Spin waves in an inhomogeneously magnetized stripe

Abstract

We have observed collective spin-wave modes in inhomogeneously magnetized ${\mathrm{Ni}}_{0.81}{\mathrm{Fe}}_{0.19}$ thin-film stripes. The stripes, 18 nm thick and $2\ensuremath{\mu}\mathrm{m}$ wide, are studied in an in-plane magnetic field oriented along their short axes. When the magnetic field is on the order of the shape anisotropy field, the equilibrium magnetization near the stripe edges rotates 90 deg over a length scale of order $100\mathrm{nm}--1\ensuremath{\mu}\mathrm{m}.$ Time-resolved Kerr microscopy is used to detect a hierarchy of spin-wave modes in these edge regions. Using a combination of semianalytical theory and micromagnetic simulations, we show that these modes span the entire stripe but can only be detected near the edges, where the effective wave vector is small.