Yu. N. Nozdrin

Rectangular lattices of permalloy nanoparticles: Interplay of single-particle magnetization distribution and interparticle interaction

Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in diameter) were prepared by the method of the electron lithography. The magnetization curves were studied by Hall magnetometry with the compensation technique for different external field orientations at 4.2K and 77K. The shape of hysteresis curves indicates that there is magnetostatic interaction between the particles. The main peculiarity is the existence of remanent magnetization perpendicular to easy plain. By numerical simulation it is shown, that the character of the magnetization reversal is a result of the interplay of the interparticle interaction and the magnetization distribution within the particles (vortex or uniform).

Properties of Josephson junctions in the inhomogeneous magnetic field of a system of ferromagnetic particles

The effect of a system of ferromagnetic particles on the field-dependent critical current of a Josephson junction is experimentally studied for junctions of different geometries. For edge junctions, the effect of commensurability between the periodic magnetic field of the particles and the Josephson vortex lattice is observed. The effect manifests itself in additional maxima of the field-dependent critical current. For overlap junctions, giant (greater than sixfold) variations of the maximum critical current are observed depending on the magnetic state of the particles. The changes in the “Fraunhofer” pattern of the overlaped Josephson junctions are attributed to the formation of Abrikosov vortices due to the effect of uniformly magnetized particles. The effects revealed in the experiments can be used to analyze the inhomogeneous magnetic field of a system of submicron particles and to control the transport properties of Josephson junctions.

Microstructure and electrical properties of YBCO films

YBCO thin films were fabricated in situ on R-plane sapphire with YSZ buffer layers by inverted cylindrical magnetron sputtering. The films with , transition width , surface microwave resistance at 10 GHz and critical current density at 77 K were routinely fabricated at optimum deposition temperature and gas mixture pressure. The relations between the growth conditions, microstructure and electrical properties of YBCO thin films were investigated for a wide range of deposition temperatures. The variation of the film properties with deposition temperature is substantiated by a thorough analysis of changes in the microstructure and state of Cu-rich particles on the surface YBCO thin films. The particle formation observed in our experiment can be described using the classical thin film nucleation and growth model based on the concept of capture zones.

Tunable hot hole FIR lasers and CR masers

Abstract Basic principles for arranging population inversion and stimulated emission in hot hole systems at low temperature are discussed. Recent experimental results on observation of emissions from intersubband lasers, CR NEMAGs and CR lasers made from p-Ge are given.

Interfacial superconductivity in bilayer and multilayer IV–VI semiconductor heterostructures

A comprehensive investigation and comparison of the superconducting properties of bilayer and multilayer epitaxial heterostructures of IV–VI semiconductors exhibiting superconductivity at critical temperatures Tc⩽6.5K is carried out. The superconductivity of these systems is due to inversion of the bands in the narrow-gap semiconductors on account of the nonuniform stresses created by the grids of misfit dislocations arising at the interfaces during the epitaxial growth. It is found that Tc and the character of the superconducting transition of bilayer PbTe∕PbS heterostructures depend on the thickness d of the semiconductor layers and are directly related to the quality of the grids of misfit dislocations at the interfaces (the number and type of structural defects in the grids). Substantial differences in the behavior of bilayer sandwiches and superlattices are found. The minimum thickness d at which superconductivity appears is several times larger for bilayer than for multilayer systems. The upper crit...

Transport in GaAs/AlxGa1−xAs superlattices with narrow minibands: Effects of interminiband tunneling

The results of experimental investigations for the I–V characteristics are presented for superlattices based on GaAs/AlxGa1−xAs with thin barriers in the electric-field region with an intense interminiband tunneling. The regular features for the I–V characteristics are found in the voltage range adequate to the static positive differential conductivity in the superlattice. On the basis of calculations for the Wannier-Stark levels, it is established that the observed features are associated with the resonant tunneling between these levels belonging to quantum wells located at a distance from 6–13 superlattice periods from each other. It is noted that the similar resonant delocalization of Wannier-Stark wave functions can lead to the existence of dynamic negative differential conductivity for the laser type of an appreciable value in such superlattices.

Phase transitions in hybrid SFS structures with thin superconducting layers

Features of a phase transition between 0 and π states in superconductor/ferromagnet/superconductor (SFS) Josephson structures with thin superconducting layers and a ferromagnetic barrier are studied experimentally and theoretically. The dependence of the critical temperature Tc of a transition of the hybrid structure to a superconducting state on the thickness of superconducting layers ds is analyzed by a local method involving measurements of the nonlinear microwave response of the system by a near-field probe. An anomalous increase in the measured temperature Tc at the reduction of the thickness ds is detected and is attributed to the 0-π transition.

Stimulated radiation of optically pumped Cd xHg1 − x Te-Based heterostructures at room temperature

The experimental observation of stimulated radiation of optically pumped CdxHg1 − x Te-based heterostructures in the wavelength range of 1.4–4.5 μm is reported. In the experiments, graded-gap Cd xHg1 − x Te samples grown on GaAs and Si substrates by molecular beam epitaxy were used. Superluminescence of such structures was observed at 77–300 K under the pulsed pumping of the samples by a Nd:YAG laser at a wavelength of 1.064 μm. At room temperature, stimulated radiation was observed at wavelengths of 1.4–1.7 μm. The obtained experimental data are the first results on the observation of stimulated radiation from graded-gap Cd x Hg1 − x Te structures on Si and GaAs substrates at these wavelengths at room temperature.

Spontaneous and stimulated emission from CdxHg1−x Te semiconductor films

The experimental data on observation of spontaneous and stimulated emission from thin epitaxial CdxHg1−x Te films optically pumped by Nd: YAG laser radiation are reported. A simple theoretical model is suggested to describe the initiation of population inversion under these conditions. The parameters realized under the experimental conditions are theoretically estimated.

Induced emission from CdxHg1-xTe at a wavelength of 3400 nm at 77 K

The results are reported on the observation of the induced emission from CdxHg1−x Te samples optically pumped by a pulsed Nd:YAG laser at temperatures T<77 K. In the wave range λ∼ 3300–3600 nm, both stimulated and spontaneous emission were observed. The experimentally measured emission spectra are analyzed. The properties of the spectra from the samples are discussed and the possible applications are considered.