AbstractSpecificities of spin wave focusing in EuO and EuS crystals are studied. It is shown that spin wave focusing is absent in the long-wave approximation: it is observed only for wave vectors in the second half of the Brillouin zone ( aq $$ \gtrsim $$ π, where a is the lattice constant and q is the magnitude of the wave vector). It was found that, for EuO and EuS crystals, the directions of spin wave focusing differ due to the different signs of the exchange integrals responsible for the exchange interaction of the magnetic moment with the second neighbors. The directions along which a magnon caustic is formed are determined.

Abstract—Features of focusing spin waves in ferromagnets with magnetic moment exchange interaction with the closest neighbors and second neighbors are explored. It is shown that in the long-wave approximation, no spin wave focusing occurs: it is observed only in the wavevectors in the second half of the Brillouin zone (at aq ≥ π/2, where a is the lattice constant, q is the value of wavevector). Additionally, it is shown that magnons in such system are focused along directions [110], and are defocused in directions [100]. It is found that the external magnetic field and the magnetic anisotropy field do not cause changes in directions of magnon focusing. When the parameter of exchange interaction with the second neighbors near directions [110] and [111] is negative, magnons form a caustic, near which the intensity of the spin-wave field surges.

Abstract —Features of focusing spin waves in ferromagnets with magnetic moment exchange interaction with the closest neighbors and second neighbors are explored. It is shown that in the long-wave approximation, no spin wave focusing occurs: it is observed only in the wavevectors in the second half of the Brillouin zone (at aq ≥ π/2, where a is the lattice constant, q is the value of wavevector). Additionally, it is shown that magnons in such system are focused along directions [110], and are defocused in directions [100]. It is found that the external magnetic field and the magnetic anisotropy field do not cause changes in directions of magnon focusing. When the parameter of exchange interaction with the second neighbors near directions [110] and [111] is negative, magnons form a caustic, near which the intensity of the spin-wave field surges.

AbstractMagnetization dynamics in spheroidal ferromagnetic samples is studied theoretically. It is shown that, in a magnetostatic approximation, electronic-nuclear magnetostatic modes with a discrete spectrum of eigen oscillations exist in such samples. The structure and the field dependence of the frequencies of these oscillations are substantially dependent on the parameter of the spheroid shape that is the ratio of it’s axes and also on the external magnetic field value. In a certain region of values of these parameters, the dependence of the eigenfrequencies of the system on them becomes nontrivial. The external field strength and the sample shape determine not only the eigenfrequencies in the system, but also the number of the eigenmodes. In addition, for each of the eigenmodes, there exists a “forbidden” region of magnetic fields and shape parameters in which this mode cannot be observed.

The structure of the domain wall in a magnetically uniaxial ferromagnetic film placed in an external electric field has been studied. It has been shown that the domain wall has a complex twisted structure whose characteristics (thickness, profile, and limit velocity of steady motion) depend on the film thickness, quality factor, and external electric field. The effect of the electric field on the domain wall is caused by inhomogeneous magnetoelectric coupling taking place in domain walls with a twisted structure.

The micromagnetic structure of the domain wall (DW) with periodically distributed horizontal Bloch lines in a ferromagnetic film in an external electric field has been studied. The effect of the electric field on the internal DW micromagnetic structure is caused by inhomogeneous magnetoelectric coupling. Possible scenarios of the DW internal structure transformations implemented with varying the electric fields strength have been analyzed in detail. For each scenario, static characteristics of the system, such as the energy, DW profile, DW effective thickness, and electric polarization have been calculated.

In this paper we propose a method to generate pure dark solitons by a periodic external field with a slowly varying frequency, which allows to control amplitude of the excited solitons and period of soliton trains. Our approach to generate dark solitons is based on the effect of autoresonance when the excited wave is phase-locked by the drive after the crossing the resonance. The resonant frequency and the threshold condition on the amplitude of the driving were found.

Проанализированы статические и динамические свойства магнетика с анизотропией типа “легкая плоскость” со спиральной магнитной структурой, находящегося во внешнем магнитном поле. Рассчитан энергетический спектр и амплитуды линейных спиновых возбуждений в рассматриваемой структуре. Проведен детальный анализ особенностей их полевых зависимостей. Получены тензоры локальной и интегральной динамических магнитных восприимчивостей. Рассчитаны спин-волновые вклады в температурно-полевую зависимость намагниченности. Обсуждается возможность приложения полученных результатов к исследованию ЯМР в магнетиках со спиральной магнитной структурой.

Настоящая работа посвящена известному ученому в области физики магнитных явлений, члену-корреспонденту РАН Евгению Акимовичу Турову. Статья включает анализ актуальных вопросов физики магнетизма начала XX1 века, а также вклада Е.А. Турова и созданной им школы в науку о магнетизме. В 2014 г. исполняется 90 лет со дня рождения Евгения Акимовича, и данная статья приурочена к этой памятной дате. В ней приводится список основных трудов ученого.

Исследованы особенности теплоемкости, намагниченности и магнитной восприимчивости кирального магнетика, обусловленные магнонным вкладом. Показано, что локальные теплоемкость и намагниченность являются функциями координаты, и их поведение зависит от величины приложенного магнитного поля. Исследованы температурные зависимости этих величин. Сравниваются результаты приближенных аналитических и численных расчетов.

Static and dynamic properties of a magnet with an easy-plane anisotropy with a spiral magnetic structure placed in an external magnetic field have been analyzed. The energy spectrum and the amplitudes of linear spin excitations have been calculated for this structure. Their field dependences have been analyzed in detail. Tensors of the local and integral dynamic magnetic susceptibilities have been derived. The spin-wave contributions to the temperature-field dependence of the magnetization have been calculated. The possibility of applying the results obtained to the study of NMR in magnets with a spiral magnetic structure is discussed.

Исследованы особенности ядерного магнитного резонанса (ЯМР) в ферромагнетике с кристаллографической магнитной анизотропией типа “легкая плоскость”, помещенном в постоянное магнитное поле. Симметрия магнетика допускает существование взаимодействия Дзялошинского–Мория, приводящего к образованию нового основного состояния – солитонной решетки (спиральной структуры). В рамках спин-волнового приближения рассчитаны базовые локальные характеристики ЯМР этой структуры: частота резонанса, коэффициент усиления и уширение линии. Исследованы их полевые зависимости. Рассчитана интегральная магнитная резонансная восприимчивость электронно-ядерной спиновой системы, проведен анализ особенностей формы линии ЯМР поглощения. Решена задача об эволюции линии ЯМР поглощения при изменении величины внешнего магнитного поля. Обсуждается возможность экспериментального обнаружения и исследования структурных и динамических особенностей спиральной магнитной структуры с помощью ЯМР.

The formation of Fe layers in Fe/Cr superlattices has been studied by Mössbauer spectroscopy. It is established that magnetic clusters, which appear in the initial stage of formation of Fe layers and impart superparamagnetic properties to these nanostructures, involve not only Fe atoms constituting a core of the three-dimensional cluster but also the neighboring Cr atoms exchange-coupled to this core. The thicknesses of Fe layers corresponding to their transition from superparamagnetic to ferromagnetic state are determined.

In the framework of an extended Boussinesq equation, a new class of localized two-parameter states has been obtained and studied in detail. It has been shown that three principal parameters of the problem (elasticity moduli describing quadratic and cubic nonlinearities and dispersion, which vary over a wide range) determine the necessary conditions of their formation. At the plane of two parameters (“pedestal” of a localized state and its width), two regions where the conditions of formation of these distributions are satisfied have been constructed. The results obtained can be used for the interpretation of experimental data on the structure and dynamic properties of localized acoustic states, including solitons in solids.

Nonlinear dynamic models taking into account magnetostatic interactions, size effects, and higher order linear and nonlinear dispersions in layered ferromagnet-dielectric-metal structures have been constructed. Analytical and numerical algorithms for analysis of scenarios of emergence and evolution of quasisolitons, as well as the processes of their interaction, transformation, and decay under the action of external monochromatic radiation, have been developed.

Structure of nonlinear stationary states of the extended nonlinear Schrödinger equation (ENSE) with a source has been analyzed with allowance for both third-order and nonlinearity dispersion. A new class of particular solutions (solitary waves) of the ENSe has been obtained. The scenario of the destruction of these states under the effect of an external perturbation has been investigated analytically and numerically. The results obtained can be used to interpret experimental data on the weakly nonlinear dynamics of the magnetostatic envelope in heterophase ferromagnet-insulator-metal, metal-insulator-ferromagnet-insulator-metal, and other similar structures and upon the simulation of nonlinear processes in optical systems.

The dynamics of a magnetization reversal nucleus in a magnetic field has been investigated. The existence of slow and fast magnetization waves, describing the propagation of pulsations and growth of a magnetization reversal nucleus, is shown.