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 Optical absorption in aluminium and the effect of temperature

  A G Mathewson and H P Myers 1972 J. Phys. F: Met. Phys. 2 403 Tag this article

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  Measurements of the optical absorption of clean evaporated aluminium films have been made at several different temperatures and the results interpreted in terms of the theory of parallel band absorption. Values of the Fourier coefficient of the pseudopotential mod U ₂₀₀ mod have been derived and its temperature variation satisfactorily explained. The derived value of this coefficient for 0 K is 0.79+or- 0.01 eV which is somewhat higher than that obtained from Fermi surface data, but the difference may in part be due to an energy dependence of the coefficient. Values of optical mass, interband and Drude relaxation times at the different temperatures have been derived. Some data appropriate to partially disordered films are also presented.

• Open/close Observations on the martensitic transition in sodium

  R Stedman 1976 J. Phys. F: Met. Phys. 6 2239 Tag this article

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  In the course of neutron scattering measurements on sodium near the martensitic transition at 36K, large single crystals were subjected to transformation cycles. On three occasions the original BCC orientation completely disappeared when the partially transformed crystal went through the reverse transition, and large grains (in one case a new excellent single crystal) with different orientations appeared. Analysis of relative orientations before and after a transformation cycle revealed no relationship akin to twinning. Reflections from the HCP phase indicated that it was very poorly developed. No significant changes in phonons in the BCC phase could be detected, neither above the transition point nor below it, apart from a large reduction in intensity in the partially transformed crystal. An explanation of this effect is suggested.

• 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 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 Spin density wave and soft phonon mode from nesting Fermi surfaces

  S -K Chan and V Heine 1973 J. Phys. F: Met. Phys. 3 795 Tag this article

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  The problems of spin density wave and of soft phonon mode leading to periodic lattice distortion as a consequence of nesting Fermi surfaces have been investigated. By examining the changes in the energy functional of the electron-lattice system as small amplitude spin density wave and periodic lattice distortion develop, the necessary and sufficient criteria for the existence of each kind of instability and for the coexistence of the two kinds have been derived. These results are expressed in terms of the generalized susceptibility function of the electron system, the Coulomb and exchange interactions between the electrons, the electron-phonon coupling and the phonon frequency.

• Open/close Electrical resistivity of ferromagnetic nickel and iron based alloys

  A Fert and I A Campbell 1976 J. Phys. F: Met. Phys. 6 849 Tag this article

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  The theoretical basis for the two-band model with spin-mixing which has been widely applied to the analysis of the transport properties of ferromagnetic metals is discussed in detail. This model is shown to have much more general validity than the original presentation suggested. The model is then applied to resistivity data in Ni and Fe based alloys to obtain a consistent set of parameters for the scattering within each spin band for various impurities, together with temperature dependent pure metal scattering rates.

• Open/close Temperature dependence of the optical properties of Au, Ag and Cu

  P Winsemius et al 1976 J. Phys. F: Met. Phys. 6 1583 Tag this article

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  The optical properties of Au and Ag are measured between 0.5 and 5.4 eV for temperatures ranging from 40 to 840K. The analysis of these spectra-also extended to the case of Cu-permits the assessment of energy separations associated with interconduction-band transitions in the vicinity of L over a wide temperature range. Notably the L _4- to L ₄₊ (nonrelativistic: L ₂' to L ₁) energy gap at 295K is found to be 4.81 eV for Cu, 4.11 eV for Ag and 4.20 eV for Au. The temperature dependence of this gap (around 295K) typically is -6.5*10 ^-4 eV K ^-1 for all noble metals, i.e., considerably larger than predicted on the basis of band calculations. The present analysis also shows the interband absorption edge of Ag to arise from transitions in extended regions of the Brillouin zone. A comparison of experimental and theoretical spectra suggests lattice expansion to be the major source of temperature dependence of the band structure. It also yields information regarding the influence of dipole matrix elements on the epsilon ₂ spectra.

• 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 structure of NaCl-type compounds of the light actinides. I. UN, UC, and UO

  M S S Brooks 1984 J. Phys. F: Met. Phys. 14 639 Tag this article

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  Self-consistent LMTO band-structure calculations for the paramagnetic ground states of UN, UC and UO are reported. Analysis of the radial charge densities reveals that the radial bonding charge density is very similar in the three compounds. The lattice parameters and bulk moduli, evaluated from the calculated equations of state, are within 3% and 11% of experiment, respectively. UO and UN satisfy the Stoner criterion for ferromagnetism, whereas UC fails to do so.