Preparation and properties of substances in the series Cd2−xAg2xP2Se6, 0⩽x⩽2

Cd₂P₂Se₆ - Ag₄P₂Se₆ system was investigated and Cd_2−xAg_2xP₂Se₆ mixed crystals have been found for 0<x<0.3. Their conductivity has been found to have ionic character. Silver ion conductivity values are reported. From diffuse reflectance data, the bandgaps for Cd₂P₂Se₆ and Ag₄P₂Se₆ have been estimated as equal to 2.4 eV and 1.8 eV, respectively.     

Critical points and points of the bifurcation of the rotating magnetized newtonian polytropes with a 1 ⩽ n ⩽ 1.6 index

The presence of critical points and the bifurcation points of rotating Newtonian polytropes with an index of 1 ? n ? 1.6 has been shown for the first time in this paper. The symbolic-numerical calculation error in metric L ₂ has reached the size of the 10^?4 order. The approximate analytical solution to the problem to the abovementioned accuracy has been set forth. A critical value of the polytropes index n = n _k = 1.51025 has been calculated which is the highest among the critical points and bifurcation points. The value n _k corresponds to the infinitely slow polytropes rotation. Furthermore, in this paper the presence of the period jump at the bifurcation point T _b has been predicted and the relative value of this jump ΔT _b /T _b ～ B _0in ^4/3 has been estimated.     

Pressure effect on magnetic properties of NdMn2−xFexGe2 (0.1⩽x⩽1.0) series of solid solutions

Temperature and pressure dependence of magnetic properties in the NdMn_2−xFe_xGe₂ series of solid solutions (0.1⩽x⩽1.0) are reported. The (P, T) magnetic phase diagrams are determined on the basis of the AC magnetic susceptibility measured in a weak magnetic field. The measurements were carried out under hydrostatic pressure up to 1.5 GPa in the temperature range 80−430 K. The reported data show that in the studied series of solid solutions, a drastic change in magnetic properties takes place in a narrow dilution parameter range (0.4⩽x⩽0.5). While taking into account the magnetic properties, the studied range of Fe content could be divided into four regions. Only in the case of x=0.3 and 0.4, the external pressure significantly influences the magnetic properties of the samples.     

Elastic scattering of 11B from 209Bi in the energy range 49.8 ⩽ E ⩽ 84.1 MeV

The elastic scattering of ¹¹B from ²⁰⁹Bi has been measured at laboratory energies of 49.8, 51.3, 52.2, 52.8, 54.3, 55.8, 59.8, 64.8, 69.8, 74.8 and 84.1 MeV. These data have been analyzed using a microscopic optical model and the energy dependence of the real and the imaginary parts of the optical potential at near barrier energies has been determined. The “threshold anomaly” observed in the real part of the potential is found to be consistent with the dispersion relation which connects the real and the imaginary parts of the potential. Inelastic scattering and transfer reactions have also been measured at energies of 51.3, 55.8, 59.8 and 74.8 MeV. DWBA calculations for the 3⁻ state in ²⁰⁹Bi are made. From the measured transfer probabilities, using a semiclassical approach the strength of the form factors have been obtained. The fusion cross sections have been derived at these energies from the corresponding quasi-elastic scattering angular distribution data. The fusion cross sections calculated using the energy dependent barriers extracted from the energy dependent real parts of the potential compare well with, that determined from quasi-elastic scattering data and are also in good agreement with simplified coupled channels calculation for fusion incorporating important inelastic and transfer channels.     

A magnetic study of HoMn6Sn6−xGax single crystals (0.14⩽x⩽1.89)

Single crystals of hexagonal HfFe₆Ge₆-type HoMn₆Sn_6−xGa_x compounds (0.14⩽x⩽1.89) have been obtained by a flux method and studied by magnetisation measurements. All the compounds order ferrimagnetically (308⩽T_c⩽386 K) with moments lying in the (0 0 1) plane and undergo a moment reorientation transition at lower temperatures (156⩽T_SR⩽195 K). At 5 K, the moments are aligned along an intermediate direction (44⩽φ_c⩽50°). These results are discussed and compared with the neutron diffraction results related to the isotypic TmMn₆Sn_6−xGa_x and TbMn₆Sn_6−xGa_x series where a change of the easy direction is observed with increasing gallium contents.     

Properties of Hg1−xZnxSe (0.09 ⩽ x ⩽ 1.0) thin films prepared by flash evaporation technique

Flash evaporated mercury zinc selenide films are observed to grow as single phase ternary alloys of the type Hg_1−xZn_xSe in the composition range 0.09 ⩽ x ⩽ 1.0, with a f.c.c./sphalerite structure on substrates maintained at T_s between 30°C and 175°C. The grain size is observed to increase with increase in T_s for all compositions. The films are observed to have a direct optical band gap which increases from 0.01 to 2.60 eV as the Zn concentration x is varied between 0.09 and 1.0. The band gap V_scomposition shows a bowing, typical of pseudobinary solid solutions. Zn rich films were observed to be p-type whereas Hg-rich films were n-type. Room temperature resistivity was observed to increase with Zn concentration x, which can be attributed to the increase in the band gap of the semiconductors. Higher resistivity in films deposited at high substrate temperatures is due to the decrease in contribution to conduction from the highly conducting grain boundaries.     

The magnetism of Zn-doped colossal magnetoresistance materials Fe1−xZnxCr2S4 (0⩽x⩽1)

The polycrystalline samples of Zn-doped Fe_1−xZn_xCr₂S₄ (0⩽x⩽1) were prepared by the conventional solid-state synthesis method. The magnetic homogeneity has been proved by the measurements of the alternating current (AC) magnetic susceptibility. We presented a detailed study of Zn-doping effect on the magnetism. It is found that the magnetism does not change monotonically with substituting nonmagnetic Zn²⁺ ions for Fe²⁺ ions. The difference between the magnetic moments for the samples with respective doping level can be ascribed to the variation of compensation between the Fe²⁺ and Cr³⁺ sublattices as the Fe²⁺ concentration is varied. The Zn-doping leads to spin reversal of Cr³⁺ ions. Based on the spin orientation of Fe²⁺ and Cr³⁺ ions in FeCr₂S₄ and ZnCr₂S₄ at 0 K, we suggest a phenomenological model describing the magnetism and the doping level dependence of the up-spin proportion of Cr³⁺ ions. The up-spin proportion of Cr³⁺ ions, denoted by y, as a function of doping level in zero fields is linear. However, y in magnetic fields cannot be fitted linearly, which shows a maximum. The above results can be described qualitatively by the effect of the applied magnetic field on the AB, AA, and BB interactions of the spinels with the formula ABS₄.     

A mean-field study on the thermo-magnetic properties of GdxCo1−x amorphous alloys (0.16⩽x⩽0.25)

We present a mean-field study on the thermo-magnetic properties of Gd_xCo_1−x amorphous alloys in the 0.16⩽x⩽0.25 composition range. A single set of exchange integrals and fixed values of the angular momenta of Gd and Co fairly describe the temperature dependence of magnetization. The magnetic specific heat and magnetic entropy show field and composition dependence. Both the specific heat anomaly and the saturated entropy, at the temperature of the magnetic phase transition, increase with increasing Co concentration. The two magnetic subnetworks and their cross-interactions contribute differently to the specific heat.     

57Fe Mössbauer spectroscopy and magnetization study of YFexAl12−x (4.4⩽x⩽5)

YFe_xAl_12−x in the composition range 4.4⩽x⩽5 was prepared by induction melting followed by annealing in vacuum at 1270 K. Magnetization data below 150 K show complex magnetic behaviour dependent on applied field, composition and temperature. The transition temperature T_c, corresponding to the main maximum of the magnetization vs. temperature curves and below which magnetic interactions are observed for a significant fraction of the Fe atoms in the Mössbauer spectra, decreases from 180 K for x=4 down to 100 K for 4.2⩽x⩽4.7 and rises again up to 160 K for x=5. The analysis of the spectra obtained at 5 K is consistent with full occupation of the 8f sites by Fe atoms and sharing of the 8j sites by Fe and Al as deduced from the Rietveld analysis of X-ray powder diffraction data. The Mössbauer spectra further show a dependence of magnetic hyperfine fields and isomer shifts on the crystallographic site and on the number of the Fe nearest neighbours similar to that observed in UFe_xAl_12−x (4⩽x⩽6) and RFe_xAl_12−x (R=Y, Lu, x=4, 4.2). The magnetic properties of the UFe_xAl_12−x and YFe_xAl_12−x series are compared and the magnetic interactions between the different Fe sublattices are discussed.     

Effects of Er substitution for Nd on structural and magnetic properties of Nd1−xErxMn2Ge2 (0⩽x⩽1)

The structure and magnetic properties of Nd_1−xEr_xMn₂Ge₂ (0.0⩽x⩽1) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr₂Si₂-type structure with space group I4/mmm. Substitution of Er for Nd led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Er for Nd in NdMn₂Ge₂ shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering. A typical SmMn₂Ge₂-like behaviour is observed for the x=0.4 sample. The results are summarized in α preliminary magnetic phase diagram.     

Mössbauer study of an amorphous iron III flouride: FeF3, xHF (0 ⩽ x ⩽ 1)

A ferric amorphous flouride FeF₃, xHF with 0 ⩽ x ⩽ 1 synthesized by a soft chemistry reaction was studied by Mössbauer spectroscopy. The hyperfine characteristics are very close to those of deposited variety previously published: they show that the Fe³⁺ ions are surrounded by weakly distorted octahedra of flourine atoms. The study under external magnetic field indicates that the spins are randomly distributed: FeF₃, xHF has a speromagnetic behaviour like deposited amorphous FeF₃. Elsewhere the similarity between the two amorphous forms is confirmed by susceptibility measurements.     

A study of the three- and four-photon final states produced in e+e− annihilation at 35⩽s⩽46.8 GeV

The reactions e⁺e⁻→γγγ and e⁺e⁻→γγγγ have been studied at center-of-mass energies between 35 and 46.8 GeV with an integrated luninosity of about 130 pb⁻¹accumulated with the CELLO detector at PETRA. The measurements are compared to QED calculations up to third and fourth orders of perturbation theory. Excellent agreement is observed.     

In-beam γ-ray spectroscopy of 103Cd

Excited states of ¹⁰³Cd were studied in the reaction ⁵⁸Ni(⁵⁰Cr,4pn)¹⁰³Cd. The NORDBALL array with neutron and charged particle detectors was employed for the detection of γ rays and light evaporated particles. The level scheme of ¹⁰³Cd was significantly extended. A strong cascade of E2 transitions connecting negative parity states was found. Shell model calculations were performed and positive parity excited states were interpreted in terms of neutron-particle and proton-hole excitations with respect to the doubly magic N = Z = 50 core. The negative parity band was well reproduced by the total routhian surface calculations.     

X-ray diffraction and Mössbauer Studies of γ′-(Fe1−xSnx)4N compounds (0.0⩽x⩽0.3)

The structure and magnetic properties of γ′-(Fe_1−xSn_x)₄N samples have been studied using X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy. It has been shown that the single-phase (Fe_1−xSn_x)₄N compounds can be prepared in the composition range of 0.0⩽x⩽0.3, which have the similar structure as γ′-Fe₄N The lattice parameter with the increase of Sn concentration can be well fitted with two linear relationships a₀(x)=3.795+0.019x (with x⩽0.10 ) and a₀(x)=3.797+0.228(x−0.10) (with 0.1⩽x⩽ 0.3). The fitting results of Mössbauer spectra indicate that the hyperfine parameters have the same changing tendency with lattice parameter, and the Sn atoms have a preference to be located at the corner site.     

Effect of Cd content on the structural characteristic and some physical properties of Zn1−x Cd x Se

The present work focuses on the structural, optical, and electrical properties of Zn_1?x Cd _x Se (0.1≤x≤0.25) compounds. The compounds were synthesized by solid state reaction. X-ray diffraction (XRD) patterns confirm that the samples have cubic single phase (zinc-blende) crystal structure with space group F-43m. The crystal structural parameters were refined by the Rietveld method using the FullProf program. It was found that the lattice parameters increase linearly with increasing the Cd content and obeys Vegard’s law. The refined values of the crystallite size and the bond lengths increase with increasing the Cd content. The energy band gap of the samples has been calculated and it was found that it decreased as Cd increased. The conductivity of the samples increases with increasing both of composition parameter x and temperature, and showing semiconducting behavior.     

Investigation of the 2νEC/EC Decay of 106Cd

Search for the β⁺β⁺, β⁺ EC, and EC/EC modes of the ¹⁰⁶Cd decay was carried out with the TGV-2 (Telescope Germanium Vertical) low-background multidetector spectrometer installed at the Modane underground laboratory (4800 m w.e.). The measured foil samples ～50 μm thick and 52 mm in diameter were placed between the entrance windows of the neighboring detectors inside the cryostat. The total measurement time for 10 g of ¹⁰⁶Cd enriched to 75% was 8687 h. New limits (at the 90% confidence level, CL) were obtained for the ¹⁰⁶Cd half-lives against various branches of the decay to the ground state 0⁺ and excited states 2⁺ of the ¹⁰⁶Pd daughter nucleus. They are T _1/2(2νβ⁺β⁺) ≥ 6.0 × 10¹⁹ y, and T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 3.0 × 10²⁰ y for the transitions to the 0⁺ ground state of ¹⁰⁶Pd; T _1/2(2νβ⁺β⁺) ≥ 5.7 × 10¹⁹ y, T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 4.2 × 10¹⁹ y for the transitions to the 2⁺, 512-keV excited state of ¹⁰⁶Pd; and T _1/2(2νEC/EC) ≥ 3.1 × 10¹⁹ y for the transition to the 0 ₁ ⁺ , 1334-keV excited state of ¹⁰⁶Pd.