Magnetostatic interaction in arrays of nanometric permalloy wires: A magneto-optic Kerr effect and a Brillouin light scattering study

Two arrays of permalloy parallel wires, $20\mathrm{nm}$ thick, having the same width of $175\mathrm{nm}$ and different spacing of 35 and $175\mathrm{nm}$ were prepared by means of deep ultraviolet lithography and lift-off process. The effect of magnetostatic interaction on both the static and dynamic magnetic properties of arrays of wires has been investigated by means of magneto-optic and Brillouin light scattering techniques, respectively. In particular, the magnetization switching of the samples, measured by vectorial magneto-optical Kerr effect magnetometry and microscopy shows the effects of dipolar interaction in the case of $35\mathrm{nm}$ spaced wires, while in the other sample the measurements show that the wires are substantially noninteracting. The Brillouin light scattering measurements showed that for the sample with interwire spacing of $35\mathrm{nm}$, dipolar coupling between magnetic wires leads to the formation of a collective mode which has a continuous spectrum and exists in a range of frequencies, while for the $175\mathrm{nm}$ spaced wires the spin modes are dispersionless. To quantify the investigated effects, a theory developed earlier for an isolated wire has been extended to the case of a one-dimensional array of ferromagnetic wires.