A.C. susceptibility and magnetisation measurements on polysulphur nitride, (SN)x

Measurements of the complex A.C. susceptibility and magnetization of crystals of polysulphur nitride, (SN)_x, are reported. At temperatures near 0.2K both the in-phase and quadrature components of the A.C. susceptibility show a marked change which can be related to the onset of superconductivity. However, changes in the sample magnetization could not be detected.     

X-ray magnetic circular dichroism and resonant photomission of V(TCNE)x hybrid magnets

Thin films of V(TCNE)x were deposited in ultrahigh vacuum using a film growth technique based on in situ chemical vapor deposition of tetracyanoethylene, TCNE, and bis-benzene vanadium, V(C6H6)2. The in situ preparation method enabled, for the first time, experimental analysis of oxygen-free films. X-ray magnetic circular dichroism measurements recorded at the V L(2,3) edge confirmed room temperature magnetic ordering. A combination of conventional photoelectron spectroscopy (PES) and resonant photoemission (RPE) measured at the V L3 edge shows that the highest occupied electronic state is V(3d) derived. The rearrangements of the TCNE- related valence electronic states observed in PES and the evidence of V(3d) and TCNE- pi(pi*) orbital overlap contained in RPE spectra, indicate that strong, covalent type bonding occurs between the vanadium and the TCNE molecules.     

Theoretical total ionization cross-sections of CH x,CF x,SiH x,SiF x ( ) and CCl 4 targets by electron impact

Total ionization cross-sections of electron impact are calculated for the molecular targets CH_x, CF_x, SiH_x, SiF_x (x = 1-4) and CCl₄ at incident energies 20-3 000 eV. The calculation is based on Complex Scattering Potential approach, as developed by us recently. This leads to total inelastic cross-sections, from which the total ionization cross-sections are extracted by reasonable physical arguments. Extensive comparisons are made here with the previous theoretical and experimental data. The present results are satisfactory except for the CF_x and SiF_x (x = 1-3) radicals, for which the experimental data are lower than most of the theories by more than 50%. Received 23 May 2002 / Received in final form 24 October 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: knjoshipura@yahoo.com     

Hyperfine interactions in (CuFe2O4)1 − x (SnO2) x (x = 0, 1, 5, 10 and 20 wt.%) nanocomposites studied by Mössbauer spectroscopy

A series of (CuFe₂O₄)_1???x (SnO₂) _x nanocomposites (x = 0, 1, 5, 10, 20 wt.%) have been prepared by urea–nitrate combustion method. The room temperature Mössbauer spectra of CuFe₂O₄ and (CuFe₂O₄)_0.99(SnO₂)_0.01 contained two sextets while remaining samples contained at least four sextets with additional doublet indicating the presence of paramagnetic phase. The variations of isomer shift, quadruple splitting and magnetic hyperfine field values were found with the addition of SnO₂.     

Mössbauer and D.C. magnetization studies of (CuFe2O4)1−x (SnO2) x (x = 0 and 5 wt.%) nanocomposites

CuFe₂O₄ nanoparticles and (CuFe₂O₄)_0.95(SnO₂)_0.05 nanocomposites were studied by XRD, Mössbauer spectroscopy and SQUID magnetometer. The XRD pattern shows the well-defined sharp peaks characterized tetragonal structure of CuFe₂O₄. The Mössbauer spectrum of CuFe₂O₄ showed ferrimagnetic structure while spectrum of (CuFe₂O₄)_0.95(SnO₂)_0.05 composite demonstrated a mixture of ferrimagnetic and paramagnetic components. The D.C. magnetization revealed that SnO₂ addition leads to overcoming the “superparamagnetic limit.”     

14MeV中子引起的Pb(n,x)203Hg, W(n,x)182Ta和W(n,x)183Ta的核反应截面测量

利用活化方法测量了14MeV中子引起的Pb(n,x)²⁰³Hg,W(n,x)¹⁸²Ta和W(n,x)¹⁸³Ta的反应截面.中子注量由监督反应⁹³Nb(n,2n)^92mNb给出,中子能量利用⁹⁰Zr(n,2n)^89m+gZr和⁹³Nb(n,2n)^92mNb反应的截面比来确定.     

A study of the microstructure of La1 − x Ca x MnO3 (x = 0.5, 0.8) solid solutions

HREM and XPD methods are used to study the microstructure of La_{1 − x} Ca _x MnO₃ perovskite-like oxides synthesized by pyrolysis of polymer-salt compositions. The XPD data show that the samples studied are single-phase solid solutions. Morphological transitions are observed in series of samples depending on the substitution parameter x. At 0 ≤ x ≤ 0.4 the samples can be characterized by rhombic symmetry (space group Pnmb); at 0.5 ≤ x ≤ 0.8 the symmetry increases to the tetragonal space group I4/mmm; at 0.9 ≤ x ≤ 1 the symmetry lowers to the monoclinic space group P1121. Heating of samples with x = 0.5 and 0.8 up to 1200°C in air does not lead to noticeable changes in the sample structure, which indicates their high thermal stability. When the La_0.2Ca_0.8MnO₃ sample is heated to 1100°C in vacuum nanocrystalline states with particle disintegration into microphases of different structures form because of a partial decomposition of the solid solution. As a result, a system of Mn₃O₄ nanoparticles appears, which is coherently bound with the perovskite phase of a defective structure.     

A study of87Zr by (α,x n) reactions

The reactions⁸⁴Sr(α,n)⁸⁷Zr and⁸⁶Sr(α, 3n)⁸⁷Zr were used to populate excited states in⁸⁷Zr. The de-excitation of these states was studied by in-beamγ-ray spectroscopy. A number of new high-spin states were observed. Lifetime measurements were also performed. The results are discussed within the frame-works of the shell model and the particle-core coupling model.     

Local atomic structure of Cu(In x Ga1−x )Se2 (x = 0.25, 0.5, and 0.75) systems for solar cells

The local atomic structure of thin surface layers of crystalline quasi-binary Cu(In _x Ga_1?x )Se₂ solid solutions was studied by SIMS and EXAFS techniques. The SIMS method showed that the elemental composition of the sample changes most significantly in thin layers at a depth of 5–10 nm; in deeper layers, the component concentrations correspond to the bulk values. The EXAFS method in the x-ray fluorescence mode showed that the results obtained are in agreement with the assumption that quaternary crystalline quasi-binary Cu(In _x Ga_1?x )Se₂ solid solutions exhibit local disorder while average long-range order is detected from x-ray diffraction data.     

Genetic stability assessment of plants regenerated from cryopreserved embryogenic tissues of Dioscorea bulbifera l. Using RAPD,biochemical and morphological analysis

Embryogenic tissues of Dioscorea bulbifera were cryopreserved using the encapsulation-dehydration technique. Genetic stability of plants regenerated from cryopreserved embryogenic tissues was assessed using molecular, biochemical and morphological analysis. The random amplified polymorphic DNA (RAPD) analysis of 60 cryopreserved-derived and 20 in vitro grown (control) plantlets showed that 10 primers produced 62 clear reproducible DNA fragment profiles. The amplification products were monomorphic for all the plantlets except one. A total of 4960 DNA fragments were obtained from this study showing no variation in RAPD profiles. The diosgenin content of cryopreserved-derived plants, analyzed using HPLC, was similar to that of control plants. Morphology and the ability to form microtuber were also found to be unaltered in cryopreserved embryo-derived plantlets. Thus, the D. bulbifera plants regenerated from cryopreserved embryogenic tissues were genetically stable at the molecular, biochemical and morphological levels.     

Magnetic properties and microstructure of x/FePt (x=Ge,GePt) bilayer

We have investigated the effect of Ge, GePt underlayers on the formation of ordered L1₀ FePt films. With Ge underlayer, the Ge₃Pt₂ compound was formed during post-annealing at 400 °C for 1 h. Interlayer diffusion of Ge and FePt layer suppress the formation of ordered L1₀ FePt phase. With Ge₂Pt₃ underlayer, the FePt film was ordered at 350 °C and the in-plane coercivity was 5.1 kOe. The ordering temperature was reduced to about 50 °C compared to the single-layer FePt film.     

Optical spectroscopy and electronic structure of the GdCu x compounds (x = 1, 2, 5)

Physics of the Solid State - Optical properties of the GdCu, GdCu2, and GdCu5 compounds with various crystal lattices have been investigated using ellipsometry in a spectral range of 0.22–16...     

A comparative study of magnetic and dielectric behaviors for La(1-x)Bi(x)Mn(1-y)Fe(y)O3 series (with x = 0.5, 0.7 and y = 0.3, 0.7)

We have carried out an extensive investigation into the effect of doping on both the A- and B-sites for the multiferroic La(0.5)Bi(0.5)Mn(0.5)Fe(0.5)O(3) in relation to its physical properties. The temperature dependent magnetization and dielectric response are determined for different percentages of Bi- and Fe-substitutions. For La(0.5)Bi(0.5)Mn(0.7)Fe(0.3)O(3), there is a prominent ferromagnetic transition T(C) around 110 K, whereas the other La(0.5)Bi(0.5)Mn(0.3)Fe(0.7)O(3) and La(0.3)Bi(0.7)Mn(0.3)Fe(0.7)O(3) phases fail to exhibit any clear transition. On the other hand, for the Fe-rich phases, the coercive field increases to 2450 Oe compared to 1720 Oe (for the Mn-rich phase). All the compositions exhibit coexistence of ferromagnetic and antiferromagnetic phases at low temperatures. The temperature dependent dielectric constant of the investigated samples varies from 32,000 to 500 at room temperature and the data has been analyzed using the universal dielectric response model.     

Morphology,Structure, and Optical Properties of SnO (x) Films

Russian Physics Journal - The paper presents the morphological, structural, and optical properties of nanostructured SnO (x) films obtained by molecular beam epitaxy using deposition of tin in an...     

The crystal and grain structure and physical properties of Bi1 − x A x FeO3 (A = La, Nd) solid solutions

High-quality ceramics were synthesized on the basis of Bi_{1 ? x} A _x FeO₃ (A = La, Nd; 0.00 ≤ x ≤ 0.20) solid solutions. Their crystal and grain structure, Mössbauer spectra, and other dielectric and magnetic characteristics were studied. It was shown that an increase in the content of A elements in the studied samples considerably enhanced their magnetic susceptibility and magnetoelectric effect.     

A computational NICS and 13C NMR characterization of the substitution patterns of C70−2x(BN)x fullerenes (x=1–25)

A density functional study has been performed to investigate the electronic and magnetic properties of BN substituted fullerenes C_70?2x(BN)_x (x=1, 2, 3, 6, 9, 12, 15, 17, 19, 21, 23 and 25) based on the NMR parameters and NICS index. The calculated ¹³C chemical shielding (CS) tensors are found to be perturbed at the first and second neighbors of the doped atoms while the other distant carbon atoms not to be influenced significantly. ¹³C Chemical shifts (δ_iso) of the second neighbors of nitrogen and boron are significantly shifted to upfield and downfield (the second neighboring effects), respectively. Besides, chemical shifts are also affected by the curvature of the corresponding sites; for example, the perturbed sites at the caps yield smaller absolute values of chemical shifts than those located at the equator. Nucleus independent chemical shifts (NICS) at the cage centers of heterofullerenes (from ?25.29 to ?8.80) demonstrate that all the substituted species are aromatic, but less than C₇₀ (?27.29). The predicted NICS values may be useful for identification of the heterofullerenes through their endohedral ³He NMR chemical shifts.