In the last 30 days

• Open/close Theory of spin glasses

  S F Edwards and P W Anderson 1975 J. Phys. F: Met. Phys. 5 965 Tag this article

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  A new theory of the class of dilute magnetic alloys, called the spin glasses, is proposed which offers a simple explanation of the cusp found experimentally in the susceptibility. The argument is that because the interaction between the spins dissolved in the matrix oscillates in sign according to distance, there will be no mean ferro- or antiferromagnetism, but there will be a ground state with the spins aligned in definite directions, even if these directions appear to be at random. At the critical temperature the existence of these preferred directions affects the orientation of the spins, leading to a cusp in the susceptibility. This cusp is smoothed by an external field. Although the behaviour at low t needs a quantum mechanical treatment, it is interesting to complete the classical calculations down to t=0. Classically the susceptibility tends to a constant value at t=0, and the specific heat to a constant value.

• Open/close Highly convergent schemes for the calculation of bulk and surface Green functions

  M P Lopez Sancho et al 1985 J. Phys. F: Met. Phys. 15 851 Tag this article

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  The surface and bulk densities of states of a solid described by the stacking of principal layers are obtained by means of an iterative procedure which allows (i) the inclusion of 2 ⁿ layers after n iterations, (ii) the simultaneous calculation of the Green functions for both the 'right' and 'left' surfaces as well as for the bulk (or central) principal layer, and (iii) the use of imaginary parts eta as small as one wishes in the energy without any large increase in computing time, so that the limit eta to 0 can really be obtained. As a by-product the authors obtain (i) the 'right' and 'left' transfer matrices of the 'effective field' or continuous fraction approach and (ii) a factorisation theorem which relates the Green functions of both surfaces to the Green functions of both surfaces to the Green functions of the bulk and the free metal atom.

• Open/close Grain boundary segregation

  M P Seah 1980 J. Phys. F: Met. Phys. 10 1043 Tag this article

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  Equilibrium grain boundary segregation is assessed in terms of its measurement, theory and industrial significance. Aspects of the phenomenon of this segregation, namely the localisation, chemical system dependence, response to environmental parameters, etc., are discussed in relation to the measurement techniques for grain boundary segregation. These techniques-the interfacial energy approach, AES, XPS, STEM with X-ray analysis and the atom-probe FIM-are analysed in terms of their unique contributions. The theories of segregation are presented in a unified framework which uses analogues of the theories for gas adsorption on free surfaces. The cases of limited and unlimited numbers of sites are treated. Thus, McLean's segregation theory is seen to be the counterpart of Langmuir adsorption and a self-interacting segregant is seen to follow the analogue of the Fowler theory. The Fowler theory is extended to ternary systems and accurate methods of estimating the value of the relevant fixed parameters are presented. The kinetics of segregation and desegregation are then outlined. A range of material aspects affected by grain boundary segregation are described.

• Open/close Electronic structure of platinum

  A K Bordoloi and S Auluck 1983 J. Phys. F: Met. Phys. 13 2101 Tag this article

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  An attempt is made to obtain a good fit to the Fermi surface of platinum using the interpolation scheme. The starting point is a set of parameters which give a good fit to the optical data. The authors find that it is possible to obtain a good fit to the Fermi surface as well as to the optical data.

• Open/close The atomic sphere approximation to the KKR-CPA: electronic structure of paramagnetic Cu_cNi_1-c alloys

  W M Temmerman et al 1978 J. Phys. F: Met. Phys. 8 2461 Tag this article

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  The authors considered the coherent potential approximation (CPA) for a substitutionally disordered alloy crystal potential which is of the nonoverlapping muffin-tin form. The authors simplified the KKR-CPA theory using the atomic sphere approximation (ASA) of Andersen (1975). In its new form the fundamental equations of the theory can be solved numerically. The computational effort is not particularly large on the scale of modern bandstructure calculations. As an illustration of the authors' method they calculated the Bloch spectral functions and the partially averaged local density of states for a number of alloy potentials designed to represent paramagnetic Cu _cNi _1-c alloys. Where comparison is possible the authors found good agreement with previous calculations. Their results are also consistent with various experimental data.

• Open/close Band structure of Cu, Ag and Au: location of direct transitions on the Λ line using angle-resolved photoelectron spectroscopy (ARUPS)

  R Courths et al 1984 J. Phys. F: Met. Phys. 14 1559 Tag this article

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  The triangulation method of angle-resolved photoemission for the absolute location of direct transitions in k space has been used on (110) and (111) faces in the Gamma KLUX or (110) mirror plane in order to determine some points of the electronic bulk band structure of Cu, Ag and Au along the Lambda line. It is found that the experimental points for the occupied bands are in excellent agreement with recent calculations based on the local density functional theory for the noble metals. The experimental points for the final-state bands deviate by no more than about 0.5 eV which is within the experimental error of k determination. The emission from surface states of sp character on the (110) faces at the Y point of the surface Brillouin zone has been used to accurately determine the external emission angles. The sp surface states on Ag(110) have not been published previously. A refinement of the triangulation method using polarised excitation light is demonstrated for location of transitions along Gamma L which are energetically degenerate for negligible spin-orbit interaction.

• Open/close Quick iterative scheme for the calculation of transfer matrices: application to Mo (100)

  M P Lopez Sancho et al 1984 J. Phys. F: Met. Phys. 14 1205 Tag this article

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  The transfer matrix of a solid described by the stacking of principal layers is obtained by an iterative procedure which takes into account 2" layers after n iterations, in contrast to usual schemes where each iteration includes just one more layer. The Green function and density of states at the surface of the corresponding semi-infinite crystal are then given by well known formulae in terms of the transfer matrix. This method, especially convenient near singularities, is applied to the calculation of the spectral as well as the total densities of states for the (100) face of molybdenum. The Slater-Koster algorithm for the calculation of tight-binding parameters is used with a basis of nine orbitals per atom (4d, 5s, 5p). Surface states and resonances are first identified and then analysed into orbital components to find their dominant symmetry. Their evolution along the main symmetry lines of the two-dimensional Brillouin zone is given explicitly. The surface-state peak just below the Fermi level (Swanson hump) is not obtained. This is traced to the difficulty in placing an appropriate boundary condition at the surface with the tight-binding parameterisation scheme.

• Open/close Effect of pressure on the optical absorption in aluminium

  H Tups and K Syassen 1984 J. Phys. F: Met. Phys. 14 2753 Tag this article

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  The optical reflectivity of Al below 3 eV has been investigated in the 300 kbar pressure range (22% volume change) at T=300K. The dominant optical interband absorption at h(cross) omega =1.5 eV associated with the splitting between parallel bands shifts to higher proton energy at an initial rate of 4.35+or-0.3 meV kbar ^-1. The volume dependence of the corresponding pseudopotential Fourier coefficients is dU(200)/d ln V=-1.58 eV. The second parallel band absorption feature at energy 2U(111) ( approximately=0.4 eV at 1 bar) exhibits a similar pressure shift and becomes clearly observable in high-pressure reflection spectra. The optical response of Al under pressure basically follow the predictions derived from an empty-core pseudopotential in combination with the Ashcroft-Sturm expression for optical interband absorption in polyvalent nearly-free-electron metals, but with a significantly larger width of the low-energy absorption band at energy 2U(111). X-ray diffraction studies support the stability of the FCC phase up to 300 kbar.

• Open/close Study of plasmon structure in XPS spectra of silver and gold

  J Leiro et al 1983 J. Phys. F: Met. Phys. 13 215 Tag this article

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  Measurements of the low-energy satellites of the core X-ray photoemission lines of silver and gold are presented. The results are compared with electron energy loss spectra and dielectric measurements. Interpretation of the results on the basis of plasmon excitation is given and compared with earlier interpretations.

• Open/close Electronic properties of small silver particles: the optical constants and their temperature dependence

  U Kreibig 1974 J. Phys. F: Met. Phys. 4 999 Tag this article

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  Specimen size dependences of the dielectric constant and of its variations with temperature have been investigated by measuring the optical plasma resonance absorption of small silver particles embedded in glass. The following relations hold at the wavelength 405 nm: epsilon ₂ (imaginary part at 300K)=0.23+2.64/R, and epsilon ₂(300K)- epsilon ₂(1.5K) approximately=0.07-0.08/R where R is the particle radius in nm. Agreement has been found with the free path effect but not with the quantum size effect theories of Kawabata and Kubo (1966) and of Glauberman and Adamyan (1969). The behaviour of the temperature dependence can partly be explained by thermal lattice contraction. The ratio of electron density to the optical effective mass shows no distinct changes as R varies from 10.5 nm to 1.1 nm. It may hence be concluded that normal metallic properties are present in silver particles embedded in glass which contain more than about 400 atoms.