We investigate bi-component magnonic crystals consisting of periodic square lattices of Co nanodiscs embedded in Permalloy thin films. Micromagnetic simulations are used to analyse experimental data obtained with both all-electrical broadband spectroscopy and inelastic light scattering. We find that complementary spin-wave nanochannels form for in-plane fields H applied even along a non-high symmetry direction of bi-component magnonic crystals in contrast to previously reported magnetic antidot lattices. Depending on the excitation frequency, complementary channels might be functionalized for spin-wave signals transmitted in different spatial directions.

The excitation of spin waves by a microwave current injected into a coplanar waveguide with finite-width ground lines on a continuous Permalloy film is investigated both experimentally and numerically. Phase sensitive micro-focused Brillouin light scattering has been employed to reveal the spatial profile of the propagating spin waves in the magnetostatic surface wave geometry. The experimental results have been satisfactorily reproduced by means of micromagnetic simulations. The exciting microwave field used in this simulation has the spatial profile defined by the coplanar waveguide and user-defined periodic boundary conditions were employed in order to simulate the extended system. The resulting space and time dependent evolution of the magnetization has been analyzed by means of one and two dimensional fast Fourier transform algorithm in order to obtain the spatial profile and the frequency spectrum of the excited spin waves as well as their dispersion relations. Evidence is given to asymmetric emission from the two sides of the coplanar waveguide due to the symmetry breaking related to the sense of precession of the dynamical magnetization, as well as to the near-field effects of the extended spin wave emitter.

We investigate the magnonic band structure of in-plane magnetized two-dimensional magnonic crystals composed of cobalt dots embedded into a permalloy antidot lattice. Our analysis is based on the results of numerical calculations carried out by the plane wave method. The complex magnonic band structure found in square-lattice magnonic crystals is explained on the basis of the spin wave dispersion relations calculated in the empty lattice model. We show that four principal effects influence the formation of a magnonic band structure in planar two-dimensional bi-component magnonic crystals: a folding effect, Bragg scattering, hybridization between various spin wave modes, and a demagnetizing field. While the first two effects are found for other types of waves in periodic composites, the third one exists in an anisotropic medium and the last one is specific to spin waves propagating in magnonic crystals with magnetization in the film plane. The strong anisotropy in the dispersion relation of spin waves in thin ferromagnetic films results in the crossing and anti-crossing of the fast, Damon–Eshbach-like mode with a number of other spin waves folded to the first Brillouin zone. The demagnetizing field can induce the formation of channels for spin waves which are propagating perpendicular to the external magnetic field direction, but this property exists only in the limiting range of the thicknesses and the lattice constants of the bi-component magnonic crystals. Based on the model analysis we propose a modification of the magnonic crystal structure by changing its thickness, lattice constant and aspect ratio along the direction of the applied magnetic field to significantly modify the magnonic band structure and obtain partial magnonic band gaps.

Magnonics as an emerging nanotechnology offers functionalities beyond current semiconductor technology. Spin waves used in cellular nonlinear networks are expected to speed up technologically, demanding tasks such as image processing and speech recognition at low power consumption. However, efficient coupling to microelectronics poses a vital challenge. Previously developed techniques for spin-wave excitation (for example, by using parametric pumping in a cavity) may not allow for the relevant downscaling or provide only individual point-like sources. Here we demonstrate that a grating coupler of periodically nanostructured magnets provokes multidirectional emission of short-wavelength spin waves with giantly enhanced amplitude compared with a bare microwave antenna. Exploring the dependence on ferromagnetic materials, lattice constants and the applied magnetic field, we find the magnonic grating coupler to be more versatile compared with gratings in photonics and plasmonics. Our results allow one to convert, in particular, straight microwave antennas into omnidirectional emitters for short-wavelength spin waves, which are key to cellular nonlinear networks and integrated magnonics.

We report a combined experimental and theoretical study of the quasistatic hysteresis and dynamic excitations in large-area arrays of NiFe nanodisks forming a hexagonal lattice with the lattice constant of 390 nm. Arrays were fabricated by patterning a 20-nm-thick NiFe film using the etched nanosphere lithography. We have studied a close-packed (edge-to-edge separation between disks d(cp) = 65 nm) and an ultraclosed packed (d(ucp) = 20 nm) array. Hysteresis loops for both arrays were qualitatively similar and nearly isotropic, i.e., independent on the in-plane external field orientation. The shape of these loops revealed that magnetization reversal is governed by the formation and expulsion of vortices inside the nanodisks. When we assumed that the nanodisks' magnetization significantly decreases near their edges, micromagnetic simulations with material parameters deter-mined independently from continuous film measu-rements could satisfactorily reproduce the hysteresis. Despite the isotropic hysteresis, significant in-plane anisotropy of the dynamic response of the ultraclose-packed array was found experimentally by the all-electrical spin-wave spectroscopy and Brillouin light scattering. Dynamical simulations could successfully reproduce the difference between excitation spectra for fields directed along the two main symmetry axes of the hexagonal lattice. Simulations revealed that this difference is caused by the magnetodipolar interaction between nanodisks, which leads to a strong variation of the spatial distribution of the oscillation power both for bulk and edge modes as a function of the bias field orientation. Comparison of simulated and measured frequencies enabled the unambiguous identification of experimentally observed modes. Results of this systematic research are relevant both for fundamental studies of spin-wave modes in patterned magnetic structures and for the design of magnonic crystals for potential applications as, e. g., spin-wave guides and filters.

We report spin-wave (SW) propagation in a one-dimensional magnonic crystal (MC) explored by all electrical spectroscopy. The MC consists of a periodic array of 255 nm wide permalloy nanowires with a small edge-to-edge separation of 45 nm. Provoking antiparallel alignment of the magnetization of neighboring nanowires, we unexpectedly find reciprocal excitation of Damon-Eshbach type SWs. The characteristics are in contrast to ferromagnetic thin films and controlled via, both, the external magnetic field and magnetic states. The observed reciprocal excitation is a metamaterial property for SWs and attributed to the peculiar magnetic symmetry of the artificially tailored magnetic material. The findings offer great perspectives for nanoscale SW interference devices.

Periodic nanopatterning of metallic ferromagnets allows one to create devices with artificially tailored band structures for spin waves. We discuss our recent experiments performed on two-dimensional periodic lattices of nanoholes created in thin Ni80Fe20 films which exhibit man-made allowed minibands and forbidden frequency gaps provoking artificial crystal behavior and metamaterials properties.

We study spin-wave propagation in 360-nm wide Ni(80)Fe(20) nanowires using all-electrical spin-wave spectroscopy. Creating a zigzag-like magnetization state, we find enhanced spin-wave transmission compared to the states of more homogeneous magnetization. Micromagnetic simulations show that the spin waves propagate in narrow channels, which in particular, are remotely positioned from the edges. The internal channels reflect field-controlled self-cladding. Interestingly, rotation of the magnetic field at a specific value is found to vary the propagation velocity without changing the eigenfrequency. This opens the perspective of the velocity modulation transistor following a concept known from semiconductor electronics.

The spin-wave band structure of a two-dimensional bicomponent magnonic crystal, consisting of Co nanodisks partially embedded in a Permalloy thin film, is experimentally investigated along a high-symmetry direction by Brillouin light scattering. The eigenfrequencies and scattering cross sections are interpreted using plane wave method calculations and micromagnetic simulations. At the boundary of both the first and the second Brillouin zones, we measure a forbidden frequency gap whose width depends on the magnetic contrast between the constituent materials. The modes above and below the gap exhibit resonant spin-precession amplitudes in the complementary regions of periodically varying magnetic parameters. Our findings are key to advance both the physics and the technology of band gap engineering in magnonics.

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.

We report on the formation of a complete band gap for spin waves in a two-dimensional magnonic crystal consisting of a periodic hole lattice. We go beyond the partial band gaps observed so far in that we apply a magnetic field perpendicular to the permalloy thin film. We explore the relevant geometrical parameters using micromagnetic simulations. In nanopatterned devices we obtain complete band gaps of up to 1.4 GHz. The magnetostatic forward volume waves addressed here overcome in particular spin-wave localization effects. These effects have led to complicated and highly anisotropic miniband formation or Bragg reflection in in-plane fields for a long time. We demonstrate how direct band-gap tailoring via geometrical lattice symmetries becomes possible in nanostructured magnetic antidot lattices.

Spin wave propagation in a magnetron-sputtered CoFeB thin film is investigated. We apply both in-plane and out-of-plane magnetic fields. At room temperature, we find velocities of up to 25 and 3.5 km/s, respectively. These values are much larger compared to a thin permalloy film. Analyzing the resonance linewidth, we obtain an intrinsic Gilbert damping parameter of about 0.007 at room temperature. It increases to 0.023 at 5K. CoFeB is a promising material for magnonic devices supporting fast propagating spin waves. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731273]

Antidot lattices fabricated from permalloy thin films have been investigated by all-electrical spin-wave spectroscopy and Brillouin light scattering. Periodic arrays of 120-nm-diameter nanoholes have been prepared using focused ion beam etching. The periodicity of the square lattices was varied from 300 to 4000 nm. By applying an in-plane field of 40 mT, we discover surprisingly large spin-wave velocities of up to 6 km/s for a periodicity <400 nm. Using micromagnetic modeling and the further-developed plane wave method, we show that edge excitations at neighboring holes couple and form an allowed miniband supporting fast spin waves. By varying the orientation of the magnetic field we control the miniband characteristics. The coupling of edge modes opens interesting perspectives for magnonic crystals.

Combined all-electrical spin-wave and micro-focused Brillouin light scattering spectroscopies have been used to study spin-wave eigenmodes in bicomponent lattices formed by periodic Co nanodisks introduced in nanotroughs etched into a thin Ni80Fe20 film. We find two characteristic spin-wave modes extending through the lattice perpendicular to the applied field. Their spatial positions depend crucially on the Co nanodisks as they reverse locally the polarity of the internal field. Embedded nanodisks are found to offer control of spin waves at nearly the same eigenfrequency in periodically patterned magnetic devices and magnonic crystals.

We have coupled electromagnetic waves in the GHz frequency regime to collective spin excitations in ferromagnetic thin films which are periodically patterned on the nanoscale. For this we use pairs of micro- and nanostructured coplanar waveguides (CPWs) connected to a vector network analyzer. In a short period antidot lattice we find spin-wave propagation between two collinear CPWs with velocities of up to several km/s. Our findings open novel perspectives for nanostructured magnonic devices and magnetic metamaterials offering fast processing of GHz signals.

This paper discusses nanomagnetic structures enabling the manipulation of propagating spin waves. We address in particular how domain walls, or more generally speaking inhomogeneous spin configurations, enhance the control of spin-wave transmission and thereby the functionality of magnonic devices. Three different microscopic mechanisms are outlined, considering an interference device, a spin-wave bus and a magnonic crystal. Inhomogeneous spin configurations are argued to shift the spin-wave phase, guide spin waves in nanochannels and allow for reprogrammable spin-wave band structures in periodic nanostructures, respectively. Such devices and functionalities are relevant for further developments in magnonics.

All-electrical spin-wave spectroscopy and frequency-resolved magneto-optical Kerr-effect measurements are combined to study spin waves propagating through a magnetic antidot lattice nanopatterned from a Ni${}_{80}$Fe${}_{20}$ thin film. Spin waves are injected from a plain film into the antidot lattice and the transmission across the interface is explored in detail for different wavelengths. We find that spin waves with a wavelength much greater than the lattice periodicity are not described well by recently discussed approaches. Instead the spin-wave dispersion is consistent with an effective magnetization smaller than the saturation magnetization measured on the unstructured ferromagnetic material. Consistently, we find that the transmission coefficients are modeled well by assuming an effectively continuous metamaterial for spin waves characterized by the reduced magnetization. The experimental data and interpretation are substantiated theoretically using the plane-wave method and micromagnetic modeling. The results are interesting for the development of frequency-selective mirrors in magnonics through lateral nanopatterning.

All-electrical spin-wave spectroscopy, Brillouin light scattering, as well as the magneto-optical Kerr effect are combined to study spin-wave propagation through a magnetic antidot lattice nanopatterned into a Ni(80)Fe(20) thin film. The propagation velocities and, in particular, the relaxation are found to depend characteristically on the applied in-plane magnetic field. We explain the observed anisotropies by magnetic field-controlled spin-wave guiding in a network of interconnected nanowires which takes place over distances of up to 20  μm.