The propagation of slit shear waves in a quasi-symmetric structure of piezoelectrics of the 4mm symmetry class has been theoretically studied. It has been shown that taking into account the unequal level of loss and gain in piezoelectrics results in either intersection, touching, or convergence of two modes at the point of their degeneracy (singular point) in the shear wave spectrum. It has been found that the intersection of the mode spectra occurs only in the case of equal loss and gain magnitudes (a PT-symmetric structure). Based on this, it is concluded that using the pattern of the spectra near a singular point, it is possible to determine the level of imbalance of gain and loss in piezoelectric waveguides. As in the case of a purely PT-symmetric structure, the frequency dependence of the amplitude at an exceptional point of a quasi PT-symmetric structure (with a rather small difference in loss and gain levels) exhibits a very narrow peak, which opens up the possibility of creating hypersensitive sensors based on them. Thus, it has been shown that even at unequal loss and gain levels in piezoelectrics (a quasi PT-symmetric structure), it is possible to obtain a structure with all the characteristics of a PT-symmetric structure.

In the frequency range from 16 to 50 THz, the transmission, reflection, and absorption spectra of arrays of heterogeneous Ni/Co, FeNi/Co, and Ni/Fe nanowires grown in track polymer membranes by the galvanic method have been studied. The absorption spectra showed that the fraction of the radiation power absorbed by the nanowires and its spectrum depend on the materials of the nanowires. The features of the spectra can be explained by the accumulation of nonequilibrium spin due to electron diffusion and its relaxation stimulated by external terahertz (THz) radiation, which can be used to create a THz radiation detector. In addition, negative absorption was found for FeNi/Co nanowires, which can be explained by the laser effect on spin-flip transitions, which can be used to create a THz radiation source operating at room temperature. Keywords: nanowires, THz radiation, THz spectroscopy, spin-flip transitions, metamaterial.

Dispersion properties of electroacoustic waves in the gap structure of two different piezoelectrics are considered. It is shown that in the considered structure PbTiO3 – vacuum gap – BaTiO3 in the presence of a difference of shear wave velocities in piezoelectrics there are no purely symmetric and antisymmetric modes, and the coefficients of the boundary localization of the shear wave will be significantly different.

The propagation of slit shear waves in the quasi-symmetric structure of piezoelectrics of the 4mm symmetry class has been theoretically investigated. It has been shown that taking into account the unequal level of losses and amplification in piezoelectrics leads in the shear wave spectrum either to an intersection, or to a touch, or to a convergence of two modes at the point of their degeneracy (singular point). It is established that the intersection of the mode spectra occurs only in the case of equal loss and gain values (PT is a symmetric structure). Based on this, it is concluded that by the nature of the spectra near a singular point, it is possible to determine the level of imbalance of gain and loss in piezoelectric waveguides. As in the case of a purely PT-symmetric structure, the frequency dependence of the amplitude at an exceptional point of a quasi PT-symmetric structure (with a fairly small difference in loss and gain levels) has a very narrow peak, which opens up the possibility of creating hypersensitive sensors based on them. Thus, it is demonstrated that even with unequal levels of loss and gain in piezoelectrics (quasi PT-symmetric structure), it is possible to obtain a structure with all the properties of a PT-symmetric structure.

An experimental approach to the problem of the energy distribution of radiation in the THz range created by an electron flow passing through a magnetic junction between thermal and dynamic is considered. The experimental results obtained during the operation of a spin-injection emitter based on an array of heterogeneous magnetic nanowires (NWs) confirmed the assumption about the "competition" of thermal and dynamic radiation processes.

The modes of occurrence of Three-band electromagnetic oscillations during the flow of current in magnetic nanocontacts and in a heterogeneous Fe/Mo structure with a heavy metal nanofilm are compared, and the similarity of the dependences of the change in radiated power on the change in current in the region of radiation occurrence is established. Based on this, a conclusion is made about the identity of the processes of THz radiation formation in the structures under study and the possibility of spreading physical ideas about the excitation of THz radiation during spin injection by current in the case of a heterogeneous Fe/Mo structure with a heavy metal nanofilm.

The spectral properties of gap electroacoustic waves in a PT-symmetric structure of piezoelectrics of symmetry class 6 mm separated by a gap are theoretically investigated. The spectra were calculated for lead germanate (non-zero transverse piezoactivity) and barium titanate (symmetry class 4 mm-zero transverse piezoactivity). It has been established that at a certain level of losses and gain in piezoelectrics, the symmetric and antisymmetric modes intersect. The intersection point determines the singular point of the PT-symmetric structure. Beyond this point, there is a violation of the symmetric and antisymmetric distribution of electric fields in the gap of the slotted structure of two identical piezoelectrics, which is confirmed by the calculation of the electric field profiles. It is shown that the dependence of the amplitude on the frequency at an exceptional point has an extremely narrow resonance peak, which opens up the possibility of creating supersensitive sensors based on PT-symmetric physical structures.

In the frequency range from 16 to 50 THz, the transmission, reflection, and absorption spectra of arrays of heterogeneous Ni/Co, FeNi/Co, and Ni/Fe nanowires grown in track polymer membranes by the galvanic method have been studied. The absorption spectra showed that the fraction of the radiation power absorbed by the nanowires and its spectrum depend on the materials of the nanowires. The features of the spectra can be explained by the accumulation of nonequilibrium spin due to electron diffusion and its relaxation stimulated by external terahertz (THz) radiation, which can be used to create a THz radiation detector. In addition, negative absorption was found for FeNi/Co nanowires, which can be explained by the laser effect on spin-flip transitions, which can be used to create a THz radiation source operating at room temperature.

Dynamic interaction of acoustic and magnetic systems is of strong current interest, triggered by the promises of almost lossless new concepts of magnet-based information technology. In such concepts, a significant role is often given to domain walls (DW). Therefore, here we investigate how launching an acoustic shear wave, we can control the DW motion. Surprisingly, at sufficiently large amplitudes of the shear displacement, the speed of the forced DW motion can reach sizeable fraction of the speed of sound. This was shown to happen due to certain resonance conditions depending on the wave frequency, its angle of incidence, and shear displacement amplitudes, leading to a total reflection of the wave and maximizing the impact. Most interesting, strong nonlinearity appears in the interaction of the elastic and magnetic subsystems, expressed by the negative slope of the resonant reflection peak and the s-shaped dependence of the domain wall velocity on the shear displacement amplitude, typical for nonlinear systems.

The spectral properties of gap electroacoustic waves in PT-symmetric piezoelectric structures of symmetry class 6 are investigated theoretically. It was found out that, at a certain level of loss and gain in piezoelectrics, the symmetric and antisymmetric modes intersect. The intersection point defines an exceptional point of the PT-symmetric structure. It was shown that the frequency dependence of the amplitude at the exceptional point has an extremely narrow resonance peak, which opens up the possibility of creating supersensitive sensors based on PT-symmetric physical structures. Keywords: PT-symmetry, piezoelectrics, electroacoustic waves, gap structure.

This article is devoted to the study of the possibility of excitation of the intrinsic magnetization in the FeMn antiferromagnetic (AFM) film by injecting spins into it with a relatively low current. Such a possibility is shown on the basis of the operation of spin injection THz sources using this effect. It has been shown that the use of this effect in THz spin-injection emitters is of interest both from the point of view of developing theoretical ideas about the magnetic properties of AFMs and from a practical point of view of the use of these sources. New experimental results have been obtained, developing theoretical ideas about the intrinsic magnetization of thin films of AFMs.

The transmission and reflection spectra of arrays of heterogeneous nanowires made of Ni/Co, FeNi/Co, and Ni/Fe, formed in track polymer membranes by the galvanic method, have been studied in the frequency range from 16 to 250 THz. Many peaks in the 16-20 THz range were found in the transmission spectra, while they are not observed in the spectrum of a track membrane without nanowires. The absorption spectra of an array of nanowires in a track membrane and a membrane without wires are calculated from the obtained spectra. It was found that the fraction of the THz radiation power absorbed by nanowires and its spectrum depend on the materials of the nanowires. The features of the observed spectra can be explained by two mechanisms. The first is the inverse laser effect in magnetic nanocontacts. And the second is the change in electrical resistance due to spin-flip transitions between the spin subbands in the case of a non-coplanar distribution of the magnetization of the magnetic layers. This class of quasi-one-dimensional structures looks promising for creating THz radiation detectors in a wide spectral range and at room temperature.

The operation of a spin-injection THz emitter is used to establish the possibility of competition between thermal and spin-injection (dynamic) radiation. It is shown experimentally that raising the intensity of dynamic radiation lowers that of thermal radiation. This is explained by the relationship between dynamic radiation and indirect interband spin-flip transitions accompanied by a change in momentum, and thus the absorption of phonons.

The spectral properties of electrosound waves in the gap of PT-symmetric piezoelectrics of symmetry class 6 are investigated theoretically. It is found that at a certain level of loss and gain in piezoelectrics, the symmetric and antisymmetric modes are coupled. The coupling point defines an exceptional point of PT-symmetric structure. It is shown that the frequency dependence of the amplitude at the exceptional point has an extremely narrow resonance peak, which opens up the possibility of creating supersensitive sensors based on PT-symmetric physical structures.

Arrays of magnetic nanocontacts are fabricated by growing Fe island films and filling the space between the islands with antiferromagnetic layers. The magnetic structures of the islands and their dependences on their dimensions are studied using atomic-force microscopy and micromagnetic calculations. Micromagnetic numerical calculations of the influence of the spin-polarized current flowing from the ferromagnetic edge into the antiferromagnetic interlayer on magnetization in magnetic antiferromagnet sublattices are carried out. The magnetization skew angle in magnetic antiferromagnet sublattices is found as a function of the current density.

Впервые рассмотрена работа спин-инжекционного излучателя электромагнитных колебаний с туннельным магнитным переходом Ni/NiO/Fe. С использованием NiO в качестве непроводящего спейсера в магнитном переходе определено влияние интерфейсной разности потенциалов на границе раздела магнитных слоев на эффективность работы спин-инжекционных излучателей. Приведено теоретическое описание модели исследуемого излучателя и результаты экспериментального сравнения эффективности работы излучателя с туннельным магнитным переходом и магнитным переходом без спейсера Ni/Fe. Показана возможность увеличения эффективности работы спин-инжекционного излучателя при использовании туннельного магнитного переход

The mechanism of formation of spin nonequilibrium with inverse population in spin subbands in quasi-one- dimensional chains of magnetic metal tunnel junctions is considered. The ability of induced spin-injected radiation is discussed. A model of a one-dimensional chain of ferromagnetic metal grains separated by a tunneling dielectric under the influence of electric current is considered. The radiation spectra of grainy metamaterials were measured in the terahertz range depending on the average current density in the Q1D-labyrinth structures.

An investigation was made of THz radiation in the Fe/Mo magnetic junction arising from the pumping by a high-density current of the upper spin subband in the induced ferromagnetism layer in Mo. The tensor character of the exchange interaction constant at the Fe / Mo interface, associated with the presence of the Dzyaloshinsky-Moriya interaction, promotes radiative relaxation.

An investigation was made of THz radiation spectra in the Fe/Mo and Fe/Co2FeAl magnetic junctions arising from the pumping by a high-density current of the upper spin subband at the Fe/Mo interface. The tensor character of the exchange interaction constant at the Fe/Mo interface, associated with the presence of the DMI-like interaction, promotes radiative relaxation.