Exchange bias in spin-engineered double superlattices

Exchange bias has been observed in sputtered magnetic double superlattices which consist of a ferromagnetically coupled superlattice grown on an antiferromagnetically (AF) coupled superlattice. This system exhibits a parallel domain wall, a spin flop transition, and exchange bias when the anisotropy is large in the AF block. This work shows that neither the domain wall nor the spin flop are directly related to exchange bias but that the anisotropy is essential.     

Charged-particle pseudorapidity density distributions from Au+Au collisions at sqrt[s(NN)]=130 GeV

The charged-particle pseudorapidity density dN(ch)/d eta has been measured for Au+Au collisions at sqrt[s(NN)] = 130 GeV at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the 3% most-central Au+Au collisions for /eta/相似文献   

Phase equilibria,thermal analysis,and reactivity of tin tungsten bronzes and related phases

Crystal chemistry and phase relations of the bronze forming region of the SnWO system have been investigated. Above 780°C the tin bronzes Sn_xWO₃ are shown to be thermally unstable and an equilibrium diagram is established at 700°C which shows that the composition limits of the tetragonal phase are 0.21 ? x ? 0.29. Below x = 0.21 a series of single and two phase regions containing orthorhombic bronzes exists for which the composition limits have been established. In the range 0.29 ? x ? 0.76 the system comprises the tetragonal bronze, Sn₂W₃O₈ and SnWO₄, while above 0.76 there is no bronze, only Sn₂W₃O₈, SnWO₄ and free Sn. The phase Sn₂W₃O₈ has been isolated and shown to have a hexagonal unit cell, a = 7.696 Å, c = 18.654 Å. The evidence of differential thermal analysis and X-ray studies suggests that this hexagonal phase arises from the decomposition of the tungsten bronze phase and is itself decomposed to cubic SnWO₄ above 700°C. Small thermal effects observed in the DTA scans of tin-containing tetragonal bronzes are interpreted in terms of an order-disorder phenomenon arising from asymmetric tunnel occupancy by Sn²⁺ ions caused by the presence of the lone pair of electrons. Hydrogen reduction of Sn_xWO₃ has been shown to result in complete removal of oxygen, producing Sn + α-W in the range 600–850°C. Some activation energy data are given for the reduction process.     

Advances in the understanding of multiferroics through soft X-ray diffraction

The magneto-electric multiferroic TbMn₂O₅ has a complex magnetic structure in three different magnetically ordered phases. We have determined the nature of the induced magnetic order on the oxygen sites in the commensurate magnetic phase through full linear X-ray polarisation analysis at the oxygen K edge. This has been achieved rotating the linear polarisation of the incident beam at the source, and using multilayers to analyse the polarisation state of the scattered X-ray beam. We have confirmed that the anisotropy of the magnetic scattering at the oxygen edge is consistent with the anisotropy of the manganese magnetic structure.     

Step interactions on Pt(111) vicinal surfaces determined by grazing incidence X-ray diffraction: Influence of the step orientation

We have studied the step–step interactions on the Pt(997) vicinal surface. Grazing incidence X-ray diffraction (GIXD) allowed us to measure the elastic atomic relaxations near the surface due to the steps. By means of the model of buried elastic dipoles, within the framework of anisotropic linear elasticity (ALE) calculations, the surface stress of Pt(111), and the elastic interaction between steps are deduced. The values so-obtained are compared to the values previously measured on the Pt(779) surface with the same technique. The comparison shows the strong influence of step geometry on step interactions.     

Stereocontrolled total synthesis of (+)-concanamycin F: the strategic use of boron-mediated aldol reactions of chiral ketones

A highly stereocontrolled total synthesis of the 18-membered macrolide (+)-concanamycin F, a potent inhibitor of vacuolar ATPases, is described that proceeds in 5.8% yield over 26 steps. The three key fragments, C1-C13 vinyl iodide, C14-C22 vinyl stannane and C23-C28 aldehyde, were efficiently constructed using asymmetric boron-mediated aldol reactions of appropriate chiral ketone building blocks. The nature of the silyl protection of the C7/C9 hydroxyls proved to be critical for achieving macrocyclisation, with TES ethers being superior to a cyclic silylene derivative. Following a Liebeskind-Stille cross-coupling reaction between the C1-C13 vinyl iodide and C14-C22 vinyl stannane fragments to assemble the (12E,14E)-diene, a modified Yamaguchi macrolactonisation delivered the requisite 18-membered macrocyclic core. This advanced intermediate was also obtained by an alternative sequence using an esterification step to connect the C1-C13 and C14-C22 fragments followed by a Pd-catalysed intramolecular Stille reaction to install the (12E,14E)-diene. Conversion of the resulting macrocyclic intermediate into a methyl ketone then enabled a highly diastereoselective Mukaiyama aldol coupling of the derived silyl enol ether with the C13-C28 aldehyde fragment to install the fully elaborated side chain, whereby subsequent global deprotection of the resulting β-hydroxyketone under suitable conditions (TASF followed by p-TsOH) afforded (+)-concanamycin F.     

Pre-equilibrium alpha emission accompanying deep-inelastic16O+58Ni collisions

α particles were measured in coincidence with projectile-like reaction products (oxygen and carbon) produced in deep-inelastic¹⁶O+⁵⁸Ni collisions at about 6 MeV/N bombarding energy. The kinematic analysis of the HI andα energies measured as a function ofΘ _α gives strong evidence for a sequential process: the target-like fragments are excited by the deep-inelastic collision and undergo subsequentα decay. In contrast, the angular correlations show a pronounced forward peak, indicative of direct or pre-equilibriumα emission. The emission time for the latter is estimated to be of the order of 2×10^?21 s. To resolve this conflict of co-existing statistical and direct features of the pre-equilibrium emission, the concept of a hot spot is proposed. From the angular correlation and from theα multiplicities, a local temperature ofT?3.5 MeV is deduced which agrees well with the temperature derived from the shape of theα spectra. The spot size is estimated to be 1/5 of the sphere.     

Ratios of charged antiparticles-to-particles near mid-rapidity in Au + Au collisions at sqrt[s(NN)]=130 GeV

We have measured the ratios of antiparticles to particles for charged pions, kaons, and protons near mid-rapidity in central Au+Au collisions at sqrt[s(NN)] = 130 GeV. We observe / = 1.00+/-0.01(stat)+/-0.02(syst), / = 0.91+/-0.07(stat)+/-0.06(syst), and

/

= 0.60+/-0.04(stat)+/-0.06(syst). The / and

/

ratios give a consistent estimate of the baryo-chemical potential mu(B) of 45 MeV, a factor of 5-6 smaller than in central Pb+Pb collisions at sqrt[s(NN)] = 17.2 GeV.