Dynamics and efficiency of magnetic vortex circulation reversal

Abstract

Dynamic switching of the vortex circulation in magnetic nanodisks by fast rising magnetic field pulse requires annihilation of the vortex core at the disk boundary and reforming a new vortex with the opposite sense of circulation. Here we study the influence of pulse parameters on the dynamics and efficiency of the vortex core annihilation in permalloy (Ni80Fe20) nanodisks. We use magnetic transmission soft x-ray microscopy to experimentally determine a pulse rise time -pulse amplitude phase diagram for vortex circulation switching and investigate the time-resolved evolution of magnetization in different regions of the phase diagram. The experimental phase diagram is compared with an analytical model based on Thiele's equation describing high amplitude vortex core motion in a parabolic potential. We find that the analytical model is in a good agreement with experimental data for a wide range of disk geometries. From the outputs of the analytical model and in accordance with our experimental finding we determine the geometrical condition for dynamic vortex core annihilation and pulse parameters needed for the most efficient and fastest circulation switching. The comparison of our experimental results with micromagnetic simulations show that the micromagnetic simulations of 'ideal' disks with diameters larger than ∼250 nm overestimate nonlinearities in susceptibility and eigenfrequency. This overestimation leads to the core polarity switching near the disk boundary, which then in disagreement with experimental findings prevents the core annihilation and circulation switching. We modify the micromagnetic simulations by introducing the 'boundary region' of reduced magnetization to simulate the experimentally determined susceptibility and in these modified micromagnetic simulations we are able to reproduce the experimentally observed dynamic vortex core annihilation and circulation switching.

Magnetic vortex nucleation modes in static magnetic fields

“…The size of the dip is influenced by the exact placement of the gold contacts (which may slightly differ between the experiment and simulation) and by the assumption of constant current density within the disk. The experimental values of the nucleation and annihilation fields are lower than the simulated values in agreement with previous observations 18,24 and may be explained by the edge roughness and oxidation leading to deteriorations of the magnetic properties of the disk material 14 and by temperature effects. 30,31 The AMR data in Fig.…”

“…Controlling the vortex states by switching the vortex polarity or circulation has been shown both in dynamic [10][11][12][13][14] and static [15][16][17][18][19] vortex by displacing the vortex core out of the magnetic disk, followed by nucleation of a new vortex in decreasing external field. The resulting state of the newly nucleated vortex can be controlled by asymmetric disk geometry [20][21][22] or by symmetry breaking arising from the Dzyaloshinskii-Moriya interaction.…”

Highly Enhanced Curie Temperature in Ga‐Implanted Fe3GeTe2 van der Waals Material

“…We find that the circulation direction doesn't change until after applying an in‐plane magnetic field pulse greater than 120 Oe (Figure 3a). Recalling that vortex circulation can only be changed after the vortex core is pushed out of the circle, [ 28 ] the result of Figure 3a shows that 120 Oe corresponds roughly the field to saturate the magnetic vortex into a single domain. At 110 K which is below the bulk T C of Fe 3 GeTe 2 , both the Ga implanted and un‐implanted area exhibit out‐of‐plane magnetic stripe domains (Figure 3b) with similar domain width (the greater magnetic contrast in the Ga implanted area is due to the removal of the Pd protection layer by Ga sputtering), proving again our previous assertion that the magnetization in the Ga implanted area is from the majority of Fe rather than from tiny amount of Fe around the implanted Ga atoms.…”

Magnetic vortex nucleation/annihilation in artificial-ferrimagnet microdisks

“…More fundamental aspects, like a magnetic structure of a vortex core or microscopic mechanisms of vortex nucleation/annihilation, have also attracted a lot of attention and have been investigated using a variety of tools. [9][10][11][12][13][14][15] Thus, fabrication of multilayered microdisks in which different layers are either coupled to each other 16,17 or exchange biased with an antiferromagnet 18 has proved to be an efficient way to control magnetization reversal.…”