The magnetic hyperfine field at140Ce in nickel

The hyperfine interaction of¹⁴⁰Ce in nickel has been investigated by the time-differential perturbed-angular-correlation technique (TDPAC). The probe was produced by isotope separator implantation of the fission product¹⁴⁰Xe, the ^- decay chain of which finally populates excited states of¹⁴⁰Ce.Different spin rotation spectra were observed before and after an 8 h annealing at 415°C. The analysis of the spectra led to the conclusion that the Ce ions were in the diamagnetic 4⁺ state. The dominant contributions to the hyperfine interaction are two different magnetic hyperfine fields: |H _hf ¹|=385±7 kOe and |H _hf ²|=276±12 kOe.H _hf ¹ disappears after annealing. The fraction of nuclei which observeH _hf ² is increased by the annealing procedure from 16% to 75%. It is assumed thatH _hf ¹ is the hyperfine field of CeNi in an unperturbed substitutional site andH _hf ² is attributed to Ce ions which have trapped a single vacancy.     

UV excitable Y2? x ? y Gd y SiO5:Ce x phosphors for cool white light emission

Cool white light was realized in Y_2−x−y Gd _x SiO₅: Ce _y phosphor under near UV excitation, due to the occupation Ce³⁺ in Y³⁺ 1st and 2nd site, synthesized using solid state carbothermal reduction route. SEM with elemental analysis show the existence of Gd in Y₂SiO₅:Ce enhances the particles size in comparison to Y₂SiO₅:Ce phosphors alone. Gd³⁺ (0.00≤x≤0.75) and Ce³⁺ (0.02≤y≤0.10) concentration was optimized to 0.50 and 0.08 in Y₂SiO₅, respectively. The CIE chromaticity color coordinates (0.24, 0.20) are close to cool white light value which could be useful for the fabrication of cool white LED.     

Growth and the luminescence properties of a lutetium gadolinium garnet doped with Ce3+ and Pr3+ ions

Crystals of lutetium gadolinium garnet solid solutions (Lu_{1 − x} Gd _x )Al₅O₁₂ (0 ≤ x ≤ 0.6) doped with Ce³⁺ and Pr³⁺ ions have been prepared by the horizontal directional crystallization method, and their optical and luminescence properties have been investigated. It has been established that the introduction of gadolinium into the lutetium garnet lattice leads to a decrease in the antisite luminescence (Lu_Al centers) in the UV spectral range and to sensitization of the Ce³⁺ ion luminescence. By contrast, the presence of gadolinium results in the quenching of the Pr³⁺ luminescence due to the nonradiative excitation transfer from Pr³⁺ ions to Gd³⁺ ions.     

μ + SR studies of antiferromagnetic chromiumSR studies of antiferromagnetic chromium

μ ⁺ SR measurements have been performed on Cr single crystals at temperatures 60 mK≤T≤295 K in applied magnetic fields 0≤B _appl≤1.5 T. The temperature dependence of the observed precession frequencies and transverse relaxation rates can be explained by the assumption that theμ ⁺ are hopping between adjacent tetrahedral interstices. At temperaturesT≤11 K evidence for an interaction between theμ ⁺ and the spin-density waves in Cr has been found. The directions and magnitudes of the lattice magnetic moments are unaffected by the applied magnetic fields.     

IR reflection and Raman spectra of β-Tl1 ? x Cu x InS2 (0 ≤ x ≤ 0.015) single crystals

The IR reflection and Raman spectra of β-Tl_{1 − x} Cu _x InS₂ (0 ≤ x ≤ 0.015) single crystals have been studied in the temperature range 84–300 K. It is shown that partial replacement of thallium by copper atoms leads to a decrease in the frequencies of the corresponding oscillations in the frequency range 40–500 cm⁻¹ and does not induce (at given concentrations) local oscillations. Analysis of the transformation of the IR reflection spectra at T ₂ ≈ 185 K revealed a ferroelectric phase transition. Original Russian Text ? A.N. Georgobiani, A.Kh. Matiyev, C.V. Bulyarski, T.A. Matiyeva, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 138–140.     

Investigation of low-temperature quantum diffusion in α-iron byμ + SR experiments on a single-crystal sphereSR experiments on a single-crystal sphere

The longitudinalμ ⁺-spin relaxation rate has been measured on a high-purity spherical α-iron single crystal at temperaturesT down to 20 mK and in applied magnetic fieldsB _appl parallel to 〈111〉 up to 3 T. Only above 1 K can the data be satisfactorily described by one rate constantГ. At 1 T≤B _appl≤2 T and 50 mK≤T≤300 mK, oscillations (“wiggles”) were in addition superimposed on the longitudinal relaxation. A qualitative understanding of the measurements may be achieved in terms of the increasing influence of internal stresses onμ ⁺ diffusion as the temperature is lowered.     

Influence of magnetic field on the superconducting transition in a Nd1.82Ce0.18CuO4−δ film

The temperature and magnetic-field dependences of the resistivity ρ and Hall effect R(j‖ab, B‖c) in a Nd_1.82Ce_0.18CuO_4−δ single crystal film (T _c =6 K) is investigated at temperatures 1.4≤T≤20 K and magnetic fields 0≤B≤5.5 T. At the lowest temperature T=1.4 K the resistive state (exhibiting resistivity and the Hall effect) arises in a magnetic field B=0.5 T. A transition to the normal state is completed at B _c 2≃3 T, where the Hall coefficient becomes nearly constant. The negative magnetoresistance due to the weak-localization effect in the normal state is observed for B>3 T. The nonmonotonic behavior and the inversion of the sign of R(B) in the mixed state are explained in a reasonable way by the flux-flow model with the effect of pinning taken into account. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 6, 407–411 (25 September 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Description of cross sections for photonucleon reactions on tin isotopes at photon energies in the range 2 ≤ <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">γ</Emphasis></Subscript> ≤ 140 MeV

A modified model of preequilibrium decay is considered. This model makes it possible to calculate cross sections for multiparticle photonucleon reactions with allowance for the impact of collective isospin effects. Features of the photodisintegration of 101 ≤ A ≤ 135 tin isotopes in the energy range 2 ≤ E _γ ≤ 140 MeV are studied on the basis of this model.     

Diamagnetism and muon knight shift in semimetallic and semiconducting BiSb single crystals

A series of single crystalline Bi_1−x Sb _x alloys (x=0,0.03, 0.14, 0.19, 0.37) covering both the semimetallic (0≤x≤0.07 orx≥0.22) and the semiconducting region (0.07≤x≤0.22) was examined using the stroboscopic μ⁺ SR method. The μ⁺ Knight shift, negative for all Sb concentrations, shows pronounced temperature dependences and large anisotropies. A scaling with the-negative-total magnetic susceptibility [1] is found in the semiconducting alloys. In detail, the isotropic part of the μ⁺ Knight shift is proportional to the isotropic part of the susceptibility, and the anisotropic Knight shift scales with the anisotropic susceptibility. Possible mechanisms leading to this relation are investigated.     

Investigation of the Magnetic Hyperfine Field at 140Ce on Gd Sites in GdCo2 Compound

Perturbed angular correlation experiments on ¹⁴⁰La–¹⁴⁰Ce probes substituting for the Gd positions on GdCo2 demonstrate that the magnetic hyperfine field (MHF) on Ce atoms follows an expected Brillouin function but with a substantially reduced saturation value as compared with the MHF acting on free Ce⁺³ ions. The results were interpreted with the aid of first principles electronic structure calculations showing that the reduced value of the MHF is a consequence of a small orbital contribution to the MHF which was attributed to the de-localization of the Ce 4f electronic state.     

Theψ-particles in an SU4 scheme with anomalous currents

The recently discovered narrow peaks (theψ-particles) in e⁺e⁻ system at 3.105 and 3.695 GeV are interpreted as hadrons in a broken SU₄ symmetry scheme. A new additional additive quantum number, parachargeZ, is combined with the usual SU₃ quantum numbers in the group SU₄. Theψ (3.1) is assigned to a near ideally mixed15⊕1 multiplet of vector mesons (containing theρ) as theI=Y=0, charge conjugationC=−combination ofZ=±1.members. Theψ (3.7) is assigned correspondingly to another mixed15⊕1 multiplet containing theρ′ (1600). The hadronic electromagnetic interactions are modified by the addition of (non-minimal) anomalous pieces that can changeZ. The decays of theψ-particles are discussed. New enlarged SU₄ multiplets of other hadrons are proposed. Tests of our scheme are put forward. The most crucial test will be the observation of two rather broad resonances in e⁺ e⁻ collisions with masses around 4.2 GeV and 5.1 GeV. Another prediction is the presence of energetic photons in the decays of theψ-particles. Important results concerning the recently observed phenomena in the process e⁺e⁻→hadrons follow in this scheme.     

High-resolution measurement of NMR-ON for191PtFe

NMR-ON measurements on¹⁹¹PtFe were repeated to look for a reported quadrupole splitting effect: a sample annealed at 850°C and measured at 15.1(6) mK gives a spectrum with a single gaussian peak with a line width of 0.39(4) MHz, the narrowest ever observed. The spectrum obtained with another sample annealed at 650°C and measured at 8.3(4) mK resembles one with a quadrupole splitting, but the ratio of the second sub-resonance to the first is inconsisten with the estimation from a model which takes account of a quadrupole splitting and fast relaxation limit. The present study shows the quadrupole splitting ofv _Q (¹⁹¹PtFe)≤0.86 MHz.     

Low-Temperature Dynamics of the Curie-Weiss Model: Periodic Orbits,Multiple Histories,and Loss of Gibbsianness

We consider the Curie-Weiss model at initial temperature 0<β ⁻¹≤∞ in vanishing external field evolving under a Glauber spin-flip dynamics with temperature 0<β′⁻¹≤∞. We study the limiting conditional probabilities and their continuity properties and discuss their set of points of discontinuity (bad points). We provide a complete analysis of the transition between Gibbsian and non-Gibbsian behavior as a function of time, extending earlier work for the case of independent spin-flip dynamics.     

Superhyperfine structure of the EPR spectra of Ce<Superscript>3+</Superscript> ions in Li<Emphasis Type="Italic">R</Emphasis>F<Subscript>4</Subscript> (<Emphasis Type="Italic">R</Emphasis> = Y,Lu, Tm) double fluorides

The EPR spectra of Ce³⁺ impurity ions in LiYF₄, LiLuF₄, and LiTmF₄ double-fluoride single crystals have been investigated at a frequency of ∼9.3 GHz in the temperature range 5–25 K. The effective g factors of the ground Kramers doublet of the cerium ions in three crystals are close to each other (g _‖ = 2.737, g _⊥ = 1.475 for LiYF₄:Ce³⁺). A superhyperfine structure of the EPR spectrum of Ce³⁺ ions in the LiTmF₄ Van Vleck paramagnet has been observed in the external magnetic field B oriented along the crystallographic axis c (B ‖ c). The superhyperfine structure of the EPR soectra of the Ce³⁺ ions in the LiYF₄ and LiLuF₄ diamagnetic matrices is resolved for B ⊥ c. Possible factors responsible for this pronounced difference in the properties of the systems studied have been discussed.     

Calculation of spectroscopic constants and radiative parameters for A1Σ u+ -X1Σ g+ and B1Πu-X1Σ g+ electronic transitions of sodium dimer

Vibrational, rotational, and centrifugal spectroscopic constants and radiative parameters, i.e., the Einstein coefficients, oscillator strengths, and wave numbers for vibrational transitions in electronic systems of bands A ¹Σ _u ⁺-X ¹Σ _g ⁺ (0 ≤ v′ ≤ 25; 0 ≤ v″ ≤ 44), B ¹Π _u -X ¹Σ _g ⁺ (0 ≤ v′ ≤ 29; 0 ≤ v″ ≤ 47), and the radiative lifetimes for the vibrational levels of excited states of the sodium dimer, are calculated. The calculations are carried out based on semiempirical potential curves constructed in this study. The calculated spectroscopic constants and radiative lifetimes are compared to the experimental values.     

Adjoint representation admixture to weak nonleptonic decays in SU(4) and SU(8)

In order to remove some of the unsatisfactory features of the GIM model, we consider15-admixture in SU(4). ΔC=±ΔS decays remain unaffected. Lee-Sugawara sum-rule is obtained.15-admixture is extended then to63-admixture in SU(8). The most general Hamiltonian (H _w∼63⊕720⊕1232) in SU(8) is found to give Lee-Sugawara relation and Σ₊ ⁺=0 forS-wave decays of uncharmed baryons. Decay amplitude relations for ΔC=−1, ΔS=0 mode are obtained.     

Dc and Ac conductivity of La2CuO4+δ

The complex conductivity of La₂CuO_4+δ has been investigated for frequencies 20 Hz≤ν≤4 GHz and temperatures 1.5K≤T≤450 K. Two single crystals with δ≈0 and δ≈0.02 were investigated, using dc (four-probe), reflectometric and contact-free techniques. At high temperatures the dc conductivity is thermally activated with low values of the activation energy. For low temperatures Mott's variable range hopping dominates. The real and imaginary parts of the ac conductivity follow a power-law dependence σ∼v ^s, typical for charge transport by hopping processes. A careful analysis of the temperature dependence of the ac conductivity and of the frequency exponents has been performed. It is not possible to explain all aspects of the ac conductivity in La₂CuO_4+δ by standart hopping models. However, the observed minimum in the temperature dependence of the frequency exponents strongly suggests tunneling of large polarons as dominant transport process.     

NMR-ON measurements of187WFe,182,183,186ReNi,186ReFe and203PbFe

The magnetic hyperfine splitting frequencies of¹⁸⁷WFe,¹⁸²Re(j ^π=2⁺)Ni,¹⁸³ReNi,¹⁸⁶ReNi,¹⁸⁶ReFe and²⁰³PbFe in a zero external magnetic field have been determined by the NMR-ON method at about 7 mK as 225.56(6), 130.9(1), 98.17(4), 136.6(4), 1007.0(3) and 58.43(3) MHz, respectively. With the knowng-factors ofg(¹⁸⁶Re, 1⁻)=1.739(3) andg(²⁰³Pb, 5/2⁻)=0.27456(20), the following hyperfine fields were deduced:B _HF(¹⁸⁶ReNi)=−103.05(35) kG;B _HF(¹⁸⁶ReFe)=−759.7(13) kG;B _HF(²⁰³PbFe)=+279.18(25) kG. Taking hyperfine anomalies into account, theg-factor of¹⁸³Re was deduced as |g(¹⁸³Re, 5/2⁺)|=1.267(6). With the assumption of Knight shift factorK=0, theg-factors of¹⁸²Re and¹⁸⁷W and the hyperfine field of¹⁸⁷WFe were determined as |g(¹⁸²Re, 2⁺)|=1.63(5), |g(¹⁸⁷W, 3/2⁻)|=0.414(10) andB _HF(¹⁸⁷WFe) =−714(18) kG. The large hyperfine anomaly was deduced to be¹⁸³W Δ¹⁸⁷W =−0.124(22).     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Band structure and dominating electron-scattering mechanisms in Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis>−<Emphasis Type="Italic">y</Emphasis></Subscript>Mn<Subscript>x</Subscript>Fe<Subscript>y</Subscript>Se

Magnetic and kinetic properties as well as transmission and absorption spectra of Hg _1−x−y Mn _x Fe _ySe (0.09 ≤ x ≤ 0.099 and 0.001 ≤ y ≤ 0.01) crystals are investigated at H ≈ 0.5–6 kOe in the temperature range T = 77–300 K. The band parameters are determined on the basis of experimental data. It is found that in the crystals under study at T ≈ 300 K, electron scattering by polar optical phonons dominates, direct optical band-to-band transitions occur, and replacement of a part of Mn atoms by Fe for x + y = 0.1 results in an increase in E_g ^op with Fe content. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 35–39, March, 2007.