Magnetostatic waves in the gap of ferromagnetic crystals with relative longitudinal displacement

The propagation of magnetostatic gap waves in the gap between two oppositely magnetized ferromagnets with a relative longitudinal displacement is considered. It is shown that the relative motion of the crystals has the form of the spectrum of magnetostatic waves. In particular, it is found that for certain values of the gap width, the velocity of relative motion of the crystals, and the magnetostatic wavelength, normal (anomalous) dispersion of the symmetric (antisymmetric) mode of the gap structure is transformed into the anomalous (normal) type of dispersion.     

Hysteresis of the characteristics of magnetostatic waves in ferrite films with stripe domains whose magnetization vectors are oriented close to the plane of the film

The propagation of zero-exchange spin waves (magnetostatic waves) is investigated in yttrium iron garnet films having a regular stripe domain structure with almost in-plane orientation of the domain magnetization vectors. The characteristics of the waves are studied for magnetizations of the film parallel and perpendicular to projections of the [111] crystallographic axes onto the plane of the film. It is established, in contrast with films having the domain magnetization vectors oriented close to the normal to the plane of the film, that both the propagation of magnetostatic waves and the variation of the parameters of the domain structure exhibit a distinctly pronounced hysteretic character as the magnetizing field is varied. The hysteresis of the amplitude-frequency response, equiphase, and dispersion curves of the magnetostatic waves is investigated. The authors examine how the hysteresis of these parameters is related to the hysteresis of the domain structure. The spectrum of magnetostatic waves is found to have an interval of wavelengths (wave numbers) that are not excited in the unsaturated film when the applied field is close to the saturation value, and this phenomenon as well exhibits hysteresis. Zh. éksp. Teor. Fiz. 114, 1430–1450 (October 1998)     

Effect of magnetostatic pressure on the stabilization of a two-phase domain structure in thin garnet ferrite films

The coexistence of two domain phases, namely, a spiral domain and a bubble-domain lattice, is investigated experimentally in thin garnet ferrite films with uniaxial anisotropy. The condition for this coexistence is shown to be the equality of the magnetostatic pressures of the two phases. It is also shown that the possible formation of a spiral domain structure is determined by the magnetostatic pressure.     

Magnetostatic modes of a lateral ferromagnetic/ferromagnetic superlattice

In this Letter, we calculate the magnetostatic modes of a semi-infinite lateral ferromagnetic/ferromagnetic superlattice with the effective-medium theory and present the general features of the modes. The numerical calculations for Co/Ni superlattice show some interesting properties which different from the lateral ferromagnetic/nonmagnetic superlattice. Two branches of the surface modes appear for the superlattice. Comparing with the surface magnetostatic modes of bulk Ni, one branch of the mode is of high frequency; the other branch of mode is of low frequency.     

Static and dynamic properties of a ferrite-garnet film in the neighborhood of orientational phase transitions

The static susceptibility and the spectrum of a magnetic-resonance mode of a single-crystal garnet-ferrite film with a domain structure are experimentally investigated. It is found that, in a magnetic field perpendicular to the film plane, these characteristics have features associated with the reorientation of the domain structure. The spin-wave spectrum of the film is calculated on the basis of the domain structure model proposed. It is shown that the experimentally observed features of the spectrum can be accounted for by the reorientation of magnetizations in the domains. A good agreement is obtained between experimental and theoretical values of the gap in the spin-wave spectrum at the “starting and end points of reorientation.”     

Shear Surface Wave on a Moving Bloch Wall

Using Galileo's transformation for moving to the rest frame of the Bloch wall in the exchange-free magnetostatic approximation, we obtain the dispersion relation for a shear surface wave guided by a moving 180-degree domain boundary of a ferromagnetic crystal. It is found that the motion of the domain boundary has the orienting action on the wave normal of the shear surface wave and significantly changes the spectrum of forward-propagating waves in the frequency band below the scattered-field ferromagnetic resonance.     

Features of a Domain Structure with Asymmetric Magnetic Heterogeneity in Film Materials with High Anisotropy

The theory of magnetic domain ordering in magnetic film materials with asymmetric magnetic heterogeneity is considered, with allowance for changes in the magnetostatic energy and that of the anisotropy of a curved domain boundary. The effect the parameters that determine changes in the energy of the magnetostatic interaction of the domain structure and the energy of the anisotropy of the curved domain boundary have on the shape and value of domain boundary bending is analyzed.     

Ferromagnetic resonance in interacting magnetic microstrips

The results of the micromagnetic simulation of forced oscillations of the magnetization in a system of two interacting microstrips located at an angle to each other have been presented. The ferromagnetic resonance spectra and the mode composition of resonant oscillations of the system have been investigated under the conditions of magnetostatic and exchange interactions between the microstrips. It has been shown that the magnetostatic interaction leads to the possibility of the excitation of in-phase and out-of-phase coupled oscillations of the magnetization of the microstrips. In the systems of exchange-coupled microstrips, there are intense resonances due to oscillations of the domain walls. The transformation of the ferromagnetic resonance spectrum and the change in the mode composition of resonant oscillations in different equilibrium configurations of the magnetization of the system have been discussed, as well as the conditions for the excitation of oscillations of different types depending on the direction of the microwave magnetic field.     

Domain formation in films of magnetic nanoparticles with a random distribution of anisotropy axes

A theoretical model describing the magnetization distribution in a system of closely packed ferromagnetic grains with a random distribution of easy magnetization axes is constructed. It is demonstrated that, in this system, the domain structure with domains characterized by a random distribution of magnetization axes is formed even if the magnetostatic energy is negligible and can be ignored. The domain size increases linearly with an increase in the ratio of the exchange energy of the interaction between grains to the anisotropy energy of a single grain. The inclusion of the magnetostatic energy only insignificantly changes the domain size but leads to the formation of a vortex magnetization distribution inside the domains. The behavior of the system is numerically simulated by the Monte Carlo method. The results of the simulation confirm the conclusions drawn from the theoretical model.     

Shear magnetoelastic modes in a ferromagnetic cylinder

Features of the mode spectrum of shear magnetoelastic waves circulating along the boundary of a ferromagnetic cylinder are discussed in the nonexchange magnetostatic approximation. Depending on the level of the spin-phonon coupling in the crystal and on the frequency, the lowest order normal mode may be either fast or slow relative to the bulk shear wave in an infinite crystal. It is shown that, unlike the lowest order mode, the higher order modes, which primarily depend on the curvature of the boundary, demonstrate a weak nonreciprocity of propagation in directions with opposite azimuths. Conditions for the slow propagation of the lowest order mode, when it is identified with a surface magnetoelastic wave, are only possible sufficiently far away from the cutoff frequency of the mode spectrum in ferromagnetic cylinders with a strong spin-phonon coupling and a small curvature of the boundary.     

Disordered domain structures and domain boundaries in thin magnetic films

The behavior of a disordered domain structure and domain boundaries with a change in temperature and magnetic field has been studied. The concept of magnetostatic pressure is used to explain the experimental results. It is shown that “the memory effect” and stability interval of a domain structure with a change in temperature or magnetic field depends on the degree of domain structure disorder and the domain boundary energy.     

Theory of magnetostatic waves in a ferrite film with transition layers

A dispersion relation is derived for magnetostatic waves in a ferrite film with inhomogeneous layers near the interfaces. It is shown that the transition layers can be taken into account using a single integrated parameter, namely, the effective film thickness. It is established that the layered structure of the film causes an extra wave damping. The relations obtained can be used to analyze the dispersion and damping of the main modes of magnetostatic waves.     

Effect of magnetization of the rare earth sublattice on the domain structure of a two-layer ferrite-garnet film

The temperature behavior of the domain structure in a two-layer ferrite-garnet film with one of the layers having a compensation point T _c , as well as in single-layer witness films, has been experimentally investigated. It is shown that the rare earth sublattice affects phase transitions in the domain structure of a two-layer film. The phase transitions observed were explained in terms of the concept of magnetostatic pressure in the domain structure.     

Micromagnetic simulation on the dynamic susceptibility spectra of cobalt nanowires arrays: the effect of magnetostatic interaction

<正>Micromagnetic simulations have been performed to obtain the dynamic susceptibility spectra of 4×4 cobalt nanowire arrays with different spatial configurations and geometries.The susceptibility spectra of isolated wires have also been simulated for comparison purposes.It is found that the susceptibility spectrum of nanowire array bears a lot of similarities to that of an isolated wire,such as the occurrences of the edge mode and the bulk resonance mode. The simulation results also reveal that the susceptibility spectrum of nanowire array behaves like that of single isolated wire as the interwire distance grows to an extent,which is believed due to the decrease of magnetostatic interaction among nanowires,and can be further confirmed by the static magnetic hysteresis simulations.In comparison with single nanowire,magnetostatic interaction may increase or decrease the resonance frequencies of nanowire arrays assuming a certain interwire distance when the length of array increases.Our simulation results are also analysed by employing the Kittel equation and recent theoretical studies.     

Magnetostatic interaction effects in an ordering hexagonal array of ferromagnetic nanoparticles

The results from investigating magnetostatic interaction effects in ordered hexagonal arrays of anisotropic single-domain ferromagnetic nanoparticles are presented. It is demonstrated theoretically and experimentally that two stable states (with quasi-uniform configurations of magnetic moments and with zero averaged magnetic moment configurations) can be easily attained in such arrays. It is shown that the structure of an ferromagnetic resonance spectrum depends strongly on the extent of magnetostatic interaction and the spatial configuration of the magnetic moments in the array.     

Behavior of domain structure in a Co/Ag superlattice with dispersion of magnetic anisotropy

It is found that the magnetization reversal of an array of superthin Co films coupled by the ferromagnetic exchange interaction through the Ag layers may result in a domain structure of an unexpected new type. Due to the incoherent different-sense spin rotation upon lowering the field perpendicular to the easy axis, the specific macrodomains first form in a sample. They are separated not by the Neél domain wall but by a wide transition region containing high-density microdomains of sizes correlating with the grain sizes in the films. Further magnetization reversal proceeds through the formation of standard domain walls in the macrodomain in a magnetostatic field at the plate edge and through their shifting toward the transition region. These processes are explained with taking into account the character of the revealed magnetic anisotropy dispersion.     

Wideband chaotic oscillation in a self-oscillatory system with a nonlinear transmission line on magnetostatic waves

Wideband chaotic microwave oscillation in a ring self-oscillatory system is studied. The system includes a solid-state power amplifier and a wideband nonlinear transmission line with a ferromagnetic film in which magnetostatic waves of different types are excited. It is found that the eigenmodes of the self-oscillatory system excited in the passband of the transmission line on magnetostatic waves become noisy because of spin wave parametric excitation due to the magnetostatic wave and nonlinearity of the power amplifier. A continuous spectrum of modes observed in the wideband chaotic signal is associated with the presence of a descending portion in the dynamic characteristic of the nonlinear transmission line, which arises when a magnetostatic surface wave is excited.     

Nonlinearity of magnetoacoustic excitations in planar structures

This paper reports on the results of experimental investigations into the threshold power of the onset of nonlinearity of magnetoacoustic vibrations in planar structures (such as a ferrite film-dielectric substrate structure) in the range of phase matching of the higher bulk magnetostatic and acoustic modes. Under the experimental conditions, the wavelength of the higher bulk magnetostatic modes is of the order of 1 μm and shorter. On this basis, the energy of these vibrations with respect to the origin of the magnetostatic wave spectrum is determined by the energy of the inhomogeneous exchange interaction. The standing magnetoacoustic waves are examined in conventional yttrium iron garnet films with free surface spins in which, under standard conditions, only dipole magnetostatic vibrations are excited in planar resonators. Consideration is given to the threshold power of the onset of precession instability of the dipole exchange acoustic modes which, as was shown earlier by the authors, are excited in the range of the phase matching of the exchange and acoustic modes. A comparative analysis is performed for the threshold powers of dipole magnetostatic, exchange acoustic, and dipole exchange acoustic modes. It is demonstrated that the threshold power of the instability of magnetostatic modes decreases significantly when the natural frequencies of the dipole modes coincide with those of the exchange acoustic modes. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 7, 2002, pp. 1285–1289. Original Russian Text Copyright ? 2002 by Bugaev, Gorsky.     

Modulation instability of magnetostatic waves in a magnetically coupled two-layer structure

Modulation instability of direct bulk magnetostatic waves in structures consisting of two magnetically coupled planar films separated by a nonmagnetic layer is studied. It is found that, depending on the type of excitation of the waveguide modes, mode coupling can either change the characteristics of the modulation wave instability or ensure their stability with respect to the corresponding perturbations by affecting the dispersion properties of the structure.     

Propagation of surface magnetostatic waves in a one-dimensional magnon crystal of a variable thickness

The propagation of surface magnetostatic waves in a ferromagnetic film of variable thickness having a planar periodic structure in the form of a grating of etched parallel strips (one-dimensional magnon crystal) has been investigated. The dispersion characteristics of surface magnetostatic waves have been calculated using the Wentzel-Kramers-Brillouin method. The intrinsic error of the method has been estimated, and the magnon spectrum of the surface magnetostatic wave has been studied. An analysis of the dispersion characteristics and the transmission capacity of these structures has demonstrated that they can be used for designing narrow-band and comb filters.