Probing the dynamic magnetic domain of permanent magnet materials under an external AC magnetic field using magnetic force microscopy is challenging as well as important to reveal their pinning sites and local magnetization processes. In this work, we develop alternating magnetic force microscopy (A-MFM) with a Co-GdOx superparamagnetic tip for observing the dynamic magnetic domain wall (DW) motion in a, b plane Nd-Fe-B sintered magnets by stimulating the magnetization of the superparamagnetic tip and Nd-Fe-B sample using an external AC magnetic field. This method enables the simultaneous measurement of DC and AC magnetic fields from the sample surface. The measurement results reveal that the DW motion does not happen until the amplitude of the external AC magnetic field reached 77 Oe0-p (zero to peak). Further increasing the external AC magnetic field strength leads to DW motion with larger movement area and stronger AC magnetic field originating from the DW motion. In addition, A-MFM images shows the pinning sites of the DW motion. The present work provides a direct and effective approach to studying the local dynamic magnetization processes of the magnetic materials on the nanometer scale.

中文翻译：

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使用 Co-GdO 超顺磁性尖端通过交变磁力显微镜直接可视化 Nd-Fe-B 磁体中的磁畴壁运动

使用磁力显微镜在外部交流磁场下探测永磁材料的动态磁畴具有挑战性，同时对于揭示其钉扎位点和局部磁化过程也很重要。在这项工作中，我们开发了具有 Co-GdOx 超顺磁性尖端的交变磁力显微镜 (A-MFM)，用于通过刺激磁化来观察 a、b 平面 Nd-Fe-B 烧结磁体中的动态磁畴壁 (DW) 运动。使用外部交流磁场的超顺磁性尖端和 Nd-Fe-B 样品。这种方法可以同时测量来自样品表面的直流和交流磁场。测量结果表明，直到外部交流磁场的幅度达到 77 Oe0-p（零到峰值）时，才会发生 DW 运动。进一步增加外部交流磁场强度导致 DW 运动具有更大的运动面积和更强的源于 DW 运动的交流磁场。此外，A-MFM 图像显示了 DW 运动的固定位置。目前的工作为在纳米尺度上研究磁性材料的局部动态磁化过程提供了一种直接有效的方法。