MORPHOLOGY AND COMPOSITION OF THE INTERFACE BOUNDARY OF SODIUM CHLORIDE SINGLE CRYSTALS WITH LEAD

Методами электронной микроскопии и рентгеноспектрального анализа исследована межфазная граница раздела жидкого свинца с хлоридом натрия после охлаждения и разрыва контакта. На поверхностях разрыва образцов обнаружено накопление поверхностно-активных примесей, содержащихся как объеме свинца, так и в хлориде натрия. Как показывают результаты рентгеноспектрального анализа, содержание примесей на поверхности подложки хлорида натрия превышает объемное содержание на несколько порядков. На поверхности свинца также наблюдается значительное накопление примесей кремния и индия. В исследованных образцах наблюдается анизотропия растекания жидкого свинца по поверхности монокристаллов хлорида натрия. Линия разрыва, затвердевшей капли свинца с монокристаллической поверхностью хлорида натрия ориентации (110), заметно отклоняются от круга. Кроме того, на электронно-микроскопическом изображении межфазной поверхности свинца после отрыва от подложки хлорида натрия ориентации (100), наблюдаются участки в виде «сигары», в которых обнаружено накопление примесей. Данные участки имеют ориентации, совпадающие с кристаллографическим направлением подложки. The interface between liquid lead and sodium chloride after cooling and breaking the contact was investigated by the electron microscopy and X-ray spectral analysis. Accumulation of surface-active impurities, contained both in the bulk of lead and in sodium chloride was found on the fracture surface of the samples. As shown by the results of the X-ray diffraction analysis, the content of impurities on the surface of the sodium chloride substrate exceeds the bulk content by several orders of magnitude. A significant accumulation of silicon and indium impurities is also observed on the lead surface. Anisotropy of spreading of liquid lead over the surface of sodium chloride monocrystals is observed in the studied samples. The separation line of a solidified lead droplet on the surface of sodium chloride with orientation (110) deviates noticeably from a circle. In addition, on the electron microscopic image of the lead interface after detachment from the substrate of sodium chloride of orientation (110), there are areas in the form of a «cigar», in which the accumulation of impurities was detected. The orientation of these regions coincides with the crystallographic direction of the substrate.

New Strategy for Inducing Surface Anisotropy in Polyimide Films for Nematics Orientation in Display Applications

The operability of liquid crystal displays is strongly impacted by the orientation aspects of nematics, which in turn are affected by the alignment layer surface features. In this work, two polyimide (PI) structures are obtained based on a cycloaliphatic dianhydride and aromatic or aliphatic diamines with distinct flexibility. The attained PI films have high transmittance (T) for visible radiations, i.e., at 550 nm T > 80%. Here, a novel strategy for creating surface anisotropy in the samples that combines rubbing with a cloth and stretching via pressing is reported. Birefringence and atomic force microscopy (AFM) scans reveal that the generated orientation of the chains is affected by the chemical structure of the polymer and order of the steps involved in the surface treatment. Molecular modeling computations and wettability tests show that the PI structure and produced surface topography are competitive factors, which are impacting the intensity of the interactions with the nematic liquid crystals. The achieved results are of great relevance for designing of reliable display devices with improved uniform orientation of liquid crystals.

Creation and Annihilation of Magnetic Skyrmions for Neuromorphic Computing Applications

In this work we present the creation, annihilation and dynamics of a topologically protected magnetic structure, a skyrmion, for neuromorphic computing application. We study the effect of Dzyaloshinskii Moriya interaction (DMI) and surface anisotropy on the skyrmion density. The relation between skyrmion annihilation threshold anisotropy Kth and DMI coefficient is evaluated. Furthermore, the skyrmion diameter dependence on these two parameters is studied. Using MOKE analysis we study the effect of external magnetic field on the skyrmion density and predict the threshold magnetic field for the transition of magnetic texture from Labriynth domains to skyrmions. These results are further supported by the MuMax simulations. The spin orbit torque SOT manipulation of skyrmion size and density is also presented for skyrmion applications in the race-track memory and neuromorphic computing. Motivated by the results, we propose a Skyrmionic neuromorphic device and using SOT switching mechanism, show its applicability as spintronic synapse and neuron. The MuMax simulations are coupled to the Non- Equilibrium Green’s Function formalism to model the neuron and synapse behavior. Finally, we conclude with the possibility of using these devices for pattern recognition and other unconventional computing paradigms.

Creation and Annihilation of Magnetic Skyrmions for Neuromorphic Computing Applications

In this work we present the creation, annihilation and dynamics of a topologically protected magnetic structure, a skyrmion, for neuromorphic computing application. We study the effect of Dzyaloshinskii Moriya interaction (DMI) and surface anisotropy on the skyrmion density. The relation between skyrmion annihilation threshold anisotropy Kth and DMI coefficient is evaluated. Furthermore, the skyrmion diameter dependence on these two parameters is studied. Using MOKE analysis we study the effect of external magnetic field on the skyrmion density and predict the threshold magnetic field for the transition of magnetic texture from Labriynth domains to skyrmions. These results are further supported by the MuMax simulations. The spin orbit torque SOT manipulation of skyrmion size and density is also presented for skyrmion applications in the race-track memory and neuromorphic computing. Motivated by the results, we propose a Skyrmionic neuromorphic device and using SOT switching mechanism, show its applicability as spintronic synapse and neuron. The MuMax simulations are coupled to the Non- Equilibrium Green’s Function formalism to model the neuron and synapse behavior. Finally, we conclude with the possibility of using these devices for pattern recognition and other unconventional computing paradigms.

STUDY OF NEAR-SURFACE ANISOTROPY FOR THE KLUCHI CITE BY REFRACTED WAVES SUTVEYING

Refracted waves are often used in neat-surface exploration. A limited observation system in the form of unidirectional profiles is often used. In our work, we selected an object with a known anisotropic upper part of the cross-section. The results of refracted waves processing show the anisotropy of one of the layers of the medium, the azimuthal anisotropy of which led to the observation that the refraction on its top ceases from the first arrivals, for the direction of the profile aligned with the axis of symmetry of the azimuthally anisotropic layer.

Route towards efficient magnetization reversal driven by voltage control of magnetic anisotropy

The voltage controlled magnetic anisotropy (VCMA) becomes a subject of major interest for spintronics due to its promising potential outcome: fast magnetization manipulation in magnetoresistive random access memories with enhanced storage density and very low power consumption. Using a macrospin approach, we carried out a thorough analysis of the role of the VCMA on the magnetization dynamics of nanostructures with out-of-plane magnetic anisotropy. Diagrams of the magnetization switching have been computed depending on the material and experiment parameters (surface anisotropy, Gilbert damping, duration/amplitude of electric and magnetic field pulses) thus allowing predictive sets of parameters for optimum switching experiments. Two characteristic times of the trajectory of the magnetization were analyzed analytically and numerically setting a lower limit for the duration of the pulses. An interesting switching regime has been identified where the precessional reversal of magnetization does not depend on the voltage pulse duration. This represents a promising path for the magnetization control by VCMA with enhanced versatility.

The Influence of Thickness on the Magnetic Properties of Nanocrystalline Thin Films: A Computational Approach

A study of the magnetic behaviour of polycrystalline thin films as a function of their thickness is presented in this work. The grain volume was kept approximately constant in the virtual samples. The model includes the exchange interaction, magneto-crystalline anisotropy, surface anisotropy, boundary grain anisotropy, dipolar interaction, and Zeeman effect. The thickness-dependence of the critical temperature, blocking temperature, and irreversibility temperature are presented. Surface anisotropy exerts a great influence at very low thicknesses, producing a monodomain regime. As the thickness increases, the dipolar interaction produces a coupling in-plane of single domains per grain which favours superparamagnetic states. At higher thicknesses, the effects of the in-plane anisotropy produced by dipolar interaction and surface anisotropy decrease dramatically. As a result, the superparamagnetic states present three-dimensional local anisotropies by the grain.