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In spite of a projected shortage of physicians in the USA, the relatively long time and duration of training and high expense, the education of U.S. physicians has changed little over the past 120 years.To address these issues, Tulane University developed a program, the Tulane accelerated physician training program (TAP-TP). This unique program allows selected Tulane undergraduate students to complete two years of undergraduate studies, followed by a mandatory year of public service, prior to four years of medical school.Students almost exclusively major in Cell and Molecular Biology (CMB), and used credits earned in Medical School to complete the required hours for their Bachelor's degree. The program was judged to be successful based on its ability to attract, retain, and graduate students into medical residency programs. The shortened time frame needed to complete the undergraduate program is associated with significant cost savings for the students. Educational outcomes were not statistically different between TAP-TP and traditional students despite the accelerated curriculum.TAP-TP is a unique model to graduate physicians in an accelerated fashion at significant cost savings.

First principles calculations based upon density functional theory have been used to investigate the magnetic properties of various Fe-Pt and Co-Pt alloys. At the 50:50 composition, the technologically important L1/sub 0/ alloys CoPt and FePt show large magnetocrystalline anisotropies consistent with the natural layering of the crystal structure. Calculated values for the magnetocrystalline anisotropy and magnetizations are found to be in close agreement with measured values. Since the L1/sub 0/ phase forms over a range of compositions, the influence of composition on magnetic properties has also been examined. A simple expression, derived from the Ne/spl acute/el model, relates the anisotropy to the composition, or degree of disorder in the structure, and is found to be of value for understanding anisotropy in imperfect structures. At greater Fe of Co compositions there are several interesting crystal structures including the metastable pmm/sub 2/ phase that is composed of alternating pure and mixed planes. Again, fairly large anisotropies are seen as a consequence of layering and symmetry. Growing Fe/sub 3/Pt pmm/sub 2/ films seems less promising than Co/sub 3/Pt pmm/sub 2/ films given the larger energy difference between the pmm/sub 2/ and cubic L1/sub 2/ phases.

Grain boundaries play a crucial role in determining the macroscopic properties of magnetic recording media. The authors employ electronic structure theory, based on the local spin density approximation, to calculate the exchange energy, anisotropy energy, and magnetization at two types of grain boundaries. They incorporate these values into a micromagnetic simulation, thus correlating hysteresis loops and switching properties to atomic features. The authors show that small intergranular spacings (less than 0.2 nm) effectively break exchange, while a larger Cr thickness is required to achieve the same effect.

In this paper we report the results of a theoretical study of the ballistic tunnelling of electrons in magnetic tunnel junctions. We show how first-principles band-structure calculations and published magnetization data can be used as inputs to the model, which is then used to predict the magnetoresistance of a tunnel junction. This approach provides a convenient way to examine effects not readily treated by purely first-principles calculations such as finite bias and finite temperature as well as providing a way to treat the amorphous nature of most tunnelling barriers. Ultimately, the model is used to show how the tunnelling magnetoresistance depends on extrinsic factors such as applied bias, and temperature, as well as on the intrinsic properties of the junction such as the barrier height and thickness. The model generates the asymmetry in the magnetoresistance often seen for forward and reverse bias in asymmetric junctions.

Titanium carbosulphide (Ti2CS) is encountered as an inclusion phase in Ti-containing steels. Ductile fracture in steels is associated with the growth and coalescence of voids initiated at second phase particles such as inclusions. When S in steels is gettered as Ti2CS rather than as the more common manganese sulphide (MnS), a significant improvement in fracture toughness can be obtained when the fracture mode is ductile. This improvement is believed to be associated with the higher strains reauired for void nucleation at the particle-matrix interface when the particles are Ti2CS. The enhanced void nucleation resistance of Ti2CS particles may be due to stronger interfacial bonding. To begin to understand the nature of the metal-inclusion interfacial bonding, it is first essential to understand the bonding characteristics within the individual phases present at the interface. This paper investigates the bonding characteristics of bulk Ti2CS. The ground state properties of Ti2CS have been investigat...

The semiclassical Boltzmann equation is applied to spin-dependent transport in magnetic multilayers. The origin of the giant magnetoresistance effect is explained for both the case in which the current flows parallel to the layers and the case in which it is perpendicular to the layers. The approach is first-principles based and includes effects of vertex corrections and local fields.

Giant magnetoresistance (GMR) and spin-dependent tunneling may be used to make magnetic random access memory devices. We have applied first-principles based electronic structure techniques to understand these effects and in the case of GMR to model the transport properties of the devices.

Bloch waves may be reflected and transmitted by planar interfaces. In this paper, we show how the reflection and transmission amplitudes for Bloch waves can be calculated within the layer Korringa-Kohn-Rostoker formalism. The calculated transmission probability is used to calculate the spin-dependent tunneling conductance for magnetic tunnel junctions formed from ZnSe semiconducting layers sandwiched between two ferromagnetic Fe layers. {copyright} {ital 1999} {ital The American Physical Society}

We calculate the canting-angle and thickness dependence of the current-in-plane giant magnetoresistance (GMR) of a system consisting of a copper slab between two cobalt slabs, where the canting angle is the angle between the magnetization vectors of the two cobalt slabs. We utilize the layer-Kohn-Korringa-Rostoker method to self-consistently calculate the electronic structure. Electron scattering by impurities, phonons, magnons, etc., is modeled with a layer- and spin-dependent complex self-energy. Scattering rates are chosen to match Cu and Co resistivities. The scattering rate for minority Co is assumed to be seven times larger than for majority Co, the same ratio as for the Fermi energy density of states in the two channels. The nonlocal layer-dependent conductivity is calculated using the Kubo-Greenwood formula. We find that the GMR decreases with copper thickness in a nonuniform manner due to changes in the behavior of waveguidelike modes in the copper slab. For fixed copper thickness the GMR dependence on costhinsp{theta}, where {theta} is the relative angle between the cobalt slabs magnetization directions, deviates from a linear dependence on costhinsp{theta}. {copyright} {ital 1998} {ital The American Physical Society}

Green’s-function methods are frequently used in the calculation of both the extended and the near-edge structures observed in x-ray-absorption and electron-energy-loss spectroscopies. To date, calculations based upon these methods have tended to be based upon a superposition of atomic potentials used to represent the crystal potential, with no attempt to calculate the self-consistent electronic potential. Many features in the near-edge region relate to charge redistribution and therefore are only approximately described by non-selfconsistent electronic potentials. In this paper we show that the layer Korringa-Kohn-Rostoker method can be used in the same way as conventional Green’s-function theories for near-edge structure, with the added advantage that the self-consistent ground-state charge is used. Spectra calculated in this manner, and compared with those obtained from other Green’s-function methods, demonstrate that self-consistency is necessary to show certain features such as molecular orbital splitting in TiO 2 ~rutile!. @S0163-1829~98!10903-7#

Grain-boundary embrittlement, caused by the segregation of impurity and alloying elements, occurs in many systems and has been the focus of a large amount of research owing to its technological importance. However, the exact mechanism by which the segregating elements cause embrittlement remains unclear. In this paper the localized changes in the electronic structure in the classical embrittling system of Bi in Cu have been studied. Experimental results were obtained by examining the fine structure in the electron energy loss spectrum which was then compared to calculations using the layer Korringa-Kohn-Rostoker (LKKR) method. A change in the d density of states has been observed for the Cu atoms at the grain boundary, associated with Bi, and an electronic model to explain embrittlement is described.

We present measurements of the conductance and magnetoconductance as a function of cobalt layer thickness for cobalt-copper-cobalt spin valves deposited by magnetron sputtering. We compare these measurements to calculations of the conductance and magnetoconductance, which are based on first-principles calculations of the self-consistent electronic structure of the cobalt-copper-cobalt system. The calculations are performed using a generalized Kubo formula for the nonlocal layer dependent conductivity, which is implemented within the layer Korringa-Kohn-Rostoker method for electronic-structure calculations. The scattering rates within each layer are adjusted phenomenologically to be consistent with the experimentally observed resistivity of thick films of cobalt and copper. The magnetoconductance and its dependence on the thickness of the cobalt layer are consistent with calculations that include strong bulk spin-dependent scattering within the cobalt layers and possibly some channeling of electrons in the copper layer. We find that the transmission and reflection of electrons at the interfaces are strongly spin dependent and that it is not necessary to invoke additional diffuse spin-dependent scattering at the interfaces to explain the conductance and magnetoconductance of these samples. {copyright} {ital 1997} {ital The American Physical Society}

We consider spin-dependent tunneling between two ferromagnets separated by a simple step barrier, and examine four models for the magnetoconductance ratio $\ensuremath{\Delta}G/G:$ A model due to Julliere which characterizes the magnetoconductance solely in terms of the tunneling spin polarization, a model due to Slonczewski which provides an approximate expression for the magnetoconductance of free electrons tunneling through a barrier, the exact expression for the magnetoconductance of free electrons tunneling through a barrier, and the numerical calculation of the magnetoconductance of band electrons in iron tunneling through a barrier. We find that the Julliere model does not accurately describe the magnetoconductance of free electrons tunneling through a barrier. Although Slonczewski's model provides a good approximation to the exact expression for free electrons in the limit of thick barriers, we find that the tunneling of band electrons shows features that are not described well by any free electron picture and which reflect the details of the band structure of iron at the Fermi energy.

We present a technique which allows the efficient calculation of the electrical conductivity of large systems which retain periodicity in only two dimensions. We use this technique to calculate the nonlocal electrical conductivity of cobalt with stacking faults. These calculations use a realistic first-principles electronic structure and evaluate the conductivity using the Kubo-Greenwood formula with a phenomenological electron lifetime. We find that the change in the electronic structure induced by the stacking faults leads to an enhancement of the spin dependence of the nonlocal electrical conductivity. A similar enhancement of the spin dependence of the conductivity is found when the crystal structure of Co is changed to hexagonal closed packed. The effect can be traced back to the shape of the Fermi surface which is almost independent of the crystal structure in the majority channel but is strongly structure dependent in the minority channel. {copyright} {ital 1997} {ital The American Physical Society}

The polar Kerr effect for red light reflected from PtMnSb or NiMnSb crystals is shown to be independent of the half-metallic-ferromagnetic property of these compounds. At low photon energies the interband contribution to the Kerr rotation is attributed to transitions between parallel sheets of energy bands that project onto the metallic spin channel. A previously proposed mechanism in which spin-orbit coupling creates an imbalance in optical transitions between states in the vicinity of the $\ensuremath{\Gamma}$ point, in the semiconducting minority spin channel, does not apply to either PtMnSb or NiMnSb. Only upon inclusion of intraband effects is reasonable agreement with experiment achieved.

Variations in planar fault energies, generated by changes in alloy composition, can influence thermally activated processes which govern plasticity in intermetallic alloys. Predicting variations in defect energy as a function of alloy composition would aid both alloy design and the interrogation of models of yield stress. In this paper, layered Korringa-Kohn-Rostoker coherent potential approximation calculations are reported for the superlattice intrinsic stacking fault (SISF) and antiphase-boundary (APB) energies in binary and ternary Ti-Al alloys. The planar fault energies were calculated over a range of alloy composition: (Ti1−xAlx)1−y My with 0·48 ≤ × ≤ 0·51, 0·00 ≤ y ≤ 0·02 and M = Cr, NB. For the Ti-rich alloys, ternary additions up to 4at.% were also considered. APB (010) energies were calculated for the binary alloy while the SISF and APB (111) energies were calculated for all the binary and ternary alloys. The compositions Ti50Al50 and (Ti50Al50)1−yCry have the maximum defect energies fo...

Using first-principles methods, we have calculated structural and magnetic properties of face-centered (L12) and orthorhombic (Pmm2, DO19) phases of Fe3Pt and Fe3Pd. For both alloys, the L12 cubic phase was determined to be the ground state. Unlike the related Co3Pt alloy, the Pmm2 phase cannot be artificially stabilized by controlling, that is, slightly increasing or decreasing, the basal lattice constant (by growing the samples on an appropriate substrate).

The magnetoresistance was calculated for a layered Co/Re hcp(1010) superlattice as a function of external magnetic field. Similar to recent experiments which showed a maximum magnetoresistance of 4.5%, the system modeled here had its growth axis along the (1010) axis and the magnetic easy axis in the plane of the film. Orientations of the magnetic moments in each Co layer as a function of external field were calculated using a self-consistent mean-field method, and were used as input parameters in the calculation of the conductivity tensor. The conductivity tensor was calculated via the Kubo–Greenwood linear response formalism within the layered-Korringa–Kohn–Rostoker approach to density functional theory. The total magnetoresistance is explained as a sum of anisotropic magnetoresistance and giant magnetoresistance. A calculated spin–flop transition at low fields has obvious consequences on the calculated magnetoresistance.

First principles calculations of Zn11X1S12 supercells in the zincblende structure, where X is a magnetic ion, show that when X=Cr, Fe, and Ni the materials are calculated to be half metallic and ferromagnetic, i.e., the densities of states of these bulk materials at the Fermi energy is calculated to be 100% spin polarized and the exchange interaction is ferromagnetic. This behavior persists even when on-site Coulomb “Hubbard U” potentials are applied.

We consider the origins of the spin-dependent scattering which is believed to be responsible for the giant magnetoresistance effect. We argue on the basis of first-principles calculations of the electronic structure, magnetic moments, and electrical resistivities that this spin-dependent scattering originates largely from the tendency of spin-dependent atomic potentials to ‘match’ in one of the spin channels of magnetic alloys or multilayers. We also argue that the matched channel will tend to have a lower density of states at the Fermi energy. Both of these effects will contribute to the GMR. We argue that there is the potential for a very large GMR in an ideal system, but that spin-independent scattering possibly coming from misaligned spins near the interfaces prevents its observation.

We show that the Kubo formula can be used to calculate the nonlocal electrical conductivity of layered systems from first principles. We use the layer Korringa-Kohn-Rostoker method to calculate the electronic structure and Green function of a slab of copper embedded in cobalt. The electronic structure is calculated self-consistently within the local density approximation to density functional theory. We use the Green function to evaluate the Kubo formula and calculate the conductivity for both majority and minority spins and for alignment and antialignment of the Co moments on either side of the Cu spacer layers. This allows us to determine the giant magnetoresistance from first principles. We investigate three possibilities for the scattering in Co{vert_bar}Cu{vert_bar}Co: (i) equal electron lifetimes for Cu, majority-spin Co, and minority-spin Co, (ii) equal electron lifetimes for majority and minority Co, weaker scattering in Cu, and spin-dependent interfacial scattering, (iii) electron lifetimes for majority- and minority-spin cobalt proportional to their Fermi energy densities of states, spin-dependent interfacial scattering, and spin-independent boundary scattering.

Using first principles electronic structure calculations we investigated structural and magnetic properties of three distinct phases of Co3Pt. Relaxed lattice constants, total energies, magnetocrystalline anisotropies, and density of states were calculated for each phase at their equilibrium lattice constants, as well as under expansion and contraction stresses. These computations may help clarify the results of some recent but ambiguous experiments on Co3Pt.

The first ab initio electronic structure calculations of the magnetocrystalline anisotropy of superlattices with imperfect interfaces are presented. Specifically the possibility of an interdiffusion between the layers at the interface in Co/Pd and Co/Pt superlattices is considered. The electronic structure calculations use the local spin‐density formalism as implemented with the layer Korringa–Kohn–Rostoker method. Interdiffusion at the interface is modeled in two distinct ways. In the first approach a diffuse interface is represented by ordered arrangement of substitutions, while in the second approach interdiffusion is assumed to produce a substitutionally disordered random alloy on the layers at the interface, which is solved using the coherent potential approximation. The calculated interface anisotropies for superlattices with perfect and imperfect interfaces are, on average, modeled accurately by a simple Neel‐type model. This model always predicts a reduction in magnetic anisotropy resulting from t...

The Poisson equation for the electrostatic potential in a solid is solved using three different cellular techniques. The relative merits of these different approaches are discussed for two test charge densities for which an analytic solution to the Poisson equation is known. The first approach uses full-cell multiple-scattering theory and results in the famililar structure constant and multipole moment expansion. This solution is shown to be valid everywhere inside the cell, although for points outside the muffin-tin sphere but inside the cell the sums must be performed in the correct order to yield meaningful results. A modification of the multiple-scattering-theory approach yields a second method, a Green-function cellular method, which only requires the solution of a nearest-neighbor linear system of equations. A third approach, a related variational cellular method, is also derived. The variational cellular approach is shown to be the most accurate and reliable, and to have the best convergence in angular momentum of the three methods. Coulomb energies accurate to within 10[sup [minus]6] hartree are easily achieved with the variational cellular approach, demonstrating the practicality of the approach in electronic structure calculations.

Electronic structure calculations are used to predict the magnetic anisotropy of Co/Pd, Co/Pt, Co/Cu, Fe/Pt, and Fe/Ag superlattices. In the case of Co/Pd and Co/Pt, the magnetic anisotropy is analyzed as a deconvolution of volume and interface contributions. The experimental result of an orientation-independent interface anisotropy of 0.63+or-0.05 ergs/cm/sup 2/ for Co/Pd superlattices is also predicted by theory. The theoretical interface anisotropy is found to be 0.62+or-0.06 ergs/cm/sup 2/, in close agreement with the experiment. This result is not universally observed, and, based upon calculations for strained and unstrained superlattices, appears to be a consequence of the degree of strain found in the Co/Pd system. A symmetry derived model based upon summing L(M.R)/sup 2/ pair interactions accurately reproduces the observed anisotropy and the dependence upon atomic constituents, strain and growth direction. >

The existence of relationships between structure and properties provides one avenue permitting the design of materials with chosen properties. Unfortunately, rules relating the properties of intermetallic alloys to their crystal structure have not been forthcoming. We believe that this is because the structure of intermetallic alloys is interpreted too narrowly. By extending the definition of structure to include elements of the electronic charge distribution we show, through examples, that there may in fact be relationships between intrinsic mechanical properties and this extended structure. A description of this extended structure requires only a knowledge of the critical points of the total charge density. This knowledge can be obtained through any method of electronic structure or, in principle, through experimental techniques.

A fundamental understanding of the atomic mechanisms responsible for the stress-induced bond failure of solid-state materials will facilitate the synthesis of materials with desired mechanical properties. Outside of a small group of network solids and polymers, no such understanding is available. By adopting an appropriate model for solid-state bonding, based on features of the total charge density, it is possible to apply chemical reaction theory to an investigation of this process. First-principle local-density-functional techniques were used to model the transgranular fracture of two alloys with the same crystal structure but different mechanical properties, a hitherto unexplained observation

A definition for structure of atomic scale systems is introduced which extends the typical crystallographic description to include elements of the total charge density. We argue that the mechanical properties of intermetallic alloys are related to this extended structure. These relationships have their origin in the nature of the charge redistribution accompanying strain. The direction of this charge redistribution is determined solely by the extended structure, while its magnitude can be correlated with a quantification of this extended structure. We demonstrate these facts by determining the extended structure and nature of the charge redistribution resulting from uniaxial strain for two alloys with the L10 structure: CuAu and TiAl. While these alloys share the same crystallographic structure, their extended structures are different, with CuAu possessing the same extended structure as the allotropic fcc metals while TiAl does not. These different extended structures give rise to different charge redistributions, which are argued to be related to the intrinsically ductile behavior of CuAu and the tendency for TiAl to fail transgranularly.

Self-consistent electronic structure calculations are used to study the changes in magnetic properties (specifically the magnetocrystalline anisotropy and exchange coupling) of a Co1Pt5 superlattice induced by a grain boundary. Guided by experiment, several possible grain boundaries have been studied, and we find as a result of calculations that the intergrain exchange coupling can be reduced by up to an order of magnitude. The local anisotropy is also reduced in the neighborhood of the boundary. These calculations are aimed at developing a more realistic description of magnetic thin films that takes into account details of the microstructure and thereby provide input to micromagnetic simulations.

We report a study of the anisotropic exchange interactions in bulk ${\text{CrO}}_{2}$ calculated from first principles within density functional theory (DFT) [W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965)]. We determine the exchange coupling energies, using both the experimental lattice parameters and those obtained within DFT, within a modified Heisenberg model Hamiltonian in two ways. We employ a supercell method in which certain spins within a cell are rotated and the energy dependence is calculated and a spin-spiral method that modifies the periodic boundary conditions of the problem to allow for an overall rotation of the spins between unit cells. Using the results from each of these methods, we calculate the spin-wave stiffness constant $D$ from the exchange energies using the magnon dispersion relation. We employ a Monte Carlo method to determine the DFT-predicted Curie temperature from these calculated energies and compare with accepted values. Finally, we offer an evaluation of the accuracy of the DFT-based methods and suggest implications of the competing ferromagnetic and antiferromagnetic interactions.

Present theories of giant magnetoresistance (GMR) for current perpendicular to the planes (CPP) are based on an extremely restricted solution to the Boltzmann equation that assumes a single free electron band structure for all layers and all spin channels. Within this model only the scattering rate changes from one layer to the next. This model leads to the remarkable result that the resistance of a layered material is simply the sum of the resistances of each layer. We present a solution to the Boltzmann equation for CPP for the case in which the electronic structure can be different for different layers. The problem of matching boundary conditions between layers is much more complicated than in the current in the planes (CIP) geometry because it is necessary to include the scattering-in term of the Boltzmann equation even for the case of isotropic scattering. This term couples different values of the momentum parallel to the planes. When the electronic structure is different in different layers there is...

Results of theoretical studies of spin dependent tunneling in magnetic tunnel junctions at finite bias are presented. A simple model which extends Slonczewski’s ideas is developed. For each spin it assumes tunneling from a single free electron band through a simple barrier. The model predicts a decrease in conductance ratio with bias in good agreement with experimental observations. We find that the decrease of the magnetoconductance ratio, universally seen in experiment, has an intrinsic component resulting from the underlying electronic structure.

Commonly used approximate forms for the exchange-correlation energy and potential within the local density approximation are summarised, and FORTRAN code is included for the evaluation of these various forms. Included are the following: Xα, Kohn-Sham-Gaspar, Hedin-Lundqvist-Wilkins, Janak-Moruzzi-Williams, Von Barth-Hedin, Ceperley-Alder (Perdew-Zunger), and Ceperley-Alder (Vosko-Wilk-Nusair). Both the Vosko-Wilk-Nusair and the Von Barth-Hedin expressions for spin interpolation between paramagnetic and ferromagnetic limits are also provided.

The electronic and magnetic structure of layered Fe/(Au)„Fe/Ag„, Cr/Au„, and Cr/Ag„ (n=1, 3, 5, 7, 9) multilayers and interface (sandwich) geometries (n =~) have been investigated using the layer Korringa-Kohn-Rostoker method. Enhanced magnetism for Fe and Cr (T) monolayers is observed in all the layered configurations examined. These results are consistent with weak coupling between the Fe or Cr d bands and those of the noble-metal (N) host lead to localization of d states orthogonal to the T/N interface. Fe and Cr moments are shown to vary systematically with the number of mediating Ag or Au planes as well as with the Fermi energy of the system. Interface and multilayer geometries show similar magnetic properties, suggesting that exchange coupling between the Fe or Cr planes in the multilayer geometry is short ranged and not responsible for the observed variations of the moment. A model, based on the compositional modulation of the Fermi energy coupled with the constraint of charge neutrality, solved in the limit of strong ferromagnetism is shown to explain the systematics of the moment variation for diff'erent layered configurations. There has been considerable recent growth in the field of interfacial, surface, and multilayer magnetism. ' Much of the fundamental interest in these materials stems from predictions of enhanced local moments ' and interesting phenomena associated with predictions of two-dimensional (2D) magnetism. The increasing ability to fabricate (i.e., with techniques such as molecular-beam epitaxy) a seemingly infinite number of possible configurations involvirig layers of magnetic species coupled with other magnetic or nonmagnetic layers has fed a productive interplay between theoretical and experimental endeavors in this field. Technological interest in these structures lies in their potential importance in thin-film recording and magneto-optic devices. Properties such as perpendicular magnetic anisotropy and square hysteresis loops, enhanced local moments, novel exchangecoupling effects, large magnetoresistive response, and sizable Kerr rotation angles (without rare-earth components)

The electronic and magnetic structure of {l brace}111{r brace} stacking faults in nickel is investigated utilizing a fully self-consistent, layered multiple-scattering approach which does not require full three-dimensional symmetry or the use of finite-size slabs. The electronic and magnetic structures of a twin boundary, an intrinsic fault, an extrinsic fault, and two other stacking sequences are calculated. In addition, total energies of the faults are calculated and found to be in good agreement with the available experimental results. Localized states appear in all the studied stacking faults; the state's energies and exchange splittings are tabulated. The presence of a stacking fault results in a decrease in the spin polarization near the faults. This decrease arises from subtle changes in the electronic structure arising from the fault. For all the faults, the spin polarization is found to be insensitive to the orientation of the nearest-neighbor atoms, but instead can be related to the distance to the nearest atom in the direction perpendicular to the fault plane. Very simple empirical expressions for calculating the total energy and spin polarization of {ital any} stacking configuration are presented.

Modern chemistry frequently describes the structure and reaction dynamics of molecules in terms of the general principle of “competition for bonds”; consequently, bonding forms the basis of the language of chemistry. The actual models used to represent these bonds are frequently system specific. Organic reactions are described in terms of bonds based on pairs of atomic valence electrons. Reactions of inorganic coordination complexes are described in terms of bonds based on a molecular orbital representation. In analogy to those chemistries, a representation for a bond and bond strength, suitable for describing the cohesive and adhesive properties of all classes of materials, is introduced. This representation proves to yield an explanation for the observed cohesive properties of a specific class of materials (cleavage in bcc metals), and it also provides a framework for exploring and analyzing the more complex phenomena of cohesion and adhesion, such as environmentally-induced embrittlement. A complete chemistry of cohesion and adhesion will require the demonstration that the specific bonding model used can form the basis for consistent interpretations for a wealth of experimental phenomena beyond environmentally-induced embrittlement; thus, as presented, this model does not provide a complete chemistry of cohesion and adhesion, but does embody the first steps in that direction.

Fe–Co alloys in the α phase are soft magnetic materials which have high saturation inductions over a wide range of compositions. However, above about 1250 K, an α to γ phase transition occurs. The fcc-based, γ, high-temperature phase is paramagnetic at this temperature. In this work the low-temperature ordered B2, or α′, phase, as well as the disordered bcc phase of FeCo alloys, have been studied with first-principles electronic-structure calculations using the layer Korringa–Kohn–Rostoker method. The variation of moment with composition (Slater–Pauling curve) is discussed. For equiatomic FeCo, interatomic exchange couplings are derived from first principles. These exchange interactions are compared to those obtained for pure Fe and Co, and are used within a mean-field theory to estimate the hypothetical Curie temperature of the α phase.

This paper presents a study of the calculated electronic properties of the Zn-based II--VI dilute magnetic semiconductors in a ${\text{Zn}}_{22}{A}_{2}{B}_{24}$ structure, where $A=\text{Cr}$, Mn, Fe, Co, and Ni, and $B=\text{S}$, Se, and Te. In this study we investigate the local densities of states of the magnetic ions and host semiconductor, the magnetic exchange interactions as a function of transition-metal ion separation and orientation, the origins of the magnetic coupling, the tendency for impurity atoms to cluster creating impurity rich regions---at least thermodynamically, and the local magnetic moments. The results show half-metallic behavior for Cr, Fe, and Ni impurities, and in the case of Cr and Ni a ferromagnetic coupling consistent with the double-exchange mechanism. The Mn- and Co-doped materials are found to be semiconducting and couple antiferromagnetically, which can be explained by the superexchange model. The Fe-doped materials show the sign of the coupling is dependent on the orientation and separation of the impurities.

The one-electron theory of metals is applied to the calculation of stacking fault energies in face-centered cubic metals. The extreme difficulties in calculating fault energies of the order of 0.01 eV/(interface unit-cell area) are overcome by applying the Force theorem and using the layer–Korringer–Kohn–Rostoker method to determine the charge density of isolated defects. A simple scheme is presented for accommodating deviations from charge neutrality inherent in this approach. The agreement between theoretical and experimental values for the stacking fault energy is generally good, with contributions localized to within three atomic planes of the fault, but suggest the quoted value for Rh is a significant overestimation.

A program is presented which implements the layer Koringer-Kohn-Rostoker theory for the electronic structure of both bulk systems and those characterised by two-dimensional periodicity. The one-electron Green function is obtained by recursively assembling the layers of the system, permitting the study of interface regions embedded in otherwise perfect host materials. The program enables the calculation of self-consistent charge densities and localised states.

The electronic and magnetic structure of Fe/Au superlattices and interfaces are investigated with the, recently developed, layer Korringa-Kohn-Rostoker method. Enhanced magnetism is seen in the Fe layer in all supercell and interface geometries studied with weak coupling between the Fe and Au layers. The Fe moment decreases gradually from 2.78 to 2.74μ B as the number of mediating Au planes increases, converging to that obtained in the interface calculations. The Fe minority-hole states consist mainly of d-states with character orthogonal to the Fe plane which, if analysed in terms of a vector model for the orbital moment, would suggest a tendency for out-of-plane (perpendicular) anisotropy. Localized states, in gaps in the two-dimensional (2-D) band structure, were found at the X-point of the 2-D Brillouin Zone. These states are strongly localized, both in energy and space.

The electronic structure of TiAl, TiB 2 , TiAlTiB 2 interfaces are studied with the layer Korringa-Kohn-Rostoker method. These interfaces occur in titanium aluminide composites produced by a casting process known as XD TM technology, which allows engineering of the microstructure to achieve specified properties. By examining and comparing the bonding in TiAl and TiB 2 , the calculations suggest that the bonding between the titanium and the boron at the interface is inhibited by the presence of aluminum. The implications of these results are then explored for other alloying additions at the interface, and for the interaction between the chemistry at the interface and mechanical behavior of these materials.

The use of materials with otherwise attractive properties is often limited by unacceptable mechanical performance. Fortunately, modern processing techniques are sometimes able to overcome such defi...

We present a first principles based semiclassical model for transport in an inhomogeneous magnetic layered structure. The approach solves the Boltzmann transport equation using the band structure, Bloch wave velocities and scattering matrices, describing the reflection and transmission of Bloch waves from interfaces, derived from ab-initio local spin density electronic structure calculations. The model has been tested for thick Co and Cu films as well as for a set of Co/Cu/Co spin valves.

We present first principles based calculations of the tunneling conductance between iron electrodes separated by semiconducting ZnSe. We assume that Fe (100) and ZnSe (100) atomic planes are epitaxed. We find that the conductance depends strongly on the relative alignment of the magnetic moments in the two Fe electrodes. The relative change in conductance increases dramatically as the thickness of the semiconductor increases. We show that this effect is due to the fact that electrons from a particular majority spin band are injected efficiently into the ZnSe from the Fe and also that electrons are ejected efficiently from the ZnSe into this band. Our calculations are based upon the Landauer–Buttiker expression for the conductance which is expressed in terms of the transmission matrix elements.

We consider the in-plane electrical conductivity of a spin valve, specifically, a system consisting of a copper slab between two cobalt slabs. We calculate the dependence of the resistivity on the canting angle, where the canting angle θ is defined as the angle between the magnetization vectors of two ferromagnetic slabs in a spin valve. To calculate the electronic structure, we utilize the layer-KKR formalism. Electron scattering by impurities, phonons, magnons, etc. is modeled using a layer and spin-dependent complex self-energy. Scattering rates are chosen to match Cu and Co resistivities. We assume a spin asymmetry scattering rate factor of 7 in Co, matching the Fermi-level minority-to-majority density-of-states ratio. No additional interfacial scattering is included. The nonlocal layer dependent conductivity is calculated using the Kubo–Greenwood formula for systems consisting of 3 and 7 monolayer fcc (111) Cu slabs in Co. We find electron channeling in Cu dominates the conductivity and at θ=π/2 the resistivity is increased by 4.9% and 2.3% from a linear 1−cos θ dependence. We find giant magnetoresistive GMR values of 64% and 36% for 3 and 7 monolayers of Cu, respectively.

Permalloy (Ni{sub .8}Fe{sub .2}) is an important alloy for magnetic devices. The authors present calculations of the electronic and magnetic structure of permalloy and of an interdiffused interface between permalloy and copper. They also present the results of calculations of the transport properties of permalloy. They find that the magnetic moments in permalloy are collinear, however, there may be non-collinear moments near an interface between permalloy and copper. They find that the calculated electrical conductivity is very sensitive to the details of the electronic and magnetic structure, however calculations which include relativistic effects yield a value for the conductivity that is in reasonable agreement with experiment.

Theoretical spectra for the magneto-optical Kerr effect in polar geometry have been obtained for four series of L21 Heusler alloys Fe2 YZ and Co2 YZ, with Y=V, Cr, Mn, Fe, Co, Ni and Z=Al or Ga. Selected spectra are presented. Trends are identified in the relation between electronic structure and the polar Kerr angle spectrum for L21. Further it is shown that the large Kerr rotation in the C1b compound PtMnSb cannot be attributed to a few states close to the Fermi level.

We have calculated the electronic structure of the spin-dependent tunneling structures, Fe|Ge|Fe and Fe|GaAs|Fe, using first principles techniques. We find that there is a large charge transfer from the metal layer to the semiconductor layer; 0.21 electrons are transferred from Fe to Ge and 0.27 electrons are transferred from Fe to GaAs at each interface. The density of states of the interfacial metal layer is dramatically different from the other metal layers; there is a large peak in the density of states at the Fermi energy for the minority electrons. The electronic structure of the semiconductor layer is quite different for the majority and the minority spins although its total magnetic moment is negligible. Our results suggest that the theory of spin-dependent tunneling using the simple model of a potential barrier or a model based on densities of states taken from bulk band structures may not apply to these systems.