Magnetic phase diagram of diluted spinel Zn1−xCuxCr2Se4 system

By using mean field theory, we have evaluated the nearest-neighbour and the next-neighbour super-exchange J₁(x) and J₂(x), respectively, for Zn_1−xCu_xCr₂Se₄ in the range 0?x?1. The intraplanar and the interplanar interactions are deduced. High-temperature series expansions are derived for the magnetic susceptibility and two-spin correlation functions for a Heisenberg ferromagnetic model on the B-spinel lattice. The calculations are developed in the framework of the random phase approximation. The magnetic phase diagram is deduced. A spin glass phase is predicted for intermediate range of concentration. The results are comparable with those obtained by magnetic measurements. The critical exponents associated with the magnetic susceptibility (γ) and the correlation lengths (ν) have been deduced. The values are comparable to those of the 3D Heisenberg model, and are insensitive to the dilution x.     

Elastic properties of the RIV-RIII rotator phases of alkanes

A model free energy has been constructed to describe the R_IV-R_III rotator phase transition in alkanes in terms of the elastic strains and order parameter. The conditions for the R_IV-R_III phase transition are discussed. From the free energy, the order parameter and the elastic strains are determined. The model free energy describes the first or second order character of the R_IV-R_III transition depending on the strength of the coupling. The elastic properties in the vicinity of the R_IV-R_III transition are discussed on the basis of a free energy expansion. The temperature dependence of the elastic constants is calculated on both sides of the transition. The coupling between the order parameter and elastic stains is shown to have a crucial influence on the phase behavior and the order of the transition.     

Laser absorption spectroscopy of the A1Σu+-X1Σg+(v′, v″) bands of Na2

Laser absorption spectra of the band system A¹Σ_u⁺-X¹Σ_g⁺(v′,v″) of Na₂ in the range between 16835 and 16960 cm^?1 are analyzed. The spectra are free of first-order-Doppler broadening at low internal temperature. Rotational and vibrational assignments of 10 bands are reported. Rotational and vibrational levels, especially the (22, 1) band, are found to be perturbed by the b³Π_u state. The band origins and line frequencies calculated from previously reported constants do not reproduce the observed values. The disagreement between the calculated and observed values is discussed. More accurate constants are needed to predict the line locations.     

Magnetization reorientation in HoCo5-xNix and HoCo5-xCux compounds

The studies of magnetic anisotropy of HoCo_5-xNi_x and HoCo_5-xCu_x compounds in the temperature range between 60 and 293 K are presented. The magnetization reorientation from the c-axis to the base plane has been observed. The experimental results are analyzed on the base of the Irchin and Rozenfeld model.     

Multi-nucleus IBA calculations in the NπNν scheme

IBA-1 calculations for ～ 100 nuclei in three mass regions from A = 100–200 are carried out according to a recently proposed N_πN_ν parametrization. The calculations use a total of only seven constants consisting of four parameters which are constant for all 100 nuclei and one parameter which takes on a separate value for each of the three regions. The changes in nuclear structure for each region are reproduced and the detailed values of individual energy levels and B(E2) values are reasonably well accounted for. The implications of the extreme economy in parameters are discussed and the usefulness of the present approach for other collective models is pointed out.     

πℓ2, Kℓ3and K0−K0 constraints on leptoquarks and supersymmetric particles

Mass bounds from different processes for charged Higgs particles, for pseudoscalar leptoquarks occurring in dynamically broken theories, for vector leptoquarks occurring in the Pati-Salam type of grand unified theories and for the exotic particles of supersymmetric theories are studied. The processes considered are the π → eν to π → μν branching ratio, the CP-violating K?3 decay parameters, and the CP-violating part of the K_L ? K_S mass difference. The π → eν to π → μν branching ratio sets the most stringent bounds, 0.5 TeV for charged Higgs particles, 1 TeV for pseudoscalar leptoquarks, 125 TeV for vector leptoquarks and 0.1–1 TeV for the supersymmetric partners of ordinary particles. The π?2 branching ratio should be sensitive at the present experimental accuracy to the effects of pseudoscalar leptoquarks.     

Electronic and structural properties of ZnxCd1−xSySe1−y alloys lattice matched to GaAs and InP: An EPM study

The electronic, optical and structural properties of Zn_xCd_1−xS_ySe_1−y quaternary alloys lattice matched to GaAs and InP are studied. The electronic band structure and density of states are computed using empirical pseudopotential method. The disorder effects are included via modified virtual crystal approximation. The bandgap computed from band structures are utilized to evaluate refractive indices, dielectric constants and ionicity factors for the alloys. Among structural properties elastic constants and bulk moduli are computed by combining the EPM with Harrison bond orbital model. All possible semiconductors from the ZnCdSSe system are found to have direct bandgap. The lattice matched alloys have larger band gap and more ionic character than the lattice matched compounds.     

Oscillator strengths for the 2s2, 2p2, 2s3s(1S)-2s2p(1P) transitions of B(II)

Accurate configuration interaction wavefunctions for the 2s²(¹S), 2p²(¹S), 2s3s(¹S) and 2s2p (¹P) states of B(II) are calculated in a single optimized orbital basis of 7s, 6p and 4d Slater-type orbitals. 95, 84, 57 and 90% of the correlation energies, respectively, are realized by these wavefunctions. Oscillator strengths for the three ¹S-¹P transitions are calculated from these and from less accurate wavefunctions in the same orbital basis. The length values obtained from our most accurate wavefunctions, in order of increasing ¹S energy, are 0.9885, 0.202 and 0.007. The degree of accuracy of these oscillator strengths is estimated by noting the convergence to final values as increasing percentages of correlation energies are included in the wavefunctions together with the increasing agreement between length and velocity formulas. The exact theoretical oscillator strength for the resonant line is projected to be 0.985 with an error almost certainly not greater than ±0.015. The theoretical oscillator strengths for the other lines are considered to be 0.21±0.02 and less than 0.007, respectively.     

40Ca(d, α)38K and isospin

We investigate the ⁴⁰Ca(d, α_{0, 1, 2, 4})³⁸K reactions for E_d = 4.00–4.61 MeV. The α₁ and α₄ transitions are isospin forbidden. The resonant-like structures observed in the α₀, α₁, α₂, and α₄ transitions are consistent with Ericson theory. In addition we can fit a portion of the α₁, data with a few interfering Breit-Wigner resonances. The level parameters for the corresponding ⁴²Sc levels are given.     

The crystal structures of the ion conductors (NH+4)Zr2(PO4)3and (H3O+)Zr2(PO4)3

The crystal structures of (NH⁺₄)Zr₂(PO₄)₃ and (H₃O⁺)Zr₂(PO₄)₃ have been determined from neutron time-of-flight powder diffraction data obtained at 15 K. Both compounds are rhombohedral, $\text{R}\text{3}\text{c}$, with cell parameters a=8.7088(1) and c=24.2197(4) Å for the ammonium compound and a=8.7528(2), c=23.6833(11) Å for the hydronium compound. In both cases the ions are completely localized in the type I cavities and hydrogen bonded to lattice oxygens. The measured unit cell parameters are relatively large for this class of compounds but the entrance ways into the cavities are still too small to allow for unrestricted movement of the ions. Thus the low conductivity of the hydronium ion is related to this and other structural features.     

Structure and magnetic order of Cr-rich Rb2Cr1-xMnxCl4 crystals

The distorted K₂NiF₄-structure and the magnetic behaviour of the quasi two-dimensional magnetic system Rb₂Cr_1-xMn_xCl₄ (0 ? x ? 0.5) are studied by neutron diffraction and magnetic measurements. Strong correlations between ferromagnetic coupling and cooperative Jahn—Teller order are indicated by their occurence in the same concentration range 0 ? x ? 0.41.The percolation threshold x_F near x = 0.41 and the x, T-dependence of the para- to ferro-magnetic phase boundary are quite similar to that found in systems with non-magnetic impurities. Further we report the magnetic moment magnitudes in this percolative system.     

ω Production in the reaction π−p → π+π−π0n at 8 and 12 GeV/c

The reaction π^?p → ωn has been studied at 8 and 12 GeV/c incident momenta with the CERN Omega spectrometer using a neutron time of flight trigger. The differential cross sections and the ω-decay density matrix elements are presented as functions of the momentum transfer squared ?t in the range of 0.02 to 0.80 GeV². The data are used to evaluate the intercept and slope of both the natural and unnatural parity exchange trajectories. Regge exchange amplitude factorisation tests involving the reaction πN → ωN are investigated.     

Electronic structure of cubic ErxGa1−xN using the LSDA+U approach

Electronic structure calculations were performed for substitutional erbium rare-earth impurity in cubic GaN using density-functional theory calculations within the LSDA+U approach (local spin-density approximation with Hubbard-U corrections). The LSDA+U method is applied to the rare-earth 4f states. The Er_xGa_1−xN is found to be a semiconductor, where the filled f-states are located in the valence bands and the empty ones above the conduction band edge. The filled and empty f-states are also shown to shift downwards and upwards in the valence and conduction bands, respectively, with increase in the U potentials.     

Magnetic properties of Mg1-pMnpTe2 near p = 0.5

Precise magnetization measurements and neutron diffraction measurements are carried out for Mg_1-pMn_pTe₂ near the critical concentration p = 0.5 for the antiferromagnetic ordering. A magnetization property which is similar to micto-magnetism is observed for p = 0.35 and p = 0.45 samples. The susceptibility shows an anomaly at T_f and field-cooling effect is notable below T_f. Neutron diffraction experiments show that most of the manganese moments are ordered antiferromagnetically for p = 0.53 while small fractions of Mn²⁺ are ordered for p = 0.45 and p = 0.35.     

On the induced cobalt moments in (GdxY1−x)Co3 compounds

We report the results of magnetic measurements on (Gd_xY_1?x)Co₃ compounds with x ? 0.2, in the temperature range (4.2–1300) K. The compounds are ferrimagnetically ordered, the cobalt magnetization being anti-parallel oriented to that of gadolinium. The mean cobalt moment is dependent on composition. In the paramagnetic range the reciprocal susceptibility obeys a non-linear variation. By using a two sublattices model, the mean values of the exchange interactions inside and between sublattices are determined. The analysis of the data shows that the changes of the cobalt moments are due to the variations of the exchange fields acting on these atoms. Finally, the magnetic behaviour of cobalt atoms in these compounds is discussed.     

Use of calculated centrifugal distortion constants (Dν, Hν, Lν and Mν) in the analysis of the B ← X system of I2

Fourier spectroscopy measurements of 14 703 lines from the B-X band system of I₂ are analyzed using centrifugal distortion constants calculated from RKR curves by the perturbation theory method of Hutson [J. Phys. B14, 851–857 (1981)]. Only vibrational and rotational constants are varied in the least-squares fits, with the centrifugal distortion constants fixed at the calculated values. The fit obtained in the present work is as good as when the centrifugal distortion constants are treated as independent parameters, but the molecular constants obtained are physically more meaningful because the statistical correlation between parameters is reduced. The analysis includes B-state vibrational levels up to v′ = 72, which is bound by only 0.5% of the well depth; the method used for calculating centrifugal distortion constants remains reliable even this close to dissociation. It is found that centrifugal distortion constants up to fifth order make significant contributions to the observed line positions.     

The analyzing power Ay(θ) for the 9Be(p, n)9B reaction from 8 TO 15 MeV

The analyzing power A_y(θ) for the ⁹Be(p, n)⁹B reaction was measured at seven energies between 8.1 to 15.0 MeV for reaction angles between 0° and 100° (c.m.). The A_y(θ) values are predominantly negative and exhibit a smooth variation with energy. The significance of these results in Lane optical- model calculations for the ⁹Be + nucleon system and in comparisons between the observables P^y(θ) and A_y(θ) is indicated.     

Investigations of crystal and magnetic properties of the Mn5−xFexGe3 intermetallic compounds

The Mn_5?xFe_xGe₃ intermetallic compounds are investigated with X-ray, neutron diffraction, magnetometric and Mössbauer effect methods. It is found that crystal structure of x = 1 compound is of D8₈ type while the structure of x = 3, 4 and 5 compounds is of B8₂ type. All are ferromagnets with collinearly ordered atomic spins. The lattice constants are derived from X-ray diffraction patterns, while magnetometric measurements yield the Curie temperatures and Weiss constants as well as the values of magnetic moments per molecule in ferromagnetic and paramagnetics states. The distributions of Fe and Mn atoms among two non-equivalent crystal sites are determined with the neutron diffraction method and are confirmed by the Mössbauer effect measurements. The parameters of hyperfine interactions are derived from Mössbauer absorption spectra and are attributed to iron atoms in two non-equivalent crystal sites.     

Analysis of the ν9ν10 band system of allene

The infrared spectrum of allene has been recorded with high resolution (0.002-0.004 cm^?1) on a Fourier transform instrument in the region 730 to 1170 cm^?1 containing the perpendicular bands, ν₉ and ν₁₀. A total of 21 subbands with KΔK ranging from ?6 to +14 have been assigned in the ν₉ band, and 26 subbands with KΔK = ?10 to +15 have been assigned in the ν₁₀ band. The bands are affected by a combination of a J_z-Coriolis and a quartic anharmonic interaction between their upper states ν₉ and ν₁₀. In addition, several other more localized perturbations are found in the spectrum. The nature of the interactions responsible for these perturbations is discussed, and five of the strongest perturbations are quantitatively accounted for by constructing a Hamiltonian matrix which includes five different perturbing states and their Coriolis and anharmonic resonances with the ν₉ and ν₁₀ upper states. A set of spectroscopic constants for the ν₉ and ν₁₀ states and for some of the perturbing states is reported.     

Elastic anomalies of La0.67Sr0.33−xBaxMnO3 in the vicinity of TC

With a view to understand the elastic behaviour of a material system, La_0.67Sr_0.33−xBa_xMnO₃ (where x=0, 0.1, 0.2, and 0.33) especially in the vicinity of their magnetic transition temperature T_C, a systematic investigation of ultrasonic velocity over a temperature range 300-400 K has been carried out. The materials prepared by citrate gel route, were characterized structurally by XRD and on analyzing the XRD patterns, it has been concluded that all the samples are having rhombohedral structure with space group of R3?c. The magnetic (T_C) transition temperatures determined by AC susceptibility measurements are found to decrease continuously with increasing barium concentration. Finally, the ultrasonic longitudinal velocities of all the samples are found to exhibit considerable softening in the vicinity of their magnetic transition temperatures, T_C and the observed behaviour is explained using mean field theory and Jahn-Teller theorem.