Excitations in vortex-state permalloy dots

Zaspel, C. E.; Иванов, Б. А.; Park, J. P.; Crowell, P. A.

doi:10.1103/physrevb.72.024427

Cited by 85 publications

(79 citation statements)

References 24 publications

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“…The frequency splitting in our experiments and simulations clearly exceeds the splitting from the calculations of Zaspel et al, 18 but it is comparable with the experiments of other groups. 10,11 Thus, a satisfying explanation for the discrepancy between experiment and theory for the magnitude of this splitting is still missing and calls for the refinement of the theoretical model.…”

supporting

confidence: 72%

“…Up to now, only the theoretical calculations by Zaspel et al 18 allow one to calculate the splitting of the azimuthal mode ͑1,1͒. This approach includes both the exchange interaction and the spin-wave scattering at the vortex core.…”

mentioning

confidence: 99%

“…10,11,18 The frequency dependence of the first azimuthal mode ͑1, ±1͒ is shown in Fig. 4 for both regular disks and disks with hole.…”

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Mode degeneracy due to vortex core removal in magnetic disks

et al. 2007

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The mode spectrum of micrometer-sized ferromagnetic Permalloy disks, exhibiting a vortex ground state, is investigated by means of time-resolved scanning Kerr microscopy. The temporal evolution of the magnetization is probed after application of a fast in-plane field pulse. The lowest order azimuthal mode, a mode with only one diametric node, splits into a doublet as the disk diameter decreases. Theoretical models show that this splitting is a consequence of the interaction of the mode with the gyrotropic motion of the vortex core. Our experiments and micromagnetic simulations confirm that by removing the vortex core from the disk, the mode splitting vanishes. DOI: 10.1103/PhysRevB.76.014416 PACS number͑s͒: 75.75.ϩa, 75.40.Gb The spectra and spatial structure of spin-wave modes in small ferromagnetic elements characterized by an almost flux-closed ͑stray field free͒ magnetization state have been thoroughly investigated in recent years. Among the magnetic elements which have been investigated in detail, one may find squares, 1-3 rings, 4,5 stripes, 6-8 and circular disks. [9][10][11] In some recent papers, the attempts to manipulate the structure of spin-wave modes in confined magnetic elements by modification of the elements' physical properties have been reported. [10][11][12] A particular attention has been paid to diskshaped elements due to their simplicity. The response of these elements to the external excitation with pulsed and continuous magnetic fields has been studied both experimentally and theoretically. 10,11,13,14 In general, two types of dynamic excitations can be found in these cylindrically shaped elements that exist in the vortex ground state. The first type, known as a gyrotropic mode, 1,15,16 is the oscillatory motion of the vortex core itself. In the absence of an external bias field, the vortex core is located at the center of the disk. After the application of an in-plane magnetic field pulse, the vortex is displaced from the center. While the system relaxes toward its equilibrium state, the vortex gyrates around the disk center. With the disk diameters in the micrometer range, the frequencies of this gyrotropic mode lie in the subgigahertz range. In the experiments described below, the accessible time range was about 3.4 ns and, therefore, the gyrotropic mode could not be observed.The second type of modes, known as magnetostatic modes, is the relatively high-frequency ͑several gigahertz͒ spin-wave excitations. These modes in the cylindrical geometry might have circular nodal lines ͑characterized by the radial index n͒ and diametric nodal lines ͑characterized by the azimuthal index m͒. In a recent paper, 9 it has been shown that for disks having a large aspect ratio of diameter ͑e.g., several micrometers͒ to thickness ͑e.g., 20 nm͒, the experimentally measured frequencies of these excitations can be well described by considering only the dipolar energy and pinned boundary conditions.When the disk diameter is decreased, the influence of the vortex core and of the exchange interaction mus...

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Mode degeneracy due to vortex core removal in magnetic disks

et al. 2007

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“…For disk-shaped structures, it has been theoretically and experimentally found that for given material parameters, the gyration frequency approximately scales with the geometrical aspect ratio, with only a slight dependence on the thickness and lateral size separately. [4][5][6] On the other hand, pinning of the magnetization may lead to a deviation from this ideal resonance behavior. Compton and Crowell 7 found that in films with relatively large grains, the vortex core can be trapped in a pinning potential.…”

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confidence: 99%

Influence of domain wall pinning on the dynamic behavior of magnetic vortex structures: Time-resolved scanning x-ray transmission microscopy in NiFe thin film structures

et al. 2008

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Artificial domain wall pinning sites were created in micron-sized thin-film Ni 80 Fe 20 structures, and their influence on the vortex dynamics was investigated by using time-resolved scanning transmission x-ray microscopy. The domain wall pinning sites were introduced by means of focused ion beam etching in the form of antidots. The vortex gyration frequency increased in square-shaped structures but not in similarly modified disk-shaped structures, where no domain walls are present. This demonstrates that the domain wall pinning is causing the increased frequency. The effect is explained by the confinement of the domain wall motion to the portion of the structure that is circumscribed by the antidots and is in agreement with micromagnetic simulations.

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“…[1][2][3][4] In addition, nanoscale studies may shed light on the heavily investigated mechanism of exchange bias [5][6][7][8][9] existing in ferromagnet ͑FM͒-antiferromagnet ͑AF͒ bilayers. Fabrication of sub-100-nm FM single layer and FM/AF bilayer nanostructures offers a great opportunity for research on fundamental magnetism at the nanoscale.…”

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confidence: 99%

Fabrication and structural characterization of highly ordered sub-100-nm planar magnetic nanodot arrays over 1cm2 coverage area

Roshchin

Batlle

et al. 2006

Journal of Applied Physics

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Porous alumina masks are fabricated by anodization of aluminum films grown on both semiconducting and insulating substrates. For these self-assembled alumina masks, pore diameters and periodicities within the ranges of 10-130 and 20-200 nm, respectively, can be controlled by varying anodization conditions. 20 nm periodicities correspond to pore densities in excess of 10 12 per square inch, close to the holy grail of media with 1 Tbit/ in. 2 density. With these alumina masks, ordered sub-100-nm planar ferromagnetic nanodot arrays covering over 1 cm 2 were fabricated by electron beam evaporation and subsequent mask lift-off. Moreover, exchange-biased bilayer nanodots were fabricated using argon-ion milling. The average dot diameter and periodicity are tuned between 25 and 130 nm and between 45 and 200 nm, respectively. Quantitative analyses of scanning electron microscopy ͑SEM͒ images of pore and dot arrays show a high degree of hexagonal ordering and narrow size distributions. The dot periodicity obtained from grazing incidence small angle neutron scattering on nanodot arrays covering ϳ2.5 cm 2 is in good agreement with SEM image characterization. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2356606͔ INTRODUCTIONNanostructured magnets have attracted great attention recently due to their unique magnetic properties which are completely different from those of continuous films and bulk materials. [1][2][3][4] In addition, nanoscale studies may shed light on the heavily investigated mechanism of exchange bias 5-9 existing in ferromagnet ͑FM͒-antiferromagnet ͑AF͒ bilayers. Fabrication of sub-100-nm FM single layer and FM/AF bilayer nanostructures offers a great opportunity for research on fundamental magnetism at the nanoscale.A variety of methods are used for nanofabrication, including electron beam and optical lithography. The low throughput and high cost of electron beam lithography lead to limited applicability for the fabrication of nanopatterns with large coverage area. Although optical lithography has high throughput, the smallest size of features that can be produced is limited by the long optical wavelength. Among many nanofabrication methods, 10-15 a promising technique is based on masks with sub-100-nm self-assembled pores. Such masks, for example, can be fabricated by the anodization of aluminum under appropriate experimental conditions. [16][17][18][19][20][21][22] Arrays of nanopores with tunable pore diameter covering more than 1 cm 2 demonstrate the potential application of porous alumina ͑AlO x ͒ masks for nanostructure fabrication. Previously, alumina membranes obtained from the anodization of thick ͑Ͼ100 m͒ aluminum foils were mostly used for the fabrication of nanowires. [23][24][25][26][27][28][29][30] These nanowires were grown by electrodeposition, which cannot be easily adapted for the fabrication of nanodots with controlled and uniform thickness. Moreover, this method requires transfer of the alumina membranes onto a substrate. Insufficient adhesion between the membrane and substrate,...

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Excitations in vortex-state permalloy dots

Cited by 85 publications

References 24 publications

Mode degeneracy due to vortex core removal in magnetic disks

Mode degeneracy due to vortex core removal in magnetic disks

Influence of domain wall pinning on the dynamic behavior of magnetic vortex structures: Time-resolved scanning x-ray transmission microscopy in NiFe thin film structures

Fabrication and structural characterization of highly ordered sub-100-nm planar magnetic nanodot arrays over 1cm2 coverage area

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