The spin-wave band structure of a two-dimensional square array of NiFe circular antidots (hole diameter 120 nm, periodicity 800 nm) is investigated. Brillouin light scattering experiments and band structure calculations, carried out by means of the dynamical matrix method, provide evidence for either extended or localized magnonic modes. Both families exhibit band gaps at Brillouin zone boundaries, attributed to Bragg reflection. Their calculated magnitude agrees with the one obtained by using an analytical model that takes into account the periodic variation of the internal field. This is in contrast to antidots in photonics and electronics, where the back-reflection is directly caused by the presence of holes. The results are important for advancing research on nanostructured two-dimensional magnonic crystals. DOI: http://dx.doi.org/10.1103/PhysRevB.85.012403 Received 16 December 2011Published 11 January 2012©2012 American Physical Society

A study of the in-phase (“acoustical”) and of the out-of-phase (“optical”) spin modes in layered ferromagnetic structures with both ferromagnetic and antiferromagnetic coupling is presented, in particular for the system Fe(20 Å)/Cr(20 Å)/Fe(20 Å)/Cr(9 Å)/Fe(100 Å). A calculation of the dynamic magnetization, assumed constant in each film, gives an explanation of the behavior of the two kinds of modes at different magnetic fields. The “acoustical” mode is the lowest frequency one for low applied fields, but its frequency switches with that of the “optical” modes at higher fields. It is found that the system exhibits soft modes as a function of the applied field. One of these is a Goldstone mode. DOI: http://dx.doi.org/10.1103/PhysRevB.62.14950 © 2000 The American Physical Society

We present results of ferromagnetic resonance (FMR) experiments and micromagnetic simulations for a distorted, two-dimensional (2D) kagome artificial spin ice. The distorted structure is created by continuously modulating the 2D primitive lattice translation vectors of a periodic honeycomb lattice, according to an aperiodic Fibonacci sequence used to generate 1D quasicrystals. Experimental data and micromagnetic simulations show that the Fibonacci distortion causes broadening and splitting of FMR modes into multiple branches, which accompany the increasing number of segment lengths and orientations that develop with increasing distortion. When the applied field is increased in the opposite direction to the net magnetization of a segment, spin wave modes appear, disappear, or suddenly shift, to signal segment magnetization reversal events. These results show that the complex behavior of reversal events, as well as well-defined frequencies and frequency-field slopes of FMR modes, can be precisely tuned by varying the severity of the aperiodic lattice distortion. This type of distorted structure could therefore provide a tool for the design of complicated magnonic systems.

Using Brillouin light scattering spectroscopy and dynamical matrix method calculations, we study collective spin waves in dense arrays of periodically double-side width-modulated Permalloy nanowires. Width modulation is achieved by creating a sequence of triangular notches on the two parallel nanowire sides, with a periodicity of p = 1000 nm and a tunable relative displacement (Δ) of the notch sequence on the two lateral sides. Both symmetric (Δ = 0) and asymmetric (Δ = 250 and 500 nm) width-modulated nanowires were investigated. We have found that the detected modes have Bloch-type character and belong to a doublet derived from the splitting of the mode characteristics of the nanowire with the homogeneous width. Interestingly, the amplitude of the magnonic band, the frequency difference of the doublet, and their relative scattering intensity can be efficiently controlled by increasing Δ rather than having single- or symmetric (Δ = 0) double-side width-modulation.

In Brillouin light-scattering (BLS) measurements of an ion-milled Si(001) surface grating with grating wavelength ${\mathrm{\Lambda }}_{\mathit{G}}$=0.35 μm, we have observed numerous high-order zone-folded surface acoustic modes between the second and third zone boundaries associated with the grating. A surprisingly intense signal from a zone-folded longitudinal resonance was observed in the absence of direct hybridization with the Rayleigh modes. The relative intensities of all of the modes have been calculated by allowing for coupling between modes related by up to two grating reciprocal-lattice vectors, and for a grating profile with nonzero first and second Fourier amplitudes. The Fourier amplitudes inferred from the BLS measurements and calculations agree very well with those obtained from a direct measurement of the grating profile using atomic-force microscopy.

Brillouin light spectroscopy in p-p backscattering geometry is used to study sagittal surface acoustic phonons in silicon on insulator structures formed on a silicon buffer. The experimental spectra show, near the longitudinal threshold of silicon, two peaks whose physical meaning is discussed by comparison with theoretical cross sections. Calculations of Brillouin cross sections were performed, taking into account both the ripple and elastooptic coupling mechanisms. The peaks originate from two pseudomodes: the first is highly localized in the buried ${\mathrm{SiO}}_2$ layer and the second in the top silicon layer. The dependence of the pseudomode localization and cross section intensity with the parallel wave vector and with the thickness of the top silicon layer are discussed.