I. A. Shereshevskii

Inhomogeneous states and the mechanism of magnetization reversal of a chain of classical dipoles

The inhomogeneous states (solitons) in a single chain of classical dipoles are studied numerically and analytically. An analytical solution to the problem is based on the long-wave approximation for dipole sums which holds for high magnetic fields perpendicular to the dipole chain. The analytical and numerical solutions are in reasonable agreement. The magnetization reversal is investigated by numerical simulation based on the Landau-Lifshitz stochastic equations. It is demonstrated that the magnetization reversal of a dipole chain at a finite temperature has a thermal activation nature and occurs through the formation of a stable phase nucleus (a soliton at the edge of the chain) and its growth (the motion of the soliton along the chain).

Microwave Corona Breakdown Around Metal Corners and Wedges

This paper presents an analytical, numerical, and experimental analysis of the breakdown strength of microwave gas-filled RF devices containing sharp corners and wedges. For the idealized case of a wedge-shaped geometry, it is shown that only under certain physical circumstances does the singularity and the concomitant strongly enhanced microwave field determine the breakdown strength. In particular, when diffusion is the dominating loss mechanism for the electron density, breakdown is a volumetric process, and the field singularity does not determine the breakdown threshold. In such situations, excessive accuracy in numerical calculations is not required. Conditions for volumetric and localized breakdown, respectively, are established analytically, and the validity is demonstrated by numerical simulations. Finally, the analysis is extrapolated and compared with experimentally observed breakdown thresholds in commercially available resonators of nonidealized geometry. Good agreement between theoretical predictions and experimental results is demonstrated.

Microwave Breakdown in RF Devices Containing Sharp Corners

The present work reports on an analytical, numerical, and experimental analysis of the importance of electric field singularities around sharp corners for the determination of the breakdown strength of microwave RF devices. It is shown that only under certain physical circumstances, does the singularity and the concomitant strongly enhanced microwave field determine the breakdown strength. In particular, in situations where diffusion is the dominating loss mechanism for the electron density, it is shown that breakdown is a volumetric process and that the field singularity does not determine the breakdown threshold. Conditions for volumetric and localized breakdown respectively are established analytically and the validity is demonstrated by numerical simulations. Finally an experimental investigation is made which confirms the predicted behavior and demonstrates the accuracy which is possible to obtain for the determination of the breakdown threshold

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.

Approach to electrochemical C-V profiling in semiconductor with sub-Debye-length resolution

Three methods for the determination of the detailed structure of dopant distribution in semiconductors, based on the data of electrochemical C-V profiling, are proposed. The methods give the possibility of determining a dopant distribution directly from a semiconductor surface and providing a sub-Debye length resolution. The results of numerical simulation confirm the possibility of determination of semiconductor dopant profile with nanometer depth resolution.

Magnetostatic mechanism for control of chirality of magnetization distributions

It has been shown that the magnetostatic interaction in an inhomogeneous medium leads to the removal of the chiral degeneracy of magnetic distributions. Noncollinear states of two magnetic dipoles and a helical cycloid placed over a superconducting half-space have been considered as examples. The influence of a finite penetration depth of the magnetic field on the efficiency of removal of the chiral degeneracy has been studied in the framework of the London approximation.

Numerical investigation of the effect of material parameters on magnetization reversal of a magnetic nanoparticle

The dependence of the magnetization reversal field of an elliptic submicrometer magnetic particle on the parameters of the material and sample configuration has been numerically studied. A method for calculating the magnetostatic field using the Fourier transform has been described in detail. The simulation results have demonstrated, in particular, that the normalized magnetization reversal field of a particle is independent of the exchange length at its rather large values.

Simple method for reconstructing the doping fine structure in semiconductors from C–V measurements in an electrolytic cell

A simple method is proposed for reconstructing the doping fine structure in semiconductors from capacitance-versus-voltage measurements with electrochemical etching. The method makes it possible to determine the doping profile directly from the semiconductor surface and provides resolution on scales of less than the Debye screening length. Numerical calculations confirm that the doping profile in semiconductors can be reconstructed with a resolution of several nanometers.