Interaction effects on microwave-assisted switching of Ni80Fe20 nanowires in densely packed arrays

We perform broadband microwave absorption spectroscopy and explore the switching behavior of 300-nm-wide and 20-nm-thick Ni80Fe20 nanowires under irradiation of a magnetic rf field. In particular, we investigate two arrays where the nanowires exhibit a different edge-to-edge separation, a=100 and 700 nm. In the arrays we observe microwave-assisted switching (MAS). The MAS process with a resonant behavior near 6 GHz is attributed to the excitation of a confined Damon-Eshbach-type mode. Dipolar interactions between nanowires are found to decrease the optimum frequency for MAS and to increase the switching efficiency for the small separation a. The observed characteristics are substantiated by model considerations. We propose a modification of the previously introduced analytical demagnetization factors of an individual thin wire and incorporate the effect of dipolar interactions occurring in the array. The approach explains the dependence of the MAS-relevant eigenmode on the edge-to-edge separation a. MAS is also found to narrow the switching field distribution of the nanowire array.