Criterion for transformation of transverse domain wall to vortex or antivortex wall in soft magnetic thin-film nanostripes

Spin Dynamics of a Magnetic Antivortex

We report on a study of the dynamics of a magnetic antivortex in a submicron, asteroid shaped, permalloy ferromagnet using micromagnetic simulations. As with vortex states in disk and square geometries, a gyrotropic mode was found in which a shifted antivortex core orbits about the center of the asteroid. Pulsed magnetic fields were used to generate azimuthal or radial spin wave modes, depending on the field orientation. The degeneracy of low frequency azimuthal mode frequencies is lifted by gyrotropic motion of the antivortex core, and restored by inserting a hole in the center of the particl…

Electrically stabilized magnetic vortex and antivortex states in magnetic dielectrics

The micromagnetic distribution in a dielectric nanoparticle is theoretically considered. It is shown that the existence of inhomogeneous magnetoelectric interaction in magnetic dielectrics provides the possibility to stabilize the vortex and antivortex state. The estimation of the critical voltage necessary for vortex/antivortex nucleation in bismuth ferrite and iron garnet nanoparticles yields a value of +/-150 V. This system can be considered as electrically switchable two state-logic magnetic element.

受限铁磁纳米条带中电流调控的斯格明子数

Current-Controlled Skyrmion Number in Confined Ferromagnetic Nanostripes

本文在受限Fe3Sn2纳米条带中利用电流诱导焦耳热与磁滞效应，通过斯格明子链和条纹畴的可逆拓扑转变实现对斯格明子数的可靠操控，为拓扑自旋电子器件发展提供支撑。

Dynamical influence of vortex-antivortex pairs in magnetic vortex oscillators

We study the magnetization dynamics in a nanocontact magnetic vortex oscillators as function of temperature. Low temperature experiments reveal that the dynamics at low and high currents differ qualitatively. At low currents, we excite a temperature independent standard oscillation mode, consisting in the gyrotropic motion of a free layer vortex about the nanocontact. Above a critical current, a sudden jump of the frequency is observed, concomitant with a substantial increase of the frequency versus current slope factor. Using micromagnetic simulation and analytical modeling, we associate this…

Precessing vortices and antivortices in ferromagnetic elements

A micromagnetic numerical study of the precessional motion of the vortex and antivortex states in soft ferromagnetic circular nanodots is presented using Landau-Lifshitz-Gilbert dynamics. For sufficiently small dot thickness and diameter, the vortex state is metastable and spirals toward the center of the dot when its initial displacement is smaller than a critical value. Otherwise, the vortex spirals away from the center and eventually exits the dot which remains in a state of in-plane magnetization (ground state). In contrast, the antivortex is always unstable and performs damped precession …

Dynamics of vortex-antivortex pairs in ferromagnets

We study the dynamics of vortex-antivortex (VA) pairs in an infinitely thin ferromagnetic film with easy-plane anisotropy. These are localized excitations with finite energy that are characterized by a topological (skyrmion) number N = 0,+1,-1. Topologically trivial (N=0) VA pairs undergo Kelvin motion analogous to that encountered in fluid dynamics. In contrast, topologically nontrivial (N = +1,-1) VA pairs perform rotational motion around a fixed guiding center. We present the results of a detailed study in both cases and further demonstrate that in the presence of dissipation a rotating N =…

Berezinskii-Kosterlitz-Thouless极性涡旋-反涡旋的原子尺度相变动力学追踪

Atomic-Scale Tracking Phase Transition Dynamics of Berezinskii-Kosterlitz-Thouless Polar Vortex-Antivortex

该研究利用原位透射电子显微镜和相场模拟，在原子尺度追踪极性涡旋-反涡旋对在热场与电场下的转变路径，揭示其无BKT相变及湮灭机制。

Rotating vortex dipoles in ferromagnets

Vortex-antivortex pairs are localized excitations and have been found to be spontaneously created in magnetic elements. In the case that the vortex and the antivortex have opposite polarities the pair has a nonzero topological charge, and it behaves as a rotating vortex dipole. We find theoretically, and confirm numerically, the form of the energy as a function of the angular momentum of the system and the associated rotation frequencies. We discuss the process of annihilation of the pair which changes the topological charge of the system by unity while its energy is monotonically decreasing. …

Optical Manipulation of Magnetic Vortex Visualized in situ by 4D Electron Microscopy

Understanding the fundamental dynamics of topological vortex and antivortex naturally formed in micro/nanoscale ferromagnetic building blocks under external perturbations is crucial to magnetic vortex based information processing and spintronic devices. All previous studies have focused on magnetic vortex-core switching via external magnetic fields, spin-polarized currents, or spin waves, which have largely prohibited the investigation of novel spin configurations that could emerge from the ground states in ferromagnetic disks and their underlying dynamics. Here, we report in situ visualizatio…

Nanomagnetic toggle switching of vortex cores on the picosecond time scale

We present an ultrafast route for a controlled, toggle switching of magnetic vortex cores with ultrashort unipolar magnetic field pulses. The switching process is found to be largely insensitive to extrinsic parameters, like sample size and shape, and it is faster than any field-driven magnetization reversal process previously known from micromagnetic theory. Micromagnetic simulations demonstrate that the vortex core reversal is mediated by a rapid sequence of vortex-antivortex pair-creation and annihilation sub-processes. Specific combinations of field pulse strength and duration are required…