Stability of magnetic vortices in flat submicron permalloy cylinders

Abstract

Lattice symmetry and magnetization reversal in micron-size antidot arrays in Permalloy filmWe have investigated the magnetic properties of flat permalloy cylinders by Lorentz transmission electron microscopy and micromagnetic simulations. The magnetization patterns during in situ magnetizing experiments have been imaged and they revealed that the magnetization reversal of the cylindrically shaped dots investigated is determined by the formation and annihilation of magnetic vortices. Furthermore, the experiments and micromagnetic simulations showed a dependence of the vortex annihilation field not only on the aspect ratio but also on the absolute thickness of the cylinders. The diameter of the cylindrical dots was varied between 150 and 1000 nm, and the thicknesses were 3, 5.5, 8.3, 15, and 20 nm, respectively. The formation of inhomogeneous magnetization patterns prior to vortex evolution was observed and by a comparison of the experimental to simulated Fresnel images these patterns can be identified as S-and C-like states.

Collective modes for an array of magnetic dots in the vortex state

“…When the dot radius, R is above a critical value, the vortex state with almost closed magnetic flux occurs [7]. This vortex state has been experimentally observed [8][9][10][11][12][13][14][15][16][17][18] for cylinder -shaped magnetic dots in the diameter range 2R = 100 ÷ 800 nm and thickness range L = 20 ÷ 60 nm. Recent work [19] even reduced these values, demonstrating that the critical size can be as small as L = 40 nm and R =43 nm, for permalloy.…”

Direct evidence of imprinted vortex states in the antiferromagnet of exchange biased microdisks

“…However, measurements carried out on the reversed layer structure, Ta͑5 nm͒/Cu͑3 nm͒/ NiFe͑12 nm͒/IrMn͑5 nm͒/Al͑1.5 nm͒, exclude the possibility that the uncompensated vortex state extends throughout the IrMn layer. As for purely FM structures, [23][24][25] the set of patterned array structures demonstrates that vortex stability in FM/ AFM confined systems strongly depends on the geometry. The microdisk arrays here, all with 6 nm NiFe thick layers, exhibit an optimum diameter for vortex formation around 1 m ͑see Fig.…”

Probing nanoscale behavior of magnetic materials with soft X-ray spectromicroscopy

“…The fi rst experimental images of magnetic vortex cores have been obtained by magnetic force microscopy (MFM) [33] (Figure 2 A) and Lorentz transmission electron microscopy (L-TEM) [38] (Figure 2B). The static internal structure of a vortex has been studied at almost atomic spatial resolution by spin-polarized scanning tunneling microscopy (SP-STM) ( Figure 2C) [39] .…”