A metamaterial description of two-dimensional (2D) magnonic crystals as the most representative examples of magnonic crystals according to micromagnetic and analytical calculations is given. Micromagnetic calculations were performed by using the Hamiltonian-based Dynamical Matrix Method extended to periodic systems. The one-component 2D systems are composed by periodic square arrays of circular nanoholes embedded into a permalloy ferromagnetic film. Magnonic modes dispersion is calculated and opening of band gaps at Brillouin zone boundaries is explained by accounting for the inhomogeneity of the internal field. The dynamics is described in terms of effective properties by means of the definition of new effective quantities like the effective wavelength and the effective wave vector in the stationary regime and their relation with the corresponding Bloch quantities characteristic of periodic systems. an effective medium approximation is used to model the metamaterial wave in the propagative regime. The bi-component systems are composed by 2D periodic arrangements of circular nanodots of cobalts partially or totally embedded into a permalloy film. Band structure of the most representative collective modes is studied and the dependence of band gap amplitudes on cobalt volume and on cobalt position within the unit cell is also discussed. Effective surface magnetic charges are defined to explain the behaviour of demagnetizing fields and their influence on collective mode dispersion. The effect of the interchange between the two materials on mode dispersion is also investigated. Effective quantities like an effective magnetization are introduced to calculate the dispersion of the corresponding metamaterial wave in the propagative regime. An energy concentration factor able to describe collective mode localization properties is also introduced in analogy with the corresponding one describing electromagnetic waves in photonic crystals.

Magnonic Crystals: a New Class of Metamaterials - Invited talk

ZIVIERI, Roberto
2015

Abstract

A metamaterial description of two-dimensional (2D) magnonic crystals as the most representative examples of magnonic crystals according to micromagnetic and analytical calculations is given. Micromagnetic calculations were performed by using the Hamiltonian-based Dynamical Matrix Method extended to periodic systems. The one-component 2D systems are composed by periodic square arrays of circular nanoholes embedded into a permalloy ferromagnetic film. Magnonic modes dispersion is calculated and opening of band gaps at Brillouin zone boundaries is explained by accounting for the inhomogeneity of the internal field. The dynamics is described in terms of effective properties by means of the definition of new effective quantities like the effective wavelength and the effective wave vector in the stationary regime and their relation with the corresponding Bloch quantities characteristic of periodic systems. an effective medium approximation is used to model the metamaterial wave in the propagative regime. The bi-component systems are composed by 2D periodic arrangements of circular nanodots of cobalts partially or totally embedded into a permalloy film. Band structure of the most representative collective modes is studied and the dependence of band gap amplitudes on cobalt volume and on cobalt position within the unit cell is also discussed. Effective surface magnetic charges are defined to explain the behaviour of demagnetizing fields and their influence on collective mode dispersion. The effect of the interchange between the two materials on mode dispersion is also investigated. Effective quantities like an effective magnetization are introduced to calculate the dispersion of the corresponding metamaterial wave in the propagative regime. An energy concentration factor able to describe collective mode localization properties is also introduced in analogy with the corresponding one describing electromagnetic waves in photonic crystals.
2015
Magnonic crystals, metamaterials, periodic magnetic systems
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2335403
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