Discrete modes of a ferromagnetic stripe dipolarly coupled to a ferromagnetic film: aBrillouin light scattering study

Abstract

Spin wave excitations in a magnetic structure consisting of a series of long permalloystripes of a rectangular cross section magnetized along the stripe length and situated abovea continuous permalloy film are studied both experimentally and theoretically. Stripes andcontinuous film are coupled by dipole–dipole interaction across 10 nm thick Cuspacers. Experimental measurements made using the Brillouin light scatteringtechnique (with the light wavevector oriented along the stripe width) provideevidence for one dispersive spin wave mode associated with the continuous film andseveral discrete non-dispersive modes resonating within the finite width of thestripes.To interpret the experimental spectra, an analytic theory based on the spin wave formalismfor finite-width magnetic stripes has been developed, achieving a good qualitative andpartly quantitative description of the experimentally observed spin wave spectrum of thesystem. In particular, it is explained why the presence of a continuous magnetic film nearthe magnetic stripe leads to a substantial decrease of the frequencies of the discrete dipolarspin wave modes localized within the stripes. A more quantitative description of themeasured frequencies and of the spatial profiles of the spin wave eigenmodes has beenobtained by numerical calculations performed using a finite element method.