Spin dynamics and mode structure in nanomagnet arrays: Effects of size and thickness on linewidth and damping

Abstract

We use frequency resolved magneto-optic Kerr effect to probe the spin dynamics and mode structure in 50-200-nm-diameter Ni 80 Fe 20 nanomagnets ranging from 3 to 10 nm in thickness. We find that the intrinsic Gilbert damping parameter is largely unaffected by the nanopatterning process despite a large linewidth dependence on the size of the nanomagnets. In the larger nanomagnets, both end and center modes are observed. The linewidth of these two modes differ considerably, which is most likely the result of the sensitivity of the end mode to small variations and imperfection of the shape and edge materials. We show that this effect can be exploited as a means to separately characterize the magnetic properties of the nanomagnets as well as the size and shape variations within the array.

Three-dimensional shape dependence of spin-wave modes in single FePt nanomagnets

“…While spin dynamics in idealized geometries such as infinite films or ellipsoids of revolution can be treated analytically, the situation in realistic structures of finite size is more complex due to nonuniform internal fields within the element. A number of shapes, including ellipses, squares, wires, and asymmetric "eggs," have been studied [5][6][7][8][9][10][11][12][13][14][15], with varying parameters such as size or aspect ratio [7][8][9], as well as applied field direction [10]. One common observation is the formation of spin wave wells, that is,regions that can support localized magnetization oscillations [16].…”

Spectroscopy and Imaging of Edge Modes in Permalloy Nanodisks

“…These spectra show quantitatively similar results with one negative-going resonance around 130 mT and several peaks at higher field. In contrast to the symmetric profiles predicted by the micromagnetic model, these measured high field resonances occur at different field values for different edges, probably due to the non-ideal, inhomogeneous edges resulted from the lift-off process [6,10,11,[13][14][15][16].…”

“…The edge properties have been intensively studied [6][7][8][9][10][11][12][13][14][15][16] both experimentally and theoretically, including the effects of sidewall angle [10], intralayer interactions [12], influence of the oxidation [11], structure size and shape [13][14][15] and film thickness [13,16]. In a majority of these studies, the net response of a large array of nanostructures is measured, and the measurements represent the average properties over the large number of structures and/or edges in the array.…”

Ultrafast magnetization dynamics of spintronic nanostructures

“…It is clear from figure 4 that different geometries and ground states can lead to differences in precession amplitude and damping, in addition to differences in the resonant mode spectra, all of which can be difficult to identify in arrays of interacting elements. It has also been reported by Shaw et al [84] that the damping and line width of the excited modes are very sensitive to small differences in element shape, giving further impetus to efforts to measure individual nanomagnets.…”

“…On the other hand, the excitation of spin-wave modes has also been suggested as a mechanism for the enhanced damping observed for large-angle magnetization dynamics [9]. If the spin-wave spectrum of an individual nanomagnet is sensitive to slight shape variations [84], and if the damping is related to the excitation of the spin waves, then large-angle reorientation or switching times may also be found to vary between individual nanomagnets.…”