Nanoscale Domain Wall Dynamics in Micromagnetic Structures with Weak Perpendicular Anisotropy

Abstract

Time-resolved pump-probe soft X-ray ptychography and Scanning Transmission X-ray Microscopy (STXM) were employed to study the magnetic domain wall dynamics in microstructures of permalloy (Ni$_{81}$Fe$_{19}$; Py) with a weak growth-induced perpendicular magnetic anisotropy. The X-ray magnetic circular dichroism (XMCD) 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.