Table of contents

ELS spectra of (100) and polycrystalline faces of Fe have been measured with 100 eV<or=E_p<or=1 keV. The characteristic features in the spectra are discussed in comparison with those found on Ni and Cu and are mainly interpreted on the basis of one-electron transitions from the Fe valence band to unoccupied states above E_F.

Electrical and magnetic properties of CeFe₂ were investigated from the temperature dependence of the electrical resistivity in the range 1.5-300K. The critical temperature, determined from the maximum of d rho /dT, gives T_c=220K and the temperature-independent magnetic resistivity is 87 mu Omega cm. This value is compared with the corresponding value in YFe₂. At low temperatures the resistivity shows a fairly large term proportional to AT² up to about 32K with A=1.2*10^-2 mu Omega cmK^-2.

A structural magnetoresistance, in which the presence of nonconducting particles in metals is essential, has been observed for a composite of indium and granular glass at 4.2K in magnetic fields up to 6 T. In the composite samples, glass beads about 0.2 mm in diameter were randomly distributed with the volume fraction (f) ranging from 0.027 to 0.133. The observed magnetoresistance is linear in magnetic field strength and grows high with increasing f. The Hall coefficient also increases in proportion to f.

It is shown that, in an isotropic three-dimensional spin glass with an axial anisotropy energy, three spin wave branches exist in the limit k to O. The two transverse branches have an identical gap in this limit while the longitudinal branch does not. The transverse branches are split by an external static field. Dispersion is initially quadratic for the transverse branches but linear for the longitudinal branch. For vanishingly small anisotropy all the branches are linear.

The results of magnetic measurements performed on (Gd_xY_1-x)Fe₃ compounds, in the temperature range 4.2K-1300K, are reported. The YFe₃ compound is ferromagnetic. Replacing Y by Gd, the iron magnetisation is oriented antiparallel to that of the gadolinium. The two magnetisations compensate at the composition x approximately=0.76. The thermal variation of reciprocal susceptibility for YFe₃ shows Curie-Weiss behaviour, while in the case of ferrimagnetic compounds this shows a non-linear dependence of the Neel type. The effective iron moments, as well as the exchange interactions inside and between sublattices, are determined. The composition dependence of the iron moments is due to the variations of the exchange field acting on these atoms.

Clustering of vacancies during annealing of plastically deformed aluminium is studied by means of positron annihilation.. Clusters are observed to form in spite of the presence of a large density of sinks for vacancies. The sinks, however, influence the annealing process.

Resistivity measurements were used to monitor the short-range ordering rates associated with equilibrium, quenched-in or irradiation-produced vacancies in an alpha -Cu-30 at.% Zn solid solution. The procedure by which the ordering kinetics are analysed is presented and discussed. The quench studies give activation energies of 0.64+or-0.05 eV, 1.03+or-0.05 eV and 1.59+or-0.05 eV for the migration and formation of single vacancies and the relevant self-diffusion, respectively. Radiation studies yielded a vacancy migration energy of 0.65 eV. Previous quenching work is reinterpreted in the light of these results and a consistent picture for the quench and irradiation-enhanced ordering effects is proposed.

Ultrasonic pulse-echo overlap measurements of the elastic moduli in the alloys Mn-6.5 at.%Fe, Cr-80.4 at.%Ni and Fe-14.5 at.%Ni-14.5 at.%Cr-2.5 at.%Mo were carried out between 300 and 600K. All of the moduli C, C' and B decreased linearly with increasing temperature in the Cr-Ni and Fe-Ni-Cr-Mo alloys. In the Mn-Fe alloy, C' underwent a rapid increase and B fell to a minimum near the Neel point at 496K while C was only slightly affected by magnetic order. The bulk modulus B is largest in the Cr-Ni alloy and smallest in the Mn-Fe alloy The shear modulus C' is smaller in the Fe-Ni-Cr-Mo alloy than in the other two cases. The anisotropy ratios are 3.918, 3.702 and 2.746 for the Mn-Fe, Fe-Ni-Cr-Mo and Cr-Ni alloys, respectively.

The composition dependence of the elastic moduli B, C and C' of FCC transition metal alloys is analysed by separating it into a contribution from the change in the atomic volume and an intrinsic contribution of the electron concentration X. When the volume contribution is taken into account, there are not great differences in the X dependence of B and C in different alloy systems. Differences in the intrinsic X dependence of C' in different alloys with X in the neighbourhood of 8.8. B is relatively insensitive to changes in X except in the regions X<7.7 and 8.6<X<8.9 where it decreases with decreasing X. The temperature dependence of all the moduli is also anomalous in these regions of X.

Reports a theoretical calculation of the lattice dynamics of the HCP metal zirconium. The Coulombic ion-ion interaction contribution to the dynamical matrix is calculated by the standard Ewald (1921) and Keller (1940) method, while for the electronic or bandstructure contribution a transition metal model potential of the Heine-Abarenkov type has been used. The effect of s-d hybridisation has been incorporated in this calculation through the renormalisation of the s state well-depth, while for the electron screening, the self-consistent dielectric screening due to Hubbard et al.. (1958) has been used. Phonon dispersion relations obtained along the symmetry directions compare reasonably well with the existing experimental results.

Mode Gruneisen parameters ( gamma _i) of transverse optic phonons, and a few selected acoustic phonons, have been measured by inelastic neutron scattering in PdD_0.71. The results show gamma _i for the optic modes between 3 and 6, which are somewhat higher values than those reported previously in the literature. Using the present results the authors have calculated d ln T_c/dP by the McMillan (1968) and Kakitani (1969) formulae and a reasonable agreement with experimentally measured values has been reached. They therefore conclude that d ln T_c/dP is dominated by the Gruneisen parameter of the optic modes.

A method of obtaining a local bare-electron-ion pseudopotential from the phonon dispersion curves is proposed. The major assumption made is that the bare-electron-ion plus the ion-ion interactions can be represented by short-range two-body force constants. This allows the coefficients of any appropriate series expansion for the bare-electron-ion potential to be found in terms of the force constants, the values of which are then determined by a least-squares fit to the phonon dispersion curves. It is hoped that this method can reproduce the phonon dispersion curves more accurately, using fewer parameters than current methods. It may also be used to reveal whether different formulations of the dielectric function are correct, and the pseudopotential may enable accurate calculations of other material properties. The preliminary application, reproducing the phonon dispersion curves of potassium, is presented and is found to be quite encouraging.

A unified approach, able to take into account the martensitic phase transition onset in binary alloys of transition metals as well as the connected role and influence of ternary additions to the alloy, is presented. The electronic mechanism on which the transition is based is strongly dependent on the electron-phonon coupling in such metals. The concept of electronic behaviour which is donor-like and acceptor-like is tested for the nearly equiatomic shape memory NiTi alloy, leading to very good agreement with the available experimental data.

A density functional pseudopotential method is used to calculate the heat of formation of disordered alkali metal-alkali metal solid alloys, as a function of the concentration. In modelling the alloy crystal potential a modified virtual crystal approximation is used, which makes the alloy calculations formally identical to pure metal calculations. The results agree with the experiments and with other theoretical calculations.

The authors investigate the structural as well as some of the thermodynamic properties of the heavy alkali metals, namely K, Rb and Cs by using the local transition metal pseudopotential. The BCC structure is found to have the lowest energy for all of these alkali metals. By employing the Einstein model to account for the lattice vibrations and using the Gibbs-Bogoliubov inequality they calculate the Helmholtz free energy, internal energy, entropy and Einstein temperature for these metals. The roles of the various structural contributions and the effects of lattice vibrations in predicting crystal structure are also investigated.

The asymptotic behaviour of the recursion coefficients is studied. It is shown that the inclusion of tight-binding interactions between second nearest neighbours in ordered binary systems produced undamped asymptotic oscillations of the recursion coefficients. A method for testing continued fractions with this sort of behaviour of the coefficients is presented and tested for the case of the binary chain of the s orbitals. The resulting local densities of states consist of two bands with different widths. The formalism is applied to intermetallic compounds with B2 (CsCl) structure. Local partial densities of states are given for bulk TiFe and CuZn. The local partial densities of states are good approximations for X-ray L spectra, although only d orbitals have been included.

In the present multi-band CPA calculation, the spin-dependent potential is treated in the Hartree-Fock (HF) approximation. The host (Ni) parameters are chosen self-consistently. Various solutions are discussed depending upon the choice of the Ru parameters and the solution which is consistent with the experimental situation and also satisfies energy considerations is accepted. Its salient features are fairly sharp impurity virtual bound states around E_F for low Ru concentration. The variation of the site moment, and the Ru concentration at which the transition to the paramagnetic state occurs, are in accord with magnetisation data. However, the predicted variation of the site moment asphericity with Ru concentration for very low Ru disagrees with polarised neutron data. A possible reason for this discrepancy is discussed. Finally, the authors conclude that the CPA, like any other mean field theory, is able to predict broadly the observed features in an NiRu system which is characterised by strong local environmental effects.

The possibility of obtaining the true energy dependence of the parameter lambda ₁ of the Animalu pseudopotential (1966) for the spin-orbit interaction, based upon the experimental data for the conduction-electron spin scattering due to dislocations is shown. Such a dependence for copper, where energy levels are disturbed by configurational interaction, is reconstructed.

The electrical resistivity arising from electron-electron scattering in a model one-dimensional metal is calculated using the standard variational method for solving the Boltzmann equation,. A linear temperature dependence is obtained for the two-band case considered. The magnitude of the linear term is compared with experimental values for highly conducting organic salts of the TTF-TCNQ family.

Calculations of the electrical resistivity of liquid Fe, Co, Ni and Cu are reported using the single-site t matrix approximation. Inclusion of mean free path corrections to the resistivity integral in modified Ziman theory are shown to reduce the resistivity substantially for those liquid metals with very short mean free paths. An assessment is made of the relative importance of multiple scattering corrections to the single-site approximation for these liquid metals.

The effects of co-existing atomic and magnetic clustering on electrical resistivity are considered. It is shown that in Cu-Ni alloys such clustering produces competing effects and that while atomic clustering dominates the behaviour in alloys containing more than about 25% Ni, the magnetic clustering effects are predominant in lower Ni content alloys. The results in a resistivity which decreases with increased clustering in alloys with more than 25% Ni but which increases with clustering at lower Ni contents. This change in behaviour results from the non-linear dependence of the magnetic moments of the Ni-rich clusters upon composition and degree of clustering, which is due in turn to the dependence of the magnetic state of the Ni atoms upon their near-neighbour environment.

The transport properties of disordered concentrated ferromagnetic NiT alloys, with T=Cr, Fe, Co or Cu, are analysed at low temperatures within the framework of the two-current model. A theoretical expression for the spontaneous resistivity anisotropy is derived using the method of the force-force correlation functions. Starting from the two-current formula for the electrical resistivity the sub-band resistivities rho spin up and rho spin down are calculated approximately. The results are compared with CPA calculations.

The authors give a qualitative interpretation of the field and temperature dependences of the electrical resistivity, the Hall effect and transverse magnetoresistance of the ferromagnetic alloy Ni₂MnSn. The experiments cover the ranges 4-400K and 0-47*10⁵ A m^-1, with supporting measurements of the magnetisation in the range 4-490K. The results are interpreted in terms of conduction by s-p electrons that are scattered by the spin system and by a resonant s-d-s mechanism at the Mn ions. The results show the different manifestations in the galvanomagnetic effects of magnon scattering, spin-disorder scattering, spin-orbit coupling and the freezing out of spin-flip processes.

The thermoelectric power of dilute CuNi alloys, and of two sets of ternary alloys CuNiGe and CuAuGe, has been measured at room temperature and also at low temperatures (1-9K). Since these particular ternary alloys have been shown to scatter conduction electrons isotropically, the object of the work has been to investigate the influence of scattering anisotropy on the Nordheim-Gorter rule. The unexpected result of the work is the absence of deviations from the Nordheim-Gorter rule not only in CuNiGe as anticipated, but also in CuNi.

A low-temperature magnetoresistance of CeAl₃ is discussed using a model in which the potential scattering at Ce sites leads to a virtual bound state beow epsilon _F and the scattering on the 4f magnetic fluctuations gives rise to a narrow Kondo resonance at epsilon _F. Positive magnetoresistance is predicted in the zero-temperature limit while it decreases with the increase of temperature and changes sign at T approximately=T_K/2 pi . The minimum magnetoresistance is reached at about T-T_K/2.

From low-field magnetisation measurements the authors give evidence for the existence of helimagnetism in magnetically ordered Fe_xCo_1-xSi alloys. They report small-angle neutron scattering experiments on two samples which are confirmed to be helimagnetic with a helix long period of 430 AA for Fe_0.9Co_0.1Si and 295 AA for Fe_0.8Co_0.2Si.

Magnetic properties as well as hyperfine interactions in Ti(Fe, -xCo,) and some of its hydrides have been studied. With the concept of antistructure (AS) atoms proposed recently by Brommer et al. the two critical concentrations at x = 0.25 and x = 0.65, the correlation between the iron hyperfine field and the bulk magnetisation and concentration dependence of the magnetisation can be explained consistently. A hyperfine pattern with a field of 23.5 T (corresponding to the proposed value of 1.5 pR) presents direct experimental evidence for the presence of iron AS atoms. These, together with an increasing N (E F ) as the cobalt concentration grows. are supposed to influence the onset of long-range magnetic order. Furthermore i t is suggested that, upon hydrogen absorption, additional AS atoms are created, and it is these, rather than the surface segregations which are responsible for the change in the bulk magnetic properties of the 2 phase Ti(Fe,Co) hydrides.

Both the coherent and incoherent scattering of polarised neutrons were measured for a single crystal of the Fe_0.70Ni_0.30 alloy in the FCC phase. The interest in this alloy comes from the fact that its magnetic moment falls far below the Slater-Pauling curve. A deformation of the spherical part of the form factor was observed. The values of the total magnetic moment, of the spherical magnetic moment (as deduced from the coherent scattering), of the local magnetic moments, and of the variance of the magnetic moment (these two quantities being deduced from the incoherent scattering), all fit together in a model in which the Fe atoms have two different magnetic moments, one large and positive, 2.7 mu _B, and the other small and negative, -0.4 mu _B. The model appears well able to reproduce the experimental results and the general trend of the concentration dependence of the total and aspherical magnetic moments as obtained by different experiments.

Reports measurements of the dynamic response, chi '( omega ), for AuFe alloys. It is shown that this experiment can indicate the infinite percolation cluster concentration C_p. The thermal critical behaviour of the zero field chi '( omega ) in alloys containing an infinite cluster is discussed in terms of the cross-over from isotropic short-range exchange-dominated to dipolar-dominated behaviour, although renormalisation of the critical exponents is necessary. Coexistence of finite clusters with the infinite cluster is also confirmed; the freezing temperature of these finite clusters well below T_c shows up very clearly in the simple magnetic response experiments. (These effects should not be associated with a phase transition from a ferromagnetic to a spin-glass regime.) For alloys below the percolation threshold the fluctuations within very large clusters of highly correlated spins are essentially quasi-critical and very similar to those in alloys containing an infinite cluster. The critical temperature T_c of the percolation cluster, however, was found to be finite and non-zero, suggesting a possible modification of the pure percolation processes by the long-range RKKY interactions between clusters.