Table of contents

Motivated by some inconsistencies in the literature, the authors review the formulation of problems involving interfacial dislocations. It is demonstrated that an attractive result of Braekhus and Lothe (1971) was derived from some inappropriate equations and that a paradox, cited by Chou and Pande (1973) as indicating a deficiency in the mathematical formulation of interfacial dislocation problems, cannot exist.

Measurements of the soft X-ray K absorption threshold of lithium in Li_1-xCu_x alloys indicate that the present many electron theory of the threshold anomalies does not describe the Li threshold.

Studies are reported of the effects of change of hydrogen content on the resonance vibration frequencies (in the approximate 20000 Hz range) and internal friction of discs of palladium and three palladium-silver alloys over the temperature range 120-300K.

Measurements of the attenuation of high frequency ( approximately 100 GHz) phonons in copper and in superconducting aluminium are described. The phonons are generated and detected by means of superconducting tunnel junctions; a brief analysis of this novel experimental technique is included. The attenuation lengths observed are of the same order as, but rather less than, values calculated using free electron theory. The role played by elastic phonon scattering in determining the attenuation length is considered, and some measurements of the phonon propagation through granular copper presented. These can be explained in terms of the interaction of elastic and inelastic phonon scattering.

This paper is concerned with the properties of thin film phonon transducers, which have recently begun to have wide application in the study of solids. Using the basic parameters of film thickness, elastic and inelastic phonon scattering lengths and phonon transmission coefficient to the underlying substrate, a simple model for the response time and generated frequency spectrum of a particular type of transducer, the superconducting tunnel junction working at its gap frequency, is developed and experimental evidence in its favour reviewed. From this discussion of a particular case, the argument is generalized to consider the properties of a wide variety of thin film transducers.

The authors have made a theoretical study of the temperature dependence of the lattice specific heat of Ag-3.97 at% Au alloy by using realistic models both for the host lattice and the defect. It is observed that the mass defect contribution to the enhanced lattice specific heat is on the average 70% larger than the experimental values in the temperature range 2-4K. The specific heat is found to be very sensitive to force constant changes. A reasonable agreement with the experimental data has been obtained.

The theory of the renormalized atom is analysed for the case of the alkali metals. A proper way to calculate the total energy of a renormalized atom is suggested, and this approach is used to demonstrate that the difference in total Hartree-Fock energy between a free and renormalized alkali atom is the Wigner-Seitz boundary correction. The relationship of the boundary correction to the cohesive energy is reviewed, and calculations for the various relevant parameters are presented in detail for potassium.

The Heine-Abarenkov model potential for metals was developed by Shaw (1968) to avoid arbitrary choice of the model radius. Here the parameters have been calculated for a large number of the metallic elements in each case including selfconsistent iteration through the calculated shifted Fermi level. The expressions used in the calculations are discussed and results are presented of the Fermi level calculations together with selfconsistent optimized model potential parameters and their energy derivatives.

The electron energy spectrum in a long period superlattice structure is investigated. It is shown that for a one dimensional model consisting of an array of delta functions it is possible to obtain the eigenvalues and wavefunctions exactly for all antiphase domain sizes. These results are used to examine the accuracy of calculations previously made by various approximate methods.

A study has been made of acoustic quantum oscillations in pure single crystals of white tin, using 50 MHz longitudinal ultrasound and magnetic fields of up to 6.7 T. The resulting oscillations have been analysed and interpreted in terms of the known Fermi surface of white tin, including magnetic breakdown effects. The results complement de Haas-van Alphen effect studies and include an observation interpreted as an oscillation in magnetic breakdown probability.

The Thomas-Fermi approximation is applied to calculate the electron charge distributions of vacancies and edge dislocations in aluminium within the jellium model. The various factors affecting positron trapping, at crystal defects are discussed. A method is derived to evaluate the momentum dependent annihilation rate in a nonuniform electron gas. The calculation gives a value of 24% of the bulk value for the electron density at the centre of a vacancy. The annihilation characteristics are calculated for the trapped positron, and a good agreement with experimental results is established. An edge dislocation is described by a hollow core model. The hole radius of 0.85 AA is found to reproduce the experimental lifetime of positrons in deformed aluminium. The electron density at the centre of the dislocation core reduces to 37% of its value in the bulk material. The momentum distributions of the annihilation quanta are calculated for various dislocation orientations, and a remarkable anisotropy in angular correlation curves is found.

De Haas-van Alphen oscillations from the second zone and the third zone Fermi surface in indium have been studied. Emphasis is placed on the high frequency oscillations attributed to the second zone, which show a strong mixing with the medium frequency oscillations from the third zone. The results combined with the low frequency oscillations from the third zone surface measured by Hughes and Shepherd (1969) have been used to obtain the parameters on an empirical pseudopotential calculation. The parameters in eV are: V₁₁₁=-0.601, V₀₀₂=-0.435, V₂₀₀=0.167 and E_F=8.702.

An approximate selfconsistent scheme generalizing the single site CPA is derived in order to account for the effect of local environment on electronic and magnetic properties of substitutional alloys.

Skew scattering by magnetic impurities in dilute magnetic alloys induces an extraordinary Hall effect which has now been observed in many systems. The author calculates the extraordinary Hall effect induced by cerium impurities for which the conduction electron-impurity interaction is mainly due to resonant scattering. The results are compared with experimental data on La-Ce alloys. The anisotropy of the magneto-resistance of such alloys is calculated and compared with some preliminary experimental results.

The calculation of the potential seen by an electron due to its interaction with the other electrons in the system has been extensively studied in homogeneous systems and most of the physical processes are well understood. The concepts of self energy quasi-particles and the exchange and correlation potential have been qualitatively and quantitatively described. The author presents as an extension a study of a simple inhomogeneous medium, in this case the semi-infinite electron gas from a dynamic non local viewpoint. The electron states considered are of fairly high energies, i.e. above the vacuum zero. The effect of the bulk and surface plasmons on the effective exchange and correlation potential are described. A complex potential is obtained which varies with the position and electron state. There are threshold phenomena in the imaginary part representing the onset of surface and bulk plasmon excitation. These results are obtained by way of a self energy formalism using approximations to the Green function and electron-electron interaction of the system.

The superconducting transition temperature and the temperature of the structural instability in (Hf_1-xZr_x)V₂(0<or=x<or=1) and (Hf_1-xTa_x)V₂(0<or=x<or=0.2) alloys have been determined as a function of hydrostatic pressure to 24 kbar. T_c either increases or remains essentially constant under pressure, depending on whether the alloy is HfV₂ or ZrV₂ rich. A correlation is found between the increase of T_c and the temperature T₀ at which the structure becomes unstable.

It is shown that an RF driven toroidal resistive SQUID (superconducting quantum interferometer) has a response to flux modulation independent of frequency, even though it be made entirely from normal metal-apart from a small niobium screw and two patches of soft solder making contact with the screw. Moreover, the response is independent of the presence or absence of a superconducting screen and is the same incorporating no resistive material.

The requirements of spin conservation in the form of a Ward identity, are exploited to make a selfconsistent theory of itinerant ferromagnetism in terms of electron-magnon interactions. Earlier results are extended to weak ferromagnets and the structure of self energies and single particle spectral weight functions is discussed. The theory is also applied to the calculation of the spin wave stiffness constant.

For pt. I, see ibid., vol.3, no.12, 2174 (1973). The strongly ferromagnetic limit of the theory developed in the preceding paper is examined in detail. The self energy expression obtained there from a Ward identity has a simple alternative diagrammatic derivation in terms of electron-magnon scattering processes. General features of the resultant single particle excitation spectrum are investigated and the question of the stability of strong ferromagnetism in the Hubbard model is considered. Numerical calculations of self energies, spectral weight functions and densities of states are presented for a simple spherically symmetric band structure whose parameters are chosen to simulate the band structure of nickel. Experimental implications of the work are discussed.

⁵⁷Fe nuclear spin configurations in the (rare earth)Fe₂ intermetallics have been deduced from Mossbauer experiments on polycrystalline samples. It is shown that the ⁵⁷Fe nuclei do not, in general, point exactly along the direction of magnetization M. For example the nuclear spins in DyFe₂ and HoFe₂ at room temperature are tipped away from the (001) magnetic axis by about 4 degrees . The origin of this tipping is traced to the local dipolar fields in these compounds. The situation in intermetallics with a (111) direction of magnetization is more complex because of the presence of two nonequivalent ion sites. The case of TbFe₂ is dealt with in some detail and it is shown that the nuclei in 'triangular nets' are collinear with M whereas those in 'kagome nets' make a small angle with the (111) direction of magnetization. Some comments are also made on the possibility of magnetically induced electric field gradients in these compounds.

The pressure dependence of the Curie temperature (T_c) was determined up to 40 kbar for the compounds R₂Co₁₇ (R=Nd, Gd, Er, Y and Th), RCo₅ (R=Gd, Y and Th), R₂Co₇ (R=Gd and Y), RCo₃ (Gd, Y and Pr) and RCo₂ (R=Gd and Tb). Single phase compounds with off-stoichiometric composition were included in this investigation. The experimental data are discussed in terms of the collective electron model. With few exceptions the pressure derivative of T_c of the various compounds can be represented by a general relation of the form dT_c/dP=⁵/₃ kappa T_c-⁵/₆ kappa B/T_c with B=3.5*10⁶K² and T_c ranging from 400-1200K. For the compounds Y₂Co₁₇, YCo₅, YCo₃, YCo₂, GdCo₅, ThCo₅ and Th₂Co₁₇ the compressibility kappa was determined.