Brillouin investigation of the dynamic properties of cobalt wire arrays

We have investigated the long-wavelength spin waves in 400 Angstrom thick cobalt wires with various width/period ratios: 0.5/1, 1/1.5, and 2/3 mm, using Brillouin light scattering. All of them show a new low-frequency line which is absent in the unpatterned films: it is attributed to modes originating from the uniform bulk mode of the infinite layer which give rise to a measurable Brillouin intensity only when both anisotropy and patterning are present in the sample. The variations of the frequency of the magnetostatic surface mode (the so-called Damon-Eshbach mode) were studied versus a magnetic-field H applied parallel or perpendicular to the axis of the wires. Compared with unpatterned layers, the Brillouin frequencies are higher when H lies along the wire axis; they are not found to be significantly sensitive to the width or to the separation of the wires. We interpret this result in terms of a slight reduction of the magnetic anisotropy for the wires. For H perpendicular to the wire axis, the spin wave frequencies are reduced by the shape-and orientation-dependent demagnetizing field H-d. The experimental determinations of H-d agree with our calculations of its mean value assuming a uniform magnetization and taking into account the interaction between the wires. (C) 1999 American Institute of Physics. [S0021-8979(99)63108-5].