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

建立了一种从电子全息观测中提取退磁场的新方法（即，在上一个财政年度的重建相位图像）。为了验证该方法的有效性，我们将其应用于一个真实的平行六面体形状的薄箔硬晶Nd_2Fe_（14）B试样。因此，可以在样品内观察到退磁场。此外，退磁场的计算结果与基于微磁学理论的模拟结果吻合较好，精度<0.065 T（Tesla）。该方法可应用于永磁体，有助于理解磁致伸缩机理。该成果发表在2022年11月的《显微镜》杂志上。另一个课题是提高Nd-Fe-B薄箔的相移分析精度，该薄箔由于含有重元素（即，Nd元素）。对比度较差的电子全息图在相位恢复过程中会产生不期望的相位不连续性。为此，我们利用小波隐马尔可夫模型（WHMM）对电子全息观测数据进行了降噪处理，该模型可以分辨出比噪声更弱的信号。因此，它被证明，使用WHMM降噪是有效的抑制不必要的不连续性。采用WHMM去噪方法可以提高本研究方法推导出的退磁场的分析精度。

We established a new method that extracts the demagnetization field from electron holography observation (i.e., reconstructed phase image) in the last fiscal year. In the next step, to prove the validity of the method, we applied it to a real thin-foiled singlecrystalline Nd2Fe14B specimen with a parallelepiped shape. As a result, the demagnetization field could be observed within the specimen. Furthermore, the result of demagnetization field in this research agrees with the simulation based on micromagnetic theory showing the accuracy of <0.065 T (Tesla). The method can be applied to a permanent magnet and help with the understanding on the coercivity mechanism. The achievements were published in Microscopy in November 2022.The other subject is the precision improvement of phase-shift analysis on a Nd-Fe-B thin foil that causes a poor contrast of electron hologram because of consisting of heavy element (i.e., Nd element). The electron holograms with a poor contrast produces the undesired phase discontinuities during the process of phase retrieval. For this purpose, we carried out the noise reduction of electron hologram observations with the the wavelet hidden Markov model (WHMM) that can distinguish the signal even weaker than the noise. Consequently, it was demonstrated that the noise reduction using WHMM was effective for suppressing the unwanted discontinuity. The denoising with WHMM can be helpful to improve the precision in the analysis of demagnetization field deduced from the method in this research.