Magnetoresistance of n-GaAs at filamentary current flow

A large number of sharp structures are observed in the 4.2 K magnetoresistance of n-GaAs biased above impurity breakdown in a regime where current flow is filamentary. Most of the structures cannot be attributed to spectral properties of the semiconductor such as impact excitation of shallow donors or the magnetoimpurity effect. Experimental results give evidence that these structures are caused by a redistribution of the filamentary current flow when one filament border is swept across an imperfection in the material

Generation and reduction of nitrogen oxides in firing different kinds of fuel in a circulating fluidized bed

The processes through which nitrogen oxides are generated and reduced in the course of firing different kinds of fuel in a circulating fluidized bed are addressed. All experimental studies were carried by the authors on their own laboratory installations. To construct a model simulating the generation of nitrogen oxides, the fuel combustion process in a fluidized bed was subdivided into two stages: combustion of volatiles and combustion of coke residue. The processes through which nitrogen oxides are generated and reduced under the conditions of firing fuel with shortage of oxygen (which is one of efficient methods for reducing nitrogen oxide emissions in firing fuel in a fluidized bed) are considered. © 2013 Pleiades Publishing, Inc

Formation and reduction of nitrogen oxides in the combustion of fuels in a circulating fluidized bed

This paper is devoted to the study of the processes of forming and reducing nitrogen oxides in the combustion of fuels in a circulating fluidized bed (CFB). All experimental studies were conducted using special laboratory equipment. To develop a model of the nitrogen oxides formation, the process of fuel combustion in a fluidized bed was split into two stages: the combustion of volatiles and coke residue burning. Nitrogen formation and reduction in combustion with oxygen deficiency are discussed, which is one of the most effective ways of reducing nitrogen oxides emissions in the combustion of the fuel in the CFB. © 2014 WIT Press.International Journal of Safety and Security Engineering;International Journal of Sustainable Development and Planning;WIT Transactions on Ecology and the Environmen

Domain wall effects in ferromagnet-superconductor structures

We investigate how domain structure of the ferromagnet in superconductor-ferromagnet heterostructures may change their transport properties. We calculate the distribution of current in the superconductor induced by magnetic field of Bloch domain walls, find the ``lower critical'' magnetization of the ferromagnet that provides vortices in the superconductor

The solitary re-entrant superconductivity in the clean four-layered superconductor/ferromagnet system

The superconducting critical temperature Tc for asymmetric four-layered system ferromagnet/superconductor/ferromagnet/superconductor (F' /S/F/S') in the clean limit using the boundary value problem for Eilenberger function is investigated. An electron-electron coupling constant in ferromagnetic metals and pair amplitude changes along the F/S interfaces are taken into account. It is shown that 0- and π - phase superconducting states of pure thin F'/S/F/S' fourlayers are controlled by the magnitude and sign of electron correlations in the F and F' layers, as well as by the competition between homogeneous Bardeen-Cooper-Schneffer (BCS) pairing and inhomogeneous Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) pairing. A solitary re-entrant superconductivity for the 00π state is predicted. The results of numeric calculations allow to explain the absence of the suppression of three dimensional superconductivity in short period Gd/La superlattices

Theoretical description of the ferromagnetic π\pi -junctions near the critical temperature

The theory of ferromagnetic Pi-junction near the critical temperature is presented. It is demonstrated that in the dirty limit the modified Usadel equation adequately describes the proximity effect in ferromagnets. To provide the description of an experimentally relevant situation, oscillations of the Josephson critical current are calculated as a function of ferromagnetic layer thickness for different transparencies of the superconductor-ferromagnet interfaces.Comment: 12 pages, 4 figures, submitted to Phys. Rev.

Competition between FFLO and BCS superconducting states in clean asymmetrical ferromagnet-superconductor structures

The theory of proximity effect, based on the boundaryvalue problem for the Eilenberger function in view of the in-plane Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, is proposed for thin asymmetrical structures FS, where F is a ferromagnetic metal and S is a BCS superconductor. The dependencies of critical temperature on an exchange field of the F metal, electronic correlations in the S and F metals, and thicknesses of layers F and S are calculated for four-layered FS systems and FS superlattices. A proposed classification of states includes up to 8 different states which are characterized by phase shifts between superconducting order parameters for neighboring S(F) layers and mutual orientation of magnetizations in adjacent F layers. For asymmetrical FS systems the solitary reentrant superconductivity is predicted. It is shown that the 2D-FFLO state prevails over the BCS one on the solitary peaks wings. The real candidate for observing predicted phenomena is Gd/La system, for which we found the sign and value of the constant of electronelectron interaction in gadolinium and explain the experimentally observed absence of the suppression of three dimensional superconductivity for symmetrical Gd/La superlattice. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Hierarchy of critical temperatures in four-layered ferromagnet/ superconductor nanostructures and control devices

The four-layered F/S/F′/S′ nanostructure consisting of rather dirty superconducting (S) and ferromagnetic (F) metals is studied within the theory of the proximity effect taking detailed account of the boundary conditions. The F/S structures with four F and S layers are shown to have considerably richer physics than the F/S/F trilayer (due to the interplay between the 0 and π phase superconductivity and the 0 and π phase magnetism) and even the F/S superlattices. The extra π phase superconducting states obtained for the four-layered F/S/F′/S′ system are found to be different from the known "superlattice" states. The dependence of the critical temperatures versus the F layer thicknesses is investigated. An optimal set of parameters is determined, for which the difference between the critical temperatures for different states becomes significant, and the corresponding phase diagrams are plotted. It is proven that this system can have different critical temperatures for different S and S′ layers. A conceptual scheme of a control device with superconducting and magnetic recording channels that can be controlled separately using a weak external magnetic field is proposed on the basis of the F/S/F′/S′ nanostructure. The devices with four, five, six, and seven different states are explored. © 2006 The American Physical Society

Thermodynamic properties of ferromagnetic/superconductor/ferromagnetic nanostructures

The theoretical description of the thermodynamic properties of ferromagnetic/superconductor/ferromagnetic (F/S/F) systems of nanoscopic scale is proposed. Their superconducting characteristics strongly depend on the mutual orientation of the ferromagnetic layers. In addition, depending on the transparency of S/F interfaces, the superconducting critical temperature can exhibit four different types of dependences on the thickness of the F-layer. The obtained results permit to give some practical recommendations for the spin-valve effect experimental observation. In this spin-valve sandwich, we also expect a spontaneous transition from parallel to anti-parallel ferromagnetic moment orientation, due to the gain in the superconducting condensation energy.Comment: 20 pages, 5 figures, submitted to PR