Showing papers in "Journal of Physics F: Metal Physics in 1978"
TL;DR: In this article, a simple formula for the static electron gas dielectric function, incorporating exchange and correlation effects, was proposed, which generates calculated physical properties with surprisingly good precision and has a very good formal justification.
Abstract: It is pointed out that there exists a simple formula for the static electron gas dielectric function, incorporating exchange and correlation effects, which generates calculated physical properties with surprisingly good precision and which has a very good formal justification.
226 citations
TL;DR: In this paper, the Kirkendall effect was extended to include the effect of superimposed vacancy gradients in binary alloys and applied to the case of an irradiated metal.
Abstract: The phenomenon of segregation of major alloy constituents under irradiation is considered. The available evidence on segregation of nickel to sinks in Fe-Cr-Ni alloys is reviewed, and some new data presented. The theory of the Kirkendall effect is extended to include the effect of superimposed vacancy gradients in binary alloys and applied to the case of an irradiated metal. It is found that if the effect of the interstitial flux is neutral, then solute segregation can occur at sinks because of differences in the vacancy diffusion coefficients of the alloy constituents. The theory predicts that slow-diffusing solutes will be enriched at sinks, as observed in Fe-Cr-Ni alloys. It is pointed out that one consequence of segregation is that an extra vacancy flux (the 'Kirkendall flux') is induced, which opposes the radiation induced flux to the sink. The consequences of this for void nucleation and growth are discussed.
169 citations
TL;DR: In this paper, a recursion formula is established which gives the relevant upper (+) and lower (-) bounds for the tensor Ceff of effective elastic moduli of the overall grade n material.
Abstract: Using elasticity as an illustration a recursion formula is established which gives the relevant upper (+) and lower (-) bounds C(+or-n), (n=2,3,4... infinity ) for the tensor Ceff of effective elastic moduli of the overall grade n material. It follows from this formula that for n to infinity both C(+n) and C(-n) converge towards the well known self-consistent tensor Csc which therefore represents a material which, in a statistical sense, is perfectly homogeneous, isotropic and disordered. All these results also have implications for other material properties and for disordered structures other than polycrystals. Since the self-consistent approach is isomorphic to the coherent potential approximation, some of the conclusions should also be relevant for other areas of solid state physics.
126 citations
TL;DR: In this article, it is shown that whereas Friedel's d bond contribution is primarily responsible for the cohesive energy, the s electrons are crucial for providing the repulsive pressure to counter the attractive d contribution at the equilibrium atomic volume.
Abstract: For pt.II see ibid., vol.7, p.1009 (1978). The s and d contributions to the pressure and bulk modulus across the series and as a function of volume are presented using Pettifor's partial pressure expression and the results of part I of this series on the behaviour of the energy bands. It is shown that whereas Friedel's d bond contribution is primarily responsible for the cohesive energy, the s electrons are crucial for providing the repulsive pressure to counter the attractive d contribution at the equilibrium atomic volume. Moreover, because of ion core orthogonality constraints, the s electrons determine the bulk modulus away from the noble metal end of the series. The hybridisation contribution is included by assuming it to be proportional to the d resonant width. The cohesive energy is predicted to better than about 10%, the equilibrium atomic volume to 25%, and the bulk modulus (excluding Pd and Ag) to better than 20% across the 4d series. The importance of the neglected second-order contributions such as three-centre integrals is demonstrated.
112 citations
TL;DR: In this paper, the time decays of the remanences IRM and TRM are given for a range of temperatures up to and including the spin glass temperature, Tf. All the decays are best described by the relation M=M0-Snlnt.
Abstract: Studies of magnetic viscosity in Au-Fe alloys containing 2 at.% and 7 at.% Fe are presented. The time decays of the remanences IRM and TRM are given for a range of temperatures up to and including the spin glass temperature, Tf. All the decays are best described by the relation M=M0-Snlnt. STRM(T), SIRM(T) both have maxima at 0.6 Tf. The IRM data suggests a linear relation between S and M0. Plots of S/M0=V against T suggest the existence of two regimes of temperature below Tf: (1)T
106 citations
TL;DR: The temperature dependence of the positron annihilation peak coincidence rate has been measured in iron from 20 degrees C to 1320 degrees C and the correlation between Ef and Tt, where Tt is the threshold temperature, has been derived from the trapping model.
Abstract: The temperature dependence of the positron annihilation peak coincidence rate has been measured in iron from 20 degrees C to 1320 degrees C. The peak rate did not change across the ferro-para magnetic transition at approximately 770 degrees C but decreases by 1.5% across the alpha - gamma phase transition at 910 degrees C. The trapping model analysis of the data yields values of the vacancy formation energies (Ef) of 1.4+or-0.1 eV in alpha -Fe and 1.7+or-0.2 eV in gamma -Fe. The correlation between Ef and Tt, where Tt is the threshold temperature, has been derived from the trapping model.
105 citations
TL;DR: In this article, the beta phase of FeTiD was shown to be orthorhombic with lattice parameters a=2.956+or-0.004 AA, b=4.543+or 0.006 AA, and c= 4.388+or -0.06 AA.
Abstract: The beta phase of FeTiD is shown to be orthorhombic with lattice parameters a=2.956+or-0.004 AA, b=4.543+or-0.006 AA and c=4.388+or-0.006 AA. The deuterium atoms are ordered on certain octahedral interstitial sites with two nearest-neighbour iron atoms.
83 citations
TL;DR: The magnetic properties of the tetragonal ternary compounds RFe4Al8 (R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Th) were investigated in this paper.
Abstract: The magnetic properties of the tetragonal ternary compounds RFe4Al8(R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Th) were investigated. An analysis of the data is given in terms of a molecular field model involving three magnetic sublattices: the R sublattice and two antiparallel-coupled Fe sublattices. It was found that in RFe4Al8 the iron moments are coupled antiparallel to the rare earth spin moments. Estimates are given of the molecular field constants associated with the R-Fe interaction and the Fe intrasublattice interaction. Most of these compounds were also investigated by 57Fe Mossbauer spectroscopy. Values are given for the effective hyperfine fields and the isomer shifts. This technique also made possible an accurate determination of the magnetic ordering temperatures, which were difficult to detect by magnetic measurements, even though the Fe moment is about 0.7 mu B/Fe in the magnetically ordered state. The magnetic ordering temperatures range from 140 to 200K. The effective moment of the Fe atom in the paramagnetic regime is about 3.8 mu B/Fe. The magnetic properties of GdMn4Al8 and YMn4Al8 were also determined.
81 citations
TL;DR: In this article, relativistic bandstructure calculations for face centred cubic lanthanum, cerium and thorium have been performed using the linear muffin-tin orbital (LMTO) method and the local spin density (LSD) approximation for exchange and correlation.
Abstract: Self-consistent relativistic bandstructure calculations for face centred cubic lanthanum, cerium and thorium have been performed using the linear muffin-tin orbital (LMTO) method and the local spin density (LSD) approximation for exchange and correlation. Results are given for equilibrium distance, bulk modulus, spin susceptibility and the electron-phonon matrix element in each case. A significant contribution of f partial waves to the crystal bonding for all three metals has been found. At the atomic volume corresponding to the gamma phase, cerium exhibits a ferromagnetic instability.
75 citations
TL;DR: In this paper, the influence of Ho substitution on the Co moments in (HoxY1-x)Co2 has been investigated by means of magnetic, resistivity and lattice parameter measurements.
Abstract: The influence of the Ho substitution on the Co moments in (HoxY1-x)Co2 has been investigated by means of magnetic, resistivity and lattice parameter measurements. A first-order phase transition and a field-induced metamagnetism can be detected for x>or=0.7. At the magnetic transition temperature anomalies of the lattice parameters were measured for x>or=0.3. In connection with the first-order transition a discontinuity in the rho (T) curves appears for x>or=0.7. For 0.3 150K) the rho (T) curves show a tendency to saturation, which is the same for all x values. Considering the substitution of Ho into YCo2 the existence of a critical RE concentration (x>0.1) for the appearance of a long-range magnetic order is evidenced. The Co moments mu Co are compared with neutron diffraction results. The overall agreement is very good and supports the assumption of induced Co moments. For the whole pseudobinary system, a Fermi energy situated in a steep flank of the density of states function was assumed.
69 citations
TL;DR: In this article, the intermetallic compound Fe3Sn2 has been studied by Mossbauer spectroscopy and magnetisation measurements and the transferred fields at the 119Sn nucleus agree with the model deduced from 57Fe MMS.
Abstract: The intermetallic compound Fe3Sn2 has been studied by Mossbauer spectroscopy and magnetisation measurements. This compound is ferromagnetic from approximately 220K to Tc=657K. In this temperature range, the spin directions are close to or parallel to the c axis while at low temperature they are perpendicular to it. The mean magnetic moment is 2.1 mu B per iron atom at 4K. The spread in the 57Fe hyperfine fields is due to anisotropic contributions while the spread in the spin directions at low temperature is related to a weak basal plane anisotropy energy. The transferred fields at the 119Sn nucleus agree with the model deduced from 57Fe Mossbauer spectroscopy.
TL;DR: The lattice parameter of Pd has been measured between room temperature and 6K and has been found to be a smooth function of temperature over this range as mentioned in this paper, i.e., no indication of homogeneous lattice strain in excess of 2.5*10-5, nor evidence of line broadening indicative of inhomogeneous strains.
Abstract: The lattice parameter of Pd has been measured between room temperature and 6K and has been found to be a smooth function of temperature over this range. An investigation of the X-ray diffraction patterns of some beta phase Pd-H alloys and a mixed ( alpha + beta ) phase alloy and of their dependence on cooling through the 50K region, where anomalies in a number of physical properties of beta -phase Pd-H are known to occur, showed no discernible effect on the state of strain of the Pd lattice, i.e., no indication of homogeneous lattice strain in excess of 2.5*10-5, nor evidence of line broadening indicative of inhomogeneous strains. Some consequences of this result for mechanisms which have been suggested to account for these anomalies are considered.
TL;DR: Doppler broadening measurements have been performed on Cu samples containing vacancies and/or hydrogen and the positron measurements also show that quenched-in vacancies become mobile at about 273K and form clusters as discussed by the authors.
Abstract: Doppler broadening measurements have been performed on Cu samples containing vacancies and/or hydrogen. Trapping of hydrogen by vacancies is indicated above about 150K. Vacancies occupied by hydrogen show a strongly reduced positron-trapping probability as compared to hydrogen-free vacancies. Detrapping of hydrogen is not observed below 450K. Therefore, the vacancy-hydrogen binding energy must be greater than 0.4 eV. The positron measurements also show that quenched-in vacancies become mobile at about 273K and form clusters. The close analogy to the annealing behaviour of electron-irradiated Cu confirms the interpretation of annealing stage III by single-vacancy migration.
TL;DR: In this article, total angular momentum projected density-of-state functions have been derived for Pd, Ag, Pt, and Au, and the results show that the d3/2 and d5/2 components are well separated by the spin-orbit interaction.
Abstract: Total angular momentum projected density-of-states functions have been derived for Pd, Ag, Pt, and Au. In particular, the d density-of-states functions, i.e. the partial density-of-states for l=2, j=3/2, and j=5/2 are considered. The results show that, for Ag, Pt, and Au, the d3/2 and d5/2 components are well separated by the spin-orbit interaction.
TL;DR: In this article, the magnetic properties of the Laves phase system Y(Fe1-cAlc)2 have been studied by means of bulk magnetisation measurements in fields up to 72 kOe for 0 or =n0=15 iron neighbours; this moment remains constant and equal to that of YFe2 at least up to 32.6 at.
Abstract: The magnetic properties of the Laves phase system Y(Fe1-cAlc)2 have been studied by means of bulk magnetisation measurements in fields up to 72 kOe for 0 or=n0=15 iron neighbours; this moment remains constant and equal to that of YFe2 at least up to 32.6 at.% Al. This model accounts for the variation with c of the spontaneous magnetisation related to the magnetic atoms, the high-field susceptibility which arises from the nonmagnetic Fe atoms, and for the hyperfine field distributions.
TL;DR: In this paper, the dominant anomaly of the static electron density response function is derived within the RPA and substituted in a perturbation formula (derived from the general formulation of Pick, Cohen and Martin (1970)) which relates a phonon energy change to perturbative variation of the irreducible electronic polarisability.
Abstract: The general behaviour of a T=0K metal phonon spectrum near a Fermi surface (FS) topology transition is studied in the framework of the quasiharmonic adiabatic approximation. The transition parameter is taken as the separation Delta =EF-Ec between the Fermi level and the energy of the electronic Van Hove singularity responsible for the transition. The dominant anomaly of the static electron density response function is first derived within the RPA and substituted in a perturbation formula (derived from the general formulation of Pick, Cohen and Martin (1970)) which relates a phonon energy change to a perturbative variation of the irreducible electronic polarisability. The overall variation Delta omega 2 with Delta has been estimated from a crude model involving a cut-off parameter related to the 'critical states' bandwidth ( Delta omega 2 includes the cut-off independent dominant anomaly Delta omega 2); phonons dips, as observed in Nb or Pb for instance, are expected quite generally when a Van Hove singularity is near EF. These results have been used to study the Delta dependence of a phonon spectrum average of a frequency-dependent function (such as ( omega n)); a C+or- mod Delta mod 3/2 anomaly is found, with different coefficients C+or- when Delta to +or-0. The theory is applied in a semiphenomenological way to the Tl-Bi-Pb alloys phonon softening at the X point.
TL;DR: In this paper, the authors compared tracer diffusion coefficients, D, in Pb and in alpha-Zr, at 0.6 Tm, where Tm(K) is the melting temperature of the host metal.
Abstract: Published diffusion data permit an extensive comparison to be made between tracer diffusion coefficients, D, in Pb and in alpha -Zr, at 0.6 Tm, where Tm(K) is the melting temperature of the host metal. For these metals, a striking correlation is found between D and the metallic radius, r, of the corresponding tracer element; except for the smallest r values, the correlation may be expressed in the general form lg D=A+exp(-br+c) where A, b and c are individual constants for each host metal. There is, for tracer diffusion in Pb, sufficient experimental data to permit the evaluation of an additional relationship, of the type proposed by Zener, between the preexponential factor, D0, and the activation enthalpy, Delta H, in the usual expressions D=D0exp(- Delta H/RT) describing the temperature dependence of D. A combination of these relationships allows the evaluation of expressions for D0 and Delta H in which r is the only variable. In order to compare tracer diffusion in these 'open' metals (i.e. metals with a relatively large metallic/ionic radius ratio) with tracer diffusion in a 'full' metal, values of D at 0.6 Tm have been calculated from published data for diffusion in Cu.
TL;DR: In this article, the authors simplified the KKR-CPA theory using the atomic sphere approximation (ASA) of Andersen (1975) in its new form the fundamental equations of the theory can be solved numerically.
Abstract: The authors considered the coherent potential approximation (CPA) for a substitutionally disordered alloy crystal potential which is of the nonoverlapping muffin-tin form. The authors simplified the KKR-CPA theory using the atomic sphere approximation (ASA) of Andersen (1975). In its new form the fundamental equations of the theory can be solved numerically. The computational effort is not particularly large on the scale of modern bandstructure calculations. As an illustration of the authors' method they calculated the Bloch spectral functions and the partially averaged local density of states for a number of alloy potentials designed to represent paramagnetic CucNi1-c alloys. Where comparison is possible the authors found good agreement with previous calculations. Their results are also consistent with various experimental data.
TL;DR: In this article, the authors studied transition and noble metal site NMR spectra of stoichiometric, off-stoichiometric and substituted Heusler alloys and analyzed the hyperfine fields in terms of local and transferred contributions.
Abstract: The authors have studied transition and noble metal site NMR spectra of stoichiometric, off-stoichiometric and substituted Heusler alloys. The hyperfine fields can be analysed consistently in terms of local and transferred contributions. The transferred fields are negative at near neighbour and second neighbour to a Mn site, and positive at third neighbour. In many cases excess Mn atoms substituted onto Z sites form antiferromagnetic good local moments in these ferromagnetic hosts with strongly anomalous hyperfine field temperature dependences. Both the transferred fields and the Mn-Mn coupling follow the predictions of a Friedel-Anderson d resonance model correctly treated in the preasymptotic region. The local hyperfine fields at Mn sites are very similar to fields in dilute Mn alloys, while the local fields at Co sites are positive indicating unquenched local orbital moments on the Co atoms.
TL;DR: In this article, the authors measured the AC susceptibility with applied magnetic fields between 0 and 1500 Oe for two AuFe alloys above the ferromagnetic percolation concentration.
Abstract: The authors have measured the AC susceptibility with applied magnetic fields between 0 and 1500 Oe for two AuFe alloys above the ferromagnetic percolation concentration. The results indicate that spin glass ordering occurs at low temperatures and an extended T-c phase diagram is proposed.
TL;DR: In this paper, the positron pseudopotential method is employed in calculations of the effects of structure and specifically, volume expansion and lattice vibration on positron density distribution in metals.
Abstract: The positron pseudopotential method is employed in calculations of the effects of structure and specifically the effects of volume expansion and lattice vibration on the positron density distribution in metals. Calculations of the prevacancy temperature dependence of annihilation rates in several metals provide results in good agreement with observations.
TL;DR: The Mossbauer spectra of BCC Fe-V alloys in the concentration range 40-80 at.% V have been obtained for both the ordered and disordered states as mentioned in this paper.
Abstract: The Mossbauer spectra of BCC Fe-V alloys in the concentration range 40-80 at.% V have been obtained for both the ordered and disordered states. No broadening of the absorption line has been detected in an 80 at.% V alloy even at liquid He temperature indicating that the alloy is nonmagnetic. Broadening of absorption lines due to the magnetic hyperfine field has been observed for the alloys containing less than 70 at.% V. The spectra obtained at 5K were analysed to yield the hyperfine field distribution curves. It was found that the hyperfine field is notably reduced by atomic ordering. This change in hyperfine field is explained as the result of the change in Fe atomic moment which increases with increasing the number of Fe nearest neighbours. Profiles of the hyperfine field distribution curves are explained on the same basis. The dependence of the Fe atomic moment on the near-neighbour Fe composition is compared with the result of CPA calculations. Correlation between the lattice constant and the magnetic moment is discussed.
TL;DR: A group-theoretical treatment of the symmetry properties of electron momentum distributions in cubic crystals is given in this paper, where the contribution to the momentum density from a band not belonging to the totally symmetric representation possesses nodes in certain directions.
Abstract: A group-theoretical treatment of the symmetry properties of electron momentum distributions in cubic crystals is given. The contribution to the momentum density from a band not belonging to the totally symmetric representation possesses nodes in certain directions. A selection rule allows the location of these nodes. Tables are presented which summarise the consequences of the selection rule for simple cubic, FCC and BCC lattices, and some examples are discussed.
TL;DR: The magnetic susceptibilities of YCo2 and LuCo2 at 4.2 and 77K, as determined from magnetisation measurements in fields up to 38 Tesla, are found to increase with field in an anomalous way as discussed by the authors.
Abstract: The magnetic susceptibilities of YCo2 and LuCo2 at 4.2 and 77K, as determined from magnetisation measurements in fields up to 38 Tesla, are found to increase with field in an anomalous way.
TL;DR: A metallic amorphous structure model has been constructed on a computer such that an assembly of atoms are spread at random in a cube, under the restriction that no two atoms are closer than a given core diameter, and are then subjected to relaxation through Johnson's interatomic potential to obtain a minimal energy configuration as discussed by the authors.
Abstract: A metallic amorphous structure model has been constructed on a computer such that an assembly of atoms are spread at random in a cube, under the restriction that no two atoms are closer than a given core diameter, and are then subjected to relaxation through Johnson's interatomic potential (1964) to obtain a minimal energy configuration. The results, without depending on the core diameter, show both a high packing fraction ( eta =0.74) and a realistic pair distribution function.
TL;DR: The magnetisation and Mossbauer effect have been measured for the Invar type FCC Fe-Pt alloys, and the atomic moment of the alloys varies linearly with concentration, following the Slater-Pauling curve, which indicates that the iron atom possesses a full moment of 2.7 mu B as mentioned in this paper.
Abstract: The magnetisation and Mossbauer effect have been measured for the Invar type FCC Fe-Pt alloys. The atomic moment of the alloys varies linearly with concentration, following the Slater-Pauling curve, which indicates that the iron atom possesses a full moment of 2.7 mu B even in the Invar region. The hyperfine field acting on the Fe nucleus in these alloys is independent of concentration. These results imply that the Fe-Pt Invar alloys are strong ferromagnets, i.e., weak itinerant ferromagnetism is not responsible for the Invar properties of Fe-Pt alloys, in contrast to the Fe-Ni Invar alloys.
TL;DR: In this paper, the Mossbauer effect of the 21.53 keV transition of 151Eu was used to study EuNi5, EuMg2 and their hydrides.
Abstract: The Mossbauer effect of the 21.53 keV transition of 151Eu was utilised to study EuNi5, EuMg2 and their hydrides. Measurements of isomer shift and hyperfine field were made at various temperatures between 77K and 2.6K. The experimental data were used to interpret the hydrogen absorption mechanism acting in these intermetallics. In both cases results indicate that hydrogen absorption occurs primarily through the formation of europium hydride 'complexes'.
TL;DR: In this article, it was shown that a model of magnetic amorphous rare earth alloys with nonaxial electric field gradients is equivalent to the simple model with axial crystal fields -DJz(i)2 and D positive, when the rare earth moment is large and z(i is a local axis varying randomly from site to site.
Abstract: The authors show that a model of magnetic amorphous rare earth alloys with nonaxial electric field gradients is equivalent to the simple model with axial crystal fields -DJz(i)2 and D positive, when the rare earth moment is large and z(i) is a local axis varying randomly from site to site. For small values of J, the axial-field model is less justifiable, especially for non-Kramers ions. They discuss the consequences of nonaxial field gradients for some magnetic and nonmagnetic properties.
TL;DR: In this article, the antiferromagnetic phase boundary in the Cr-Fe system has been determined by neutron diffraction, and it is shown that no long-range order exists in alloys between 16 and 19 at.% Fe.
Abstract: The antiferromagnetic phase boundary in the Cr-Fe system has been determined by neutron diffraction. Antiferromagnetism disappears at a concentration of 16.0+or-0.5 at.% Fe. Resistivity measurements indicate that TN is marked by the maximum in the temperature coefficient of resistivity rather than the minimum in the resistivity. On the basis of these measurements it is apparent that no long-range order exists in Cr-Fe alloys between 16 and 19 at.% Fe.
TL;DR: Mossbauer conversion electron scattering is used to analyse the phases present in copper-iron alloys produced by 57Fe implantation at doses between 1*1015 and 5*1016 ions cm-2.
Abstract: Mossbauer conversion electron scattering is used to analyse the phases present in copper-iron alloys produced by 57Fe implantation at doses between 1*1015 and 5*1016 ions cm-2. The observed effects of defect clusters on the iron hyperfine parameters are discussed. A significantly different spectrum observed for the highest dose is associated both with the effects of sputtering and with the presence of widespread damaged regions.