Spin excitations of nanometric cylindrical dots in vortex and saturated magnetic states

Giovannini, L.; Montoncello, F.; Nizzoli, F.; Gubbiotti, G.; Carlotti, G.; Okuno, T.; Shinjo, Teruya; Grimsditch, M.

doi:10.1103/physrevb.70.172404

Cited by 155 publications

(134 citation statements)

References 19 publications

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“…The lack of nanoscale spatial resolution has been circumvented by measuring the frequency [16][17][18][19][20][21] or time 22,23 domain response from sufficiently large arrays of nanomagnets and comparing the measured signals with analytical theories [18][19][20] and/or micromagnetic simulations. 16,17,[21][22][23][24][25][26][27][28][29] In particular, this approach has led to the discovery of a crossover from a center to edge localized mode as the magnetic element size is reduced to less than 220 nm. 22,23 In this paper, numerical simulations performed with the object oriented micromagnetic framework 30 ͑OOMMF͒ have been used to study various factors affecting the high frequency response of the nanoscale magnetic elements, and the degree to which such simulations can reproduce the data reported in Refs.…”

Section: Introductionmentioning

confidence: 99%

Time resolved studies of edge modes in magnetic nanoelements (invited)

Kruglyak

Keatley

Hicken

et al. 2006

Journal of Applied Physics

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Micromagnetic simulations have been performed to investigate the frequencies and relative amplitudes of resonant magnetic modes within nanomagnetic elements of varying size that have been previously studied by time resolved Kerr magnetometry. The magnetic response of a nanoscale element generally consists of the edge and center localized modes. For 2.5 nm thick elements, a crossover from center to edge mode excitation occurs as the element size is reduced to less than 220 nm. Additional modes appear in the spin wave spectrum as the thickness of the element is increased. The frequency of the edge mode is particularly sensitive to the strength of the exchange interaction, dipolar interactions with nearest neighbor elements, and rounding of the corners of the element. Simulations with in-plane pulsed fields show that the edge mode becomes dominant in elements of somewhat larger size, emphasizing the importance of the edge mode in technological applications.

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Section: Introductionmentioning

confidence: 99%

Time resolved studies of edge modes in magnetic nanoelements (invited)

Kruglyak

Keatley

Hicken

et al. 2006

Journal of Applied Physics

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show abstract

“…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.…”

mentioning

confidence: 99%

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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“…The high-frequency coupled spin waves in the vortex state were experimentally observed for the first time with the use of Brillouin light scattering (BLS) spectroscopy, in which reflected light is scattered on acoustic hypersonic wave generated by an excited nanodot due to magnetostriction [39]. The high-frequency spin waves were studied in detail and eigenfrequencies in the subgigahertz range were not revealed [40,41].…”

Section: Controlling the Magnetic Vortex Statementioning

confidence: 99%