Gigahertz vortex gyrotropic excitations in magnetic nanodot
Prof. Gleb Kakazei (University of Porto)

Date, Time
18.05, 15:00 - 16:00

Movement towards the 3rd dimension allows obtaining spintronic nanodevices with much richer functionality, compared to traditional realizations in planar 2D magnetic structures. In this work two dimensional magnetic vortex structure, known for producing an efficient dynamical response to external stimuli without bias magnetic field, is extended into the 3rd dimension. This extension leads to a drastic vortex frequency increase, up to 5 GHz, contrasted with typical sub-GHz range reported for planar vortex oscillators. A systematic study reveals a complex pattern of vortex excitation modes, which provides explanations for the fall of the thickness-homogenous oscillation mode frequency, vortex mode intensities inversion, and nontrivial spatial distribution of the vortex dynamical magnetization reported in earlier works. The observed phenomena allow for optimization of both oscillation frequency and frequency reproducibility (by minimizing the effect of uncontrolled size uncertainties) of such magnetic devices.

In the second part, magnetization dynamics in three-layered dots soft layer(SL)/non-magnetic layer/hard layer with perpendicular magnetization will be discussed. It was revealed that under certain conditions the ground state of SL is radial vortex. Remarkably, for SL thicknesses around 1 nm and diameters below 50 nm, gyrotropic frequencies up to 5 GHz were obtained in micromagnetic simulations.

Simulated thickness (t) dependence of the gyrotropic modes frequencies for 500nm diameter nanodots. Two kinds of approximation curves are present: for a homogenous mode a theoretical dependence of the lowest vortex gyrotropic frequency G₀; other curves represent hyperbolae ∼ t^−b; fits of the high frequency and high thickness assymptotics of modes G₁, G₂, G₃. Colour represents in-plane microwave magnetic field response intensity of the vortex gyromodes.