2021 Fiscal Year Annual Research Report
電子線ホログラフィーによる磁場解析の高度化と磁石材料への応用
| Project/Area Number |
21J12607
|
|---|
| Research Institution | Kyushu University |
|---|
Principal Investigator |
LEE SUJIN 九州大学, 工学府, 特別研究員(DC2)
|
|---|
| Project Period (FY) |
2021-04-28 – 2023-03-31
|
| Keywords | electron holography / demagnetization field / phase shift / permanent magnet / Nd-Fe-B magnet / 3D magnetic simulation / TEM |
|---|
| Outline of Annual Research Achievements |
In this fiscal year, by utilizing electron holography, we established a new method which allows for the examination of demagnetization field within a thin-foiled magnet. Electron holography provides a map of the phase shift of incident electron which traversed a thin-foiled specimen. When the specimen is ferromagnetic, the phase analysis can reveal the distribution of magnetic flux lines. Following electromagnetism, magnetic flux density is composed of (1) magnetization, (2) stray magnetic field outside specimen, and (3) demagnetization field inside specimen. Contribution from (1) can be determined by the orientation of c-axis (easy-magnetization direction) with TEM observations. Contribution from (2) can be calculated by 3D magnetic simulation with reference to the crystal orientation, specimen thickness, and specimen shape. As a result, the distribution of demagnetization field can be imaged by subtracting the contributions of (1)+(2) from the observed phase image. Following this procedure, we revealed the demagnetization field within an artificial, rectangular-shaped specimen in the Nd2Fe14B phase. In addition, the method was applied to an actual Nd-Fe-B foil, which will be thoroughly examined in the second year.
|
| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The original research plan in this fiscal year contains (1) construction of the basic theory and procedure which allows for extracting the information about the demagnetization field within a thin-foiled permanent magnet, (2) validation of the proposed method based on simulations, and (3) applications of this method to an actual Nd-Fe-B specimen that is transparent to incident electrons. To complete the subjects (1) and (2) with the aid of simulations, we referrer to a virtual specimen (i.e., an artificial, rectangular-shaped specimen) in a single-crystalline Nd2Fe14B phase. As far as this model specimen was referred to, the extraction of the demagnetization field was almost perfect. Following this achievement, we have started the application of this method to the actual specimen. Preliminary results using the actual specimen have been obtained. Intensive analysis will be carried out in the next fiscal year 2022.
|
| Strategy for Future Research Activity |
Our method will be applied to the study using an actual specimen composed of a single crystalline Nd2Fe14B. The map of demagnetization field will be compared with the simulation based on the micromagnetic theory. The results will be summarized in a full-length paper and submitted to an international journal.
The other target in the fiscal year 2022 is denoising of electron holograms using the wavelet hidden Markov (WHM) model, which aims at improvement of the phase retrieval accuracy. Getting holograms with a good contrast is difficult especially for Nd-Fe-B magnets composed of heavy elements. A narrow fringe pitch of holograms is essential for precise phase analysis, but the contrast of holograms is significantly reduced. Therefore, to investigate the effectiveness of the noise reduction of holograms, the WHM model will be applied to a Nd-Fe-B magnet. The results will be summarized in a short-length paper and submitted to an international journal.
|
