Nanoscale domain-wall dynamics in micromagnetic structures with weak perpendicular anisotropy

Time-resolved pump-probe soft x-ray ptychography and scanning transmission x-ray microscopy were employed to study the magnetic domain-wall dynamics in microstructures of permalloy (Ni81Fe19; Py) with a weak growth-induced perpendicular magnetic anisotropy. The x-ray magnetic circular dichroism images of a micrometer-sized Py square (160 nm thickness) and an elliptical disk (80 nm thickness) show flux-closure patterns with domain walls that fall into alternating out-of-plane (OOP) magnetization states precipitated by the perpendicular anisotropy, which is a precursor of the nucleation of stripe domains at higher thicknesses. An oscillating magnetic field at frequencies from tens of MHz to GHz and up to 4 mT magnitude excited dynamic modes in the domain walls along with the vortex core gyration. The domain-wall dynamics include the translation of inversion points of the OOP magnetization and nucleation of one-dimensional spin waves.