Twisted domain walls and skyrmions in perpendicularly magnetized multilayers

We present an analytical theory to describe three-dimensional magnetic textures in perpendicularly magnetized magnetic multilayers that arise in the presence of magnetostatic interactions and the Dzyaloshinskii-Moriya interaction (DMI). We demonstrate that domain walls in multilayers develop a complex twisted structure, which persists even for films with strong DMI. The origin of this twist is surface-volume stray field interactions that manifest as a depth-dependent effective field whose form mimics the DMI effective field. We find that the wall twist has a minor impact on the equilibrium skyrmion or domain size, but can significantly affect current-driven dynamics. Our conclusions are based on the derived analytical expressions for the magnetostatic energy and confirmed by micromagnetic simulations.Comment: 30 pages, 8 figure

Biological wastewater treatment in aeration tanks

Development of mathematical model for prediction of output parameters of aeration tank with account of dissolved oxygen, oxygen , sludge, substrate transfer and biological treatment. The mathematical model may be used in predicting the effectiveness of aeration tank under different regimes of work

Full phase diagram of isolated skyrmions in a ferromagnet

Magnetic skyrmions are topological quasi particles of great interest for data storage applications because of their small size, high stability, and ease of manipulation via electric current. Theoretically, however, skyrmions are poorly understood since existing theories are not applicable to small skyrmion sizes and finite material thicknesses. Here, we present a complete theoretical framework to determine the energy of any skyrmion in any material, assuming only a circular symmetric 360$^\circ$ domain wall profile and a homogeneous magnetization profile in the out-of-plane direction. Our model precisely agrees with existing experimental data and micromagnetic simulations. Surprisingly, we can prove that there is no topological protection of skyrmions. We discover and confirm new phases, such as bi-stability, a phenomenon unknown in magnetism so far. The outstanding computational performance and precision of our model allow us to obtain the complete phase diagram of static skyrmions and to tackle the inverse problem of finding materials corresponding to given skyrmion properties, a milestone of skyrmion engineering

Simplified model to simulate the aeration tank work

Построена математическая модель, позволяющая в течение нескольких секунд оценить эффективность работы аэротенка с учетом влияния на процесс биологической очистки сточных вод следующих параметров: концентрация активного ила, растворенного в воде кислорода, концентрации загрязняющего вещества в сточной воде. Выполнена программная имплементация разработанной численной модели.Побудовано математичну модель, що дозволяє протягом декількох секунд оцінити ефективність роботи аеротенку з урахуванням впливу на процес біологічного очищення стічних вод наступних параметрів: концентрація активного мулу, розчиненого у воді кисню, концентрації забруднюючої речовини в стічній воді. Виконана програмна імплементація розробленої чисельної моделі.A mathematical model is constructed that allows to estimate the efficiency of the aeration tank in a few seconds, taking into account the influence of the following parameters on the process of biological treatment of wastewater: concentration of activated sludge, dissolved oxygen in water, concentration of pollutant in sewage. The program implementation of the developed numerical model has been completed

Моделирование работы аэротенка

Разработана численная модель для оценки эффективности работы аэротенка. Модель основана на применении уравнений гидродинамики и массопереноса. При моделировании очистки сточных вод в аэротенке учитываются биологические процессы. Для численного интегрирования моделирующих уравнений используется метод конечных разностей. Разрабо- танная численная модель позволяет учитывать геометрическую форму аэротенка. Представлены результаты вычислительного эксперимента.Розроблена численна модель для оцінки ефективності роботи аэротенка. Модель заснована на застосуванні рівнянь гідродинаміки та масопереносу. При моделюванні очищення стічних вод у аеротенці враховуються біологічні процеси. Для чисельного інтегрування моделюючих рівнянь використовується метод кінцевих різниць. Розроблена численна модель дозволяє враховувати геометричну форму аеротенка. Представлені результати обчислювального експерименту.The results of the study, dedicated to the process of biological treatment in aeration tank

Investigation of the Dzyaloshinskii-Moriya interaction and room temperature skyrmions in W/CoFeB/MgO thin films and microwires

Recent studies have shown that material structures, which lack structural inversion symmetry and have high spin-orbit coupling can exhibit chiral magnetic textures and skyrmions which could be a key component for next generation storage devices. The Dzyaloshinskii-Moriya Interaction (DMI) that stabilizes skyrmions is an anti-symmetric exchange interaction favoring non-collinear orientation of neighboring spins. It has been shown that material systems with high DMI can lead to very efficient domain wall and skyrmion motion by spin-orbit torques. To engineer such devices, it is important to quantify the DMI for a given material system. Here we extract the DMI at the Heavy Metal (HM) /Ferromagnet (FM) interface using two complementary measurement schemes namely asymmetric domain wall motion and the magnetic stripe annihilation. By using the two different measurement schemes, we find for W(5 nm)/Co20Fe60B20(0.6 nm)/MgO(2 nm) the DMI to be 0.68 +/- 0.05 mJ/m2 and 0.73 +/- 0.5 mJ/m2, respectively. Furthermore, we show that this DMI stabilizes skyrmions at room temperature and that there is a strong dependence of the DMI on the relative composition of the CoFeB alloy. Finally we optimize the layers and the interfaces using different growth conditions and demonstrate that a higher deposition rate leads to a more uniform film with reduced pinning and skyrmions that can be manipulated by Spin-Orbit Torques

Field-free deterministic ultra fast creation of skyrmions by spin orbit torques

Magnetic skyrmions are currently the most promising option to realize current-driven magnetic shift registers. A variety of concepts to create skyrmions were proposed and demonstrated. However, none of the reported experiments show controlled creation of single skyrmions using integrated designs. Here, we demonstrate that skyrmions can be generated deterministically on subnanosecond timescales in magnetic racetracks at artificial or natural defects using spin orbit torque (SOT) pulses. The mechanism is largely similar to SOT-induced switching of uniformly magnetized elements, but due to the effect of the Dzyaloshinskii-Moriya interaction (DMI), external fields are not required. Our observations provide a simple and reliable means for skyrmion writing that can be readily integrated into racetrack devices

Skyrmion Hall Effect Revealed by Direct Time-Resolved X-Ray Microscopy

Magnetic skyrmions are highly promising candidates for future spintronic applications such as skyrmion racetrack memories and logic devices. They exhibit exotic and complex dynamics governed by topology and are less influenced by defects, such as edge roughness, than conventionally used domain walls. In particular, their finite topological charge leads to a predicted "skyrmion Hall effect", in which current-driven skyrmions acquire a transverse velocity component analogous to charged particles in the conventional Hall effect. Here, we present nanoscale pump-probe imaging that for the first time reveals the real-time dynamics of skyrmions driven by current-induced spin orbit torque (SOT). We find that skyrmions move at a well-defined angle {\Theta}_{SH} that can exceed 30{\deg} with respect to the current flow, but in contrast to theoretical expectations, {\Theta}_{SH} increases linearly with velocity up to at least 100 m/s. We explain our observation based on internal mode excitations in combination with a field-like SOT, showing that one must go beyond the usual rigid skyrmion description to unravel the dynamics.Comment: pdf document arxiv_v1.1. 24 pages (incl. 9 figures and supplementary information

Первичные преобразователи концентрации токсичных газов в воздухе вдоль автомагистралей населенных пунктов

Розглянуто результати створення і впровадження первинних перетворювачів (ПП) концентрації токсичних газів у повітрі вздовж автомагістралей населених пунктів.Are considered creation and implementation of the primary concentration transfers (sensing devices) of toxic gases in mid air of populated locality along motorways.Рассмотрены результаты создания и внедрения первичных преобразователей (ПП) концентрации токсичных газов в воздухе вдоль автомагистралей населенных пунктов

Этапы перехода в систему государственного аудита в Республике Беларусь

В настоящее время в развитых странах в той или иной степени функционирует государственный аудит. В материале рассматриваются этапы перехода в систему государственного аудита в Республике Беларусь