Table of contents

Examination of the unit cell dimensions of gamma Mn-Cu alloys indicates that the martensitic transformation which occurs in manganese-rich alloys is accompanied by a decrease in volume. The incorporation of this decrease into the existing description of the transformation, in place of the increase suggested previously, produces a better fit between theory and experiment as shown by neutron diffraction data. The result is relevant to the study of the metastability of gamma Mn alloys, and to current measurements on gamma Mn-Ni alloys.

It is shown that the anomalies in the resistivity of rare earth and transition metals and their alloys occurring at intermediate temperatures (e.g. the Woodward-Cody anomaly (1964) in A15 alloys) can be explained within the framework of standard transport theory. The extra resistance at the intermediate temperatures arises because ion cores with d or f electrons in different, nearly degenerate configurations present different scattering cross sections to the conduction electrons.

The authors have measured the resistivity of DyNi₃ and HoNi₃ amorphous thin films between 1.2K and 290K. They find that the magnetic ordering at low temperature results in a definite increase of the resistivity. It is shown that this positive contribution from magnetic ordering to the resistivity can be ascribed to coherent exchange scattering by neighbouring magnetic ions.

Monte Carlo calculations have been performed for an Ising system on a square lattice with nearest-neighbour interactions distributed according to a Gaussian with zero mean. The susceptibility is computed from the time averages of the fluctuating magnetisation and its square, and exhibits the characteristic maximum as a function of temperature. The height and position of this peak are found to depend on the 'observation time' used for the computation of the time averages. This is interpreted as evidence for the absence of a phase transition.

The Kondo effect in superconductivity can be investigated for Kondo alloys which are not intrinsic superconductors by inducing superconductivity using the proximity effect. The author's calculations predict re-entrant behaviour of the transition temperature of the proximity sandwich as a function of impurity concentration for certain cases.

The X-ray photoelectron 1s peak from pure iron was detected using an ES200 electron spectrometer with a silicon channel-cut crystal monochromator and synchrotron radiation from the 5 GeV electron synchrotron NINA at the SRC Daresbury laboratory. Intensity was too low for a determination of the core-level width but the estimated width is in line with the known X-ray Fe K alpha linewidth.

Measurements of the thermal diffuse X-ray scattering (TDS) have been performed in the longitudinal and transverse branches along the (110) direction of sodium single crystals in the temperature range 303.1-369.2K. Furthermore, the TDS of a lattice of nondeformable ions has been calculated in quasiharmonic approximation and then been compared to the experiments. Concerning the scattering from longitudinal modes, deviations up to 100% relative to the one-phonon scattering have been observed. The temperature dependence of these deviations suggests that the main part is caused by anharmonic processes rather than by effects stemming from ionic deformations. The scattering from transverse modes does not show any influences of anharmonic effects nor of ionic deformations within the experimental error.

Structural study of liquid eutectic Ag-Ge alloy has been performed at 1123K by means of neutron diffraction. The experiments were carried out using the 'concentration method' and the isotopic substitution method. The pair partial correlation functions, the partial nearest-neighbour numbers and the distances d₁ between Ag-Ag, Ge-Ge and Ag-Ge pairs are given. Predominant Ag-Ge interactions are explained in a way that is consistent with the thermodynamic properties.

Photoelectric yield measurements at the Li K edge and in an extended energy range 54-80 eV are presented. The sample temperature was varied in the range 79-480K (the liquid state). The edge consists of a steeply rising part due to the onset of transitions and a more slowly rising part which is interpreted as a rising density of states at the Fermi energy. With rising temperature the edge shifts to higher energy and broadens. Phonon broadening appears to contribute also at 79K to the width while the edge shape is consistent with a threshold exponent alpha ₁ approximately=0. The structures in the range 54-80 eV are washed out on melting. These structures are well described by APW calculations by Bross (1973) of the optical density including plasmon damping.

The thermopower S has been measured in the temperature range 1.3-13K (reference: superconductor) on aluminium containing Frenkel defects (FD), i.e. self-interstitials and vacancies of equal concentration c (maximum 850 PPM). The FD have been produced in varying concentration and configuration by reactor irradiation at 15K ('isolated' FD) and subsequent annealing ('agglomerated' FD). A whole such cycle could be made on the same sample, and the measuring accuracy was very high. Applying the Nordheim-Gorter rule the authors obtained the specific coefficients of vacancies A_V and interstitials A_I. The 'phonon drag' coefficient B, however, was independent of the electron scattering anisotropy (further mod B mod decreased monotonically with c). This behaviour is unexpected from the Bailyn theory and obviously has to do with the exceptionally strong phonon scattering on the FD.

Calculations of the electrical resistivity and thermoelectric power of several nonsimple metals have been carried out using a t matrix approach based on density matrix formalism, scattering theory, and the muffin-tin model of a solid. For most non-simple metals the calculated results have been found to be in good agreement with experiment.

The variation of the conduction electron scattering rate over the Fermi surface in potassium has been determined from de Haas-van Alphen effect studies in dilute alloys of K(Rb) and K(Na). A new method has been devised for the accurate determination of small changes in Dingle temperature with a resolution of approximately +or-10 mK. The anisotropy of the scattering rate is found to be 10.8% and 19.4% for the scattering by Rb and Na impurities respectively.

The anisotropic scattering of conduction electrons in potassium by dilute concentrations of rubidium or sodium impurities, is discussed in terms of two theoretical models. In one, the anisotropy derives from the lattice strain field surrounding a substitutional impurity, whilst in the other it arises from the variation in the character of the electron wavefunctions over the Fermi surface in potassium. Both effects contribute in approximately equal measure and the present results, in a simple metal, highlight the need for a unified theory, such as might be provided by a cluster type of calculation.

The static magnetic susceptibility of Ag containing small amounts of Fe impurities has been measured in the temperature and field ranges 1.4-300K and 0.9-9 kOe. The impurity contribution to the susceptibility shows a Curie-Weiss-like temperature dependence which is compared with theoretical calculations within the Anderson model. The experimental results agree with the theoretical model using an impurity spin S_Fe=³/₂ and a characteristic, or Kondo, temperature T_K=1.2K as scaling parameters.

Spin echo NMR measurements have been made of the hyperfine fields at a number of sp element sites in Heusler alloys. The results confirm the systematic trends observed previously.

Small-angle diffuse neutron scattering measurements have been performed upon Co-rich CoGa alloys using the D11 diffractometer at ILL, Grenoble. These measurements, in conjunction with a re-investigation of the magnetic properties of the alloys, have revealed the existence of superparamagnetic behaviour associated with regions of correlated spins extending over approximately 60 AA. A relationship between the superparamagnetic assemblies and groups of Co atoms on the Ga sublattice is suggested by the differences in the observed scattering from alloys in the quenched and slow cooled conditions. Beyond a critical concentration of 55 at.% Co the onset of ferromagnetism is observed in the quenched alloys, although superparamagnetic behaviour is found to persist well into the ferromagnetic region.

A polarised neutron diffraction study of three iron-vanadium alloys containing 5, 15 and 22 at.% of vanadium has been carried out. The localised 3d spin moment, the diffuse negative moment and the asphericity parameter have been determined from these measurements, and are compared with results from bandstructure calculations.

The longitudinal nuclear relaxation rates R(c,T) have been measured for the ¹¹⁵In and ²⁰⁹Bi nuclei in liquid alloys of In_cSn_1-c, Bi_cSn_1-c and In_cPb_1-c, Bi_cPb_1-c within the concentration and temperature ranges 0.1<or=c<or=1.0 and 400K<or=T<or=640K, respectively. Although the magnetic dipolar rate R_m exceeds the electric quadrupolar rate R_e by almost an order of magnitude, both the separation of R into R_m and R_e and of R_e into its coherent part R_e,coh and its incoherent part R_e,inc could be carried out to approximately 10%. Details of the spectrometer (combination of a commercial pulse set up with an on line computer) and of the alloy preparation (capillary bunch samples) are given. The concentration and temperature dependence of both parts of R_e can be described by the current theory of R_e(c,T) for random substitutional metallic alloys.

The band electron momentum distributions in the 3d transition metals V, Cr, Fe, Ni and Cu are calculated by employing the bandstructure method of Hubbard (1969) and Mijnarends (1967 and 1973). The results are qualitatively analysed in terms of the respective bandstructures and Fermi surfaces and general systematics are pointed out. The analysis shows that the anisotropy in the electron momentum distributions arises mainly from the character of the Fermi surface and the d electron wavefunctions.

Reports the optical properties of thin tin films deposited in ultrahigh vacuum on cooled pyrex substrates. The normal incidence reflectance measurements were carried out in the energy range 2-15 eV and the optical constants were deduced by Kramers-Kronig analysis of the reflectance data. The optical conductivity sigma and real part of the permittivity epsilon ₁ are compared with the theoretical ones calculated from Ashcroft's theory (1971). The agreement concerning the overall optical absorption appears to be good. Structures superimposed on optical spectra are tentatively interpreted by comparison with theoretical spectra. The energy-loss function peaks at (13.85+or-0.02) eV.

Electron binding energies obtained from X-ray photoemission and workfunctions obtained from UV photoemission have been recorded for caesium adsorbed on nickel (100) at coverages from 0.1 to >1.0 monolayer. Analysis of coverage as a function of Cs⁺ dose suggests a sticking coefficient of 0.5 for Cs⁺ on nickel (100) in submonolayer range and 0.05 above a monolayer of deposited caesium. The binding energy of the caesium 3d_5/2 level, referred to the Fermi energy of the adsorption system, is 726.0+or-0.2 eV, independent of coverage. Comparison of binding energies of atomic caesium and caesium adsorbed at saturation coverage shows that the total change in electron binding energy, Delta E_B, depends on the core levels studied (5s to 3s); subtracting a modified relaxation energy yields a solid state shift in binding energy of 2-4 eV.

For pt.I see ibid., vol.6, p.1375 (1976). This new method is shown to give the exact result for U=0. It is implied that the same expansion in V_kd will converge in both the large U, magnetic regime, and the small U, nonmagnetic regime.