The Yenisei iconography of the South of Siberia was discovered by the Finnish expedition led by I.R. Aspelin (1887) and the monuments of the expeditions of 2000-2010 in the same area along the rivers ...Black and White Iyusy (Northern Khakassia) are taken into consideration. On the basis of the new iconography in the period of military expansion of medieval Kyrgyz in the northern Mongolian steppes (840), the Kyrgyz administration came in contact with the representatives of other syncretic religious groups on the Yenisei. The complex image is embodied in one person who was a Buddhist monk, a Manichaean envoy and a Central Asian spiritual leader. The Uighur Manichaean factor (8th century) was, to some extent, a cultural and historical impulse in the advancement of the syncretism on the Yenisei. Symbolic epigraphy: Buddhist stupas, swastika, endless crosses, cosmic signs accompany figurative reproduction of alien elements. Moreover, these reproductions are conjugated with a similar kind of epigraphy witnessed by researchers of the 20th century in the Chiglit area (Northern Ladakh). The crossroads of the Sogdian trade routes in Southern Turkestan and the northern end of trade routes on the Yeniseiindicate a Manichaean route unknown earlier.
Change management in the field of training and certification of academic personnel implies a reliable information support in the form of statistical and sociological data that enable the monitoring ...of the effectiveness of the institution of doctoral education. The current system for monitoring the activities of doctoral schools does not fully meet these requirements, thus making it difficult to assess objectively the implementation of doctoral education’s main function – the training of researchers and faculty for higher education. The article attempts to fill this information lacuna by presenting an analysis of the database created by the authors which contains information about the defense of dissertations and research results of PhD students who graduated in 2013 from nine Russian universities over the five-year period after their graduation (N = 1178). Information on the results of each graduate’s research activities was obtained from open sources: the portal of the Higher Attestation Commission, the electronic catalog of the Russian State Library, Scopus and eLibrary.ru databases, as well as the database of the Industrial Property Institute. As a result of our research, it was established that the actual timeframe of doctoral students’ advancement to their academic degree is determined by discipline-related factors. In the sample as a whole, the share of persons who defended their dissertations was 45% of the total number of graduates, which is 1.7 times higher than the share of graduates who defended their dissertations in the course of their studies at the doctoral school. Approximately 90% of graduates defend their dissertations no later than two years after graduation from the doctoral school. The quantitative data of doctoral school graduates’ retention in the academic field are given, with the breakdown by discipline. On average, more than 60% of Candidate of Sciences degree holders continue their careers in academic positions. The obtained data on Russian doctoral school graduates are in good agreement with the results of monitoring doctoral programs’ graduates in Europe and the USA. The results of this work make it possible to take a fresh look at the methodology for diagnosing the effectiveness of university doctoral schools.
Chiral magnetic skyrmions
are nanoscale vortex-like spin textures that form in the presence of an applied magnetic field in ferromagnets that support the Dzyaloshinskii-Moriya interaction (DMI) ...because of strong spin-orbit coupling and broken inversion symmetry of the crystal
. In sharp contrast to other systems
that allow for the formation of a variety of two-dimensional (2D) skyrmions, in chiral magnets the presence of the DMI commonly prevents the stability and coexistence of topological excitations of different types
. Recently, a new type of localized particle-like object-the chiral bobber (ChB)-was predicted theoretically in such materials
. However, its existence has not yet been verified experimentally. Here, we report the direct observation of ChBs in thin films of B20-type FeGe by means of quantitative off-axis electron holography (EH). We identify the part of the temperature-magnetic field phase diagram in which ChBs exist and distinguish two mechanisms for their nucleation. Furthermore, we show that ChBs are able to coexist with skyrmions over a wide range of parameters, which suggests their possible practical applications in novel magnetic solid-state memory devices, in which a stream of binary data bits can be encoded by a sequence of skyrmions and bobbers.
We report direct evidence of the field-dependent character of the interaction between individual magnetic skyrmions as well as between skyrmions and edges in B20-type FeGe nanostripes observed by ...means of high-resolution Lorentz transmission electron microscopy. It is shown that above certain critical values of an external magnetic field the character of such long-range skyrmion interactions changes from attraction to repulsion. Experimentally measured equilibrium inter-skyrmion and skyrmion-edge distances as a function of the applied magnetic field shows quantitative agreement with the results of micromagnetic simulations. The important role of demagnetizing fields and the internal symmetry of three-dimensional magnetic skyrmions are discussed in detail.
Lifetime of racetrack skyrmions Bessarab, Pavel F; Müller, Gideon P; Lobanov, Igor S ...
Scientific reports,
02/2018, Letnik:
8, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The skyrmion racetrack is a promising concept for future information technology. There, binary bits are carried by nanoscale spin swirls-skyrmions-driven along magnetic strips. Stability of the ...skyrmions is a critical issue for realising this technology. Here we demonstrate that the racetrack skyrmion lifetime can be calculated from first principles as a function of temperature, magnetic field and track width. Our method combines harmonic transition state theory extended to include Goldstone modes, with an atomistic spin Hamiltonian parametrized from density functional theory calculations. We demonstrate that two annihilation mechanisms contribute to the skyrmion stability: At low external magnetic field, escape through the track boundary prevails, but a crossover field exists, above which the collapse in the interior becomes dominant. Considering a Pd/Fe bilayer on an Ir(111) substrate as a well-established model system, the calculated skyrmion lifetime is found to be consistent with reported experimental measurements. Our simulations also show that the Arrhenius pre-exponential factor of escape depends only weakly on the external magnetic field, whereas the pre-exponential factor for collapse is strongly field dependent. Our results open the door for predictive simulations, free from empirical parameters, to aid the design of skyrmion-based information technology.
Magnetic skyrmion braids Zheng, Fengshan; Rybakov, Filipp N.; Kiselev, Nikolai S. ...
Nature communications,
09/2021, Letnik:
12, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
Skyrmions are vortex-like spin textures that form strings in magnetic crystals. Due to the analogy to elastic strings, skyrmion strings are naturally expected to braid and form complex ...three-dimensional patterns, but this phenomenon has not been explored yet. We found that skyrmion strings can form braids in cubic crystals of chiral magnets. This finding is confirmed by direct observations of skyrmion braids in B20-type FeGe using transmission electron microscopy. The theoretical analysis predicts that the discovered phenomenon is general for a wide family of chiral magnets. These findings have important implications for skyrmionics and propose a solid-state framework for applications of the mathematical theory of braids.
The ability to controllably manipulate magnetic skyrmions, small magnetic whirls with particle-like properties, in nanostructured elements is a prerequisite for incorporating them into spintronic ...devices. Here, we use state-of-the-art electron holographic imaging to directly visualize the morphology and nucleation of magnetic skyrmions in a wedge-shaped FeGe nanostripe that has a width in the range of 45-150 nm. We find that geometrically-confined skyrmions are able to adopt a wide range of sizes and ellipticities in a nanostripe that are absent in both thin films and bulk materials and can be created from a helical magnetic state with a distorted edge twist in a simple and efficient manner. We perform a theoretical analysis based on a three-dimensional general model of isotropic chiral magnets to confirm our experimental results. The flexibility and ease of formation of geometrically confined magnetic skyrmions may help to optimize the design of skyrmion-based memory devices.
We present the phase diagram of magnetic states for films of isotropic chiral magnets (ChMs) calculated as function of applied magnetic field and thickness of the film. We have found a novel magnetic ...state driven by the natural confinement of the crystal, localized at the surface and stacked on top of the conical bulk phase. This magnetic surface state has a three-dimensional (3D) chiral spin-texture described by the superposition of helical and cycloidal spin spirals. This surface state exists for a large range of applied magnetic fields and for any film thickness beyond a critical one. We also identified the whole thickness and field range for which the skyrmion lattice becomes the ground state of the system. Below a certain critical thickness the surface state and bulk conical phase are suppressed in favor of the skyrmion lattice. Unraveling of those phases and the construction of the phase diagram became possible using advanced computational techniques for direct energy minimization applied to a basic 3D model for ChMs. Presented results provide a comprehensive theoretical description for those effects already observed in experiments on thin films of ChMs, predict new effects important for applications and open perspectives for experimental studies of such systems.
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