Vortex dynamics in Permalloy disks with artificial defects: Suppression of the gyrotropic mode

Abstract

The dynamics of magnetic vortices in thin Permalloy disks having artificial defects in the form of small holes at different locations within the disk has been investigated by means of frequency-domain spatially resolved ferromagnetic resonance. It is found that the vortex can be effectively captured by such a defect. Consequently the commonly observed gyrotropic vortex motion in an applied microwave field of 1 mT is suppressed. However, if in addition a static magnetic field of at least 4.3 mT is applied, the vortex core is nucleated from the artificial defect and a modified gyrotropic motion starts again.

How hole defects modify vortex dynamics in ferromagnetic nanodisks

“…For instance, like an external field a hole may trigger the formation of non-homogeneous magnetization pattern at the disk and hole borders [10,11,12]; also, when its center is captured by the hole its gyrotropic motion is suppressed [27]. Other possibilities will be discussed in what follows.…”

“…In addition, Hoffmann et al [26] have verified that the two magnetostatic spin-wave modes degenerate to a single frequency when the vortex core is captured by a hole. Here, we shall show that a number of facts, including some ones observed by Kuepper et al [27], may be well understood in terms of very basic physical properties of the vortex structure and dynamics in the presence of a cavity. Qualitatively, our arguments and results may be useful for other similar systems were pinning sites/defects concern.…”

“…Hoffman et al [26] have also observed a remarkable asymmetry in the magnetization reversal mechanism which they credited to such small defects. Kuepper et al [27] have studied this mode when a (cylindrical) cavity is intentionally introduced in the sample. Their results clearly show how these cavities affect vortex motion as a whole, particularly its gyrotropic frequencies.…”

Switching probabilities of magnetic vortex core reversal studied by table top magneto optic Kerr microscopy

“…Lett. 108, 022401 (2016) in conjunction with fluctuations further contribute to nondeterministic switching, as, for example, vortex core trapping could influence the initial vortex core position, 14 or small deviations in the vortex core trajectory may be crucial for an interaction of the vortex core with a defect. The presented measurement technique allows, due to the large number of repetitions of the switching experiment, for analyzing stochastic events with a high accuracy compared to other methods and without the need of synchrotron radiation.…”

Influence of domain wall pinning on the dynamic behavior of magnetic vortex structures: Time-resolved scanning x-ray transmission microscopy in NiFe thin film structures

“…These trap the vortex core and lead to a total suppression of the gyration movement. 8 In this work, the antidots were introduced further away from the structure center to avoid complete trapping and only pin the domain walls ͑if present͒. In this way, naturally occurring domain wall pinning sites are mimicked in a controlled manner.…”