Table of contents

The contribution of three-ion interactions to the vacancy formation energy have been qualitatively (or semi-quantitatively) estimated for the alkali metals by using the asymptotic approximation proposed by Harrison (1973). The pseudopotential formalism is also used. The volume dependence of the screened pseudopotential has been considered adequately. The authors have found that the contribution from the third-order term to the vacancy formation energy was far larger than 10% of the corresponding second-order one.

The lattice dynamical model for FCC transition metals due to Fielek (1975) has been extended to BCC transition metals. The phonon dispersion curves for tungsten have been calculated. It has been shown that all the characteristic features observed in the phonon dispersion curves of tungsten can be reproduced by Fielek's model. The results obtained are far better than those reported previously on the basis of any of the lattice dynamical models.

It is proved here that for macroscopically homogeneous disordered systems the corner and central formulations of the MCPN method are equivalent.

Reports the concentration dependence of the density of states and the optical phonon contribution to the resistivity of Pd-H_x. The variation of density of states found agrees well with specific heat results.

The authors have examined the magnetoresistance of a single crystal of gadolinium which had been refined by solid state electrotransport processing. The anisotropy of resistance at 4.2K in a field of 75 kG is consistent with open orbits along (0001) and in the basal plane: this being in agreement with the effect of exchange splitting on the RAPW band structure.

The electronic structure of the (100) surface of Cu has been calculated within a tight-binding description of the electron states, using the layer method. With respect to the calculation with pure d bands, it is found that the inclusion of sp-d hybridization modifies the d surface states and introduces a new state localized in the first two layers. This state is identified as a Schockley-type surface state arising at the lower edge of sp-d gap.

The effect of the s-d exchange scattering on the nuclear spin-lattice relaxation (NSLR) time of dilute magnetic alloys has been calculated and the correction term to the NSLR time of a pure metal is found to be significant in the limit mu tau <<1, where tau is the transport relaxation time and mu is a parameter.

The electrical resistivity of DHCP beta Ce has been found to be anomalously large above 60K and to exhibit an order of magnitude drop below 20K. The magnetic susceptibility exhibits a Curie-Weiss behaviour above 40K, and magnetic ordering occurs at approximately 13K. The large resistivity is thought to be due to Kondo-like spin flip scattering which, at low temperatures, is quenched by the internal field associated with magnetic ordering.

For pt.I see ibid., vol.6, no.2, p.L49 (1976). A detailed explanation of the anomalous electrical resistivity of beta cerium is given.

The difficulties in interpreting the observed anomalies in the elastic moduli of Invar alloys below the Curie point are briefly reviewed. An intrinsic magnetic component is obtained explicitly on the basis of the itinerant electron model and found to be given by the spontaneous volume magnetostriction and is thus proportional to the square of the magnetization.

A study of the liquid alloys of the simple eutectic systems Au-Si and Au-Ge at selected compositions has demonstrated a pattern of behaviour very similar to that seen in the related gold-based system Au-Sn. The sharp X-ray diffraction profile of Au-Ge liquid alloys at the gold-rich end demonstrates that the structure, like that of pure Au, is simple, close-packed but with a mean closet distance for neighbouring atoms smaller than that for liquid Au or Ge. This result is also obtained for liquid Au-Si alloys. The packing in the liquid phase can only be interpreted in terms of A-B bonding, i.e. unlike atom interaction, a feature attributed to a high electrochemical factor. With higher Ge content, the X-ray diffraction profile broadens in a manner consistent with a more open liquid structure. The author accounts for the latter in terms of the increasing influence of Ge-Ge nearest neighbour packing.

Phonon dispersion curves for nine symmetry lines in q space are presented and a table of frequencies for six symmetry points. Experimental details are described. The results are compared with previously published calculated dispersion curves based on two-body and three-body forces. The importance of three-body forces in Be is pointed out and interpreted in general terms, but no attempt has been made to fit the experimental data by a calculation incorporating this difficult feature.

The trapping of hydrogen in niobium by nitrogen interstitials was investigated by resistance measurements. The results showed that only about one hydrogen atom can be trapped per nitrogen interstitial at low temperatures and that the trapping enthalpy is 0.12+or-0.02 eV. Due to the trapping process the hydrogen-induced resistivity increase is reduced by about 40% and the occurrence of precipitations is shifted to higher hydrogen concentrations.

A method is presented for obtaining a highly accurate empirical form factor v(q) for the alkali metals from the measured temperature dependence of the electrical resistivity. Two parameters are required for v(q), one determined from the high-temperature and the other from the low-temperature resistivity data. The method is applied to potassium and sodium. The error in the resulting v(q) does not exceed 0.002 Ryd for potassium and 0.003 Ryd for sodium throughout the range q<or=2k_F.

A preliminary non-self-consistent band calculation on V₃Ga using the LMTO method is reported. The concept of canonical bands and density-of-states has been studied with respect to their usefulness in describing the gross features of the band structure and to perform self-consistent calculations. The method is found to be very convenient in studies of compounds, and it is conjectured that the accuracy of the eigenvalues are 0.01 Ryd. The author focuses on the properties of the LMTO method applied to compounds rather than on comparison with experimental data. Since no attempt has been made to find an 'optimized' non-self-consistent potential, the results should not be trusted too far in comparisons with experiments.

High precision de Haas-van Alphen (dHvA) Dingle temperature measurements were carried out for six orbits in the (110) plane, in six different samples of Au (150 atomic p.p.m. Co) annealed under different conditions. No significant differences in Dingle temperature was observed due to annealing. Waveshape analysis, and observations of both fundamental and second harmonic spin-splitting zeros, revealed no significant spin-dependent scattering or exchange energy shifts of the electronic Landau level. A phase-shift analysis of the measured Dingle temperature anisotropy was carried out, with the result that d-d interaction and d wave scattering is heavily dominant. Both the Friedel sum and the impurity resistivity are correctly calculated using the dHvA-derived phase shifts, if the effect of impurity-induced strain fields is taken into account. An approximate method for obtaining a phase-shift description of these strain fields is demonstrated using the measured dHvA phase shifts and the experimental resistivity value. Finally a connection between dHvA scattering measurements and the screening of impurity states is shown.

The authors establish the CPA expression of electrical conductivity of the two s-d hybridized band model of Brouers and Vedyayev (1972) taking into account the effect of d off-diagonal disorder which is described in Shiba's approximation (1971). This model allows the consideration of the electrical conductivity of noble and transition metal alloys which have constituents with different d-bandwidths.

The generalized Landau model is applied to disordered strongly 'paramagnetic' alloys. It is shown that there is a close analogy between the susceptibility of such magnetic alloys and the Green's function of ordinary (nonmagnetic) disordered binary alloys. The Green's function analogy is used to prove that within the generalized Landau theory, disordered alloys similar to PdNi do not exhibit a critical concentration for ferromagnetism. The magnetization of such alloys is estimated on the basis of a simple statistical model and it is proved quite rigorously that a spontaneous magnetization exists even in the so called 'paramagnetic' region (below 2.3% Ni for PdNi). These general conclusions are illustrated by a CPA calculation of the susceptibility of PdNi alloys. In contrast to previous CPA calculations, it is found that the CPA susceptibility never diverges, thus indicating the absence of a well-defined critical concentration.

The pair interaction between local magnetic moments in a non-magnetic metallic host is investigated within the framework of the Anderson model and the Hartree-Fock approximation. The resulting interaction reduces to the Caroli-Blandin interaction at asymptotically large distances, but differs considerably in magnitude and phase at smaller distances.

The Mossbauer effect has been used to investigate the magnetic properties of Cu-Fe alloys of concentration 0.24-4.6% Fe in the temperature range 4.2-100K and in applied magnetic fields of up to 8.0 T. Alloys containing more than about 0.5% Fe exhibited magnetic broadening at 4.2K and the transition temperatures at which the broadening first occurred have been determined. The distributions of hyperfine magnetic fields observed in these specimens below the transition temperatures have been studied as functions of iron concentration and of temperature. The saturation hyperfine fields for isolated iron atoms are found to vary with concentration, exhibiting a linear variation at high concentrations but falling more rapidly at lower concentration. This is interpreted as evidence for the formation of a Kondo state. Spectra obtained at high magnetic fields indicate some anisotropy in the impurity response to the applied field.

Mossbauer measurements on Ni-Mn alloys with 25.5 and 33 at.% Mn have been carried out and analysed using some of the concepts used in an earlier study of Ni-Mn alloys with smaller Mn concentration by Ray et al. (1974). The spectra have been explained by a distribution of hyperfine fields arising from Fe atoms located in different nearest-neighbour environments. The value of these hyperfine fields is related to their corresponding Fe exchange fields in these environments. It is found that an Fe atom occupying Mn sites shows a stronger temperature dependence of hyperfine field than those occupying Ni sites. The nature of the Fe moments in these alloys is also discussed.

The optical constants of Ta-W-Re alloys at 4.2K in a vacuum of 10^-10 Torr are measured from 0.5 to 5 eV by means of a Drude method. Starting from the known calculations on the electronic energy band of Ta, W and Re, the structure of the interband part of the dielectric function epsilon ₂ is discussed in terms of direct transitions near Delta , G and Sigma . The changes of the optical properties of the alloys cannot be explained by extrapolations of the electronic energy bands of the pure elements only.

Photoelectron spectra (40.81 eV) of the Ag-Cd and Ag-In alloy systems are presented and are discussed in connection with both d band overlap and crystal-field models. The Ag 4d bands in each system show similar dependences on Ag concentration. This favours the former model. It is not clear which mechanism is responsible for the variation and increase in Cd 4d band splitting over the Cd free-ion value as a function of Cd concentration. The In 4d bands which have large binding energy show little dependence on concentration, apparently due to the small effect of neighbouring atoms.