Vortex nucleation in submicrometer ferromagnetic disks

Abstract

We investigate both experimentally and by means of micromagnetic calculations magnetic states preceding vortex formation in permalloy nanodisks. In experiment, we used micro-Hall sensors fabricated from GaAs/AlGaAs heterojunction material to measure stray field hysteresis loops of individual disks. Micromagnetic calculations involving different micromagnetic codes allowed us to interpret the experimental results. Both calculations and experiments suggest that vortex formation can be reached via different precursor states.

How hole defects modify vortex dynamics in ferromagnetic nanodisks

“…Therefore, each non-centered defect may provide an additional EP for the vortex center, as observed in experiments [7,8,9] and predicted theoretically [10,11,12,28]. Namely, note that if ρ > ρ cr then the potential well at the hole is deeper than that at the disk center (see Fig.…”

“…As long as one could manipulate these states other possibilities would emerge. In fact, one way towards this control is obtained by removing some small portions of the magnetic nanodisk, in such a way that the defects (cavities) so created work by attracting and eventually pinning the vortex around themselves [7,8,9,10,11,12,13,14] (similar effect also applies to soliton-like spin excitations [15]). Based upon such an idea, Rahm and coworkers [16] have studied the cases of two, three and four holes (each of them with diameter ∼ 85 nm) inserted in a disk with diameter ∼ 500 nm, separated by around 150 nm − 200 nm.…”

Emergence of skyrmion lattices and bimerons in chiral magnetic thin films with nonmagnetic impurities

“…In more general grounds, it is known that a spin vacancy in 2D nearly classical isotropic magnets generates an interaction potential that attracts the skyrmion center [10][11][12] . Hence, in these magnets containing a low impurity density, such potential allows a vacancy to be at the skyrmion center (similarly, these kind of defects also attract the vortex center in easy-plane magnets 13 and magnetic nanodisks [14][15][16][17] ). Particularly, in easy-plane magnets, a low concentration of nonmagnetic impurities has a strong influence on the Berezinskii-Kosterlitz-Thouless (BKT ) transition temperature 18 and in magnetic nanostructures they generate the physical mechanism behinds the experimental observation of the Barkhauser effect 19,20 .…”

Experimental observation of switching in ferromagnetic nanoscale double disks

“…[1][2][3] The hysteresis curve measured for an applied in-plane magnetic field shows zero remanence and the magnetization reversal involves nucleation of a vortex, shift of the vortex's center perpendicular to the applied field and annihilation of the vortex. 4 The reversal of the out of plane center by means of microwave-or ac-current excitation is currently an interesting topic 5,6 which offers the possibility to use the up and down orientation of vortex's center in memory applications. Here we address experimentally the question whether different modes of switching can be achieved if two ferromagnetic disks overlap forming a peanut shaped structure.…”