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Superconductivity in absence of inversion symmetry of the crystal structure is basically controlled by a Rashba-like antisymmetric spin orbit coupling which splits the Fermi surface and removes the spin degeneracy of electrons. The Fermi surface splitting can originate a mixing of spin-singlet and spin-triplet states in the superconducting condensate. The presence of spin-triplet states is expected to be responsible for various uncommon features of the superconducting ground state. Experimentally, distinct deviations from the expectations of the BCS theory are found, in general, only in those systems where beside the missing of inversion symmetry strong correlations among electrons are present. Materials of this group are primarily based on Ce, Yb or U. For the much larger group of materials without substantial electronic correlations, BCS-like superconductivity was observed in the overwhelming number of known examples. Hence, unconventional superconductivity requires, in general, the mutual presence of electronic correlations and non-centrosymmetric crystal structures.

Investigating the phase relations of the system ${\mathrm{Th},\mathrm{U}}$-Pt-B at $900{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ the formation of two compounds has been observed: cubic ${\mathrm{ThPt}}_{3}\mathrm{B}$ with $Pm\overline{3}m$ structure as a representative of the perovskites, and tetragonal ${\mathrm{UPt}}_{3}\mathrm{B}$ with $P4mm$ structure being isotypic to the noncentrosymmetric structure of ${\mathrm{CePt}}_{3}\mathrm{B}$. The crystal structures of the two compounds are defined by combined x-ray diffraction and transmission electron microscopy. Characterization of physical properties for ${\mathrm{ThPt}}_{3}\mathrm{B}$ reveals a superconducting transition at 0.75 K and an upper critical field at $T=0$ exceeding 0.4 T. For nonsuperconducting ${\mathrm{UPt}}_{3}\mathrm{B}$ a metallic resistivity behavior was found in the entire temperature range; at very low temperatures spin fluctuations become evident and the resistivity $\ensuremath{\rho}(T)$ follows non-Fermi liquid characteristics, $\ensuremath{\rho}={\ensuremath{\rho}}_{0}+A{T}^{n}$ with $n=1.6$. Density functional theory (DFT) calculations were performed for both compounds for both types of structures. They predict that the experimentally claimed cubic structure of ${\mathrm{ThPt}}_{3}\mathrm{B}$ is thermodynamically not stable in comparison to a tetragonal phase, with a very large enthalpy difference of 25 kJ/mol, which cannot be explained by the formation energy of B vacancies. However, the presence of random boron vacancies possibly stabilizes the cubic structure via a local strain compensation mechanism during the growth of the crystal. For ${\mathrm{UPt}}_{3}\mathrm{B}$ the DFT results agree well with the experimental findings.

Based on the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method and the Kubo-Greenwood eauation as formulated for layered systems the interlayer exchange coupling (IEC) as well as the magneto-resistance (MR) for the current in-plane (CIP) geometry is calculated for Fe/Cr/ Fe trilayer systems. For the IEC not only short periods of 2 monolayers (ML) but also long periods of about 18 ML are found. For large Cr thicknesses the magnetic moments oscillate with a period of 8-9 ML for even numbers of Cr layers and 18 for odd. The calculated CIP MR and corresponding resistivities are in the range of available experimental data. It is found that the peaks in the CIP MR have little in common with the oscillation periods characterizing the IEC.

Ternary intermetallics Ep-T-X, crystallizing in ordered variants of the ${\mathrm{BaAl}}_{4}$ structure type, have been investigated systematically with respect to their formation and stability. For this, a comprehensive overview of the ${\mathrm{BaAl}}_{4}$ derivative structure types including group-subgroup relations was established. Special emphasis was laid on compounds where inversion symmetry is missing in the respective crystal structures and where superconductivity is observed at low temperatures. ${\mathrm{EpTX}}_{3}$ compounds crystallize in the noncentrosymmetric ${\mathrm{BaNiSn}}_{3}$ structure type (space-group $I4mm$; $a\ensuremath{\approx}0.4$ and $c\ensuremath{\approx}1$ nm), an ordered ternary derivative of ${\mathrm{BaAl}}_{4}$. Superconductivity below 3 K was found for seven members of this series, as evidenced from heat capacity and electrical resistivity measurements. Although the Rashba-like spin-orbit coupling in noncentrosymmetric systems can enable a mixture of spin-singlet and spin-triplet pairs in the superconducting condensate, the experimental data basically indicate a predominant $s$-wave superconducting state in all of these compounds. For this family of compounds, fully relativistic density functional theory (DFT) calculations of the electronic structure and phonon properties were done. Despite the different size of spin-orbit coupling depending on the actual choice of elements for Ep, T, and X that result in different spin-orbit splittings of the Fermi surfaces, the experimental observation of a prevalent spin-singlet pairing in the superconducting phases of the ${\mathrm{EpTX}}_{3}$ compounds is supported.

The current-perpendicular-to-plane ~CPP! magnetotransport of a metallic sample sandwiched by two ideal leads is described at an ab initio level. The so-called ‘‘active’’ part of the system is either a trilayer consisting of two magnetic slabs of finite thickness separated by a nonmagnetic spacer or a multilayer formed by alternating magnetic and nonmagnetic layers. We use a transmission matrix formulation of the conductance based on surface Green’s functions as formulated by means of the tight-binding linear muffin-tin orbital method. The formalism is extended to the case of lateral supercells with random arrangements of atoms of two types, which in turn allows to deal with specular and diffusive scattering on equal footing, and which is applicable also to the case of noncollinear alignments of the magnetization in the layers. Applications refer to fcc-based Co/Cu/Co~001! trilayers and multilayers, considering in detail the effect of substitutional alloying in the spacer and in the magnetic layers, as well as interdiffusion at the interfaces.

The magnetic properties of (ConPdm)r superstructures on Pd(100) and Pd(111) are evaluated using the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only in the case of a Pd(111) substrate such superstructures exhibit perpendicular magnetism, while on a Pd(100) substrate the magnetization is oriented in-plane. Also investigated is the effect of interdiffusion in repeated superstructures. By using the inhomogeneous coherent potential approximation (CPA) for layered systems the effect of ordering into (repeated) superstructures can be described in an ab-initio-like manner. It is found that already small amounts of interdiffusion can be decisive for the actual value of the magnetic anisotropy energy.

The transmission matrix approach is used to evaluate perpendicular magnetotransport in metallic multilayers that consist of two magnetic slabs separated by a non-magnetic spacer. We employ the spin-polarized surface Green function technique within the framework of the tight-binding linear muYn-tin orbital method. Our approach allows both the ballistic and the diVusive regime of magnetotransport to be treated on equal footing. The eVect of disorder is included in terms of lateral supercells confined to individual atomic layers. In this paper, we apply the method to fcc-based Co/Cu/Co(001) trilayers. © 2000 Elsevier Science B.V. All rights reserved.

The magnetic properties of ${\mathrm{Co}}_{n}/\mathrm{Pt}(100),$ ${\mathrm{Co}}_{n}/\mathrm{Pt}(111),$ $({\mathrm{Co}}_{0.5}{\mathrm{Pt}}_{0.5}{)}_{n}/\mathrm{Pt}(100),$ $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(100)$, and $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(111),$ $nl~15$, are investigated using the relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only the artificial superstructures $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(100)$ and $(\mathrm{CoPt}{)}_{n}/\mathrm{Pt}(111)$ show a perpendicular magnetic anisotropy beyond $n=10$. For the free surfaces of Co on Pt in the case of the (100) orientation, a multiple reorientation transition below $n=7$ is found, while along (111) such a transition is predicted at about four layers of Co. For the homogeneous, statistically disordered alloy ${\mathrm{Co}}_{0.5}{\mathrm{Pt}}_{0.5}$ on Pt(100) the orientation of the magnetization remains in-plane for all n investigated. A comparison to experiment yields interesting insight into aspects of order and disorder, surface segregation, and phase separation frequently encountered in experimental studies of perpendicular magnetism in the Co/Pt system.

We have used the spin-polarized relativistic screened Korringa-Kohn-Rostoker method for layered systems together with the Kubo-Greenwood formalism and the coherent-potential approximation to describe electrical transport properties of magnetic multilayers. We are able to calculate resistivities and magnetoresistance of model structures with no adjustable parameters by simultaneously determining contributions to the giant magnetoresistance of multilayers coming from both the electronic structure and spin-dependent scattering off impurities. @S0163-1829~99!05125-5#

The functional dependence of the giant magnetoresistance (GMR) with respect to the relative angle between the orientations of the magnetization in the magnetic slabs of a trilayer system is calculated by using the Kubo-Greenwood formula for electrical transport together with the fully-relativistic spin- polarized screened Korringa-Kohn-Rostoker method for semi-innite systems and the coherent potential approximation. It is found that the functional dependence of the GMR is essentially of the form (1 cos').

The current-perpendicular-to-plane (CPP) magnetoconductance of a trilayer consisting of a spacer sandwiched between two ideal leads is described on anab initio level. We employ the transmission matrix formulation of the conductance within the framework of the spin-polarized surface Green function technique as formulated in terms of the tight-binding linear muffin-tin orbital method. The formalism is extended to the case of lateral supercells in each layer with random arrangements of atoms which allows to treat both the ballistic and diffusive transports on equal footing. The application is made to fcc-based Co/Cu/Co(001) trilayers.

The resistivity and giant magnetoresistance (GMR) of (Cu3Ni3) n embedded in Cu(100), for n ≤ 11, that originates from the electronic structure of these finite, yet otherwise perfect, systems is calculated for currents in the plane of the layers (CIP) by using the Kubo–Greenwood formula for semi-infinite systems and the fully relativistic, spin-polarized screened Korringa-Kohn-Rostoker method. We find that for this particular type of repeated structure the CIP resistivity decreases from about 6 to 2 cm as the number of repeats increases from 2 to 11, and the CIP-GMR while starting out at 4% for n = 2 goes up to 16% at n = 11.

Five tribal populations (Hindu Mahadeo Koli, Vatankar, Madia Gond, Halbi, Pardhan) from different regions of Maharasthra with t total of n - 534 male and female individuals were typed for four seru...

The problem of superlattice symmetry, i.e., the question of periodicity along the growth direction ~surface normal! in magnetic multilayer systems, is discussed using discrete Fourier transformations for the anisotropy energy, as well as, for the antiparallel and perpendicular interface exchange coupling. We analyze the system Cu~100!/~Cu 3Ni 3) n , where n is the number of repetitions, for the case of free surfaces and surfaces capped semi-infinitely by Cu~100!. It will be shown that for some magnetic properties, and only in certain situations, ~almost! periodic behavior with respect to n applies, while for other properties an oscillatory behavior is characteristic. Also discussed are implications with respect to typical experimental situations and with respect to traditional supercell approaches. @S0163-1829~98!00313-0#

The oscillatory behavior of the magnetic-anisotropy energy in different types of ${\mathrm{Co}}_{n}$ multilayers on a Cu(100) substrate, including free surfaces, capped surfaces, and Co/Cu spacer systems, is shown in terms of ab initio\char21{}like calculations using the self-consistent fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method. Deduced from direct representations and discrete (linear) Fourier transformations with respect to the number of Co layers, a period of two monolayers seems to be characteristic for these oscillations, whereas for a given number of Co layers and viewed with respect to the number of Cu-spacer layers they rapidly approach the value of the magnetic anisotropy energy for the corresponding ${\mathrm{Co}}_{n}$ multilayer on Cu(100) with a semi-infinite Cu cap, the so-called biased value. By excluding the so-called preasymptotic regime a short and a long period of 2.5 and 5.5 monolayers, respectively, can be traced for the oscillations with respect to the number of Cu-spacer layers. All types of oscillations, namely, either with respect to the number of Co layers or with respect to the number of Cu-spacer layers, are analyzed in terms of layer-resolved band-energy contributions to the magnetic-anisotropy energy. Such a layerwise distribution of the magnetic-anisotropy energy allows one not only to characterize different regimes of thicknesses, but also to discuss the effect of the actual interface on the absolute values of the magnetic-anisotropy energy, shown in particular by considering a system with Co/Au interfaces.

In the present work we report on the synthesis, crystal structure, and physical properties (resistivity, magnetization, heat capacity) in combination with density functional theory (DFT) calculations of the electronic structure and phonon properties for the intermetallic compound LaPtSi. LaPtSi crystallizes in its own noncentrosymmetric structure type $($space group $I{4}_{1}md$; $a=0.42502(1)$ nm and $c=1.4525(5)$ nm$)$, which is an ordered ternary derivative of the centrosymmetric $\ensuremath{\alpha}$-ThSi${}_{2}$-structure. The weakly correlated compound LaPtSi (Sommerfeld value $\ensuremath{\gamma}=6.5$ mJ/molK${}^{2})$ exhibits superconductivity below ${T}_{c}=3.35$ K and appears to be a fully gapped, weakly coupled $s$-wave BCS superconductor. The experimental observations are supported by DFT calculations which show that, despite a substantial spin-orbit splitting of the Fermi surfaces, a spin-singlet pairing is prevalent.

Directional Compton profiles of the transition-metal alloys FeAl, CoAl, and NiAl have been measured. Both a conventional technique (resolution 0.55 a.u. of momentum), based on a 59.3-keV x-ray source with a solid- state detector, and a high-resolution spectrometer (0.15 a.u. of momentum) with 50-keV x rays from a synchrotron source have been used. The results are interpreted using a theory based on a full-potential linearized augmented-plane-wave method. The agreement between the experimental and the theoretical momentum density anisotropy is very good. It is shown that the anisotropies at low momenta are heavily influenced by the particular shape of the Fermi surface. \textcopyright{} 1996 The American Physical Society.

Based on density functional theory the noncentrosymmetric superconductor Mo${}_{3}$Al${}_{2}$C in its well-established $\ensuremath{\beta}$-Mn-type (P4${}_{1}$32) crystal structure is investigated. In particular, its thermodynamical and dynamical stabilities are studied by calculating lattice vibrations within the harmonic approximation. It is found that the fully stoichiometric compound is dynamically unstable. However, compounds with carbon vacancies (i.e., Mo${}_{3}$Al${}_{2}$C${}_{1\ensuremath{-}x}$) can be dynamically stabilized for vacancy concentrations $xg0.09$. By means of a simple thermodynamical model we estimate $x\ensuremath{\sim}0.13--0.14$ for Mo${}_{3}$Al${}_{2}$C${}_{1\ensuremath{-}x}$ at the experimental preparation temperatures. The influence of the carbon vacancy concentration on the electronic structure is investigated.

Corneal grafts are needed in ophthalmology for curative surgery on a regular basis. Thus transplants are often used in connatal abnormalities like a dermoid, to replace scarred tissue or in healing dystrophical defects like pemphigoid. There are several possibilities for their production, the most common being mechanical shaping and cutting of donor tissue.

The current-in-plane resistivities and corresponding magnetoresistance ratios are calculated for realistic Co/Cu/Co-based spin-valve samples by applying the Kubo-Greenwood approach together with the fully relativistic, spin-polarized, screened Korringa-Kohn-Rostoker method for layered structures. We study the effects of both alloying in the spacer layers with a selection of 3d, 4d, and 5d elements as well as different profiles for interdiffusion at the Co/Cu interfaces, On comparing our results to available experimental data we find that both interdiffusion and confinement effects, due to the finite overall thickness of the spin valve, strongly influence the magnetoresistance of spin-valve structures.

Based on the Kubo-Greenwood equation as formulated for layered systems, an approach is discussed that allows us to separate the resistance of the current leads from that of the region whose resistance we wish to calculate for current perpendicular to the plane of the layers. By applying this approach to Fe/Ge/Fe model structures related to the parent lattice of bcc Fe we find that at least nine layers of the magnetic electrodes should be considered as being part of the calculation in order to perform such a separation. With different structures in the Ge spacer, we find that the concentration of vacancies plays a crucial role for the existence of a sizeable magnetoresistance (MR), while the actual structure in the spacer seems to be of less importance. Depending on the type of structure and the number of spacer layers (in a typical regime of 6--21 layers) the MR for ordered structure varies between 35% and 45%. Vacancy concentrations of more than 10%, however, wipe out the MR completely. Interdiffusion at the Fe/Ge interfaces produces very similar effects.

Within the Kubo-Greenwood formalism we use the fully relativistic, spin-polarized, screened Korringa-Kohn-Rostoker method together with the coherent-potential approximation for layered systems to calculate the resistivity for the permalloy series ${\mathrm{Ni}}_{c}{\mathrm{Fe}}_{1\ensuremath{-}c}.$ We are able to reproduce the variation of the resistivity across the entire series; notably the discontinuous behavior in the vicinity of the structural phase transition from bcc to fcc. The absolute values for the resistivity are within a factor of 2 of the experimental data. Also the giant magnetoresistance of a series of permalloy-based spin-valve structures is estimated; we are able to reproduce the trends observed on prototypical spin-valve structures.

Using the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method the magnetic properties of bulk NicFe12c alloys, their free surfaces, and ~free surfaces! of related spin valves of the type NicFe12c /Co4Cu5Co4 /NicFe12c are calculated. It is found that in the bulk systems the phase transition between fcc and bcc can be described very well in terms of spin and orbital magnetic moments, but also in terms of the magnetic anisotropy energy. The free surfaces and the spin-valve systems differ considerably from the corresponding bulk systems: free surfaces show a reorientation transition from a perpendicular orientation of the magnetization to in-plane at about 60% Ni, whereas the overall in-plane magnetization found in permalloy related spin valves can be mainly related to the contributions of the Co slabs to the band energy part of the magnetic anisotropy energy. In all cases investigated the ~spin and orbital! magnetic moments for the free surfaces are considerably enhanced at the surface with similar effects pertaining at the interfaces and the surface of the spin valves.

The current-perpendicular-to-plane (CPP) magnetoconductance of a sample sandwiched by two ideal non-magnetic leads is described at an ab initio level. The socalled ‘active’ part of the system is a trilayer consisting of two magnetic slabs of finite thickness separated by a non-magnetic spacer. We use a transmission matrix formulation of the conductance based on surface Green functions as formulated by means of the tight-binding linear muffin-tin orbital method. An equivalent and computationally more efficient formulation of the problem based on reflection matrices is also presented. The formalism is extended to the case of lateral supercells with random arrangements of atoms which in turn allows to deal with ballistic and diffusive transport on equal footing. Applications refer to fcc-based Co/Cu/Co(001) trilayers.

Excimer Laser Corneal Shaping using an 193 nm Excimer Laser (ArF) provides a possibility for the fabrication of corneal transplants of various forms for various clinical applications such as (epi-)keratoplasty. Another area of application envisioned is the production of 'living contact lenses' for epikeratophakia. A device for lathing and perforating corneal donor tissue with a scanning laser beam is presented. A new ablation algorithm (Optimized Scanning Laser Ablation) was recently developed and increased the quality of lenticules and donor buttons considerably.

Im letzten Jahr wurde das auf der Hornhautbank des AKH aufgestellte Excimer Laser Corneal Shaping System (ELCS-S) einer vollstandigen Uberarbeitung unterzogen, wobei es — hauptsachlich durch die Entwicklung (P.H., R.B.) und Implementation (R.B., C.B.) eines vollstandig neuen Ablationsalgorithmus — gelang, die erreichbare Oberflachenqualitat so wesentlich zu verbessern, das die Herstellung von hochprazisen Transplantaten, wie etwa Lentikeln fur die Epikeratophakie, nun in naher Zukunft auch im Routinebetrieb machbar erscheint. Erste Tests (R.B.) sind sehr erfolgversprechend, sowohl was die Dicke als auch die Oberflachenqualitat der hergestellten Transplantate betrifft.

We found that formation of an ordered phase in alloyed magnetic layers induces new periods of exchange coupling oscillations in metallic multilayer systems. We studied on an {ital ab} {ital initio} level the case of {ital c}(2{times}2) ordering of random Co{sub 50}Fe{sub 50}(001) magnetic slabs embedded in fcc Cu. The origin of the new periods can be correlated to critical points of the spacer Fermi surface folded down to the Brillouin zone corresponding to the {ital c}(2{times}2) superlattice. {copyright} {ital 1996 The American Physical Society.}

The family of intermetallics crystallizing in the BaAl4 type is rich in sub-groups with different ordered variants. Novel ternary compounds EpTMX3 (Ep = Ba,Sr; TM = Pt,Pd; X = Si,Ge) crystallizes in the body-centred tetragonal BaNiSn3 structure (space group I4mm) which does not possess a centre of inversion. Superconductivity in terms of a fully gapped s-wave type occurs for SrPdGe3 at Tc = 1.49 K and SrPtGe3 at Tc = 1.0 K.

The interstage 213 of the Ariane 4 launcher has been redesigned in CFRP as an alternative for the original aluminium alloy structure. The objective was to save mass and to demonstrate that costs can be competitive. The application of CFRP is limited to the curved blade-stiffened panels; the ring frames are metal. Initial sizing was performed with simple formulas, while the final design was analysed with NASTRAN and BOSOR4. Flat stiffened panels were tested in compression to verify selected design details of the cylinder. Three different sizes of subcomponent panels were tested to (1) determine the local buckling behaviour, at room temperature and at 180 "C (in accordance with maximum in-flight conditions) (2) determine the strength of the panel to end-ring connections and (3) establish the global panel buckling behaviour between ring frames. Verification tests of the stiffener run-out configuration resulted in a modification to prevent premature separation at the tip. Subsequent tests proved that the modification was adequate. A full scale test on the first article is scheduled for March 1986.

The transmission matrix approach was used to evaluate the perpendicular magnetotransport in metallic multilayers on an abinitio level. The spin-polarized, surface Green function technique was employed within the framework of the tight-binding, linear muffin-tin orbital method. The effect of impurities was included in terms of lateral supercells with random arrangements of two types of atoms. This approach treats both the ballistic and the diffusive regimes of magnetotransport on equal footing. The method was also applied to face-centered-cubic-based Co/Cu/Co(001) trilayers.