Iron sesquilayers are ultrathin films with coverages between one and two atomic mono-layers. They consist of an almost defect-free monolayer with compact islands of a second atomic layer on top. This variation of the film thickness results in a strong interaction between domain walls and the island structure. It makes these systems an ideal laboratory to study the dynamics of domain walls driven by weak external fields. We present computer simulations which provide insight into the role of the thermally activated nucleation processes by which a driven domain wall overcomes the obstacles created by the islands.

In order to elucidate the mechanism of spin-polarized electron tunneling in thin-film ferromagnet-insulator junctions, self-consistent band structure calculations of the CO/Al2O3 interface have been performed using a new LMTO technique. Since the results of the calculations are very sensitive to the distance between the Co and Al planes, we have minimised the total energy with respect to this distance. Our calculations show that at the Fermi energy a strong bonding between the 3d-electrons of Co with the sp-electrons of Al at the interface can have an important influence on the spin polarization of the layer-projected density of states (LPDOS) of inner Al and O layers. Since the Fermi energy lies within the minority-spin d-band of Co but above the majority-spin d-band, the sp-d bonding results in a smaller LPDOS of the minority-spin electrons of the interfacial Al layers in comparison to that of the majority-spin electrons. This asymmetry in the LPDOS extends to the inner Al2O3 layers implying a positive spin polarization of the tunneling density of states. The result is consistent with experimental observations on tunnelling from cobalt through alumina where positive values of the spin polarization of the tunnelling current were measured.

Molecular dynamics simulations are used to examine the effect of a uniform perpendicular magnetic field on a two-dimensional (2D) interacting electron system and we analyze how the magnetic field affects the single-particle properties of the system. In this simulation, we include the effect of the magnetic field classically through the Lorentz force. Both the Coulomb interaction and the magnetic field are included directly in the electron dynamics to study their combined effect on the transport properties of the 2D system. Results are presented for the pair correlation function, the mean square displacement and the density correlation function, in the presence and absence of an external magnetic field. Our simulation results, obtained from a first-principles calculation, clearly show that the external magnetic field has no effect on the static properties, but it affects the dynamics.

The dielectric response of inhomogeneous media presents a complex boundary problem dependent upon dielectric susceptibility and volume fraction of its components, as well as the physical size of the heterogeneities. In this paper, we have used the LOCALF method to examine the size dependent problem for cubic and columnar defects for ZrO2 dielectric films of varying microstructure size and volume fraction. Both the alignments of low dielectric components with respect to the applied field and their size can effectively modulate the composite response. Comparison of these results with the conventional effective medium approximation methods reinforces the need to include microstructural detail in the modeling approach.

Based on the analysis of the dielectric behavior of relaxor ferroelectrics, it is assumed that the material has two polarization processes. Thus, a formula, which can fit the experimental results very well, is proposed to describe the temperature and frequency dependence of the dielectric constant. The fitted results show that there is a resonance process in the material and the peak of the dielectric constant is determined with both the relaxation and resonance processes. The relaxation time analysis shows that the peak of the dielectric constant indeed consists of two parts.

The role of various interfaces in deformation and fracture behavior of two-phase TiAl-Ti3Al alloys is analyzed on the basis of the specific interfacial and surface energies determined from ab initio calculations. The propensity of twinning observed in these alloys is consistent with the low true-twin boundary energy. The strong plastic anisotropy reported in TiAl polysynthetically twinned (PST) crystals is attributed partly to the localized slip along lamellar interfaces, thus lowering the yield stress for soft orientations. Interfacial fracture energies are estimated to be the highest for the α2/γ lamellar boundary and the lowest for the 120° rotational γ/γ boundary. The fracture mode mixity plays an important role in the crack-tip plasticity by ordinary slip and true-twinning, leading to translamellar and interfacial fracture.

Molecular dynamics computer simulations of high load plastic deformation at temperatures up to 500K of Ni nanophase samples with mean grain size of 5 nm are reported. Two types of samples are considered: a polycrystal nucleated from different seeds, each having random location and random orientation, representing a sample with mainly high angle grain boundaries, and polycrystals with seeds located at the same places as before, but with a limited missorientation representing samples with mainly low angle grain boundaries. The structure of the grain boundaries is studied by means of pair distribution functions, coordination number, atom energetics, and common neighbour analysis. Plastic behaviour is interpreted in terms of grain-boundary viscosity, controlled by a self diffusion mechanism at the disordered interface activated by thermal energy and stress.

A previous model is refined to predict the adhesion energy of nonreactive ceramic-liquid metal wetting using the radii of metal atoms and ceramic ions and the enthalpies of mixing at infinite dilution. This method is convenient in that no fit to experiment data is required.

The effect of various impurities and micro-alloying additions (B, N, C, O, Al, Si, S and P) on the intrinsic resistance of the Σ3 (111) GB in Tungsten has been investigated using Molecular Dynamics simulation. The atomic interactions have been accounted for through the use of the Finnis-Sinclair interatomic potentials. The fracture resistance of the GB has been characterized by computing, in each case, the ideal work of GB separation, the Mode I stress intensity factor and the Eshelby F - conservation integral at the onset of crack propagation. The results obtained suggest that pure Tungsten is relatively resistant toward GB decohesion and that this resistance is further enhanced by the presence of B, C and N. Elements such as O, Al and Si on the other hand, have a relatively minor effect on the cohesion strength of the Σ3 (111) GB. In sharp contrast, S and P greatly reduce this strength making Tungsten quite brittle. These findings have been correlated with the effect of the impurity atoms on material evolution at the crack tip.

We use the Peierls-Nabarro continuum mechanics model of dislocation nucleation, modified according to the results of atomistic simulations, to interpret the experimental results of fracture response in symmetric-tilt grain boundaries in Cu. We then directly perform Molecular Dynamics simulations of fracture propagation and dislocation emission from a microcrack placed in the interface plane of the symmetric-tilt (221)(221) grain boundary in fee Cu. Direction-dependent fracture response is observed in agreement with experiments, namely the microcrack advancing by brittle fracture along the [114] direction and being blunted by dislocation emission along the opposite [114] direction. Moreover, we are able to quantify important differences with respect to the continuum model due to the shielding of the stress field at the crack-tip and to the presence of the excess stress at the interface.

We present x-ray diffraction analysis of interfacial strain fields in crystalline semiconductor microstructures. In particular we report the observations of diffuse interference fringes, asymmetric grating diffraction patterns, and asymmetric crystal-truncation-rod profiles due to the straw-varying regions in a microstructure. From these diffraction features, both the longitudinal and the transverse strain gradients are determined, in addition to the average stram. These experimental results can be used to interpret other physical properties in microstructures such as band-gap energies and surface morphologies.

The atomistic processes and stress-strain-curves during uniaxial tensile deformation of a single α-Fe nanocrystal have been studied with the molecular static method. Periodic boundary conditions are imposed along one direction perpendicular to the tensile axis to model plane strain conditions. The effects of the model sizes in plane, boundary conditions and crystal orientations on the stress-strain curves are systematically analyzed. Various deformation evidences such as dislocation movement, dislocation piling up and twinning are clearly observed. The deformation and fracture characteristics of a-Fe and their dependencies on the boundary conditions are investigated.

In this work we have studied magnetite scale adhesion on a tube made from some different type materials, and treated metal oxide interfaces between magnetite scales (Fe3O4) and stainless steel tube surface oxides (NiFe2O4) or chromium coating tube surface oxides (Cr2O3, FeCr2O4). In this paper we have defined new MEAM (Modified Embedded Atom Method) parameters for Fe-O, Cr-O, Ni-O, Fe-Ni, and Fe-Cr pair interactions based on experimental information such as lattice constants, cohesive energies, bulk moduli of those metal oxides, and have calculated the work of adhesion at Fe3O4 (110) / Fe3O4 (110), NiFe2O4(110), Cr2O3(110), Cr2O3(100), FeCr2O4(110) interfaces where a cluster-surface interfacial model is adopted. As the results of the calculation, it was found that there is an energy barrier, which prevents scales from approaching a tube surface, in a potential energy curve vs. a separation between scales and chromium coating surfaces. We further discuss the effect of surface directions at interfaces on the work of adhesion.