Table of contents

Results are reported for four Nb-Ta single-crystal superlattices with 50 AA wavelength grown simultaneously on chosen substrates such that the crystal growth and superlattice structure take the (100), (110), (111) and (211) orientations in the respective cases.

The author has calculated the coincidence site lattice Sigma twist boundary energies for copper and aluminium. The boundaries were on (100) planes and he considered Sigma values of 5, 13, 17, 25, 29 and 37. The method employed was a wavenumber space summation which includes all effects due to the long-ranged potentials. The trend was for the twist boundary energy, gamma , to be proportional to Sigma independent of the metal and the potential used.

The local density of states (LDOS) of the most stable self-interstitial ((100) split interstitial) in copper and its neighbouring atoms were calculated by the recursion method. Three resonant modes were found in the low-frequency region in the LDOS of the self-interstitial atom.

Phase transitions into the ferro-magnetic and antiferromagnetic states for the stoichiometric FeRh alloy are discussed taking into account the self-consistent band structure calculations for the paramagnetic phase. A Peierls-type instability is one reason for the antiferromagnetic transition.

Approximate coupled Hartree-Fock estimates of the Sternheimer antishielding function gamma (r) are reported for the first time corresponding to the 3d transition metal atoms.

Electrical resistivity in an amorphous simple metal alloy host Mg₇₀Zn₃₀ containing up to 4 at.%Gd has been studied. the 'non Kondo' upturn in resistivity at low temperature is interpreted in terms of conduction electrons scattering from correlated pairs of spins. A universal behaviour of excess resistivity per at.%Gd versus reduced temperature T/ theta _s (where theta _s marks the onset of excess resistivity) is observed. Comparison is made with theoretical predictions. Magnetic susceptibility data are found to correlate well with resistivity measurements. No significant attenuation of magnetic interaction is observed.

The new results of resistance, low-field magnetoresistance and AC susceptibility measurements in Y₉Co₇ show that the superconducting interactions coexist with strong magnetic correlations up to about 5.5K. This hybrid state has some very interesting magnetic properties.

A simple atomistic model for the fusion process of metals is derived from a combination of the atomic model of the lattices and the simple theory of harmonic vibration of the atoms of A₁ (FCC), A₂ (BCC) and A₃ (HCP) type crystals. The lattice factors L_j of these metals and a new physical quantity rho _j identical to L_j delta _j= alpha /L_j with j=1, 2 and 3 for the fusion transitions BCC to liquid, FCC to liquid and HCP to liquid, involved with the vibrational instability fusion hypothesis of Lindemann, are defined. The derived structure-dependent simple fusion equation is related to a similar equation obtained from the combination of the Debye-Waller-Lindemann (DWL) formulae through a numerical factor f=(3/2)¹2/. Vibration amplitudes of atoms A_j (root-mean-square displacements A_j (DWL)=((U_i²))¹2/), Lindemann parameters delta _j and the physical quantities rho _j of 54 metals are calculated through the simple and DWL sets of equations above by using the empirical Lindemann constants L_j. The L_1.2 and rho _1.2 are constants, L₃( gamma ) and rho ₃( gamma ) for HCP metals are smoothly varying functions of the axial ratio gamma =c/a, although L₃ (HCP) and delta ₃ (HCP) are not. A firm conclusion is made that the Lindemann constants L_j and Lindemann parameters delta _j for the BCC, FCC and HCP metals are significantly different and the Lindemann law holds for each structure separately including the HCP metals.

The heat capacity of Ti, V and Cr has been measured between 350 and about 1700K. At low temperatures the description of the electronic heat capacity by simple electron band theory is quite satisfactory for V and Cr. The temperature dependence of the electronic heat capacity determined from self-consistent band structure calculations is in reasonable accordance with the experimental data for V only. The large discrepancies in the case of Cr demand mechanisms different from simple electron band theory.

A method is described for combining resistivity and thermodynamic observations of the same sample of a liquid binary alloy. The concentrations are varied in situ by using a solid electrolyte. The method is applied to Na-In and Na-Sn for which new resistivity and thermodynamic data are obtained up to 600 degrees C and for Na concentrations up to 0.7.

The thermodynamic data of liquid Hg-Na alloys have been analysed in terms of the idea of compound formation. However, little deviations from a linearly interpolated curve are observed in the magnetic susceptibility of those alloys, suggesting that the electronic structures are not changed by the compound formation. The anomalous behaviour of the electrical resistivity of these liquid alloys is also interpreted in terms of the Faber-Ziman formula.

The electronic structures of the Heusler alloys Co₂MnSn, Co₂TiSn and Co₂TiAl are calculated using the SAPW method. The common properties and characteristics of these three alloys are seen in their band structures. Whether or not the orbital angular momentum is quenched in the three alloys is discussed on the basis of the band structures. For the Co atom in the Co₂MnSn, Co₂TiSn and Co₂TiAl alloys, the orbital angular momentum is expected to contribute to the magnetic moment and the internal magnetic field.

The electronic band structure and partial densities of states of paramagnetic, ferromagnetic and antiferromagnetic ordered FeRh are calculated self-consistently, using the linear muffin-tin orbitals (LMTO) method. Comparison is made with other theoretical results and the experimental data. The computer values of the electronic specific heat coefficient and the magnetic moments on each site are in godd agreement with the available calorimetric, magnetisation and neutron diffraction data.

A calculation of the changes in five representative areas of the Fermi surface of Cu resulting from alloying of both Al and 3d transition-metal impurities is presented. The theoretical results of Cu(Al) and Cu(Ni) are compared with experimental Fermi surface changes obtained from de Haas-van Alphen investigations.

A Hamiltonian with a localised Jahn-Teller electron-phonon interaction plus a band-coupling term belonging to a metal cluster state adjacent to interstitial hydrogen in the Vb metals is presented. It is shown that in a low-frequency approximation, this problem is analogous to that of magnetic impurities in metals. The role of hydrogen in triggering the Jahn-Teller instability is clarified in the context of the Hartree-Fock solutions of the low-frequency Hamiltonian. Anelastic relaxation mechanisms are described and an elastic susceptibility expression is derived and compared with an observed elastic relaxation. The empirical connection of the hypothesised Jahn-Teller distorted metal cluster to the experimentally determined elastic dipole tensor is also discussed. Several experiments suggested by the model are proposed.

The authors use the bottleneck phenomena in YbAl₂:Gd and YbAl₂:Eu to extract the conduction electrons' spin-flip relaxation to the lattice, delta _eL^(O). The values observed are compared with those observed in the other dialuminides, XAl₂:Gd (X=Sc, Y, La, Lu). A correlation between delta _eL^(O) and the atomic number of the host X atom is clearly demonstrated, and is similar to that found by others for rare-earth beryllides. A simple model is suggested to explain this observed phenomenon. The ESSR isothermal limit of the R ion in YbAl₂ enables one to extract the dependence of the ion-conduction electron exchange coupling of the 4f occupation number. The authors' results shed some light on the nature of the Yb ions in YbAl₂ at low temperatures.

A new model of surface scattering in thin metal wires of circular cross section is developed based on Soffer's angular-dependent specularity parameter. It is shown how this approach yields much greater surface-induced deviations from Matthiessen's rule than Dingle's theory which has been used previously to interpret data on the resistivity of thin wires. The use of this latter theory has led to the conclusion that there are temperature-dependent variations in the parameter rho _infinity lambda _infinity . This new approach explains why this apparent variation has occurred and shows that for single values of rho _infinity lambda _infinity and surface roughness the data can be readily fitted to theory. Results for aluminium, platinum, indium and mercury are favourably compared with the present theory.

A theory is presented for surface magnetoplasmons in a metal film with a uniform magnetic field perpendicular to the surfaces. In the model, electrons from a free electron gas bounded by a pair of surfaces which are represented by an infinite potential barrier. Within the RPA, the authors work out the non-local response function, first ignoring quantum interference effects induced by the surfaces. A Ritchie-Marusak expression for the magnetoplasmon dispersion relation is derived, as first obtained by Horing and Yildiz (1973). The long-wavelength dispersion due to non-local effects is discussed both for a half-space and for very thin films. For the full infinite barrier model, they show how one can write the basic RPA integral equation for the density response function in a way in which the semiclassical RPA is the zeroth-order approximation. Generalising Beck's argument (1971) they prove that the local approximation for the long-wavelength surface magnetoplasmon is exact in the q/sub /// to O limit of the full infinite barrier model.

Calculations of the effect of electron-magnon interactions on the electronic structure of nickel are extended to nickel-iron alloys by varying the electron concentration. A realistic tight-binding d band is used and the Coulomb interaction parameter is fixed at the value determined for pure Ni. It is found that the strongly ferromagnetic state, in which the majority-spin d band is full, becomes unstable at about 50% Fe, thus explaining the observed deviation from the Slater-Pauling curve.

Magnetisation, AC and DC susceptibility measurements of the pseudobinary systems Y(Fe_1-xAl_x)₂ and Zr(Fe_1-xAl_x)₂ are reported. On substituting Al for Fe the transition from ferromagnetism to paramagnetism in Y(Fe_1-xAl_x)₂ is found to be dominated by freezing phenomena which are characteristic of a cluster-glass regime (0.1<x<0.35), while such freezing phenomena are not observed around the critical concentration for ferromagnetism (x_c=0.55) in Zr(Fe_1-xAl_x)₂. The analysis of the DC susceptibility data yields finite paramagnetic Curie temperatures and mu _eff values up to about 90% Al for Y(Fe,Al)₂, whereas for Zr(Fe,Al)₂ both mu _eff and theta exhibit the usual concentration dependence vanishing above x_c. From these results the authors deduce that the Fe moment can be regarded as more delocalised in the Zr system than in the Y pseudobinaries which may be attributed to a larger degree of hybridisation of the d electrons in the Zr compounds when compared with those of Y.

Specific heat, AC susceptibility and magnetisation measurements are reported for EuS_ySe_1-y samples. The samples are antiferromagnetic for y<or=0.075 and ferromagnetic for y>or=0.125. In the intermediate concentration range (0.075<y<0.125) mictomagnetism is observed. A magnetic phase diagram for EuS_ySe_1-y is derived and a model of the magnetic microstructure within the mictomagnetic regime is developed.

The magnetic and crystallographic properties of GdCu₂ and its ternary hydride GdCu₂H_x have been investigated. Upon hydrogen absorption the crystal structure of GdCu₂ changes from orthorhombic (CeCu₂-type) to tetragonal (MoSi₂-type), accompanied by a lattice expansion of 29%. The uncharged intermetallic compound GdCu₂ orders antiferromagnetically (T_N=37K). After H₂ absorption it becomes ferromagnetic (T_C=45K). There is a strong increase in the asymptotic Curie temperature (from theta _p=7K to theta _p=57K). Studies of the ¹⁵⁵Gd Mossbauer effect in the uncharged and charged compounds show that the H₂ absorption leads to an increase in isomer shift and in the absolute value of the hyperfine field at 4.2K. Both changes have been discussed in terms of a changing conduction electron concentration.

From measurements of the electrical resistance of CrMo alloys containing up to 5 at.%Fe, the authors have been able to give quantitative values for the coupling between the Fe moment and the spin density wave in Cr and CrMo. The results tend to confirm a proposal by Friedel and Hedman (1978) that single Fe moments are strongly coupled to the spin density wave. Estimates are also given of the change in the nesting of the Fermi surface with the addition of Fe.

An expression is derived for the thermopower in disordered ferromagnetic metals; it differs from the well known formula by Mott. The theory accounts for the unusual behaviour of the thermopower recently observed in amorphous ferromagnets.

Bulk Cu samples containing up to 4 at.% Kr have been produced by the Harwell combined ion implantation and sputtering method at temperatures near ambient, and then examined by the positron annihilation technique. Both angular correlation and lifetime measurements were made and, in addition, the specimen substructure was examined by transmission electron microscopy. The main results were a very large increase in angular correlation peak counts and a single measured positron lifetime of approximately 260 ps. The possible defects which might act as positron traps, and give rise to the observed changes, are discussed, with particular emphasis on the very high concentration of small Kr bubbles (approximately 1.5-3 nm in diameter) in the material.