Complete mapping of the spin-wave spectrum in a vortex-state nanodisk

Taurel, Boris; Valet, T.; Naletov, V. V.; Vukadinovic, N.; Loubens, G. de; Klein, O.

doi:10.1103/physrevb.93.184427

Cited by 31 publications

(16 citation statements)

References 42 publications

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“…It was also observed near the transition of the vortex to the saturated state of the dots, when the gyrotropic mode transforms into the quasi-uniform Kittel mode. 26 The minimum of frequency corresponds to two magnetization configurations with smallest (ii) and largest (iv) skyrmion radius, the states closest to the uniform state.…”

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confidence: 99%

“…21 In this paper we consider spin excitation spectra on the magnetic soliton background in thin circular dots with effective easy plane anisotropy with micromagnetic simulations. To do that we identify a set of parameters that allows for the continuous phase transitions (preserving continuity of the magnetization components) 25,26 in transformations between various magnetic soliton stable states, i.e., vortex, Bloch-like skyrmion and Néel-like skyrmion (see Fig. 1).…”

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Spin excitation spectrum in a magnetic nanodot with continuous transitions between the vortex, Bloch-type skyrmion, and Néel-type skyrmion states

2017

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We study spin-wave excitations in a circular ferromagnetic nanodot in different inhomogeneous, topologically non-trivial magnetization states, specifically, vortex and skyrmion states. Gradual change in the strength of the out-of-plane magnetic anisotropy and the Dzyaloshinskii-Moriya exchange interaction leads to continuous phase transitions between different stable magnetic configurations and allows for mapping of dynamic spin modes in and between the vortex, Bloch-type skyrmion and Néel-type skyrmion states. Our study elucidates the connections between gyrotropic modes, azimuthal spin waves and breathing modes in various stable magnetization states and helps to understand the rich spin excitation spectrum on the skyrmion background.

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confidence: 99%

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Spin excitation spectrum in a magnetic nanodot with continuous transitions between the vortex, Bloch-type skyrmion, and Néel-type skyrmion states

2017

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“…Even though magnon spectra in magnetic vortices have been intensively studied in the past 19,[21][22][23] , magnons with large azimuthal wave vectors have not yet been measured experimentally and were only observed in micromagnetic simulations 24 . The challenge to generate such magnons and, thereby, to reach out to whispering gallery magnons is finding an efficient excitation mechanism in a micronsized vortex.…”

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Excitation of Whispering Gallery Magnons in a Magnetic Vortex

et al. 2019

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One of the most fascinating topics in current quantum physics are hybridised systems, in which different quantum resonators are strongly coupled. Prominent examples are circular resonators with high quality factors that allow the coupling of optical whispering gallery modes 1-5 to microwave cavities 6 or magnon resonances in optomagnonics 7-9 . Whispering gallery modes play a special role in this endeavour because of their high quality factor and strong localisation, which ultimately increases the overlap of the wavefunctions of quantum particles in hybridised systems. The hybridisation with magnons, the collective quantum excitations of the electron spins in a magnetically ordered material, is of particular interest because magnons can take over two functionalities: due to their collective nature they are robust and can serve as a quantum memory 10 and, moreover, they can act as a wavelength converter between microwave and THz photons 9 . However, the observation of whispering gallery magnons has not yet been achieved due to the lack of efficient excitation schemes for magnons with large wave vectors in a circular geometry. To tackle this problem, we studied nonlinear 3-magnon scattering 11-14 as a means to generate whispering gallery magnons. This Letter discusses the basics of this non-linear mechanism in a confined, circular geometry from experimental and theoretical point of view.Whispering gallery magnons can only live in systems with rotational symmetry. This not only applies to the geometry of the magnetic element but also to the magnetisation texture therein. For that reason, we study a Ni 81 Fe 19 disc that inherently exhibits a magnetic vortex structure [15][16][17][18][19] . The arrows in Fig. 1a depict the generic features of such a vortex state: the magnetic moments curl in plane along circular lines around the vortex core, a nanoscopic region in the center of the disc where the magnetisation tilts out of plane. According to this rotational symmetry, the magnon eigenmodes in a vortex are characterised by mode numbers (n, m), with n = 0, 1, 2, ... counting the number of nodes across the disc radius and m = 0, ±1, ±2, ... counting the number of nodes in azimuthal direction over half the disc 20,21 .Other than commonly known waves, like sound, water or electromagnetic waves, magnons exhibit a strongly anisotropic dispersion relation in in-plane magnetised thin films 20 . In a vortex, this results in increasing (decreasing) mode energies for increasing n (m) as shown by the analytic calculations in Fig. 1b. The four exemplary intensity profiles for the eigenmodes (0, 0), (0, 10), (0, 20), and (0, 30), that are shown in Fig. 1c, reveal the character of whispering gallery magnons: the larger m, the more the magnon intensity is pushed toward the perimeter of the disc which can be understood intuitively by the reduction of exchange energy: Leaving an extended area around the vortex core with zero amplitude avoids a strong tilt of neighbouring spins close to the vortex core and, therefore, reduces the total ...

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“…We start with the analysis of circular disks. Spin wave spectra of circular nanodots has been studied intensively in the past [28,29]. When applying an in-plane excitation, the lowest state mode that can be observed is related to a gyrotropic motion of the vortex core, with the frequency of gyration highly dependent on the aspect ratio of the dot [30].…”

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confidence: 99%

Dynamics of spiral spin waves in magnetic nanopatches: Influence of thickness and shape

et al. 2019

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We explore the dynamics of spiral spin waves in Permalloy nano-elements with variable aspect ratio of geometric dimensions, and their potential use as improved spin wave emitters with no or little biasing field required. Numerical results show that above a certain thickness, propagating spiral waves can be obtained in circular and square shaped elements in a flux closure state. VNA-FMR experiments on 20 nm (thin) and 80 nm (thick) samples confirm two type of spectra corresponding to different dispersions for thinner and thicker elements. We show that, for the thicker films, the vortex core region acts as a source of large amplitude spiral spin waves, which dominate over other modes. In case of the thinner elements, these modes are critically damped. For different shapes of the patch, we show that a rich collection of confined propagating modes can also be excited, modifying the final wave front and enriching the potential of the nano-dot as a spin wave emitter. We give an explanation for the intense spiral modes from the perspective of a balance of dipolar and exchange energies in the sample. arXiv:2001.09053v1 [cond-mat.mes-hall]

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Complete mapping of the spin-wave spectrum in a vortex-state nanodisk

Cited by 31 publications

References 42 publications

Spin excitation spectrum in a magnetic nanodot with continuous transitions between the vortex, Bloch-type skyrmion, and Néel-type skyrmion states

Spin excitation spectrum in a magnetic nanodot with continuous transitions between the vortex, Bloch-type skyrmion, and Néel-type skyrmion states

Excitation of Whispering Gallery Magnons in a Magnetic Vortex

Dynamics of spiral spin waves in magnetic nanopatches: Influence of thickness and shape

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