Rotating Vortex Dipoles in Ferromagnets

Abstract

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. Such a change in the topological charge affects profoundly the dynamics in the magnetic system. We finally discuss the connection of our results with Bloch Points (BP) and the implications for BP dynamics.

Micromagnetic simulations of magnetization dynamics in a nanowire induced by a spin-polarized current injected via a point contact

“…This localization is due to the strong inhomogeneity of the CoFe stray field acting on the Py wire. In this sense, our system differs qualitatively from extended multilayer devices employing the point contact current injection 8 , where the localization of the ST-induced oscillations is caused by the strong non-linearity of the auto-oscillation modes (e.g., bullet 33 , vortex 34 or vortex-antivortex pairs 35,36,37 ). In our case, magnetization oscillations in the linear regime are already localized within the Py nanowire area under the CoFe nanomagnet due to the stray field form the CoFe nanomagnet.…”

Discrete double core skyrmions in magnetic thin films

“…Therefore, as expected, the static character and the usual energy of the Belavin-Polyakov skyrmion is achieved only for infinite lattices. Rotating vortices in ferromagnets with planar symmetry (or easy-plane anisotropy) were also found (in the continuum limit) recently by Komineas [9]. This author uses a solution of the form (2) as an ansatz for a vortex-antivortex pair with opposite polarities in easy-plane ferromagnets.…”

Визуализация Динамических Вихревых Структур В Магнитных Пленках С Одноосной Анизотропией (Микромагнитное Моделирование)

“…1, b, c. Инвариант χ может быть использован и для описания вихревых структур. Можно показать [28,29], что если распределение намагниченности, определенной в точках некоторой плоскости, имеет вид одиночного вихря и на больших расстояниях от центра вихря намагничен-ность параллельна этой плоскости, результат вычисле-ния интеграла (4) по всей плоскости равен χ = −λq/2. Здесь q = 1 для вихря, q = −1 для антивихря; λ = ±1.…”