Table of contents

Thermal volume expansion data for liquid T, V, Mo, Pd and W in the temperature range from melting to boiling are presented. The data were obtained by a fast resistive pulse heating method based on heating wire-shaped samples in an RCL discharge circuit and simultaneously determining the enthalpy, temperature and volume of the sample. The results are compared with data from literature and good agreement is found.

The authors report measurements of the electrical resistance of aluminium in the temperature range 30-40 degrees C and the pressure range 0.2-1.0 GPa. From these experiments the pressure dependence of the electron-photon interaction lambda is evaluated. With p in GPa the result is lambda (p)= lambda ₀ exp(-0.0467p+4.7*10^-4 p²). This expression for lambda describes accurately the observed pressure dependence of the superconducting T_c for pressures up to about 4 GPa.

In some spin glasses, notably AuFe, the magnetisation and remanent moment below the spin glass temperature, T_f, are time-dependent of the magnetisation is observed in fields smaller than about 100 Oe, in contrast to present spin glass theories which predict slow relaxation below T_f. A possible explanation is that a threshold field exists below which relaxation is too rapid to observe on the usual laboratory time scales.

The pressure dependence of the hyperfine field at ¹¹⁹Sn nuclei in hexagonal and FCC cobalt has been measured in the pressure range 0-60 kbar, and is found to be dH/dp=-0.39+or-0.08 and -0.26+or-0.05 kOe kbar^-1 respectively. These values are discussed in the light of the two component model of Delyagin and Kronienko (1970).

The electronic structures of ordered and disordered transition metal alloys are described in a tight-binding scheme. Charge transfer and magnetism are treated within a self-consistent Hartree-Fock model. The authors show that the rigid band splitting fails to take account of the ferromagnetism of these compounds. The densities of states of FeCo and Ni₃Fe are found to be more sensitive to order than the ferromagnetic properties. Energetic calculations are performed giving an estimation of the ordering energy, and comparisons are made with experimental results.

Starting from electronic symmetrised APW wavefunctions the author derives the expression of the direct coulombic contribution of the conduction electrons to the crystalline electric field in cubic rare earth intermetallics, taking into account the exact symmetry of the conduction band. Numerical results are deduced for the compounds DyRh, DyCu, DyZn, LaAg and YMg.

For pt.I, see ibid., vol.9, no.9, p.1745 (1979). Starting from the many-electron angular 4f wave functions the author performed a numerical calculation of the exchange coulombic contribution of the conduction electrons to the crystalline electric field in cubic rare earth intermetallics. The results are applied to the compounds DyRh, DyCu, DyZn, LaAg and YMg. The exchange contribution to the sixth-order CEF parameters arising from the f character of the conduction band is found to be one order of magnitude larger than the direct contribution.

The electronic structures of alpha (HCP, atmospheric pressure) and omega (simple hexagonal, high-pressure) phases of Ti andZr have been calculated using the nonrelativistic APW method. The discriminating features of the bandstructure of the omega phase as compared to the alpha -phase are the reduced s-d spacing, a broad d band without sharp resonances and the location of the Fermi level. In the case of the alpha phase the Fermi level lies in a valley, while in the case of the omega phase it lies near the centre of a broad maximum. Comparison of the theoretical electronic structures is also made with empirical bonding models of the omega phase. AnESCA (XPS) study of the alpha and omega samples shows the principal features of the d band and location of the Fermi level in agreement with the theoretical predictions, though the XPS patterns are inescapably affected by surface oxygen contamination.

The temperature dependence of radio frequency size effect (RFSE) signals was observed in aluminium using both the parallel and tilted field geometries. Electron-phonon collision frequencies were obtained for electrons on different regions of the Fermi surface and the results compared with those obtained from surface Landau level (SLL) experiments and also from theoretical calculations. Collision frequencies were obtained from orbits near the (100) and (111) limiting points of the second zone hole surface and also from orbits around the central (100) section of the zone hole surface and the (100), (111) and (110) sections of the third zone electron surface.

The authors study the HCP ( epsilon phase) alloys of Fe with Ru and Os, containing 15 and 30 at.% of the alloying element, using ⁵⁷Fe Mossbauer absorption spectroscopy. The existence of antiferromagnetism in the Fe-Ru and probably the Fe_0.85 Os_0.15 alloys was indicated. The saturated hyperfine fields and Neel temperatures for the 15 and 30 at. Ru and 15 at.% Os alloys were 15 kG and 210K, 13 kG and 60K, 3.3 kG and 30K, respectively, orientated at 50+or-10 degrees to the nuclear EFG; the latter showed a slight negative temperature gradient and was deduced to be probably negative in sign. The alloy Fe_0.7 Os_0.3 showed no sign of magnetism, at any temperature. The magnitude of the EFGs was consistent with the quantity and size of the solute atoms, and extrapolated to the experimentally observed value for pure HCP Fe. Extrapolations of the hyperfine fields and Neel temperatures to pure epsilon -Fe yielded 17 kG and 360K, respectively, consistent with a theoretical, physically unrealisable, 'negative pressure' HCP phase.

The temperature dependences of the Doppler-broadening lineshape parameter W and the positron lifetime have been measured for positron annihilation taking place in Au in the prevacancy temperature range 27K to 592K. The results are consistent with a linear temperature dependence of these annihilation parameters. It is suggested that this observation represents correctly the intrinsic behaviour of the positron in the Au lattice. The results are compared with earlier work over similar temperature ranges, which has shown additional contributions to these annihilation characteristics.

Amorphous SnAu alloys are produced by quench condensation from the vapour phase on substrates held at 77K or lower temperature in ultra-high vacuum. It is shown that film thickness and thermal expansion of the substrate have only a minor influence upon the electrical resistivity, so that bulk properties of the amorphous state are measured. The electrical resistivity of amorphous SnAu has a negative temperature coefficient within the stability region from 15 to 80 at.% Au at temperatures higher than about 16K. With respect to concentration the electrical resistivity and the negative temperature coefficient show a maximum near 50 at.%. Compared with liquid SnAu the resistivity of amorphous SnAu alloys can be considered as the low-temperature limit of the hypothetical supercooled liquid. The transition temperature of superconductivity and the temperature of the amorphous-crystalline transformation are given.

The magnetoresistance of a large single crystal sphere of high purity aluminium was investigated at 4.2K in fields up to 5 T using two electrodeless methods, eddy current decay and soft helicons. Both methods confirmed that the transverse magnetoresistance is an oscillatory function of field at directions close to (100); at other orientations in (100) planes it increased at a rate faster than linear. This is discussed in terms of magnetic breakdown. Observation in certain orientations of oscillatory magnetoresistance with soft helicons, but not with eddy current decay, might be interpreted as indicating a strongly oscillatory longitudinal magnetoresistance in contrast to direct measurements which have revealed no oscillations. The theory used implies that the de Haas-van Alphen effect, which influences both real and imaginary parts of the helicon frequency, should do so in a way that cancels when the resistance is calculated, and careful analysis of disturbing mechanisms does not upset this conclusion.

A path integral calculation of the Hall coefficient R_H of Al using the currently accepted ratio of the third-zone/second-zone relaxation times shows that the third-zone states makes no appreciable contribution to R_H in the low-field condition. To match experimental results, an anisotropic relaxation time tau _h(k) on the second-zone surface has to be introduced. This is deduced for various scattering centres in Al, including Mn and Cr from new measurements. Cr and Mn are found to be the most interstitially localised scattering centres yet found in Al. Some possible explanations are considered.

The high-temperature perturbative expansions for the thermal quantities of a type II superconducting film are extrapolated to the critical region near H_c2 by means of new rational approximants of the Pade type. The new approximants are forced to reproduce the leading correction to the flux lattice contribution on the low-temperature side of the transition. Compared to those previously considered in the literature: (i) the mutual consistency of the approximants is improved: and (ii) they are nearer to the exact solution of the zero-dimensional Landau-Ginsburg model.

Bulk magnetisation and polarised neutron elastic diffuse scattering measurements in the scattering vector range 0.2 AA^-1<or=k<or=2 AA^-1 have been performed on two ferromagnetic nickel-ruthenium alloys with 1.7 and 2.7 at.% of Ru. Analysis of the room temperature data shows that the Ru atoms carry a positive magnetic moment which increases from 0.21(20) mu _B to 0.65(13) mu _B for the alloy with higher impurity concentration. The nickel moment decreases linearly by about 4.4 mu _B for every additional 1 at.% of ruthenium. The scattering k vector dependence of the difference of differential cross sections for neutron spin polarisation parallel and antiparallel to the sample magnetisation indicates the existence of extended moment disturbances produced by Ru impurities on their neighbours in the nickel lattice. These exhibit a kind of oscillating behaviour passing from one shell of atoms to another with a large negative value on the second nearest neighbours, and is more important for the alloy with lower impurity concentration.

The change c Delta chi in the magnetic susceptibility of monovalent metals due to a concentration c of substitutional impurities is theoretically investigated, for the limit c to 0. The free-electron gas model is used. It is shown that there are divergences in the expressions for Delta chi due to the Friedel oscillations. These divergences have no physical effects and a procedure for overcoming the calculational problems is developed. Realistic impurity potentials are used to calculate Delta chi using this procedure. The results for Cd and In impurities in sodium are in agreement with experiment; the results for impurities in copper are not, and the reasons for this are analysed.

For pt.I see ibid., vol.9, no.9, p.187 (1979). Theoretical and experimental evidence about the susceptibilities of pure and dilute alloys of noble metals is analysed, and shows that the reason for the large diamagnetic increase when impurities are added to copper is the change in the solvent's Fermi surface. This change can be deduced from a knowledge of the bandstructure of the pure metal, using the rigid-band model. These changes, and the resulting changes in magnetic susceptibility, are calculated using the eight-cone model for the Fermi surface. The results for copper as solvent show remarkable agreement with experiment, especially when dilation of the lattice is taken into account. The validity of the calculations is discussed.

The magnetic properties of the pseudobinary Zr(Fe_1-xCo_x)₂ system were studied by magnetic, Mossbauer and low-temperature specific heat measurements. ZrFe₂ is a strong ferromagnet, whereas ZrCo₂ shows Pauli paramagnetism. Both the spontaneous magnetisation and the Curie temperature decrease with increasing Co content and the system becomes a weak ferromagnet for x=0.3 and 0.4, where remarkable Invar anomalies are observed. In x=0.5 approximately 0.7, the system shows micromagnetism. No spin freezing has been detected down to 4.2K for x-0.8 approximately 1.0. It has been shown that ferromagnetism is markedly enhanced by excess Fe and Co atoms which occupy Zr sites.

For pt.II see ibid., vol.8, p.2389 (1978). The intermetallic compound Fe₃Sn₂ has been studied by ¹¹⁹Sn Mossbauer spectroscopy between 5 and 670K. Between approximately 60 and 250K the spins rotate from the basal plane to the c axis; a fraction alpha (T) of the spins remain in the basal plane while the remainder rotate continuously, in agreement with previous ⁵⁷Fe Mossbauer and neutron diffraction experiments. The Sn(1) hyperfine field decreases more rapidly than the magnetisation does, while the Sn(2) hyperfine field increases from about 0.7 to about 2.4 T between 5 and 540K. These anomalous temperature dependences are attributed to the influence of thermal expansion and lattice vibrations of the transferred hyperfine fields.