Sp Impurities Research Articles

Hyperfine magnetic fields at sp-sites in Co2YZ Heusler alloys

The systematics of hyperfine magnetic fields at sp impurities on the Z-sites in Co based Heusler alloys are investigated. New TDPAC measurements of Cd hyperfine fields are reported.

Influence of charge transfer on ab initio calculated impurity resistivities in noble metals

AbstractA method is proposed to obtain values for the impurity resistivity, given an alloy potential. Correct single‐site values which account for the bandstructure of the host and which are calculated by solving the Boltzmann transport equation form the starting‐point. Effects due to charge transfer and lattice distortion can be estimated reliably using an approximate finite‐cluster model method. The selfconsistent potentials for impurities in copper and silver represent correctly the differences between the sp impurities and the 3d and 4d impurities in a host and also the difference between the two hosts for a given impurity. The agreement of the absolute values with experiment is not yet satisfactory.

Isomer shifts of sp impurities in metallic hosts

Isomer shifts for119Sn and121Sb impurities in different metallic hosts are compared. In the frame of the Miedema and van der Woude model three contributions to the isomer shifts due to the charge transfer, electron density mismatch and volume adjustment are calculated.

Internal oxidation of 5sp impurities in noble metals

The internal oxidation of ion-implanted radioactive119In,119Cd, and119Sb in high-purity (5N) copper, silver, and gold single crystals has been investigated. The formation of the impurity-oxygen defect structures was monitored by Mossbauer emission spectroscopy on the 24 keVγ-radiation from the daughter119Sn after theΒ-decay of the implanted radioactive isotopes. Molecule-like complexes are formed consisting of the implanted impurity and several oxygen atoms. The various Mossbauer parameters (isomer shift, quadrupole splitting, and Debye temperature) enable a distinction between different Sn-IV and Sn-II complexes, as well as between substitutional and vacancy-associated Sn atoms, which result from the ion implantations. The evolution of oxygen complexes with temperature during isochronal annealing was studied in the temperature range 300–1000 K. The formation (around 500 K) and the disintegration (around 900 K) of the complexes, in' silver in particular, are explained on the basis of diffusion properties of oxygen. A comparison of results from oxidations due to either thermal diffusion of oxygen or due to recoil implantations from a surface-oxide layer indicates that Sn-IV complexes are invariably formed in the first case, whereas in the latter case, a mixture of Sn-IV and Sn-II complexes is formed. Relations of the present results to similar results from PAC measurements on111Cd in silver and from Mossbauer experiments on AgSn alloys are discussed.

Ab initio calculations for impurities in Cu and Ni

Abstract By using the KKR-Green function method, the electronic structure of impurities in transition metals has been calculated within the local spin-density approximation. The electronic structure of 3d impurities in Cu are discussed, with particular reference to the formation of local moments and their interactions. An evaluation of the electronic structure of d and sp impurities in ferromagnetic Ni is given and results are presented for the hyperfine fields of the impurities. The calculations reproduce well the experimentally observed trends for the local moments and the hyperfine fields.

Electronic properties of dilute copper alloys III. Influence on the de haas‐van alphen effect

AbstractA calculation of the Dingle temperatures and changes of the Fermi surface areas of Cu resulting from alloying with 4d transition metal impurities and with sp impurities of the third, fourth, and fifth rows of the Periodic System is presented. The theoretical results are compared with experimental information obtained from de Haas‐van Alphen investigations.

Electronic Properties of Dilute Copper Alloys II. Residual Resistivity

AbstractThe residual resistivity of 4d transition metal impurities and of sp impurities of the third, fourth, and fifth rows of the periodic system in a Cu host is calculated. The linearized Boltzmann equation is solved using the degenerate kernel technique taking into account the full anisotropic band structure of the host. The results are compared with experimental information and some other theoretical treatments.

Electronic properties of dilute copper alloys I. theory

AbstractThe electronic properties of 4d transition metal impurities and sp impurities of the third, fourth, and fifth rows of the periodic table in a Cu host are calculated self‐consistently. The impurity is embedded in the perfect crystal environment and described by a single perturbed muffin‐tin potential in the KKR‐Green function scheme. The influence of the impurities on the de Haasvan Alphen effect (Dingle temperatures and changes in areas of the Fermi surface) and the residual resistivity are discussed. For the residual resistivity the linearized Boltzmann equation is solved taking into account the full anisotropic band structure of the host.

Cluster model residual resistivities in 35 Copper Alloys

AbstractResidual resistivities are calculated for dilute copper alloys with 4d and 3d transition metal impurities and sp impurities from the third, fourth, and fifth row of the periodic system. Finite cluster model (FCM) results are compared with values obtained from the simple Friedel formula, from the Gupta‐Benedek (GB) formula which accounts for backscattering, and from the formula by Coleridge, Holzwarth, and Lee (CHL), accounting in addition for Fermi surface effects. In the FCM the effect of lattice distortion is studied by placing the first shell of host atoms around the impurity at relaxed positions. Self‐consistent potentials are used for host and impurities. In general the FCM accounts for backscattering in a more sensitive way than the GB formula.

Electronic structure of non-magnetic impurities in Cu

Using density functional theory the electronic structure of 4d transition metal and sp impurities from the third, fourth and fifth rows of the periodic system in a Cu matrix is calculated self-consistently. The authors use the local spin density approximation of Hedin and Lundqvist. The impurity is embedded in the perfect crystal environment and described by a single perturbed muffin-tin potential in the KKR-Green function scheme used previously for other impurities in Cu, Ag and Al. Results are given for the local density of states, scattering phase shifts, local charges, change of density of states at the Fermi level and residual resistivity. The density of states of the virtual bound states of 4d impurities is not very Lorentzian-shaped due to a rather large d-d interaction and the local density of states at the bottom of the Cu d band is more similar to pure Cu than it was for 3d impurities. The sp impurities are electronically characterised by a piling up of s or p bonding and antibonding states at both sides of the Cu d energy region gradually shifting to lower energies when they are filled.

Local density of states of impurities in Al

Using the KKR-Green function method, the electronic structure of impurities in Al is calculated self-consistently by applying the density functional theory in the local spin-density approximation of von Barth and Hedin (1972). The impurity is described by a single perturbed muffin-tin potential, which is determined self-consistently. The authors give results for the local density of states, scattering phase shifts and local charges for 3d impurities and sp-impurities (Si, P, S, Cl, Ga, Ge, As). The virtual bound states of some 3d impurities show strong deviations from a Lorentzian form arising from the band structure of Al. The impurities Cr, Mn and Fe turn out to be magnetic, with local moments of 2.0, 2.5 and 1.75 Bohr magnetons. The electronic structure of the sp impurities Si, P, Ge and As is characterised by a shift to lower energies of the s density of states, leading to localised s states for P and As, and by a filling up of the p density of states.

Simple Electronic Structure Calculation of Substitutional sp Impurities in α‐Iron

AbstractTaking into account a Slater‐Koster fit to first‐principles band structures for the host, a simple tight‐binding model is proposed for the electronic structure of sp impurities (Al, Si, P … Sb) substituted in ferromagnetic metals. The aim of the model is to extend calculations to future more complicated problems like chemical binding energies between point defects. The method is applied to dilute σ‐iron based alloys: it is shown that a localized impurity model gives reasonable accord with experimental data on saturation magnetization, every time the dilution law is almost satisfied (FeAl, FeSi, FeP).

Calculation of the transferred hyperfine field (volume overlap) contribution on nonmagnetic impurities in Fe and the Heusler alloys

The transferred hyperfine fields (hff) at 4sp and 5sp solute atoms in Fe and the sp sites of the Heusler alloys have been calculated using a volume overlap model. The main difference between this and previous calculations is that the host wavefunction in the solid is represented by an orbital that is simulated from band calculations. The contributions from 2nn and 3nn atoms are also included. The calculated transferred hff values are compared to the hff contributions obtained by substracting the hff due to the host s conduction electron polarization from measured hff values. For the 4sp and 5sp impurities in Fe the calculated transferred hff contributions agree excellently with those obtained from the measured hff. The experimental data for sp impurities at the Z site of Heusler alloys is less complete than that for an Fe host, but again the calculated transferred hyperfine fields agree satisfactorily with those deduced from the measured values. Since for the Heusler alloys there are no arbitrary procedures or parameters relative to the Fe data, the agreement between the calculated and experimental values gives strong evidence in support of the volume overlap model.

Magnetic hyperfine field of129I impurities in Pd2MnSb

In the Heusler alloy Pd2MnSb (Z′) agreement has been found between the experimental values of magnetic hyperfine fields of 5sp shell impurities Z′ that substitute Sb and the theoretical predictions of Blandin and Campbell |2|. The decrease of the field when the 5sp shell is nearly full lends support to conduction electron polarization models based on the Daniel Friedel |4| type of theory. In view of these results, the rise of the field of 5sp impurities in iron right up to shell closure remains puzzling.

Hyperfine interactions at Fe57and Sn119nuclei in MnSb

The ferromagnetic compound MnSb was studied using Mossbauer spectroscopy of the isotopes Fe57 and Sn119. The saturation values for the hyperfine magnetic fields at the nuclei of Fe57 and Sn119 impurities in MnSb are -110 kOe and -45 kOe respectively. The value of the field for Fe is similar to that observed in the related system FeSb. A spin-flop transition is observed depending on temperature and sample composition. The Fe saturation magnetic field scales with the saturation magnetisation of the host material. The difference between room temperature and liquid nitrogen temperature results suggests a relatively weak coupling between the Fe moment and the host magnetisation. The value of the Sn field is in agreement with trends observed for non-magnetic 5sp impurities in magnetic hosts.