Table of contents

A value of the optical mass for clean silver of 0.85+or-0.01 electron mass units has been measured. This is lower than any previously published value but found to be in good agreement with the measurement of Dujardin and Theye (1971) when the effect of silver sulphide surface layers is taken into account. The optical mass is independent of temperature in the range 145-575 K. The low value implies an electron-electron contribution to the effective mass of some 15%, the sign being negative.

The optical transitions of copper and alpha brass are explained on the basis of the direct transition hypothesis. The studies pertain to the alloys with 10, 20 and 30 atomic per cent zinc concentrations and the changes in transition energy with alloy composition are calculated for some important transitions in alpha brass.

Attention is drawn to some unusual magnetic effects which may occur when samarium is dissolved in strongly paramagnetic metals.

It is suggested that the RKKY form of indirect interaction for rare earths in metals cannot adequately explain the experimental results. A mechanism with positive f-d exchange and direct d-d interactions is proposed and is shown to give satisfactory agreement with experiment.

The zero wave vector partial structure factors for liquid Na-K and K-Hg alloys have been evaluated from thermodynamic data, using a formula due to Bhatia and Thornton (1970). There is significant variation with composition, in disagreement with the frequency assumption that the partial structure factors are independent of composition.

The magnetization of nearly magnetic dilute alloys is examined in and beyond the linear response region. Explanation of existing data using a localized enhancement model is shown to be impossible without the condition of charge neutrality on the impurity. A field dependent impurity-host coupling is found which also considerably affects the observed field dependence, mainly because the host susceptibility is exchange enhanced.

The athermal martensitic 'burst' transformation in ferrous alloys is considered to be activated by stimulated emission of phonons. The autocatalytic process occurring in the 'burst' is identical with a phonon-maser effect. After a brief consideration of the analytical and experimental background, the results of the new theory are discussed and they are in excellent accordance with the phenomenological crystallography of ferrous martensites.

The effect of quenching on positron annihilation in single crystals of pure copper and Cu-0.5 at% Mn was studied. From the results, the nature of electrons at the vacancy sites and the vacancy-impurity binding were discussed.

The temperature dependence of the motion of light interstitials is calculated using the quantum theory of Flynn and Stoneham (1970). The results are compared with the asymptotic expressions given previously. They show that the high temperature asymptotic is accurate over a wider range of temperature than expected, whereas the low temperature form is of very restricted application. Deviations from the asymptote depend both on the temperature and on the ratio of the activation energy to the Debye energy. Results for protons in Ta agree remarkably well with the theory for an activation energy 0.188 eV and for a hopping integral J of 29% of the Debye energy.

The frequencies of the normal modes of vibration of ordered Pd₃Fe have been measured at 80K using neutron inelastic scattering techniques. Extensive measurements were made of the modes propagating along (00 zeta ), ( zeta zeta 0), and a few measurements along ( zeta zeta zeta ) directions. The frequencies are similar to those of pure palladium except near the new zone boundaries of the ordered structure where appreciable splittings were observed. Born-von Karman models were fitted to the results and showed that Pd-Pd forces were probably slightly larger than in pure Pd while Pd-Fe forces were only 60% of these of pure Pd.

A comparative study of angular force models proposed by Clark et al (1964) and deLauney (1956) including the electron-ion interaction on the lines of Behari and Tripathi (1970) as applied to the cubic metals has been made. The forces are considered up to second neighbours only. Analytically it is found that the two models are equivalent for bcc structures but they give different results for fcc metals. The phonon dispersion curves for three transition metals (V,Nb,Ta) have been computed and the numerical results from both the models are found to be exactly coincident and also in good agreement with the experimental data.

Thermal conductivity measurements have been made on lead over the range 620-880K and on indium over the range 520-845K using a new apparatus of the axial flow type. In each case, the Lorentz number for the liquid metal falls steadily with increasing temperature.

Experiments have been carried out on the melting of particles of lead and indium in the size range 3 to 50 nm. Electron diffraction patterns were used to determine melting points and electron micrographs were used to determine the size of the particles. The melting points were found to decrease with diminishing size in both cases; in the case of lead the melting point was depressed by about 200K for particles of 3nm radius.

The results of the electronic energy band structures for alpha and gamma cerium are reported. The exchange potential has been parametrized and the energy bands computed following the augmented plane wave method. The position of the f band has been found to be extremely sensitive to the value of the parameter. The remaining structure of the bands, however, is not as sensitive, and has been discussed for different electronic configurations for the two phases of cerium.

The annihilation characteristics of positrons in aluminium have been studied for the distinct cases of annihilation in the perfect lattice and annihilation after trapping at vacancies or dislocations. A controlled production of vacancies and dislocation in single crystal aluminium specimens was achieved with a quenching and annealing procedure. The annihilation lifetime in the perfect lattice is 166+or-2 ps, whereas it is 246+or-4 ps for positrons trapped in vacancies and 250+or-30 ps for positrons trapped in dislocations. The mean lifetime is found to increase with increasing dislocation density, but saturation is not attained with the dislocation densities obtainable by the quenching process. The trapping probabilities are (0.23+or-0.05)*10¹⁵ s^-1 for vacancies and (0.08+or-0.05)*10¹⁵ s^-1 for dislocations.

Some generalizations of the coherent potential approximation taking into account cluster effects are presented and discussed. Several different approximations giving the same exact terms in various limiting cases are shown to coexist. In particular the propagator and locator formalisms are proved to yield different results when going beyond the single site approximation.

The Fermi surfaces of copper, silver and gold are described in the KKRZ formalism with the phase shifts as parameters. The areas computed with this parametrization scheme are in very good agreement with the experimentally determined de Haas-van Alphen areas. It is demonstrated that the description of the Fermi surface geometry is independent of the Fermi energy and of Fourier components in the interstitial region. In addition, the dependence of the phase shifts and the Friedel sum on the Fermi energy is considered.

The temperature dependence of the impurity resistivity of dilute AlMn alloys was measured between 80 and 300K. The low temperature behaviour is given by a T² law which around 150K changes gradually to linear T dependence. Comparison with measurements made on high concentration alloys shows the importance of impurity-impurity interactions.

The author has measured the electrical resistivity of two AuTi alloys containing 0.22 and 1.06 at% Ti. The results indicate the presence of a very weak residual resistance minimum after the subtraction of the pure Au resistivity. The low temperature behaviour can be described by an equation of the form (1-T/T_K)²) with T_K=650+or-100K for the 0.22 at% alloy and 400+or-200K for the 1.06 at% alloy. The concentration dependence is thought to be a real effect and is considered to be the result of interactions between Ti atoms. Above 4K the total alloy resistivity follows the T³ variation as predicted on current theories of momentum nonconservation (MNC) and phonon drag. Analysis of the data on these bases indicates that the parabolic (1-T/T_K)²) behaviour persists up to at least 20K. Comparison is made between the predicted coefficients of the T³ term and those found experimentally. The phonon drag calculation correctly predicts the concentration dependence of the T³ terms.

The macroscopic theory of force free magnetic fields in the mixed state of type II superconductors is presented. Solutions for cylindrical geometry are compared with experimental data from a Pb-40 at% Tl alloy. In the experiments the sample is subjected to combinations of field and current in a longitudinal configuration and both axial magnetization and axial resistance are simultaneously monitored. The observed paramagnetic moment is in good agreement with the predictions. An unexpected feature of the experimental results is the appearance of flux flow resistance at high currents. Coupled magnetic and resistive oscillations and discontinuities are observed in the flux flow regime. The system is magnetically irreversible in the resistance less state and reversible during flux flow. The results are discussed in the context of force free field theory.

Solutions for the magnetic flux configuration inside a current carrying Lorentz force free superconducting sphere are presented. Experiments have been conducted on a 0.95 cm diameter Pb-40 at % Tl sphere at 4.2K in which the sphere is subjected to a range of fields (0 to H_c2) and currents (0 to 1000 A) in a longitudinal configuration, to test its behaviour against the theoretical predictions. Axial magnetization is found to be in quite good agreement with the calculated values. Polar potential probes show, however, that a flux flow resistance occurs over a wide range of current and field values. An attempt to compress flux isotropically into the sphere so as to establish a final configuration in which there is no current across the sphere surfaces, but in which the field is stronger in the interior than that applied, has been unsuccessful. This inability to establish a metastable state has led to the conclusion that the order of application of field and current constraints has no influence on the final configurations achieved.

The interaction between the fluxon lattice and a random array of pinning sites can be analyzed with the help of a simple model. The critical current calculated from the model corresponds to the more refined calculation of Labusch (1969). The model is used to analyse the response of a fluxon lattice to very small forces. It is shown that the displacement of the fluxon lattice is reversible and linear in the applied force up to a certain maximum displacement. Measurement of the displacement due to small forces can be performed by measuring the electric field in a slab carrying a small alternating current. Such measurements can yield useful information about pinning centres.

For Pt.I see ibid., vol. 2, 547 (1972). A small alternating current is passed through a slab of type II superconductor which is in the mixed state and the resulting alternating voltage is measured. Analysis of the observations enables the distribution, density and strength of pinning sites to be deduced with the help of a simple model developed in Pt.I, providing that the assumptions of this model hold good. The validity of this model can be checked experimentally. In the case of a PbIn sample, properties of the pinning sites deduced from experiment are consistent with the assumption that pinning is due to second phase precipitates. Measurements on cold-rolled NbTa cannot be successfully analysed, probably because the analysis is valid only in the case of widely separated pinning sites.

The dynamical screening of a core hole by the conduction electrons in a metal is discussed with specific reference to the Auger spectrum. The main effect is the introduction of plasmon gain peaks and a calculation for aluminium gives a gain peak of comparable magnitude to that observed by Suleman and Pattinson (1971).

A new type of time dependent magnetization has been found in the pseudobinary compound series Dy(Co,Ni)₂. This has been associated with the narrow domain wall processes reported previously by several workers and is thought to be an intrinsic aftereffect connected with materials for which the ratio of the anisotropy and exchange energies is large.

The longitudinal relaxation of the ⁷Li nuclear spins in dilute Li alloys containing 2.0, 4.0, 8.0 at%Mg; 1.5, 3.0 at%Cd; 1.5 and 2.75 at%Ag is measured. In all these alloys below 0 degrees C the relaxation rate T₁^-1=AT+B, where A and B are constants depending on composition. Above 0 degrees C T₁^-1 goes through a maximum typical of the diffusion dominated relaxation previously observed in pure Li. The maximum value of the relaxation rate due to the diffusion processes, T_1(diff)^-1, increases from 7.1 s^-1 for pure Li to 9.7 s^-1 for the 8 at%Mg, 12.6 s^-1 for the 3 at%Cd, and 12 s^-1 for the 2.75 at%Ag alloys. For the Mg and Cd alloys the increase is shown to be due to the interaction of the ⁷Li quadrupole moment with the time dependent electric field gradients in the alloys, and consistent with the broadening observed at low temperatures. The crease in the Ag alloys is apparently too large to be explained on the basis of the line broadening, and it is concluded that the enhanced effect may be evidence for an interstitial mode of diffusion in these alloys.

The optical properties of AuCr and AuV alloy systems have been investigated through a photon energy range 0.6 eV to 4 eV using an ellipsometric technique on bulk specimens. In the infrared region nearly Drude type absorptions is observed with collision frequency dependent on both concentration and impurity. The movement of the absorption edge on alloying is found to lie between the predictions of the rigid band model and of Friedel's work. Both parts of the main absorption edge are consistent with the assumption that they are associated with transitions from the d band to the Fermi level. In the case of AuCr extra absorption bands were detected compared with pure Au and these were interpreted in terms of virtual energy levels in the region of 1.2 eV from the Fermi level.

An investigation of single crystal specimens of FeCr alloy using the Mossbauer method is described. Evidence is presented which indicates that the hyperfine field at first neighbours of a Cr atom is reduced by 10.2%, and at fifth neighbours by 7.2%. A picture of the spin disturbance is proposed. The electric quadrupole coupling at first neighbours of a Cr atom is found to be e²Qq=0.31 mms^-1 and at second neighbours -0.07 mms^-1. The pseudo dipole moments at first and second neighbours are -6.1 mu _B and -2.5 mu _B. Some qualitative observations are made on other solutes.