Magnetic vortex echoes

Abstract

The dynamic properties of magnetic vortices have many potential applications in fast magnetic devices. Here we present a micromagnetic study of the motion of magnetic vortices in arrays of 100 nanodisks that have a normal distribution of diameters, as expected in real array systems, e.g., produced by nanolithography. The micromagnetic simulated experiments follow a protocol with an initial preparation and magnetic pulses that enable the control of the magnetic vortices initial positions and circular motion direction. The results show a new effect-the magnetic vortex echo (MVE) that arises from the refocusing of the overall array magnetization. We show, by using arrays with different interdisk separations, that MVE affords a means of characterizing them as regards the homogeneity and intensity of the interaction between its elements, properties that are relevant for device applications. We also show that a simple analytical model, analogous to the one that describes the spin echo in magnetic resonance, can be used to explain most features of the simulated magnetic vortex echo. V

Interaction between magnetic vortex cores in a pair of nonidentical nanodisks

“…The coupling integrals I x and I y , when fitted to a single term of the formd −n , lead to values of n = 3.41 ± 0.02 and n = 4.08 ± 0.07, for I x and I y , respectively. These values of n are similar to those found by Sukhostavets et al 23 and Garcia et al 17 for equivalent parameters.…”

“…MVE is an effect of the vortex gyrotropic motion around an equilibrium position, and arises from the refocusing of the overall magnetization of the ensemble containing many nanoelements. MVE can be used as a tool to characterize nanostructures that exhibit a vortex ground state as regards the homogeneity and intensity of the interaction between its elements, properties that are relevant for device applications, as explained by Garcia et al 17 . In the previous work, the system studied was a matrix of nanodisks, here we have applied the method to pairs of nanodisks.…”

“…Conversely, when the vortex structure is out of equilibrium, with its core displaced e.g., by an external magnetic field or a spin-polarized current, magnetostatic coupling with the neighbor elements results. The dependence with distance of this coupling has been the subject of several studies in recent years [14][15][16][17] .…”

Indirect switching of vortex polarity through magnetic dynamic coupling

“…22 This coupling is strongly dependent on the distance d between the centers of the vortices, and on their relative polarities. 12,[25][26][27] The aim of this work is to demonstrate, using micromagnetic simulation, that it is possible to switch remotely the polarity of a given vortex, through a non-local excitation of a neighbor vortex; this was reached by suitably combining the perpendicular magnetic anisotropies of the nanostructures. In order to achieve this goal we initially investigated the influence of the uniaxial perpendicular magnetic anisotropy (K z ) on the dynamic properties of isolated disks, particularly the switching of the vortex core, induced by a rotating magnetic field in the plane of the disk.…”

“…[5][6][7] The dynamic behavior of the magnetic vortices has been studied extensively. [8][9][10][11][12] When the vortex core is displaced from the equilibrium position, two relevant consequences are the asymmetry of the dip and the appearance of a restoring force. This force is responsible for the motion -gyrotropic motion -toward the disk center.…”