Institute of Physics, University of Mainz, Mainz, Germany.
J Microsc. 2011 May;242(2):216-20. doi: 10.1111/j.1365-2818.2010.03472.x. Epub 2010 Dec 13.
By example of a Permalloy particle (40 × 40 μm(2) size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cause a change of contrast and an image deformation of the particles geometry (curvature of its edge). The magnetic stray fields are calculated from a deformation of the X-ray magnetic circular dichroism (XMCD) images taken after the magnetic field pulse in a 1 ns interval. These measurements reveal a decrease of magnetic stray fields with time. An estimate of the lower limit of the domain wall velocity yields about 2 × 10(3) m s(-1).
通过 Permalloy 粒子（40×40μm² 大小，30nm 厚度）的例子，我们展示了一种定量研究超快磁化反转过程中磁串扰场动力学的方法。该测量是在时间分辨光发射电子显微镜中使用 X 射线磁圆二色性进行的。在所研究的粒子中，我们观察到磁通封闭主导的磁基结构，从而使样品外的磁串扰场最小化。引入的快速磁场脉冲会引起微磁结构的变化，并伴有不完全的磁通封闭。结果，畴边缘会产生串扰场，导致粒子几何形状的对比度变化和图像变形（边缘曲率）。磁串扰场是从磁场脉冲后 1ns 间隔内拍摄的 X 射线磁圆二色性（XMCD）图像的变形中计算出来的。这些测量结果表明磁串扰场随时间减小。对畴壁速度下限的估计约为 2×10³m/s。
