Anisotropy, damping, and coherence of magnetization dynamics in a 10 μm square Ni81Fe19 element

We have studied magnetization precession in a square Ni81Fe19 element, of 10 μm width, by time-resolved scanning Kerr effect microscopy. From the frequency of precession, we deduce a fourfold in-plane anisotropy of about 30 Oe at the center of the square. Larger damping of the precession was observed at the center of the element when the static field was applied parallel to a diagonal rather than to an edge of the square. Dynamic images show that the apparent increase in damping is associated with nonuniformity of the dynamic magnetization that is associated with the sample shape.