Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy

Summary 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 fluxclosure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic fieldpulseintroducedchangesinthemicromagneticstructure 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(curvatureofitsedge).Themagneticstrayfieldsare calculated from a deformation of the X-ray magnetic circular dichroism (XMCD)imagestakenafterthemagneticfield 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 ms −1 .