frequency MRI system with improved resolution, stability. Measurement speed was greatly improved so that we could measure the true 3 dimensional MRI image in 30 minutes. With this improvement we could determine the direction of magnetic domain wall without any assumption. It is [110] in the bcc lattice, which confirmed our previous determination under some assumption. We also investigated how the stable phase evolve during the field induced phase transition between U2D2 phase and CNAF phase. It showed two stage time evolution. During the first stage, a seed of stable phase appeared at many places in a crystal. This seed grew rapidly until it stoped growing at some certain size, due to a loss of chemical potential by the latent heat release. During this stage, time evolution is controlled by the nucleation rate. Nucleation of other seeds kept occuring until the entire crystal reached to a temperature of coexistence for two phases. Then the slow second stage, which is controlled by the thermal conduction and latent heat release throgh liquid-solid interface, and thus phase transition proceeded from liquid-solid interface side of a crystal. Through the analysis of the first stage and memory effect, we proposed a possibility that this nucleation occured on the magnetic planar defect associated with crystalline linear defect.

我们已经完成了针对超低温度MRI和可变频率MRI系统的新冰箱的结构，具有改善的分辨率，稳定性。测量速度大大提高，因此我们可以在30分钟内测量真正的3维MRI图像。通过这种改进，我们可以在没有任何假设的情况下确定磁性域壁的方向。它在BCC晶格中是[110]，它在某些假设下证实了我们以前的确定。我们还研究了稳定相在田间诱导U2D2相和CNAF相之间的变化。它显示了两个阶段时间的演变。在第一阶段，稳定期的种子出现在晶体中的许多地方。这种种子迅速生长，直到由于潜在热量释放失去化学势而停止生长一定尺寸。在此阶段，时间演化由成核速率控制。其他种子的成核一直发生，直到整个晶体达到两个相的温度。然后，第二阶段由热传导和潜在热释放液体固定界面控制，因此相变从晶体的液体固定界面侧进行。通过对第一阶段和记忆效应的分析，我们提出了这种成核发生在与晶体线性缺陷相关的磁性平面缺陷上。