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An upper bound for the correlation length l of the boson peak vibrations in glassy is estimated using precise measurements of the dependence of Raman scattering spectra on the scattering angle. No such dependence in the region of the boson peak down to was found, with accuracy 0.3%. This provides an upper limit for l that is less than the acoustic phonon wavelength . The same result is obtained also for polycarbonate glass using light scattering data obtained by Surovtsev et al (Surovtsev N V, Wiedersich J, Novikov V N, Rössler E and Sokolov A P 1998 submitted). These results lead to the conclusion that the vibrations which contribute to the low-frequency light scattering spectra (the boson peak) in silica and polycarbonate are localized in the sense of the Ioffe - Regel criterion formulated as .

Recent transport, specific heat and magnetization measurements indicated that the Heusler-type compound is a candidate for a 3d heavy-fermion system. As a first step towards a detailed theoretical understanding of the observed anomalous electronic properties of this compound, we have performed first-principles electronic structure and total energy calculations for and . The calculated lattice constants and magnetic moments are in good agreement with experiments. Remarkably, we find that, unlike , Heusler-type is a nonmagnetic semimetal with a narrow pseudogap at the Fermi level. Furthermore, our calculations suggest that the observed large enhancement of electronic specific heat coefficient is largely caused by the mechanisms such as spin-fluctuations rather than electron - phonon coupling in . The relations between the existence of the Fermi surface and negative temperature dependence of the low-temperature electrical resistivity in are discussed and further experimental and theoretical work is suggested.

By using the Green's function method, the localized state energy for an electron trapped in the chain-oxygen vacancy in has been calculated. At reasonable parameter values it lies above the chain- and plane-oxygen band top. Correspondingly the formation of a stable chain centre can be supposed, as in the mechanism (Federici J F et al 1995 Phys. Rev. B 52 15592) of photoinduced conductivity.

We present a theoretical study of an Fe/Cr multilayer film which may be thought of as a synthetic antiferromagnetic superlattice. We clarify certain aspects of the surface-spin-flop transition in which a domain wall nucleates at the outer layer and eventually migrates to the centre with increasing bias field. In particular, the nonvanishing ferromagnetic moment predicted earlier for bulk domain walls at vanishing field is shown to drive a prolonged hysteresis cycle and could thus be detected experimentally.

The saturation magnetoelastic stress (MS), , breaking the basal plane cylindrical symmetry of the hexagonal structure, has been measured for the series of superlattices (n = 8 to 85 atomic planes, with separation c/2). The MS was directly measured using a low-temperature cantilever technique. The Ho block MSs in the superlattices are larger than in an Ho film of Å thickness and in bulk Ho. An analysis accounting for the contributions to coming from: the volume, , the interface, with magnetoelastic parameter , and the epitaxial strain shows that the interfacial magnetoelastic stress is strong, up to about six times larger than for n = 8, and of the opposite sign.

Differences have been found in the depth resolution of dynamic SIMS profiles from polysilicon films on silicon carried out with and without sample rotation. Corresponding differences in the surface topography have been observed using atomic force microscopy. Both amorphous and polycrystalline silicon films implanted with fluorine and arsenic and subjected to rapid thermal annealing were examined. For the polycrystalline film, conventional SIMS analysis led to a significantly roughened crater, with a somewhat lesser roughening effect in the case of the rotational SIMS. The crater in the amorphous film showed slight roughening in the conventional analysis mode whereas with rotation the crater base appears to preserve the initial topography of the film.

The electrical resistivity and temperature coefficient of resistivity (TCR) of Cu and Nb thin films have been measured over a range of layer thicknesses between 5.6 nm and 1106 nm. The structure of the films has been characterized using transmission electron microscopy (TEM) and x-ray diffraction. The experimental results have been compared with the semi-classical theory of thin-film resistivity due to Dimmich. The grain boundary reflectivity, R, has been found to vary with grain size in the Nb films.

Dimmich's theoretical expression for the TCR does not match experiment, but by adapting the theoretical treatment a satisfactory fit has been obtained. The semi-classical expression predicts a negative TCR for certain thin-film and multilayer systems without the need to appeal to localization or correlation.

Thin films of copper phthalocyanine and of a perylene derivative have been deposited on NaCl and quartz glass. The effective thickness of these films ranged between approximately one monolayer and 50 nm. The films were prepared by thermal evaporation in ultrahigh vacuum. For ultrathin layers, we detected a blue-shift of the optical absorption bands of about 400 wavenumbers with respect to those of the corresponding bulk material. This shift is nearly the same for phthalocyanine and the perylene derivative. The shape of the absorption pattern is also thickness dependent. Additionally, model calculations have been performed to estimate the classical local field contribution to these shifting effects. The classical contribution was found to be of the order of the experimentally observed effect.

On the basis of a quantum approach, the formula for the complex self-energy, and hence also that for the energy-loss cross-section, are derived for fast electrons penetrating through the surface from the interior of a solid. Both the angular and depth dependence are included in the expression. Use of a Drude-Lindhard model bulk dielectric function for describing a bulk plasmon excitation in a free-electron-like material has yielded an analytical expression for the surface dielectric function which satisfies surface sum rules. The calculated imaginary and real parts of the electron self-energy for Si have indicated, in detail, the excitation processes of the surface plasmon and the bulk plasmon for an electron passing through the surface, with the dependency on electron energy and take-off angle. This approach provides quantitatively the electron inelastic scattering cross-section in the surface region for use in surface electron spectroscopy.

A scheme for calculating the complex self-energy of electrons moving in a real metal surface region is proposed. The approach is based on a quantum formula that uses a Drude-Lindhard model bulk dielectric function for describing free-electron metal. The experimental energy-loss function is fitted to a finite sum of the modelled energy-loss functions and a corresponding expression for the complex self-energy is derived. Calculated differential inelastic scattering cross-section results are given for Mg, Ag and Au to show the surface and bulk excitation modes in these metals. The z-dependent inelastic mean free path and stopping power near a surface region are also obtained. The approach provides a practical scheme to be used in quantitative surface electron spectroscopy.

Transmission electron microscopy and neutron diffraction have been used to characterize ceramics and single crystals from the rhombohedral region of the (x = 0.06-0.45) phase diagram. Electron diffraction patterns showed the existence of superlattice reflections of the type , where h = k = l, and , which are not observed by neutron powder diffraction. The analysis of these reflections also revealed satellite spots around the , which are associated with periodic antiphase boundaries. The origin of these superlattice reflections is explained by the existence of local regions presenting antiparallel cation displacements, and models for this are suggested

In order to clarify the mechanism of hydrogen diffusion in cubic Laves phase , we have performed high-resolution quasielastic neutron scattering measurements on (x = 0.6 and 1.1) in the temperature range 10-320 K. It is found that the diffusive motion of hydrogen in this system can be described in terms of two jump processes: the fast localized H motion within hexagons formed by interstitial g sites and the slower hopping from one hexagon to the other. This model is also supported by neutron diffraction measurements showing that the sublattice of g sites in is split into hexagons well separated from each other. The behaviour of the elastic incoherent structure factor for suggests that only a fraction of the H atoms participate in the fast localized motion, and this fraction increases with temperature. Comparison of the properties of and other Laves phase hydrides with g-site occupation shows a clear correlation between the parameters of the two jump processes and the g-g distances (within the hexagons) and (between different hexagons).

Theoretical phase diagrams for betaine calcium chloride dihydrate are constructed. A phenomenological approach is used. Expressions for the thermodynamic potentials of different phases and for the boundaries between these phases are given in an explicit form. The theoretical temperature-pressure phase diagram is plotted and is found to be in agreement with the experimental diagram. The approximations and assumptions made in the construction of the diagrams are discussed.

An approximate computational scheme is proposed for treating complex systems. The proposed method relies on the quadratic approximation to the multiple-scattering theory of Korringa, Kohn and Rostoker, which allows one to implement potential shifts in the solution of the Schrödinger equation for impurities. Choosing these shifts appropriately, one can simulate various physical processes in complex systems in an efficient computational way. The efficiency of our method is demonstrated by two example calculations. In the first, we calculate the charge transfer towards (or outwards from) a 3d or a 4d single substitutional impurity in a Cu or Ni host metal. In the second example, we calculate the binding energies of the 2s electrons of 3d atoms in solids in a quasi-adiabatic approximation.

The influence of the substitutional atoms Cr, Mn, Ni, Cu, Mo in iron-based alloys on the stability of the crystalline fcc structure and the change of the electron state density at the Fermi surface are studied by means of conduction electron spin resonance (CESR). The temperature dependence of the CESR g-factor and of its integral intensity is measured and analysed in relation to theoretical predictions. It is shown that Cr, Mn and Mo decrease the state density at the Fermi surface in the fcc iron, whereas Ni and Cu increase it. The study singles out the contributions of three electron subsystems (conduction s electrons, localized isolated d electrons and those included in superparamagnetic clusters) to g(T) and traces the important role of substitutional alloying elements in the formation of clusters in fcc solid solution.

Structures consisting of ZnTe fractional monolayers embedded coherently in a CdTe quantum well are investigated by means of optical measurements. This study is designed to study the influence of the strained ZnTe islands on excitonic recombination and to explore the dependence of the self-organizing effects of the ZnTe island on growth temperatures. The experimental results show that the strained ZnTe islands can strongly modify the excitonic transitions related to the quantization of the excitonic centre-of-mass motion (CM quantization). We have shown that the striking increase of the effective g-factor of the CM quantized excitons is due to the change of the hole g-factor involved since it is found experimentally that the electron g-factor is unchanged. The experimental results also show that a coherent distribution of the ZnTe islands is formed at higher growth temperatures , while a random distribution of the ZnTe islands is formed at lower growth temperatures . A coherent alignment of the islands along the growth direction is concluded.

It is shown that the nonhomogeneous structure of the superconducting phase in the diamond-like carbon-silicon nanocomposites containing tungsten with concentration close to the metal-insulator transition is responsible for the perculiarities in the character of the superconducting resistive response. The observed nontrivial quasireentrant resistive transitions can be explained in terms of the phase coherence destruction between the superconducting grains and by the renewal of superconducting phase generation at lower temperatures defined by the presence of the two scales of inhomogeneity in the investigated films. The resistance-current characteristics in the vicinity to the superconducting transition and magnetic measurements do not contradict the qualitative model proposed.

Dynamical phase transitions in the Ising model on hypercubic lattices are considered. Under a linearly swept magnetic field, the hysteresis loop that characterizes the field-driven first-order phase transition is studied carefully. Using the Glauber dynamics, we find that, in the mean-field approximation, the energy dissipation of this phase transition or the hysteresis loop area A of the M-H curve can be scaled with respect to the sweep rate h of magnetic field in the form with a = 2 and b = 2/3. However, b varies when fluctuations and spin correlations are taken into account. Monte Carlo simulation is used to obtain the scaling relation for A in two-, three- and four-dimensional Ising models and we obtain the exponents and respectively. These exponents are obviously different from those obtained by scaling A as for any temperatures in Ising models under a sinusoidal field. Finally we point out that, in the concept of universality, field-driven first-order phase transitions in the Ising model in different dimensions belong to different universal classes due to the spin fluctuation and correlation below the Curie temperature.

Measurement of the magnetic susceptibilities and their anisotropy in single crystals of ErDG in the temperature range of 300-22 K are reported here for the first time. The anisotropy value became constant at and below 32 K and this was associated with a possible rotation of each of the three structurally equivalent lanthanide sites in the unit cell without destroying the overall trigonal symmetry of the crystal field (CF), as also observed earlier in NdDG and . CF analysis was performed and the fitted CF parameters were found to be close to the values reported from optical absorption study. The g-values were calculated and found to be and . The calculated values of Schottky specific heat showed a maximum at about 100 K.

The low-field magnetoresistance and the magnetization of ceramic oxides have been studied as a function of the grain size. It is shown that these ceramics become magnetically harder when reducing the particle size, exhibiting large magnetic anisotropy that also increases when reducing the grain size. In concomitance with this enhancement of the magnetic hardness a gradual increase of the low-field magnetoresistance is also detected. We suggest that both phenomena are closely related and associated with the existence of some degree of spin disorder at the grain boundaries. Implications of these findings for improvements of the field response sensitivity of these materials are discussed.

The transmission of electromagnetic radiation at normal incidence through a magnetic film is considered for film thickness L small enough to require the inclusion of exchange effects arising from the wave-number component . We apply the continuum form of the dynamical equations with parametrized spin boundary conditions including pinned and unpinned spins as special cases. For applied field normal to the interfaces (Faraday geometry) the propagating modes are circularly polarized but because of the exchange there are two modes, say optical and spin, in each polarization. Equations for the transmission are given in a general form that allows for partial mirrors at the interfaces and applies to a film on a substrate as well as a free-standing film. Computed transmission spectra show that spin-wave fringes are unlikely to be observable for ferromagnets but can be significant in antiferromagnets. Some discussion is given of the implications for the characterization of antiferromagnetic film systems by means of far-infrared spectroscopy.

Blue emission at 486 nm corresponding to the transition in (GGG) thin epitaxial film was generated after excitation with infra-red radiation at around 890 nm. The upconversion mechanism was shown to be excited-state absorption from the multiplet. The spectroscopic properties of the state of in GGG were also studied. The emission spectra of bulk crystals and thin film are centred at , and the measured lifetime is about at room temperature. Blue-wavelength upconversion excitation spectra and direct infra-red excitation spectra allowed us to determine the Stark energy levels in the and multiplets.

We report normal and magnetic extended x-ray absorption fine-structure (EXAFS) measurements made on 30 ML Fe films on Cu(001) substrates at the edges. The magnetic EXAFS at the L edges of 3d metals is particularly important as it can be used to probe the magnetism of the d states. Magnetic EXAFS oscillations were detected up to 500 eV above the edge, corresponding to in k-space. Over such a large range, we were able to see long-wavelength wiggles and separate them from Fe nearest-neighbour backscattering and the fast oscillations that had been previously seen. It is shown that without using any deconvolution procedure, a meaningful analysis can be performed despite the interference of the and edges. The experimental data were compared with the results of multiple-scattering calculations, and this enabled us to assign all of the features in both the normal and the magnetic EXAFS Fourier transforms to various single- and multiple-scattering paths. Also, there was found to be less temperature-dependent damping for magnetic EXAFS as than for the normal EXAFS between 75 K and 300 K.

The valence- and conduction-band electronic densities of states (DOSs) in amorphous (a-) GeSe and GeTe were investigated by means of ultraviolet photoemission and inverse-photoemission spectroscopy (UPS and IPES), respectively. The UPS spectra for both a-GeSe and a-GeTe are very similar to those obtained in previous experiments; a distinct peak appears near the top of the valence band. The IPES spectra for both a-GeSe and a-GeTe corrected by subtracting the background exclude the possibility of a structure with 3(Ge):3(chalcogen) coordination if one compares them with the theoretical DOS calculated by O'Reilly, Robertson and Kelly. The corrected IPES spectrum for a-GeSe resembles the broadened theoretical DOS for chemically ordered 4(Ge):2(Se) structure, whereas that for a-GeTe resembles the theoretical DOS for randomly bonded 4(Ge):2(Te) structure. The characters of the conduction-band DOSs for a-GeSe and a-GeTe were also examined by means of soft-x-ray core absorption spectroscopy. The Ge and Se core absorption spectra of a-GeSe are very similar to those of a-, and were discussed using a simple bonding model with a 4(Ge):2(Se) local configuration. The Ge and Te core absorption spectra of a-GeTe were also discussed using a simple local bonding model. All of the present measurements indicate that both a-GeSe and a-GeTe have structures with 4(Ge):2(chalcogen) coordination.