Table of contents

Backscattering coefficients for noble metal lattices have been calculated by an extension of the KKR method of band structure calculation. The results are applied to interpret the Dingle temperature anisotropies of dilute silver alloys.

The Compton profiles of the alloys TiNi, Ti₂Ni and TiNi₃ were measured using 60 keV gamma -rays. The results were found to be in good agreement with the corresponding superposition of the Compton profiles of the pure metals of both constituents. This additivity of Compton profile indicates that the metallic binding in these alloys is similar to the binding in pure titanium and nickel metals.

The theory of Horwitz and Jacobi (1972) for the effect of the t-matrix pole on narrow-band systems is applied to the Anderson model (1967) for resonant impurity states in dilute alloys. The effect of the pole on the superconductivity and the magnetic susceptibility is examined, and a new critical criterion for the formation of localized moments is obtained.

Using partial structure factors a_ij obtained from conformal solution theory, the concentration dependence of the electrical resistivity rho and the thermoelectric parameter xi of liquid metal alloys is exhibited explicitly. The equivalent binary system Mg-Cd may be an example for which conformal solution theory can remove the discrepancy between the substitutional model of Faber and Ziman and experiment. However, nonlocal effects in the pseudopotential may also be important in this system.

The high-pressure superconducting phase of evaporated Bi films has been studied by electron tunnelling, using Schottky barriers. The values of the transition temperature, energy gap and phonon energies of Bi III are very similar to those for Pb and for amorphous Bi. A comparative discussion of the strong coupling superconductivity in these materials is given.

The importance of orbital relaxation in the computation of Auger transition rates for low-Z atoms is demonstrated for atomic Li (1s, 2s² to 1s²,ks), where relaxation enhances the computed Auger width by a factor of approximately 16. Solid-state effects are estimated to account for at least a factor-of-three additional enhancement for Li metal: Gamma >or approximately=130 meV. Experimental and theoretical implications of these results are discussed.

Characteristic energy loss peaks are reported at 9.6(1) eV and 8.5(1) eV respectively in the electron impact spectra of Zn and Cd obtained under UHV conditions. From a consideration of the binding energies of the outer 'd' bands of these materials it is concluded that the observed peaks result from plasmon creation rather than from interband transitions.

Localized spin fluctuations in alloys containing a small concentration of nearly magnetic solute atoms give rise to a resistivity whose temperature dependence relative to a spin fluctuation temperature T_sf is predicted to follow a universal law whether the temperature coefficient is negative or positive. It is well known that the Kondo effect is observed in Mo-rich alloys of the (Nb-Mo)Fe system, and the spin fluctuation resistivity of alloys of the equivalent 3d system (V-Cr)Fe has now been measured. Here a negative temperature coefficient is observed and T_sf is found to decrease as the Cr content is increased. T_sf is found to be sensitive to the amount of Fe dissolved, the effect of interactions between iron atoms being to stabilize the moments (reduce T_sf) and, if sufficient iron is present, to produce spin glass ordering.

The intra-atomic electron-electron Coulomb correlation energy U, which appears in the Hubbard Hamiltonian (1963), is shown to be well approximated by the change in eigenvalue of a localized Hartree-Fock state that occurs when the occupation of that state is changed. A selfconsistent calculation of all the Hartree-Fock states within a neutral Wigner-Seitz cell is made for three electronic configurations of each of the transition metals. Values of U are deduced from the differences in the d electron eigenvalues of the configurations. It is found that the ratios U/W, where W is the bandwidth, show a trend across the transition metals which is in excellent agreement with the known magnetic properties of their ground states.

Positron annihilation in the liquid alkali metals at just above their melting points is theoretically studied. A perturbation approach based on NFE model is used. The positron and electron momentum distributions including only the ionic density correlation have been selfconsistently calculated within a complex energy approximation. The positron resolution functions including both the ionic correlation and coulombic interactions have also been calculated by taking the simplest self energy diagram in the combined perturbation expansion into consideration. The angular correlation curves for liquid Na agrees well with the corresponding experimental curve over the full range of momentum within the error limits but there are still some appreciable deviations between them for liquid Rb.

High precision measurements of positron lifetimes in indium have been carried out at five temperatures in the range 83K to 405K. Constraint free analyses of the results clearly establish the multicomponent nature of the lifetime spectra and the fitness of the 'no escape' models of positron defect trapping phenomena. The implications for positron studies of vacancy formation energy are discussed.

The Hall effect and resistivity have been measured in a series of dilute binary Al-Cu and Al-Si alloys, and a number of ternary Al-Cu-Si alloys. The results have been compared with the predictions of the two band model of Takano (1966), and show that the model is invalid in these cases. There is a simple, nearly linear, relationship between the Hall effect change and the resistivity change in all the alloys and it is concluded that scattering terms dominate the Hall effect changes: in comparison, effects on the Fermi surface due to changes in electron to atom ratio seem negligible. Theory suggests however that normally the resistivity does not appear in expressions for Hall effect, but only the anisotropy of the resistivity. The present results do not permit this anomaly to be resolved.

A resonance of the type postulated early by Korringa and Gerritsen (1953) is found in the energy dependence of conduction electron scattering from interaction spin pairs. Added to the well known effect of spin freezing, this resonance drastically reduces Kondo's giant TEP of the free spin limit. A sign change can be caused by antiferromagnetic interactions in systems with low Kondo temperature. For the average interaction effect in a random alloy a scaling in C/T is derived. Spin changes and low temperature maxima in the experimental TEP of AuMn and CuMn are interpreted.

The ⁶³Cu nuclear spin lattice relaxation rate (T₁)^-1 in Cu-Mn and Cu-Cr dilute alloys, measured between 0.32 and 20K, are interpreted in the light of recent spin diffusion studies done by the authors (1972) in Cu-Mn alloys. It is shown that, the most important impurity contribution to (T₁)^-1 is through the RKY coupling with the transverse fluctuations of the impurity moment. The impurity spin relaxation rate involved in the NMR data is different from the ESR linewidth and is associated with simple impurity fluctuations.

Paramagnetic susceptibilities and nuclear magnetic resonance of ⁹Be and ⁵¹V isotopes are reported for (V_1-xCr_x(Be₁₂ alloys. The magnetic susceptibility and the root square of the relaxation rate (T₁T)^-1/2 are found to vary with temperature and composition. The Knight shift of beryllium is positive at 293K for 0<or=x<or=0.7 and becomes negative at 77K for all samples. Between 293K and 77K, the temperature change of the vanadium Knight shift is found to be small for samples of composition x=0.14; 0.28; 0.42; 0.56.

A magnetometer system utilizing a SQUID and a superconducting flux transformer has been used to monitor the internal oxidation process in very pure copper. Both remanent moment and low field susceptibility have been measured for copper containing 0.1-1 at ppm Fe and 70 at ppm Fe in various states of anneal. The results suggest that the oxidation process proceeds quite differently in the previously unobserved situation where very dilute amounts of iron are present than in the case of relatively high impurity concentrations.

The spin density distribution in the ferromagnetic alloy FeB has been determined from neutron diffraction measurements. Features are: an aspherical distribution of magnetization density around the iron atoms. Particular features found in the study are a moment of 0.95 mu _B associated with the iron atoms, an interaction between minority spin 3d and boron 2sp electrons and a weak magnetization density which can be associated with a covalent interaction along the boron chain. The result of the study is not consistent with the rigid band model which is commonly used to explain the properties of the iron borides. An alternative model for the electronic structures is proposed.

Mossbauer spectra were taken of the compounds YFe₂, YFe₃, Y₆Fe₂₃ and Y₂Fe₁₇ at temperatures ranging from 15K to well above the Curie temperatures (T_c=540, 538, 496 and 358K, respectively). The various spectra were analysed by means of subspectra due to the different nonequivalent Fe sites occurring in these compounds. For each of these sites the temperature dependence of the hyperfine field was determined and shown to be similar for different sites within the same compound.

Using a simple two band model and some recent theoretical work (Velicky and Levin 1970) on disordered systems, it is shown that it is possible to get qualitative information about the effect of disorder on the optical relaxation time and its variation with frequency in Au, Ag and Au_xAg_1-x films.

L absorption spectra of 4f heavy rare earth elements, ⁶⁵Tb to ⁶⁹Tm and ⁷¹Lu, in the pure metallic state have been investigated with a 40 cm curved mica crystal spectrograph of transmission type. Microphotometer records of L₂ and L₃ absorption edges taken at 25* magnification exhibit two distinct abrupt rises in absorption (L'₂ and L'₃ edges) except for ⁷¹Lu. Wavelengths of L absorption edges of these metals have been measured. A prominent absorption maximum (or so called 'white line') has been detected at the L₂ and L₃ edges. Peak position of the white line, its distance from the L edge position and its full width at half maximum have been reported. An attempt has been made to estimate the position of 4f unoccupied levels and to interpret the observed spectral features in the light of available theoretical data on the rare earth metals in question.

Using a 1m radius bent crystal spectrograph, the X-ray K absorption edge of zirconium in zirconium metal, zirconium oxide, zirconium tetrachloride and in zirconium oxychloride has been studied. In all the compounds investigated, it has been observed that the absorption discontinuity shifts towards the high energy side with respect to the pure metal. The shift which is due to the change in the distribution of the valence electrons is a maximum in the case of zirconium nitrate. The relative magnitude of the shifts in the compounds studied are tentatively explained on the basis of considerations involving electronegativity and interatomic distances.