Table of contents

Structural disordering upon annealing of the Ni - Zr multilayers was investigated by molecular-dynamics simulation using an n-body potential. It was found that amorphization was initiated from the interfaces through mutual diffusion and alloying between Ni and Zr layers and that the structure of the resultant Ni - Zr alloy was verified to be indeed an amorphous phase.

A comprehensive analysis of magnetoimpedance (MI) phenomena in Fe-based nanocrystalline ribbons is presented in this paper. Giant MI responses have been observed in nanocrystalline samples annealed over the temperature range 490 and . More than 400% increases of the MI ratio were obtained both in and in ribbons. The sensitivity can reach a value larger than in the field range 3 - 7.2 Oe at 800 kHz for ribbons. No MI effect was observed in an as-quenched amorphous sample, because of its very low permeability. A mostly resistive feature was found in an as-quenched amorphous sample. The field dependences of the effective permeability show a typical transverse anisotropy property, and the development of the transverse anisotropy in naturally annealed Fe-based ribbons was analysed.

Enhanced planar Hall voltage changes were measured for a cross-diagonal current - voltage configuration in multilayers deposited on square Si(100) substrates by magnetron sputtering. A voltage maximum change is observed with an current flow along one diagonal of the square and the voltage output measured along the other diagonal, for external magnetic fields of applied in the film plane perpendicular to the edges. This result is discussed in terms of known galvanomagnetic effects in ferromagnetic thin films used in sensors.

There are two molecular adsorption states of CO in the system. One is , with lower C - O frequency, and the other is , with higher C - O frequency. The latter is similar to that on a clean surface. The two states of CO are occupied sequentially during the exposure to CO. The C - O stretch frequency of both states shifts to a higher value with the exposure to CO and to a lower value with higher Cs precoverage. The electronic structure of the molecule is different from that of the molecule and is of the same character as CO in a tilted mode.

Total current spectroscopy (TCS) was used to study an evolution of unoccupied states through the process of thin-layer copper deposition and its oxidation on polar ZnO(0001) and surfaces. Zn-derived and O-derived unoccupied bands were identified in the TC spectrum at 7.7 and 9.8 eV, respectively, from the clean and well ordered polar ZnO faces, while the spectra from a thin CuO layer reveal an intensive fine structure in the 6 - 25 eV energy range above the Fermi level, which is discussed in comparison with previously reported results of experimental and theoretical investigations. The obtained data provide additional information on the energy location of the edges of unoccupied bands in CuO in the 6 - 25 eV range relative to .

A density-functional-based non-orthogonal tight-binding (DF-TB) scheme is used to investigate models for the reconstructions of GaAs(110), (100) and (111) surfaces. The relative stabilities of the competing reconstructions are then determined as a function of the chemical potential, thus simulating a wide range of possible MBE growth conditions. We find a good agreement with recent experiments and ab initio calculations, and establish the validity of the scheme for large-scale applications.

The structure of solid confined in porous Vycor glass has been studied as a function of temperature via x-ray diffraction. The confined solid has the same structure as the bulk solid but with a slightly larger lattice constant of 5.644 Å at 150 K compared to the bulk lattice constant of 5.624 Å at the same temperature. Broad diffraction peaks are observed indicating that the solid phase of the in the pores forms in small crystallites approximately 160 Å in diameter. This is comparable to the pore dimensions in the Vycor indicating that solidification occurs separately in each of the pores. A large temperature-independent static disorder, analogous to the Debye - Waller factor, was observed in the form of strong damping of the Bragg peaks with increasing Q.

We present elastic band-structure results for a new geometry of two-dimensional phononic crystals: the boron nitride- (BN-) like structure. This array is constituted of two kinds of infinite elastic parallel cylinder located at the vertices of a regular hexagon and surrounded by an elastic background. This geometry includes both the triangular and graphite structures as particular cases. The inclusions and matrix are either both fluids or both solids, the constituent materials being water and mercury, and carbon (or tungsten) and epoxy.

We discuss the evolution of the band structure, and especially the existence of absolute band gaps, as a function of the ratio between the radii of the two cylinders in the BN geometry. We also discuss the existence of these gaps in relation to the physical parameters of the materials involved, and compare the results with those for square and triangular structures.

We introduce Gutzwiller-correlated wave functions for the variational investigation of general multi-band Hubbard models. We set up a diagrammatic formalism which allows us to evaluate analytically ground-state properties in the limit of infinite spatial dimensions. In this limit recent results obtained within the Gutzwiller approximation are seen to become exact for these wave functions. We further show that the slave-boson mean-field theory for degenerate bands becomes variationally controlled at zero temperature in infinite dimensions. Lastly, we briefly comment on the variational approach to the Anderson transition in strongly correlated electron systems.

A recently developed dynamical mean-field theory, in the iterated perturbation theory approximation, was used as a basis for the construction of a `first-principles' calculation scheme for investigating the electronic structure of strongly correlated electron systems. This scheme is based on the local density approximation (LDA) within the framework of the linearized muffin-tin orbitals (LMTO) method. The classical example of the doped Mott insulator was studied by the new method, and the results showed qualitative improvement when compared with experimental photoemission spectra.

Persistent charge and spin currents due to Aharonov - Bohm and Aharonov - Casher interferences of correlated electrons moving along a mesoscopic ring are discussed at finite temperature. As a function of applied flux the ground-state persistent currents have the shape of a generalized saw-tooth, i.e. they consist of piecewise straight segments. The periods and amplitudes of the oscillations are associated with the properties of the Fermi surface of the elementary excitations (two Dirac seas), namely the group velocities and the matrix of dressed generalized charges (Luttinger parameters). The temperature reduces the amplitudes of oscillation by smearing the Fermi surface in a similar way to that for the de Haas - van Alphen effect in 3D metals. The amplitude of higher harmonics decreases more quickly with T than the fundamental one, changing the saw-tooth to a more sinusoidal form with much smaller amplitude. The controlling parameters are the ratios of the thermal energy to the level spacings in the ring. The results are discussed in the context of the exact Bethe ansatz solutions for the Hubbard chain and the supersymmetric t - J model.

The phonon effects on a multichannel resonant-level model have been studied by a bosonization technique and canonical transformations. We found that the model can be mapped onto a single-channel Kondo model and the non-Fermi-liquid transition is modified by local electron - phonon interaction. At strong interaction, only one channel of conducting electrons is necessary in order to realize this transition and it is the phonon effects that control the behaviour of the system.

The parallel transport in semiconductor superlattices and the associated transfer of electrons from high- to low-mobility layers are treated on the basis of quantum kinetic equations. Due to the assumed dominant role of impurity scattering in the barriers, the description of transport properties simplifies considerably. The superlattice band structure is replaced by a two-band model that simulates electronic states in the narrow quantum wells and in the adjacent broad barriers. Using the quasi-elastic approximation for the electron - phonon scattering in the narrow miniband, analytical results are derived for the current density that provide a qualitative understanding of the main physics taking place in the device. The approximate description of the real-space transfer encompasses scattering on acoustic and optical phonons as well as on impurities. Particular emphasis is put on the negative differential resistance and its dependence on the well width.

A quantum theory of high-field miniband transport in semiconductor superlattices is developed that is applicable in the electric field range where negative differential conductance appears. The lateral electron distribution function is determined from a quantum kinetic equation, in which intracollisional field effects are included. Scattering on polar optical phonons is taken into account. Unlike the Boltzmann equation approach, our theory reproduces the experimentally detected temperature dependence of the current in both the hopping and band transport regimes. Numerical and analytical results show that at low temperatures the lateral electron distribution function strongly deviates from its equilibrium expression and exhibits sharp edges. For a superlattice with a narrow miniband the existence of electro-phonon resonance effects is predicted. The associated resonant-type current anomalies depend strongly on temperature and are most pronounced at low temperatures.

Magnetic and transport behaviours of (R = La, Pr, Gd, Tb, Ho and Er) systems have been studied between 2 and 300 K. At low temperatures, all the systems except for R = La exhibit complex magnetic ordering effects. The R = La system exhibits superconductivity. At high temperatures, the transport behaviour has been explained in the framework of the s - d model arising from the interaction between the 3d and the 5d electrons of Ni and R, respectively.

Boundary conditions for unconventional superconducting order parameters at a superconductor-to-insulator boundary with a combination of diffusive and specular scattering are derived from quasiclassical weak-coupling theory for a general Fermi surface. The resulting variational result for the extrapolation length is compared to recent numerical results for a d-wave order parameter and good agreement is found.

DyCu (CsCl-type) orders antiferromagnetically at . By measuring magnetization curves, the (H, T) phase diagrams are established for magnetic fields applied along fourfold and threefold axes. On the basis of neutron diffraction experiments on single crystals, magnetic structures are associated with each of the phases seen. The spontaneous and field-stabilized structures are multiaxial, with moments pointing along threefold or twofold directions. The phase sequence in the ordered range of DyCu reveals antiferroquadrupolar couplings of trigonal symmetry.

Magnetic and electrical properties of the (R = Sm, Eu, Gd, Tb, Dy, Y) compounds have been studied. All the samples have the same pseudo-cubic perovskite structure with small unit-cell distortions. The decreasing of rare-earth ion radii leads to destruction of both the long-range ferromagnetic and charge order and stabilizes a spin-glass-like state. The ferromagnet compound exhibits a peak of resistivity and anomalous behaviour of elastic properties at around whereas the resistivity and magnetoresistance of the (R = Eu, Gd, Tb) spin glass increase gradually with decreasing temperature.

The stability, crystal structure and magnetic properties of have been investigated by x-ray powder diffraction and magnetic measurements. With increasing Ce content x, the solubility y of the Si and the stability of the -type structure decrease. The crystal structure of was refined by the Rietveld method. The refined result indicates that Si atoms preferentially occupy the 96(i) positions in the -type structure. The substitution of Ce for La in results in a compression of the lattice cell volume and a decrease of the Curie temperature and the saturation magnetization. Taking the free ion value for the moment of the , the moment of the Fe atom was derived according to the antiparallel coupling model. The calculated results indicate that the moment of the Fe atom is weakly dependent on the value of x.

Terbium vanadate is a paramagnet with the tetragonal zircon structure (Wyckoff R W 1965 Crystal Structures vol 3 (New York: Interscience)), with space group . The ground state is split by the crystal field into three doublets and seven singlets. At a temperature of 33 K, a cooperative Jahn - Teller interaction produces a lattice distortion with extensive changes in the electronic energy levels. At the lowest temperatures the ground levels are two singlets, split by nearly 30 GHz. The present paper reports a new determination by means of electron spin resonance of this splitting; this is correlated with earlier measurements, in particular that of the heat capacity below 1 K. Magnetic hyperfine interaction, not previously considered, produces a complex ground state with large enhanced nuclear moments. The antiferromagnetic state below is attributed to spin - spin interaction between these moments.

High-field Mössbauer spectroscopy was performed on a range of tin-containing ternary and binary silicate glass systems. All the glasses unambiguously exhibited a positive value for for the valence state. Determination of the sign of indicates that the electron distribution around each Sn nucleus is similar at all the tin atoms, which is a significant finding for glasses. These results suggest that the electronic state of the is dictated by its non-bonding electron orbital, which has strong character, and which provides the dominant contribution to the electric field gradient present at the nucleus.

We report a structural evolution analysis of the long-range and local order and disorder of lead scandium niobate (PSN) down to 10 K, using a combination of neutron and x-ray diffraction on powder and single crystals. The structure of PSN is discussed and compared with those of simple perovskite compounds and . In PSN the existence of a long-range but still disordered ferroelectric phase, different from those of simple perovskites, is evidenced. The disorder of lead and scandium/niobium atoms on short-, medium- and long-range scales is discussed in connection with the dielectric properties of these materials.

The electrostatic resonant scattering of x-rays by an ion is discussed in terms of the relevant part of the scattering length. A formula, which applies for both E1 and E2 absorption events, is given for the product of matrix elements in the scattering length. The formula refers to an intermediate state that is labelled by the full set of quantum numbers of the core state into which a photon is absorbed. Idealized scattering lengths, discussed in our previous papers, are obtained by eliminating one or both quantum numbers of the core state.

We report temperature dependences of transport and magnetic properties of controlled by charge carrier doping (x = 0.0 - 0.5). The system exhibits an insulator-to-metal transition concomitant with an antiferromagnetic-to-paramagnetic transition near x = 0.2 with increasing substitution. Disorder effects are found to influence the low-temperature transport properties of both insulating and metallic compositions near the critical concentration. At higher temperature resistivity of the metallic compositions has a dependence close to the critical concentration (x = 0.2 and 0.3) and thus provides an example of disordered Fermi liquid behaviour near the Mott transition. In contrast, at larger doping (x = 0.4 and 0.5) the resistivity exhibits a dependence. The molar susceptibility for the metallic samples indicates substantial enhancements due to electron correlation.