Motivated by recent experimental developments for fabricating and characterizing nanometer-scale magnetic elements, either singly or in arrays, we present a mainly theoretical study of some spinwave properties in ferromagnetic nanostructures. In doing so, we make comparisons with related experiments that employ Brillouin light scattering spectroscopy and ferromagnetic resonance. The nanostructures considered here are single- and multilayer (or composite) ferromagnetic nanowires, along with the 1D magnonic crystal arrays formed from them. For all these structures we use a discrete-lattice approach to establish a microscopic (or Hamiltonian-based) theory for describing the dependence of the spin-wave frequencies on the applied magnetic field and on the wave vector in the dipole exchange regime. In all cases the effective lattice parameter a, which describes the cell size of the effective spins used for the calculations, is chosen to be smaller than the exchange correlation length. The Hamiltonian includes both the short-range exchange and the long-range magnetic dipole-dipole interactions, as well as the effects of an external magnetic field, single-ion anisotropy, biquadratic exchange, and the so-called Ruderman- Kittel-Kasuya-Yosida (RKKY) exchange interactions, as appropriate. In some structures, where there may be competing interactions in a multicomponent nanowire and/or in an array, it becomes necessary to solve first for the distribution of the static magnetization before considering the spin-wave dynamics. One aspect of particular note that we emphasize through examples later in this chapter relates to the increased interest in nanowires (and theirmagnonic crystal arrays) that are fabricated to have a multilayered structure with different thicknesses of the layers and thus multiple reprogrammable magnetization configurations and dynamic responses. This makes layered structures interesting as prototypes of multiple magnetic storage layers and as nonvolatile vertical magnetic logic gates. The exploration of the third dimension in magnonics also follows trends in CMOS electronics.

Dipole Exchange Theory of Magnons in Structured Composite Nanowires and Magnonic Crystal Arrays

2019

Abstract

Motivated by recent experimental developments for fabricating and characterizing nanometer-scale magnetic elements, either singly or in arrays, we present a mainly theoretical study of some spinwave properties in ferromagnetic nanostructures. In doing so, we make comparisons with related experiments that employ Brillouin light scattering spectroscopy and ferromagnetic resonance. The nanostructures considered here are single- and multilayer (or composite) ferromagnetic nanowires, along with the 1D magnonic crystal arrays formed from them. For all these structures we use a discrete-lattice approach to establish a microscopic (or Hamiltonian-based) theory for describing the dependence of the spin-wave frequencies on the applied magnetic field and on the wave vector in the dipole exchange regime. In all cases the effective lattice parameter a, which describes the cell size of the effective spins used for the calculations, is chosen to be smaller than the exchange correlation length. The Hamiltonian includes both the short-range exchange and the long-range magnetic dipole-dipole interactions, as well as the effects of an external magnetic field, single-ion anisotropy, biquadratic exchange, and the so-called Ruderman- Kittel-Kasuya-Yosida (RKKY) exchange interactions, as appropriate. In some structures, where there may be competing interactions in a multicomponent nanowire and/or in an array, it becomes necessary to solve first for the distribution of the static magnetization before considering the spin-wave dynamics. One aspect of particular note that we emphasize through examples later in this chapter relates to the increased interest in nanowires (and theirmagnonic crystal arrays) that are fabricated to have a multilayered structure with different thicknesses of the layers and thus multiple reprogrammable magnetization configurations and dynamic responses. This makes layered structures interesting as prototypes of multiple magnetic storage layers and as nonvolatile vertical magnetic logic gates. The exploration of the third dimension in magnonics also follows trends in CMOS electronics.
2019
9789814800730
Spin wave
Magnonic crystals
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.14243/380377
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