Table of contents

A five parameter model for fcc metals is proposed by combining ion-ion central, ion-ion angular and ion-electron interactions. The present scheme has given excellent agreement between the calculated and experimental frequencies of copper.

In the Pauli paramagnetic limit the tunnelling density of states depends strongly of spin-orbit interaction leading to an additional peak in the tunnelling conductance between two superconducting films. The author discusses the finite temperature tunnelling conductance for a superconducting-normal metal and a superconducting- superconducting metal contact. In the latter case the peak induced by spin-orbit interaction should be detectable in a wide temperature range.

NMR spectra of ¹⁵⁵Gd and ¹⁵⁷Gd in ferromagnetic gadolinium metal have been measured at 4.2 K in zero external field. The interpretation the authors propose is consistent with the positions and the intensities of the observed lines. The isotropic hyperfine field of ferromagnetic gadolinium metal was found to be -357+or-7 kOe.

It is shown that the normally accepted condition for the independence of electron-phonon and electron-impurity scattering, q lambda >>1, is wrong and a much stronger condition is needed: q( lambda lambda _F/4 pi )¹2/>>1 in a free electron approximation, where lambda _F is the de Broglie Fermi wavelength. Experimental evidence is cited to support this contention, and it is pointed out that analogues exist in optics.

The electrical resistivity of spherical clusters of vacancies (voids) in the three simple metals sodium, magnesium and aluminium has been calculated by two different methods, one based on phase shift scattering and the other on pseudopotentials. In the phase shift method the clusters were represented by a spherical potential well, whose radius was adjusted to give a volume equal to that of the vacancies in the cluster and whose depth was determined so as to satisfy the Friedel sum rule for the phase shifts. In the other method, local screened pseudopotentials, situated at the vacant lattice sites, were used and the cross section of the cluster was determined from perturbation theory. The absolute values of the resistivity found by the two methods were in close agreement for magnesium and aluminium, though there was a substantial discrepancy in the case of sodium. Similar calculations for spherical interstitial clusters were also performed, although such clusters have not been observed experimentally. The results have the same general features as for the voids.

Acoustic waves in metals can couple energy to the nuclear spin system via the nuclear electric quadrupole interaction. Measurements of the acoustic attenuation due to this interaction allow the determination of the components of the fourth rank tensor connecting the electric field gradient to the elastic strains. The magnitude of the two independent components (S₁₁-S₁₂) and S₄₄ of the gradient-elastic tensor have been determined in aluminium single crystals and found to be mod S₁₁-S₁₂ mod =2.5*10¹⁵ stat C cm^-3, mod S₄₄ mod =3.0*10¹⁵ stat C cm^-3. The comparison of the measured and lattice point charge value indicates the dominant effect of the conduction electrons to the electric field gradient in aluminium.

The temperature dependence of the friction stress for (1010) (1120) type dislocations in beryllium has been measured in the range 300-500 K. For each temperature investigated, the friction stress was computed from the maximum loop width and the corresponding irreversible work data, obtained from the family of closed hysteresis loops developed by the cyclic compression of appropriately oriented single crystals. In addition, the values were also determined using the alternative method involving the elastic limit as obtained by extrapolation of the maximum shear stress against the maximum loop width curve to zero loop width. Both methods of analysis give essentially the same results. The data show that the friction stress for this system decreases in an almost linear fashion with increasing temperature from 0.28 kg mm^-2 at 300 K to 0.13 kg mm^-2 at 500 K. In magnitude, these values are approximately five times the corresponding values previously reported for (0001) (1120) type dislocations in beryllium.

A continued fraction technique is used to derive an approximation to the density of states of a disordered alloy with a tree of Bethe lattice. The approximation in the case of only diagonal disorder provides a new simple derivation of the coherent potential approximation for a certain density of states. For an alloy with both diagonal and off-diagonal disorder the density of states is given in terms of the solution of a certain cubic equation. The self energy in this case is also obtained and used to provide the starting point for a theory of alloys with both diagonal and off-diagonal disorder and a general lattice which is equivalent to a special case of the theory of Blackman et al. Extensive calculations are presented.

The authors have discussed the electronic structure of disordered binary alloys within the framework of the tight binding approximation by using a diagrammatic approach proposed and discussed by Edwards and Loveluck. These authors approximate the tight binding integral by its average value which amount to replacing the potentials by the virtual crystal potentials. This approximation is not appropriate for situations where the constituent potentials differ a great deal. In the present paper the authors have taken into account constituent potentials without resorting to such an approximation. In the second order of the perturbation they have obtained a set of new diagrams which contribute to the lifetime of the electronic states. The authors have illustrated the difference of their calculation from that of Edwards and Loveluck in a linear chain in which the overlap integral is nonvanishing only for the first nearest neighbours.

A model potential of the form omega _b(q)=(1/ Omega ₀)(-(4 pi Ze²/q²)+ beta (sin qr_c-qr_ccos qr_c)exp(-q gamma _c)) is employed to study some electronic properties of aluminium, by considering electron gas screening with and without the inclusion of exchange and correlation effects as in the self-consistent theory of Singwi et al and in the random phase approximation respectively. A calculation is carried out to obtain form factor, binding energy, monovacancy resistivity and also the resistivity, temperature coefficient of resistivity and the thermoelectric power in the liquid state. The temperature coefficient of the Knight shift at constant volume is also calculated in both solid and liquid phases. The results show a fairly good agreement with the available experimental data. It has also been found that the two sets of results obtained using either form of the dielectric function are significantly different.

The author presents a new calculation for the electronic lifetime, related to the generalized pseudopotential theory. Application to CUNi and CuCo alloys is given and discussed.

The pseudo alloy atom model was applied to the Cs-K alloy system. Total binding energies, bulk moduli and heats of solution were calculated as a function of alloy compositions over the full composition range from pure Cs to pure K. The calculated values of total binding energies showed a good agreement with experiments. The results suggest that the pseudo alloy atom model is suitable for the description of disordered alloys. It was concluded that the potential of an ion in alloys is appreciably different from that in the pure metal case.

Azbel'-Kaner cyclotron resonance has been studied in the three principal crystal planes of zinc at 34 GHz and temperatures between 1.5 and 4.2 K. The results are in general agreement with those of other workers. Two new mass series have been observed which have been assigned to an orbit on the first band caps and a limiting point orbit on the inside ring of the monster. The temperature dependence of the lifetime has been determined for the central orbit on the third band lens in the plane normal to the c axis. The temperature dependent part of the lifetime was found to satisfy the relation 1/ tau _th=cT³ where c=(8.70+or-0.38)*10⁶ s^-1K^-3. The lineshape for this resonance was also found to be in excellent agreement with Chambers' theory of lineshapes in AKCR. A noticeable anisotropy in the mass enhancement was found for orbits on the third band lens. Anomalies in the surface impedance associated with the propagation of short wavelength cyclotron waves have also been observed.

Calculations are given of the d resonant contribution to the resistivity and thermopower of liquid Ni and Pd, using the T matrix formulation of Evans et al. The d wave resonance energies and widths are taken from recent calculations in the literature and the parameters entering the model calculations are taken from recent experimental data. A comparison of results is given using the measured liquid structure factor of Ni and the theoretical hard sphere model results of Percus-Yevick. A comparison with other recent calculations and with existing experimental data is given.

The effect of lattice distortion on the residual resistivity of dilute alkali alloys has been calculated using the lattice statics method due to Kanaki and the empty core Ashcroft model pseudopotential. The dielectric function due to Singwi et al was used for calculating the ion-ion and ion-electron interaction potentials. The correction for lattice distortion was found to be 5-30%, which confirms the estimate given by Ziman. The overall agreement with experiment is of the same order as the phase shift calculation without lattice distortion.

The magnetic susceptibility of first row transition metals in liquid gallium has been measured. It was found that manganese and chromium are both magnetic, with a p_eff of (5.9+or-0.2) mu _B, a Curie-Weiss intercept theta of -590+or-20K for manganese, and a p_eff of (4.2+or-0.3) mu _B with a possible concentration dependent theta for chromium. The susceptibility of the nonmagnetic alloys was separated into orbital spin contributions by a comparison with the susceptibility and NMR data of the same impurities in aluminium. The value of J derived was 0.74+or-0.06 eV for manganese in aluminium. A lower limit was obtained for U+4J of 4.5 eV in these systems and of 1.4 eV and 1.6 eV for the virtual level width for gallium and aluminium alloys respectively.

The polycrystalline paramagnetic susceptibility of the intermetallic compound SmZn₁₂ is found to obey a Curie-Weiss law in the temperature range 45 K to 270 K in agreement with a recently proposed theory. The parameters obtained from the experimental fit are in good agreement with those obtained from the susceptibilities of other RZn₁₂ compounds where R is a rare earth. It is suggested that previously published arguments, which assert that s-f mixing plays an important part in some gadolinium compounds, are invalid.

Ferromagnetic resonances in nickel platelets were measured as a function of the orientation of the sample at room temperature. The line width indicates a strong dependence on the angle between the applied magnetic field and the normal to the film plane. The dependence can be well described as a sum of a constant term and a term resulting from the Gilbert type equation of motion. No spin wave resonance was observed.

Results of specific heat measurements between 1.5 K and 15 K on a large number of alloys in the range of existence of the Ni₃Al and Ni₃Ga intermetallic phases are reported. For four Ni₃Ga samples the measurements were extended down to 0.2 K, and the effect of various heat treatments on the specific heat was measured on two Ni₃Ga samples. The results, especially their concentration dependence, definitely exclude the presence of any appreciable contribution of the form predicted for paramagnon enhancement, but an interpretation in terms of superparamagnetic clusters also runs into serious difficulties.

Experiments are reported which show that the tetragonal distortion in an AuMn alloy containing a little more than 50 at% Mn (t₂) depends on the antiferromagnetic order parameter in much the same way as in the case of an alloy containing a little less than 50 at% Mn. An investigation has also been made on the antiferromagnetic ordering in the t₂ phase of the AuMn alloy using neutron diffraction techniques on a nearly single domain of the alloy. The magnetic structure was found to agree closely with that predicted by Overhauser using spin density wave theory.

The displaced charge (or Friedel) sum rule has been used extensively in discussions of defect properties such as the residual resistivity. The authors derive a simple microscopic expression for the effect of lattice relaxation on the sum rule in terms of the perturbing force due to the defect and the phonon polarization vectors and dispersion curves in the small momentum limit. It is shown explicitly how the result is related to the displaced volume induced by the defect. Numerical estimates of the lattice displaced charge for the case of the alkalis are presented.

The nuclear magnetic relaxation rate, R₁, of the ²³Na nuclear spin in liquid Na and its alloys containing up to 15 at% Hg and Tl has been measured. R₁ is typically about 100s^-1 at 400 K. The temperature dependence of R₁ is shown to be different in the alloys from the pure metal because of a quadrupole relaxation mechanism which occurs in the alloys. In contrast R₁ in the metal is consistent with relaxation by the contact hyperfine coupling to the conduction electrons. The quadrupolar contribution is related to the atomic diffusion and may be explained by an extension of the theory of quadrupolar relaxation in liquid metals to the problem of a binary alloy.

The optical absorption spectrum of clean thallium metal has been determined over the energy range 0.6-3.8 eV. The observed spectral features are in very good qualitative agreement with transitions predicted by the recent band structure calculation of Holtham and Priestley (1971).