Vortex pinning properties of –Ba–Cu–O and –Ba–Cu–O superconducting bulks

We have studied the effect of a small amount of Y-site substitution by La or Pr ions on the vortex pinning in the Y–Ba–Cu–O system. (Y_1-xLa_x)–Ba–Cu–O and (Y_1-xPr_x)–Ba–Cu–O bulks were fabricated by the melt-textured growth, in which x was varied from 0 to 0.01. The critical current density J_c at 77 K is improved in magnetic fields parallel to the c-axis above 2–4.5 T and the corresponding irreversibility field, H_irr, shifts to the higher value in both bulks.     

Infrared magneto-photoluminescence spectra and electron–hole g-factor of an InAs-inserted channel InGaAs/InAlAs heterostructure

We performed infrared magneto-photoluminescence (PL) spectroscopy on an InAs-inserted-channel InGaAs/InAlAs heterostructure. Series of Landau levels were clearly observed in the infrared PL spectra. From the energy separation between σ+ and σ− components of PL, the electron–hole g-factor in each Landau level were determined. We discuss the obtained Landau fan-diagram from the points that nonparabolicity of conduction band structure and penetration of electron wavefunction into InGaAs layer.     

Analogous study in low magnetic field between Cu–Ge and Cu–Si ferrites

Two series of mixed copper ferrites, Cu_1+x Ge_x Fe_2−2x O₄ and Cu_1+x Si_x Fe_2−2x O₄, have been analogously investigated for x=0.0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3. The two systems were prepared using the standard ceramic techniques. X-ray diffraction analysis indicates that both systems formed in a single phase cubic spinel structure. The lattice parameter has a constant value (0.838 nm±0.001) for the two series. The grain diameter was estimated from the scanning electron microscope micrographs for the two series. Some magnetic properties were measured at room temperature. The magnetization M was measured in the range of magnetizing field up to 5500 Am⁻¹. The relative permeability (μ_r) was calculated from the B–H relation. The B–H loops were measured at constant magnetizing current (I=2.5 A which is equivalent to 900 Am⁻¹). Also, the hystersis area and the magnetic parameters B_r, B_s, m_R (B_r/B_s) and apparent energy loss (E) were estimated from the B–H loops; μ_r, B_r, B_s and E are composition dependent.     

Elektronen-Spin-Resonanz an (La1−−x Gd y Ce x )Al2

In the EPR of (La_1––x Gd _y Ce _x )Al₂ a bottleneck in the relaxation of the conduction electrons to the lattice is present at sufficiently high Gd-concentrations. The bottleneck can be broken by decreasing the Gd-concentration or by adding Cerium as a spin-flip-scatterer.g-factor and line broadening are measured for (La_1–y Gd _y )Al₂ and (La_1––x Gd _y Ce _x )Al₂ as a function of temperature and Gd- and Ce-concentrations. The Cerium induced relaxationsrate _eL (Ce) increases linearly with Ce-concentration up tox0.025. This corresponds to the fact, well known by measurements of the Kondo anomalies, that Cerium impurities show no significant interaction up to rather high concentrations.     

Elektronen-Spin-Resonanz an (La1??xGdyCex)Al2

In the EPR of (La_1––x Gd _y Ce _x )Al₂ a bottleneck in the relaxation of the conduction electrons to the lattice is present at sufficiently high Gd-concentrations. The bottleneck can be broken by decreasing the Gd-concentration or by adding Cerium as a spin-flip-scatterer.g-factor and line broadening are measured for (La_1–y Gd _y )Al₂ and (La_1––x Gd _y Ce _x )Al₂ as a function of temperature and Gd- and Ce-concentrations. The Cerium induced relaxationsrate _eL (Ce) increases linearly with Ce-concentration up tox0.025. This corresponds to the fact, well known by measurements of the Kondo anomalies, that Cerium impurities show no significant interaction up to rather high concentrations.     

Growth and physical properties of sol–gel derived Co doped ZnO thin film

Zn_1−xCo_xO films were grown on glass by sol–gel spin coating process. The Zn_1−xCo_xO thin films with 10 at.% Co were highly c-axis oriented. The electrical resistivity of the films at 10 at.% Co had the lowest value due to the highest c-axis orientation. XPS and AGM analyses indicated that Co metal clusters weren’t formed, and the ferromagnetism was appeared at room temperature. The characteristics of the electrical resistivity and room temperature ferromagnetism of sol–gel derived Zn_1−xCo_xO films suggest a potential application to dilute magnetic semiconductor devices.     

Dispersive optical constants of a-Se100−xSbx films

Thin films of amorphous Se_100−xSb_x (x=5,10 and 20 at%) system are deposited on a silicon substrate at room temperature (300 K) by thermal evaporation technique. The optical constant such as refractive index (n) has been determined by a method based on the envelope curves of the optical transmission spectrum at normal incidence by a Swanpoel method. The oscillator energy (E_o), dispersion energy (E_d) and other parameters have been determined by the Wemple–DiDomenico method. The absorption coefficient (α) has been determined from the reflectivity and transmitivity spectrum in the range 300–2500 nm. The optical-absorption data indicate that the absorption mechanism is a non-direct transition. We found that the optical band gap, E_g^opt, decreases from 1.66±0.01 to 1.35±0.01 eV with increase Sb content.     

Formation of silicon oxide nanowires directly from Au/Si and Pd–Au/Si substrates

Amorphous silicon oxide (SiO_x) nanowires were directly grown by thermal processing of Si substrates. Au and Pd–Au thin films with thicknesses of 3 nm deposited on Si (0 0 1) substrates were used as catalysts for the growth of nanowires. High-yield synthesis of SiO_x nanowires was achieved by a simple heating process (1000–1150 °C) in an Ar ambient atmosphere without introducing any additional Si source materials. The as-synthesized products were characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy measurements. The SiO_x nanowires with lengths of a few and tens of micrometers had an amorphous crystal structure. The solid–liquid–solid model of nanowire formation was shown to be valid.     

Electron–hole symmetry and spin–orbit splitting in IV–VI asymmetric quantum wells

It is shown that, due to the electron–hole symmetry of the fundamental gap of the lead–salts (PbTe, PbSe and PbS), the Rashba spin splitting in their flat band asymmetric quantum wells is much reduced with the usual equal conduction and valence band-offsets. Different from the III–V case, we find that the important structure inversion asymmetry for the Rashba splitting in IV–VI quantum wells with different left and right barriers is not a material property (i.e., barrier height, effective mass or band gap) but results from the band alignment. This is shown by specific envelope function calculations of the spin-dependent subband structure of Pb_1−xEu_xTe/PbTe/Pb_1−yEu_yTe asymmetric quantum wells (x≠y), based on a simple but accurate four-band kp model for the bulk band structure near the gap, which takes into account band anisotropy, nonparabolicity and multi-valley effects.     

Ferromagnetic Resonance Spectra in Single-Crystal Hexagonal Ferrites

Theoretical and experimental studies of ferromagnetic resonance in single-crystal hexagonal ferrites with different types of magnetocrystalline anisotropy (axis and plane of easy magnetization) are reported. The ferromagnetic resonance is examined in the 12–38 GHz frequency range in the state of homogeneous magnetization and in the presence of a strip domain structure inherent in materials with an axis of easy magnetization. This comprehensive ferromagnetic resonance investigation is shown to allow determination of not only anisotropy fields and g-factors but also saturation magnetization of a material from testing one sample alone. The anisotropy of g-factor of Zn₂Y is found experimentally.     

Electrical characteristics of a metal–insulator–semiconductor memory structure containing Ge nanocrystals

A metal–insulator–semiconductor structure device with Ge nanocrystals in SiO₂ was synthesized and the electrical characteristics were investigated. Capacitance–voltage (C–V) curves show hysteresis and the measurements indicate that the device has charge storage effects and stores more holes than electrons. For decreasing measurement frequencies from 1 MHz to 500 Hz, both branches of the C–V hysteresis shift in the positive voltage direction. The slope of the left flank of the C–V hysteresis curve becomes stretched out with decreasing frequency. The slope of the right one appears frequency independent, while there is a small hump/step on the right flank of the C–V hysteresis curve for the lower frequency cases (500 Hz and 1 kHz). The role of Si/SiO₂ interface states is discussed.     

Synthesis, characterization and low field emission of CNx nanotubes

Aligned CN_x nanotubes were fabricated by pyrolyzing ethylenediamine on p-type Si(1 1 1) substrates using iron as the catalyst. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrum (XPS) and Raman spectroscopy were used to characterize the CN_x nanotubes. The CN_x nanotubes with the average length of 20 μm and diameters in the range of 50–100 nm have the “bamboo-like” structure and worse crystalline order. The low-field emission measurements of the CN_x nanotubes indicated that 20 μA/cm² current densities were observed at an electric field of 1.4 V/μm and 1.280 mA/cm² were obtained at 2.54 V/μm. The CN_x nanotubes exhibit better field emission properties than the carbon nanotubes and the BCN nanotubes. The emission mechanism of CN_x nanotubes is also discussed.     

Structural and optical properties of ZnSe x Te1−-x solid solutions in thin-film form

Solid solutions of ZnSe _x Te_1–x (0. 1 x 1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc-blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fractionx following Vegard's law:a(x) = 6.165 – 0.485x. Thin films of ZnSe _x Te_1–x (0.1 x 1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10^–4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe _x Te_1–x polycrystalline films of different compositions have two direct transitions with corresponding energy gapsE _g andE _g + _so The variations in bothE _g andE _g + _so, withx indicate that ZnSe _x Te_1–x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.     

g-factor of the 9/2+ isomeric state in 65Ni from transfer reaction

We report a measurement of the g-factor of the I ^π = 9/2⁺, t _1/2 = 22ns isomer in ⁶⁵Ni. The state of interest was populated and spin-oriented using a single-neutron transfer on an enriched ⁶⁴Ni target. The value, which was obtained, g(9/2⁺,^65m Ni) = - 0.296(3) is well in agreement with the g-factors of the other 9/2⁺ states in the region and with large-basis shell model calculations. The known g-factor of the 9/2⁺ isomer in ⁶³Ni was used in order to verify the strength of the hyperfine field of Ni( Ni) at room temperature.     

The influence of indium on the structural modification of the amorphous Ge–In–Se system

The effect of both the chemical composition and the nature of the chemical bonding of amorphous alloyed samples of Ge_xIn_ySe_100−x−y prepared under vacuum with x=20, 4y15 on the efficiency of the structural modification Δφ is analysed using a simple consideration based on the coordination number Z, and the number of topological constraints N_co. The previously obtained parameters have been used for the determination of the number of continuous deformation (i.e. zero-frequency modes f ), and for the estimation of the cohesive energies of these glasses, assuming simple additivity of bond energies. A trial has been made to correlate the results of this paper with the previously published data of glass transition temperature T_g, activation energy ₀ and the shift of the K-absorption edge (ΔE_K) of the composition of vacuum prepared Ge_xIn_ySe_100−x−y. It was found that there is a correlation between the lone-pair electrons and the stability of the vitreous state. According to the criterion of Liang, the above correlation has been interpreted in terms of Δφ.     

Anisotropy of phosphorous electron donor state in strained clusters in silicon at low temperatures

An anisotropic EPR spectrum at T = 4 K was observed in silicon samples irradiated by phosphorus ions and subsequently annealed at 1000°C. Epitaxial silicon layers with a natural isotope composition and enriched by ²⁸Si isotope grown on a natural silicon wafer were investigated. The spectrum consisted of three lines corresponding to different g-factor components: g _x ,g _y , and g _z . The central line was overlapped by the isotropic line coinciding by its g-factor with the line of the conduction electrons in silicon. The shape of the spectral lines indicated that the spectrum was due to the paramagnetic centers which belong to the randomly oriented clusters with the anisotropic g-factor. The nature of the anisotropic EPR spectrum is due to the electrons localized on donors located in the strained phosphorous clusters. The strains were caused by either incompletely annealed defects after the phosphorous implantation (E = 40 keV, D = 2 × 10¹⁴ cm⁻², T _ann = 1000°C, 1 h) or phosphorous atoms in clusters. The distance between the components strongly depended on the temperature and microwave power and decreased as they increased.     

Optical Investigation of the Phase State of a Dilute Antiferromagnet

The behavior of exciton-magnon light absorption bands of Rb₂Mn _x Cd_1–x Cl₄ crystals in the region of the ⁶ A _1g ⁴ T _2g (⁴ D) optical transition of manganese ions in a magnetic field is used to construct magnetic phase state diagrams. The x-H and x-T diagrams are constructed. The components of the g-factor are determined for the examined excited state.     

Structural and optical properties of Ba(Ti1−x,Nix)O3 thin films prepared by sol–gel process

Ba(Ti_1−x,Ni_x)O₃ thin films were prepared on fused quartz substrates by a sol–gel process. X-ray diffraction and Raman scattering measurements showed that the films are of pseudo-cubic perovskite structure with random orientation and the change of lattice constant caused by Ni-doping with different concentrations is very small. Optical transmittance spectra indicated that Ni-doping has an obvious effect on the energy band structure. The energy gap of Ba(Ti_1−x,Ni_x)O₃ decreased linearly with the increase of Ni concentration. It indicates that the adjusting of band gap can be achieved by controlling the Ni-doping content accurately in Ba(Ti_1−x,Ni_x)O₃ thin films. This has potential application in devices based on ferroelectric thin films.     

Measurement of the Magnetic Moment of the First Excited State in 93Sr Using on-line TDPAC technique

The g-factor of the first excited state of ⁹³Sr (E = 213 keV, T _1/2 = 4.6 ns) was measured by an on-line TDPAC technique with use of the strong hyperfine field in Fe metal. The Larmor frequency ω _L = (2.60 ± 0.15) × 10⁸ rad/s was obtained. The g-factor is derived as g = −0.227 ± 0.013 from g = −ℏω _L/B _hf μ _N. If the spin of the first excited state of ⁹³Sr is assumed to be 3/2, the g-factor is predicted by a simple core-excitation model as g = −0.22, which is in good agreement with the present experimental result.     

The AΠu state of : Electric properties, fine and hyperfine coupling constants, and magnetic moments (g-factors). A theoretical study

Several properties are calculated for A²Π_u of —the majority for the first time—including electric and magnetic moments, and fine/hyperfine structure (fs/hfs) parameters. The new results are compared with our previous ones for X² and B² of [P.J. Bruna, F. Grein, J. Mol. Spectrosc. 227 (2004) 67–80]. The electric quadrupole Θ and hexadecapole Φ moments, polarizability α, and hfs constants a, b, c, d, eQq₀, eQq₂ are evaluated at the density functional theory (DFT) level [B3LYP/aug-cc-pVQZ]. The fs constants (spin–orbit coupling A_Π, Λ-doubling p, q, spin-rotation γ_Π), and magnetic moments (g-factors) are obtained via 2nd-order sum-over-states expansions, using wavefunctions and matrix elements obtained with a multireference configuration interaction (MRDCI) method, and the Breit–Pauli Hamiltonian. At equilibrium, 2nd-order properties of A²Π_u are dominated by its coupling with B². For the A state, two independent components are reported for traceless tensor properties (multipoles Θ and Φ; hfs parameters c/d and q₀/q₂) and three for traced properties (polarizability α and g-factors), i.e., one more component than for axially symmetric Σ states. The currently available experimental data on — limited to A_Π, p, and q—are well reproduced by our theoretical results.