Statics and fast dynamics of nanomagnets with vortex structure

Abstract

Within the framework of the Landau-Lifshitz-Gilbert equation, using permalloy parameters, we study the statics and dynamics of flat circular magnetic nano-structures with an in-plane magnetic vortex configuration, putting particular emphasis on the vorticity of the magnetic state and on the (perpendicular) polarisation of the vortex center, which may be shifted with respect to the center of the circle. These binary degrees of freedom can in principle be used to manipulate two independent bits of information.Studying switching processes induced by in-plane and out-of plane field pulses we find that it is possible to switch the vorticity of the magnetic dot on a time scale of 40 ps in strong enough and short enough perpendicular external field pulses (B ext z ≈ 0.5 T, duration ≈ 40 ps). But for realistically small values of the Gilbert damping, only the vorticity can be switched this fast, and it turns out that it is better to dismiss the center of the circle totally, concentrating on flat 'nano-rings' with an inner radius R 1 and an outer radius R 2 . On these 'nano-rings' the vortex state is more stable, and with respect to the switching of the vorticity these structures have similar properties as circular dots.

Vortex core size in interacting cylindrical nanodot arrays

“…[25,26,27,28] Figure 2 illustrates the calculated magnetization profile m z (ρ) for a Fe dot (R = 28.2 nm and H = 37.6 nm) using different models. The (gray) dash-dotted line corresponds to the model by Usov et al [26], the (blue) thin line corresponds to the one proposed by Aharoni, [27] the (black) thick line corresponds to our model [14] with n = 4, the dashed (red) line represents m z (ρ) using the model proposed by Feldtkeller et al [25], and the dotted (green) line represents the profile using the model presented by Höllinger et al [28]. Note that the model proposed by A. Aharoni [27] is equivalent to our model (Eq.…”

Self-Assembled Three-Dimensional Non-Volatile Memories

“…Assuming a 25 nm radius sense wire with a length L of 100 µm and a specific resistance ρ of 1.7 × 10 −8 Ωm, R becomes 866 Ω. In that case a should be smaller than about 10 −15 s. Micromagnetic simulations show that these short switching times cannot be reached, certainly not under low field conditions [39]. The situation worsens when dimensions shrink.…”

Development of vortex state in circular magnetic nanodots: Theory and experiment

“…Also it does not take account on the "halo" effect at the boundary of the core. 34 We adopt a vortex-core model 25,32 with a functional form…”

“…Although alternative expressions for M z ͑͒ have been proposed in the literature 25,34,35 any value of n Ն 4 can approximately describe the magnetic vortexcore configuration in nanodots, 25,32 provided the out-of-plane magnetization at the boundary of the core 34 is small. The total energy, consisting of dipolar and exchange contributions, can be calculated analytically 25,32 as given, e.g., by Eq.…”