A sequence of two ferrotoroidal phase transitions in nickel-bromine boracite Ni3B7O13Br

The phenomenological theory of a sequence of two second-order phase transitions in Ni-Br boracite is presented. Two different components of the toroidal moment vector T _i are the order parameters of these transitions. Expressions are derived for the temperature dependences of the spontaneous values of T _i , polarization P _i , and magnetization M _i and the dielectric χ_ij=dP _i /dE _j , magnetic k _ij =dM _i /H _j , and magnetoelectric α _ij=dP _i /dH _j =dM _j /dE _i susceptibilities. Some of these susceptibilities display sharp temperature peaks in the vicinity of phase transitions.     

High-resolution infrared study on DCCI: harmonic force field of monoiodoacetylene

A high-resolution infrared spectrum of DCCI has been measured in the regions of the bands of 2ν₁, ν₁+ν₂, ν₂+ν₃, ν₂+ν₄, ν₂+ν₅, and ν₄+ν₅. Using these bands together with the spectra measured previously, the rovibrational states of 2ν₁, ν₁+ν₂, ν₁+ν₃, ν₁+ν₄, ν₁+ν₅, ν₁+2ν₅, ν₂+ν₃, ν₂+ν₄, ν₂+ν₅, ν₂+2ν₅, ν₃+ν₄, ν₄+ν₅, and ν₄+2ν₅ have been analyzed. Various l-type and Fermi resonances have been taken into account in the analysis. In addition, the weak Coriolis resonance between the levels υ₃=υ₄=1 and υ₄=2 has been considered. Accurate values for the molecular constants and the appropriate resonance parameters have been obtained. The unperturbed normal vibrational frequencies associated to the equilibrium state have been calculated for both isotopic species HCCI and DCCI. Then the harmonic force constants for monoiodoacetylene have been determined.     

CriticalZ N spin systems andφ 4 theory

The continuum limit ofZ _N (N≧4) spin systems at the critical point is identified with a two-component massless scalar field with quartic self-interactionf _αβγδ φ _α φ _β φ _γ φ _δ , withf _αβγδ = 1/3 (δ _αβ δ _γδ +δ _αγ δ _βδ +δ _αδ δ _βγ ) ≡S _αβγδ forN≧5 andf _αβγδ =S _αβγδ ? 2/3δ _αβ δ _αγ δ _αδ forN=4. The result is based on the study of the two and four-point irreducible correlation functions in the one-loop approximation.     

Structural and electronic properties of zincblende phase of Tl x Ga1−x As y P1−y quaternary alloys: First-principles study

Using the first-principles band-structure method, we have calculated the structural and electronic properties of zincblende TlAs, TlP, GaAs and GaP compounds and their new semiconductor Tl _x Ga_1?x As _y P_1?y quaternary alloys. Structural properties of these semiconductors are obtained with the Perdew and Wang local-density approximation. The lattice constants of Tl _x Ga_1?x As, Tl _x Ga_1?x P ternary and Tl _x Ga_1?x As _y P_1?y quaternary alloys were composed by Vegard’s law. Our investigation on the effect of the doping (Thallium and Arsenic) on lattice constants and band gap shows a non-linear dependence for Tl _x Ga_1?x As _y P_1?y quaternary alloys. The band gap of Tl _x Ga_1?x As _y P_1?y , E _g (x, y) concerned by the compositions x and y. To our awareness, there is no theoretical survey on Tl _x Ga_1?x As _y P_1?y quaternary alloys and needs experimental verification.     

Die Auger-Spektren derL 2- undL 3-Schale von Argon

TheL ₂ MM andL ₃ MM-Auger spectra of gaseous argon have been investigated with an electrostatic spectrometer with energy resolution of 0.17%. The ionization in theL ₂ andL ₃ shell was caused by electron impact. It was possible to separate allL ₂ MM andL ₃ MM lines except the components of transitions to triplet final states. The experimental relative intensities of transitions within theL ₂ M _2,3 M _2,3 andL ₃ M _2,3 M _2,3 groups agree well with theoretical values, calculated byRubenstein, whereas the relative intensities of transitions of the groupsL ₂ M ₁ M ₁,L ₃ M ₁ M ₁,L ₂ M ₁ M _2,3 andL ₃ M ₁ M _2,3 differ systematically from theoretical values.     

Ab initio determination of spectroscopic parameters for ethane-like molecules in the ground vibrational state

The quadratic rotational constants A and B and torsional barrier V₃, distortion parameters D_J, D_K, and D_JK, torsional distortion parameters D_m, D_Jm, and D_Km, and barrier-dependence parameters F_3J, F_3K, and F_3m have been determined for CH₃CH₃, CH₃CD₃, CD₃CD₃, and CH₃SiH₃ from the results of ab initio calculations done at the CCSD(T) level. Calculated values for the first six parameters are consistently within about 1% of experimental values, while the relative errors for D_m, D_Km, F_3J, and F_3K are generally less than 20%. Calculation of the parameters D_Jm and D_sJ is found to be more problematic, even with the application of vibrational averaging in the harmonic oscillator approximation. There is evidence that this is due to the influence of vibrational contact transformations in the experimental values.     

Microwave vibration rotation spectrum of diacetylene

Microwave spectrum of diacetylene (HCCCCH) arising from vibration-rotation transitions between closely lying excited vibrational states was observed. The ν₈-ν₆ band which has been reported in our previous paper was reinvestigated in a frequency region extended to 175 GHz, where ν₆ and ν₈ respectively represent the symmetric (π_g) and antisymmetric (π_u) CCH bending vibrations. The ν₈ + ν₉ ? ν₆ ? ν₉ band, where ν₉ is the lowest frequency (220 cm^?1) bending mode with π_u symmetry, was newly identified. Precise molecular constants associated with the ν₈ - ν₆ band and the three subbands Σ_g⁺ - Σ_u⁺, Σ_g^? - Σ_u^?, and Δ_g - Δ_u of the ν₈ + ν₉ ? ν₆ ? ν₉ band were determined by least-squares analyses. l-Type resonance interactions in the ν₆ + ν₉ and ν₈ + ν₉ vibrational states were analyzed. Also, a Fermi resonance which perturbs the Σ_g⁺ substate of the ν₈ + ν₉ state was discussed. The transition dipole moments were determined from the Stark effect for the Σ_g⁺ - Σ_u⁺ and Σ_g^? - Σ_u^? subbands of ν₈ + ν₉ ? ν₆ ? ν₉.     

Transport studies of YBa2Cu3Oy/YxPr1−xBa2Cu3Oy and YBa2Cu3Oy/R0.7M0–3MnO3 superlattices,in which R=La or Nd,and M=Ca or Sr

We report the transport studies of YBa₂Cu₃O_y/Y_xPr_1−xBa₂Cu₃O_y and YBa₂Cu₃Oy/R_1−xM_xMnO₃ superlattices in magnetic fields in which R=La or Nd, and M=Ca or Sr. The X-ray diffraction of samples shows superlattice structure. The resistive transition in a magnetic field shows thermal activated behavior. The flux pinning is reduced when the coupling strength between YBCO layers is decreased. The angular dependence of the critical current of YBa₂Cu₃O_y/PrBa₂Cu₃O_y superlattices reveals the dimensionality of superlattices. The magnetoresistance ratio (MR), |Δρ(H=7 T)−Δρ(H=0)|/Δρ(H=7 T), of YBa₂Cu₃O_y/R_1−xM_xMnO₃ superlattices is affected by the layer coupling of R_1−xM_xMnO₃ layers. The enhancement of the MR ratio in the tri-layer YBa₂Cu₃O_y/La_0.7M_0.3MnO₃/YBa₂Cu₃O_y film in the low temperature regime is significant and has a value of 33650% at T=75 K. We attribute this enhancement of the MR to the ordering of magnetic moment in ferromagnetic layers in magnetic fields. The results are discussed in terms of existing theories.     

The influence of actinides on the superconducting properties of molybdenum chalcogenides

The results of the investigations of molybdenum chalcogenides: U_xPb_1?xMo₆S₈, U_xPb_1?xMo_6.4S₈, Th_xPb_1?xMo₆S₈, U_x1?xMo₆S₈ with actinides as a component, are presented. As a rule the decrease of superconducting parameters with x was observed. Possible influence of magnetic interaction in this system is noted.     

The magnetic properties of oxide spinel Li0.5Fe2.5−2xAlxCrxO4 solid solutions

The exchange interactions (J_BB and J_AB are the intra and the inter-sublattice exchange interactions between neighbouring spins, respectively) are obtained by using the general expressions of canting angle and critical temperature obtained by mean field theory of Li_0.5Fe_2.5−2xAl_xCr_xO₄. The expression of magnetic energy of Li_0.5Fe_2.5−2xAl_xCr_xO₄ is obtained for different spin configurations and dilution x. The saturation magnetisation of Li_0.5Fe_2.5-2xAl_xCr_xO₄ is obtained with different values of dilution x. The magnetic phase diagram of Li_0.5Fe_2.5-2xAl_xCr_xO₄ materials is obtained by high temperature series expansions (HTSEs). The critical exponent associated with the magnetic susceptibility of Li_0.5Fe_2.5−2xAl_xCr_xO₄ is deduced.     

Magnetic anisotropy of single-domain particles

The competition between uniaxial and cubic magnetic anisotropies of single-domain particles is analyzed theoretically. As long as K _1c /K _1u < 5 (K _1c and K _1u are the first constants of the crystallographic and uniaxial anisotropies), the value of K _1u noticeably affects coercive force H _c and relative residual magnetization j _r of particle ensembles. If the uniaxial anisotropy direction coincides with crystallographic axis 〈111〉 or 〈100〉, the dependences of H _c and j _r on ratio K _1c /K _1u have a minimum. The competition between the induced uniaxial anisotropy and cubic anisotropy was detected experimentally when the effect of temperature T on the H _c (T) and j _r (T) dependences for single-domain spherical particles of magnetic 3d alloys and γ-Fe₂O₃ oxide was investigated. For all single-domain particles studied here, the effect of crystallographic anisotropy on H _c and j _r is manifested at low temperatures, while uniaxial anisotropy plays a decisive role in the temperature range T > 250 K. The effect of second constant K ₂ on H _c and j _r of ensembles of single-domain particles with uniaxial and cubic anisotropies is investigated theoretically. It is shown that the value of K ₂ may substantially change the value of H _c for a particle ensemble, preserving the value of j _r unchanged.     

Relation of the 2S + 1 states per site potts model to a nonlinear spin-S ising model

The interaction energy of the Potts model with 2S + 1 states per site is of the form ∑_〈i,j〉δS_iS_j where δS_iS_j is the Kronecker delta symbol. The expansion of δS_iS_j in a finite power series in S_j and S_j is explicitly given.     

Embedding of the Galilei algebra into complex semisimple lie algebras

The following result is proven: Complex simple Lie algebras L? have subalgebras ε(?) isomorphic to the complex Galilei algebra ? if and only if L? ∈ {A_r (r ? 5); B_r (r ? 3); C_r, D_r (r ? 4); F₄; E₆; E₇; E₈}.The set of subalgebras ε(?) in A₅ decomposes intoconjugacy classes labelled by a complex number; there is only one conjugacy class in B?₃ and in C₄.     

Some tips on the decomposition of tensor product representations of compact connected lie groups

Let ?₁, ?₂, ?₃, ?₄ be irreducible representations of a compact connected semisimple Lie group G with highest weights Λ₁, Λ₂, Λ₃, Λ₄, respectively. Let ?₁?₂ (resp. ?₃?₄) be irreducible representations of G with highest weights Λ₁·Λ₂ (resp. Λ₃·Λ₄). It is assumed that one knows the Clebsch-Gordan series of ?₁??₃ and ?₂??₄ (resp. of S²?₁, S²?₂, A²?₁ and A²?₂). Then we formulate a result (Theorem 2) which gives information on the decomposition of ?₁?₂??₃?₄ (resp. of S²(?₁?₂) and A²(?₁?₂)). Though this result is not complete, it is useful because it delivers the information very quickly and in a very simple manner.     

The microwave spectra and structures of epihalohydrins: Epichlorohydrin

The microwave spectrum of the two chlorine isotopic species of epichlorohydrin ($\text{CH}{}_2\text{OCH}$CH₂Cl) is reported. The structure is a gauche conformation with the Cl atom twisted toward the oxygen side of the ring. The observed rotational constants (in MHz) and centrifugal distortion constants (in kHz) are: C₂H₃OCH₂³⁵Cl; A = 13 373.02, B = 2080.353, C = 1932.469, Δ_JK = ? 6, Δ_K = 2400, δ_J = ? 0.43, δ_K = 17, H_KJ = ? 0.13, H_K = 570, h_JK = 0.061, h_K = ? 5.1: C₂H₃OCH₂³⁷Cl; A = 13 361.24, B = 2028.853, C = 1887.990, Δ_JK = 0.31, Δ_K = 1669., δ_J = ? 0.16, δ_K = 54.1.     

Anomalous X-ray scattering studies on superionic glassy (As2Se3)-(AgX) systems (X = halides)

Anomalous X-ray scattering experiments for glassy room-temperature superionic conductors (As₂Se₃)_0.4 (AgI)_0.6 and (As₂Se₃)_0.4(AgBr)_0.6 were performed close to the As, Se, Ag, and Br K edges using a third-generation synchrotron radiation facility, ESRF. The differential structure factors, Δ_iS(Q), were obtained from detailed analyses, indicating that Δ_AsS(Q) and Δ_SeS(Q) of both the glassy superionic semiconductors are similar to those of glassy As₂ Se₃ except the prepeak in Δ_SeS(Q). The Δ_AgS(Q) spectrum of (As₂Se₃)_0.4 (AgI)_0.6 looks molten salt-like. However, the Δ_Ag S(Q) of (As₂Se₃)_0.4(AgBr)_0.6 glass have quite different features from that of (As₂Se₃)_0.4 (AgI)_0.6 glass in the low Q range, and the Δ_BrS(Q) has even a pre-shoulder around 13 nm^? 1 unlike molten salts. In the differential pair distribution functions Δ_ig(r) obtained from the Fourier transforms of Δ_iS(Q), the first peaks of Δ_Asg(r) and Δ_Seg(r) show no correlation with those of Δ_Agg(r) and Δ_Brg(r), and vice versa. From these results, it can be concluded that a pseudo-binary mixture of the As₂Se₃ network matrix and AgX-related ionic conduction pathways is a good structural model for these superionic glasses. Differences between the AgBr- and AgI mixtures were found in the second-neighbor structures around the Ag atoms, which may reflect those in the crystal structures of the AgX salts.     

Heterojunction band discontinuities of quaternary semiconductor alloys

A simple sp³ hybrid-orbital model for predicting valence-band discontinuities is proposed and applied to quaternaries. The effects of anion and cation disorder are taken into account explicitly within the coherent-potential approximation. Results for In_1?xGa_xP_1?yAs_y, In_1?xGa_xAs_1?ySb_y, Ga_1?xAl_xAs_1?ySb_y and In_1?xAl_xP_1?ySb_y lattice-matched to some binaries are shown. The broadening of valence-band-top levels due to alloy scattering is found negligible.     

The electrooptic effect in NH4IO3

The static electrooptic coefficients of NH₄IO₃ at room temperature are r₄₃ = 4.9, r₆₁ = 1.0, r₁₂n²₁ ? r₃₂n³₃ = 59.6, r₂₂n³₂ ? r₃₂n³₃ = 116.8 [ X 10^-12m/V]. The electrooptic effect depends on temperature and shows two ph ase transitions at 82.5°C and near 120°C.     

Magnetic transitions and magnetostrictive properties of Laves compounds Sm0.88Nd0.12(Fe1−xCox)1.93

The structure, magnetic and magnetostrictive properties of Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 (0≤x≤1.0) alloys have been investigated. The alloys have the cubic MgCu₂ structure over the whole composition range and the lattice parameter a decreases with increasing x. For 0≤x≤0.2, substitution of Co for Fe slightly increases the saturation magnetization M_s and Curie temperature T_c, while further substitution causes a decrease in both M_s and T_c. The spin reorientation is observed, and a phase diagram for the spin configurations of the Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 system is determined. The spontaneous magnetostriction λ₁₁₁ increases as x is increased, while a monotonic decrease of the saturation magnetostriction λ_s with x originates from the increase of λ₁₀₀ with opposite sign to that of λ₁₁₁, which may be caused by the filling of the d band due to Co substitution.