Time-resolved precessional dynamics of arrays of nanomagnets with varying areal density
We present the experimental study of precessional dynamics in planar arrays of magnetostatically coupled square Ni81Fe19 (permalloy) elements with systematically varying areal density by an all-optical time-resolved magneto-optical Kerr effect measurement. The observation is interpreted with the aid of micromagnetic simulations. The dynamics shows a single uniform collective mode at very high areal density, which broadens and splits up into a number of non-uniform modes with the reduction of areal density. At very low density the collective dynamics disappears and modes of the individual elements become dominant. The observations are important for applications of arrays of nanomagnets in patterned magnetic media and magnonic crystals.