arXiv subjects

A. A. Serga

Publications and source records attributed to A. A. Serga.

At least 37 records · Page 2Linked to original sources

arXiv2011

Storage-recovery phenomenon in magnonic crystal

The phenomenon of wave trapping in an artificial crystal with limited number of periods is demonstrated experimentally using spin waves in a magnonic crystal. The information stored in the crystal is recovered afterwards by parametric amplification of the trapped wave. The storage process is based on the excitation of standing internal crystal modes and differs principally from the well-known phenomenon of deceleration of light in photonic crystals.

physics.optics↗

arXiv2011

Optical detection of spin transport in non-magnetic metals

We determine the dynamic magnetization induced in non-magnetic metal wedges composed of silver, copper and platinum by means of Brillouin light scattering (BLS) microscopy. The magnetization is transferred from a ferromagnetic Ni80Fe20 layer to the metal wedge via the spin pumping effect. The spin pumping efficiency can be controlled by adding an insulating but transparent interlayer between the magnetic and non-magnetic layer. By comparing the experimental results to a dynamical macroscopic spin-transport model we determine the transverse relaxation time of the pumped spin current which is much smaller than the longitudinal relaxation time.

cond-mat.other↗

arXiv2011

Temporal behavior of the inverse spin Hall voltage in a magnetic insulator-nonmagnetic metal structure

It is demonstrated that upon pulsed microwave excitation, the temporal behavior of a spin-wave induced inverse spin Hall voltage in a magnetic insulator-nonmagnetic metal structure is distinctly different from the temporal evolution of the directly excited spin-wave mode from which it originates. The difference in temporal behavior is attributed to the excitation of long-lived secondary spin-wave modes localized at the insulator-metal interface.

cond-mat.mes-hall↗

arXiv2011

Variable damping and coherence in a high-density magnon gas

We report on the fast relaxation behavior of a high-density magnon gas created by a parametric amplification process. The magnon gas is probed using the technique of spin-wave packet recovery by parallel parametric pumping. Experimental results show a damping behavior which is in disagreement with both the standard model of exponential decay and with earlier observations of non-linear damping. In particular, the inherent magnon damping is found to depend upon the presence of the parametric pumping field. A phenomenological model which accounts for the dephasing of the earlier injected magnons is in good agreement with the experimental data.

cond-mat.mtrl-sci↗

arXiv2011

Radiation of caustic beams from a collapsing bullet

Collapse of an intense (2+1)-dimensional wave packet in a medium with cubic nonlinearity and a two-dimensional dispersion of an order higher than parabolic is studied both theoretically and experimentally. The carrier waves are microwave backward volume spin waves which propagate in a stripe made from a thin ferrimagnetic film and the packet is a spin-wave bullet. We show that before being self-destroyed the bullet irradiates untrapped dispersive waves, which is in agreement with a previous theoretical prediction. Since, in addition, the ferromagnetic medium is characterized by an induced uniaxial anisotropy, this radiation takes the form of narrow beams of continuous waves at very specific angles to its propagation direction. Based on our theoretical calculations we find that these beams are caustic beams and the angles are the characteristic spin-wave caustic angles modified by the motion of the source.

nlin.PS↗

arXiv2010

Wide-range wavevector selectivity of magnon gases in Brillouin light scattering spectroscopy

Brillouin light scattering spectroscopy is a powerful technique for the study of fast magnetization dynamics with both frequency- and wavevector resolution. Here, we report on a distinct improvement of this spectroscopic technique towards two-dimensional wide-range wavevector selectivity in a backward scattering geometry. Spin-wave wavevectors oriented perpendicular to the bias magnetic field are investigated by tilting the sample within the magnet gap. Wavevectors which are oriented parallel to the applied magnetic field are analyzed by turning the entire setup, including the magnet system. The setup features a wide selectivity of wavevectors up to 2.04\cdot 10E5 rad/cm for both orientations, and allows selecting and measuring wavevectors of dipole- and exchange-dominated spin waves of any orientation to the magnetization simultaneously.

physics.ins-det↗

arXiv2010

Magnonic crystal based forced dominant wavenumber selection in a spin-wave active ring

Spontaneous excitation of the dominant mode in a spin-wave active ring -- a self-exciting positive-feedback system incorporating a spin-wave transmission structure -- occurs at a certain threshold value of external gain. In general, the wavenumber of the dominant mode is extremely sensitive to the properties and environment of the spin-wave transmission medium, and is almost impossible to predict. In this letter, we report on a backward volume magnetostatic spin-wave active ring system incorporating a magnonic crystal. When mode enhancement conditions -- readily predicted by a theoretical model -- are satisfied, the ring geometry permits highly robust and consistent forced dominant wavenumber selection.

cond-mat.other↗

arXiv2009

Spin-wave propagation in a microstructured magnonic crystal

Transmission of microwave spin waves through a microstructured magnonic crystal in the form of a permalloy waveguide of a periodically varying width was studied experimentally and theoretically. The spin wave characteristics were measured by spatially-resolved Brillouin light scattering microscopy. A rejection frequency band was clearly observed. The band gap frequency was controlled by the applied magnetic field. The measured spin-wave intensity as a function of frequency and propagation distance is in good agreement with a model calculation.

cond-mat.mes-hall↗

arXiv2009

Reverse Doppler effect in backward spin waves scattered on acoustic waves

We report on the observation of reverse Doppler effect in backward spin waves reflected off of surface acoustic waves. The spin waves are excited in a yttrium iron garnet (YIG) film. Simultaneously, acoustic waves are also generated. The strain induced by the acoustic waves in the magnetostrictive YIG film results in the periodic modulation of the magnetic anisotropy in the film. Thus, in effect, a travelling Bragg grating for the spin waves is produced. The backward spin waves reflecting off of this grating exhibit a reverse Doppler shift: shifting down rather than up in frequency when reflecting off of an approaching acoustic wave. Similarly, the spin waves are shifted up in frequency when reflecting from receding acoustic waves.

cond-mat.other↗

arXiv2009

Direct current control of three magnon scattering processes in spin-valve nanocontacts

We have investigated the generation of spin waves in the free layer of an extended spin-valve structure with a nano-scaled point contact driven by both microwave and direct electric current using Brillouin light scattering microscopy. Simultaneously with the directly excited spin waves, strong nonlinear effects are observed, namely the generation of eigenmodes with integer multiple frequencies (2 \emph{f}, 3 \emph{f}, 4 \emph{f}) and modes with non-integer factors (0.5 \emph{f}, 1.5 \emph{f}) with respect to the excitation frequency \emph{f}. The origin of these nonlinear modes is traced back to three magnon scattering processes. The direct current influence on the generation of the fundamental mode at frequency \emph{f} can be related to the spin-transfer torque, while the efficiency of three-magnon-scattering processes is controlled by the Oersted field as an additional effect of the direct current.

cond-mat.mes-hall↗

arXiv2009

Current-controlled dynamic magnonic crystal

We demonstrate a current-controlled, dynamic magnonic crystal. It consists of a ferrite film whose internal magnetic field exhibits a periodic, cosine-like variation. The field modulation is created by a direct current flowing through an array of parallel wires placed on top of a spin-wave waveguide. A single, pronounced rejection band in the spin-wave transmission characteristics is formed due to spin-wave scattering from the inhomogeneous magnetic field. With increasing current the rejection band depth and its width increase strongly. The magnonic crystal allows a fast control of its operational characteristics via the applied direct current. Simulations confirm the experimental results.

cond-mat.other↗

arXiv2009

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 etched on a surface of a magnetic film, were compared for magnetostatic surface spin waves and backward volume magnetostatic spin waves. In both cases the formation of rejection frequency bands 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 thickness volume modes on the rejection efficiency are discussed.

cond-mat.other↗

arXiv2009

An EOM-assisted wave-vector-resolving Brillouin light scattering setup

Brillouin light scattering spectroscopy is a powerful technique which incorporates several extensions such as space-, time-, phase- and wave-vector resolution. Here, we report on the improvement of the wave-vector resolution by including an electro-optical modulator. This provides a reference to calibrate the position of the diaphragm hole which is used for wave-vector selection. The accuracy of this calibration is only limited by the accuracy of the wave-vector measurement itself. To demonstrate the validity of the approach the wave vectors of dipole-dominated spin waves excited by a microstrip antenna were measured.

cond-mat.other↗

arXiv2009

Field-induced transition from parallel to perpendicular parametric pumping for a microstrip transducer

Microstrip transducers used for the excitation of spin waves in magnetic films possess two characteristic properties: high spatial localization of the microwave magnetic field and the presence of field components parallel and perpendicular to the bias field. Here, the effects of these features on the process of parametric pumping are presented. By microwave measurements of the spin-wave instability threshold a transition from parallel pumping to perpendicular pumping at the critical field $H_{\rm c}$ with the minimal threshold is observed. This transition is accompanied by a sharp threshold increase above the critical field due to the spatial confinement of the pump region.

cond-mat.other↗

arXiv2009

Phase sensitive Brillouin scattering measurements with a novel magneto-optic modulator

A recently reported phase sensitive Brillouin light scattering technique is improved by use of a magnetic modulator. This modulator is based on Brillouin light scattering in a thin ferrite film. Using this magnetic modulator in time- and space Brillouin light scattering measurements we have increased phase contrast and excluded influence of optical inhomogeneities in the sample. We also demonstrate that the quality of the resulting interference patterns can be improved by data postprocessing using the simultaneously recorded information about the reference light.

cond-mat.other↗

arXiv2009

Generation of pulse trains by current-controlled magnetic mirrors

The evolution of a spin-wave packet trapped between two direct current-carrying wires placed on the surface of a ferrite film is observed by Brillouin light scattering. The wires act as semi-transparent mirrors confining the packet. Because the spin-wave energy partially passes through these mirrors, trains of spin-wave packets are generated outside the trap. A numerical model of this process is presented and applied to the case when the current in the wires is dynamically controlled. This dynamical control of the mirror reflectivity provides new functionalities interesting for the field of spin-wave logic like that of a spin-wave memory cell.

cond-mat.other↗

arXiv2008

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 rejections bands 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.

cond-mat.other↗

arXiv2008

Frequency-dependent reflection of spin waves from a magnetic inhomogeneity induced by a surface DC-current

The reflectivity of a highly localized magnetic inhomogeneity is experimentally studied. The inhomogeneity is created by a dc-current carrying wire placed on the surface of a ferrite film. The reflection of propagating dipole-dominated spin-wave pulses is found to be strongly dependent on the spin-wave frequency if the current locally increases the magnetic field. In the opposite case the frequency dependence is negligible.

cond-mat.other↗