A. B. Rinkevich

Spin Hall controlled magnonic microwaveguides

We use space-resolved magneto-optical spectroscopy to study the influence of spin Hall effect on the excitation and propagation of spin waves in microscopic magnonic waveguides. We find that the spin Hall effect not only increases the spin-wave propagation length, but also results in an increased excitation efficiency due to the increase of the dynamic susceptibility in the vicinity of the inductive antenna. We show that the efficiency of the propagation length enhancement is strongly dependant on the type of the excited spin-wave mode and its wavelength.

Millimeter-Wave Properties and Structure of Gradient Co–Ir Films Deposited on Opal Matrix

The millimeter-waveband properties of gradient cobalt and iridium films deposited on the surface of opal matrix have been studied. The transmission and reflection coefficients are measured in frequency range from 26 to 38 GHz. The algorithm is developed to extract the value of microwave effective conductivity from the frequency dependence of transmission coefficient. The values of microwave conductivity are three orders of magnitude greater than dc conductivity. Besides microwave measurements, electron microscopy and chemical composition studies are carried out.

Three-dimensional nanocomposite metal dielectric materials on the basis of opal matrices

The microwave properties of 3D nanocomposites based on opal matrices containing one or two transition metal particles have been investigated. Phase analysis of the nanocomposites has been carried out. Magnetic field dependences of transmission and reflection coefficients were obtained. Magnetic resonance and antiresonance spectra have been reconstructed. Frequency dependences of resonance and antiresonance amplitude have been obtained. It has been found that the magnetic resonance amplitude of a nanocomposite containing particles of two metals is essentially higher than that of a nanocomposite with particles of one metal.

Interaction of Pulse Ultrasonic Signals with Reflectors of Different Types

The results of experimental studies of the processes of interaction of pulse ultrasonic signals with artificial reflectors of different types are presented. To estimate nonstationary frequency characteristics of echo signals, it is proposed to use an algorithm for determining the instantaneous frequency that is based on the use of a wavelet transform characterized by increased noise immunity. It is shown that the instantaneous frequency of the reflected pulse signal may substantially differ from the rated frequency of a piezoelectric transducer for different types of reflectors. The frequency difference has a minimum value at a minimum curvature of the reflected-wave front. The obtained results must be considered during implementation of conventional methods of ultrasonic nondestructive testing because disregarding the effect of frequency deviation from the rated value may lead to a violation of the requirements of the acting standards for the tolerance for the operating frequency of a piezoelectric transducer. The difference of the instantaneous frequency from the rated frequency depends on the reflector type and can be used as an informative indicator of a flaw’s shape.

Instantaneous frequency estimation used for the classification of echo signals from different reflectors

A comparative analysis of the frequency parameters of echo signals from artificial reflectors of different shapes and from a natural spill-type flaw has been performed. The use of the instantaneous frequencies of ultrasonic signals that correspond to certain instants inside a pulse was suggested as an informative parameter for determining the flaw type. Instantaneous frequency is estimated based on the algorithm of the continuous wavelet transform, which increases the noise immunity of the method. It is shown that for the algorithm to be practically implemented it is appropriate to present the results in the form of dimensionless parameters, namely, normalized frequency deviations determined between the pulse center, edge, and tail. Their joint application makes it possible, in particular, to reliably distinguish echo signals that are reflected at junction flaws that rise to the surface of a test object (notches, dihedral angles, and spills of the weld joints), flat specimen surfaces, and local flaws, such as cylindrical side through holes and flat bottom drills.

Chemical potential of quasi-equilibrium magnon gas driven by pure spin current

Pure spin currents provide the possibility to control the magnetization state of conducting and insulating magnetic materials. They allow one to increase or reduce the density of magnons, and achieve coherent dynamic states of magnetization reminiscent of the Bose–Einstein condensation. However, until now there was no direct evidence that the state of the magnon gas subjected to spin current can be treated thermodynamically. Here, we show experimentally that the spin current generated by the spin-Hall effect drives the magnon gas into a quasi-equilibrium state that can be described by the Bose–Einstein statistics. The magnon population function is characterized either by an increased effective chemical potential or by a reduced effective temperature, depending on the spin current polarization. In the former case, the chemical potential can closely approach, at large driving currents, the lowest-energy magnon state, indicating the possibility of spin current-driven Bose–Einstein condensation.Spin current-induced quasi-equilibrium state of magnon gas described by the Bose–Einstein statistics has been previously theoretically predicted. Here, authors experimentally show that the spin current-driven magnon distribution can be treated thermodynamically, and potentially form a Bose–Einstein condensate.

Mutual synchronization of nano-oscillators driven by pure spin current

We report the experimental observation of mutual synchronization of magnetic nano-oscillators driven by pure spin current generated by nonlocal spin injection. We show that the oscillators efficiently synchronize due to the direct spatial overlap of the dynamical modes excited by the spin current, which is facilitated by the large size of the auto-oscillation area inherent to these devices. The synchronization occurs within an interval of the driving current determined by the competition between the dynamic nonlinearity that facilitates synchronization and the short-wavelength magnetic fluctuations enhanced by the spin current that suppress synchronization. The demonstrated synchronization effects can be utilized to control the spatial and spectral characteristics of the dynamical states induced by the spin currents.

Detection of subsurface microflaws using the high-frequency acoustic microscopy method

The possibility of detecting subsurface flaws in solids using the scanning high-frequency acoustic-microscopy method was investigated. The influence of a distortion of the focal region and aberrations, which appear during focusing to a subsurface region in a solid, on the formation of the output signal of a microscope is estimated via mathematical simulation of the refraction of focused acoustic beams in a solid and during experiments on a laboratory scanning acoustic microscope at a 400-MHz frequency of probing acoustic waves.

Spectral linewidth of spin-current nano-oscillators driven by nonlocal spin injection

We study experimentally the auto-oscillation characteristics of magnetic nano-oscillators driven by pure spin currents generated by nonlocal spin injection. By combining micro-focus Brillouin light scattering spectroscopy with electronic microwave spectroscopy, we are able to simultaneously perform both the spatial and the high-resolution spectral analyses of auto-oscillations induced by spin current. We find that the devices exhibit a highly coherent dynamics with the spectral linewidth of a few megahertz at room temperature. This narrow linewidth can be achieved over a wide range of operational frequencies, demonstrating a significant potential of nonlocal oscillators for applications.

Scanning acoustic microscope for visualization of microflaws in solids

A laboratory scanning acoustic microscope working in a pulsed regime at a frequency of 400 MHz with a resolution of approximately 3 μm for investigation and visualization of flaws and microflaws in surface and subsurface layers in solids is described. Acoustic images of various types of microflaws (micropores and microcracks) are obtained and analyzed; the images contain new information n the degree of microdamage to a material compared to that presented by the light microscopy method.