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We have studied the effect of adiabatic spin-transfer torque on mode interference of spin waves. The mode interference generates amplitude-localized spots at special positions which do not move with time. When applying current, th...
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We have studied the effect of adiabatic spin-transfer torque on mode interference of spin waves. The mode interference generates amplitude-localized spots at special positions which do not move with time. When applying current, the wavevector of spin wave is modified, resulting in current-dependent displacement of amplitude-localized spots. This current-dependent change in the mode interference may allow to probe current-induced spin wave Doppler shift in space-domain. In favorable situations, it can be used to estimate the intrinsic properties of magnetic materials such as spin polarization.
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We show that magnetostatic modes with amplitude localized in different regions of the sample along the direction of the magnetic field occur in ferromagnetic stripes: bulk-dead modes, with amplitude localized in two regions and co...
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We show that magnetostatic modes with amplitude localized in different regions of the sample along the direction of the magnetic field occur in ferromagnetic stripes: bulk-dead modes, with amplitude localized in two regions and comb modes localized in its central part. We also demonstrate these localization properties can be studied by Brillouin light scattering techniques and applied in practice. Having established that the localization of these modes varies with their frequency, we use this finding as the basis of a trial reinterpretation of experimental results obtained by Demidov et al. [Appl. Phys. Lett. 92 (2008) 232503].
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Interest in spin waves has recently been revived in light of the potential of spin waves for novel spintronic applications. This review focuses on the fundamental characteristics of spin waves and introduces recent developments in...
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Interest in spin waves has recently been revived in light of the potential of spin waves for novel spintronic applications. This review focuses on the fundamental characteristics of spin waves and introduces recent developments in the magnonics field. We begin with a basic description of magnetostatic modes and experimental methods and then report the propagation characteristics of spin waves in permalloy films, including the damping properties, nonreciprocity, and tangentially angle dependence of the spin wave propagation. We close with a brief review of recent topics in spin wave applications, including a spin wave logic gate and magnonic crystals.
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It is of current interest to understand the electromagnetic response of different nanostructures. In this study, we focus on the role of geometry, in the so-called static limit. In this limit, the incoming wavelength is much great...
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It is of current interest to understand the electromagnetic response of different nanostructures. In this study, we focus on the role of geometry, in the so-called static limit. In this limit, the incoming wavelength is much greater than the relevant scales of the object, retardation can be neglected, there are no inductive effects, and the electric and magnetic problems decouple, thus one studies plasmonic and magnonic responses separately. In particular, it is of interest to study enhancements of the fields associated with geometric features of the samples as well as the development of artificial structures that may show desired behaviors. With this in mind, in this work, we study a structure with a periodic geometric perturbation that shows a behavior of interest: plasmons and magnons propagate in it with band gaps associated with the geometry, i.e., they may be controlled by design. The structures in question are dielectric or ferromagnetic thin films whose surfaces are modulated periodically in one direction: we study modes of infinite wavelength along the nonmodulated direction. The results are analogous to those found for electronic wave functions in periodic potentials, i.e., one can introduce a reduced Brillouin zone scheme to describe the modes (its width is 2π/A, with A the period of the geometric perturbations), which are of the Bloch type. Different bands are identified, and they are calculated numerically. For small geometric perturbations, we develop a perturbation theory that agrees well with our numerical results, and we do obtain analytic expressions for the band gaps at the edges of the Brillouin zone (proportional to the amplitudes of the geometric perturbation of the surfaces and very simple in the case of plasmons). The underlying theory used to calculate the modes was previously developed and relies on solving integral equations along the edges of the sample for the electrostatic and magnetostatic potentials, respectively. Interesting features of this method are that it is practical and computationally nonintensive, film perturbations of arbitrary shapes and amplitudes can be addressed, and it merges in one framework the study of magnons and plasmons.
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In systems combining type-Ⅱ superconductivity and magnetism the nonstationary magnetic field of moving Abrikosov vortices may excite spin waves, or magnons. This effect leads to the appearance of an additional damping force actin...
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In systems combining type-Ⅱ superconductivity and magnetism the nonstationary magnetic field of moving Abrikosov vortices may excite spin waves, or magnons. This effect leads to the appearance of an additional damping force acting on the vortices. By solving the London and Landau-Lifshitz-Gilbert equations we calculate the magnetic-moment-induced force acting on vortices in ferromagnetic superconductors and superconductor-ferromagnet superlattices. If the vortices are driven by a dc force, magnon generation due to the Cherenkov resonance starts as the vortex velocity exceeds some threshold value. For an ideal vortex lattice this leads to an anisotropic contribution to the resistivity and to the appearance of resonance peaks on the current-voltage characteristics. For a disordered vortex array the current will exhibit a steplike increase at some critical voltage. If the vortices are driven by an ac force with a frequency ω, the interaction with magnetic moments will lead to a frequency-dependent magnetic contribution η_M to the vortex viscosity. If ω is below the ferromagnetic resonance frequency ω_F, vortices acquire additional inertia. For ω ＞ ω_F dissipation is enhanced due to magnon generation. The viscosity η_M can be extracted from the surface impedance of the ferromagnetic superconductor. Estimates of the magnetic force acting on vortices for the U-based ferromagnetic superconductors and cuprate-manganite superlattices are given.
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We analyze the dynamics of a domain wall in an easy-axis antiferromagnet driven by circularly polarized magnons. Magnons pass through a stationary domain wall without reflection and thus exert no force on it. However, they reverse...
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We analyze the dynamics of a domain wall in an easy-axis antiferromagnet driven by circularly polarized magnons. Magnons pass through a stationary domain wall without reflection and thus exert no force on it. However, they reverse their spin upon transmission, thereby transferring two quanta of angular momentum to the domain wall and causing it to precess. A precessing domain wall partially reflects magnons back to the source. The reflection of spin waves creates a previously identified reactive force. We point out a second mechanism of propulsion, which we term redshift: magnons passing through a precessing domain wall lower their frequency by twice the angular velocity of the domain wall; the concomitant reduction of the magnons' linear momentum indicates momentum transfer to the domain wall. We solve the equations of motion for spin waves in the background of a uniformly precessing domain wall with the aid of supersymmetric quantum mechanics and compute the net force and torque applied by magnons to the domain wall. Redshift is the dominant mechanism of propulsion at low spin-wave intensities; reflection dominates at higher intensities. We derive a set of coupled algebraic equations to determine the linear velocity and angular frequency of the domain wall in a steady state. The theory agrees well with numerical micromagnetic simulations.
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A general theory of collective spin-wave excitations in a two-dimensional array of magnetic nanodots coupled by magnetodipolar interaction is developed. The theory allows one to analytically calculate spectra, damping rates, excit...
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A general theory of collective spin-wave excitations in a two-dimensional array of magnetic nanodots coupled by magnetodipolar interaction is developed. The theory allows one to analytically calculate spectra, damping rates, excitation efficiencies, and other characteristics of spin waves in both periodic and aperiodic ground states of an array. It is demonstrated that all the properties of collective spin waves in an array existing in any spatially periodic ground state (e.g., ferromagnetic or chessboard antiferromagnetic) are determined by the same state-independent array's demagnetization tensor F_k, which is determined by the spin-wave wave vector k, the size and shape of the array's elements (nanodots), and the geometry of the array's lattice. The applications of the developed general theory are illustrated on particular examples: (Ⅰ) spin waves in ferromagnetic and chessboard antiferromagnetic states of a square array, and (Ⅱ) localized spin-wave excitations associated with an isolated "defect" in a uniform ferromagnetic ground state of a square array.
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Spin wave spectra of ultrathin epitaxial cobalt films deposited on W(110), Cu(111), and Au(111) surfaces are studied in the wave-vector regime between 0.1 A~(-1) and 0.7 A~(-1) using inelastic electron scattering with 6 meV energy...
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Spin wave spectra of ultrathin epitaxial cobalt films deposited on W(110), Cu(111), and Au(111) surfaces are studied in the wave-vector regime between 0.1 A~(-1) and 0.7 A~(-1) using inelastic electron scattering with 6 meV energy resolution. Up to three different spin wave modes are resolved for wave vectors q_‖ ＜ 0.35 A~(-1) . The modes are identified as the acoustic mode and standing modes with one and two nodes inside the film. The relative weight of the modes in a particular spectrum may depend critically on the electron impact energy. For larger wave vectors beyond q_‖ ＞ 0.35 A~(-1) and layers thicker than five atom layers the separate modes merge into a single, broad loss feature. Since the shape and position of the loss feature depend on the electron impact energy, a separation into different modes is nevertheless possible for not too large wave vectors. The spin wave dispersion curves of films grown on W( 110) agree with those observed on Cu( 111) if one takes into account that on copper the cobalt grows in islands so that the mean height of the islands is higher than the nominal coverage. On films grown on Au(111) the low wave vector spin waves are buried in the high elastic diffuse scattering caused by the considerable disorder in the films. The broader appearance of the spectra at higher wave vectors compared to films grown on W(110) and Cu(111) is quantitatively accounted for by disorder-induced kinematic broadening. Because of the granular growth on copper and gold primarily the spin wave spectrum of cobalt films on W(110) is amenable to quantitative theoretical analysis. Such an analysis is not available at present. We show however, that the dispersion curves are incompatible with the Heisenberg model as long as only a single, layer-independent exchange coupling constant is invoked.
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A general theory of forward volume magnetostatic spin-wave multiple scattering by a finite two-dimensional ensemble of cylindrical magnetic inclusions in a ferromagnetic film (matrix) metallized from both sides is developed. It is...
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A general theory of forward volume magnetostatic spin-wave multiple scattering by a finite two-dimensional ensemble of cylindrical magnetic inclusions in a ferromagnetic film (matrix) metallized from both sides is developed. It is predicted that bound spin-wave modes are excited around these inclusions. The set of self-consistent equations for spin-wave multiple scattering inside the matrix with inclusions is obtained by using an invariant addition theorem for the cylindrical wave functions. This set of equations is solved by an iterative process. We derive simple expressions for eigenmodes (bound modes) in a form of Bloch-like spin waves propagating along the inclusion circular array. The theory is illustrated on practically significant examples: (ⅰ) bound-mode excitation by propagating spin waves; (ⅱ) helix components of the spin-wave-scattered field around magnetic inclusions; and (ⅲ) a high-quality spin-wave resonator based on a small number of magnetic inclusions.
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A theory of a ground-state switching in an array of axially magnetized cylindrical magnetic dots arranged in a square lattice is developed. An array can be switched into a quasiregular chessboard-antiferromagnetic state by the app...
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A theory of a ground-state switching in an array of axially magnetized cylindrical magnetic dots arranged in a square lattice is developed. An array can be switched into a quasiregular chessboard-antiferromagnetic state by the application of a short pulse of external in-plane magnetic field having a sufficiently long trailing front. The statistical properties of an array magnetization in its final (after switching) state are determined at the linear stage of growth of unstable collective spin-wave modes of the array under the action of a time-dependent magnetic field, and depend critically on the rate of the field decrease: the slower this decrease, the more regular is the final magnetization state. An analytical procedure is presented that allows one to relate the statistical properties of the final demagnetized state of the array and the linewidth of the array's microwave absorption to the parameters of the external switching pulse. The comparison of the developed analytic theory with the results of numerical simulations is presented and demonstrates good agreement between analytical and numerical results.
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