Issue 6, 2024

Study of the domain walls dynamics in transparent ferromagnets using high-speed photography

T. B. Shapaeva

The work is devoted to studying the dynamics of domain walls and magnetic vortices arising in the domain walls of transparent ferromagnets. First, a review of methods for studying the magnetization reversal dynamics is given. Of the variety of these methods, the method of high-speed photography based on the Faraday effect was chosen for a more detailed consideration, since it allows one to observe the dynamic domain structure and determine the domain wall velocity with high accuracy. For optimal use of the chosen method, the work describes experimental studies of the magnetization reversal dynamics in materials with a high magneto-optical quality factor: films of Bi-containing ferrite garnet, GdFeCo and yttrium orthoferrite. The choice of these materials is due to the fact that they exhibit high velocity of domain wall and magnetic vortices, the value of which can reach 1.2 km/s in GdFeCo, about 10 km/s in garnet ferrites and up to 20 km/s in yttrium orthoferrite. In addition, ferrite garnets exhibit a periodic labyrinthine domain structure, which makes it possible to use magneto-optical diffraction to study the domain wall dynamics with high spatial resolution.

A. P. Oreshko$^1$, V. A. Bushuev$^1$, M. A. Andreeva$^1$, E. N. Ovchinnikova$^1$, R. A. Baulin$^1$, K. A. Akimova$^1$

New X-ray methods are discussed that make it possible to study, including in dynamics, the features of electronic, nuclear, magnetic, spin ordering in weakly absorbing biological objects and molecules, nanoparticles and atoms on the surface and embedded in various matrices, multilayer nanostructures and transition layers, nanofacet surfaces and porous materials, locally anisotropic and locally chiral media.

A. S. Kaminskiy$^1$, A. A. Karpacheva$^1$, T. B. Kosykh$^1$, N. V. Myasnikov$^1$, E. P. Nikolaeva$^1$, A. V. Nikolaev$^1$, A. P. Pyatakov$^1$, A. S. Sergeev$^1$

In magnetoelectric media besides conventional micromagnetic interactions like exhange stiffnes, magnetic anisotropy and magnetostatic interaction there is an additional term in thermodynamic potential that is proportional to the electric field and spatial derivatives of magnetization vector. This inhomogeneous magnetoelectric interaction leads to the domain boundaries energy modulation that manifest itself as the electrostatic attraction or repulsion of magnetic domain walls to the electrode and their refraction in the vicinity of the stripe electrode, as well as electric field induced magnetic bubble domain nucleation. On submicron level the inhomogeneous magnetoelectric interaction enables electric field control of Bloch lines, the inhomogeneities inside the domain walls, and supports the vortex state of magnetization as well as skyrmions.

T. A. Nadzharyan$^{1,2}$, S. A. Kostrov$^{1,2}$, E. Yu. Kramarenko$^{1,2}$

Magnetoactive polymer composites are polymer matrices containing magnetic micro- and/or nanoparticles. They belong to the class of “smart” materials and are currently of great fundamental and practical interest. This article focuses on magnetoactive elastomers (MAE), the research of which has been carried out at the faculty of physics of Moscow State University since the late 90s of the 20th century. A definition of MAE and the properties of its main components – the polymer matrix and magnetic particles – are given. A review of the physical phenomena exhibited by these materials when external magnetic fields are applied is provided. The influence of the material composition on its magnetic response is discussed in detail, with emphasis on the magneto-mechanical properties that are most important for practical applications. The results of recent studies related to the synthesis of new matrices for MAE, the influence of the shape and distribution of magnetic particles in the polymer matrix, as well as modern theoretical approaches to describing the behavior of MAEs in an external magnetic field are analyzed. In conclusion, the prospects for further development of the field related to the development of magnetically active polymer materials and the prospects for their practical application are discussed.

A. O. Kurbatov, N. K. Balabaev, E. Yu. Kramarenko

Dendrimers, hyperbranched molecules with a regular tree-like structure, are a relatively new class of polymeric materials. They are attracting increasing interest because of the unique properties determined by their structural features. To date, a complete fundamental understanding of the relationship between structure and properties of these unusual objects has not been achieved. Computer simulation, based on the molecular dynamics method using an atomistic approach, is an effective research method that allows one to obtain detailed information about the intramolecular structure of dendrimers, the nature of intermolecular interactions, and the response to external influences. The article provides an overview of advances in the theoretical and experimental study of the conformational behavior of dendrimers. The focus is on approaches to computer modeling of dendrimers and the results obtained from our studies of silicon-containing dendrimers, namely polybutylcarbosilane and polysiloxane, in solutions, melts, and at interfacial boundaries. The choice of these objects is due to the absence of groups with specific interactions in their structure, which makes them promising model systems for identifying the general patterns of influence of the regular tree structure of dendrimers on their equilibrium and dynamic properties. The results obtained can be used for the targeted development of new materials based on dendrimers.

N. Yu. Pankratov$^1$, G. A. Politova$^{2,3}$, I. S. Tereshina$^1$, S. A. Nikitin$^1$

The review displays experimental data and their theoretical discussion for volume magnetostriction induced by an external magnetic field in rare-earth metals and alloys in the region of magnetic phase transitions. Magnetostriction of the paraprocess was studied above the Curie temperature. From these data, the dependence of the exchange integrals on the unit cell volume was obtained. It was also discovered that in the region of magnetic phase transition in rare earth metals (REMs) and alloys, a gigantic volume magnetostriction takes place. It has been established that in binary RCo2 alloys with a high content of rare earth metals, giant volumetric magnetostriction is caused by an increase in the magnetic moment of the cobalt 3d sublattice in magnetic fields above the critical one. It has been shown that in intermetallic compounds of the R2Fe17 type, giant volume magnetostriction in the Curie temperature region arises due to the strong deformation dependence of both the exchange interaction integrals and the width of the 3d electron band.

A. S. Shurup

The review of the most important results obtained recently at the Physics Faculty of MSU in the field of acoustic tomography of natural media with regard to the specifics of hydro- and seismoacoustic applications is presented. The most urgent problems encountered in this area of research are highlighted and approaches to their solution are proposed. New methods for solving the problems of seismohydroacoustic tomography of a layered geophysical environment of “lithosphere-hydrosphere-ice cover” type have been theoretically developed and experimentally tested by using information about vector-phase structure of acoustic field. Capabilities and limitations of active and passive tomographic methods utilizing data from single receivers recording natural noise over a wide frequency range are described. New approaches to the solution of mode tomography problem for inhomogeneous moving ocean based on functional-analytical methods for solving inverse scattering problems are proposed and numerically investigated. The presented results make it possible to simplify technical difficulties and reduce the cost of tomographic experiment, which opens up the possibility of widespread application of acoustic tomography methods both in research activities and for solving purely applied problems.

M. I. Tribelsky$^1$, B. S. Lukyanchuk$^2$

We present a concise overview of the current advancements in understanding the singularities of the electromagnetic field, which emerge in the contexts of light refraction and scattering by material objects. We initiate the discussion with the formation of caustics in geometric optics, where beams of light are traced, and progressively refine our examination towards smaller scales with increasing accuracy. This exploration culminates in a detailed description of singularities associated with light scattering by subwavelength particles. Our review highlights both common and unique characteristics of various singularities, emphasizing the influence of problem symmetry and the principle of energy conservation. Additionally, we delve into the fundamental principles underlying these phenomena and explore methods to surpass the diffraction limit. The theoretical framework is enriched with experimental examples and a range of practical applications stemming from the discussed effects.Through this review, we aim to provide a comprehensive understanding of the singularities in the electromagnetic field and their implications in modern optics and related disciplines.

I. V. Yaminsky

Thanks to the invention of the tunnel microscope in 1981 by Gerd Binnig and Heinrich Rohrer, an entire industry of scanning probe microscopy was born with fundamental capabilities and a wide range of equipment for studying substances with subnanometer volumetric changes in vacuum, atmosphere and liquids. One of the subjects of observation was objects of living nature - biomolecules, viruses, bacteria, cells, nervous tissue, etc. Thus, a new section of physical measurements appeared – bionanoscopy – scanning probe microscopy of biological objects. Methods, equipment, objects of bionanoscopy are the subject of this article.

O. N. Melnikova

A review of experimental and numerical studies of the boundary layer of water and air flows, the speed of which decreases along the flow, is given. It has been experimentally established that the reverse pressure gradient in water and air flows leads to periodic braking of the boundary layer of a plane-parallel flow. During the braking process, the vertical velocity profile is deformed: a local minimum appears, located between two inflection points above the viscous layer. It is shown that in a thin layer containing the upper inflection point, the plane-parallel flow is unstable, which was confirmed in experiment - the formation of a cylindrical vortex was recorded in this layer at a critical value of the reverse pressure gradient at the end of the braking cycle. The parameters of the vortex chain were obtained, the deformation of vortices in a flow with a velocity shift, and the effect of vortices on the underlying surface were studied. The physical mechanisms of the formation of ridges on an eroded surface by a water flow and the generation of wind waves on an initially flat water surface, the formation of a wall of water and soil in flows when a dam breaks, were obtained

M. A. Nosov$^{1,2}$, A. V. Bolshakova$^1$, S. V. Kolesov$^1$, K. A. Sementsov$^1$

The review provides basic concepts about the earthquake source and presents empirical relationships that link the size of the fault area, the slip value and the energy of seismic waves with the magnitude of the earthquake. The complex and ambiguous relationship between earthquake magnitude and tsunami intensity according to the Soloviev-Imamura scale is discussed. Some empirical regularities are presented that link the size of the tsunami source, the height of the initial disturbance of the water surface and the tsunami energy with the magnitude of the earthquake. Based on the analytical solution of the problem of the generation of gravity waves by bottom movements and physical assessments, it is shown that the leading role in the generation of tsunami waves by seismic bottom movements belongs to residual bottom displacements that occur in the direction normal to the bottom surface. A model is described that assumes the approximation of the source of a tsunamigenic earthquake by a rectangular fault area, as well as an approach to describing tsunami generation using data on the structure of slip distribution in the source of an earthquake. Based on data on the structure of slip distribution in the sources of strong underwater earthquakes (200 sources), empirical relationships were found between the amplitude of the bottom displacement in the tsunami source, the displaced volume of water and the tsunami energy with the moment magnitude of the earthquake. It is shown that the part of earthquake energy passed on to tsunamis increases with increasing magnitude and ranges from 0.004% (at ) to 0.1% (at ). It is shown that horizontal displacements of the bottom, as a rule, provide an additional contribution to the displaced water volume and energy of the tsunami.