Spin transfer torque in non-collinear magnetic tunnel junctions exhibiting quasiparticle bands: a non-equilibrium Green’s function study

A non-equilibrium Green’s function formulation to study the spin transfer torque (STT) in non-collinear magnetic tunnel junctions (MTJs) exhibiting quasiparticle bands is developed. The formulation can be used to study the magnetoresistance and spin current too. The formulation is used to study the STT in model tunnel junctions exhibiting multiple layers and quasiparticle bands. The many body interaction that gives rise to quasiparticle bands is assumed to be a s ? f exchange interaction at the electrode regions of the MTJ. The quasiparticle bands are obtained using a many body procedure and the single particle band structure is obtained using the tight binding model. The bias dependence of the STT as well as the influence of band occupancy and s ? f exchange coupling strength on the STT are studied. We find from our studies that the band occupancy plays a significant role in deciding the STT and the s ? f interaction strength too influences the STT significantly. Anomalous behavior in both the parallel and perpendicular components of the STT is obtained from our studies. Our results obtained for certain values of the band occupation are found to show the trend observed from the experimental measurements of STT.     

Forward-backward multiplicity correlations of pions and protons for different temperature events in heavy-ion interactions

A comparison of transverse momentum (P _T) distribution of the alpha particles emitted as projectile fragments from¹²C-emulsion interaction at 4.5 A GeV/c with double Maxwell-Boltzmann distribution yields two temperatures in the projectile fragmentation region, i.e., 10 MeV and 40 MeV with different reaction mechanisms, thereby giving rise to two classes of events. This work presents a detailed study of the multiplicity characteristics for pions and protons emitted in both forward and backward hemispheres in these two classes of events. The results show some interesting features in these two classes.     

Kinetics and mechanism of the oxidation of some vicinal and non-vicinal diols by tetrabutylammonium tribromide

Kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers, by tetrabutylammonium tribromide (TBATB) has been studied. The vicinal diols yield products arising out of glycol-bond fission, while the non-vicinal diols produce the hydroxycarbonyl compounds. The reaction is first-order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to diols. The reaction fails to induce the polymerization of acrylonitrile. There is no effect of tetrabutylammonium chloride on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The oxidation of [1,1,2,2-²H₄] ethanediol shows the absence of any primary kinetic isotope effect. Values of solvent isotope effect, k(H₂O)/k(D₂O), at 288 K for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutan-1-ol are 3.41, 0.98 and 1.02 respectively. A mechanism involving a glycol-bond fission has been proposed for the oxidation of vicinal diols. Non-vicinal diols are oxidised by a hydride-transfer mechanism, as they are monohydric alcohols.     

Indecomposable cycles on special quartics in ℙ<Superscript>3</Superscript>

 In this note we give an example of an indecomposable higher Chow cycle on a special family of quartics in ℙ³. The example is obtained as an extension of a cycle in the higher Chow group CH ² (K,1) of a singular Kummer surface. Received: 19 June 2002 / Revised version: 17 October 2002 Published online: 24 April 2003 Mathematics Subject Classification (2000): 14C15, 14C25, 14H10, 14H28, 14F42     

Synthesis and characterization of Sb-doped CdTe films

Antimony doped CdTe films electrodeposited in a non-aqueous bath have been characterized using in- and ex-situ techniques. Cyclic voltammetry in dark and under illumination has been used as an in-situ probe to investigate Sb incorporation. The effect of Sb-doping on the composition, structure, morphology, optical and electronic properties have also been investigated using XPS, PIXE, XRD, SEM, AFM, Optical Absorption spectroscopy, resistivity and thermoemf measurements.     

Asymmetric synthesis of the pyran antibiotic (−)-centrolobine

An expedient total synthesis of (−)-centrolobine is achieved involving asymmetric Keck allylation and stereoselective intramolecular oxy-Michael reactions as key steps in 8% overall yield.     

Crystalline inclusion compounds of tetrabenzo-18-crown-6 with uncharged organic molecules. Solid-state structure of the nitroethane complex

Tetrabenzo-18-crown-6 (1) shows distinct solid-state inclusion properties towards a number of OH-acidic, CH-acidic and low-polar uncharged organic molecules. The single crystal X-ray analysis of the inclusion complex between1 and EtNO₂ (11) is reported. Crystals are monoclinic,P2₁/c, witha=12.887(1),b=19.365(2),c=10.776(1) Å, =96.33(2)^o,D _c=1.321g cm^–1,Z=4. The host macroring has a conformation similar to a dentist's-chair. The complex is stabilized mainly by C–H...O type interactions involving the methyl group of the EtNO₂ guest molecule which is highly disordered. The nitroethane guests are trapped in channels formed by the host macrocycles. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82150 (11 pages)     

Kinetics and mechanism of oxidation of some reducing sugars by diperiodatoargentate(III) in alkaline medium

Summary The kinetics of oxidation of d-glucose, d-galactose, d-fructose, d-ribose, d-arabinose, d-xylose and 2-deoxyd-glucose by diperiodatoargentate(III) (DPA) have been investigated in alkaline medium. The order of the reaction with respect to [DPA] is unity while the order with respect to [sugar] is < 1 over the concentration range studied. The rate increases with an increase in [OH ^–] and there is a marginal decrease in the rate with an increase in [IO _inf4 ^sup– ]. No significant dependence on ionic strength was found, but the rate increases with a decreasing dielectric constant. Formic acid and the corresponding aldonic acids were detected as the products of oxidation. The participation of the open chain form of the sugar and a mechanism involving the initial formation of a complex between the enediol of the sugar and Ag^III are proposed.