Materials Literature
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An increase in the Fr\"ohlich-electron-LO-phonon interaction strength with decreasing nanocrystal size in the strong confinement limited is reported. This results from the size dependence of resonant Raman scattering by $\mathrm{Cd}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ nanocrystals embedded in a glass slab…
We propose a model for concentrated emulsions based on the speculation that a macroscopic shear strain does not produce an affine deformation in the randomly close-packed droplet structure. The model yields an anomalous contribution to the complex dynamic shear modulus that varies as the square root of frequency. We t…
A theory of superexchange in Cr-based ${\mathit{A}}_{\mathrm{II}}$${\mathit{B}}_{\mathrm{VI}}$ diluted magnetic semiconductors (DMS's) is presented. The spin interaction between ${\mathrm{Cr}}^{2+}$ ions, calculated numerically for zinc chalcogenides, exhibits properties unique in DMS's, it is ferromagnetic, and depen…
Thin films (≊0.4 μm) of cobalt ferrite (CoFe2O4) have been grown on single-crystal (100) MgO substrates using pulsed laser deposition (PLD). The phase, orientation, and microstructure of the as-deposited films were investigated as a function of substrate temperature (i.e., 200–800 °C) at a constant oxygen deposition p…
A model to reproduce inelastic electron scattering cross sections as determined from reflection-electron-energy-loss experiments is proposed. This model is an extension of model B from Yubero and Tougaard [Phys. Rev. B 46, 2486 (1992)]. Here, a more general geometry is considered where the incidence and exit angles ca…
Phenomena of colossal magnetoresistance (MR) or magnetic field induced insulator–metal (I–M) transitions have been investigated for single crystals of perovskite-type manganese oxides with controlled carrier density and one-electron bandwidth. In addition to the canonical MR behavior near the Curie temperature, the fi…
Effect of particle size on the electron transport and magnetic properties of La0.7Ca0.3MnO3 has been investigated. While the ferromagnetic Tc, low field magnetic susceptibility, and insulator-metal transition are markedly affected by the particle size, the maximum magnetoresistance exhibited by the samples near Tc is…
This article presents evidence that cobalt forms a series of optically active defect centers in diamond grown by high-temperature, high-pressure synthesis. Photoluminescence (PL) studies reveal that the newly observed vibronic systems with zero-phonon energies at 1.989, 2.135, 2.207, 2.277, 2.367, and 2.590 eV appear…
We introduce three models of fragmentation in which the largest fragment in the system can be broken at each time step with a fixed probability, p. We solve these models exactly in the long time limit to reveal stable time invariant (scaling) solutions which depend on p and the precise details of the fragmentation pro…
The D022-type (Al3Ti-type) phase in the Mn–Ga system is ferrimagnetic; the spin direction is parallel to the tetragonal c axis. The Curie temperature is about 765 K (for δ=0.67), near the decomposition temperature. We have prepared the D022-type alloys by annealing the quenched ingots of the high-temperature phase (γM…
\ensuremath{\sigma} and \ensuremath{\pi} plasmons in coaxial carbon nanotubes and multishell fullerenes are modeled in analogy with coupled collective excitations in finite, layered, two-dimensional-electron-gas, planar semiconductor superlattices. The curvature of the surface of these complex carbon clusters plays an…
High performance Nd2Fe14B-based permanent magnets are produced with different composition and various processing techniques. The composition and the processing route influence the complex, multiphase microstructure of the magnets, such as grain size, alignment, and distribution of phases. Grain sizes in the range betw…
We consider two models (A and B) which can describe both two dimensional fragmentation and stochastic fractals. Model A exhibits multifractality on a unique support when describing a fragmentation process and on one of infinitely many possible supports when describing stochastic fractals. Model B obeys simple scaling.
A deviation from the X-ray magnetic circular dichroism (MCD) spin sum rule, which is derived assuming well separated core spin-orbit multiplets in the final state of X-ray absorption, is calculated for the L 2,3 edge in the magnetized Ni, Co, Fe and Mn ions on the basis of an atomic model including the full multiplet…
Solid solutions (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 with 0.20≤x≤0.40 were studied using impedance measurements and high resolution x-ray powder diffraction. The dependence of the real and imaginary parts of the dielectric constant with temperature was investigated on unpoled and poled ceramics, showing several transition po…
We present semiempirical tight-binding and ab initio local density calculations demonstrating the (meta)stability of self-trapped excitons at the surface of silicon nanocrystallites. These are obtained for dimer bonds passivated, for instance, by hydrogen atoms or by silicon oxide. Light emission from these trapped ex…
General features of the energetics and electronic states of carbon nanotubes, containing pentagon-heptagon pair (5/7) topological defects in the hexagonal network of the zigzag configuration, are investigated within simple tight-binding models. This 5/7 pair defect on the nanotube structure is not only responsible for…
Polycrystalline samples of Ir4LaGe3Sb9, Ir4NdGe3Sb9, and Ir4SmGe3Sb9 have been made by hot isostatic pressing of powders. The lattice thermal conductivity of these filled skutterudites is markedly smaller than that of IrSb3; thus, void filling shows promise as a method for improving the thermoelectric properties of th…
A plane-wave semiempirical pseudopotential method with nonlocal potentials and spin-orbit coupling is used to calculate the electronic structure of surface-passivated wurtzite CdSe quantum dots with up to 1000 atoms. The calculated optical absorption spectrum reproduces the features of the experimental results and the…
Recently, it has been shown theoretically that it may be possible to increase the thermoelectric figure of merit ($Z$) of certain materials by preparing them in the form of two-dimensional quantum-well structures. Using $\mathrm{PbTe}/{\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}\mathrm{Te}$ multiple-quantum-well…