A. M. Shutyi

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.

Equilibrium states and dynamics of the dipole moment of square arrays of dipoles

The dipole lattices in the form of 3 × 3–8 × 8 dipole square arrays have been considered. It has been shown that, after turning off the external field orienting dipoles along the edges of the array, two types of equilibrium configurations of dipole moments can exist depending on the size of the system, namely, the state symmetric with respect to the diagonal of the array and the state with the total dipole moment directed along the edges of the array. It has been found that there are differences in these types of configurations with respect to the alternating-field-induced oscillation modes of the total dipole moment of the system. The dependence of the oscillation modes on the direction of linear polarization of the alternating field has been investigated.

Equilibrium configurations and phase transitions in dipole lattices

Two-dimensional square and hexagonal lattices of magnetic dipoles with the number of rows 1–4 have been studied. Based on the numerical analysis, equilibrium stable domain configurations, including the minimum number of lattice dipoles, have been revealed; the conditions for the creation and destruction of domains have been determined; and their associated changes in the magnetic moment of the lattice and in the energy of the dipole interaction have been found. The conditions for the occurrence of phase transitions that change the configuration of the lattices have been investigated and the conditions for unidirectional propagation of the front of the phase transition have been established. A comparative analysis of different square and hexagonal lattices has been performed in terms of the specific features of the formed domains and the observed orientation phase transitions.

Stochastic high-frequency precession of magnetization in layered structures with antiferromagnetic ordering

The conditions for the appearance of self-oscillating and stochastic regimes in an exchange-coupled multilayer structure in the presence of a longitudinal high-frequency magnetic field are studied. Bifurcational diagrams are constructed that reveal various types of dynamic states of magnetic moments in the multilayer structure and transitions between these states with varying the frequency of the ac field. Attractors of stochastic oscillations are studied, and Lyapunov exponents determining the divergence of their phase trajectories are numerically calculated.

Response of a magnetic nanoparticle lattice to a magnetic field pulse near the stability boundary

The dynamic response of a system being near the stable equilibrium boundary to an external magnetic field pulse is studied for 2D lattices of magnetic nanoparticles with cubic crystallographic anisotropy. The conditions under which magnetic moment oscillations from individual dipoles propagate to the entire system are revealed. This effect results in the lattice response are significantly larger in the external pulse duration and with an amplitude rather weakly depending on initial conditions and external field parameters, the processes during which the pulse results in reorientation of only individual lattice dipoles.

Dynamics of a magnetic moment of finite dipolar lattices in the AC field

Dynamic regimes of a magnetic moment of 2 × 2, 3 × 3, and 4 × 4 square dipole lattices in the linearly and circularly polarized ac magnetic field and the perpendicular static field have been investigated. The possibility of regular and chaotic precession dynamics of the magnetic moment of the lattices has been demonstrated. A shift of the main magnetic resonance owing to the dipole–dipole interaction and additional resonances have been revealed. Quasiperiodic regimes and bistability states with a metastable chaotic attractor have been discovered.

Simulation of the dynamics of the magnetic moment of a chain of dipoles in the domain wall motion

The dynamics of the magnetic moment of a single-row chain of magnetic nanodots in the motion of a domain wall under the influence of an external static magnetic field has been investigated using the computer simulation. Oscillation modes of transverse components of the magnetic moment of the system have been revealed. It has been found that the frequency of the oscillation modes is determined by the external field and their amplitude is determined by the energy of interaction between the chain elements. These oscillations are modulated and represent a sequence of trains in a weak exchange interaction and approach single-frequency harmonic oscillations in a strong exchange interaction. When the external field deviates from the axis of the chain, the oscillations become chaotic. The dependence of the velocity of a domain wall in the chain on the exchange interaction energy and the applied field has been obtained. The effect of anisotropy on the dynamics of the system has been revealed.

Dynamics of magnetization reversal of double-row magnetic moment arrays

Double-row magnetic moment arrays coupled by dipole-dipole and exchange interactions have been studied. The processes of system excitation by a local external field affecting a fraction of magnetic moments have been considered; the conditions of partial and complete magnetization reversal of the system have been investigated. It has been shown that excitation of even two magnetic moments can cause magnetization reversal of the entire array. It has been revealed that the interface between oppositely oriented array regions can have both zero and nonzero total magnetic moments, depending on the exchange interaction parameter. The interdomain wall displacement due to the external magnetic field affecting the entire system has been considered.

Bifurcation magnetic resonance in type (100) films upon in-plane magnetization

The magnetization dynamics in (100) single-crystal films with a cubic anisotropy has been studied by numerical simulation. It has been shown that the additional (bifurcation) resonance caused by the bistability, i.e., two closely spaced equilibrium magnetization states, appears upon in-plane magnetization along the hard axis. The change in the resonance region and the corresponding dynamic regimes with a variation in the RF field or with a small detuning of the magnetizing field has been investigated. The regular and chaotic precession regimes near the bifurcation resonance have been revealed. The states of dynamic bistability have been found.

Dynamic magnetization reversal and bistable states in antiferromagnetic multilayer structures

The dynamic behavior of the magnetization under a transverse microwave field is investigated in a system of magnetic layers with cubic crystallographic anisotropy coupled through interlayer antiferromagnetic exchange interaction. An orientational phase transition is found to occur as the microwave field frequency and amplitude are varied. It is established that there is a frequency range in which several steady-state regimes of precession of magnetic moments exist. The limits of this range can be efficiently controlled both by varying the strength of the bias magnetic field and the amplitude of the microwave field.