Spin-glass-like behavior in ZnxCryAlzSe4

The magnetic and electrical properties of the Al-doped polycrystalline spinels Zn_xCr_yAl_zSe₄ (0.13≤z≤0.55) with the antiferromagnetic (AFM) order and semiconducting behavior were investigated. A complex antiferromagnetic structure below a Néel temperature T_N≈23 K for the samples with z up to 0.4 contrasting with the strong ferromagnetic (FM) interactions evidenced by a large positive Curie-Weiss temperature θ_CW decreasing from 62.2 K for z=0.13 to 37.5 K for z=0.55 was observed. Detailed investigations revealed a divergence between the zero-field-cooling (ZFC) and field-cooling (FC) susceptibilities at temperature less than T_N suggesting bond frustration due to competing ferromagnetic and antiferromagnetic exchange interactions in the compositional range 0.13≤z≤0.4. Meanwhile, for z=0.55 a spin-glass-like behavior of cluster type with randomly oriented magnetic moments is observed as the ZFC-FC splitting goes up to the freezing temperature T_f=11.5 K and the critical fields connected both with a transformation of the antiferromagnetic spin spiral via conical magnetic structure into ferromagnetic phase disappear.     

Evidence for the existence of two electronic states in the chalcopyrite-type alloys CuFe(S1−zSez)2

Results of Mössbauer spectroscopy for the chalcopyrite-type of alloys CuFe(S_1–z Se _z )₂ in the range of composition 0z0.45 are presented. Room temperature spectra show two contributions: one is a magnetic spectrum (six lines) with a value of the hyperfine field near to that of chalcopyrite (z=0, in which an antiferromagnetic order occurs belowT=823 K), the other having only one line. The relative area of the single-line contribution increases asz increases. Forz=0.2, we also made Mössbauer measurements as a function of temperature. The ratio of the two contributions evolves according to a Boltzmann law, in which the single line corresponds to the excited state at 81 K above the antiferromagnetic ground state.     

Local structure,magnetism, and superconductivity in Sr analogs of Fe-doped YBa2Cu3−y Fe y O6+x

The local structure, magnetism, and superconductivity of Y_1–z Ca _z Sr₂Cu_3–y Fe _y O_6+x have been investigated by magnetic susceptibility,⁵⁷Fe Mössbauer absorption spectroscopy, X-ray powder diffraction, and iodometric titration. By modification of the hole distribution between the Cu(1)O _x chains and Cu(2)O₂ sheets, we induced bulk superconductivity with a maximum superconducting critical temperatureT _c near 20 K in Y–zCa _z Sr₂Cu_2.5Fe_0.5O_6+x (0.05z0.18). We interpret the development of a broad maximum inT _c and the Meissner fractionV _f versusz nearz=0.12 to be due to an increasing transfer of holes from the Cu(1)O _x chains to the Cu(2)O₂ sheets induced by a shorterc-axis and reduced Coloumb repulsion of the positively charged Y_1–z Ca _z plane. The increase in hole transfer from the Cu(1)O _x chains to the Cu(2)O₂ sheets also modulates the magnetic ordering temperatureT _m. We show thatT _m of YSr₂Cu₂FeO_7.26 is approximately 65 K, which is much lower than that observed in YBa₂Cu_2.31Fe_0.69O_7.21 (T _m400 K).     

Reduction of hysteresis loss and large magnetocaloric effects in substituted compounds of itinerant-electron metamagnets La(FexSi1−x)13

The maximum value of hysteresis loss E_h^MAX due to the itinerant-electron metamagnetic (IEM) transition of La(Fe_xSi_1−x)₁₃ and the partially substituted compounds La_1−zCe_z(Fe_0.86Si_0.14)₁₃ and La_1−z′Pr_z′(Fe_0.86Si_0.14)₁₃ increases when the magnetocaloric effects (MCEs) become large. It should be noted that the reduction of E_h^MAX without the decrease of large MCEs is achieved in La_1−zCe_z(Fe_0.86Si_0.14)₁₃ and La_1−z′Pr_z′(Fe_0.86Si_0.14)₁₃. For both the compound systems mentioned above, the critical temperature T₀ for the IEM transition decreases and the difference between T₀ and the Curie temperature T_C becomes larger with decreasing T_C. These results are consistent with the magnetic phase diagram of La(Fe_0.86Si_0.14)₁₃ under hydrostatic pressure. Consequently, the reduction of E_h^MAX in La_1−zCe_z(Fe_0.86Si_0.14)₁₃ and La_1−z′Pr_z′(Fe_0.86Si_0.14)₁₃ is closely related with the magnetovolume effects.     

Infrared Laser Spectroscopy of Jet-Cooled C2F6near 10 μm

The ν₅(A_2u) and ν₇(E_u) C–F stretching fundamentals of hexafluoroethane, C₂F₆, have been recorded in a supersonic jet by diode laser absorption spectroscopy. The parallel 5¹_oband is accompanied by five satellite bands, of which three have been assigned to hot bands. A fourth satellite band arises from¹²CF₃¹³CF₃. Transitions satisfying 0 ≤KΔK≤ 7 of the perpendicular 7¹_oband are unperturbed while those having −10 ≤KΔK≤ 7 can be fitted assuming anR_z-Coriolis interaction with a state lying at ν_p= 1256 cm⁻¹. A second localized perturbation affects lines withKΔK≥ 8. The band origins are 1117.10736 (7) cm⁻¹(5¹_o) and 1252.96950 (17) cm⁻¹(7¹_o, 0 ≤KΔK≤ 7), and the rotational constantB₀= 0.0615759 (27) cm⁻¹.     

Low temperature sintering of sub-stoichiometric Ni-Cu-Zn ferrites: Shrinkage, microstructure and permeability

We have studied sub-stoichiometric Ni-Cu-Zn ferrites with iron deficiency (i.e., <50mol% Fe₂O₃) of composition Ni_0.20Cu_0.20Zn_0.60+zFe_2−zO_4−(z/2) with 0≤z≤0.06. The temperature of maximum shrinkage rate is shifted from T=1000 °C for z=0 towards lower temperatures down to T=900 °C for a sub-stoichiometric ferrite with z=0.02. Dense samples are obtained after firing at 900 °C for z>0 only. Sub-stoichiometric compositions (z>0) do not form single-phase spinel ferrites after sintering at 900 °C, but rather represent mixtures of CuO and a stoichiometric ferrite with slightly modified composition. The formation of small amounts of CuO at grain boundaries is demonstrated by XRD and SEM. The permeability is increased from μ=80 for stoichiometric ferrites (z=0) to μ=660 for z=0.02. The formation of CuO during sintering of sub-stoichiometric ferrites supports densification and is a prerequisite for low temperature firing of multilayer inductors. Addition of 1 wt% Bi₂O₃ as liquid phase sintering aid is required to provide sufficient densification of the stoichiometric ferrite (z=0) at 900 °C. Addition of 0.37 wt% Bi₂O₃ to a sub-stoichiometric ferrite (z=0.02) results in dense samples after firing at 900 °C; however, the microstructure formation is dominated by heterogeneous grain growth.     

Exploration of layered-type pseudo four-component Li-Ni-Co-Ti oxides

A series of layered-type pseudo four-component Li-Ni-Co-Ti oxides were prepared to explore optimal cathode materials for a lithium-ion secondary battery. The new layered-type compounds were prepared using a combinatorial material-preparation system based on electrostatic spray deposition (the “M-ist Combi” system), and combinatorial powder X-ray diffraction. The composition region of the new compounds (Li_α(Ni_xCo_yTi_z)O₂ (α∼1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, z∼0.2, x + y + z = 1.0)) was found to be wider than the composition region previously reported (LiNi_0.8−yCo_0.2Ti_yO₂ (0 ≤ y ≤ 0.1)).     

γ irradiation effect on the polarization and resistance of Li-Co-Yb-ferrite

The effect of γ irradiation on some physical properties of rare earth ferrite of the general formula Li_0.5+zCo_z Yb_xFe_2.5−2z−xO₄, (z=0.1, x=0.00, 0.025, 0.050, … , 0.200) is discussed. The temperature dependence of the polarization and resistance is studied in the range (300 K≤T≤700 K) at different frequencies (10 kHz≤f≤1 MHz). The relaxation time and the activation energy have been calculated before and after irradiation with γ rays doses of 1 and 3 Mrad. A comparison was made between the ac resistance before and after irradiation for the samples with (0.0≤x≤0.2). The results after irradiation with 1 Mrad γ rays showed that the resistance at the critical concentration decreases from 800 to 25 kΩ at room temperature. Furthermore, with increasing temperature the resistance ranged from R≈130 kΩ at T≈310 K to R≈0.13 kΩ at T≈640 K. Thus, it is possible to improve the conductivity of this type of rare earth ferrite materials to be used in technological applications at room as well as at high temperature.     

Quantum Discord Behavior for Two Qubits Heisenberg XYZ Chain with Inhomogeneous Magnetic Field

We report the quantum correlation behavior (quantum discord (QD)) of a two-qubit anisotropic Heisenberg XYZ chain under an inhomogeneous magnetic field. It is shown that in the lower region of b QD can be enhanced evidently through increasing anisotropic parameter γ, while the effects of γ are disappear when b is strong enough. The role of J _z is nearly opposite to γ, there is a critical value of b _c , with b>b _c QD is improved with decreasing interaction J _z , while the value of QD is nearly invariable whatever changing J _z when b<b _c . In addition, one can get non-zero QD by properly tuning J _z and γ even at a higher temperature. When inhomogeneity is increased to b _c , the QD can exhibit a regrowth procession, and the regrowth value of QD can be larger than that of before dropping in the region of weak J _z . We also obtain the ground state QD properties. These investigations can imply us more control parameters on quantum correlation in solid state systems.     

Anisotropy of rotation of nitroxide probes in nematogenic liquid crystals

An electron paramagnetic resonance (EPR) line shape simulation for nitroxide spin probes in the motional narrowing region was carried out assuming axially symmetricg andA tensors and with different anisotropies of rotationN (=R _∥/R _⊥) whereR _∥ andR _⊥ are, respectively, elements of the diffusion tensor along and perpendicular to its principal axisz′. In addition, it was assumed that the principal axes of the diffusion tensor coincide with the molecular axes. Each of three casesz′=x,z′=y andz′=z, which result from cyclic permutations of the molecular axesx, y andz with thez′,y′ andx′ axes of the diffusion tensor, yields its typical EPR spectrum characterized by the relative intensities of the low-, center- and high-field lines. The parameter δ defined by and calculable from the intensities of the three lines was found to vary linearly withN for thez′=x andz′=y cases and, as anticipated, to be practically constant at a value of 1 for thez′=z case. This suggested a method for estimatingN for a probe from its EPR spectrum. Experimental spectra over a narrow temperature range (1°C) in the vicinity of the nematic-to-isotropic transition (about 34.6°C) ofN-(4-n-butylbenzilidene)-4-amino-2,2,6,6-tetramethylpiperidine-1-oxide at a mole fraction of 1·10⁻³ in 4-n-pentyl-4′-cyanobiphenyl showed a pattern of peak heights characteristic of thez′=x case with δ values that gave, neglecting effects of the mean field, higher and lowerN values in the nematic and isotropic regions, respectively. Analysis of other similar systems in the literature gave similar results.     

Focal switch of cosine-Gaussian beams

The focal switch of cosine-Gaussian (CsG) beams passing through a system with the aperture and lens separated is studied analytically and numerically. It is shown that the focal switch of CsG beams can appear not only for the apertured case, but also for the unapertured case. The necessary condition for the focal switch is that truncation parameter α > α_c and the beam parameter β > β_c, α_c, β_c being the corresponding critical values. There exists a maximum of the relative transition height Δz _sw as α varies, and Δz _sw increases with increasing β and decreasing N _w. The normalized axial intensity minimum I _min / I _max decreases with an increase of α and β, and I _min / I _max remains unchanged as N _w varies.     

Julia Sets in Parameter Spaces

Given a complex number λ of modulus 1, we show that the bifurcation locus of the one parameter family {f _b (z)=λz+b z ²+z ³} _{b ∈ ℂ} contains quasi-conformal copies of the quadratic Julia set J(λz+z ²). As a corollary, we show that when the Julia set J(λz+z ²) is not locally connected (for example when z↦λz+z ² has a Cremer point at 0), the bifurcation locus is not locally connected. To our knowledge, this is the first example of complex analytic parameter space of dimension 1, with connected but non-locally connected bifurcation locus. We also show that the set of complex numbers λ of modulus 1, for which at least one of the parameter rays has a non-trivial accumulation set, contains a dense G _δ subset of S ¹. Received: 22 September 2000 / Accepted: 16 January 2001     

Electrical conductivity of hydrogenated barium-yttrium cuprate and of oxidized hydrocuprate in the 300–450 K interval

The electrical conductivity of ceramic samples with a general formula H_xBa₂YCu₃O_7+z has been measured in the course of hydrogenation (formation of the hydrocuprate) and subsequent oxidation (formation of the oxyhydrocuprate). The hydrocuprate (x>0, −0.1<z<0) was synthesized by exposing the parent Ba₂YCu₃O_6.9 ceramic to hydrogen at a temperature of 450 K and a pressure of 50 kPa. The oxyhydrocuprate (x=2, z⩽1.5) was prepared by treating the preliminarily hydrogenated ceramic of composition H₂Ba₂YCu₃O_6.9 with oxygen at 470 K at a pressure of 70 kPa. The four-probe dc method was used in the electrophysical measurements. The measurements were performed in the temperature interval 300–450 K and within the compositional ranges 0<x<2.1, −0.1<z<1.5. The resistivity of the samples increases by nearly six orders of magnitude with hydrogenation from x=0 to x=2, and decreases by three orders of magnitude with oxidation, changing from z=−0.1 to z=0.8 for x=2. The electrode polarization effect is observed, which is apparently caused by ionic processes occurring at the electrode-ceramic interface. Water vapor is experimentally found to exert considerable effect on the electrophysical parameters of the hydrocuprate-copper electrodes system. Fiz. Tverd. Tela (St. Petersburg) 39, 823–828 (May 1997)     

Dynamic topological solitons in a two-dimensional ferromagnet

It is shown that stable, skyrmion-type, dynamic solitons can be constructed for a wide class of two-dimensional models of anisotropic ferromagnets. These solitons are stabilized as a result of the conservation of various integrals of motion: the z projection of the total spin S _z or the orbital angular momentum L _z of the magnetization field. A class of two-parameter solitons with quite complicated (almost periodic) magnetization-field dynamics exists for a purely uniaxial model (in the sense of both spin and spatial rotations) with maximum symmetry. Stable solitons with periodic magnetization dynamics exist for ferromagnets with lower symmetry (only S _z or L _z or the total angular momentum J _z =L _z +S _z is conserved). Zh. éksp. Teor. Fiz. 115, 1511–1530 (April 1999)     

On the relationship between the gradient and the bulk Richardson number for the atmospheric surface layer

Summary Semi-empirical formulations which have been proposed to describe the wind and potential temperature profiles are used to derive relationships between the gradient Richardson number, Ri, the finite-difference layer Richardson number, Ri_b, the surface layer Richardson number, Ri_s, and the bulk Richardson number,B, through the atmospheric surface layer. The theoretical analysis for stable conditions indicates that Ri (z ₃)=Ri_b, wherez ₃=(z ₂−z ₁)/ln(z ₂/z ₁), andz ₂;z ₁=upper and lower levels at which temperature and wind speed are specified. It is also found that, during stable conditions, the wind profile power law exponent,p, is computed at the heightz ₃, instead of the widely used geometric mean height,z _m, between top (z ₂) and bottom (z ₁) of the layer considered.     

Synthesis of Eu x Si6? z Al z O z N8? z green phosphor and?its?luminescent properties

Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors because of their good thermal and chemical stabilities. In this work, Eu²⁺-doped β-SiAlON phosphor with a composition of Eu _x Si_6−z Al _z O _z N_8−z (x=0.018, z=0.23) was prepared by gas-pressured solid state reaction. The crystallinity and particle morphology of the prepared phosphor were characterized. The Stokes shift and zero-phonon line were calculated mathematically and estimated from the spectral data. The temperature dependence of photoluminescence was measured from 25 to 250°C. The prepared Eu²⁺-doped β-SiAlON green phosphor showed superior thermal quenching property compared to silicate (SrBaSiO₄:Eu²⁺) green phosphor. The white light-emitting diode (LED) back-lighting unit (BLU) using the prepared β-SiAlON:Eu²⁺ green phosphor exhibited higher color gamut than a commercial silicate phosphor.     

Low-temperature conductivity and the Hall effect in (PbzSn1 ? z)0.84In0.16Te semiconducting solid solutions

The temperature dependences of the conductivity and the Hall effect in heavily doped polycrystalline samples of the (Pb _z Sn_{1 − z} )_0.84In_0.16Te solid solutions with lead content varied within the 0 ≤ z ≤ 0.9 interval have been studied. For x ≤ 0.65, the material undergoes a superconducting transition at a critical temperature T _c ≤ 4.2 K in a magnetic field H _c2(0 K) ∼ 50 kOe. As the lead concentration is increased to z ≤ 0.9, a clearly pronounced trend to transfer of the material to the dielectric state is observed at helium temperatures. The observed behavior is related to the variation in the band structure of the solid solutions with variations in the material composition, doping level, and position of the indium impurity band. The dependences of the resistivity, Hall effect, and superconducting characteristics of (Pb _z Sn_{1 − z} )_0.84In_0.16Te on the temperature and the composition of the solid solutions is observed to be related to the variation in its band structure as tin atoms are replaced with lead in the metallic sublattice of the compound. Original Russian Text ? D.V. Shamshur, S.A. Nemov, R.V. Parfen’ev, M.S. Kononchuk, V.I. Nizhankovskii, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 11, pp. 1948–1952.     

The microwave spectrum and structure of carbonyl fluoride

The ground state microwave rotational spectra of four isotopic species of carbonyl fluoride have been measured between 18 GHz and 77 GHz, and analyzed to obtain the quartic and some sextic centrifugal constants. The rotational constants have been used to obtain a r₀ structure and, using a harmonic force field, a r_z structure is also obtained: r_z(C---F) = 1.3166 (10) Å, r_z(C---O) = 1.1700 (26) Å.These values are considerably more precise than those of the previously estimated average structure.     

Gamow-Teller transitions from 58Ni to discrete states of 58Cu

Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states of T = 1, T _z = ±1 nuclei to the common excited states of the T _z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow-Teller (GT) transitions obtained from a (p, n)-type charge-exchange reaction on a target nucleus with T _z = 1 with those from the β-decay of the T _z = - 1 nucleus. The A = 58 system is the heaviest for which such a comparison is possible. As a part of the symmetry study, we measured the GT transitions from ⁵⁸Ni (T _z = 1) to ⁵⁸Cu (T _z = 0) by using the zero-degree (³ He, t) reaction at 150 MeV/nucleon. With the achieved resolution of 50 keV, many hitherto unresolved GT states have been identified. The GT transition strengths were obtained for states up to 8 MeV excitation, i.e., near to the Q window limitation ( Q _EC = 9.37 MeV) of the β-decay from ⁵⁸Zn (T _z = - 1) to ⁵⁸Cu. The strength distribution is compared with that from shell-model calculations. Received: 24 November 2001 / Accepted: 30 January 2002