Ferromagnetic resonance in (Bi,Tm)<Subscript>3</Subscript>(Fe,Ga)<Subscript>5</Subscript>O<Subscript>12</Subscript>(210) epitaxial films

It is shown that the ferromagnetic resonance spectrum in (Bi,Tm)₃(Fe,Ga)₅O₁₂ films grown in Gd₃Ga₅O₁₂(210) substrates has a single peak. The azimuthal and polar dependences of the resonance field possess 180° symmetry. The angular dependences of the ferromagnetic resonance line width and intensity are studied.     

Thermal stability of (MgO)<Subscript>12</Subscript> dimers

The cagelike (MgO)₁₂ clusters were suggested to assemble the low-density nanoporous crystalline phases by connecting in the edge-to-edge, tetragonal face-to-face and hexagonal face-to-face manners. The stabilities of the (MgO)₁₂ dimers bound in the above manners are investigated using methods of molecular dynamics (MD) and density functional theory (DFT). The MD simulations show that the (MgO)₁₂ dimer connected in the hexagonal face-to-face manner can transform to a group of the hexagonal tubelike structures, and the dimer connected in the tetragonal face-to-face manner can change to other isomers through a 2 × 4 × 6 slab structure. Both isomerizations do not require rearrangements of the ions and they occurs at about 700 K and 1000 K, respectively. The DFT calculations indicate that the energy barriers of the isomerizations are about 1 eV, which suggests a lower isomerization temperature.     

Rovibrational Intensities of the (00(0)3) <-- (10(0)0) Dyad Absorption Bands of (12)C(16)O(2)

Absolute line intensities of (12)C(16)O(2) are experimentally measured for the first time for the (00(0)3)(I) <-- (10(0)0)(II) band at 5687.17 cm(-1) and the (00(0)3)(I) <-- (10(0)0)(I) band at 5584.39 cm(-1). The spectra were obtained using a Bomem DA8 Fourier transform spectrometer and a 25-m base-path White cell at NASA-Ames Research Center. The rotationless bandstrengths at a temperature of 296 K and the Herman-Wallis parameters are S(0)(vib) = 6.68(30) x 10(-25) cm(-1)/(molecule/cm(2)); A(1) = 1.4(9) x 10(-4), and A(2) = -1.1(5) x 10(-5) for the (00(0)3)(I) <-- (10(0)0)(II) band and S(0)(vib) = 6.07(22) x 10(-25) cm(-1)/(molecule/cm(2)); A(1) = 5.2(1.5) x 10(-4) and A(2) = -4.0(7) x 10(-5) for the (00(0)3)(I) <-- (10(0)0)(I) band.     

三元配合物Eu(BA)3PIP和 Eu(BA)3phen的制备与发光性质

合成了邻菲罗啉(phen)衍生物2-苯基-咪唑并 -1,10-菲罗啉(PIP),并以其为第二配体,苯甲酸(BA)为第一配体,制备出新型稀土铕三元有机配合物Eu(BA)₃PIP;在相同条件下,第一配体不变,1,10-菲罗啉为第二配体,还制备出Eu(BA)₃phen。采用元素分析、红外光谱、热重和差热分析等技术对合成的配体PIP及配合物Eu(BA)₃PIP和Eu(BA)₃phen进行了表征。通过发光光谱研究了配合物的发光性质,结果表明第二配体PIP有较大的共轭体系,在紫外光激发下,配合物中的配体可将吸收的能量传递给稀土Eu³⁺离子,表现出较强的Eu³⁺离子的特征发射。两种配合物相比,Eu(BA)₃PIP的发光强度明显大于Eu(BA)₃phen的发光强度,说明适宜的第二配体对配合物有很好的敏化发光作用。     

Preparation of barium strontium titanate Ba(1-x)Sr(x)TiO(3) (0<or= x <or=0.2) single-crystal nanorods by a novel combined method

An ultrasonic irradiation method was applied to the sol/gel synthesis of the single-crystal cubic barium strontium titanate Ba(1-x)Sr(x)TiO(3) (0相似文献   

Nonlinear-laser effects in χ(<Superscript>3</Superscript>)-and χ(<Superscript>2</Superscript>)-active organic single crystals

The process of stimulated Raman scattering (SRS) allows one to convert laser emission wavelength of crystals, providing suitable molecular or lattice modes which contribute to third-order nonlinear optical susceptibility. Renewed interest in this field emerged because of the discovery of SRS in crystals that contain molecular units exhibiting Raman active modes. Particularly, organic nonlinear optical crystals used so far for frequency doubling and third harmonic generation seem to have a great potential for SRS application. This review paper reported same results on efficient SRS lasing effects that were discovered recently in organic crystals.     

Studies of multi-nucleon transfer reactions in <Superscript>90</Superscript>Zr(<Superscript>18</Superscript>O,X) and <Superscript>90</Superscript>Zr(<Superscript>16</Superscript>O,X)

Multi-nucleon transfer reactions in ¹⁸O + ⁹⁰Zr and ¹⁶O + ⁹⁰Zr have been studied at an incident energy of 90 MeV. The energy spectra and angular distributions are measured. The data have been analyzed to obtain cross-section dependence on the number of nucleons transferred and on the ground-state Q-values. In the ⁹⁰Zr(¹⁸O, X); X = ¹⁶O, ^17,16,15,14N, ^14,13,12C, ^12,11,10B, ^10,9,7Be and ^7,6Li reactions, 2n and 2n-correlated transfer cross-sections are observed to be enhanced as compared to the ¹⁶O + ⁹⁰Zr reaction. A detailed comparison in the multi-particle stripping and elastic-scattering cross-section between these two systems are made in order to investigate the possible influence of the two valence neutrons in ¹⁸O nucleus. Diffractional model DWBA calculations, based on the direct surface transfer model, have been performed to understand the reaction mechanism of multi-nucleon transfer to continuum.Received: 12 September 2002, Revised: 24 September 2003, Published online: 27 January 2004PACS: 25.70.Hi Transfer reactions - 25.70.Bc Elastic and quasielastic scattering     

Domain dynamics in (210)-oriented single-crystal (Bi,Y,Lu,Pr)<Subscript>3</Subscript>(Fe,Ga)<Subscript>5</Subscript>O<Subscript>12</Subscript> films

Using high-speed photography, dynamic magnetic structures are studied in Bi-containing (210)-oriented single-crystal films of (Bi,Y,Lu,Pr)₃(Fe,Ga)₅O₁₂ grown through liquid-phase epitaxy from an overcooled solution in the melt on (Gd,Ga)₃(Mg,Zr,Ga)₅O₁₂ substrates. At various temperatures, the ranges of pulsed magnetic fields are determined in which unidirectional anisotropy of domain wall velocity and spatial distortions of moving domain walls are observed.     

Infrared investigations of the one-dimensional organic conductors (perylene)<Subscript>2</Subscript> M (mnt)<Subscript>2</Subscript>, M = Au,Pt

The optical properties of the one-dimensional organic conductor (perylene)₂Pt(mnt)₂ and its Au analogue have been investigated at ambient and low temperatures. The spectra along the stacks of the molecules show a simple Drude behavior with no detectable influence of electron-electron interactions. Basing on the spectra for different polarizations an assignment of the vibrational modes is made. Perpendicular to the stacks, a wide band observed in the mid-infrared range evidences a charge transfer between perylene and anion stacks. The electronic properties are discussed in comparison with other quasi-one-dimensional synthetic metals.     

Raman spectroscopy of isotopically pure (<Superscript>12</Superscript>C, <Superscript>13</Superscript>C) and isotopically mixed (<Superscript>12.5</Superscript>C) diamond single crystals at ultrahigh pressures

The Raman scattering by isotopically pure ¹²C and ¹³C diamond single crystals and by isotopically mixed ^12.5C diamond single crystals is studied at a high accuracy. The studies are performed over a wide pressure range up to 73 GPa using helium as a hydrostatic pressure-transferring medium. It is found that the quantum effects, which determine the difference between the ratio of the Raman scattering frequencies in the ¹²C and ¹³C diamonds and the classical ratio (1.0408), increase to 30 GPa and then decrease. Thus, inversion in the sign of the quantum contribution to the physical properties of diamond during compression is detected. Our data suggest that the maximum possible difference between the bulk moduli of the ¹²C and ¹³C diamonds is 0.15%. The investigation of the isotopically mixed ^12.5C diamond shows that the effective mass, which determines the Raman frequency, decreases during compression from 12.38 au at normal pressure to 12.33 au at 73 GPa.     

A computer study of the Raman spectra of the (GaN)<Subscript>129</Subscript>, (SiO<Subscript>2</Subscript>)<Subscript>86</Subscript>, and (GaN)<Subscript>54</Subscript>(SiO<Subscript>2</Subscript>)<Subscript>50</Subscript> nanoparticles

The Raman spectra of the (GaN)₁₂₉, (SiO₂)₈₆, and (GaN)₅₄(SiO₂)₅₀ nanoparticles were calculated using the molecular dynamics method. The spectrum of (SiO₂)₈₆ had three broad bands only, whereas the Raman spectrum of (GaN)₁₂₉ contained a large number of overlapping bands. The form of the Raman spectrum of (GaN)₅₄(SiO₂)₅₀ was determined by the arrangement of the GaN and SiO₂ components in it. The nanoparticle with a GaN nucleus had a continuous fairly smooth spectrum over the frequency range 0 ≤ ω ≤ 600 cm⁻¹, whereas the spectrum of the nanoparticle with a SiO₂ nucleus contained well-defined bands caused by vibrations of groups of atoms of different kinds and atoms of the same kind.     

Intervalley electron scattering by phonons in (GaAs)<Subscript><Emphasis Type="Italic">m</Emphasis></Subscript>(AlAs)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>(001) ultrathin superlattices

The electron scattering by short-wavelength and long-wavelength phonons in (GaAs) _m (AlAs) _n (001) superlattices with ultrathin layers (n, m = 1, 2, 3) has been investigated using the pseudopotential method and the phenomenological model of bonding forces. The deformation potentials have been found for intervalley electron transitions in the conduction bands of the superlattices and solid solutions of the corresponding compositions. It has been shown that, owing to the localization of the wave functions in the quantum wells Γ, L, and X, the intensity of intervalley electron transitions in the superlattices, as a whole, is higher than that of similar transitions in the solid solutions. As the content of light Al atoms in the superlattices increases, the deformation potentials monotonically increase for the X-X transitions and decrease for the L-L and X-L transitions. The potentials of the Γ-X and Γ-L transitions change nonmonotonically depending on the layer thickness due to the pronounced quantum-well effects in the deep Γ quantum wells of GaAs. The deformation potentials averaged over phonons and related valleys in the superlattices are close to the corresponding potentials in the solid solutions.     

Domain structures of sodium tungsten bronzes,NaxWO3 (0.4 < x < 1)

Optical-microscope observations with polarized light have shown that the birefringent, twin-domain structure of sodium tungsten bronzes is exhibited by Na-deficient, epitaxial surface films and hence is not a bulk property as had been suggested elsewhere. The film is translucent, 10^-2-10^-3 mm thick or less, and often laminates to a multi-film layer The domain boundaries are sensitive to lateral stress and, apparently, to minute changes in the substrate structure. These and related properties of the film and the substrate are presented.     

Improved (1s)<Superscript>2</Superscript> variational model for helium

The ground-state energy of neutral helium is estimated variationally with a trial wavefunction of the form ϕ≈e ^−γ(rA/a _o)ⁿe^−γ(rB/a _o)ⁿ. This model represents a modification of traditional textbook examinations of this problem via inclusion of the power “n” as a second nonlinear variational parameter in addition to the usual effective nuclear charge γ and leads to an upper-limit on the ground state energy of −2.86107 E _h (E _h =1 hartree) in comparison with the traditional (n=1) result of −2.84766 E _h . This result represents a reduction of the percentage overestimate from the true ground-state energy (−2.90373 E _h ) of from 1.93 to 1.47. In comparison with the maximum accuracy obtainable from an uncorrelated trial wavefunction, −2.86168 E _h , the present trial wavefunction reduces the percentage overestimate from 0.49 (n=1) to 0.021. The optimum values of (n, γ) are determined to be ≈(0.897, 1.825).     

Surface impedance of <Emphasis Type="Italic">k</Emphasis>-(BEDT-TTF)<Subscript>2</Subscript>Cu[N(CN)<Subscript>2</Subscript>]Br crystals

Precision measurements of the real and imaginary parts of the microwave surface impedance Z _ac(T) = R _ac(T) + iX _ac(T) of the conducting ac layers of the k-(BEDT-TTF)₂Cu[N(CN)₂]Br crystals in the temperature interval of 0.5 < T < 100 K have demonstrated a series of features: (i) the temperature course of the field penetration depth is close to linear Δλ_ac(T)∞ΔX _ac(T) in the superconducting state at T T _c ∼ 11.5 K; (ii) the curves R _ac(T) = X _ac(T) coincide at T _c < T < 40 K; (iii) the X _ac(T) value at T > 40 K increases in comparison with R _ac(T); (iv) the dependence R _ac(T) at T > 40 K is nonmonotonic in thin crystals. These features of the impedance Z _ac(T) with increasing T are interpreted in terms of (i) the d-type symmetry of the superconducting order parameter, (ii) normal skin effect, (iii) manifestations of the antiferromagnetic fluctuations, and (iv) the size effect. The electrodynamic parameters of k-(BEDT-TTF)₂Cu[N(CN)₂]Br have been determined.     

Possible weakening of the many-body interactions in the organic quasi-two-dimensional metal α-(BETS)<Subscript>2</Subscript>NH<Subscript>4</Subscript>Hg(SCN)<Subscript>4</Subscript>

The behavior of the de Haas-van Alphen oscillations in the organic quasi-two-dimensional metal α-(BETS)₂NH₄Hg(SCN)₄ is comprehensively studied as a function of the angle between the magnetic-field direction and the normal to the conducting layers in it. The angular dependence of the oscillation amplitude has minima at angles of ±40° and ±62°, which are caused by the spin zero effect. The positions of these minima suggest that the electron-phonon and electron-electron interactions in this metal are significantly weakened.     

Electronic structure and thermoelectric properties of (Mg<Subscript>2</Subscript>X)<Subscript>2</Subscript> / (Mg<Subscript>2</Subscript>Y)<Subscript>2</Subscript> (X,Y = Si,Ge, Sn) superlattices from first-principle calculations

To identify thermoelectric materials containing abundant, low-cost and non-toxicelements, we have studied the electronic structures and thermoelectric properties of(Mg₂X)₂/(Mg₂Y)₂ (X, Y = Si, Ge, Sn) superlattices withstate-of-the-art first-principles calculations using a modified Becke and Johnson (mBJ)exchange potential. Our results show that (Mg₂Ge)₂/ (Mg₂Sn)₂ and(Mg₂Si)₂/(Mg₂Sn)₂ are semi-metals using mBJ plusspin-orbit coupling (mBJ +SOC), while (Mg₂Si)₂/ (Mg₂Ge)₂ ispredicted to be a direct-gap semiconductor with a mBJ gap value of 0.46 eV andmBJ + SOC gap valueof 0.44 eV. Thermoelectric properties are predicted by through solving the Boltzmanntransport equations within the constant scattering time approximation. It is found that(Mg₂Si)₂/(Mg₂Ge)₂ has a larger Seebeck coefficient andpower factor than (Mg₂Ge)₂/ (Mg₂Sn)₂ and(Mg₂Si)₂/(Mg₂Sn)₂ for both p-type and n-type doping. Thedetrimental influence of SOC on the power factor of p-type (Mg₂X)₂/(Mg₂Y)₂ (X, Y = Si, Ge, Sn) is analyzed as afunction of the carrier concentration, but there is a negligible SOC effect for n-type.These results can be explained by the influence of SOC on their valence and conductionbands near the Fermi level.     

Novel orientational ordering and reentrant metallicity in K(x)C(60) monolayers for 3 < or = x < or = 5

STM studies on K(x)C(60) monolayers reveal new behavior over a wide range of the phase diagram. As x increases from 3 to 5 K(x)C(60) monolayers undergo metal-insulator-metal reentrant phase transitions and exhibit a variety of novel orientational orderings, including a complex 7-molecule, pinwheel-like structure. The proposed driving mechanism for the orientational ordering is the lowering of electron kinetic energy by maximizing the overlap of neighboring molecular orbitals. In insulating (metallic) K(x)C(60) this gives rise to orbital versions of the superexchange (double-exchange) interaction.