S. G. Alekseev

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.

Bulk acoustic wave microwave composite resonators and filters with acoustic isolation of resonating layers

The problem of acoustic isolation of thin-film piezoelectric resonators and filters for microwaves is developed. Expressions describing operation of such devices taking into account losses in all the layers are derived. The conclusions are supported by numerical examples.

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.

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.

Frequency and magnetic field mapping of magnetoelastic spin pumping in high overtone bulk acoustic wave resonator

We report on the first observation of microvolt-scale inverse spin Hall effect (ISHE) dc voltage driven by an acoustic spin pumping (ASP) in a bulk acoustic wave (BAW) resonator formed by a Al-ZnO-Al-YIG(1)-GGG-YIG(2)-Pt structure. When 2 mW power is applied to an Al-ZnO-Al transducer, the voltage VISHE ∼ 4 μV in the Pt film is observed as a result of resonant ASP from YIG(2) to Pt in the area ∼ 170 μm. The results of frequency and magnetic field mapping of VISHE(f,H) together with reflectivity of the resonator show an obvious agreement between the positions of the voltage maxima and BAW resonance frequencies fn(H) on the (f, H) plane. At the same time a significant asymmetry of the VISHE(fn(H)) value in reference to the magnetoelastic resonance (MER) line fMER(H) position is revealed, which is explained by asymmetry of the magnetoelastic waves dispersion law.