Field dependence of collective spin modes in transversely magnetized stripes with homogeneous and alternating width

Brillouin light scattering is used to study the spin-wave properties of arrays of closely spaced magnetic stripes with both homogeneous and alternating width, thickness of 30 nm, and edge-to-edge spacing of 55 nm. Experiments are performed with both the transferred wave vector and the applied magnetic field in the direction transverse to the length of the stripes, i.e., in the hard magnetization direction. When the transverse applied field is decreased from a relatively large value (0.15 T) down to zero, the overall direction of the stripe magnetization gradually switches from the transverse to the preferred longitudinal orientation, as confirmed by the shape of the Kerr hysteresis loops. The measured frequencies were compared to numerical calculations obtained for Permalloy stripe arrays by a microscopic dipole-exchange theory. A good overall agreement is achieved between experiment and theory, thanks to the inclusion of the dynamical interstripe dipolar coupling