V. I. Shcheglov

Nonlinear excitation of hypersound in a ferrite plate under the ferromagnetic-resonance conditions

The nonlinear problem of excitation of hypersound by an alternating magnetic field in a normally magnetized ferrite plate is considered. The plate is characterized by uniaxial and cubic anisotropies and exhibits magnetostriction. The equations of motion and boundary conditions for the magnetization components and for the elastic displacement are obtained for the case of the arbitrary angle of the magnetization-vector precession. The obtained system is solved by means of the Runge-Kutta method. It is shown that, in the nonlinear regime, the amplitude of the excited hypersound may exceed the amplitude observed in the linear regime by three or four orders of magnitude and that, simultaneously, the range of effectively excited frequencies extends by a factor of one and a half or two.

Conducting and reflecting properties of nanometer-width films of various metals

The conducting and reflecting properties of silver, gold, nickel, iron, chromium, and titanium films are investigated. It is shown that a low conductivity of films relative to bulk materials results from the amorphism of the films and the porosity of their substrates. Two different techniques for measuring the film conductivity are compared: a contact technique and a reflection technique. It is shown that the conductivity values obtained via the two techniques are of the same order of magnitude but may differ by a factor of up to 4.

Application of the averaging method to calculation of propagation of electromagnetic radiation through thin films with different conductivities

The averaging method is used for calculation of the reflection and transmission coefficients of a 1D longitudinal electromagnetic wave and a 1D transverse electromagnetic wave that are incident along the normal onto a plane-parallel plate. The averaged electrodynamic boundary conditions are derived for an arbitrary conductivity of the plate. It is demonstrated that the averaging method enables one to simplify the calculations and resulting expressions owing to a decrease in the order of the system of equations and elimination of trigonometric functions. The error of this method is several percent for planes with thicknesses up to 0.35 of the wavelength in the medium.

Multiregime character of the nonlinear precession of the second-order magnetization under the conditions for the orientational transition

The forced nonlinear precession of the magnetization vector in the normally magnetized magnetic plate is considered under the conditions for the orientational transition. The time dependences and precession patterns of the oscillations of magnetization are presented. Five regimes of precession are revealed: small-amplitude circular precession, precession of the equilibrium position without encircling of center, undamped precession of equilibrium position with encircling of center, damped precession of equilibrium position with encircling of center, and full-scale circular precession. The transitions between the regimes are studied using the 3D model of potential. The domains of the regimes of precession are determined on the plane decay parameter-ac field amplitude. It is demonstrated that a variation in the amplitude of the ac field leads to the stepwise dynamic orientational transition from the fourth regime to the fifth regime. The recommendations for the practical applications are worked out using the results.

Nonlinear dynamics of the magnetization in a ferrite plate with magnetoelastic properties under the conditions for orientational transition

The nonlinear dynamics of the orientational phase transition of the magnetization vector in a magnetoelastic medium is analyzed. It is demonstrated that the transition involves the precession of the magnetization vector accompanied by the elastic oscillations at the same frequency. The critical constants of magnetoelasticity, elasticity, and magnetization needed for the transition are determined. It is shown that, in real materials, the magnetoelastic interaction leads to an increase in the field of transition by several or several tens of oersteds. The conditions for and the possibility of an increase in this field by hundreds of oersteds are revealed.

Asymmetric forced nonlinear precession of magnetization under the conditions for the orientational transition

The forced nonlinear precession of the magnetization vector in the normally magnetized magnetic plate is analyzed under the conditions for the orientational transition in the presence of the asymmetric static field. The excitation conditions for the precession of the equilibrium position of the magnetization vector are determined. It is demonstrated that the precession pattern of oscillations represents a large circular ring filled with small rings with the nonuniform densening whose position depends on the field asymmetry. The precession of the equilibrium position substantially depends on the degree of asymmetry. When the field exceeds a certain threshold level, the precession of equilibrium is changed by the conventional circular precession with a relatively large amplitude. The domains of existence with respect to dc and ac fields are analyzed for the precession of the equilibrium position. The dependence of the precession period on the degree of asymmetry of the dc field is studied. The main features of the above effects are qualitatively interpreted using complementary (energy and vector) models.

Forced nonlinear precession of the magnetization vector under the conditions of an orientation transition

Forced nonlinear precession of the magnetization vector in a normally magnetized magnetic plate under the conditions of an orientation transition is considered. It is shown that, in the field lower than the form demagnetization field, the variable circularly polarized field causes precession of the equilibrium position of the magnetization vector. It is demonstrated based on a vector model in which the precession period of the equilibrium position is inversely proportional to the squared amplitude of the variable field and the sine of the angle of deviation of the equilibrium position of magnetization from the constant field. It is shown that the critical parameters necessary for excitation of precession of the equilibrium position are the amplitude and frequency of the variable field. Diagrams determining domains of existence of precession of the equilibrium position for different saturation magnetization of a magnetic plate are constructed in terms of the coordinates variable field amplitude-frequency. The role of dissipation of magnetization oscillations in the determination of the critical parameters is elucidated. The features of precession in the presence of asymmetric excitation and in the presence of anisotropy in the plane of the plate are noted.

The energy characteristics of wave propagation through interfaces of media with complex parameters

With the use of the 1D wave equation as an example, the wave incidence on one interface and on two interfaces of media with arbitrary complex parameters is analyzed. It is noted that, when the energy reflection, transmission, and absorption coefficients are calculated by means of traditional techniques, their sum exceeds unity if the wave number in the first medium is complex. The complex character of the energy balance on the media interfaces is revealed. Definitions are introduced and the properties of complex reflection, transmission, localization, reactivity, and absorption are considered.

Reflection, transmission, and absorption coefficients calculated for the oblique incidence of an electromagnetic wave on a plate

The averaging and direct methods are applied to calculate the characteristics of propagation of an electromagnetic wave through a parallel-sided plate with an arbitrary conductance in the case when the wave is obliquely incident on the plate’s plane. On the basis of averaged electrodynamic boundary conditions, simplified expressions for the reflection, transmission, and absorption coefficients are derived for the arbitrary conductance of the plate. It is shown that the averaging method facilitates calculations and yields simplified expressions owing to reduction of the order of the system of equations to be solved and to elimination of exponents and trigonometric functions. The error of the averaging method relative to the error of the direct method is several percent for the incidence angle ranging from 0° to 90° and for a plate as thick as 0.35 of the wavelength in the medium.

Incidence of an electromagnetic wave onto one or two interfaces under the conditions of transition from dielectric propagation to metallic propagation

Penetration of electromagnetic waves into a medium, as well as reflection, transmission, and absorption of waves by a plate with an arbitrary conductivity, is analyzed under the condition of transition from dielectric propagation to metallic propagation. Two types of transition criteria are proposed: a criterion based on the penetration depth and a criterion based on the behavior of the reflection coefficient as a function of the plate depth. It is found that the critical values of conductivity corresponding to different types of criteria differ by a factor of 2.7 ± 0.3. High reflectivity of metal films with a thickness substantially less than the penetration depth is qualitatively explained. It is shown that the frequency of transition from the metallic type of wave propagation to the dielectric type increases as the prescribed value of the reflection coefficient decreases and the conductivity increases.