Table of contents

An interpretation is proposed of a strong correlation between the optical-mode excitation energy and hydrogen-metal distance in a series of fluorite-type metal hydrides. Discussion is based on central pair potentials between hydrogen and metal atoms, and is shown to give consistent results on hydrogen on T sites in BCC metals as well.

The local density of state (LDOS) of d electrons for atoms at and near the Sigma =5, (013) tilt boundary in iron was calculated by the recursion method or a simulated model structure. The characteristic feature of the LDOS at the boundary is that the densities of states near the centre of the band increase while the peaks on either side of the bulk band shift inwards. These features disappear in the bulk metal one or two atomic layers away from the boundary.

Two de Haas-van Alphen frequencies, 14.5+or-0.2 and 16.2+or-0.2 MG, have been observed in a single crystal of ZrZn₂. The magnetic field was parallel to the (1,1,5) direction. All the other orientations tested yielded the same frequencies, within the limits set by uncertainties in the demagnetising factor and the number of oscillations detected. These results restrict possible interpretation in terms of available band calculations, to a Gamma -centred spherical sheet of Fermi surface, split in two for the spin-up and spin-down sub-bands. The difference in cross-sectional area between these two surfaces corresponds to the observed frequency separation of 1.7 MG. This separation, combined with the calculated band velocity, gives an exchange splitting of 4.5 mRyd. The two frequencies had the same effective mass m*/m_o=0.90+or-0.05. Comparison with the calculated band mass gives a phonon and magnon mass enhancement parameter of lambda =1.7.

Results of resistivity measurements on a series of pure gallium single crystals with size-limited residual scattering exhibit deviations from Matthiessen's rule (DMR) that are compared with those observed in single-crystal gallium alloys with impurity-limited residual scattering. Such a comparison provides a test of the isotropisation idea which has been used to explain the deviations in a number of metals. The high degree of correlation between the results in the two cases, when considered as a function of residual resistivity, tends to indicate that some other mechanisms is responsible for the DMR in this metal.

It is demonstrated that the chemical short-range order (CSRO) which exists in the transition-metal glass Cu₆₆Ti₃₄ originates in the liquid state, and that this CSRO appears to be enhanced on vitrification. The structure factor S(Q) of the liquid alloy Cu₆₆Ti₃₄ has been obtained by neutron diffraction. The form of S(Q), and in particular the existence of a 'prepeak' at a Q value of approximately 1.9 AA^-1, provides direct experimental evidence of CSRO in the liquid state. A comparison of the S(Q) curves of Cu₆₆Ti₃₄ for the liquid and glass states indicates that the CSRO is less well developed in the liquid. This qualitative analysis is supported by a rough estimate of the value of the CSRO parameter, alpha , which appears to be reduced by a factor of about two in the liquid state.

An Al-⁵⁷Co thin-foil specimen was first quenched from high temperature and then irradiated by high-energy electrons at 77K. The annealing behaviour of the Mossbauer spectrum was compared with that of a simply irradiated specimen. Annealing at 208K the same peak appeared as that found for a simply quenched specimen, but it decreased below 273K in contrast with the latter peak. It was concluded from this that Co atoms interact preferentially with clustered vacancies but that the binding energy is not large enough to maintain the complexes at this temperature if they cannot grow further.

It is suggested that transition of the Coster-Kronig type take place in excited La³⁺ ions having a configuration 3d_3/2^-14f¹. Their presence can explain the intensity of the 3d_3/2 resonant emission and the broadening of the ¹P₁ absorption line with respect to the ³D₁ line in the 3d La³⁺ photoabsorption process.

Annealing of vacancies in electron-irradiated silver is studied by positron lifetime and residual resistivity measurements. The annealing stage III is found by both methods to be at about 250K. The activation energy associated with this stage is measured to be 0.72+or-0.05 eV. It is shown that the stage III recovery in silver is due to vacancy migration which results in formation of positron trapping sites having an exceptionally strong temperature-dependent trapping rate. The defects are interpreted as interpreted as vacancy loops,. which anneal out around 600K.

Experimental results are given, supporting a mosaic block model for Na and K crystals. An angular mosaic spread eta approximately=5-10' and an average mosaic block size t approximately=1 mm are derived from rocking curves and the integrated reflectivity measured by gamma -rays and neutron backscattering respectively. From these data an average dislocation density of less than 10 m^-2 can be estimated.

The variation of the Bordoni peaks and also the modulus defect and internal friction at very low temperature are studied during the electron bombardment of copper samples and their subsequent annealing. A substructure is apparent in each of the two Bordoni peaks which is different in well annealed and cold-worked specimens. Comparison with electron microscope observations allows a tentative identification of the different dislocation classes responsible for the relaxation processes. The temperature range of the pipe diffusion of self-interstitials on the dislocations is also determined.

The dynamical structure factors of the metallic glass Ca₇₀Mg₃₀ and the same sample after crystallisation have been determined for momentum transfers between 0.4 and 4 AA^-1 and energy transfers h(cross) omega =E₀-E between -40 and 6 meV using a thermal neutron time-of-flight spectrometer. The low-frequency modes reported in a recent experiment in a different metallic glass have been studied at room temperature with improved resolution. Their dependence on momentum transfer is discussed in detail.

The low-temperature specific heats of an amorphous Mg_0.7Zn_0.3 alloy and of the same alloy subjected to heat treatment are measured over the temperature range 1.6-4.2K. All the results fit well to the simple equation C= gamma T+ alpha T³. The electronic specific heat coefficient gamma for the amorphous phase is found to be very close to the free-electron value on the assumption that both Mg and Zn donate two conduction electrons per atom. The lattice specific heat is well described by the Debye model in sharp contrast with the metal-metalloid glasses, where the departure from the T³ dependence is appreciable. This is attributed to the difference in the packing fraction of atoms between the metal-metal and metal-metalloid glasses. The electrical resistivity is also measured over the temperature range 4.2-300K. The reliable determination of 2k_F/K_p allowed discussion of the observed negative TCR in relation to the extended Ziman theory.

The low-temperature specific heats of amorphous Fe_1-xB_x alloys (x = 0.14, 0.16, 0.18 and 0.20) have been measured over the temperature range 1.5-6K. The results are well represented by the equation C = gammaT + alphaT³ + sigmaT^3/2 and the electronic specific heat coefficient gamma , Debye temperature Theta_D and spin-wave stiffness constant D are determined. Both gamma and Theta_D values are found to decrease rapidly with increasing B concentration. The largest gamma value is twice as large as that for the pure BCC Fe. The value of Theta_D is also very high, compared with the other metal-metalloid amorphous alloys. Such high values are attributed to the existence of the covalent bond between Fe and B atoms. The present results are also discussed from the point of view of Invar characteristics particularly in comparison with a typical Invar Fe_0.65Ni_0.35 alloy. The large gamma and low D values are observed in both alloy systems, while the high Theta_D in amorphous Fe-B alloys is in sharp contrast with the lattice softening phenomena in Fe-Ni alloy, which is believed to be one of the characteristic features of an Invar alloy.

A molecular dynamics study of surface self-diffusion on four different crystal surfaces was accomplished for atoms interacting via a Lennard-Jones 12-6 potential energy function. Both the surface and adsorbed atoms experienced realistic thermal motion which included all anharmonic effects. The formation of vacancy-ad-atom defect pairs leading to surface layer melting was observed below the bulk melting temperature for the (111), (113), (110) and (100) surfaces. Diffusion activation energies and exponential prefactors were calculated. Details for unusual atomic transport mechanisms on the (111) and especially (110) surfaces are also reported. Additional features include the analysis of velocity correlations and vibrational spectra associated with different types of atomic motion at surfaces.

The electronic structure of an iron atom dissolved in very small concentrations in palladium metal is studied using the self-consistent cellular multiple-scattering cluster method. It is found that the localised, giant, magnetic moments which typically appear in these kinds of alloys (palladium plus Fe, Mn, Co and Ni transition metals) are, in the case of Fe, properly described; other properties correctly reproduced are the hyperfine magnetic field at the iron nucleus and the formation energy of the impurity.

The influence of the shape of a positron trap on some annihilation parameters has been calculated. Using an aspherical model for divacancies in aluminium, the positron lifetime is estimated to be 1.1 times that for monovacancies, and the divacancy trapping rate is estimated to be 2.0 times the monovacancy trapping rate. In comparison, a comparable spherical model gives nearly the same lifetime and a trapping rate which is about one-fifth larger.

The authors have made resistivity, magnetoresistance, Hall effect and thermoelectric power measurements on the Heusler alloys Pd₂MnSn, Ni₂MnSn and Cu₂MnAl. Results are characteristic of well-ordered spin-only local-moment ferromagnets. The thermoelectric power curves all show a unique behaviour which the authors suggest is that characteristic of any local-moment ferromagnet.

The galvanomagnetic coefficients of indium in high and intermediate magnetic fields are studied both by calculation and by measurement. It is shown that the results of a path integral calculation on the 6 OPW model Fermi surface agree in general with the measurements. A peak of the deviation from Kohler's rule (DKR) in transverse magneto-resistance is found near 5K. The origin of the peak is discussed in terms of the anisotropic relaxation time. An anisotropy of the Hall coefficient at 293K is found and discussed in terms of the Fermi surface topology.

As examples of non-ellipsoidal samples having reversible magnetic behaviour lead bars of rhomboidal cross section are studied at 4.2K. The magnetic reversibility is associated with the absence of the irreversible migration of flux tubes. The shapes of the samples used allow a calculation of the magnetisation curve which takes into account the macroscopic properties of the intermediate state, with the aid of a simple two-dimensional model. The calculated magnetisation curves are in good agreement with the experimental curves extrapolated for infinite bar lengths.

The technique of neutron polarisation analysis has been used to determine the atomic short-range order and the magnetic moment defect distributions in antiferromagnetic 90, 85, 80, 75 at.% gamma -MnNi alloys. The nuclear scattering is consistent with the presence of anticlustering whilst the magnetic scattering shows that the nickel impurity acts to reduce the manganese magnetic moments at the first and second nearest-neighbour sites. There appears to be no moment located at the defect site. The results of the neutron polarisation analysis measurements are in substantial agreement with the rate of change of sublattice moment determined in concurrent magnetic Bragg scattering measurements, which has been shown to be constant, with a value of -(2.6+or-0.5) mu _B atom^-1.

The collective magnetic excitations were studied in the pure quadrupolar phase of the compound Tm_0.9Lu_0.1Zn and analysed within a generalised susceptibility formalism. In spite of the dilution by lutetium, a 60% larger dispersion of the longitudinal mode is observed in comparison with the concentrated compound TmZn; this is a direct consequence of the quadrupolar ordering due to the presence of strong quadrupolar pair interactions in these cubic rare-earth systems.

The changes in the magnetic properties of amorphous ferromagnetic Fe_75.4B_14.2Si_10.4 ribbons have been followed as a function of annealing temperature, T_A, by Mossbauer spectroscopy and X-ray diffraction. During structural relaxation before the onset of crystallisation, the magnetic hyperfine field increases steadily with increasing T_A while the quadrupole and isomer shifts remain unchanged. The onset of bulk crystallisation is preceded by surface crystallisation in conjunction with which magnetic anisotropies with easy directions perpendicular and parallel to the ribbon plane develop in the ribbon bulk and surface layers, respectively. The anisotropies, also observed for other amorphous ribbons, are proposed to have their origin in compressive stresses appearing in the bulk portion and tensile stresses in the surface layers which are the result of the formation of higher-density crystalline surface layers. The compressive and tensile stresses produce the out-of-plane and in-plane anisotropies in the ribbon bulk and surface layers, respectively, through positive magnetostriction.

The authors have studied the conduction electron spin resonance of lithium, and the line broadening resulting from coating Li with another metal Me. In all cases, the observed linewidths can be accounted for by a single parameter, the so-called surface relaxation probability ( epsilon ). The authors have measured this spin-flip probability for several Li-Me interfaces (Me:Si, Cu, Zn, Sn, Sb, Bi). Two interpretations are suggested. In the first, the interface is considered as an infinite barrier inducing spin-flip and resistivity scattering of lithium electrons. This model is shown to be inadequate. In the second, the transmission of electrons from Li to Me is taken into account. The transmission coefficient (t) is related to epsilon through an expression involving the electronic density of states of the two metals, and the bulk relaxation properties of Me. The model predicts epsilon values independent of temperature, as observed. For sufficiently low t values (t approximately 10^-3), it gives broadenings independent of the Me thickness, in good agreement with experiments.

Pulsed nuclear magnetic resonance (NMR) techniques at high magnetic fields have been used to measure the Knight shift and spin-lattice relaxation rate of ⁶³Cu in the Laves phase system Cu_2-xZn_xMg for 0<or=x<or=0.5. The peak in the density of states near x approximately=0.3 observed earlier is confirmed. The extremely large quadrupole interaction of nu _Q=15 MHz explains why the copper resonance has not been observed previously.

The total and partial densities of states and the K X-ray emission spectrum have been calculated for copper using the results of a bandstructure calculation by the H-NFE-TB scheme and the dipole approximation. The CuK band emission was measured using a two-crystal X-ray spectrometer. The computed spectrum is in good agreement with the experiment. The results show that the observed two-peak structure of the CuK band is obtained in the dipole approximation, without including the quadrupole term or many-body effects, which are suggested in some recent studies.

It is argued that differences between the relative intensities of M_IV and M_V spectra of lanthanum in absorption and emission can be accounted for by autoionisation within a simple 'quasi-atomic' model. A relation is given between the breadths of the 3d⁹f lines and the change of relative intensities from absorption to emission.