Table of contents

Using a conventional d.c. Technique sondheimer oscillations in the magnetoresistivity of single crystals of zone refined aluminium have been studied with the magnetic field oriented close to the (111) direction. The observed oscillations are interpreted as type ii oscillations according to the gurevich (1958) theory and shown to be in a good agreement with theoretical predictions based upon the known second zone fermi surface of aluminium.

An investigation is presented of the conditions for spin glass or ferromagnetic ordering in systems with exchange interactions distributed randomly about a positive mean, using a quantum extension of a recent method of edwards and anderson (see ibid., vol.5, no.5 p.965, (1975)). The results are related to the situation relevant to a metallic magnetic alloy where they lead to a phase diagram and susceptibility cusp in good accord with experiment.

The Mossbauer spectroscopic study on some concentrated iron-chromium alloys Fe_xCr_1-x (with 0.2 < x < 0.3) gives evidence for the occurrence of a superparamagnetic state, which accounts for the typical transport and magnetic properties observed in these alloys.

The giant moment in a dilute PdMn (0.23 at% ) alloy has been investigated in the paramagnetic phase at a temperature of 1.4k by means of diffuse neutron scattering. A very high peak in the forward direction was observed, corresponding to a total moment which is much larger than that obtained from magnetization measurements. An explanation based on a distribution of effective g values of the giant moments is discussed, as well as possible critical effects. A comparison is made with earlier experiments on PdFe and PdCo alloys.

Intermediate states of arbitrary numbers of electron-hole pairs are included in the suhl equations for the Kondo effect. First approximations for the resistance yield reasonable agreement between experiment and theory, even for impurity spin s=³/₂. Resistance and static susceptibility are universal functions of T/T_k for small temperature T and some renormalized Kondo temperature T_k.

Measurements of the transport properties of ni-based alloys show deviations from the expectations of a two current conduction model when the impurity concentration is low. The deviations can be accounted for by introducing a zero temperature spin-mixing rate.

The electrical resistivity and thermopower has been measured of pure calcium, strontium and barium from room temperature to near their melting points. From discontinuities observed in these parameters as functions of temperature, the phase transition is placed, from fcc to bcc in calcium at T_c=428 +or- 2 degrees C, and that in strontium at T_c=542 +or- 2 degrees C, both at ambient pressure. No sharp discontinuity is seen in either rho(T) or s(T) for barium; s(T), however, does show a broad maximum for this metal. The data on T_c is compared with recent pseudopotential calculations.

Unique hyperfine fields of -13.2T, -2.50T and +9.1T have been observed at ⁴⁴Sc nuclei in iron, nickel and GdFe₂ respectively, using time differential perturbed angular correlation.

New measurements of the main nik emission lines are presented for nickel-aluminium alloys with up to 50 at% al. The shifts of the nikalpha/sub 1/ line of the alloys are found to be negative with respect to pure nickel, contrary to previous measurements by nemoshkalenko et al. (see abstr. A41614 of 1971). In addition to a possible charge transfer between the constituent atoms, the importance of the crystallographic phase and order is emphasized in the interpretation of the spectra. Complete filling of the d band in the nial compound is not supported by the results.

Using pseudopotential theory many electron correlation effects have been investigated on the energetics of single vacancies in the simple metals, sodium and aluminum. For each metal the effective interionic potential was generated by using the nonlocal optimized model pseudopotential of shaw (1968-70) and the recent selfconsistent treatment of electron correlations in electron liquid by vashishta and singwi (1972). Many electron correlation effects have been demonstrated by considering three other dielectric functions, and the effects of locality by taking two local potentials, screened with the new dielectric function.

The epitaxial growth of nickel and copper (111) silver has been investigated in ultra high vacuum using LEED, RHEED and Auger spectroscopy. At 570K island growth is observed in both cases, but with substrates close to room temperature more extensive flat deposits are formed. On heating, these deposits are found to draw up into more pronounced three dimensional islands. These results are shown to be consistent with surface energy and diffusion data. Some comments on the relative merits of the three analysis techniques are also presented.

In the tight binding theory of transition metals, the d band arises out of the interatomic matrix elements (phi_d?v?phi_{d minutes} ). In the resonance theory of transition metals, on the other hand, the d band is described in terms of the intra-atomic resonance parameters of the potential v. The equivalence of these two seemingly different points of view is demonstrated by deriving general analytic expressions for (phi_d?v?phi_{d minutes} ) in terms of the position and width of the resonance of v and the tail of the localized d state phi_d(r). The derivation is accomplished by expanding the d state centred on one site in terms of spherical harmonics centred on the second site and then approximating the surviving l=2 expansion coefficient. The accuracy of this procedure is verified in detail for the metals copper and iron. For special forms of the tail of phi_d(r), the general expressions can also reproduce the corresponding results obtained by pettifor via the kkr band structure equations.

The band structure in the monoclinic beta phase of gallium has been calculated by the pseudopotential method. Good agreement between predicted and experimentally observed peaks in the optical spectrum was obtained by using the atomic form factors for gallium calculated by Appapillai and Williams (see abstr. A36507 of 1973).

The electrical resistivity of liquid Ba has been measured. The value obtained at the melting point is 314+or-12 mu Omega cm and is therefore one of the largest for liquid metals. The temperature coefficient of the electrical resistivity is negative as is characteristic for liquid Zn. BaO impurities do not greatly influence the electrical resistivity in the liquid state.

The idea of formation of chemical complexes in compound forming molten systems, previously used to study the thermodynamic properties, is applied to the electronic transport in these systems. Concentration dependence of various transport coefficients as well as their temperature dependence in Mg-Bi and Tl-Te liquid alloys is investigated and the agreement with experimental data, where available, is good.

It is systematically demonstrated that data reported in the literature for f.c.c. And b.c.c. Metals obey the linear relationship rho=rho₀+c minutes epsilon between dislocation density and plastic strain at small strains. It is further shown that for hcp metals the situation is less clear.

Measurements on radio frequency size effect signals at multiple fields in Cd and Zn are reported. In these metals the temperature dependence is in good agreement with the predicted behaviour. Previous measurements in k, however, indicate a different temperature dependence.

The variation of the superconducting transition temperature T_c for bcc solid solution alloys in the system Zr-Nb-Mo-Re has been investigated as a function of hydrostatic pressure up to 25 kbar. Values of delta T_c/delta p calculated from the theoretical model of garland and bennemann are compared with those measured, which are both positive and negative in sign. Quite satisfactory agreement with the overall trend of delta T_c/delta p with composition can be obtained for a reasonable choice of the physical parameters required, though differences in detail are apparent.

A high resolution magneto-optic method employing EuS:EuF₂ films has been used to observe directly the dynamic intermediate state induced by the passage of an electric current or a heat current through thin slabs of the superconductors Pb, In and Sn. The observed flux flow velocities have been compared with and show reasonably good agreement with recent theoretical work by Andreev and Dzhikaev, if allowance is made for the effects of pinning. A detailed examination has been made of the region close to the critical current in the electric current induced motion. In the case of the thermally induced motion the existence of two competing mechanisms driving flux, as was recently suggested by Laeng and Rinderer, has been confirmed. Comparison has been made with theoretical models, again with some agreement and some disagreement.

An apw calculation has been made giving the 4f band energies in h.c.p. Tm metal for four high symmetry values of k. Crystal field parameters are determined and compared with experimental results for dilute systems. It is then argued that this type of parametrication is inadequate for pure rare earth metals and should be replaced by a model in which the hybridization matrix elements between the 4f and conduction band are parameters.

Raman scattering in a reflection experiment is discussed. It is assumed that coupling to spin flip excitations occurs due to spin-orbit coupling, as in an insulator. Within the tight binding approximation, the polarization selection rules contain one term from single site processes which has the same form as in an insulator, and one from neighbouring site processes which may be different. If the first term is dominant, the vertex coupling the excitations to the incident and scattered light is only weakly momentum dependent and scattering by the stoner excitations is much weaker than magnon scattering. The magnon line is broadened because of the finite skin depth of light in the specimen; for nickel this broadening is greater than the intrinsic linewidth as observed in ferromagnetic resonance experiments.

A new theory of the class of dilute magnetic alloys, called the spin glasses, is proposed which offers a simple explanation of the cusp found experimentally in the susceptibility. The argument is that because the interaction between the spins dissolved in the matrix oscillates in sign according to distance, there will be no mean ferro- or antiferromagnetism, but there will be a ground state with the spins aligned in definite directions, even if these directions appear to be at random. At the critical temperature the existence of these preferred directions affects the orientation of the spins, leading to a cusp in the susceptibility. This cusp is smoothed by an external field. Although the behaviour at low t needs a quantum mechanical treatment, it is interesting to complete the classical calculations down to t=0. Classically the susceptibility tends to a constant value at t=0, and the specific heat to a constant value.

A theory is presented for the study of the local environment effects on the magnetic properties in transitional binary alloys; the local environment effects are taken into account for the calculation of the one electron properties by an extension of the cpa and the electron-electron interactions are taken into account in the random phase approximation.

Numerical results are presented from the study of local environment effects on the magnetic properties of atoms in simple models corresponding to the three typical alloys rh-ni, rh-pd and cu-ni. It is shown that (i) the dependence of the susceptibilities upon concentration and environment, (ii) the importance of the selfconsistent calculation of the charge transfers and the energy levels, (iii) the connection between the relative position of the energy levels and the relative magnitude of the susceptibilities, and (iv) that the susceptibility of the central atom is mainly determined by the electron-electron interactions on the central atom for rh-ni and rh-pd but that in cu-ni atoms further than the first neighbours need to be considered.

A general theory of indirect exchange interaction in a disordered magnet is given by the use of a one electron green function. For a model green function an exact expression of the effective indirect interaction is obtained and evaluated numerically for some degrees of disorder.

Magnetic data are presented for rhco alloys with cobalt concentrations in the range 28 to 44 at.% and over temperatures ranging from 1.6 to 300k. At low concentrations the system has been previously described as an enhanced band paramagnet, however it is found that local moments are stabilized in alloys having cobalt concentrations below the critical level for long range ferromagnetism, and it is the local moments which are the dominating influence in the initial stages of magnetic order. Two stages of order are distinguished in those samples which contain local moments. Alloys with concentrations up to 42% have magnetic characteristics commonly associated with spin glasses. There are indications that samples with concentrations in excess of about 36% are ferromagnetic at low temperatures. The magnetic properties are distinctly different at 44% , possibly as a result of a change in crystal structure.

Crystallographic and magnetic properties of a range of pseudobinary (FeNi)Pt alloys based on the equiatomic binary alloy CoPt have been investigated and the results have been combined with those of previously reported investigations on (CoFe)Pt and (CoNi)Pt alloys. X-ray crystallographic investigations show that the alloys exhibit the disorder-order transformation found for CoPt. Measurements of Curie temperatures and magnetic hysteresis parameters show that substitutions for cobalt in the simple CoPt alloy adversely affect the magnetic hardness of the alloy.

Explicit expressions are derived for the energy levels of a nucleus in the presence of a strong magnetic field and a small quadrupole interaction. The case of a spin ³/₂ nucleus is considered in some detail and certain inequalities between the various zeeman energy level spacings are derived. These inequalities are used to show that computer programs which adjust the energy level separations in a least squares fit to ⁵⁷Fe mossbauer spectra can lead to unphysical results. Special reference is made to the (rare earth)Fe₃ intermetallic compounds.

See also ibid., vol.5, no.5, p.1037 (1975). The methods described in the previous paper are used to analyse the complicated ⁵⁷fe mossbauer spectra of the (re)fe₃ intermetallic compounds, where re=gd, tb, dy, ho, er and y. The resultant hyperfine parameters are then used, in conjunction with local dipolar field calculations, to infer directions of preferred magnetization. In particular, it is shown that at 77k, hofe₃ magnetizes along an a axis, tbfe₃ along a b axis and erfe₃ either along or close to a c axis. The case of dyfe₃ however is slightly more complex and it appears that this compound does not magnetize along a principal hexagonal axis. Some similarities between the mossbauer spectra of the (re)fe₂ and (re)fe₃ compounds are also noted.

The linewidth anisotropies of the resonances associated with a gamma₈ quadruplet in a metal are calculated. The broadening mechanism is assumed to be the exchange scattering of conduction electrons from the impurity spin. Results are obtained for magnetic fields in the (001), (111) and (101) directions. Comparison with recent experimental results of devine et al. (1972) on pd-er shows good agreement for the most intense (and anisotropic) transition, but also indicates that some other broadening mechanism (e.g. Strain) must be present for transitions which do not occur between kramers conjugate pairs.

The pressure dependence of the quadrupole interaction in beta gallium has been measured. The effect is linear to pressures of 240 mn m^-2 and (deltanu_q/deltap)_t has the value of 0.285 khz(mn m^-2). The temperature and pressure effects for beta gallium are compared with the corresponding values for other known metals.