Antivortex dynamics in magnetic nanostripes

Abstract

In a thin magnetic nanostripe, an antivortex nucleates inside a moving domain wall when driven by an in-plane magnetic field greater than the so-called Walker field. The nucleated antivortex must cross the width of the nanostripe before the domain wall can propagate again, leading to low average domain wall speeds. A large out-of-plane magnetic field, applied perpendicularly to the plane of the nanostripe, inhibits the nucleation of the antivortex leading to fast domain wall speeds for all in-plane driving fields. We present micromagnetic simulation results relating the antivortex dynamics to the strength of the out-of-plane field. An asymmetry in the motion is observed which depends on the alignment of the antivortex core magnetic moments to the direction of the out-of-plane field. The size of the core is directly related to its crossing speed, both depending on the strength of the perpendicular field and the alignment of the core moments and direction of the out-of-plane field.

Motion of transverse domain walls in thin magnetic nanostripes under transverse magnetic fields

“…It would be interesting to compare this DW oscillation with those in wider and thicker nanostripes above the Walker fields. 10,[18][19][20][21][22] In wider and thicker stripes, the DW oscillations come from the gyrotropic motion of nonlinear excitations, that is, magnetic topological solitons ͑vortices and antivortices͒. The DW propagations are accompanied by periodic emission, motion, and absorption of several magnetic solitons with integer and fractional topological charges.…”

“…This behavior is confirmed by a number of simulations in recent years. 10,[18][19][20][21][22] For nanowires with small cross-sections, an initially stable TDW would maintain its transverse profile during its propagation because the energy barrier between TDW and vortex/antivortex DW is too high. According to Walker's analysis, the TDW plane shall rotate around the wire axis.…”

“…Four years later, Lee et al 20 proposed an alternative way to increase the breakdown field H W by simply using a magnetic underlayer of strong perpendicular magnetic crystalline anisotropy. In the past two years, a transverse magnetic field ͑TMF͒, either lying in 10 or perpendicular to 21,22 the nanostripe plane, has been proposed to suppress the DW velocity reduction.…”

Observation of the dynamic modes of a magnetic antivortex using Brillouin light scattering

“…1), which involves spins that sweep in from two opposite sides (e.g. the top and bottom) and out from the other two (e.g., left and right), is metastable and more difficult to create as an isolated entity [3][4][5]7]. The AV state has received considerably less attention than the vortex state, even though simulations suggest that AV's should have similarly rich dynamics [8] and may, in fact, have higher potential for driving spin-waves [7,9,10].…”

“…the top and bottom) and out from the other two (e.g., left and right), is metastable and more difficult to create as an isolated entity [3][4][5]7]. The AV state has received considerably less attention than the vortex state, even though simulations suggest that AV's should have similarly rich dynamics [8] and may, in fact, have higher potential for driving spin-waves [7,9,10]. Vortices exhibit a variety of interesting dynamic properties that include sub-gigahertz gyrotropic motion driven by magnetic fields [11][12][13] or spin polarized currents [14][15][16], higher frequency (>1 GHz) quantized spin excitations [17,18], long range magnetostatic coupling interactions [19,20], dynamic core reversal [21,22], and selective ordering effects [23].…”