Table of contents

The problem of calculating the three-dimensional stress fields of complex arrays of dislocation segments has been solved. The method consists of transforming the three-dimensional problem to a two-dimensional one and then solving a set of planar problems using the integral theory. The method applies to the general anisotropic case.

Phonon dispersion relations for zinc are calculated for the first time with the fully nonlocal form of Harrison's generalized pseudopotential for d-band metals using a Lindgren-type approximation for the conduction-band/core electron exchange. Results for the phonon spectrum in the (0110) and other directions show good agreement with experimental data. To exhibit explicitly the generalization of the nonlocal pseudo-potential, comparisons are also made between phonon dispersion curves obtained with and without the hybridization term Delta .

Some experimental results obtained previously on the structure of noncrystalline films of close-packed metals are interpreted in the light of some recent publications. These concern computer-generated details of atomic packing in idealized models of amorphous structure which are applicable to material prepared by deposition methods. Agreement between experiment and the model calculations is good, but small differences are pointed out which suggest a compromise between the various approaches.

Read and Guenault have suggested that some Cu(Cr) alloys from the author's laboratory contained appreciable quantities of Fe (see abstr. A20591 of 1974). Careful analyses have shown this to be untrue, which implies that some of the published conclusions of Read and Guenault should be modified.

The electrical resistivity of the dilute magnetic alloy Au-0.13 at% Fe has been measured from 1.2 to 30 K in the pressure range 0-60 kbar. Application of pressure is found to shift the resistivity maximum from 3.5 J at zero pressure to lower temperatures at the rate of -5 mK kbar^-1, indicating a possible decrease in the interaction between Fe spins as they are brought closer together. A close analogy is found to exist between the present measurements on Au(Fe) and the investigation of Star on the Au_1-xCu_x(Fe) alloy series.

The magnetoresistivity of dilute magnetic alloys is calculated using the field-dependent infinite-U Anderson dilute alloy model. An approximate but analytic expression is obtained, valid for arbitrary magnetic fields and temperatures. The results agree qualitatively with the experiments of Fenton on Fe and Cr in a Cu(Au) matrix, and with those of Daybell and Steyert on Cr in Cu.

The diffuse neutron scattering and susceptibility from a PdMn 10 at% alloy were measured at 4.2, 30 and 293 K. The diffuse scattering was analysed by a polarization analysis technique using neutrons of wavelength 0.36 nm. The magnetic cross section at 293 K compares well at small scattering vectors with the bulk susceptibility measurements, except at 4.2 K. At this temperature, the measurements suggest that the moments are frozen into a magnetically disordered structure. The value of spin at the Mn site, estimated from the high-scattering-vector cross section, is S=1.65+or-0.2, whereas the total spin associated with an Mn atom is 2.25+or-0.15.

The effective interaction within the transition metals is split into the central interaction between the ions and the ion-electron interaction. The former contribution is accounted for by taking central forces up to fourth neighbours in Ti and Hf and up to the fifth neighbour in Y. The latter contribution is, however, obtained following Bhatia's method on cubic metals. Phonon dispersion relations along symmetry directions and theta -T curve have been plotted and compared with the available experimental results.

From a previous analysis it is known that a proper surface wave may always occur in a stable linear anisotropic half space provided that a certain real symmetric 3*3 matrix B is not positive definite for all velocities less than a limiting velocity nu _L, the velocity at which bulk wave solutions first appear. B is also the lagrangian factor matrix for a particular straight dislocation moving uniformly in an infinite medium which is elastically identical to the half space. By examining the behaviour of the dislocation lagrangian and the eigenvalues of B at nu _L, it is proved that proper surface waves may always occur except in cetain special cases. In each special case there always exists at least one bulk wave solution which satisfies the free surface condition on the half space boundary. Thus, there exist no forbidden directions for steady state propagation satisfying the free surface condition, i.e. either a proper (attenuated) surface wave and/or an unattenuated 'bulk surface wave' solution is possible. One simple numerical integration suffices to determine if a given propagation direction admits a proper surface solution.

The tight binding approximation for d electrons in liquid metals first studied by Roth (1972) using multiple scattering theory is re-examined by a diagrammatic analysis and is rederived by a new method and also extended to liquid metal alloys. The diagrammatic analysis permits a simple physical interpretation of the multiple scattering theory discussed by Schwartz and Ehrenreich (1971). Using a selfconsistent approximation the authors derive expressions for the electronic density of states N(E) using various approximations for the atomic correlation functions. In particular, it is shown that for a correlated liquid treated within SCA the electronic self energy Sigma (E) can be decomposed quite generally into a local and a non local part and that only the local part of Sigma (E) contributes to N(E).

Calculations of the anisotropic de Haas-van Alphen lifetimes in dilute alloys based on silver and gold are described and compared with the available experimental results. In the case of gold alloys, an attempt has been made to fit the experimental data with the theoretical expression of dHvA lifetime by treating the alloy dependent functions as parameters. The use of a truncated Fourier series expansion for representing the dHvA lifetimes over the Fermi surface is discussed.

Muffin tin parameters are used in the APW scheme to fit recent accurate de Haas-van Alphen data. The interpolated Fermi surface is in good agreement with magneto-acoustic and magnetoresistance data. A form factor, deduced from the fitted muffin tin parameters, is proposed which yields, when used in Ziman's theoretical expressions for the specific resistivity of the liquid and its volume derivative, excellent agreement with the experimental values.

Using a simple tight binding model the static electrical conductivity of a non dilute, substitutionally disordered, random binary alloy is discussed. The linear response theory of Kubo is used to express the electrical conductivity in terms of a two particle Green function. The authors approximately write the two particle Green function in terms of a single particle Green function within the ladder approximation. The final form of the conductivity expression demands the knowledge of the self energy correction to the single particle energies. It is found that in the weak scattering limit and in a first order approximation, the formulation is consistent with Nordheim's rule.

Low temperature thermoelectric power is calculated in the LSF approximation of the Anderson model. Theoretical results are compared with the experimental data for aluminium based transition metal alloys.

The authors present an alternative derivation of the Prange-Nee theory for the surface impedance of a metal in the presence of a weak magnetic field. Unlike the Prange-Nee theory, the present formulation does not rely on a variational formalism. The theory yields a selfconsistent expression for the electric field and current distribution in a conductor when magnetic surface states are present. The theory is capable of describing situations where the Prange-Nee formulation would be inadequate. Experimental consequences are discussed using simple numerical examples.

The magnetic field dependence of the surface reactance of superconducting tin has been measured at a frequency of 174 MHz. In the perpendicular field configuration (RF and static fields perpendicular to each other) the behaviour observed is approximately that expected from the Ginzburg-Landau theory in the static limit. In the parallel field configuration complicated behaviour is observed, even the sign of the reactance change being different at different temperatures. Near T_c there is a region where the reactance change has approximately linear dependence on the magnitude of the applied field, instead of the quadratic dependence expected in fields that not not too large.

Bulk magnetization measurements on Au-Fe alloys are widely held as indicating the onset of long range ferromagnetism in alloys with Fe concentration above about 12 at.%. The 'ordering' temperatures deduced from these measurements appear to be in reasonable agreement with temperatures of the maxima of d rho /dT in the resistivity of the alloys but are considerably higher than the values obtained from Mossbauer effect measurements for alloys in the concentration range between 12 and 20 at% Fe. Magnetization measurements on a Au-15at% Fe alloys are presented which, contrary to the above, show a behaviour usually associated with spin glass alloys and indicate a spin freezing temperature close to the 'ordering' temperature expected from Mossbauer effect measurements. The results show that the apparent ferromagnetic behaviour and higher ordering temperatures obtained by previous workers in their magnetization measurements have a simple physical explanation based on the intrinsic properties of the alloys.

Specific measurements have been made on the intermetallic compound Au₂Mn in the temperature range 0.3 to 4 K for both the antiferromagnetic spiral and ferromagnetic phases by applying an external magnetic field of up to 6 T. The Debye temperature calculated from the lattice contribution to the specific heat decreases from 163 K in zero field to 157 K in a field of 6 T in the ferromagnetic phase. The electronic specific heat coefficient, gamma , is 1.45 mJ mol^-1 K-¹ in the antiferromagnetic phase and decreases in the ferromagnetic phase from 1.70 to 1.42 mJ mol^-1 K^-1 as the external field is raised from 2 to 6T. A decrease in the nuclear Schottky contribution to the specific heat with the application of the magnetic field indicates that the sign of the hyperfine field at the ⁵⁵Mn nucleus is negative, and the zero field magnitude of this parameter is 44.2 T. Evidence is also found for an increase in the hyperfine field on the ¹⁹⁷Au nucleus from the accepted value of 160 T in zero field, to about 200 T in the ferromagnetic region.

An improved band structure of Pd calculated by the empirical pseudopotential method is used to compute the density of states and the reflectivity, R( omega ). The reflectivity of Pd with dipole matrix elements calculated by the actual wave functions is given for 0<or=h(cross) omega <or=10eV and is compared with measured results. The structure in both the density of states and the reflectivity is identified.

Ellipsometric measurements of the optical properties of bulk specimens of V, Cr and Mn are reported for the photon energy range 0.8 eV to 4 eV and compared with previous work. It is shown that, apart from some small discrepancies in spectral position, the observed structure in the absorption coefficient for each of these metals can be successfully predicted from calculations based on the assumption of nondirect transitions and using the density of states according to recent band calculations. In this way some correlation of optical structure with band structure is achieved. However no firm conclusion can be drawn about whether the predominant transitions are really nondirect or direct.

Positrons and electrons are injected by radioactive sources in aluminium absorbers, whose thicknesses are of the order of half range. The emitted particles are counted as a function of their energy, in the interval between 1.5 keV and 3.5 keV. The ratio between position and electron emission probabilities decreases very rapidly with decreasing energy; in the interval of the measurements a variation of this ratio of at least 100 is measured. Some speculations are given in connection with this experimental result.

Auger electron spectroscopy and low energy diffraction have been used to study monolayers of lead deposited in ultrahigh vacuum on to (111) and (110) faces of gold. Comparison is made with a previous study of the (100) substrate. The succession of structure is similar on all three faces: low density arrangements followed by a compact hexagonal monolayer followed by another hexagonal arrangement which is interpreted as the intermetallic compound AuPb₂. (A previous interpretation in terms of AuPb₃, based on observations on the (100) face, is corrected.) The completion of the first monolayer is marked by sharp knees in the plots of the Auger signals as a function of evaporation time. Essentially the same alloy structure is found on all three faces. There are only slight differences due to differences in the substrate symmetry and structure.