The magnetic properties of the surface layer of an epitaxial bismuth-doped iron garnet film with a weak uniaxial anisotropy are studied by magnetic force, optical, and nonlinear optical microscopy. A significant modulation of optical second harmonic generation intensity along stripe domains is detected near the free film surface. This modulation is caused by periodic distortions of the stripe domain structure near the film surface and the presence of surface closure domains detected by magnetic force microscopy (MFM). A series of MFM images of the film taken in an in-plane magnetic field varying from –400 to 400 Oe demonstrates quasi-static nucleation of closure domains periodically located along stripe domains.

Ultrafast laser-induced heating of ferrimagnetic iron garnet in an external magnetic field triggers magnetization precessional dynamics with a large amplitude. The dynamics is studied as a function of magnetic field, laser fluence, and sample temperature. Exploring the three-dimensional space of these parameters experimentally and computationally, we identify the conditions for which the amplitude of the precession is the largest and even achieves values sufficient for magnetic recording. We found that the range of external magnetic fields and temperatures, which corresponds to the magnetic recording, is rather narrow. Modeling the dynamics, using magnetization as a macroscopic parameter, reveals that this range of parameters is defined by the optimal height of the potential barrier separating two stable states. The barrier needs to be low enough to allow the switching but not so low that the stability of the states is lost.

It is found that single-cycle THz electromagnetic fields efficiently excite a GHz spin resonance mode in ferrimagnetic Tm$_3$Fe$_5$O$_{12}$, despite the near absence of GHz spectral components in the exciting THz pulse. By analyzing how the efficiency of excitation depends on the orientation and strength of the THz electric field, we show that it can be explained in terms of the nonlinear THz inverse Cotton-Mouton effect. Here, the THz electric field gets effectively rectified and acts on the ferrimagnetic spins as a uni-polar effective magnetic field pulse. This interpretation is confirmed by a theoretical model based on the phenomenological analysis of the effective magnetic field, combined with the equations of motion derived from the effective Lagrangian for a ferrimagnet. Moreover, by using the outcome of two-dimensional THz spectroscopy, we conjecture a quantum-mechanical interpretation of the observed effect in terms of stimulated Raman scattering of THz photons by the crystal-field split f-f electronic transitions of Tm$^{3+}$.

Using diffraction of femtosecond laser pulses of visible light by a magnetic domain pattern in an iron garnet, we demonstrate a proof of concept of time-resolved measurements of domain pattern movements with nanometer spatial and femtosecond temporal resolution. In this method, a femtosecond laser (pump) pulse initiates magnetization dynamics in a sample that is initially in a labyrinth domain state, while an equally short linearly polarized laser pulse (probe) is diffracted by the domain pattern. The components of the diffracted light that are polarized orthogonally to the incident light generate several concentric diffraction rings. Nanometer small changes in the relative sizes of domains with opposite magnetization result in observable changes in the intensities of the rings. We demonstrate that the signal-to-noise ratio is high enough to detect a 6 nm domain wall displacement with 100 fs temporal resolution using visible light. We also discuss possible artifacts, such as pump-induced changes of optical properties, that can affect the measurements.

The paper considers the main prerequisites of the fractionation strategy for HLW from SNF reprocessing. It analyses the composition of HLW resulting from SNF reprocessing taking into account the requirements for the quality of the glass compound and the criteria forming the basis of the classification system for solidified radioactive waste. The paper evaluates the opportunities for renouncing the idea of deep HLW disposal. It proposes basic HLW fractionation options with an assessment of their feasibility considering the engineering tools available. For the proposed strategies, the paper evaluates the volumes of solidified RW fractions and the RW disposal cost. Based on the calculations performed, it also presents the postulates of the fractionation strategy.

The results of experiments are presented on testing the separation of uranium from U-Be nuclear fuel solutions by extraction. It was shown that the degree of uranium extraction using a solution of 10 vol% TBP in RED-3 from a nitric acid solution of this fuel is 98.7%. Transfer of uranium into the re-extract is 97.9%. More than 99.99 % of beryllium goes into the extraction raffinate intended for further vitrification. The results of the study were used for the preparation of technological regulations on reprocessing of U-Be SNF at the RT-1 plant of the Mayak Production Association. The industrial-scale reprocessing of this fuel confirmed the values determined in the study.

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.

Femtosecond laser excitation heats a ferrimagnetic iron garnet across the compensation temperature and decreases the magnetizations of the constituting Fe3+ sublattices. Here, we explore the heat-induced magnetization dynamics in the ferrimagnet at different points in the H-T phase diagram. For magnetic field strengths high enough to promote a state with non-collinear magnetizations of the sublattices, the dynamics occurs on a sub-ns timescale, governed by the effective spin–lattice interaction throughout the whole Brillouin zone of the spin excitations. When the field is low and the magnetizations are collinear, the heating alone is not sufficient to initiate the dynamics. In that case, the dynamics can only start after the magnetizations experience an initial kick, which occurs on the timescale of the spin–lattice interaction in the center of the Brillouin zone, leading to a substantial delay of the response of the spins to the thermal excitation.

The results of experiments on development of dissolution modes of the uranium–beryllium nuclear fuel produced on an enlarged batch of unirradiated fuel elements, are reported. The feasibility of a two-stage fuel dissolution mode was confirmed, which makes it possible to reduce the total time of the process and reduce the rate of gas evolution. The composition of the formed gas phase was determined. The weight of undissolved solid residue was estimated. The results of the study were used in the preparation of technological regulations for the reprocessing of uranium–beryllium SNF at the RT-1 plant of the Mayak Production Association.

A two-sublattice ferrimagnet undergoes a transition from a collinear to the canted magnetic phase at magnetic field oriented along an easy magnetization direction. In this work, we study the transition by means of the magneto-optical Faraday effect in a thin film of compensated iron garnet (Lu3−xBix)(Fe5−y−zGayAlz)O12 grown on the Gd3Ga5O12 substrate. In the immediate vicinity of the compensation temperature, a precursor of the transition with a complex shape was observed. Using a special sample with variable thickness, we demonstrate an interfacial origin of the precursor. Diffusion of gadolinium from the substrate into the film forms a thin intermixed layer with enhanced magnetization. It induces an extended inhomogeneous magnetic structure in the film. A two-step shape of the precursor appears due to an easy-plane anisotropy of the intermixed magnetic layer. We emphasize that an effective width of the inhomogeneous magnetization distribution in the film grows enormously while approaching the compensation temperature.

THz magnetization dynamics of antiferromagnetically coupled spins in ferrimagnetic Tm_{3}Fe_{5}O_{12} is excited by a picosecond single-cycle pulse of a magnetic field and probed with the help of the magneto-optical Faraday effect. Data analysis combined with numerical modeling shows that the dynamics corresponds to the exchange mode excited by the Zeeman interaction of the THz magnetic field with the spins. We argue that THz-pump-IR-probe experiments on ferrimagnets offer a unique tool for quantitative studies of dynamics and mechanisms to control antiferromagnetically coupled spins.

Представлен обзор состояния исследований и разработок элементов нейроморфных устройств на базе подвижных нанообъектов спинтроники - доменных границ и скирмионов.

Ferrimagnetic materials represent unique systems where the ease of manipulating the spins with applied magnetic fields is combined with exchange-driven acceleration of the internal spin dynamics. Of particular interest is the temperature range around the magnetic and spin compensation points, finely balancing both magnetic moment and angular momentum of the system, and leading to a very particular character of magnetic switching by the domain wall motion. Here we present our studies of the temperature-dependent domain wall dynamics in the temperature range covering both angular momentum and magnetization compensation points in garnet film, and reaching up to the Curie temperature. Drastic difference in the domain wall mobility and maximum achievable velocity in the vicinities of these two compensation points is demonstrated. Also a remarkably high mobility in weak applied magnetic fields is indicated.

A continuous increase in the volume of stored and processed data leads to stricter requirements for storage media. The most common information storage technology is currently based on magnetic materials, where information in the form of "0" and "1" is associated with the local direction of magnetization, determined by the external magnetic field created by the recording device. It is known that this approach has fundamental limitations on the recording speed which is almost achieved. The requirements for energy efficiency of storage media are also being made stricter. These circumstances lead to the development of alternative approaches to recording information. One of these approaches has been demonstrated in the field of ultrafast opto-magnetism, which has been booming over the past 20 years. It consists in recording information with short optical pulses without the application of an external magnetic field. However, it requires fundamental studies of physical processes, as well as materials, in which magnetization can be controlled by short optical pulses. In this paper, we consider the spin dynamics in a magnetic dielectric: a film of iron - yttrium garnet doped with silicon. The studies were carried out using the pump – probe technique over a time range of up to 800 ns. The spot size was 30 μm, the optical pulse duration was 35 fs, and the pump fluence was about 50 mJ/cm2. It is shown that a change in the magnetocrystalline anisotropy constants due to the action of a pump pulse on the structure causes a long-decaying magnetization precession with a period of about 200 ps. The dependences of the amplitude, phase, and decay of the precession on the magnitude of the external magnetic field in the range up to 1.84 kOe were obtained and analyzed. The studied processes can be considered on the basis of the Landau-Lifshitz-Gilbert model, and be of interest for the optical switching of magnetization, as well as the creation of various spintronic devices. It is shown that films of iron-yttrium garnet doped with silicon are a promising material for magnetic information carriers based on ultrafast opto-magnetism.

Представлены результаты исследований магнитных и магнитооптических свойств тонких пленок и наноструктур, предназначенных для разработок интегрально-оптических невзаимных устройств. Проанализированы возможности применения магнитооптических устройств в быстродействующих нейро-морфных системах.

The theoretical and experimental studies of the excitation, detection, and propagation of magnons in antiferromagnetic nanostructures have been reviewed. The properties of antiferromagnetic materials such as the absence of a macroscopic magnetization, the presence of strong exchange interactions, and a complex magnetocrystalline structure make it possible to implement new types of memory and functional electronic devices. The study of possible magnon effects in antiferromagnetic materials in micro- and nanoscales requires new experimental and theoretical approaches. In this review, the recent results on the excitation of magnetic oscillations—magnons—in antiferromagnetic materials induced by the current and optical radiation are described and systematized. The main theoretical results on antiferromagnets and multilayer antiferromagnetic heterostructures are presented. Models for description of phenomena induced by the current and optical pulses in nanoheterostructures including antiferromagnets are considered. Methods for studying antiferromagnetic micro- and nanostructures by means of Brillouin scattering, as well as prospects of the application of antiferromagnetic spintronics and magnonics, are briefly discussed.

Results are presented from an experimental study of the equilibrium distribution of magnetization and processes of magnetization reversal of magnetoelastic nanostructures in the form of strips with constant or variable width. It is shown that the symmetry of the stable magnetization states in the nanostrip can be broken by a static magnetic field applied perpendicular to the ferromagnet’s easy axis. A further change in the states of magnetization allows their manipulation (e.g., moving the domain wall) using the homogeneous mechanical effects induced by applying an electric field to the piezoelectric substrate.

State-of-the-art studies of dielectric magnonics and magnon spintronics are reviewed. Theoretical and experimental approaches to exploring physical processes in and calculations of the parameters of magnonic micro- and nanostructures are described. We discuss the basic concepts of magnon spintronics, the underlying physical phenomena, and the prospects for applying magnon spintronics for data processing, transmission, and reception. Special attention is paid to the feasibility of boosting the operating frequencies of magnonic devices from the gigahertz to terahertz frequency range. We also discuss specific implementations of the component base of magnonics and ways to further develop it.