Spin-wave spectra in nanometric elliptical dots arrays

Arrays of 450 nm × 150 nm elliptical dots with a thickness of 24 and 66 nm have been fabricated by e-beam lithography. The significant difference of the hysteresis loops for the two considered thicknesses have been interpreted in terms of magnetic domain formation in the thicker sample, opposite to the single-domain behavior found in the thinner one. A marked spin-wave frequency discretization has been observed by Brillouin light scattering due to the boundary conditions imposed by lateral quantization on the spin-wave spectrum. For a large wave vector interval, several discrete and dispersionless modes were observed. The decrease of the average frequency mode, observed in the patterned sample with respect to the continuous film, is explained in terms of demagnetizing field inside the dots.