The critical magnetic behavior of the new Heusler CoXO2 alloys (X=Cu or Mn): Monte Carlo Study

In this paper, we study the effect of different physical parameters on the critical magnetic behavior of the new full Heusler CoXO2 (X=Cu or Mn) alloys, using Monte Carlo simulations (MCS) under the Metropolis algorithm.To reach this goal, we have proposed a Hamiltonian describing and modeling these compounds. The CoCuO2 alloy is formed with the spin variables of cobalt Co atoms (S_i=±2, ±1 or 0) and the copper Cu atoms modeled by the spins σ_i=±1/2. While, the compound CoMnO2 is modeled the spins of Co atoms (Si=±2, ±1 or 0) and the Mn atoms represented by the spins (Q_i=±5/2, ±3/2 or ±1/2).In fact, we have studied and discussed the ground state phase diagrams of the new Heusler alloys CoXO2(X=Cu or Mn) in different physical parameters. Moreover, we have presented and discussed the thermal behavior of the total magnetizations and the magnetic susceptibilities, for non-null temperature values.To complete this study, we have elaborated and discussed the hysteresis loops of the studied alloys when fixing the temperature values.     

Decay properties of the 19/2− isomers in113,117Sb

By means of the generalized centroid-shift method, the following half-lives were determined:T _1/2(3045 keV)=3.7±0.3 ns in¹¹³Sb using the reaction¹⁰⁴Pd(¹²C,p2n) as well asT _1/2 (1322.8 keV)=3.5±0.3 ns,T _1/2(2779.8 keV) =0.50±0.15ns,T _1/2(2874.9 keV)<0.2 ns andT _1/2(3072.9 keV)<0.1 ns in¹¹⁷Sb using the¹¹⁶In(α, 2n) reaction. Three-quasiparticle configurations of the type πd _5/2ν(h_11/2 d _3/2) in^113,117Sb are found to dominate in the wave functions of the 19/2^? states at 3045 and 2780 keV in¹¹³Sb and¹¹⁷Sb, respectively. TheB(E2, 19/2^? → 15/2^?) values in^113–119Sb are discussed.     

Magnetic hyperfine fields on 111Cd in the Pd1+xMnSb heusler alloys

The time-differential perturbed angular correlation technique has been used to measure the magnetic hyperfine fields (mhf) acting on ¹¹¹Cd impurity on the series of alloys Pd_1+xMnSb with 0 ? x ? 1. We observe three diffrent mhf's which for small values of x are of the order of +250, ?250 and ?150 kOe, decreasing slowly for larger values of x. These three fields are associated with ¹¹¹Cd occupying the sites of Mn, Sb and Pd, respectively. In addition, magnetization measurements on three of the allows (x = 0, 0.4 and 0.8) gave magnetic moments on the Mn atoms of 3.88 ± 0.08, 4.18 ± 0.08, (4.14 ± 0.08)_μB and Curie temperatures of 470 ± 2,422 ± 5 and (288 ± 2) K, respectively. Our results together with the existing data for mhf's on various 5sp elements in the Pd₂MnSb Heusler alloy are compared with the Blandin-Campbell model and show an agreement which is only qualitative.     

Determination of the positions of impurity centers in a dislocation core in a NaCl crystal from magnetoplasticity spectra

The spectra of the mean free paths l(ν) of edge dislocations have been studied in NaCl crystals exposed in the electron paramagnetic resonance scheme to the crossed magnetic fields: the Earth’s field (50 μT) and the pump field (2.5 μT, 5–440 kHz). The spectra have been measured for a series of angles θ = 0°–5° of rotation of the sample around its edge [100] with respect to the Earth’s field. The fine structure of the spectra contains a series of peaks whose resonance frequencies are described by the empirical expression v _i ^± = Asin(θ ± Δθ _i ) ≈ A(θ ± Δθ _i ). The parameters Δθ _i are independent of the angle θ within the experimental errors. Within the model of “frozen” magnetic moments associated with impurity center Ca⁺-Cl⁰, the angles Δθ _i characterize the deviation of the axis of the center from the 〈100〉 direction in the core of a dislocation. These angles can be expressed in terms of the spectra obtained: Δθ _i = (? _i ⁺ ? v _i ^? )/2A. The computer simulation of the edge dislocation core provides the set of the angles Δθ _i close to the measured values. The spin-lattice relaxation time of the center on dislocation has been estimated from the low-frequency edge of the spectrum l(ν) as τ _{s ? l} ～ 10^?4 s.     

Penetration effects in the internal conversion process of the 204 keV transition in205Tl

Penetration effects have been detected in²⁰⁵Tl by measuring theK, L and (M+N+...) internal conversion coefficients of the 204 keV, 3/2⁺→l/2⁺ transition. From the resulting values α _K =0.29±0.04, α _L =0.132±0.006 and α _M+N+...=0.0397±0.0034 the penetration parameter and the mixing ratio have been deduced to be λ=13.1±2.7 andδ ²=1.40±0.46, respectively.     

Precision determination of high-Z K-shell fluorescence yields from195Au,207Bi,and235Np decays

A new method utilizing a cooled, high resolution, windowless Si(Li) x-ray and Auger electron detector has been developed for the accurate measurement of high-Z K-shell fluorescence yields. With this method, values of theK-fluorescence yield ω _k have been determined with high accuracy atZ=78, 82, and 92 from the radioactive decay of carrier-free¹⁹⁵Au,²⁰⁷Bi, and²³⁵Np, respectively. The values of ω _k are 0.968±0.008, 0.972±0.008, and 0.970±0.005, respectively where the error limits represent 95% confidence. In addition, relativeK-Auger electron group intensities atZ=92 were measured and found to be(K-LL)∶(K-LX)∶(K-XY)=100∶(65.2±6.0)∶ (8.1±0.8). The experimental results for ω _k are compared with the relativistic calculations of Bhalla, Ramsdale and, Rosner, and satisfactory agreement is found.     

A study of the adsorption of oxygen on Ni(111) using auger electron spectroscopy: Chemical shifts and valence spectra

Auger electron spectra have been recorded when oxygen is adsorbed on a Ni(111) single crystal surface. For the coverage range θ < 1, an analysis of the plot of the peak to peak height (H) of the oxygen KVV (516 eV) transition versus the total number of molecules cm^2? impinging on the surface (molecular beam dosing) shows agreement with the kinetic mechanism proposed by Morgan and King [Surface Sci. 23 (1970) 259] for the adsorption of oxygen on polycrystalline nickel films. In this coverage range, no energy shifts of the nickel or oxygen Auger peaks were recorded.At coverages θ > 1 (standard dosing procedure) shifts in the valence spectra M_{2, 3}VV (61 eV) and L₃M_{2, 3}V (782 eV) of ?2.3 eV and ?1.8eV respectively are recorded at 1.4 × 10^?2 torr-sec. Up to these coverages no shift of the L₃VV transition (849 eV) is observed. A chemical shift of ?2.1 eV is recorded in the L₃M_{2, 3}M_{2, 3} Auger transition (716 eV) at 1.4 × 10^?2 torr-sec.In the coverage range θ > 1, shifts in the energy of the oxygen Auger peaks are observed. At 5.8 × 10^?3 torr-sec. the KVV (516 eV) and KL₁V (495.2 ± 0.3 eV) transitions show shifts of ?1.5 eV and ?(1.0 ±0.3) eV respectively. No shift up to this coverage is recorded in the KL₁L₁ (480.6 ± 0.3 eV) transition.     

Band-to-band recombination in GaxIn1−xSb

The carrier lifetimes in Ga_xIn_1−xSb for radiative and Auger recombination are calculated for the temperature range 77–300 K and the composition range 0 ⩽ x ⩽ 1. The possible band-to-band Auger recombination mechanisms in direct-gap semiconductors are investigated. The Auger rates are calculated, including Boltzmann statistics and nonparabolic bands, using the Kane-band model. In the low temperature range, for lightly doped material, the carrier lifetime is determined by radiative recombination. At higher temperatures the CHCC process is dominant in n-type Ga_xIn_1−xSb but in p-type material the CHLH process is dominant. The influence of CHSH processes on the carrier lifetime is appreciable in p-type GaSb. The calculations are compared with experimental data reported by other authors.     

Reevaluation of the conversion coefficient of the 14.4 keV transition in57Fe

Existing values of the conversion coefficient of the 14.4 keV transition in⁵⁷Fe have been reevaluated using newK-shell fluorescence yields and recent decay scheme information. Previous disagreements are removed and the mean values found are α _T =8.26±0.19, α _K =7.37±0.17.     

The MTE continuum relation with application to an argon arc at atmospheric pressure

The continuum emission coefficient relation for a plasma in Multithermal Equilibrium (MTE) is derived using the partial-MTE ionization equation. The results are presented in a form using the nonhydrogenic free-bound Gaunt factors of Schlüter. Measurements on a 200 A, 1 atm, constricted argon arc indicate that electron densities calculated from the MTE continuum relation and Schlüter's ξ_fb values exceed electron densities from the Stark broadening of H_β by 15–30%. Experimental values of ξ_fb are up to 3 times larger than Schlüter's values, but are in agreement with the values of Morris and Krey at 5 atm, which is probably one of the few similar experiments actually in or near complete LTE. In the present experiment at the arc axis: N_e(H_β) = 1.00 × 10¹⁷cm^-3 (±8%); T_e = 34,000 K (±20%); T_exa = 12,000 K (±3%); T_exβ = 9000 K (±5%); and T_a = T_i = 10,000 K (±68%). The probable errors reflect the need for more accurate transition probabilities which had an uncertainty of 25%.     

Half-lives andP n values of delayed-neutron precursors in the mass chains 85–87, 92, 135, 136 and 145

Further results are presented on half-lives and neutron emission probabilities (P _n ) of short-lived delayed-neutron precursors in the mass chains 85–87, 92, 135, 136 and 145 obtained with the recoil focussing parabola-type mass separator for unslowed fission products LOHENGRIN installed at the Grenoble high-flux reactor. A newP _n -value of (44±14)% is given for the (0.73±0.06)s⁸⁷As; theP _n -values of seven precursor nuclides have been redetermined: (1.9±0.1)s⁸⁵As with (22±8)%, 0.9s⁸⁶As with (10.5±2.2)%, (0.35±0.04)s⁹²Br with (21±8)%, (1.6±0.15)s¹³⁵Sb with (14±1)%, (0.9±0.1)s¹³⁶Sb with (19±9)%, (17.5±0.2)s¹³⁶Te with (2.0±1.0)% and 0.6s¹⁴⁵Cs with (12.5±3.0)%. The results are compared with the existing data, and the neutron emission probabilities are discussed within a simple semi-empirical picture.     

Konversionskoeffizienten und Fluoreszenzausbeuten beim Zerfall des Hg199m

Hg^199m was produced by bombarding natural HgO with fast neutrons. The conversion electrons of the cascade decay were investigated with Si(Li)-counters. By application of the summing technique the conversion coefficients andL-shell fluorescence yields of Hg were determined. The gamma rays were studied with a Ge(Li)-counter. The following results were obtained: half-lifeT _1/2=(42.6± 0.2) min; energies of the transitionsE _γ1=(374.1± 0.1) keV,E _γ1=(158.3± 0.1)keV; intensity ratio of the gamma raysI _γ(158 keV):I _γ(374keV)=(424± 42):100; conversion coefficients α_K158=0.30± 0.03, α_total158=0.94± 0.09, α_K158/α_LM...158=0.47± 0.02, α_L158/α_M...158=3.10± 0.16;α_K374=3.51± 0.28,α_total1374=6.19±0.47,α_K374/α_LM...374=1.32±0.04, α_L374/α_M...374=2.14±0.11;L-shell fluorescence yields \(\bar \omega _L \) =0.40± 0.04, ω_KL=0.41±0.04.     

Mechanistic Insights into the Inhibition of Endo-β 1,4 Xyloglucan Hydrolase by a Classical Aspartic Protease Inhibitor

This is the first report of inactivation of xyloglucanase from Thermomonospora sp by pepstatin A, a specific inhibitor towards aspartic proteases. The steady state kinetics revealed a reversible, competitive, two-step inhibition mechanism with IC ₅₀ and K _i values of 3.5?±?0.5 μM and 1.25?±?0.5 μM respectively. The rate constants determined for the isomerization of EI to EI^* and the dissociation of EI* were 14.5?±?1.5?×?10^?5?s^?1 and 2.85?±?1.2?×?10^?8?s^?1 respectively, whereas the overall inhibition constant K _i ^* was 27?±?1 nM. The conformational changes induced upon inhibitor binding to xyloglucanase were monitored by fluorescence analysis and the rate constants derived were in agreement with the kinetic data. The abolished isoindole fluorescence of o-phthalaldehyde (OPTA)-labeled xyloglucanase and far UV analysis suggested that pepstatin binds to the active site of the enzyme. Our results revealed that the inactivation of xyloglucanase is due to the interference in the electronic microenvironment and disruption of the hydrogen-bonding network between the essential histidine and other residues involved in catalysis.     

Die Feinstruktur desL-MM-Auger-Elektronenspektrums von Argon und derK-LL-Spektren von Stickstoff,Sauerstoff und Methan

The fine structure ofL-MM Auger electron spectrum of argon andK-LL spectra of the gases N₂, O₂ and CH₄ was investigated with an electrostatical spectrometer. The ionisation was caused by the continuous X-radiation from a tungsten target. From the results of Auger electron energies measured, the binding energies of the electrons of the inner shells were calculated. The results obtained with argon agreed exactly with the known values. Further it could be shown, that the value of 400 eV for the binding energy of a 1s-electron in the N₂-molecule, so far obtained, must be replaced by the value (409,4±1,0) eV. A comparison between the relative intensities of fine structure lines and the theory of the Auger process given byAsaad andBurhop could not be carried out, because the Auger electrons, having in our experiment an angular distribution relativ to the incident X-ray beam, could only be measured between an angular range of 49,3° and 61,0°.     

Investigation of the reaction 35Cl(τ, α)34Cl at Eτ = 15 MeV

The ³⁵Cl(τ, α)³⁴C reaction has been used to study the properties of ³⁴Cl levels up to an excitation energy of 5 MeV. Angular distributions of 37 levels were measured with a split-pole magnetic spectrograph, at a bombarding energy of 15 MeV. New levels have been found at 3847, 3964, 4206, 4321 and 4715 keV, all ± 10 keV. There is a strongly excited multiplet at E_x = 5.0 MeV with components at 4939 ± 11, 4958 ± 11, 4971 ± 11, 4998 ± 12 and 5010 ± 13 keV. A DWBA analysis of the α-particle angular distributions yielded l_n values and spectroscopic factors. New spin and parity assignments were obtained. The T = 1 character of the levels at E_x = 4.21 and 4.72 MeV has been determined. Experimental spectroscopic factors are compared with results from recent many-particle shell-model calculations.     

Messung derK-Fluoreszenzausbeute von Silber und Antimon

Atoms of thin Ag- and Sb-targets have been ionized by electron impact and the followingK-X-rays andK-Auger-electrons were measured simultaneously. A scintillation counter was used for the X-rays and an electrostatic mirror spectrometer with a Si-Li-detector for the electrons. From these measurements we obtained for the fluorescence yields for Ag and Sb ω _K (Ag) = 0.834±0.017; ω _K (Sb) = 0.868±0.014. These results are in agreement with the measurements of Foin et al. [2] for Ag, of Hribar et al. [3] for Sb and with the theories of McGuire [10] and Kostroun et al. [11].     

On the separation of initial and final state effects in photoelectron spectroscopy using an extension of the auger-parameter concept

First, we show that the quantity Δβ(i) = ΔE_A(kii) + 2ΔE_B(i) — ΔE_B(k) is directly related to the final state relaxation contribution ΔE_R(i) of the binding energy shift ΔE_B(i). ΔE_A(kii) is the kinetic energy shift of the Auger transition which corresponds to the decay of a hole state with a hole in level k into a final state with two holes in level i. The shift parameter Δβ(i), which is based on information on two binding energies, is conceptually similar to Wagner's Auger parameter. To establish the relation between Δβ(i) and ΔR(i) one needs, however, less drastic approximations than in the case of Auger parameter shifts. The only approximation necessary is the assumption that ΔR(i) is determined by coulomb contributions.Secondly, we use Δβ (i) to analyse the experimental data of eighteen gaseous phosphorus-containing compounds obtained by Sodhi and Cavell¹. It is shown that ΔR(P_2p) is strongly related to changes in the polarizability of the ligands. The initial state effects derived from our study deviate from those expected on the basis of simple electronegativity considerations.     

Thermal neutron induced α-particle reaction on64, 65, 67Zn and77Se

The (_n th,α) reaction spectroscopy was done on^{64, 65, 67}zn and⁷⁷Se at the 87 m curved thermal neutron guide of the Grenoble high flux reactor. In each of the⁶⁴Zn(n, α)⁶¹ Ni and⁶⁷ Ni(n, α) ⁶⁴Ni reactions, one line showed up corresponding to anα-particle transition to the first excited state in⁶¹Ni and⁶⁴Ni withσ _α1=11±3 μb and 159±20 μb respectively. In the case of the radioactive⁶⁵Zn(T _1/2=244d) nucleus, two lines showed up corresponding to the ground state and the first excited state transitions in⁶²Ni with large values ofσ _α0=1.0±0.1b andσ _α1=1.0±0.1b. For the⁷⁷Se(n, α)⁷⁴Ge reaction, the ground state and first excited transitions were present withσ _α0=940±20 μb andσ _α1 = 30±5 μb respectively. The spin-parity (J ^π) of the neutron resonance contributing at thermal energy are discussed.     

Groundstate proton radioactivity of nuclei in the tin region

Proton radioactivities with decay energies of (0.98±0.08) MeV and (0.83±0.08) MeV were produced by the fusion reactions⁵⁸Ni+⁵⁸Ni→¹¹⁶Ba ? and⁵⁸Ni+⁵⁴Fe→¹¹²Xe ?, and their halflives were measured to be (33±7) μs and (109±17) μs, respectively. The intensities of the lines correspond to production cross sections of about 30 μb and 40 μb. The two activities are assigned to the direct proton decay of¹¹³Cs and¹⁰⁹I. The measured halflives are compared with values calculated ford _5/2 andg _7/2 groundstates of¹⁰⁹I and¹¹³Cs and spectroscopic factors are deduced for the decays. An extensive search for the proton decay of¹⁰⁵Sb, produced in the reaction⁵⁰Cr(⁵⁸Ni,p2 n)¹⁰⁵Sb, had a negative result, excluding decay energies between 0.5 MeV and 1.5 MeV for halflives between 10 ns and 5 s.