Resistive properties of La2 ? x Sr x CuO4 low-dopped cuprates in the antiferromagnetic state at low temperatures

The nonlinear dependence of conductivity and negative differential resistance of ceramic samples of La_{2 ? x} Sr _x CuO₄ in the antiferromagnetic state is revealed. The possible influence of a spatially inhomoge-neous distribution of strontium impurities on the low-temperature behavior of conductivity is discussed.     

Thermal stability of modified chromium dioxide nanopowders with various magnetic properties obtained by hydrothermal route

Melt modification is a method commonly used when enhancing mechanical and microstructural properties of various alloys. The addition of heterogeneous nucleation sites generally refines the given microstructure and enhances the toughness of the material. Ferroalloys based on high-melting elements require a longer incubation time in the melt which makes them liable candidates for modification agents. A research on the effect of melt modification was conducted on an indefinite chill cast iron alloy commonly used for working layers in rolls. The goal of the research was to determine the effect of ferrovanadium and ferrotungsten melt treatment with the use of thermal analysis along with thermodynamic modelling using the CALPHAD approach. The results show a decrease in the measured liquidus temperature of the modified alloy along with a possible second eutectic reaction hidden inside the main graphite/cementite eutectic reaction. Scanning electron microscopy revealed small and evenly distributed MC type carbides rich in V with W and other carbide-forming elements. The results presented in this work enable a better understanding of the impact melt modification has on the development of microstructure and subsequently the improvement in mechanical properties of the alloy.     

Radiative recombination of excitons in semiconductors at high excitation intensities

The shape of the exciton luminescence band of the gaseous phase of free excitons in crystal Si is investigated under high level excitation. Only the exciton-exciton interaction is considered and the influence of collisions of excitons with phonons and electrons is not taken into account. The theoretical shape of the exciton luminescence band qualitatively agrees with experiment. The process of the radiative Auger-recombination of two indirect excitons without the participation of phonons is studied in Ge and Si. The expression for the frequency and temperature dependence of the probability of radiation is obtained. The band has the asymmetrical Gaussian form with the steep short-wave tail. The predicted luminescence band in Ge is shifted at the long-wavelength side from the well-known exciton luminescence bands with participation of the phonons. The selection rules for the probability amplitude of the process under consideration are obtained.     

The role of local environment in charge ordering of perovskite-like oxides

The properties of magnetically diluted perovskite-like complex oxides La_{2 ? x} A _x MO₄ (M is Fe or Mn and A is Sr or Ba) have been studied. Charge and spin ordering is suggested to be interrelated with the local structural characteristics and the electronic structure of nanoclusters of transition elements found in the ceramics studied.     

The spin state of manganese atoms in Sr2MnSbO6 complex oxides

The magnetic susceptibility of Sr₂MnSbO₆ solid solutions in a Sr₂AlSbO₆ diamagnetic diluent is investigated. Variation in the magnetic characteristics with temperature and the solution concentration indicates the coexistence of two spin states of manganese atoms: low-spin and high-spin. The possibility of spin transitions is due to temperature-dependent local distortions in the crystal structure of the solutions.     

Magnetic Ordering of Iron-Oxygen and Iron-Organic Nanostructures on a Diamagnetic Matrix

The study of the magnetic susceptibility of iron-oxygen quasi-two-dimensional nanostructures (nanolayers) showed that the dependence of the susceptibility on the number of iron-oxygen groups deposited on a silica support is nonmonotic. It was found that a two-dimensional magnetization region arises at a certain number of iron-oxygen groups in the surface layer of the support.     

Optical exciton Stark effect and quantum beats at exciton quasienergy levels in quantum wells

The optical Stark effect and quantum beats in a GaAs/AlGaAs quantum well are investigated theoretically for the case when the first two electron size-quantization levels are mixed dynamically by a high-intensity CO₂ laser pulse polarized perpendicular to the plane of the quantum well. The quasienergy spectrum of heavy-hole excitons and the ratio between the probabilities of exciton transition with and without a strong electromagnetic field are obtained. The time-dependent intensity of absorption of the sensing light is determined. It exhibits quantum beats at twice the electron Rabi frequency. Fiz. Tverd. Tela (St. Petersburg) 39, 1291–1294 (July 1997)     

State of atoms of the transition group elements in dilute solid solutions based on LiMO2 (M = Sc, Ga, Al): IV. Magnetic susceptibility of the LiMxGa1?xO2 solid solutions (M = Cr, Cu)

Magnetic dilution of LiMO₂ complex oxides (M = Cu, Cr) was studied. The results obtained were correlated to the physical and chemical properties of two-dimensional perovskite-like oxides containing copper and lithium. Various valence and spin states of copper and chromium were found, which are associated with essential anisotropy of the local surrounding of a transition element and with the influence of lithium atoms on the electron state of nanoclusters containing these elements. Original Russian Text ? N.P. Bobrysheva, A.A. Selyutin, I.A. Grigorov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 4, pp. 538–541. For communication III, see [1].     

Influence of iron ions on morphology and magnetic and electrical properties of vanadium dioxide

Russian Journal of General Chemistry -