Факультет електроніки та інформаційних технологій (ЕлІТ)
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Item Directed transport of suspended ferromagnetic nanoparticles under both gradient and uniform magnetic fields(IOP Publishing, 2020) Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denysov, Stanislav Ivanovych; Лютий, Тарас Володимирович; Лютый, Тарас Владимирович; Liutyi, Taras Volodymyrovych; Павлюк, Максим Олександрович; Павлюк, Максим Александрович; Pavliuk, Maksym OleksandrovychThe suspended ferromagnetic particles subjected to the gradient and uniform magnetic fields experience both the translational force generated by the field gradient and the rotational torque generated by the fields strengths. Although the uniform field does not contribute to the force, it nevertheless influences the translational motion of these particles. This occurs because the translational force depends on the direction of the particle magnetization, which in turn depends on the fields strengths. To study this influence, a minimal set of equations describing the coupled translational and rotational motions of nanosized ferromagnetic particles is introduced and solved in the low Reynolds number approximation. Trajectory analysis reveals that, depending on the initial positions of nanoparticles, there exist four regimes of their directed transport. The intervals of initial positions that correspond to different dynamical regimes are determined, their dependence on the uniform magnetic field is established, and strong impact of this field on the directed transport is demonstrated. The ability and efficiency of the uniform magnetic field to control the separation of suspended ferromagnetic nanoparticles is also discussed.Item Induced magnetization and power loss for a periodically driven system of ferromagnetic nanoparticles with randomly oriented easy axes(American Physical Society, 2016) Denysov, Stanislav Ivanovych; Денисов, Станислав Иванович; Денисов, Станіслав Іванович; Лютий, Тарас Володимирович; Лютый, Тарас Владимирович; Lyutyy, Taras Volodymyrovych; Педченко, Богдан Олександрович; Педченко, Богдан Александрович; Pedchenko, Bohdan Oleksandrovych; Гришко, Олександр Миколайович; Гришко, Александр Николаевич; Hryshko, Oleksandr MykolaiovychWe study the effect of an elliptically polarized magnetic field on a system of non-interacting, single-domain ferromagnetic nanoparticles characterized by a uniform distribution of easy axis directions. Our main goal is to determine the average magnetization of this system and the power loss in it. In order to calculate these quantities analytically, we develop a general perturbation theory for the Landau-Lifshitz-Gilbert (LLG) equation and find its steady-state solution for small magnetic field amplitudes. On this basis, we derive the second-order expressions for the average magnetization and power loss, investigate their dependence on the magnetic field frequency, and analyze the role of subharmonic resonances resulting from the nonlinear nature of the LLG equation. For arbitrary amplitudes, the frequency dependence of these quantities is obtained from the numerical solution of this equation. The impact of transitions between different regimes of regular and chaotic dynamics of magnetization, which can be induced in nanoparticles by changing the magnetic field frequency, is examined in detail.Item Temperature effects on drift of suspended single-domain particles induced by the Magnus force(American Physical Society, 2018) Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denisov, Stanislav Ivanovych; Лютий, Тарас Володимирович; Лютый, Тарас Владимирович; Lyutyy, Taras Volodymyrovych; Рева, Владислав Валерійович; Рева, Владислав Валериевич; Reva, Vladyslav Valeriiovych; Єрмоленко, Андрій Сергійович; Ермоленко, Андрей Сергеевич; Yermolenko, Andrii SeriyovychWe study the temperature dependence of the drift velocity of single-domain ferromagnetic particles induced by the Magnus force in a dilute suspension. A set of stochastic equations describing the translational and rotational dynamics of particles is derived, and the particle drift velocity that depends on components of the average particle magnetization is introduced. The Fokker-Planck equation for the probability density of magnetization orientations is solved analytically in the limit of strong thermal fluctuations for both the planar rotor and general models. Using these solutions, we calculate the drift velocity and show that the out-of-plane fluctuations of magnetization, which are not accounted for in the planar rotor model, play an important role. In the general case of arbitrary fluctuations, we investigate the temperature dependence of the drift velocity by numerically simulating a set of effective stochastic differential equations for the magnetization dynamics.Item Temperature Dependence of the Drift Velocity of Ferromagnetic Nanoparticles in Viscous Fluids(Sumy State University, 2018) Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denysov, Stanislav Ivanovych; Yermolenko, A.S.; Bosenko, V.S.In Refs. [1, 2], the deterministic theory of drift of single-domain ferromagnetic nanoparticles in viscous fluids, which occurs due to the Magnus effect, has recently been developed and numerically confirmed. Here, we present analytical and numerical results obtained within the stochastic theory on the influence of temperature on the drift velocity.Item Minimal Set of Equations for Drift of Ferromagnetic Nanoparticles Induced by Magnetic Fields in Fluids(Sumy State University, 2018) Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denysov, Stanislav Ivanovych; Лютий, Тарас Володимирович; Лютый, Тарас Владимирович; Liutyi, Taras Volodymyrovych; Kvasnina, O.V.; Yermolenko, A.S.Recently, it has been established that ferromagnetic nanoparticles subjected to a periodic force and a non-uniformly rotating magnetic field can drift in a viscous fluid due to the Magnus effect. Because the drift phenomenon is of interest for applications such as particle separation, in this work we present a minimal set of equations for describing this phenomenon when a periodic force is induced by a gradient magnetic field.Item Energy Spectrum of a Particle in an Infinitely Deep Potential Well with a Non-flat Bottom(Sumy State University, 2018) Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denysov, Stanislav Ivanovych; Husachenko, A.V.; Ryzhkov, O.S.To model the quantum behavior of current carriers in heterogeneous nanostructures, different potential wells and barriers are widely used. Of particular interest are those (including artificial ones) for which the corresponding Schrödinger equation can be solved exactly. One of them is an infinitely deep potential well with a flat bottom defined as 𝑈(𝑥) = ∞ for |𝑥| ≥ 𝑎 and 𝑈(𝑥) = 0 for |𝑥| < 𝑎. Here, we report on exact solution of the stationary Schrödinger equation in the case, when the potential bottom is non-flat, i.e., 𝑈(𝑥) = −𝑓𝑥 (𝑓 > 0) if |𝑥| < 𝑎. Physically, this means that the particle in the well is subjected to an external force 𝑓 in the 𝑥-direction.Item Influence of Spin-polarized Current on Spin Waves in Ferromagnets(Sumy State University, 2018) Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denysov, Stanislav Ivanovych; Shchotkin, V.V.It has been recently established that spin-polarized current can have a direct influence on the magnetization dynamics in conducting ferromagnets. This effect has quantum origin and is of great interest from both fundamental and applied viewpoints. In particular, it can be useful for developing magnetoresistance random access memory, magnetic logic elements and microwave devices, to name a few.Item Master Equation for a Localized Particle Driven by Poisson White Noise(Sumy State University, 2018) Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denysov, Stanislav Ivanovych; Bohopolskyi, V.M.; Shypilov, N.E.Fluctuations in nanosystems play an important role in forming their electric, magnetic, thermal and other properties. Usually, due to the central limit theorem of probability theory, these fluctuations obey Gaussian statistics. However, in some cases, e.g., when the system is subjected to Poisson white noise, that is a random sequence of 𝛿-pulses, the system fluctuations are not Gaussian. Here, we derive the corresponding equation for the probability density function 𝑃(𝑥, 𝑡) of the system parameter 𝑥(𝑡) interpreted as a particle coordinate within an impenetrable box.Item Langevin equations for suspended magnetic particles drifting under the Magnus force(Sumy State University, 2017) Pedchenko, B.O.; Yermolenko, A.S.; Denisov, Stanislav Ivanovych; Денисов, Станіслав Іванович; Денисов, Станислав ИвановичThe Magnus effect, i.e., dependence of the trajectory of a body on its rotation, is widely used in sport, science and technical applications. Recently we have shown [1, 2] that due to the Magnus force the single-domain ferromagnetic particles, which are suspended in a viscous fluid and subjected to a harmonic driving force and a non-uniformly rotating magnetic field, can perform drift in a preferred direction. This result has been obtained within the deterministic approach when thermal fluctuations, leading to translational and rotational Brownian motion of particles, are ignored. Our estimations show [2] that it is possible for relatively large particles (> 102 nm). Therefore, to study the drift phenomenon for smaller particles, it is necessary to account for these fluctuations in basic equations.Item New laws of anomalous superslow diffision(Sumy State University, 2013) Бистрик, Юрій Сергійович; Быстрик, Юрий Сергеевич; Bystryk, Yurii Serhiiovych; Денисов, Станіслав Іванович; Денисов, Станислав Иванович; Denysov, Stanislav IvanovychIn the present work we concern ourselves with the question of the existence of other anomalous diffusion laws generated by CTRWs. Based on our recent results on the asymptotic behavior of CTRWs with superheavytailed waiting time and asymmetric heavy-tailed jump length distributions (whose first and/or second moments are infinite), we find the conditions of superslow diffusion and establish corresponding laws by analytical methods and provide a verification using numerical simulation.
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