V. A. Luzanov

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.

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.

Diamond-Like Carbon Films Obtained by the Method of High-Frequency Diode Sputtering

Conditions for fabrication of diamond-like carbon films on the surface of oxidized single-crystalline silicon using the technique of high-frequency diode sputtering of graphite target are determined. It has been found that the deposited films have amorphous structure. The Raman spectroscopy technique has been used to show the presence of carbon phases with sp2- and sp3-hybridization, the ratio between which can be controlled by the growth conditions.

Magnetoelectric BAW resonator as a source of pure spin current

The generation of spin currents in a ferromagnet/paramagnet junction from acoustically driving magnetization precession, acoustic spin pumping (ASP), in different magnetoelectric structures draws a lot of attention because it offers great opportunities for low-power microwave spintronics. Recently, we have demonstrated for the first time the generation of pure spin current (which does not include charge current) in the high overtone bulk acoustic wave resonator (HBAR) based on YIG-Pt hybrid under resonant excitation of the magnetic dynamics in YIG [N.I. Polzikova, et al., AIP Adv. 6 (2016), 56306.]. For the practical application of this method it is necessary to understand the various factors affecting its efficiency.

Spin pumping in a composite high overtone bulk acoustic wave resonator

A new way of generating a pure spin current using a magnetoelectric composite high-overtone bulk acoustic-wave resonator (HBAR) based on a layered Al–ZnO–Al–Gd3Ga5O12–Y3Fe5O12–Pt structure is proposed. It is established that the efficiency of generating the rf magnetic field driving the spin current by this method exceeds that of sources which use surface acoustic waves for the excitation of magnetic dynamics and is not inferior to the efficiency of usual electromagnetic ways of exciting a pure spin current that employ microwave cavities.

Magnetoelectric bulk acoustic wave resonator for acoustic spin pumping

High overtone bulk acoustic wave resonator with (Al-ZnO-Al)/GGG/YIG/Pt structure was theoretically considered, fabricated and experimentally examined for acoustic spin pumping - acoustically driven generation of pure spin current at YIG/Pt interface.

Propagation of Surface Acoustic Waves in two-dimensional periodic structures

Propagation of Surface Acoustic Waves (SAW) in two mutually perpendicular directions on the substrate of YZ-cut of LiNbO3 with two-dimensional periodic surface corrugations has been investigated. To calculate the distribution of wave amplitudes as well as SAW transmission and reflection coefficients a new method based on 2D-transfer matrices was developed. Frequency dependencies of transmission and reflection coefficients for Rayleigh SAW propagating in a rectangular region occupied by the two-dimensional periodic structure with three levels of height were measured. The coupling coefficient for waves propagating along Z and X crystallographic axes was determined using the measured and calculated results. It has been shown that if the width of incident acoustic beam is quite narrower than the width of periodic structure, then a kind of channelization takes place for the incident wave, and a resonant enhancement of transmission coefficient arises near the center frequency of Bragg stop band.

Bi-epitaxial YBa2Cu3Ox Thin Films on Tilted-axes NdGaO3 Substrates with CeO2 Seeding Layer

Bi-epitaxial YBa2Cu3Ox (YBCO) thin films with out-of-plane tilt angle in the range 18 - 27? were manufactured using pulsed laser deposition on NdGaO3 tilted-axes substrates with CeO2 seeding layers. The YBCO thin film orientation over the seeding layer depended on deposition conditions. Removal of the seeding layer from part of the substrate surface by ionbeam etching resulted in formation of a bi-epitaxial thin film with different c-axis orientation of two parts of the film. The bi-epitaxial film orientation and structure were studied using X-ray diffraction techniques, and surface morphology was observed with atomic force microscope (AFM). Photolithography and ion-beam etching techniques were used for patterning bi-epitaxial thin films. Electrical characterization of the obtained structures was performed.

Metal Oxide Bicrystal Josephson Junctions of a New Type with High Critical Parameters

Film bicrystal Josephson junctions of a new type based on a metal oxide high-Tc superconductor of the YBa2Cu3O7−x (YBCO) system are suggested and studied. In junctions of the new type, in contrast to the known ones, the working surfaces situated on the opposite sides of the bicrystal interface have different crystal orientations: one is (001)YBCO, and the other is rotated (misoriented) relative to it by an asymmetric bicrystal angle around a certain axis lying in the substrate plane. The main electrical and dynamic (microwave) characteristics have been determined for junctions of the new type based on NdGaO3 bicrystal substrates with the misorientation angle varying from 13° to 28°. These junctions exhibit high values of the critical parameters at T=77 K, including the critical current density IC= (2–5)×105 A/cm2 and the characteristic voltage VC=ICRN=0.6–0.9 mV. Advantages of the bicrystal Josephson junctions of the new type over the known junctions are considered.

Possible formation of BaCeO3 during deposition of YBa2Cu3O7−x films on the surface of cerium oxide

Results are presented from an experimental study of the crystallographic parameters of (1102)Al2O3/(001)CeO2/(001)YBa2Cu3O7−x film heterostructures fabricated by cathode sputtering at high substrate temperatures T=600–800°C. It is shown that the main limitation on the temperature for deposition of a YBa2Cu3O7−x film on a CeO2 surface is due to the chemical interaction between YBa2Cu3O7−x and CeO2 to form a polycrystalline BaCeO3 layer.