Strain field due to transition metal impurities in Ni and Pd

The strain field due to body centered substitutional transition metal impurities in Ni and Pd metals are investigated. The calculations are carried out in the discrete lattice model of the metal using Kanzaki lattice static method. The effective ion-ion interaction potential due to Wills and Harrison is used to evaluate dynamical matrix and the impurity-induced forces. The results for atomic displacements due to 3d, 4d and 5d impurities (Fe, Co, Cu, Nb, Mo, Pd, Pt and Au) in Ni and (Fe, Co, Cu, Ni, Nb, Mo, Pt and Au) impurities in Pd are given up to 25 NN’s of impurity and these are compared with the available experimental data. The maximum displacements of 4.6% and 3.8% of 1NN distance are found for NiNb and PdNb alloys respectively, while the minimum displacements of 0.63% and 0.23% of 1NN distance are found for NiFe and PdFe alloys respectively. Except for Cu, the atomic displacements are found to be proportional to the core radii and d state radius. The relaxation energies for 3d impurities are found less than those for 4d and 5d impurities in Ni and Pd metals. Therefore, 3d impurities may easily be solvable in these metals.     

Table of hyperfine fields for impurities in Fe,Co, Ni and Gd

All data available in the literature for the impurity hyperfine fields in Fe, Co, Ni and Gd matrices are collected and tabulated. The literature search was carried out for all references listed in Physics Abstracts on papers published till the end of December 1978. The present work is an extension of similar earlier compilations [1–6]. The data are arranged in ten columns as explained below:     

Magnetic behavior of na films with Fe, Co, and Ni impurities

Thin films of Na with Fe, Co, and Ni impurities are investigated. The magnetization of the impurities is measured by means of the anomalous Hall resistance. Fe and Co show a moment of about 6mu(B), while for Ni no moment is detected. Furthermore, the magnetic dephasing of the conduction electrons is measured by means of weak localization. The dephasing rate 1/tau(phi) of the 3d impurities differ qualitatively. For Fe impurities, 1/tau(phi) is so large that it cannot be measured. For Co, 1/tau(phi) has a moderate value while Ni shows hardly a dephasing effect at all.     

The electrical resistivity of liquid Fe,Co, Ni and Pd

The electrical resistivity of Fe, Co, Ni and Pd has been measired at high temperatures in the solid and liquid state. We discuss the results in the light of recent ideas on the Ziman theory and the spin-disorder scattering of liquid transition metals.     

Effect of Ni and Co impurities on the electronic structure and magnetic properties of BCC iron

A theory of disordered binary alloys A_xB_1−x (A=Ni, Co; B=Fe; x0.06) is used to determine the changes in the electronic structure and magnetic properties of body centered cubic (BCC) iron induced by doping with nickel and cobalt impurities. This approximation is an extension of the cluster-Bethe lattice method, in which we incorporate electronic correlations, itinerant and localized nature of electrons 3d, and both long-range and short-range chemical correlations. The magnetism is described by means of a Hubbard Hamiltonian that in conjunction with Green's functions techniques is used to calculate local densities of electronic states. For it we take an atom in the real lattice and it is joined to a Bethe's lattice with like coordination number. The magnetic moments on sites occupied for A and B atoms are obtained self-consistently. Nickel and cobalt impurities in BCC iron can provide crucial information on the modification of the electronic band structure and magnetic moments from pure Fe. The results obtained are compared with those of both pure Fe and binary alloys of Co–Fe and Ni–Fe, which have been obtained by other authors using methods such as: first-principles electronic structure calculations using the layer Korringa–Kohn–Rostoker (KKR), the full-potential linearized augmented plane wave method, the KKR coherent potential approximation combined with the local-density functional method and by the tight-binding linear-muffin-tin orbitals method, obtained good agree. These results and other that recently we have published indicate to us that our methodology can be a new alternative for calculations of the electronic structure and magnetic properties of impurities and alloys of ferromagnetic transition metals.     

Nonlinear behaviour during methane and ethane oxidation over Ni,Co and Pd catalysts

The recent results on the oscillatory behaviour during methane and ethane oxidation over metal catalysts, including nickel, cobalt and palladium have been reviewed. The application of thermogravimetric analysis in combination with on-line mass-spectrometry and visual observations of the catalyst surface during oscillations provided the definite proof that the origin of the oscillatory behaviour in all these systems was connected with the periodical oxidation–reduction of a catalyst. The variety of spatial patterns was detected over the Ni and especially over the Co foil. Emphasis has been done on the differences and similarities of the oscillatory behaviour in various reactions over different catalysts.     

Gate-dependent orbital magnetic moments in carbon nanotubes

We investigate how the orbital magnetic moments of electron and hole states in a carbon nanotube quantum dot depend on the number of carriers on the dot. Low temperature transport measurements are carried out in a setup where the device can be rotated in an applied magnetic field, thus enabling accurate alignment with the nanotube axis. The field dependence of the level structure is measured by excited state spectroscopy and excellent correspondence with a single-particle calculation is found. In agreement with band structure calculations we find a decrease of the orbital magnetic moment with increasing electron or hole occupation of the dot, with a scale given by the band gap of the nanotube.     

Temperature dependent scattering from Cr impurities in Pd

The incremental resistivity Δ?(T) associated with small amounts (between 0.05 and 0.3 at% Cr) of Cr in Pd has been measured between 1.4 and 300 K and has been assumed to contain two principle contributions. The first decreases monotonically with increasing temperature, while the second consists of a rapid increase in Δ?(T) with increasing temperature between 15 and 60 K and has been attributed to conventional deviations from Matthiessen's rule (DMR). With the latter assumed to temperature independent above 70 K, Δ?(T > 70 K) has been fitted to

$\text{Δ?(T) = Ac + Bc 1n(T}{}^2\text{+ T}{}^2{}_{\mathrm{s}}\text{)}{}^{\mathrm{1/2}}$

yielding a concentration independent estimate of T_s ? 44 K. By comparing the experimental data with the extention of the above equation at temperatures below 70 K it is possible to estimate both the conventional DMR and the coefficient of the T² term predicted at low temperatures. While the former are in reasonable agreement with DMR observed in dilute non-magnetic Pd alloys, the T² coefficients measured in Δ?(T ? T_s) differ from their predicted values. Sources for this discrepency are discussed.     

Spin and orbital magnetic moments of free nanoparticles

The determination of spin and orbital magnetic moments from the free atom to the bulk phase is an intriguing challenge for nanoscience, in particular, since most magnetic recording materials are based on nanostructures. We present temperature-dependent x-ray magnetic circular dichroism measurements of free Co clusters (N=8-22) from which the intrinsic spin and orbital magnetic moments of noninteracting magnetic nanoparticles have been deduced. An exceptionally strong enhancement of the orbital moment is verified for free magnetic clusters which is 4-6 times larger than the bulk value. Our temperature-dependent measurements reveal that the spin orientation along the external magnetic field is nearly saturated at ~20 K and 7 T, while the orbital orientation is clearly not.     

Evidence for multiple band terminations in Pd

The level structure of ¹⁰²Pd has been investigated using data collected with the Eurogam 2 array. Several cascades of γ-rays have been established up to high spins. Termination of rotational bands has been observed at I^π = 28⁻ and 32⁺, and tentatively at I^π = 38⁺ and 42⁺. The nucleus ¹⁰²Pd is the first case where rotational bands built on valence space configurations are followed from spin close to zero up to termination and, at higher spins, a smooth rotational band which appears to terminate is built on core excited configurations.     

Frequency moments and energy shifts for dilute Mössbauer impurities in metallic solids

Theoretical evaluations of frequency moments and second order Doppler shifts have been made for dilute⁵⁷Fe impurities in the high temperature limit for a harmonic solid. The resonant energy shifts have been calculated from the Green’s function of the impure crystal containing both mass disordering and force constant change terms in the crystal Hamiltonian. High temperature frequency moments for the impurity in different metallic solids are obtained from Mc-Millan ratios using standard Mössbauerf-values at room temperature. The effect of mass disordering predominates over the force constant change term in the evaluations of second order Doppler shifts and hence the frequency moments for dilute⁵⁷Fe impurities. The variation of frequency moments for the impurity with mass modified Debye-temperature of the hosts is shown for a number of metallic solids.