DEVELOPMENT OF AN IMAGING TECHNIQUE OF MAGNETIC FLUX PENETRATING THROUGH SUPERCONDUCTING FILM

本研究的主题是观察穿透第二类超导薄膜的磁通的运动情况。我们建议使用扫描电子显微镜(SEM)中发现的I型磁衬度来观察磁通。可以找到影响超导电性的磁通钉扎效应的原因，如材料、结构、样品中的缺陷等。由于扫描电子显微镜具有纳米尺度的空间分辨率，该系统可以用来探索样品磁性特征的来源。在本研究中，我们首先假设材料的简单磁性结构。然后对电子探测器产生的磁场和电场进行了计算。计算了电子在该电磁场中的运动轨迹，得到了电子探测位置的三维分布。通过换算分布的移动，可以预测样品的磁结构。本研究制作的样品在扫描电子显微镜下的温度可达30K，证实了其超导电性。然而，目前系统中的磁对比度还没有被观测到。这可能是由于表面发射的电子的角分布和能量分布所致。它们掩盖了对比中的特征变化。仿真结果表明，在提高信噪比的同时提高了灵敏度，具有较好的效果。在实验和计算的初步对比中，即用普通磁性薄膜观测磁通，验证了模拟的有效性。

The main theme of the present research is to observe the movement of magnetic flux that is penetrating through the type-II super-conducting film. We proposed to use the type-I magnetic contrast found in the scanning electron microscope (SEM) for observing the flux. It may be possible to find the causes of the pinning effect of the flux which influences the super-conductivity, such as the material, the structure, the imperfection in the specimen. Since the SEM has a spatial resolution of nm scale, this system may be used to probe the origin of the magnetic characteristics of the specimen.In the present research, first, we assume a simple magnetic structure of the material. Then, the magnetic flux and the electric field, which is produced by the electron detector are calculated. The electron trajectories are calculated in this electromagnetic field, and the electron detection position distribution is obtained in three-dimension. By converting the movement of the distribution, the magnetic structure can be predicted.The temperature of the specimen stage made in the present research in the SEM reaches down to 30K and the super-conductivity is confirmed. However, the magnetic contrast in the present system has not been observed yet. It may be because of the angular distribution and the energy distribution of electrons emitted from the surfacde. They cover the characteristic variation in the contrast. The simulation shows some preferable conditions to improve the signal to the noise ratio, and at the same time to improve the sensitivity. In the preliminary comparison between the experiment and the calculation, that is to observe the magnetic flux using ordinary magnetic films, the validity of the simulation is confirmed.