Parametric Spin Waves Research Articles

Magnonic noise in the parametric spin-wave pumping process

This study investigates magnonic noise in the context of parametric spin-wave pumping in a yttrium iron garnet waveguide. By analyzing the input power dependence of parametric spin-wave spectra, we observed spectrum broadening and the emergence of additional pumping channels. A threshold power of 99.9 mW was determined based on spin-wave voltage. To elucidate magnon dynamics beyond the threshold, magnonic noise was examined, revealing its greater sensitivity to magnon scattering compared to spin-wave voltage. The detection of four-magnon scattering and its power-dependent behavior provides further insights into magnon interactions. Our findings contribute to a deeper understanding of magnon dynamics in parametric pumping, a critical process in magnonics.

Mode-resolved micromagnetics study of parametric spin wave excitation in thin-film disks

Mode-resolved micromagnetics study of parametric spin wave excitation in thin-film disks

Unconventional parametric spin-wave pumping in single-crystal iron films

Unconventional parametric spin-wave pumping in single-crystal iron films

Influence of three-magnon decays on electromotive force generation by magnetostatic surface waves in integral YIG – Pt structures

The purpose of this work is to find out the influence of three-magnon decay processes on the electromotive force (EMF (U)) generated by propagating magnetostatic surface waves (MSSW) with the help of the inverse spin Hall effect in the “yttrium-iron garnet (YIG) – platinum (Pt)” structure. Methods. The experiments were carried out using the delay line structures based on YIG films with the thickness of 8.8 and 14.6 µm, on the surface of which antennas were formed for MSSWs excitation and reception and a Pt film between antennas. Results. It was shown that the three-magnon parametric instability can significantly change the character of EMF dependences on frequency and on power of MSSW that resulted both from the effect of power limitation and from the participation of parametric spin waves (PSW) and secondary spin waves (SSW) in the processes of electron-magnon scattering on the YIG/Pt border. Conclusion. It was demonstrated that the effect of amplification of EMF generation at the frequencies that are close to the long-wavelength border of the MSSW spectrum is related with the PSW and SSW population of the region of anisotropic dipole-exchange spin waves spectrum, which is characterized by the presence of singularities in the magnon density of states (Van Hove singularities).

Second harmonic generation as a probe of parametric spin wave instability processes in thin magnetic films

We have explored the dynamic response of in-plane magnetized thin permalloy films excited by microwave fields of high amplitudes (up to 3 Oe) at 1 GHz. The response was detected using a microstrip line by measuring the second harmonic signal generated by the dynamic components of the uniform magnetization. The data measured at ferromagnetic resonance showed the threshold effect of the Suhl parametric instability process. With the increase of the microwave power above the threshold value, the dynamic response revealed an intricate nonlinear behavior, including the emergence of an additional threshold. This second threshold can be explained in terms of the ``stage by stage'' process of parametric spin wave excitation following the $S$ theory of Zakharov, L'vov, and Starobinets.

Effect of probing signal on the output signals spectrum of nonlinear spin waves in a cross based on waveguides of iron-yttrium garnet film

Subject. A change in the spectrum of spin waves (SW) in a magnetic cross is investigated when two signals pass through it: a pump signal and a probe signal. Objective. Detection of specific features in formation of the spectra of the output signals of SW in the multiport structure based on a yttrium iron garnet (YIG) film in the case of excitation of two magnetostatic surface waves (MSSW) simultaneously by the input antenna, where the first, with power higher than the first-order parametric instability threshold is the pump, and the second one is a probe. Methods. The experiments were performed for a cross structure from YIG film in the form of two orthogonal waveguides with the SW wire antennas placed at the ends of the waveguides, where one of the antennas on the transversely magnetized waveguide was considered as the input. Result. It was found that by choosing the probing signal frequency, one can significantly (by 10 dB) change the relative signal levels for the satellite waves at the output antennas, which are secondary MSSWs with some new frequencies and appear in the output signals spectrum as a result of the thresholdless processes of merging of parametric spin waves generated by MSSW pumping. In this case the secondary MSSWs frequencies can differ at the output antennas located on orthogonal waveguides. Discussion. The discovered effect is associated with the nonreciprocal nature of propagation of both the pumping wave and the waves generated at parametric instability condition in the structure.

Characteristics of parametric spin waves in rectangular magnonic blocks

The characteristics of parametric spin-wave pumping are investigated in three rectangular permalloy blocks with in-plane aspect ratios of 12, 6, and 4. Micro-Brillouin light scattering (BLS) spectroscopy is utilized to detect the intrinsic properties of excited spin waves under various excitation conditions of an external magnetic field and microwave power. Based on the theoretical dispersion relation and BLS intensity and its spatial profile, the parametric spin wave with a frequency of is found to be excited in fundamental mode in a block of largest aspect ratio while the other block have higher-order or edge-localized modes along the width direction. The data shows that the nature of spin waves is quite sensitive on the conditions of sample geometry, applied field and microwave power. Thus, with the appropriate combination of the three parameters, it would be possible to control the nature of spin wave in each block simultaneously, which increase the blocks’ potential in magnonic applications, such as spin-logic and interferometer.

Magnons parametric pumping in bulk acoustic waves resonator

We report on the experimental observation of excitation and detection of parametric spin waves and spin currents in the bulk acoustic wave resonator. The hybrid resonator consists of a ZnO piezoelectric film, yttrium iron garnet (YIG) films on a gallium gadolinium garnet substrate, and a heavy metal Pt layer. Shear bulk acoustic waves are electrically excited in the ZnO layer due to piezoeffect at the resonant frequencies of the resonator. The magnetoelastic interaction in the YIG film emerges magnons (spin waves) excitation by acoustic waves either on resonator's eigenfrequencies or the half-value frequencies at supercritical power. We investigate the acoustic pumping of magnons at the half-value frequencies and acoustic spin pumping from parametric magnons, using the inverse spin Hall effect in the Pt layer. The constant electric voltage in the Pt layer, depending on the frequency, the magnetic field, and the pump power, was systematically studied. We explain the low threshold obtained (∼0.4 mW) by the high efficiency of electric power transmission into the acoustic wave in the resonator.

Temporal evolution of the spin-wave intensity and phase in a local parametric amplifier

We present a time-resolved study of the evolution of the spin-wave intensity and phase in a local parametric spin-wave amplifier at pumping powers close to the threshold of parametric generation. We show that the phase of the amplified spin waves is determined by the phase of the incoming signal-carrying spin waves and that it can be preserved on long time scales as long as the energy input by the input spin waves is provided. In contrast, the phase-information is lost in such a local spin-wave amplifier as soon as the input spin-wave is switched off. These findings are an important benchmark for the use of parametric amplifiers in logic circuits relying on the spin-wave phase as information carrier.

Nonlinear spin-wave excitations at low magnetic bias fields.

Nonlinear magnetization dynamics is essential for the operation of numerous spintronic devices ranging from magnetic memory to spin torque microwave generators. Examples are microwave-assisted switching of magnetic structures and the generation of spin currents at low bias fields by high-amplitude ferromagnetic resonance. Here we use X-ray magnetic circular dichroism to determine the number density of excited magnons in magnetically soft Ni80Fe20 thin films. Our data show that the common model of nonlinear ferromagnetic resonance is not adequate for the description of the nonlinear behaviour in the low magnetic field limit. Here we derive a model of parametric spin-wave excitation, which correctly predicts nonlinear threshold amplitudes and decay rates at high and at low magnetic bias fields. In fact, a series of critical spin-wave modes with fast oscillations of the amplitude and phase is found, generalizing the theory of parametric spin-wave excitation to large modulation amplitudes.

Detection of Spin Waves in Permalloy Using Planar Hall Effect

Rectification of microwave oscillations of magnetization in a permalloy film is realized using planar Hall effect. Two different rectified signals are obtained: a signal from the linearly excited uniform magnetization precession at the frequency of the external pumping and a signal from the pairs of contra-propagating short-wavelength spin waves parametrically generated at a half of the pumping frequency. The second, most unusual, rectified signal is caused by the uniform component of the dynamic magnetization created due to the interference of the phase correlated pairs of parametric spin waves.

Time- and power-dependent operation of a parametric spin-wave amplifier

We present the experimental observation of the localized amplification of externally excited, propagating spin waves in a transversely in-plane magnetized Ni81Fe19 magnonic waveguide by means of parallel pumping. By employing microfocussed Brillouin light scattering spectroscopy, we analyze the dependency of the amplification on the applied pumping power and on the delay between the input spin-wave packet and the pumping pulse. We show that there are two different operation regimes: At large pumping powers, the spin-wave packet needs to enter the amplifier before the pumping is switched on in order to be amplified while at low powers the spin-wave packet can arrive at any time during the pumping pulse.

Parametric chaos in yttrium-iron garnet films grown from weakly dissociated solution melt

We present the results of a comparative study of the chaotic generation of parametric spin waves in yttrium-iron garnet (YIG) films grown from a standard solution melt and in the films grown from a weakly dissociated solution melt containing garnet ferrite and orthoferrite clusters. It is shown that the efficiency of magnetic chaos generation is significantly higher in the latter case.

Chaotic microwave self-generation in active rings based on ferromagnetic films

The phenomenon of chaotic microwave self-generation under conditions of a four-wave parametric spin wave interaction in active resonance rings based on ferromagnetic films has been studied for the first time. It is shown that microwave signals of various types—in particular, monochromatic, stationary soliton-like pulse trains, and dynamic chaos—can be generated by controlling the gain level in the active ring. Parameters characterizing the chaotic signal generated in the ring are determined.

Parametric spin wave excitation and cascaded processes during switching in thin films

A theory for calculating the threshold precession angles required to parametrically excite spin waves during large-angle switching of in-plane magnetized films is presented. Analytic expressions for the parametric thresholds are found for finite thickness films when due to three- and four-wave decays. Precession at the threshold angle will produce appreciable spin wave amplitudes only after infinite time. We show that much larger angles are required to experimentally observe nonlinearities within a finite time. This may explain apparent discrepancies reported between ultrafast pulsed reversal and longer time scale high-power ferromagnetic resonance experiments. A comparison of our results to published experimental data for metallic Permalloy films is made. Finally, the film thickness dependence of the threshold is examined and a minimum is found corresponding to when a particular ``cascaded'' spin wave interaction is resonant.

Direct Detection of Nonlinear Ferromagnetic Resonance in Thin Films by the Magneto-Optical Kerr Effect

The longitudinal magneto-optical Kerr effect is used to obtain a calibrated measure of the dynamic magnetization response over the ferromagnetic resonance (FMR) profile for in-plane magnetized Permalloy films excited with high power in-plane transverse microwave fields at 1.25 to 3.75 GHz and in-plane precession angles up to about 20 degrees. The data provide a profound demonstration of the Suhl threshold effect for parametric spin wave generation for angles above about 14 degrees, the magnetization precession lock-up just above threshold, and the complicated response over the full FMR profile at very high powers.

Blowout bifurcations in a model for chaos in spin-wave dynamics

Blowout bifurcations are investigated numerically in a model for chaos in the coincidence regime of high-power ferromagnetic resonance, based on interactions between the uniform mode and two pairs of parametric spin waves. This model possess two orthogonal invariant manifolds corresponding to the excitation of only one spin–wave pair above the first-order Suhl instability threshold. Marginal synchronization of the amplitudes of spin–wave pairs, the exchange of stability of the invariant manifolds, as well as both supercritical and subcritical blowout bifurcations are observed as the system parameters are varied, with the accompanying on–off intermittency, attractor bubbling and intermingled basins of attraction.

Shaping of microwave pulses using phase-sensitive spin-wave amplifier

It is shown that by introducing a phase shift between the signal microwave pulse and the double-frequency pumping pulse in a parametric spin-wave amplifier it is possible to effectively control the shape of the output microwave pulse. The observed pulse shaping results from the interference of a signal pulse with copropagating “idle” pulse parametrically excited by pumping and with the parasitic standing spin waves amplified by pumping from the thermal level. This interpretation is supported by the numerical simulation and by the results of a time-resolved Brillouin light scattering experiment.

The dependence of the auto‐oscillation frequency of parametric spin waves on the pumping power and inter mode interaction strengths

AbstractComputer simulations of spin waves parametric excitations are carried out in the framework of the two modes model. The dependence of the auto‐oscillation (AO) frequency, f, on the pumping amplitude h is investigated. The results support the expression of Lvov et al. for this dependence in cases when the parametric excitation threshold, hth is very close to the auto‐oscillation threshold hosc. In cases when hosc is considerably larger than hth, a much better fit is obtained to a slightly modified expression: f = f0 + B([h/hosc]2 –1)0.5 where f0 is the onset frequency and B is a constant. Support is given to the idea of Lvov et al. that auto oscillation evolves from an oscillation that is damped below hosc and becomes self sustained at hosc. We find that τCO, the decay time of AO below hosc exhibits a critical slowing down power law: τCO ∝ (1 – h/hosc )–2.2. The dependence of f on the inter mode interaction strengths when h is constant, satisfies the expression: f = D + C/(E + 2T11 + S11 + 2T12 + S12) where D, C, and E are constants and T11, T12, S11, and S12 are the inter mode interaction strengths. This result supports the conjecture that the dependence of the auto‐oscillation frequency on the physical parameters is very similar to that of N0, the steady state value of the total number of parametric excitations.

Marginal synchronization of spin‐wave amplitudes in a model for chaos in parallel pumping

AbstractA model for chaos in high‐power parallel pumping is considered, based on nonlinear interactions of two groups of parametric spin wave pairs. If spin wave pairs within each group have identical damping, frequencies, and interaction coefficients with other pairs, all of them are excited in the chaotic regime and marginal synchronization of amplitudes of spin wave pairs belonging to the same group is observed. In the case of small differences between spin wave pairs only a low number of pairs from each group is excited. On the basis of this result, possible explanation of the origin of low dimensional chaos usually observed experimentally in parallel pumping is proposed.