Microwave assisted switching in individual and interacting magnetic nanowires

Recent spin dynamics experiments have shown that microwave assisted switching (MAS) occurs if a magnet is excited at large excitation amplitudes, i.e., in the non-linear regime.[1,2] MAS has reduced the coercive fields $H_c $. We studied the MAS process on arrays of nanopatterned permalloy wires (20 nm thick, 300 nm wide, and 180 $\mu $m long) where we varied the edge-to-edge separation $d$ between 100 and 700 nm. MAS was found to reduce $H_c $ resonantly at the quantized center-mode eigenfrequency of the nanowires. MAS also narrowed the distribution of $H_c $ of the nanowires. The efficiency for the MAS process depended on, both, the applied in-plane field and separation $d$. To model this behavior we considered the effect of dipolar interactions. [3] MAS was most efficient for $d$ = 100 nm and reduced $H_c $ by about a factor of two. Our observations are relevant if MAS is considered for encoding information in magnetic bits of high density. [1] J. Podbielski et al., Phys. Rev. Lett. 99, 207202 (2009). [2] G. Woltersdorf et al., Phys. Rev. Lett. 99, 227207 (2009).[3] J. Topp et al., in press.