Materials Literature
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Diffusion of penetrants through polymers often does not follow the standard Fickian model. Such anomalous behavior can cause difficulty when designing polymer networks for specific uses. One type of non-Fickian behavior that results is so-called case II diffusion, where Fickian-like fronts initially move like √t with…
A model for the radiation-induced production of defects in amorphous insulators is proposed. It is shown that an irreversible creation of defects from network sites follows power law kinetics, and a reversible activation of precursor sites follows Kohlrausch kinetics. Electron spin resonance was used to measure the co…
Although the production and applications of NdFeB magnets have increased enormously in the last decade because of their outstanding magnetic properties at room temperature, some applications were limited because of poor thermal stability and corrosion resistance. To address these problems, there have been many efforts…
We have attempted to optimize the values of the giant magnetoresistance in symmetric spin valves of the type NiO/Co/Cu/Co/Cu/Co/NiO (achieving 23.4%) and in bottom spin valves of the type Co/Cu/Co/NiO (achieving 17.0%), the largest values ever reported for such structures. The key elements in this achievement are impr…
Hyperbranched polyurethanes, with varying oligoethyleneoxy spacer segments between the branching points, have been synthesized by a one-pot approach starting from the appropriately designed carbonyl azide that incorporates the different spacer segments. The structures of monomers and polymers were confirmed by IR and…
Record values for high Hall mobility and for low compensation ratio of boron doped diamond by ion implantation are reported. These are achieved, following the suggestion by Prins, by low dose Boron implantation into cold diamond (−97 °C) and in situ rapid heating (1050 °C for 10 min) and by a further anneal at higher…
The structural and magnetic properties of (R,Zr)(Fe,Co)10(R=Nd,Sm) prepared by the rapid-quenching method have been investigated. The presence of zirconium makes it possible to realize a TbCu7-type crystal structure with a high c/a ratio of more than 0.87, while the same crystal structure has a c/a ratio of just 0.84–…
We report the first observation of steps in the hysteresis loop of a high-spin molecular magnet. We propose that the steps, which occur every 0.46 T, are due to thermally assisted resonant tunneling between different quantum spin states. Magnetic relaxation increases dramatically when the field is in the neighborhood…
Angular-dependent magnetic Barkhausen noise (MBN) measurements were performed on a pipeline steel sample for various values of applied uniaxial stress at three angles with respect to the sample’s zero stress magnetic easy axis direction. It was observed that the response of the MBN signal to stress was dependent upon…
Resonant effects in diffraction from two-dimensional dielectric gratings is demonstrated experimentally. A two-layer structure, which consists of a uniform guiding layer and a grating layer, yielded symmetric, low-sideband resonance that is suitable for narrow-band filter applications. Excellent agreement between meas…
We report on a new class of critical states in the energy spectrum of general Fibonacci systems. By introducing a transfer matrix renormalization technique, we prove that the charge distribution of these states spreads over the whole system, showing transport properties characteristic of electronic extended states. Ou…
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…