D. V. Romanenko

Magnonic beam splitter: The building block of parallel magnonic circuitry

We demonstrate a magnonic beam splitter that works by inter-converting magnetostatic surface and backward-volume spin waves propagating in orthogonal sections of a T-shaped yttrium iron garnet structure. The inter-conversion is enabled by the overlap of the surface and volume spin wave bands. This overlap results from the demagnetising field induced along the transversely magnetised section(-s) of the structure and the quantization of the transverse wave number of the propagating spin waves (which are therefore better described as waveguide modes). In agreement with numerical micromagnetic simulations, our Brillouin light scattering imaging experiments reveal that, depending on the frequency, the incident fundamental waveguide magnonic modes may also be converted into higher order waveguide modes. The magnonic beam splitter demonstrated here is an important step towards the development of parallel logic circuitry of magnonics.

Generation of Chaotic Microwave Pulses in Ferromagnetic Film Ring Oscillators Under External Influence

This study reports on the experimental results of chaotic microwave (MW) pulse generation in a ferromagnetic film ring oscillator under pulse-modulated (PM) and narrowband noise forces. Chaotic dynamics of the investigated self-oscillatory system is produced through three-wave parametric interactions of spin waves. It is shown, that periodical sequences of chaotic MW pulses are generated under a PM force and solitary chaotic MW pulses are generated under a noise force. Such pulses are formed through forced chaos synchronization. For description of forced chaos synchronization phenomenon, a ferromagnetic film ring oscillator model with nonlinear amplification and delay time is constructed. This model is based on the use of the Landau-Lifshitz equation, magnetostatic approximation and the Holstein-Primakoff transformation. Calculation results of chaos suppression under an external harmonic force are demonstrated.

Band gap formation and control in coupled periodic ferromagnetic structures

We demonstrate theoretically and experimentally the formation of additional bandgaps in the spectrum of spin waves in coupled magnonic crystals. We present the analytical model, which reveals the mechanism of bandgaps formation in coupled structures. In particular, the formation of one, two, or three bandgaps in the region of the first Bragg resonance is demonstrated and control of its characteristics by the variation of the complex coupling coefficient between magnonic crystals is shown. The spatially-resolved Brillouin light scattering spectroscopy and microwave measurements demonstrate the bandgap splitting in the spin-wave spectrum. The main advantage of proposed coupled structure, as compared to the conventional magnonic crystal, is the tunability of multiple bandgaps in the spin-wave spectrum, which enables potential applications in the frequency selective magnonic devices.

Tunable Bandgaps in Layered Structure Magnonic Crystal–Ferroelectric

The spectral characteristics of the hybrid spin-electromagnetic waves in multiferroic layered structure magnonic crystal (MC)-ferroelectric were theoretically and experimentally investigated. The main features of the bandgaps formation in such a structure were compared with the case of a single MC. The possibility of the bandgap characteristics control with varying electric field is demonstrated.

Band gap control in a line-defect magnonic crystal waveguide

We report on the experimental observation of the spin wave spectrum control in a line-defect magnonic crystal (MC) waveguide. We demonstrate the possibility to control the forbidden frequency band (band gap) for spin waves tuning the line-defect width. In particular, this frequency may be greater or lower than the one of 1D MC waveguide without line-defect. By means of space-resolved Brillouin light scattering technique, we study the localization of magnetization amplitude in the line-defect area. We show that the length of this localization region depends on the line-defect width. These results agree well with theoretical calculations of spin wave spectrum using the proposed model of two coupled magnonic crystal waveguides. The proposed simple geometry of MC with line-defect can be used as a logic and multiplexing block for application in the novel field of magnonic devices.

Chaotic parametric soliton-like pulses in ferromagnetic-film active ring resonators

The generation of quasi-periodic sequences of parametric soliton-like pulses in an active ring resonator with a ferromagnetic film via the three-wave parametric instability of a magnetostatic surface wave is studied theoretically and experimentally. These dissipative structures form in time due to the competition between the cubic nonlinearity caused by parametric coupling between spin waves and the time dispersion caused by the resonant cavity that is present in a self-oscillatory system. The development of dynamic chaos due to the parametric instability of a magnetostatic surface wave results in irregular behavior of a phase. However, this behavior does not break a quasi-periodic pulse sequence when the gain changes over a wide range. The generated soliton-like pulses have a chaotic nature, which is supported by the maximum Lyapunov exponent estimated from experimental time series.

An ultrawideband spin-wave medium-power chaos generator based on field-effect transistors

A prototype of an ultrawideband (UWB) microwave chaos generator based on a nonlinear spin-wave transmission line, a multistage transistor amplifier with an output amplifier based on GaAs field-effect transistors, and a microstrip bandpass filter was constructed. The possibility of autonomous generation of a UWB chaotic microwave signal with a central frequency of 3 GHz and a total power of about 4 W in a frequency band exceeding 30% was demonstrated. The proposed chaos generator is characterized by a fairly high efficiency of about 20%.

Spatial and Temporal Dynamics of Dissipative Parametric Solitons in a Ferromagnetic Film Active Ring Resonator

This paper reports the experimental results of spatial and temporal dynamics research of dissipative parametric solitons generated in a ferromagnetic film active ring resonator. Such dissipative structures are formed through three-wave parametric decay of a magnetostatic surface wave and frequency-time filtering. The spatio-temporal dynamics of dissipative parametric solitons has been investigated using the Brillouin light scattering technique. It is shown that quasi-stationary temporal structures are formed in a ring along a ferromagnetic film and are not observed in a ferromagnetic film, which is not incorporated into the ring.

Strain reconfigurable coupling of spin waves in width modulat-ed magnonic crystal waveguide

Recent progress in the magnon-based electronics shows that spin wave (SW) can be used as a signal carrier in the magnonic waveguiding structures operating in the GHz and THz frequency range [1–3].

Conversion of magnetostatic spin waves propagating through a junction of magnonic waveguides

Wave channeling is an important problem for signal processing systems and communications within both optical and microwave frequency ranges [1-3]. In optics, the propagation path of a light can be controlled e.g. via the total internal reflection or in photonic crystal fibers. Thus, the simplest problem of wave channeling - turning a wave round a corner - is trivial in photonics, which is due to the isotropy of the optical dispersion. In magnonics [4], in contrast, the information carriers are spin waves, which have a strongly anisotropic dispersion. As a result of this, the magnonic group and phase velocities are non-collinear, while the relationship between them depends strongly on the orientation of the magnetization and the strength of the applied magnetic field. In principle, bends could be avoided in architectures in which magnonic waveguides form right angles at the junctions. However, the same anisotropy then poses another problem - that of conversion between the magnetostatic surface spin waves (MSSWs) and backward volume magnetostatic spin waves (BVMSWs), which have their wave vectors perpendicular and parallel to the direction of the magnetization, respectively.