Spin waves in stripes submitted to a perpendicular applied field

In, the dipolar approximation, we present an,analytical study of the magnetic modes occurring in a stripe submitted to a magnetic field H parallel to a principal axis of its elliptical cross section. The studied excitations oscillate within the cross section. The results differ greatly from those obtained in the previously treated case of H parallel to the stripe direction. The dependences of the frequencies upon the applied field are opposite below and above the saturation field H-s, where H-s defines the limit between the oblique phase (H < H-s) and the aligned one (H > H-s): the frequencies slow down until Hs, they vanish at H-s and they increase above. This softening was previously observed on stripes with a rectangular cross section and the measured critical field lies near the saturation field, in agreement with our calculations.