Magnetostatic Volume Waves Research Articles

Influence of magnetic anisotropy on dynamic magnonic crystals created by surface acoustic waves in yttrium iron garnet films

Experimental results on the investigation of the influence of magnetic crystallographic anisotropy onto parameters of dynamic magnonic crystals arising at surface acoustic wave (SAW) propagation in yttrium iron garnet (YIG) films are presented. The main features of such an influence, as we have shown, are: 1) appearance of extra magnonic band gaps together with the normal magnonic band gap existing without anisotropy, 2) the absence of reflections of the incident surface magnetostatic wave at the frequency of these extra gaps, 3) the same depth for the extra gaps was achieved with a relatively small SAW power, almost by the order of magnitude less than in the case of normal magnonic gaps caused by SAW. A possible explanation of the features is given on the base of inelastic scattering of surface magnetostatic waves by SAW with the transformation of the reflected surface wave to the anisotropic direct volume magnetostatic wave existence of which is due to cubic crystallographic anisotropy in YIG. These results may be useful in designing new devices of information processing.

Local probing of magnetic films by optical excitation of magnetostatic waves

Excitation of volume and surface magnetostatic spin waves in ferrite garnet films by circularly polarized laser pulses utilizing to the inverse magnetooptical Faraday effect has been studied experimentally. The region of excitation of the magnetostatic spin waves is determined by the diameter of the laser beam (∼10 μm). At the same time, the characteristic propagation length of the modes is 30 μm. A method of finding the local characteristics of a magnetic film, in particular, the cubic and uniaxial anisotropy constants, based on the analysis of the azimuthal-angle dependence of the spectrum of the magnetostatic spin waves has been proposed.

Edge Rotational Magnons in Magnonic Crystals

It is predicted that in 2D magnonic crystals the edge rotational magnons of forward vol-ume magnetostatic spin waves can exist. Under certain conditions locally bounded magnons may ap-pear within the crystal consisting of the ferromagnetic matrix and periodically inserted magnetic/non-magnetic inclusions. It is also shown that interplay of different resonances in 2D magnonic crystalmay provide conditions for spin wave modes existence with negative group velocity.

Spin-wave logic devices based on isotropic forward volume magnetostatic waves

We propose the utilization of isotropic forward volume magnetostatic spin waves in modern wave-based logic devices and suggest a concrete design for a spin-wave majority gate operating with these waves. We demonstrate by numerical simulations that the proposed out-of-plane magnetized majority gate overcomes the limitations of anisotropic in-plane magnetized majority gates due to the high spin-wave transmission through the gate, which enables a reduced energy consumption of these devices. Moreover, the functionality of the out-of-plane majority gate is increased due to the lack of parasitic generation of short-wavelength exchange spin waves.

Experimental characterization of Fabry-Perot resonances of magnetostatic volume waves in near-field metamaterials

In this work, we report on the experimental demonstration of magnetoquasistatic volume wave resonances in a 2-dimensional near field metamaterial (MM). Previous works have described only theoretically the magnetostatic waves in near field MMs and have reported peaks and valleys in the mutual coupling of MM enhanced wireless power transfer that they have attributed to Fabry-Perot resonances, however, neither has been experimentally measured nor characterized. We report on the direct magnetic field measurement of magnetostatic volume waves in a 2D near-field MM and show that the periodic peaks and valleys in mutual coupling observed previously are indeed due to a Fabry-Perot oscillation. In addition, we show that these resonances can be predicted from experimentally extracted permeability and the dimensions of the system.

Cross Junction Spin Wave Logic Architecture

Backward volume magnetostatic spin wave interference in ferromagnetic cross is explored. Spin waves are excited at the two input arms of the cross, interference signal amplitude, and phase are detected in the other two, output arms of the cross. Spin wave scattering defines the out of phase interference in the output arms of the cross: the constructive (destructive) interference is observed at different input wave phase shifts in different output arms of the cross. Numeric simulations are in a good agreement with experiment. Based on the observed interference, we propose the cross junction spin wave logic device that operates as an OR or NOR logic gates. Spin wave phase represents the logic information. Destructive and constructive interference in the cross center determines the phase of the device output.

Edge rotational magnons in magnonic crystals

It is predicted that in 2D magnonic crystals the edge rotational magnons of forward volume magnetostatic spin waves can exist. Under certain conditions, locally bounded magnons may appear within the crystal consisting of the ferromagnetic matrix and periodically inserted magnetic/non-magnetic inclusions. It is also shown that interplay of different resonances in 2D magnonic crystal may provide conditions for spin wave modes existence with negative group velocity.

Two-Dimensional Magnonic Crystal With Periodic Thickness Variation in YIG Layer for Magnetostatic Volume Wave Propagation

The propagation characteristics of magnetostatic volume waves (MSVWs), namely, magnetostatic forward volume waves (MSFVWs) and magnetostatic backward volume waves (MSBVWs), in two-dimensional (2-D) magnonic crystals (MCs) with periodic thickness variation of square lattice in YIG layer are reported. The theoretical approach based on Walker's equation was employed to determine the bandgaps associated with the MSVWs. Experiments were conducted on a 2-D MC with periodic square lattices in YIG layer thickness to measure both the magnetic field-tuned and propagation direction-dependent bandgaps. A very good agreement between the measured and the calculated results was obtained.

Magnetic control of a meta-molecule

Metamaterials offer the prospect of new science and applications. They have been designed by shaping or changing the material of the individual meta-molecules to achieve properties not naturally attainable. Composite meta-molecules incorporating a magnetic component offer new opportunities. In this work we report on the interaction between a non-magnetic split ring resonator (SRR) and a thin film of yttrium iron garnet (YIG). Strong hybridized resonances are observed. While the SRR is characterized by a magnetic and electric resonance, in practice, it is found that the YIG couples strongly to this symmetric (electric) mode of the SRR. It is also demonstrated that the anti-crossing region provides fertile ground for the creation of elementary excitations such as backward volume magnetostatic waves.

Application of the smith chart in the analysis of the relaxation properties of magnetostatic oscillations and spin waves in ferrite films

The relaxation properties of three main types of magnetostatic oscillations in a magnetostatic film resonator and nonlinear processes (parametric excitation of spin waves in the first and second bands in the presence of the tangential magnetization of the gallium-substituted yttrium-iron garnet film and foldover in the regime of normal magnetization) are studied in the frequency range 0.8–4.5 GHz. An original method is proposed for the determination of thresholds of the parametric excitation of spin waves using the deformations of Smith chart caused by variations in the measurement power level. The method is used in the highaccuracy analysis of the frequency dependences of threshold power in the presence of tangential magnetization in the regimes of resonances of both surface and backward volume magnetostatic waves. The frequencyfield dependences of the absorption spectra of three main types of magnetostatic oscillations in the linear regime are used to determine the saturation magnetization, anisotropy fields, and unloaded Q factors of resonator at each mode and to calculate the relaxation parameters of the corresponding magnetostatic oscillations. The experimentally measured threshold pump powers are used to calculate the relaxation line widths of the parametrically excited spin waves with the aid of the improved theory of parametric processes that takes into account both cubic and uniaxial anisotropy of the film.

Amplification of spin waves by the spin Seebeck effect

We observe amplification of spin-wave packets propagating along a film of single-crystal yttrium iron garnet (YIG) subject to a transverse temperature gradient. The spin waves are excited and detected with standard techniques used to study volume or surface magnetostatic waves in the 1–2 GHz frequency range. Amplification gains larger than 20 are observed in a YIG film heated by a current of 20 mA in a Pt layer in a simple YIG/Pt bilayer. The amplification is attributed to the action of a spin-transfer thermal torque acting on the magnetization that opposes the relaxation and which is created by spin currents generated through the spin Seebeck effect. The experimental data are interpreted with a spin-wave model.

Simultaneous observation of magnetostatic backward volume waves and surface waves in single crystal barium ferrite platelets with in-plane easy axis

Resonances corresponding to backward volume magnetostatic waves as well as magnetostatic surface waves have been observed in single crystal barium hexaferrite rectangular platelets with in-plane easy axis. Samples placed directly on waveguide wall or on a quartz substrate show a surface mode. A series of backward volume wave modes in the U-band are observed, with the sample placed on quartz showing a relatively few modes. Data on H-dependence of the mode frequency have been obtained for both kinds of magnetostatic waves and theoretical estimates of the mode frequencies are in reasonable agreement with the data. Quality-factor for the modes is in the range 400-750. The results are of interest for non-reciprocal ferrite devices in the U-band.

Propagation Characteristics of Magnetostatic Volume Waves in One-Dimensional Magnonic Crystals with Oblique Incidence

The propagation characteristics of magnetostatic volume waves (MSVWs), namely, magnetostatic forward volume waves (MSFVWs) and magnetostatic backward volume waves (MSBVWs), in one-dimensional (1-D) magnonic crystals (MCs) with oblique incidence are reported. The theoretical approach based on Walker's equation was used to analyze the bandgaps associated with the MSVWs. Experiments were conducted on a 1-D MC with periodic structure in YIG layer thickness to measure the bandgaps in the MSFVWs and the MSBVWs with the incident angles at 0, 14, and 25 degrees, and at 1650 and 1385 Oe bias magnetic fields, respectively. An excellent agreement between the measured and the calculated results was achieved.

Magnetostatic correlator of microwave signals with the internal wave front reversal

A new technique of the correlation processing of data based on the nonlinear interaction of signals of backward volume magnetostatic waves in yttrium-iron garnet thin films and a corresponding laboratory mock-up of the correlation receiver operating in the 6 cm wavelength range have been presented in this paper. It was proposed to use additional pumping pulse for obtaining a time-reversed signal pulse. The resultant correlation signal occurred during the nonlinear interaction of the delayed signal wave and the pumping-reversed wave. The specificity of the passage of broadband signals through the resonance system of waveguide of spin waves was taken into account. It has been found out that the resonance properties of the correlator affect the efficiency of the desired signal separation from the noise level. The resultant signal-to-noise ratio for the output signal was enhanced by more than 20 dB.

Micro-structured ferromagnetic tubes for spin wave excitation

Micron scale ferromagnetic tubes placed on the ends of ferromagnetic CoTaZr spin waveguides are explored in order to enhance the excitation of backward volume magnetostatic spin waves. The tubes produce a closed magnetic circuit about the signal line of the coplanar waveguide and are, at the same time, magnetically contiguous with the spin waveguide. This results in a ten-fold increase in spin wave amplitude. However, the tube geometry distorts the magnetic field near the spin waveguide, and relatively high biasing magnetic fields are required to establish well-defined spin waves. Only the lowest (uniform) spin wave mode is excited.

An approach for analysis of magnetostatic volume waves in magnonic crystals

A theoretical approach, based on Walker’s equation, to analyze the propagation characteristics of magnetostatic volume waves in magnonic crystals with periodic variation in magnetic layer thickness is presented. The properties of bandgaps versus the thickness parameters of the magnetic layer and the magnetically tuned bandgaps are verified experimentally.

Features of surface and volume magnetostatic waves in a tangentially magnetized slab

A special direction of the wave vector was found for volume magnetostatic waves (MSWs) that coincides with the cutoff angle for surface MSWs; when crossing this direction, the field configuration for MSWs with small wavenumbers changes sharply. It is shown that this direction corresponds to the maximum asymmetry of magnetostatic potential distribution over the film depth and the largest wave penetration depth into the film bulk from the surface. This effect occurs also for volume MSWs propagating in a wave channel.

Scattering of surface and volume spin waves in a magnonic crystal

The operational characteristics of a magnonic crystal, which was fabricated as an array of shallow grooves on a surface of a magnetic film, were compared for magnetostatic surface spin waves and backward volume magnetostatic spin waves. The rejection frequency bands formation was studied as a function of the grooves depth. It has been found that the rejection of the volume wave is considerably larger than of the surface one. The influences of the nonreciprocity of the surface spin waves, as well as of the scattering of the lowest volume spin-wave mode into higher ones on the rejection efficiency are discussed.

Design and optimization of one-dimensional ferrite-film based magnonic crystals

One-dimensional magnonic crystals have been implemented as gratings of shallow grooves chemically etched into the surface of yttrium-iron-garnet films. Scattering of backward volume magnetostatic spin waves from such structures is investigated experimentally and theoretically. Well-defined rejection frequency bands are observed in transmission characteristics of the magnonic crystals. The loss inserted by the gratings and the rejection band bandwidths are studied as a function of the film thickness, the groove depth, the number of grooves, and the groove width. The experimental data are well described by a theoretical model based on the analogy of a spin-wave film waveguide with a microwave transmission line. Our study shows that magnonic crystals with required operational characteristics can be engineered by adjusting these geometrical parameters.

Brillouin light scattering observation of the transition from the superparamagnetic to the superferromagnetic state in nanogranular (SiO2)Co films

Evolution of magnetic excitations from purely magnetostatic modes to dipole-exchange spin waves in the Damon–Eshbach geometry in nanocomposite (SiO2)100−xCox (50 at. %<x<80 at. %) films during a transition from superparamagnetic to superferromagnetic state has been studied by Brillouin light scattering. It has been shown that removal of the degeneracy of backward volume magnetostatic waves due to nonzero exchange constant manifests itself in more pronounced Stokes/anti-Stokes asymmetry. Accompanying static characterization by means of magnetic force microscopy imaging and grazing incidence small angle neutron scattering has demonstrated the presence of weak stripe domains in the superferromagnetic phase.