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As areal bit density increases, characterizing individual magnetic bits within dense arrays becomes difficult with diffraction-limited optics. We demonstrate that dynamic magneto-optical detection breaks this diffraction limit if the characteristic behavior of a nanomagnet is sufficiently different from its neighbors’. We use far-field time-resolved Kerr microscopy to resolve the high-frequency magnetization dynamics of a single, small (Ø150 nm) nanomagnet within a low-frequency background from an array of large (Ø500 nm) magnets. We use this technique to observe and quantify the effects of magnetostatic interactions on the single magnet dynamics as the intermagnet spacing is varied.

We review the influence of the magnetoelastic coupling with surface acoustic waves (SAWs) on the dynamic magnetic response of a periodic nanomagnet array. In addition to exciting the magnetization precession, an ultrafast laser pulse generates multiple SAW modes whose frequencies are determined by the array pitch. As a result, strong pinning of the magnetization precession frequency at the crossover points with the SAWs is observed over an extended field range. The complex spin wave spectrum can be analyzed in frequency and momentum spaces using finite element analysis emulating generation of SAWs. The magnetic response of the nanomagnets was then correctly reproduced with micromagnetic simulations taking into account additional magnetoelastic energy terms. This finding demonstrates control of the nanomagnet dynamics with the array geometry via magnetoelastic coupling, even when the magnetostatic interaction between the magnets is negligible.

We report the separation of the magnetization dynamics of densely packed nanomagnets depending on their orientation. The arrays consist of interleaved sublattices of identical nickel elliptical disks. By controlling the orientation of the elliptic disks relative to the external field in each sublattice, we simultaneously analyzed the magnetization dynamics in each sublattice using a time-resolved magnetooptic Kerr effect (TR-MOKE) microscopy system. The Fourier spectra showed clearly separated precession modes for sublattices with different orientations. The spectra were shown to be robust against the error in applied field orientation. The sublattice response can be tuned to a single collective frequency by choosing a symmetric field orientation. We analyzed the effect of the interelement coupling with various spacing between nanomagnets and found a relatively weak dependence on dipolar interactions in good agreement with micromagnetic simulations.