N. I. Polzikova

Magnetic field tunable acoustic resonator with ferromagnetic-ferroelectric layered structure

High overtone acoustic resonator with yttrium iron garnet/zinc oxide layered structure was theoretically considered, fabricated, and experimentally investigated. The theory of the resonator, containing an arbitrary number of magnetic and nonmagnetic dielectric/ferroelectric layers, placed in a transverse magnetic field is presented. The simulation shows the possibility to tune the resonant frequency in the range of ±1 MHz by magnetic field. This tuning is due to the resonance magnetoelastic interaction in the saturated ferrite film and the total phase shift of acoustic wave in the structure. The experiment proves the magnetic field influence on resonance frequencies and attenuation of transverse wave with polarization vector quasicollinear with the field direction. The tuning about 0.25 MHz near the acoustic resonant frequency 2 GHz was obtained in the field 260 Oe. This frequency is close to the ferromagnetic resonance frequency in ferrite film, corresponding to the field applied.

Unique properties of HBAR characteristics

It is rigorously shown that the data of the measurements of the difference between frequencies of resonance and antiresonance on high harmonic of HBAR together with the measurement of the frequencies between peculiarities of the phase of the electromagnetic wave reflection coefficient give a simple ways of the measurements of the losses in the materials composing HBAR and evaluation of the electromechanical constant of the piezoelectric film exciting acoustic waves in the HBAR.

Trapping of acoustic energy in composite resonators based on cubic crystals

An analytic solution is obtained for the problem of acoustic energy trapping in a microwave composite resonator containing a thick cubic-crystal plate with a deposited piezoelectric film and electrodes. It is found that rigorous account of the wave properties of the piezoelectric film and electrodes is of principal importance for such a structure. The problem is solved in the case when the operating frequency is a high-order harmonic of the fundamental frequency of the resonator and the resonator is much thicker than the other layers. The formulas obtained make it possible to analyze the feasibility of a multilayer resonator structure with a high Q-factor at a desired frequency.

Acoustic spin pumping in magnetoelectric bulk acoustic wave resonator

We present the generation and detection of spin currents by using magnetoelastic resonance excitation in a magnetoelectric composite high overtone bulk acoustic wave (BAW) resonator (HBAR) formed by a Al-ZnO-Al-GGG-YIG-Pt structure. Transversal BAW drives magnetization oscillations in YIG film at a given resonant magnetic field, and the resonant magneto-elastic coupling establishes the spin-current generation at the Pt/YIG interface. Due to the inverse spin Hall effect (ISHE) this BAW-driven spin current is converted to a dc voltage in the Pt layer. The dependence of the measured voltage both on magnetic field and frequency has a resonant character. The voltage is determined by the acoustic power in HBAR and changes its sign upon magnetic field reversal. We compare the experimentally observed amplitudes of the ISHE electrical field achieved by our method and other approaches to spin current generation that use surface acoustic waves and microwave resonators for ferromagnetic resonance excitation, with the theoretically expected values.

A procedure for measuring the Q factor of and attenuation in microwave composite acoustic resonators

A procedure for measuring the Q factor of a microwave composite acoustic resonator is described. The resonator consists of a relatively thick crystal plate and a piezoelectric film with electrodes that is deposited on the plate. The procedure is based on mathematical processing of the array of measurement data on the coefficient of the electromagnetic-wave reflection from the resonator structure connected to a microwave reflectometer. Via this procedure, it is possible to obtain data on the Q factor at the resonance and antiresonance frequencies.

Resonant subterahertz coherent acoustic waves excitation by Josephson junction

A superfine resonant structure with a voltage spacing of about 19 nV (corresponding frequency 9 MHz) and an extremely low differential resistance has been observed in the Josephson Flux Flow Oscillator (FFO) IVCs. We have analyzed coherent phonon radiation and detection due to the interaction of Josephsons electromagnetic oscillations with mechanical displacement field caused by piezoelectric effect or electrostriction effect. In contrast to the other works we consider sound generation in the Josephson tunneling structure, deposited on the rather thick substrate. This layered structure plays the role of high overtone composite resonator for bulk acoustic waves propagating normally to the layers.

Viscosity tensor components of the langatate and langasite

Full sets of components of viscosity tensor for langasite (La₃Ga₅SiO₁₄) and langatate (La₃Ga_5.5O₁₄Ta_0.5) were obtained. This study was done using the method of composite acoustic resonator (HBAR) spectroscopy. Using these data it is possible to evaluate the attenuation coefficient for arbitrary directions of the propagation and polarization of acoustic waves in single crystals of langatate and langasite.

Acoustically driven magnetic excitations in BAW resonators with magnetic layers

The theoretical and experimental study of a composite BAW resonator, containing layers of magnets and nonmagnetic dielectric/piezoelectric (epitaxial YIG films on GGG substrate and Al-ZnO-Al transducer), placed in bias magnetic field is presented. It is shown theoretically that due to excitations of magnetic oscillations in YIG via the magnetoelastic interaction the shift of resonance frequency in the range of intermodal distance (about 3 MHz) and Q-factor reduction of BAW resonator resonance take place. Near acoustic resonance frequency 2.5 GHz at a given effective magnetic field, corresponding to magnetoacoustic resonance, the frequency tuning in the range of ± 2 MHz was experimentally observed.

Tunable HBAR based on magnetoelectric YIG/ZnO structure

High overtone resonators with YIG/ZnO structure were prepared. For excitation of bulk transversal or/and longitudinal AW, thin ZnO films were sputtered on the layered structure, consisting of yittrium iron garnet (YIG) epitaxial film grown on the gadolinium gallium garnet substrate. The influence of 0-2 kOe bias field on AW resonance frequencies and attenuation was investigated. For the magnetic field oriented in the plane of the YIG film the obtained results prove its effective influence on the spectra of transverse AW with polarization vector quasicollinear with the field direction. Two types of non-monotonic dependences were observed. One of them was observed in the region at 260 Oe when YIG was saturated, and AW resonance frequencies were about 2 GHz. This value is close to the estimated FMR frequency. The frequency tuning about 0.25 MHz was observed. It is due to the resonance magnetoelastic interaction in the YIG film that results in the AW phase shift in the whole structure. The second one was observed for non saturated region of magnetic fields from 0 to 100 Oe. The frequency range from 0.7 to 1 GHz corresponds magnetoelectric excitation of domain resonance modes.

Stochastic resonance of elastic string motion

A model for the motion of an elastic string is studied numerically and analytically. An elastic string in two dimensions and restricted by two pinning centers is considered. We consider two stable configurations (positively or negatively curved) with pinned ends due to the action of a bistable potential. It is further assumed that the string is driven externally by periodic and white noisy forces. The noise enables the string to flip between the two configurations. The small temporally periodic force synchronizes these flippings and the phenomenon of stochastic resonance is observed. The signal-to-noise ratio (SNR) of the output is investigated and shows a maximum for a nonvanishing intensity of the applied noise. Its dependence on the stiffness of the string is studied. The peak of SNR versus the noise intensity D is found to be more pronounced and to be shifted to small values of D with an increase in the effective stiffness of a string. The calculation is extended to stochastic resonance of vortex moti...