Showing papers in "Journal of Physics F: Metal Physics in 1972"
TL;DR: In this paper, a mechanism with positive f-d exchange and direct d-d interactions is proposed and is shown to give satisfactory agreement with experiment. But it is suggested that the RKKY form of indirect interaction for rare earths in metals cannot adequately explain the experimental results.
Abstract: It is suggested that the RKKY form of indirect interaction for rare earths in metals cannot adequately explain the experimental results. A mechanism with positive f-d exchange and direct d-d interactions is proposed and is shown to give satisfactory agreement with experiment.
380 citations
TL;DR: In this paper, the melting points of lead and indium were found to decrease with diminishing size in both cases; in the case of lead the melting point was depressed by about 200K for particles of 3nm radius.
Abstract: Experiments have been carried out on the melting of particles of lead and indium in the size range 3 to 50 nm. Electron diffraction patterns were used to determine melting points and electron micrographs were used to determine the size of the particles. The melting points were found to decrease with diminishing size in both cases; in the case of lead the melting point was depressed by about 200K for particles of 3nm radius.
204 citations
TL;DR: In this article, a simple nearly free electron model for the electrical resistivity of liquid noble and transition metals and their alloys is presented, where the scattering is described in terms of the phase shifts of muffin tin potentials constructed for the liquids.
Abstract: A simple nearly free electron model for the electrical resistivity of liquid noble and transition metals and their alloys is presented. The scattering is described in terms of the phase shifts of muffin tin potentials constructed for the liquids.
198 citations
TL;DR: In this paper, the magnetic properties of these phases are discussed in relation to crystal field effects and a possible band structure.Magnetic measurements from 1.5 to 300 K on the complete series of Cu3Au-type R Pd3 phases have been made.
Abstract: Magnetic measurements from 1.5 to 300 K on the complete series of Cu3Au-type R Pd3 phases have been made. LaPd3 and LuPd3 are diamagnetic at room temperature. CePd3 shows Pauli-type paramagnetism indicative of a nonmagnetic virtual bound state. PrPd3 and NdPd3 are affected at low temperatures by the presence of the crystal field. The magnetic properties of SmPd3 and EuPd3 are determined by the energy levels of the lowest multiplet. GdPd3 and (possibly) TbPd3 become antiferromagnetic at 7.5 and 2.5 K respectively. DyPd3-ErPd3 obey the Curie law. The magnetic properties of these phases are discussed in relation to crystal field effects and a possible band structure.
122 citations
TL;DR: In this article, the magnetic susceptibility of PdH and PdD alloys over the temperature range between 4K and 300K was measured with a series of specimens with composition ranging from 0.0 to 0.7 H or D atoms/Pd atom.
Abstract: Measurements have been made of the magnetic susceptibility of PdH and PdD alloys over the temperature range between 4K and 300K. A series of specimens was studied with composition ranging from 0.0 to 0.7 H or D atoms/Pd atom. The results are interpreted in terms of the two phase nature of the PdH and PdD systems. For the alpha phase the susceptibility is large and varies with temperature in a manner similar to that of pure palladium, while the susceptibility of the beta phase is slightly diamagnetic and almost independent of temperature. The temperature dependence of the susceptibility of both pure Pd and alpha phase PdH agrees well with a theoretical relation given by Misawa (1970) based on treating the electrons in palladium as a nearly ferromagnetic Fermi liquid.
112 citations
TL;DR: In this paper, a simple model based on pinning by the cell walls of the defect structure has been developed, which depends upon the Ginsburg-Landau parameter being enhanced in the cell wall and fits the data for the material given the optimum heat treatment very well.
Abstract: Heavily cold worked Nb-60 at% Ti wires have been studied. The wires had previously been heat treated and characterized by electron microscopy (Neal et al 1971). The critical supercurrents have been measured as a function of applied magnetic field at temperatures between 4.2 K and the transition temperature, and interpreted in terms of the pinning force per unit volume on the vortex lattice. Empirically the pinning force is given by Fp=f(b)Bc2n (2
106 citations
TL;DR: In this article, the annihilation characteristics of positrons in aluminium have been studied for the distinct cases of annihilation in the perfect lattice and annihilation after trapping at vacancies or dislocations.
Abstract: The annihilation characteristics of positrons in aluminium have been studied for the distinct cases of annihilation in the perfect lattice and annihilation after trapping at vacancies or dislocations. A controlled production of vacancies and dislocation in single crystal aluminium specimens was achieved with a quenching and annealing procedure. The annihilation lifetime in the perfect lattice is 166+or-2 ps, whereas it is 246+or-4 ps for positrons trapped in vacancies and 250+or-30 ps for positrons trapped in dislocations. The mean lifetime is found to increase with increasing dislocation density, but saturation is not attained with the dislocation densities obtainable by the quenching process. The trapping probabilities are (0.23+or-0.05)*1015 s-1 for vacancies and (0.08+or-0.05)*1015 s-1 for dislocations.
98 citations
TL;DR: In this paper, the Fourier coefficient of the pseudopotential mod U200 mod has been derived and its temperature variation satisfactorily explained and the derived value of this coefficient for 0 K is 0.79+or- 0.01 eV which is somewhat higher than that obtained from Fermi surface data, but the difference may in part be due to an energy dependence of the coefficient.
Abstract: Measurements of the optical absorption of clean evaporated aluminium films have been made at several different temperatures and the results interpreted in terms of the theory of parallel band absorption. Values of the Fourier coefficient of the pseudopotential mod U200 mod have been derived and its temperature variation satisfactorily explained. The derived value of this coefficient for 0 K is 0.79+or- 0.01 eV which is somewhat higher than that obtained from Fermi surface data, but the difference may in part be due to an energy dependence of the coefficient. Values of optical mass, interband and Drude relaxation times at the different temperatures have been derived. Some data appropriate to partially disordered films are also presented.
80 citations
TL;DR: In this article, the macroscopic theory of force free magnetic fields in the mixed state of type II superconductors is presented, and solutions for cylindrical geometry are compared with experimental data from a Pb-40 at% Tl alloy.
Abstract: The macroscopic theory of force free magnetic fields in the mixed state of type II superconductors is presented. Solutions for cylindrical geometry are compared with experimental data from a Pb-40 at% Tl alloy. In the experiments the sample is subjected to combinations of field and current in a longitudinal configuration and both axial magnetization and axial resistance are simultaneously monitored. The observed paramagnetic moment is in good agreement with the predictions. An unexpected feature of the experimental results is the appearance of flux flow resistance at high currents. Coupled magnetic and resistive oscillations and discontinuities are observed in the flux flow regime. The system is magnetically irreversible in the resistance less state and reversible during flux flow. The results are discussed in the context of force free field theory.
77 citations
TL;DR: In this paper, the de Haas-van Alphen frequencies for the symmetry direction orbits and the (110) plane belly turning point have been measured in copper, silver and gold with an absolute precision of better than 2 in 105 and a relative precision approaching 1 in 106.
Abstract: The de Haas-van Alphen frequencies for the symmetry direction orbits and the (110) plane belly turning point have been measured in copper, silver and gold with an absolute precision of better than 2 in 105 and a relative precision approaching 1 in 106. The infinite-field phases have been determined by extrapolation to an accuracy of a few hundredths of a cycle. The techniques of sample alignment and measurement of de Haas-van Alphen phase in terms of in situ 27Al NMR are discussed in some detail. There is no significant disagreement with earlier frequency measurements. The infinite-field phases agree well with the predictions of the Lifshitz-Kosevich formula, and in the case of the neck orbits resolve the ambiguities in Randles' determinations of the g factors.
58 citations
TL;DR: In this article, the energy, its first derivative with respect to orientation and the line tension of straight dislocations in elastic media of arbitrary anisotropy are developed for a selection of cubic metals including iron, niobium, copper and nickel.
Abstract: Formulae for the energy, its first derivative with respect to orientation and the line tension of straight dislocations in elastic media of arbitrary anisotropy are developed. The formulae may be evaluated rapidly and precisely by numerical integration, thus avoiding the need for solving a sextic algebraic equation common to previous techniques used to calculate these quantities. Numerical results are presented in graphical and tabular form for a selection of cubic metals including iron, niobium, copper and nickel. The efficiency and accuracy of the method are compared to that of previous methods and the applications of the numerical results to the study of interactions between complex dislocation configurations using a formalism developed by Brown is discussed.
TL;DR: The resistance anomaly discovered by Coles in RhFe and occurring in several similar dilute alloys is shown to be of the same nature as the Kondo anomaly as mentioned in this paper, and is given by a universal function of the temperature, increasing as T2, T and in T to tend finally to the unitarity limit.
Abstract: The resistance anomaly discovered by Coles in RhFe and occurring in several similar dilute alloys is shown to be of the same nature as the Kondo anomaly. The resistivity is due to localized spin fluctuations (LSF) and is given by a universal function of the temperature, increasing as T2, T and in T to tend finally to the unitarity limit. The characteristic knee occurs at the spin fluctuation temperature Tsf and marks the onset of the logarithmic regime. Above Tsf there is no qualitative difference between the resistivity due to LSF and that caused by a well defined localized magnetic moment.
TL;DR: In this article, the spin density distributions in two alloys of iron and silicon (approximate compositions Fe3Si and Fe4Si) have been determined by polarized neutron diffraction, and the observed data have been corrected for the effects of extinction and have been analysed by the standard Fourier method and also by expressing the density distribution in terms of spherical harmonics.
Abstract: The spin density distributions in two alloys of iron and silicon (approximate compositions Fe3Si and Fe4Si) have been determined by polarized neutron diffraction. The observed data have been corrected for the effects of extinction and have been analysed by the standard Fourier method and also by expressing the density distribution in terms of spherical harmonics. The latter method of analysis indicated a non-centrosymmetric density around one of the iron sites and an explanation for this has been suggested in terms of a change of sign with distance for the s-d exchange interaction.
TL;DR: In this article, a new Green function method for solving the Schrodinger equation for impurity A dissolved in B is applied to Mg in Li and Al in Li, and the results are used in a discussion of charge densities, energies and sizes of impurities, and they show why a metal impurity in another metal largely retains its bulk properties.
Abstract: A new Green function method for solving the Schrodinger equation for impurity A dissolved in B is applied to Mg in Li and Al in Li. In this method the Green function for A in B is expressed in terms of Green functions for bulk A and B and so it facilitates comparison with the atoms in the bulk. It is found that the local density of states outside the impurity goes quickly to the value for bulk B and inside the impurity it is close to the value for bulk A, except at low energies where it changes to allow for states in bulk A which are below the bottom of the B band. In the Al impurity case a weakly bound state falls out from the bottom of the band. The results are used in a discussion of charge densities, energies and sizes of impurities, and they show why a metal impurity in another metal largely retains its bulk properties.
TL;DR: In this article, the scattering from impurities in copper is analyzed in terms of s, p and d partial waves, and the anisotropic transition probability between points on the Fermi surface is calculated based on scattering phase shifts characterizing the impurity.
Abstract: The scattering from impurities in copper is analysed in terms of s, p and d partial waves. The (anisotropic) transition probability between points on the Fermi surface is calculated in terms of scattering phase shifts characterizing the impurity. Maps of the calculated scattering are presented for each phase shift and the corresponding Dingle temperatures are calculated for a variety of orbits seen in the de Haas-van Alphen effect. A procedure developed to calculate the impurity resistivity and anisotropy of the corresponding relaxation time demonstrated the need to use a vector mean free path in such a calculation. The calculated scattering is compared with experimental values in the Cu(Ni), Cu(Fe) and Cu(Al) systems and values derived for the scattering phase shifts.
TL;DR: In this paper, the room temperature Mossbauer spectra obtained for CuFe alloys containing 0.05 to 2.12 at % Fe are interpreted in terms of separate doublets arising from increasing numbers of nearest neighbour iron atoms.
Abstract: Room temperature Mossbauer spectra obtained for CuFe alloys containing 0.05 to 2.12 at % Fe are interpreted in terms of separate doublets arising from increasing numbers of nearest neighbour iron atoms.
TL;DR: In this paper, a computer simulation was carried out of the edge and screw dislocations in copper and the results demonstrate that the splitting of the partials is considerably greater than would be expected from anisotropic elasticity theory so the use of this theory to deduce stacking fault energies is questionable.
Abstract: A computer simulation was carried out of the edge and screw dislocations in copper. The calculated separation of the Schockley partials is in good agreement with recent observations using weak beam electron microscopy. However, the results demonstrate that the splitting of the partials is considerably greater than would be expected from anisotropic elasticity theory so the use of this theory to deduce stacking fault energies is questionable.
TL;DR: In this article, it was shown that the displacement of the fluxon lattice is reversible and linear in the applied force up to a certain maximum displacement. But the model was used to analyze the response of a lattice to very small forces.
Abstract: The interaction between the fluxon lattice and a random array of pinning sites can be analyzed with the help of a simple model. The critical current calculated from the model corresponds to the more refined calculation of Labusch (1969). The model is used to analyse the response of a fluxon lattice to very small forces. It is shown that the displacement of the fluxon lattice is reversible and linear in the applied force up to a certain maximum displacement. Measurement of the displacement due to small forces can be performed by measuring the electric field in a slab carrying a small alternating current. Such measurements can yield useful information about pinning centres.
TL;DR: In this article, the resistivity of a dilute alloy due to localized spin fluctuations (LSF) occurring on the impurity orbitals is given by a universal function of the temperature.
Abstract: The resistivity of a dilute alloy due to localized spin fluctuations (LSF) occurring on the impurity orbitals is given by a universal function of the temperature. The resistivity is finite at T=0, then decreases with temperature as T2, T, lnT and T-1 successively. The T2 and T behaviour are in good agreement with the experimental data on AIMn. The T2 and lnT laws are expected by comparison between LSF and the Kondo effect.
TL;DR: In this paper, the first order antiferromagnetic-ferromagnetic transition of the equiatomic FeRh alloy is investigated thermodynamically and the phonon, conduction electron and magnon contributions to the free energy of both phases are calculated numerically.
Abstract: The first order antiferromagnetic-ferromagnetic transition of the equiatomic FeRh alloy is investigated thermodynamically. The phonon, conduction electron and magnon contributions to the free energy of both phases are calculated numerically. The results predict a parabolic temperature dependence of the critical field required to induce the transition which is in agreement with experiment. The calculated value of the entropy change at the transition is 14Jkg-1K-1 which agrees with the measured values. The pressure dependence of the critical field is discussed and shown to be consistent with the model. Evidence is given that an ordered magnetic moment exists on the rhodium atoms in the antiferromagnetic state.
TL;DR: In this paper, the elastic stiffness constants of beryllium have been measured in the temperature range 25 to 300 C, using a direct pulse ultrasonic technique, and the macroscopic elastic moduli computed from the experimental data, agree well with the already accepted values for polycrystalline bergs.
Abstract: The five independent elastic stiffness constants of beryllium have been measured in the temperature range 25 to 300 C, using a direct pulse ultrasonic technique. At 25 C the values for the elastic constants are C11=28.88, C33=35.42, C44=15.49, C12=2.01 and C13=0.47 in units of 1011 dyn cm-2. The macroscopic elastic moduli computed from the experimental data, agree well with the already accepted values for polycrystalline beryllium.
TL;DR: The zero wave vector partial structure factors for liquid Na-K and K-Hg alloys have been evaluated from thermodynamic data, using a formula due to Bhatia and Thornton (1970) as discussed by the authors.
Abstract: The zero wave vector partial structure factors for liquid Na-K and K-Hg alloys have been evaluated from thermodynamic data, using a formula due to Bhatia and Thornton (1970). There is significant variation with composition, in disagreement with the frequency assumption that the partial structure factors are independent of composition.
TL;DR: In this paper, a selfconsistent single site effective Hamiltonian is derived within the multiple scattering theory to describe a disordered tight binding binary alloy for which both constituent bandwidths and site potentials are different.
Abstract: A selfconsistent single site effective Hamiltonian is derived within the multiple scattering theory to describe a disordered tight binding binary alloy for which both constituent bandwidths and site potentials are different. The total density of states and the constituent partial density of states are calculated and discussed. It is shown that the multiple scattering approach provides a suitable formalism for investigating problems such as (i) the extension of the Koster-Slater formula when impurity and host have different bandwidths, (ii) the appearance of a satellite-peak structure in the broader bandwidth component density of states when the difference in bandwidths is great enough, (iii) the generalization of the theory to a two band model relevant for transition and noble metal alloys.
TL;DR: In this paper, a model for the study of various physical properties associated with the void lattices as recently observed in several metals was proposed, and the model gave the correct value for the equilibrium void lattice spacing in molybdenum.
Abstract: A model is proposed for the study of various physical properties associated with the void lattices as recently observed in several metals. The model gives the correct value for the equilibrium void lattice spacing in molybdenum and also explains the stability of the void lattice.
TL;DR: In this paper, a phase diagram has been constructed for the AgPdH alloy system showing the hydrogen to metal atomic ratio as a function of Ag concentration using the results of X-ray and Mossbauer studies reported earlier by the authors.
Abstract: Using the results of previous workers a phase diagram has been constructed for the AgPdH alloy system showing the hydrogen to metal atomic ratio as a function of Ag concentration. From the results of X-ray and Mossbauer studies reported earlier by the authors, an analogous phase diagram has been obtained for the FePdH system. In each case, the limits of stability of the alpha (low hydrogen content) and beta (high hydrogen content) phases are shown. Further analysis of Mossbauer spectra has determined the variation with temperature of hyperfine field at Fe57 nuclei for various concentrations of iron in alpha and beta phase hydrides. The saturation fields for alpha max and beta min iron-palladium hydrides are identical to within +or-5 kG at a given iron concentration. The observed Fe57 isomer shift difference between alpha and beta phase hydrides is shown to result entirely from changes in lattice parameter. An extension of the model for Fe impurities in a Pd lattice is proposed to interpret these effects. On introducing an iron atom into palladium, rearrangement of band structure occurs which localizes 4d(eg) type magnetized d states on nearest and next nearest Pd atoms. Polarization of the band t2g d states of Pd occurs to large distances via a RKKY mechanism. In the hydrides, the t2g moment is quenched but the localized eg moment is unchanged except at hydrogen concentrations beyond the normal solubility limit.
TL;DR: In this article, a general expression for the pressure dependence of the magnetization delta zeta / delta p in the itinerant electron model of ferromagnetism is derived.
Abstract: The pressure dependence of the magnetization delta zeta / delta p is calculated in the itinerant electron model of ferromagnetism. It is assumed that the relative population of s and d bands, the width of the d band W and the effective interaction Ieff vary with pressure. Under these assumptions, a general expression for delta zeta / delta p is obtained which is exact within the Stoner model. The two important parameters which govern the pressure dependence of the magnetization in this model are the s-d transfer under pressure dn/dp and the pressure dependence of the effective interaction delta Ieff/ delta W. The temperature dependence of delta zeta / delta p is evaluated numerically for a single parabolic band and the values of parameters appropriate to nickel. The calculated temperature dependence of delta zeta / delta p is compared with the experimental data of Tange and Tokunaga (1969). Good quantitative agreement is obtained in the whole range of temperatures if the following values of the parameters dn/dp and delta Ieff/ delta W are chosen: dn/dp=-1.62*10-7 bar-1, delta Ieff/ delta W=8.68*10-2. From the pressure dependence of Ieff the correlation effects in nickel are estimated. It is found that the ratio Ieff/I0=0.4+or-0.1, which implies an immediate correlation effect.
TL;DR: In this article, the nuclear spin-lattice relaxation rate was measured as a function of composition for 115In and 121Sb in liquid In-Sb, and for 209Bi in Bi50X50 where X=In, Sn, Sb, Pb, etc.
Abstract: Nuclear spin-lattice relaxation rates have been measured as a function of composition for 115In and 121Sb in liquid In-Sb and for 115In and 209Bi in In-Bi, and as a function of temperature for 209Bi in Bi50X50 where X=In, Sn, Sb, Pb, and for 27Al in Al89Si11. For 121Sb in In-Sb and for 209Bi in all the alloys investigated a relaxation rate was observed in excess of that predicted by the Korringa relation. The additional rates R1Q are attributed to an electric quadrupolar interaction with diffusing ions. The relative field gradients which must be attributed to different ions in an alloy do not bear any simple relation to their valences.
TL;DR: In this article, the quadrupole effects in nuclear magnetic resonance were used to determine the electric field gradients at nearest and in some cases next nearest host Cu nuclei to various impurities in dilute Cu alloy single crystals.
Abstract: For Pt. I see abstr. A1732 of 1972. The electric field gradients at nearest and in some cases next nearest host Cu nuclei to various impurities in dilute Cu alloy single crystals have been determined by the quadrupole effects in nuclear magnetic resonance. The impurities are In, Sn, Sb and Ge. The field gradients at nearest neighbour sites are far from rotational symmetric around the direction towards the impurity and in the case of CuGe it does not even have the main component in that direction. These results question the validity of the theoretical models assuming spherical symmetry for the charge density around the impurity, at least in host metals like copper.
TL;DR: In this article, the magnetic properties of rare earth transition metal compounds having the Fe3C structure were measured using a pulsed field magnetometer and the results obtained were appreciably different from those observed previously in static fields by other workers.
Abstract: Measurements have been made of the magnetic properties of rare earth-transition metal compounds having the Fe3C structure. The results obtained using a pulsed field magnetometer are appreciably different from those observed previously in static fields by other workers. It has proved difficult to decide from these results what type of magnetic order is present in several of the compounds. It is clear however that in some cases the observed magnetization is time dependent.
TL;DR: In this article, generalizations of the coherent potential approximation taking into account cluster effects are presented and discussed, and several different approximations giving the same exact terms in various limiting cases are shown to coexist.
Abstract: Some generalizations of the coherent potential approximation taking into account cluster effects are presented and discussed. Several different approximations giving the same exact terms in various limiting cases are shown to coexist. In particular the propagator and locator formalisms are proved to yield different results when going beyond the single site approximation.