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Structure maps have always held out the allure of being useful guides in materials design. A novel method for predicting candidate structure types demonstrates that the Pettifor maps for binary compounds are surprisingly predictive and offers a natural way for extending the predictive power of the maps to higher multicomponent systems.

We report, for the first time, simultaneous fabrication of laser-active F₂ and F₃⁺ colour centres in lithium fluoride and permanent periodic gratings with fringe spacings as fine as sub-micron size by two interfering infrared femtosecond (fs) laser pulses. In particular, the optical properties (absorption and luminescence) of F₂ and F₃⁺ colour centres produced by a single fs laser pulse are compared with those created by damage from radiation such as x-rays. The present technique of simultaneously fabricating laser-active colour centres and functional fine-periodic structures in photo-insensitive transparent materials may well be a useful method for making miniaturized optical devices.

The dynamic coercive field H_c^∗ for a 15 nm epitaxial Fe/GaAs(001) film is measured by magneto-optic Kerr effect for sinusoidal applied fields in the frequency range 1–2300 Hz. A dip in H_c^∗ is found at the cross-over from low dynamic regime to high dynamic regime, which occurs at ∼400 Hz at room temperature. The same measurement at successively lower temperatures extending down to 80 K reveals that the dip shifts to lower applied field frequencies as the temperature is reduced. This indicates both that the dip is real and that thermal activation is important in the reversal dynamics. Further, the existence of the dip implies that there are two distinct time-scales associated with the reversal process. We speculate that these time-scales correspond to domain nucleation and wall motion, respectively. An existing model for magnetization reversal dynamics in ultra-thin magnetic layers is adapted to describe the measurements empirically.

Since Pd–Ag alloys constitute a well known prototype binary alloy system, phase separation at the surface was not expected. However, we have shown direct evidence of surface-induced phase separation in Pd–Ag alloys using photoemission spectroscopy. This phenomenon is just the opposite of surface alloying between two miscible elements. The miscibility gap in this alloy near the surface is clearly observed in our core level spectra. The characteristics of this surface-induced phase separation have been probed over various composition ranges using x-ray photoelectron spectroscopy.

Silver has long been used for mirrors and tableware due to its high reflectivity, and it is still a very important component in optics. In particular, silver island films or small particles have been applied as photographic materials, tools and devices to generate localized electrical fields for molecular detection and electrical field enhancement.

It has recently been discovered that silver oxide thin films may be a very useful material for dealing with optical near-field and surface plasmons. Silver oxide decomposes into oxygen and small metallic silver particles, and this characteristic has been applied to ultrahigh-density optical data storage to create a strong light-scattering centre that resolves small pits or marks beyond the diffraction limit. More recently, it has been found that silver film can be cheaply and easily transformed into Ag nanoparticles and nanowires in a gas mixture of hydrogen and oxygen in a vacuum chamber. The particle and wire diameters are very uniform and approximately 20–50 nm, and they can be three-dimensionally fabricated on almost all material surfaces without the need for thermal annealing. Silver nanoparticles and wires will soon appear in small and cheap molecular detection sensors by small precise adjustments for generating surface plasmon conditions.

The main aspects of the fabrication and the structural and magnetic properties of epitaxial metal-insulator heterostructures are reviewed. Continuous and lithographically processed systems are discussed, with special emphasis on their crystalline nature when interpreting their physical properties. The work is placed within the scope of the previous and current activities by different groups on Fe/MgO(001), considered as a model system. The influence of deposition conditions on the epitaxy and morphology are discussed initially, correlating afterwards magnetic properties with crystalline structure. Subsequently, magnetic anisotropies and interactions are treated in both continuous and patterned film structures. Finally, the use of these fully epitaxial transition metal-insulator heterostructures for the development of magnetic tunnel junctions is described.

About one atomic layer of Pt was deposited on a Ni(110) surface to investigate the magnetic anisotropy of the interface. The magnetization of Pt atoms was probed with resonant magnetic x-ray diffraction and the magneto-optical Kerr effect was utilized to probe the average magnetization of the Ni in the near-surface region. Our results show that the magnetization of the Pt atoms in the surface plane depends on the direction of the applied field. While the [10] direction shows a hysteresis cycle of the Pt film typical of an easy magnetization axis, the [001] direction has a hard axis behaviour. In contrast, the Ni(110) substrate shows similar cycles for the two directions. A possible explanation, based on the formation of an anisotropic superstructure, as observed by means of surface x-ray diffraction, is suggested.

The static and dynamic magnetic behaviour of Fe nanoclusters with controlled sizes in the range 140–270 atoms (1.5–1.8 nm) deposited in situ from a gas aggregation source on magnetic vitrovac amorphous ribbons has been studied using synchrotron radiation. The static magnetization of the cluster films in the exchange field of the substrates was measured as a function of coverage using magnetic linear dichroism in the angular distribution (MLDAD) of the Fe 3p core level photoemission. The switching dynamics were studied on the nanosecond timescale by time-resolved spin-polarized photoemission. For a given particle size, the magnetization of the Fe cluster film increases with coverage and saturates at a coverage of about 0.4 cluster monolayers. Modelling the growth of the magnetization gives an effective exchange field at the interface of ∼20 T. Dense cluster films with several cluster layers have an MLDAD signal at saturation that is ∼5% higher than a molecular beam epitaxy (MBE)-grown film, indicating an enhanced spin moment even when clusters are in contact. Coating an exposed sub-monolayer cluster layer with Co increases the Fe MLDAD signal by 35%, indicating a substantially increased magnetic moment within the Fe clusters. At low coverages, below the percolation threshold, the switching dynamics of the sample remains the same as in the clean substrate. At around the percolation threshold, however, a significant acceleration of the magnetic reversal is observed with a fast component due to a reversal propagating through the cluster film. We show that, on average, each cluster switches in about 10 ns.

We present a determination of the magnetic structures of three Laves phase superlattice samples of structure [70/30]₆₀, [150/100]₅₀, and [50/70]₆₀, where the structure is given as [t₁ Å DyFe₂/t₂ Å YFe₂]_N, grown by molecular beam epitaxy. The experiments were performed using magnetization measurements and neutron scattering measurements at the NRU reactor at Chalk River in Canada.

For the [70/30]₆₀ sample, a magnetic field parallel to the scattering vector, Q, was applied to determine the nuclear component of the scattered intensity. The magnetic structure with the field aligned along the [001] had all the moments aligned along the field direction and the magnitude of the moment on the iron site was temperature independent with a value of 2.3(0.3) μ_B. The moment on the dysprosium site was found to decrease with temperature from about 10 μ_B to a value of 6(0.5) μ_B at 300 K. When the field was applied in the [10] direction the magnetic moments were found to rotate out of the (110) epitaxial plane towards the [110] direction by an angle ψ = 10° at 300 K, which increased at 4 K to an angle of ψ = 40° close to the [100] out-of-plane direction.

For the [150/100]₅₀ sample, when a 6 T magnetic field was applied along the [10] direction, the main peak of the magnetically sensitive (11) reflection was found to decrease in intensity while the scattering at the satellite peaks increased. This change in intensity is due to the formation of magnetic exchange springs in the 'soft' YFe₂ layers of the superlattice. Detailed measurements around the (11) reflection and calculations for an exchange spring model give excellent agreement between the model and the experiment.

Finally, the [50/70]₆₀ sample showed unexpected behaviour because the moments aligned largely perpendicular to an applied field. This is similar to a spin-flop phase of an antiferromagnet and it is argued that this occurs because the net moments on the DyFe₂ and YFe₂ layers are nearly equal.

Thermal properties - specific heat and heat conductivity coefficient—of polycrystalline BaTiO₃ films on massive substrates were studied as a function of the temperature and the film thickness by the ac-hot probe method. The anomalies of specific heat with the film thickness decreasing from 1100 to 20 nm revealed the reduction of T_c and excess entropy of the ferroelectric phase transition which becomes diffused. The critical thickness of the film at which T_c = 0 has been estimated as 2.5 nm.

Ab initio density functional plane-wave calculations are performed for a number Met-Car analogue clusters of special stability which are assembled to form hypothetical three-dimensional structures and linear chains. The stabilization energies of various competing structures are determined and their atomic and electronic properties are predicted. Some of the solid phases are found to be metallic (B₈C₁₂ and Si₈C₁₂) while others are semiconducting (N₈C₁₂) which suggests a range of new potential applications. The B₈C₁₂ phase is also considered to be a possible high-T_c superconductor. The solid phases of P₈C₁₂ are not predicted to be stable. The results demonstrate the viability of assembling new solid phases from clusters of various Met-Car analogues.

A neutron powder diffraction study of ErFe₂D₅, synthesized under 1 GPa hydrogen pressure, shows that it crystallizes at room temperature in an orthorhombic structure described by the Pmn2₁ space group with a = 5.42 Å, b = 5.79 Å, c = 8.00 Å. The deuterium atoms order preferentially in some A₂ B₂ and AB₃ interstitial sites. Below 5 K the erbium moments order in a canted magnetic structure, with an erbium moment of 6.6 μ_B at 1.4 K. The ⁵⁷Fe Mössbauer spectra of ErFe₂D₅ from 4.2 to 300 K indicate that there are no ordered Fe moments at zero field. These results are discussed in relation to the influence of hydrogen absorption on the magnetic interactions.

The ability to predict the crystal structure of a material, given its constituent atoms, is one of the most fundamental problems in materials research. There exist a number of empirical methods which make predictions by clustering existing experimental data, generally using a few simple physical parameters. Although Pettifor maps are perhaps the best known and most successful of these empirical methods, the implementation and assessment of Pettifor maps has not been formalized. Here we propose well-defined algorithms for transforming data from a standard materials crystal structure database into a Pettifor map, using the map to predict the crystal structure for a new system, and assessing the predictive accuracy of the map. We introduce the idea of a candidate crystal structure list, demonstrating that by predicting more than one candidate for a new system the utility of the maps can be enhanced. We assess the accuracy of the maps by testing predictive accuracy using a cross-validation technique on all AB and A₃B compounds in the CRYSTMET database. We show that for a new unknown alloy with a stable structure at the stoichiometry of the Pettifor map, a candidate list of five structures will contain the correct crystal structure for the alloy 86% of the time. The algorithms presented here can be used to automate Pettifor maps in materials crystal structure databases, making it possible for users to construct, apply and assess entirely new Pettifor maps quickly and easily.

Monodomain regions are observed in the uppermost ferroelectric parts of the factory-roof-shaped phase front during the KD₂PO₄ 218 K first-order transition. It is also demonstrated that the existence of the phase front induces high values of dielectric and loss constants (along the c axis). An explanation is proposed assuming specific properties for the observed monodomain regions.

The microscopic structure of a silicon vacancy is studied theoretically using first-principles supercell calculations. Both the standard Kohn–Sham local-density approximation (LDA) scheme and the generalized Kohn–Sham screened-exchange local-density approximation (sX-LDA) scheme are used. The latter approximation is expected to improve the description of electronic levels in the gap region substantially, while providing accurate total energies and bond lengths.

The present LDA calculations are in line with the earlier corresponding calculations of the silicon vacancy, predicting an inward relaxation of the nearest neighbours of the vacant site. The LDA calculations also predict the Jahn–Teller distortions and negative effective-U effects for charged vacancies, qualitatively in agreement with the experimental results and the Watkins model. In contrast to LDA results, the present sX-LDA calculations predict an outward relaxation and sp² type hybridization for the ions surrounding the vacancy. This somewhat surprising result is explained by the removal of the systematic overbinding associated with LDA.

The effective medium approximation (EMA) is derived to investigate the effective linear and nonlinear responses of two-component composites in which one component is nonspherical and distributed in shape. Both components with the volume fractions p and q are assumed to obey a current–field J–E relation of the form J = σ_iE + χ_i|E|²E, where σ_i and χ_i are the linear conductivity and nonlinear response of the component i (i = 1, 2) respectively. As the percolation threshold p_c (or q_c) is approached from above (or below), the effective linear conductivity σ_e and effective nonlinear response χ_e behave as σ_e ∼ [p − p_c(Δ)]^t and χ_e ∼ [p − p_c(Δ)]^t₂ in the conductor/insulator (C/I) limit, and σ_e ∼ [q_c(Δ) − q]^−s and χ_e ∼ [q_c(Δ) − q]^−s₂ in the superconductor/conductor (S/C) limit, where the exponents are found to be t = s = 1 and t₂ = s₂ = 2, independent of the shape variance parameter Δ, and p_c(Δ) (or q_c(Δ)) is a monotonically decreasing (or increasing) function with Δ. For a finite-conductivity ratio h = σ₁/σ₂, numerical results show that σ_e may be increased or decreased with increasing Δ, dependent on whether the first component is a good or a poor conductor, while χ_e can exhibit a monotonic increase, monotonic decrease and nonmonotonic behaviour. Therefore, χ_e can be greatly enhanced by the adjustment of the shape variance parameter, and thereby provides an alternative way to achieve large enhancement of effective nonlinear response. The results of EMA with shape distribution are also compared with exact solutions in the dilute limit and reasonable agreement is found.

Momentum-and energy-balance equations are developed for steady-state electron transport and optical absorption under the influence of a dc electric field and an intense ac electric field of terahertz (THz) frequency in a two-dimensional (2D) semiconductor in the presence of a strong magnetic field perpendicular to the 2D plane. These equations are applied to study the intensity-dependent cyclotron resonance (CR) in far-infrared transmission and THz-radiation-induced photoconductivity of GaAs heterostructures in the Faraday geometry. We find that the CR peaks and line shapes of the transmittance exhibit different intensity dependences when the intensity of the THz field increases in the ranges above or below a certain critical value. The CR in the photoresistivity, however, is always enhanced on increasing the intensity of the THz field. These results agree qualitatively with the experimental observations. We have clarified that the CR in the photoconductivity is not only a result of the electron heating, but also arises from photon-assisted scattering enhancement, especially at high temperatures. The effects of an intense THz field on the Faraday angle and ellipticity of magnetically biased 2D semiconductors have also been demonstrated.

The single-site two-electron exchange amplitude J_sd between the Cu 4s and Cu 3d_x²−y² states is found to be the pairing mechanism of high-T_c overdoped cuprates. The noninteracting part of the Hamiltonian spans the copper Cu 4s, Cu 3d_x²−y² and oxygen O 2p_x and O 2p_y states. Within the standard BCS treatment an explicit expression for the momentum dependence of the gap Δ_p is derived and shown to fit the angle-resolved photoemission spectroscopy data. The basic thermodynamic and electrodynamic properties of the model (specific heat C(T) and London penetration depth λ(T)) are analytically derived. These are directly applicable to cuprates without complicating structural accessories (chains, double CuO₂ planes etc). We advocate that the pairing mechanism of overdoped and underdoped cuprates is the same, as T_c displays smooth doping dependence. Thus, a long-standing puzzle in physics is possibly solved.

We calculate the normal metal–s + g-wave superconductor tunnelling spectrum for various junction orientations and for two forms of the superconducting gap, one which allows for point nodes and the other which allows for line nodes. For a junction oriented with its normal parallel to the ab plane of the tetragonal superconductor, we find that the tunnelling spectrum is strongly dependent on orientation in the plane. The spectrum contains two peaks at energies equivalent to the magnitudes of the gap function in the direction parallel to the interface normal and in the direction making a π/4 angle with the normal. These two peaks appear in both superconductors with point nodes and line nodes, but are more prominent in the latter. For the tunnelling along the c axis, we find a sharp peak at the gap maximum in the conductance spectrum of the superconductor with line nodes, whereas with point nodes we find a peak occurring at the value of the gap function along the c axis. We discuss the relevance of our result to borocarbide systems.

La–Sb–Mn–O compounds have been prepared by the solid-state reaction of La₂O₃, Sb₂O₃ and MnCO₃. The materials have a perovskite structure and exhibit the colossal magnetoresistance (CMR) effect, and the maximum magnetoresistance ratio could reach as high as 60% (at 225 K under 5 T) for La_0.9Sb_0.1MnO₃. The valence states of manganese and antimony have been identified as Mn³⁺, Mn²⁺ and Sb⁵⁺. The temperature dependences of electrical transport and magnetic properties have been studied. The results suggest that the mechanism of CMR for La_1−xSb_xMnO₃ is probably due to the double exchange interaction between Mn³⁺ and Mn²⁺ ions.

The magnetic properties of [Cu₄(ndpa)₂(H₂O)₆Cl₂]·2H₂O are studied by static and dynamic magnetic susceptibility measurements. The static susceptibility measurements between 2 and 300 K reveal ferromagnetically coupled Cu(II) dimers (J/k_B = +24.0 ± 0.5 K). Two further exchange constants J^'/k_B = −0.40 ± 0.02 K and J^''/k_B = 2.2 ± 0.2 K are determined by zero-field ac-susceptibility measurements in the temperature range between 12 and 0.4 K. The exchange couplings are assigned by means of electron spin resonance measurements which show that Cu₄: Cl realizes a ferromagnetic alternating spin-1/2 Heisenberg chain with an antiferromagnetic interchain coupling.

The A₁-symmetry Raman spectra of berlinite in a broad temperature range, encompassing the α–β phase transition, are reported. The temperature dependence of the lattice mode parameters is presented, particularly concerning the 'soft' mode at ∼220 cm⁻¹, which exhibits a complex behaviour in the α phase. This is accounted for by coupling with another A₁ mode and two-phonon background in the α phase. It is shown that the soft-mode parameters do not show appreciable discontinuities at the transition. The fact that four Raman active A₁ modes instead of three are observed in the hexagonal β phase can be understood by assuming a dynamical disorder of Al and P atoms over trigonal α-phase sites.

An ultrasonic pulse–echo method was used to measure the transit time of longitudinal and transverse (10 MHz) elastic waves in a Nd₆₀Al₁₀Fe₂₀Co₁₀ bulk metallic glass (BMG). The measurements were carried out under hydrostatic pressure up to 0.5 GPa at room temperature. On the basis of experimental data for the sound velocities and density, the elastic moduli and Debye temperature of the BMG were derived as a function of pressure. Murnaghan's equation of state is obtained. The normal behaviour of the positive pressure dependence of the ultrasonic velocities was observed for this glass. Moreover, the compression curve, the elastic constants, and the Debye temperature of the BMG are calculated on the basis of the similarity between their physical properties in the glassy state and those in corresponding crystalline state. These results confirm qualitatively the theoretical predictions concerning the features of the microstructure and interatomic bonding in the Nd₆₀Al₁₀Fe₂₀Co₁₀ BMG.