Contribution Of Conduction Electrons Research Articles

Positronium emission from GaN(0001) and AlN(0001) surfaces

Positronium emission from wurtzite GaN(0001) and AlN(0001) surfaces was observed by positronium time-of-flight spectroscopy. The positronium energy spectra contained two positronium components distinguished by their energies. Through detailed analyses based on Monte Carlo simulations, these two components were attributed to positronium formed from valence and conduction electrons. The obtained results augment the previous arguments regarding the contribution of conduction electrons to positronium emission from 4H SiC(0001) and Si(111) surfaces.

Metallic state in the vicinity of molecular orbital crystallization in the d 1 thiospinel ZnTi2S4 prepared via a reductive ion-exchange reaction

A novel Ti3+-based thiospinel ZnTi2S4 is successfully synthesized via a low-temperature ion-exchange reaction. ZnTi2S4 shows a signature of metallic ground state evidenced by a contribution of conduction electrons in the heat capacity and Pauli-like paramagnetic susceptibility. These observations contrast to the electronic state of similar Ti3+-based spinel MgTi2O4 exhibiting the metal–insulator transition associated with a molecular orbital crystallization (MOC). Furthermore, the magnetic susceptibility of ZnTi2S4 shows a pseudogap-like behavior indicated by a vast peak in the magnetic susceptibility around 110 K, likely originating from the MOC fluctuation. The origin of the difference in the electronic states of MgTi2O4 and ZnTi2S4 would be due to the different magnitude of overlap between Ti 3d and p orbitals (O: 2p and S: 3p). The presence of a MOC state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in a MOC.

Optical, charge transport and magnetic properties of palladium retrieved from photometric measurements: approaching the quantum mechanics background

A parametric Drude–Lorentz (DL) model is used to describe the spectral variation of the dielectric functions of bulk palladium samples at low and room temperature. In addition to the contribution of conduction electrons, the contribution of holes is also explicitly accounted for in the model. A simulated annealing method is applied to obtain the optimized values of the parameters involved in the model: volume plasma frequency of conduction electrons, high frequency dielectric constant, collision frequency of holes and corresponding relaxation time, and two additional parameters from which the effective mass of holes and collision frequency of conduction electrons are evaluated. Oscillatior strengths, resonance frequencies, and widths entering in the Lorentz contribution to the dielectric function are also optimized. Renormalization of the oscillator strengths requires the introduction of a new parameter in the context of the DL model: the ratio between number density of conduction electrons and number density of metal atoms, whose optimized value fits very well with its evaluation from band structure calculations and from independent measurements. Inclusion of this parameter in the framework allows us to evaluate additional quantities related to the charge-carrier transport: average effective masses, Fermi energies and electronic densities of states at the corresponding Fermi energies, intrinsic electrical resistivity, intrinsic mean free paths, heat capacities, mobilities, as well as paramagnetic and diamagnetic susceptibilities, for both electrons and holes. The optimized resonance frequencies are compared with energy differences between plausible interband transitions, in accordance with reported band structure diagrams and with our own band structure obtained from density functional theory calculations.

Surface plasmon resonances in ellipsoidal bimetallic nanoparticles

The surface plasmon response of three-layered bimetallic nanoparticles embedded in a SiO2 host matrix is studied for different geometries. The analytical solution for the electromagnetic response in relation to the extinction cross section of the bimetallic nanoparticles is obtained by means of quasistatic theory. To show the extinction spectra of the three-layered bimetallic nanoparticles, we chose two different metals, namely, Ag and Au-Ag 50:50 alloy. The optical properties of the metals studied are described within the modified Drude-Sommerfeld model of the dielectric function with parameters accounting for the contribution of conduction electrons and interband transitions. We found that the position of the surface plasmon resonance depends on the dielectric function of the intermediate medium between the Au-Ag 50:50 alloy core and the Ag shell, the thickness of the Ag shell, the thickness of the intermediate medium, and the aspect ratio of the three-layered nanoparticles.

Role of lanthanum in modifying the magnetic state in RNi2 solid solutions with R = Tb, Dy, Ho

Comparative analysis and generalization of the influence of La on the structural and magnetic properties of R1−xLaxNi2 (R = Tb, Dy, Ho) solid solutions is presented. All the studied R1−xLaxNi2 solid solutions solidify with the formation of a Laves-phase superstructure corresponding to the F4¯3m space group. The magnetic properties are dominated by rare earth interactions and the substitution of R atoms with La significantly modifies the magnetic behaviour of the R1−xLaxNi2 system. Replacing of magnetic R with the nonmagnetic La results in magnetic dilution leading to the weakening of exchange interactions and decrease of the ordering temperature. In the case of Tb1−xLaxNi2 and Dy1−xLaxNi2 the ferromagnetic properties are reduced as the lanthanum content increases to 80% and for Ho1−xLaxNi2 the ferromagnetic ordering is destroyed as the lanthanum content increases to the values above 80%. The magnetic transition in all the studied samples is of second order character. The Debye temperature, phonon and conduction electron contributions as well as a magnetic contribution to the heat capacity have been determined from heat capacity measurements. The magnetocaloric effect and the refrigerant cooling power for selected solid solutions was determined in magnetic fields up to 4.2 T.

Magnetic and transport properties of Sm7Rh3 single crystal

A Sm7Rh3 single crystal with Th7Fe3-type hexagonal structure was grown by the Czochralski method. The magnetic and transport measurements revealed a uniaxial magnetocrystalline anisotropy in the magnetic susceptibility, magnetization and electrical resistivity. Sm7Rh3 was found to exhibit antiferromagnetic transition at TN=54.0K and another magnetic transition at Tt=25.0K. The specific heat data clearly showed the bulk nature of paramagnetic to ordered magnetic phase transition by the presence of a sharp peak at TN and a small anomaly at Tt. The paramagnetic susceptibility does not obey the Curie–Weiss law, attributing to the temperature independent Van Vleck contribution and Pauli paramagnetism of conduction electrons. Metamagnetic phase transitions were observed along the c-axis in the ordered states. The magnetic field H–temperature T phase diagram was constructed. Anisotropic paramagnetic electrical resistivity showed the small negative temperature coefficients.

Magnetization and magnetic circular dichroism of La0.7Sr0.3MnO3/YSZ polycrystalline films

The magnetic and magneto-optical properties as well as the surface morphology and structure of La0.7Sr0.3MnO3 polycrystalline films of different thicknesses have been investigated. It has been shown that films have a rough surface with a characteristic in-plane linear dimension of ∼30 nm, and crystallites with linear dimensions of 10–20 nm are randomly oriented in the plane. The temperature and field dependences of the magnetization of the films indicate their magnetic inhomogeneity. The magnetic circular dichroism spectra contain a number of bands, one of which at 2.4 eV is explained by the contribution of conduction electrons.

Magnetic and magnetocaloric properties of Gd1−xScxNi2 solid solutions

Magnetic and heat capacity measurements have been carried out on the polycrystalline Gd1−xScxNi2 solid solutions (0≤x≤1), which crystallize in the cubic C15 Laves phases superstructure (space group F4−3m). These solid solutions are ferromagnetic with a Curie temperature below 76K. Their Curie temperature decreases from 75.4K for GdNi2 to 13.6K for Gd0.2Sc0.8Ni2. At high temperatures, all solid solutions, except ScNi2, are Curie–Weiss paramagnets. The Debye temperature as well as phonon, conduction electron and magnetic contributions to the heat capacity have been determined from heat capacity measurements. The magnetocaloric effect has been estimated both in terms of isothermal magnetic entropy change and adiabatic temperature change for selected solid solutions in magnetic fields up to 3T.

Magnetic properties and magnetocaloric effect in (Dy0.6Er0.4)1−xGdxCo2 multicomponent compounds

We report magnetic and magnetocaloric properties of the polycrystalline series of (Dy0.6Er0.4)1−xGdxCo2 (x = 0.2, 0.3 and 0.4) intermetallic compounds. These samples were synthesized using high purity rare earth metals. X-ray diffraction patterns taken at room temperature revealed that all the (Dy0.6Er0.4)1−xGdxCo2 compounds have the C15 cubic Laves phase superstructure. Magnetization measurements were carried out using a vibration sample magnetometer with a step motor in applied fields up to 14 T using a Bitter-type magnet. Heat capacity measurements have been performed in temperature range 2-300 K. The Debye temperatures, phonon and conduction electron contributions as well as the magnetic part of heat capacity were estimated. The magnetocaloric effect has been estimated both in terms of isothermal magnetic entropy change and adiabatic temperature change for selected solid solutions in magnetic fields up to 3 T. The raising amount of the Gd in samples on magnetic and magnetocaloric properties will be discussed.

Strong electron correlations inFeSb2: An optical investigation and comparison withRuSb2

We report investigations of the optical properties of the narrow gap semiconductor FeSb2 in comparison with the structural homolog RuSb2. In the infrared region the latter shows insulating behavior in whole investigated temperature range (10 - 300 K) whereas the optical reflectivity of FeSb2 shows typical semiconductor behavior upon decreasing the temperature. The conduction electron contribution to the reflectivity is suppressed and the opening of a direct and an indirect charge excitation gap in the far-infrared energy region is observed. Those gap openings are characterized by a redistribution of spectral weight of the optical conductivity in an energy region much larger than the gap energies indicating that strong electron-electron correlations are involved in the formation of the charge gap. Calculations of the optical conductivity from the band structure also provided evidence for the presence of strong electronic correlations. Analyzing the spectra with a fundamental absorption across the gap of parabolic bands yields a direct gap at 130 meV and two indirect gaps at 6 and 31 meV. The strong reduction in the free-carrier concentration at low energies and low temperatures is also reflected in a change in the asymmetry of the phonon absorption which indicates a change in the phonon-conduction-electron interaction.

Electronic structures, mechanical and thermodynamic properties of ThN from first-principles calculations

Lattice parameter, electronic structure, mechanical and thermodynamic properties of ThN are systematically studied using the projector-augmented-wave method and the generalized gradient approximation based on the density functional theory. The calculated electronic structure indicates the important contributions of Th 6 d and 5 f states to the Fermi-level electron occupation. Through Bader analysis it is found that the effective valencies in ThN can be represented as Th +1.82 N −1.82. Elastic constant calculations show that ThN is mechanically stable and elastically anisotropic. Furthermore, the melting curve of ThN is presented up to 120 GPa. Based on the phonon dispersion data, our calculated specific heat capacities including both lattice and conduction electron contributions agree well with experimental results in a wide range of temperature.

Magnetic properties and magnetocaloric effect in Dy 1− xSc xNi 2 solid solutions

X-ray diffraction, magnetization, magnetic susceptibility, and heat capacity data are reported for the solid solutions Dy 1− x Sc x Ni 2 (0 ≤ x ≥ 1). All the Dy 1− x Sc x Ni 2 solid solutions are single phase with the C15 cubic Laves phase superstructure. The alloys with x ≤ 0.8 are ferromagnets with a low (below 22 K) Curie temperature that decreases from 21.1 K for DyNi 2 to 4.5 K for Dy 0.2Sc 0.8Ni 2. Dy 0.1Sc 0.9Ni 2 and ScNi 2 have no long-range magnetic order down to 2 K. At high temperatures, all the Dy 1− x Sc x Ni 2 solid solutions, except ScNi 2, are Curie–Weiss paramagnets. The Debye temperature, phonon and conduction electron contributions as well as a magnetic contribution to the heat capacity have been determined from heat capacity measurements. The magnetocaloric effect for selected solid solutions was determined in magnetic fields up to 3 T.

Study of dynamic spin susceptibility in Kondo lattice

Abstract The dynamic spin susceptibility χ ( q , ω ) , which is related to the inelastic neutron scattering cross-section, gives important information about the low energy excitations of the systems. The spectral density distribution function (SDF) of the neutron scattering is directly proportional to the imaginary part of the χ ( q , ω ) . Attempt is made in the present communication to calculate the longitudinal spin susceptibility for heavy fermion systems (HFS) to study resonance peaks at correlation temperature ( T N ) and Kondo temperature ( T K ) . The model Hamiltonian consists of c–f electron exchange term and Heisenberg type inter-site spin–spin correlation in a mean-field approximation, besides the terms containing the conduction electron and f-electron contributions in presence of the hybridization between them in the Hamiltonian. The two particle Green functions are calculated using the equations of motion by method of Zubarev's technique. The microscopic model calculation shows two resonance peaks, one at Kondo excitation energy and another at correlation energy exhibiting the excellent interplay between them for different model parameters.

Calculation of the contribution of conduction electrons to the atomic factors of simple metals

An expression for the Fourier transform of the screening electron density of simple metals has been derived using smooth nonlocal model potentials of simple metals. The expression describes the contribution of conduction electrons to the atomic factors of X-ray scattering in simple metals. Aluminum was used as an example for numerical checking. Comparison with the results of similar calculations for the form factor of the Krasko-Gurskii model potential shows the importance of taking the nonlocality of the model potential into account.

Size dependence of multipolar plasmon resonance frequencies and damping rates in simple metal spherical nanoparticles

Multipolar plasmon oscillation frequencies and corresponding damping rates for nanospheres formed of the simplest free-electron metals are studied. The possibility of controlling plasmon features by choosing the size and dielectric properties of the sphere surroundings is discussed. Optical properties of the studied metals are described within the Drude-Sommerfeld model of the dielectric function with effective parameters acounting for the contribution of conduction electrons and of interband transitions. No approximation is made in respect of the size of a particle; plasmon size characteristics are described rigorously. The results of our experiment on sodium nanodroplets [1] are compared with the oscillation frequency size dependence of dipole and quadrupole plasmon.

Temperature dependence of the magnetic hyperfine field at cerium impurity in Co

Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the magnetic hyperfine field (B hf ) at Ce impurity in Co using 140La→140Ce probe. The radioactive 140La produced by neutron irradiation of lanthanum metal with thermal neutrons was introduced in Co by arc melting in argon atmosphere. The present measurements cover the temperature range from 4.2–1300 K. Two pure magnetic interactions were observed at impurity sites, corresponding to a ferromagnetic ordering of Co moments in hcp and fcc phases. The temperature dependence of B hf for both phases, however, shows a sharp deviation from an expected standard Brillouin-like behavior for the host magnetization. The results are discussed in terms of a simple molecular-field model where the localized moment at impurity ions as well as the conduction electron contributions to the hyperfine field are taken into account.

The effect of substitution of Lu for Ho on some physical properties of Lu xHo 1−xNi 2 solid solutions

Experimental data on the structure, magnetization, electrical resistivity and heat capacity of polycrystalline Lu x Ho 1− x Ni 2 alloys with x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 are represented. X-ray diffraction analysis performed at room temperature was used to study the structure of the Lu x Ho 1− x Ni 2 solid solutions and parent binary compounds. It was found the formation of the C15-type Laves-phase superstructure (space group F 4 ¯ 3 m ). Magnetic measurements showed that the samples with x ⩽ 0.8 are ferromagnets with relatively low (below 20 K) Curie temperatures T C. At high temperatures, all studied solid solutions are Curie–Weiss paramagnets. Temperature dependences of the electrical resistivity are typical of alloys exhibiting the metallic conductivity. The Debye temperature, phonon and conduction-electron contributions as well as magnetic part of the heat capacity have been determined from heat capacity measurements. The magnetocaloric effect was estimated from measurements performed in a low magnetic field of 0.42 T.

Specific heat of the ScxHo1−xNi2 solid solutions

Measurements of the specific heat of polycrystalline HoNi2, ScNi2 and their solid solutions ScxHo1−xNi2 (x=0.2, 0.4) have been performed. The Debye temperatures, phonon and conduction electron contributions as well as the magnetic part of the heat capacity were determined and discussed.

Heat Capacity of the LuxHo1-xNi2 Solid Solutions

Results of the heat capacity measurements are presented for polycrystalline HoNi2, LuNi2 and their solid solutions, LuxHo1-xNi2 (x=0.2, 0.4). The Debye temperatures, phonon and conduction electron contributions as well as the magnetic part of the heat capacity were determined and discussed. The magnetocaloric effect for LuxHo1-xNi2 and HoNi2 was estimated.

Some Physical Properties of YxHo1-xNi2 Solid Solutions.

Abstract Polycrystalline samples of YxHo1−xNi2 solid solutions with 1≥x≥0 have been studied using X-ray diffraction analysis and magnetic, electrical resistivity, and heat capacity measurements. The X-ray diffraction performed at room temperature allowed us to reveal that the YxHo1−xNi2 solid solutions solidify with the formation of a Laves-phase superstructure corresponding to the space group F 4 3m ; no Laves-phase structure is formed. At low temperatures, the YxHo1−xNi2 solid solutions with 0.6≥x≥0 are ferromagnets. Their Curie temperatures decrease linearly from 17.6 K for HoNi2 to 4.8 K for Y0.6Ho0.4Ni2. The compounds with x≥0.8 and YNi2 do not show any long-range magnetic order. At high temperatures, all solid solutions are Curie–Weiss paramagnets. The temperature dependencies of the electrical resistivity were found to be typical of alloys exhibiting metallic conductivity. The Debye temperatures, phonon and conduction electron contributions as well as the magnetic part of heat capacity were determined from the heat capacity measurements. The magnetocaloric effect was estimated from measurements performed in a low magnetic field of 0.42 T.