Influence of Dipolar Interaction on Vortex Dynamics in Arrays of Ferromagnetic Disks

Abstract

The influence of the magnetostatic interaction on vortex dynamics in arrays of ferromagnetic disks is investigated by means of a broadband ferromagnetic-resonance setup. Transmission spectra reveal a strong dependence of the resonance frequency of vortex-core motion on the ratio between the center-to-center distance and the element size. For a decreasing ratio, a considerable broadening of the absorption peak is observed following an inverse sixth power law. An analogy between the vortex system and rotating dipoles is confirmed by micromagnetic simulations.

Inductive detection of magnetic vortex gyration

“…5,13,26 In permalloy squares the resonance shift depends on the direction of the external field. In squares a redshift is expected for fields applied along an edge of the square, a blueshift if the field is applied along a diagonal.…”

“…1 Especially permalloy (Ni 80 Fe 20 ) elements are extensively investigated because this material has vanishing crystalline anisotropy; i.e., only the exchange energy and the strayfield energy significantly contribute to the magnetic properties. Transport measurements such as pulsed inductive microwave magnetometry 2,3 and absorption spectroscopy 4,5 allow one to examine the magnetization dynamics of films and ensembles of uniform elements. But uniformity can be a challenge because a single element never equals another one on the scale of single crystallites.…”

Stochastic formation of magnetic vortex structures in asymmetric disks triggered by chaotic dynamics

“…To explain why the unconventional chaotic dynamics appears only in the disks with a particular interdisk distance, d ¼ 501 nm, we took into account the stray fields induced by adjacent disks considering that the magnetic quantity, which most sensitively depend on the interdisk distance in disk arrays, is the strength of stray fields 42,43 . pointing in þ x direction.…”

Observation of coupled vortex gyrations by 70-ps-time- and 20-nm-space-resolved full-field magnetic transmission soft x-ray microscopy

“…In cases of sufficiently short distances between nearest neighboring disks, dipolar interaction alters their dynamics. [13][14][15] Thus, the examination of the influence of dipolar interaction on vortex oscillations is important. To characterize the interaction between individual elements a time-and space-resolving measurement technique is mandatory.…”

“…The vortex eigenfrequency of around 157Ϯ 3 MHz in the isolated Py disks was measured on an array of Py disk pairs of identical dimensions 18 using a broadbandferromagnetic resonance setup. 15 Measurements of the dynamic evolution of vortex-core gyrations were carried out by full-field magnetic transmission soft x-ray microscopy ͑MTXM͒ at beamline 6.1.2, Advanced Light Source ͑ALS͒, Berkeley, CA, utilizing a stroboscopic pump-and-probe technique. The optical setup of the x-ray microscope, 19 shown in Fig.…”