The crystallization of Fe1−x P x , 0.09≦x≦0.26

The crystallization behaviour of about 60 samples of electrodeposited Fe_1–x P _x , 0.09<x<0.26, was investigated with DSC and X-ray diffraction. Several subsequenting transformations during heating at 10 K/min were identified. The corresponding transformation temperatures, reaction heats and reaction rates were measured. If the as-deposited samples contain metal-rich crystallites (microcrystalline and partly amorphous material) crystallization starts with primary precipitation of -iron followed by polymorphous crystallization of Fe₃P. In amorphous samples these two processes become less important compared with the eutectoid reaction the higher the phosphorus content. In a small concentration range around 19 at% P this transformation is the only one. Above this range the primary crystallization of Fe₃P becomes more and more dominant.     

57Fe Mössbauer studies in a new cluster spin glass system RuxFeGa (0.5≦x≦1.5)

⁵⁷Fe Mössbauer and bulk magnetization studies have been carried out in a new magnetic system Ru_xFeGa for 0.5x1.5. The system is seen to freeze into a cluster spin glass phase at 70 K. The freezing temperature and the hyperfine field at Fe at the lowest measured temperature, 190 kOe, is essentially same for all values of x investigated.     

Beta-delayed proton precursors with 59≦Z≦62

The new, beta-delayed proton emitters¹²⁸Pr(3.2 _?0.4 ^+0.5 s),¹³⁰Pm(2.2 _?0.4 ^+0.6 s), and¹³²Pm(5.0 _?0.6 ^+0.8 s) have been observed at the on-line isotope separator OASIS. Also studied were¹²⁹Nd and¹³³Sm. Our on-going study of the decay properties of very neutron-deficient lanthanides has led to detailed information about beta-delayed proton emitters with 59≤Z≤62. The isotopes were produced at the SuperHILAC's on-line isotope separator OASIS [1] in reactions of⁴⁰Ca projectiles on⁹²Mo and⁹⁶Ru targets enriched to >95%. Decay studies were carried out in a low background spectroscopy laboratory. The isotope of interest was passed through a slit in the focal plane of the mass separator, transported ionoptically to a fast cycling tape, and periodically positioned between a silicon charged particle telescope, a HPGe x-ray detector, and a GAMMA-X Ge detector. Decays involving beta-delayed gamma rays and protons along with any coincident positrons, x-rays and gamma rays were measured event-by-event and written to computer tape for subsequent replay and analysis.     

IsoscalarE2 transition strengths in 10≦A≦48 nuclei

Electric quadrupole transition strengths for the 2 ₁ ⁺ ,T=1→0 ₁ ⁺ ,T=1γ-decay branches are summarized for 10≦A≦42 nuclei. In¹⁰B the corresponding branch has been remeasured by use of the⁹Be(p, γ)¹⁰B resonance reaction atE _p =320 keV; an upper limit of 0.6% is found. The variation of theE2 strengths within each individualT=1 isobaric multiplet reveals the particleor hole-character of the levels involved. The isoscalar 2 ₁ ⁺ →0 ₁ ⁺ transition strengths in 10≦A≦48 nuclei vary between 2 and 20 Weißkopf units showing drastic shell effects. Results for the ratio of neutron and proton matrix elements deduced from analogγ-decay studies and from inelastic pion scattering are compared.     

Proton and Two-proton Emissions from Proton-rich Nuclei with 10≦Z≦20

Proton (p) and two-proton (2p) emissions from the proton-rich nuclei with 10≦Z≦20 have been explored by the in-fight decay and implantation decay methods, respectively, in a series of experiments at the HIRFL-RIBLL facility. The in-flight 2p emissions from the excited states of 28,29S /26,27P and 17;18Ne were studied by complete-kinematics measurements. Mechanisms of 2p decay and related p-p correlations have been explored. Obvious 2p correlated emissions have been observed in the cases of 28,29S but not in 27,28P, indicating the 2p halo plays an important role in the diproton emission. In the 17;18Ne cases, a small 2p opening angles were deduced by the HBT analyses, implying the BCS-BEC crossover may occur in the dilute nuclear matter. Moreover, 27S/26P/25Si, 22Si/20Mg, 23Si/22Al/21Mg, 24Si/23Al, and 36;37Ca were implanted in a thin double-sided-silicon-strip detector and their -delayed p and 2p decays have been measured by a surrounding silicon detector array under the continuous-beam mode. Important information on the nuclear spectroscopy, such as energy, lifetime, branching-ratio, and so on, has been extracted, which helps us to understand the nuclear structures of proton-rich exotic nuclei close to the drip-line.     

On the magnetic susceptibility of Pd1−x Ag x in the range 0.5≦x≦1

The weak variation of the magnetic bulk susceptibility of Pd_1–x Ag _x with temperature T and silver mole fractionx within 0.5x1 has been investigated in the range 5KT400K. Experimental evidence can be given for an intersection point of the susceptibility isotherms (T=const,x) atx=0.55. The observed dependence of on T andx is interpreted by means of a semiphenomenological alloy susceptibility function (T,x).     

Low temperature properties in Ce(Cu x Al1−x )5, [0.60≦x≦1.00]

We report on the formation of a heavy fermion state in Ce(Cu _x Al_1–x )₅, with 0.60x1.00. This state evolves upon the exchange of Cu by Al in the hexagonal CeCu₅. Furthermore, this exchange causes a suppression of a common type of long range magnetic order. Both phenomena are driven by Kondo interaction.     

Measurement ofK αcross sections and fluorescence yields for elements in the range 42≦Z≦57 using radioisotope X-ray fluorescence

TheK x-ray fluorescence (XRF) cross sections have been experimentally determined for elements in the range 42Z57 at excitation energy of 59.54keV associated with gamma rays of Am-241 radioisotope. In addition, measurements of XRF yields of theK shell (w _k) for the same elements at the same excitation energy have also been carried out. Our measurements were shown to agree with theoretical calculations.     

Plasmon dispersion in Al atk≦k F using electron energy loss spectroscopy

We find a quasi quadratic dispersion of the plasmon up to _p = 28 eV atk=1.77 Å^–1 with no levelling off contrary to other measurements. We usedk-scans at constant energy loss andE-scans at constant wave vector, which yield different dispersions of the plasmon peak maximum because of the finite halfwidth. The levelling off in plasmon dispersion observed previously is due to multiple scattering events, which obscure the plasmon dispersion inE-scans.We confirmed the anisotropy of the dispersion coefficient by investigating polycrystalline samples of different orientation.     

BRST analysis of physical states for 2D gravity coupled toc≦1 matter

We consider 2D gravity coupled toc1 conformal matter in the conformal gauge. The Liouville system is represented by a free scalar field, ^L , with background charge such that the BRST operator imposing reparametrization invariance is nilpotent. We compute the cohomology of this BRST charge on the product of the Fock space of ^L with those of the ghosts and one other free scalar field, ^M representing the matter system. From this calculation the physical states of the full theory are determined. For thec<1 case the further projection from the Fock space of ^M to the irreducible representation, using Felder's resolution, reproduces the results of Lian and Zuckerman.Supported by the NSF Grant # PHY-88-04561Supported in part by the Department of Energy Contract # DE-FG03-84ER-40168 and by the USC Faculty Research and Innovation Fund     

Effects of Nb and Y substitution on negative thermal expansion of ZrV 2−XPXO7 (0≦X≦0.8)

Zirconium vanadates with a novel chemical composition including niobium and yttrium were synthesized by the sol-gel method. An aqueous solution of NH₄H₂PO₄ and NH₄V O₃ and an ethanol solution of ZrOCl₂,NbCl₅, and Y Cl₃ were prepared. These two solutions were stirred and mixed to prepare precursors of zirconium vanadates at 333 K, following the evaporation of the solvent at 363 K. The precursor gels obtained were heated at 373-973 K in air. A zirconium vanadate phase began to crystallize above 673 K and a single phase of zirconium vanadate was synthesized at 973 K. Although ZrV ₂O₇ generally had a positive thermal expansion in the temperature range above RT, the degree of positive thermal expansion decreased with the two types of substitution of P for V and a set of Nb and Y for Zr of ZrV ₂O₇. X-ray diffraction peaks due to a superlattice structure, causing a positive thermal expansion from RT, were not observed in the synthesized (Nb, Y)-substituted zirconium vanadates.     

Magnetotransport in core-shell Fe–Fe oxide nanostructures

Magnetic and magnetotransport measurements were performed on gas-phase synthesized Fe nanoparticles subjected to surface oxidation and cold consolidation. Two samples were investigated with α-Fe volume fraction of 0.15 and 0.60. The sample with smaller metallic fraction is below the percolation threshold for metallic conduction and the conduction mechanism is dominated by thermally activated processes across the oxide. In this case, by lowering the temperature, an increase of the negative magnetoresistance is observed up to 5% at 50 K in a magnetic field of 70 kOe. The magnetoresistance dependence on the sample magnetization, temperature and sample composition is discussed considering the magnetic correlations present in these nanostrucuterd systems.     

The Fe–Fe2P phase diagram at 6 GPa

Here, we report experimental results on melting and subsolidus phase relations in the Fe–Fe₂P system at 6?GPa and 900–1600°C. The system has two P-bearing compounds: Fe₃P and Fe₂P. X-ray diffraction patterns of these compounds correspond to schreibersite and barringerite, respectively. The Fe–Fe₃P eutectic appears at 1075°C and 16?mol% P. Schreibersite (Fe₃P) melts incongruently at 1250°C to produce barringerite (Fe₂P) and liquid containing 23?mol% P. Barringerite (Fe₂P) melts congruently at 1575°C. Maximum solid solution of P in metallic iron at 6?GPa is 5?mol%. As temperature increases to 1600°C, the P solubility in the metallic iron decreases to 0.5?mol%, whereas the P content in coexisting liquid decreases to 3?mol%. The composition of quenched phases from Fe–P melt coincides with the compositions of equilibrium phases at corresponding temperature. Consequently, the composition of quenched products of Fe-P melts in meteorites can be used for reconstruction of P–T conditions of their crystallization under ambient or low pressures or during shock melting by impact collisions.     

合成反铁磁Ni81Fe19/Co90Fe10/Ru/Co90Fe10/Ni81Fe19的研究

采用直流磁控溅射方法制备了一系列的合成反铁磁及以其为自由层的自旋阀.研究发现,在Ni81,Fe19与Ru层之间插入适当厚度的Co90Fe10层后,可有效地提高合成反铁磁两磁性层间的反铁磁耦合强度,得到具有饱和场日.更高、饱和磁化强度M.更低、热稳定性更好的合成反铁磁.另外,以这种合成反铁磁作自旋阀的自由层时,可有效提高自旋阀的稳定性.     

Hyperfine fields and Fe magnetic moments in Fe−Ni invar alloys

Mössbauer spectra of Fe_1?x Ni _x withx=0.40, 0.35 and 0.32 were taken at various temperatures and fitted withB _hf distributions. TheP(B _hf) curves generally show a peak and a low-field tail. The peakB ^* and the average \(\bar B\) were obtained in theT→0 limit. Fe moments were deduced from these data with help of a semiempirical equation. While the average \(\bar \mu _{Fe} \) decreases withx (invar anomaly), a large fraction of Fe atoms retain the strong moment (≈ 2.7 μ_B) typical of Ni-rich alloys. This result is consistent with a two-states model for invar.     

Magnetic Thermocouples Made of Co–Fe and Ni–Fe Permalloys

Technical Physics - Magnetized and unmagnetized Co–Fe and Ni–Fe alloys fabricated on a two-high casting installation in the form of thin flexible amorphous films are promising materials...     

One dimensional 1/|j − i| S percolation models: The existence of a transition forS≦2

Consider a one-dimensional independent bond percolation model withp _j denoting the probability of an occupied bond between integer sitesi andi±j,j1. Ifp _j is fixed forj2 and j ² p _j>1, then (unoriented) percolation occurs forp ₁ sufficiently close to 1. This result, analogous to the existence of spontaneous magnetization in long range one-dimensional Ising models, is proved by an inductive series of bounds based on a renormalization group approach using blocks of variable size. Oriented percolation is shown to occur forp ₁ close to 1 if j ^s p _j>0 for somes<2. Analogous results are valid for one-dimensional site-bond percolation models.John S. Guggenheim Memorial Fellow, Research Supported in Part by NSF Grant MCS-8019384     

Pd/Fe和PdFe/Fe多层膜中的振荡行为

采用磁控溅射法制备了Pd/Fe和Pd_1-xFe_x/Fe多层膜.利用变换梯度磁强计测量了样品的M_s.发现层间耦合是铁磁性的,M_s具有长程振荡,周期为4ML.振荡的相位和周期在Pd_0.966Fe_0.034/Fe和Fd_0.944Fe_0.056/Fe系统中保持不变.就Pd/Fe多层膜中是否存在内层的Pd负极化和长程的铁磁耦合振荡进行了讨论,并分析了不同计算结果以及理论计算与实验结果之间存在差异的原因. 关键词：     

Search for an enhanced production of low energy pions in C(p, π+)X,Cu(p, π+)X,and Cu(p, π∘)X reactions for 300 MeV≦Tp≦400 MeV

The observation of an enhancement in the production of low energy pions in the Cu(p, ⁺)X reaction is confirmed. The width of the bump is about 5 MeV around 350 MeV. A similar enhancement appears at 330 MeV for C(p, ⁺)X but the width has not been measured. An attempt to observe this behaviour in Cu(p, )X is described. From the data one cannot conclude about the existence of a structure around 350 MeV proton energy. The lack of resolution in the spectrometer may have washed out the small effect expected from ⁺ measurements.