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.

我们已经完成了新型超低温MRI冰箱和变频MRI系统的建设，提高了分辨率、稳定性。测量速度大大提高，30分钟内即可测量出真实的3维MRI图像。通过这一改进，我们可以在没有任何假设的情况下确定磁畴壁的方向。它是bcc格中的[110]，这证实了我们之前在某种假设下的确定。我们还研究了在 U2D2 相和 CNAF 相之间场诱导相变期间稳定相如何演化。它表现出两个阶段的时间演化。在第一阶段，晶体中的许多地方都出现了稳定相的种子。由于潜热释放导致化学势损失，该种子快速生长，直到达到一定大小时停止生长。在此阶段，时间演化由成核速率控制。其他晶种的成核不断发生，直到整个晶体达到两相共存的温度。然后是缓慢的第二阶段，该阶段受液固界面的热传导和潜热释放控制，因此相变从晶体的液固界面侧进行。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的可能性。