Time-resolved investigation of magnetization dynamics of arrays of non-ellipsoidal nanomagnets with a non-uniform ground state

TL;DR

This study investigates the magnetization dynamics of non-ellipsoidal nanomagnet arrays using time-resolved Kerr microscopy and micromagnetic simulations, revealing complex mode behaviors influenced by element size, bias field, and static magnetization states.

Contribution

It provides new insights into the non-uniform precessional modes and static magnetization canting in non-ellipsoidal nanomagnets, combining experimental and simulation approaches.

Findings

Two co-existing mode branches observed above a certain bias field.

Modes at the center and edges of elements have distinct spatial profiles.

Edge mode frequencies are strongly influenced by local magnetization distribution.

Abstract

We have performed time-resolved scanning Kerr microscopy (TRSKM) measurements upon arrays of square ferromagnetic nano-elements of different size and for a range of bias fields. The experimental results were compared to micromagnetic simulations of model arrays in order to understand the non-uniform precessional dynamics within the elements. In the experimental spectra two branches of excited modes were observed to co-exist above a particular bias field. Below the so-called crossover field, the higher frequency branch was observed to vanish. Micromagnetic simulations and Fourier imaging revealed that modes from the higher frequency branch had large amplitude at the center of the element where the effective field was parallel to the bias field and the static magnetization. Modes from the lower frequency branch had large amplitude near the edges of the element perpendicular to the bias field. The simulations revealed significant canting of the static magnetization and the effective field away from the direction of the bias field in the edge regions. For the smallest element sizes and/or at low bias field values the effective field was found to become anti-parallel to the static magnetization. The simulations revealed that the majority of the modes were de-localized with finite amplitude throughout the element, while the spatial character of a mode was found to be correlated with the spatial variation of the total effective field and the static magnetization state. The simulations also revealed that the frequencies of the edge modes are strongly affected by the spatial distribution of the static magnetization state both within an element and within its nearest neighbors.