Dynamic dephasing of magnetization precession in arrays of thin magnetic elements

We present a systematic micromagnetic simulation to demonstrate how the static and dynamic behaviors of single nanomagnets are modified in an array. We examine the precessional frequency and damping as a function of the width to separation (w/s) ratio in arrays of square and circular magnetic elements and compare it with the single nanomagnet dynamics. Both frequency and damping are significantly modified by the interelement interaction. The precessional frequency shows a general trend of increase with w/s ratio due to the increase in the dipolar magnetic field in the array and split into multiple modes when the w/s ratio becomes greater than 1. The damping of precession increases with increase in w/s ratio, i.e., with decrease in the separation between the elements. The increase in damping is found to be due to the mutual dephasing of precession of elements in an array. For larger square nanomagnets, (width=150 nm,thickness=50 nm), where the single nanomagnet dynamics is inherently nonuniform, the effect of the array only increases the incoherence in the precession. For larger circular nanomagnets, (width=150 nm,thickness=50 nm), where the single nanomagnet shows slow vortex core oscillation, the array modifies the dynamics into incoherent spin-wave dynamics whose coherence increases with the increase in w/s ratio. Analysis of static and dynamic magnetic images reveals that the dynamics is strongly dependent on the static magnetization in the arrays. The results presented here show that the dynamics of arrays of nanomagnets is significantly or entirely different from that of individual elements, and hence measurements from arrays may not be considered as the single nanomagnet dynamics. We also evaluate the role of dynamic dephasing in the increased damping coefficient.