Dynamics of the lattice of magnetic nanodipoles with cubic anisotropy

The 5 × 5 square lattices of magnetic dipoles with cubic crystallographic anisotropy were investigated by the computer simulation method. The conditions for implementing the random orientation of lattice configurations, each of which are characterized by a certain response to the influence of an external magnetic pulse, as well as by the established regime of the oscillation of the total magnetic moment under the influence of an alternating field, are revealed. Regular vibration modes with a doubled frequency and quasi-periodic and chaotic modes are detected. The dependence of the system response on the parameters of the magnetic field pulse is studied.     

Extremely small domain in the lattice of magnetic dipoles

Lattices of magnetic dipoles with 1–4 rows are investigated. Numerical analysis reveals the smallest stationary domains formed in the lattices, necessary conditions for the formation and destruction of such domains are obtained, and the change in the magnetic moment of the lattices during domain formation is considered. It is shown that the action of an external field on one of the dipoles forming a domain is sufficient for its breaking. The lattices in which the orientational phase transition appears upon perturbation of several dipoles and propagates over the entire system are revealed.     

Ground state of magnetic dipoles on a two-dimensional lattice: structural phases in complex plasmas

We study analytically and by molecular dynamics simulations the ground state configuration of a system of magnetic dipoles fixed on a two-dimensional lattice. We find different phases, in close agreement with previous results. Building on this result and on the minimum energy requirement we determine the equilibrium lattice configuration, the magnetic order (ferromagnetic versus antiferromagnetic), and the magnetic polarization direction of a system of charged mesoscopic particles with magnetic dipole moments, in the domain where the strong electrostatic coupling leads to a crystalline ground state. Orders of magnitudes of the parameters of the system relevant to possible future dusty plasma experiments are discussed.     

Periodic structure of acicular magnetic clusters in a magnetic liquid

The behavior of magnetic clusters in a magnetic liquid placed in a circular capillary is considered. When a uniform magnetic field is applied to the system, acicular clusters grow from the sediment, being aligned with the field. The interaction of the clusters as magnetic dipoles with one another and with an external gradient magnetic field is considered theoretically. In a nonuniform symmetric magnetic field with a peak, the cluster distribution is uniform near the peak. Such a distribution is fairly stable when the magnetic field gradient is varied over certain limits. The ordered (periodic) cluster configuration is realized experimentally, and it is shown that its period can be controlled. As the magnetic field gradient exceeds a certain threshold, the clusters are redistributed, forming a multirow hexagonal array.     

Phase transitions in a two-dimensional dipole ferrimagnet

The magnetic configurations of the system of magnetic dipoles that have different values and are arranged in a staggered order on a square lattice are studied. A numerical simulation is used to study the phase transitions in the system when the mismatch between the dipoles changes. The restructuring of the magnetic configuration of the system induced by a change in the mismatch is shown to proceed via sequential second-order phase transitions between collinear and noncollinear phases. The numerical simulation results are supported by analytical calculations performed with trial functions.     

Equilibrium values and dynamics of the net magnetic moment of a system of magnetic dipoles

Equilibrium states of different systems formed by coupled spherical bodies with dipole magnetic moments have been investigated using a numerical analysis. The bistable states and the corresponding values of the net magnetic moment are determined for a number of planar and three-dimensional systems of dipoles, and the conditions providing the existence of orientational configurations of coupled dipoles involved in the bistability are analyzed. The disturbances of the magnetic moment due to the quasi-static passage of an additional dipole and the dynamic modes excited by a homogeneous alternating magnetic field and represented by periodic, quasi-periodic, and chaotic oscillations of the magnetic moment of the system are considered for several types of systems. The bifurcation diagrams of the dynamic modes are constructed, and the specific features typical of the systems under consideration are revealed.     

Regular and chaotic dynamics of a chain of magnetic dipoles with moments of inertia

The nonlinear dynamic modes of a chain of coupled spherical bodies having dipole magnetic moments that are excited by a homogeneous ac magnetic field are studied using numerical analysis. Bifurcation diagrams are constructed and used to find conditions for the presence of several types of regular, chaotic, and quasi-periodic oscillations. The effect of the coupling of dipoles on the excited dynamics of the system is revealed. The specific features of the Poincaré time sections are considered for the cases of synchronous chaos with antiphase synchronization and asynchronous chaos. The spectrum of Lyapunov exponents is calculated for the dynamic modes of an individual dipole.     

Acceleration of magnetic dipoles by a sequence of current-carrying turns

Magnetic dipoles are accelerated by a running gradient of the magnetic field that is produced by sequentially energizing current-carrying turns. Magnetic dipoles d _sh = 60 mm in diameter and l _tot = 1 m in length are gasdynamically preaccelerated to velocity V _in = 1 km/s, with which they are injected into the main accelerator. The turnover of the dipoles in the field of an accelerating pulse is prevented and focusing of dipoles is provided by directing the dipoles into a titanium tube. The weight of the dipoles is m = 2 kg, and they acquire final velocity V _fin = 5 km/s over acceleration length L _acc = 300 m.     

Dynamic multistable states in a system of magnetic dipoles

Bistable and multistable states induced by a fluctuating magnetic field in a system of four magnetic dipoles were studied numerically. The possibility of performing switchings and cyclic transitions between the different oscillatory regimes by changing field parameters is examined, along with the possibility of creating conditions under which the system is sensitive to noise signals.     

磁脉冲压缩系统的仿真研究

 分析了传统磁脉冲压缩系统的原理及缺点,对基于省去磁芯复位电路的磁脉冲压缩系统进行了介绍,为了更加深入地分析这种磁脉冲压缩系统,应用Pspice仿真分析软件建立了省去磁芯复位电路的磁脉冲压缩系统模型,计算出各级压缩过程中各元件的电压波形,及饱和变压器和磁开关的磁芯感应强度变化曲线;经测试,当负载为500 Ω纯阻性负载时,系统两端输出的负极性脉冲峰值约-27 kV,半高宽约为70 ns,下降沿约为40 ns。通过分析仿真结果与实验结果,仿真中需考虑测量探头引入的并联电容对电路的影响。     

Remagnetization of synthetic antiferromagnetic cells by a magnetic field pulse

The theory of the dynamic remagnetization of a synthetic antiferromagnetic system and magnetic points located on a magnetic substrate in an external magnetic field has been considered. The energies of the equilibrium states of the system have been calculated. The conditions of switching between equilibrium states have been described. The conditions of applicability of this theory have been formulated. It has been shown that the process of remagnetization can be implemented in an inertialess regime, escaping the long-term relaxation of the system to a new equilibrium position with the use of a special shape of the field signal. The possibility of the reduction of the switching field amplitude by varying the pulse duration has been demonstrated.     

Nonlinear response to external magnetic fields

The purpose of this paper is to study conditions under which a system of itinerate spin-$\text{1}\text{2}$ fermions might exhibit a macroscopic linear response to external magnetic fields after long times. Exact expressions are obtained for the nonlinear response of the magnetization and the total energy. We find that for a constant field there is no response (our model contains no mechanism for the relaxation of spins). For an oscillatory field there is a response in which secular terms (in the time) appear which are associated both with nonlinear terms in the external field and with contributions from the background medium. The secular terms involving the magnetic field would not be seen if one used the usual approximations of microscopic linear response theory. They give rise to new conditions which must be satisfied if the system is to exhibit a macroscopic linear response in the long-time limit.     

Excitation of the orientation transition wave and chaotic dynamics in a lattice of magnetic nanoparticles

The propagation of the front of oscillatory dynamics of magnetic moments caused by the local perturbation of the lattice along a system is studied for planar three-row lattices of magnetic nanoparticles having cubic anisotropy and coupled by the dipole interaction. The propagation of both the transition between two equilibrium planar configurations and chaotic oscillations of magnetic moments in the case of their initial orientation perpendicular to the plane of the lattice is implemented. The possibility of controlling the velocity of propagation of the orientation transition wave and its stop is revealed. The appearance of the moving front of the chaotic dynamics is found at switching on and switching off the local external field and at the action of the alternating field pulse.     

The macroscopic quantum phase of ultracold degenerate gases in the asymmetrical two-dimensional magnetic lattice

We investigate the existence of the macroscopic quantum phase in trapped ultracold quantum degenerate gases in an asymmetrical two-dimensional magnetic lattice. We show the key to adiabatically control the tunneling in the new two-dimensional magnetic lattice by means of external magnetic bias fields. In solving the system of coupled time-dependent differential equations, described here by the Boson Josephson Junctions (BJJs), we used an order parameter that includes both time-dependent variational parameters to describe the fractional population at each lattice site and the phase difference to quantify the macroscopic quantum phase signature. A dynamical oscillation of the fractional population and the phase difference at each individual lattice site is observed when solving the BJJs system.     

Lamellar-like structures in ferrofluids placed in strong magnetic fields

We consider a ferrofluid system consisting of magnetic particles interacting with a magnetic dipole–dipole interaction. We study the strong magnetic field regime where all magnetic dipoles are completely polarized in the direction of the magnetic field. We introduce a lattice gas model that serves to describe space ordering phenomena in such systems. It is found that, within mean field theory, this model predicts a second order phase transition to a phase with inhomogeneous lamellar-like ordering below a certain critical temperature.     

Mathematical Modeling of the Magnetization of a Two-Dimensional System of Magnetic Moments

Using a system that reaches its minimum energy of interaction at equilibrium, the magnetization of a discrete two-dimensional system of interacting magnetic dipoles by an external magnetic field is modeled mathematically. Magnetization curves for rectangular two-dimensional clusters of dipoles and the region of the magnetic domain are calculated.     

Excitation of phase transitions in dipole lattices

Phase transitions in hexagonal lattices with three and four rows of dipoles arising as a result of the reorientation of different sets of dipoles by the external field have been studied. The conditions of the implementation of two types of symmetric phase transitions and the asymmetric transitions, when the configurations of the system to the left and to the right of the excitation region are different, have been established. Merging of two regions of the phase transitions has been considered. Unidirectional phase transitions, in which either the left or the right phase transition front propagates from the excitation region along the lattice, have been obtained in a lattice with four rows of dipoles. The variations of the total dipole moment of the system and the energy of the dipole-dipole interaction during the phase transitions have been given.     

Ground state of finite arrays of magnetic dots in the presence of an external magnetic field

The ground state of an array of magnetic particles (magnetic dots), which are ordered in a square 2D lattice and whose magnetic moment is perpendicular to the lattice plane, in the presence of an external magnetic field has been analyzed. Such a model is applicable for sufficiently small dots with perpendicular anisotropy that are in a single-domain state and for dots in a strongly inhomogeneous vortex state whose magnetic moment is determined by the vortex core. For the magnetic field perpendicular to the system plane, the entire set of the states has been analyzed from the chessboard antiferromagnetic order of magnetic moments in low fields to the saturated state of the system with the parallel orientations of the magnetic moments of all dots in strong fields. In the presence of the border, the destruction of the chessboard order first occurs at the edges of the system, then near the extended sections of the surface, and finally expands over the entire interior of the array. The critical field at which this simplest state is destroyed is much more weakly than the value characteristic of the ideal infinite system. In contrast to this scenario, the destruction of the saturated state with decreasing field always begins far from the borders. Despite such different behaviors, the magnetic structure in the intermediate range of fields that is obtained with both increasing and decreasing field for finite arrays strongly differs from that characteristic of the ideal infinite system. The role of simple stacking faults of the magnetic dot lattice (such as single vacancies or their clusters) in the remagnetization of the system has been analyzed. The presence of such faults is shown to give rise to the appearance of local destructions of the chessboard antiferromagnetic order at fields that are much weaker than those for an ideal lattice.     

Vortex structures in planar lattices of magnetic dipoles in the presence of exchange coupling

Vortex equilibrium states of planar square lattices of magnetic dipoles in the presence of the exchange interaction have been studied. It has been shown that the vortex equilibrium configurations differ in the position of the vortex center and, correspondingly, in the magnitude and direction of the total magnetic moment of the system. In the case of the position of the vortex center in the center of the array, the total magnetic moment of the system is zero. The vortex center moves in the direction perpendicular to the field under the action of the external planar magnetic field on the system. Thus, the transitions between different equilibrium vortex configurations are implemented and the magnetic moment of the system of dipoles is controlled.