II. XPS study of 3d-metal ions dissolved in noble metals

Valence and core level spectra ofAgMn,AuFe,AuCo,AuNi,CuFe,CuCo andCuNi will be reported. Clearly defined virtual bound states (vbs) can only be detected in the spin fluctuating systemsAuNi andCuNi. An increase in the density of states near the Fermi energy, in the region of the flats-p band of the host metal is observed in the other magnetic alloys. There are indications that a large hybridization between the impurity and the host metald-electrons exist. The impurity core levels show satellites. They can originate from the emission from real isolated impurities and from many body effects.     

Magnetic impurity effects inAgMn,AuFe, andCuCr studied by tunneling in superconducting proximity layers

Magnetic interactions were studied by superconducting tunneling into diluteAgMn,AuFe, andCuCr alloys in which superconductivity had been induced by a proximity effect. A detailed investigation ofAgMn, for concentrations up to 0.4 at.% Mn and at temperatures down to 0.05 K, revealed a weak impurity band within the energy gap of the density of excited states at about 0.68 of the half energy gap . The amplitude of the band, however, was twenty times smaller than expected from the theory by Müller-Hartmann and Zittartz. This makes the interpretation of the effect as being due to bulkAgMn doubtful. The localisation of the band would imply a Kondo temperature,T _K , of about 1 mK for an impurity spinS=5/2. No effect of spin-glass ordering was seen in the temperature dependence of the tunneling density of states inAgMn which contradicts a report by Schuller et al. The zero bias conductance could instead be reproduced from low temperature measurements if the temperature variation in was taken into account. InCuCr, the shape of the impurity band was found to be temperature dependent. The location of an impurity band at about 0.68 inAuFe indicates. together with previous observations, the presence of two impurity bands in this alloy. The one found here, might be due to long-range Fe pairs.     

Anisotropic impurity scattering in palladium silver alloys

Measurements have been made of the Hall coefficientR of some alloys of silver in palladium over the temperature range 1°K to 120°K. The alloys contain between ∼1 and ∼10 at.-% silver. Values ofR were also obtained at room temperature and these were in good agreement with earlier published work. The values ofR are negative in all the alloys, and |R| increases both on reducing the temperature and increasing the silver concentration,c. Below ∼10°K, |R| becomes independent of temperature but shows a linear dependence onc, increasing by a factor of 2.5 over the concentration range measured. This increase is too great to be accounted for in terms of band structure changes alone, so we have examined the effects of anisotropic impurity scattering. To a first approximation it can be shown thatR is proportional to an anisotropy parameterA, defined asA=〈τ ²(k)〉/〈τ(k)〉², whereτ(k) represents the relaxation time of an electron in a statek, and 〈〉 is an average over the Fermi surface. In palladium we assume that the majority of the current is carried by the s-electrons. In the presence of silver impurities these electrons can be scattered into s-states or d-states with relaxation times given byτ _ss α1/c(1−c) andτ _sd α1/c ²(1−c) respectively. FollowingPlate we have assumed thatτ _ss is isotropic and thatτ _sd is anisotropic, leading to an overall anisotropic relaxation time for impurity scattering. We then find the parameterA increases approximately linearly with silver content, in accordance with our experimental results.     

Positron lifetime and Doppler-broadening measurements in noble metals and their alloys

Positron annihilation measurements in pure copper and silver as well as in the alloysCuGe,CuIn,CuSb, andAgSb have been performed. Most of the measurements have been carried out in thermal equilibrium. In this way it is possible to deduce vacancy formation — and vacancy — solute atom binding energies. ForCuIn alloys with 3.3 at.% and 7.1 at.% indium precipitation effects have been studied.This paper is based upon a talk given by W.L.-T. at the Int. Symp. Production of Low-Energy Positrons with Accelerators and Applications Justus-Liebig-Universität Giessen (1986)     

Electric field gradients created by near neighbour impurity atoms in a cubic silver host

The electric quadrupole interactions produced by near neighbour impurity atoms of Cu, Au, Zn, In, Sn and Bi on¹¹¹Cd probe nuclei in a cubic Ag lattice were studied by the TDPAC method. The effects of the type of impurity and its concentration have been investigated. The results show the presence of a high-frequency interactionv _Q ^h superimposed to a smeared out low frequencyv _Q ^l . The high frequency interaction, in the range 20 to 600 MHz, is attributed to impurity atoms located in nearest neighbour sites, while the low frequency interaction, in the range 2 to 12 MHz, is generated by impurities distributed at various different atomic distances from the probe nuclei. Bothv _Q ^h andv _Q ^l increase with impurity concentration leaving the ratiov _Q ^h /v _Q ^l almost constant. The results show that the high frequencyv _Q ^h is linearly dependent on the solute valence, and a logarithmic function of the impurity concentration, in the range 0.5 to 4.5 at. %. Large size effects have been observed in CuAg and BiAg alloys. Instead for ZnAg and SnAg, thev _Q ^h andv _Q ^l variation is attributed basically to charge effects.Work supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Financiadora de Estudos e Projetos (FINEP).     

Hall effect in the ternary ordered alloys Ni3(Mn,Fe) and Ni3(Mn,Co) 1. Disordered solution solutions

The normal and anomalous Hall constants R₀ and R_s, respectively, and the resistivity have been measured for the quasibinary alloys Ni₃Mn-Ni₃Fe and Ni₃Mn-Ni₃Co. The results imply that in ternary alloys of Ni₃Mn containing slight Fe and Co impurities the hole regions of the Fermi surface make an important contribution to R₀ and that the primary scattering mechanism for the carriers corresponding to the anomalous Hall current in the alloys with Fe at room temperature is phonon scattering. It is concluded that the Fermi surface of the Ni₃Mn-Ni₃Fe alloys is closed.Translated from Izvestiya VUZ. Fizika, No. 3, pp. 21–29, March, 1970.     

Elektrischer Widerstand von metastabilenAg,Fe- undCu,Fe-Legierungen bei tiefen Temperaturen

Ag, Fe undCu, Fe alloys of high concentration (up to 20 at %), which cannot be produced as solid solution in bulk, are produced by the simultaneous condensation of both the components on a substrate at a temperature of 4.2 or 78 K. By cooling the two alloys show a minimum and a maximum of the electric resistance, both dependent on concentration and annealing temperature. In contrast toAg, Fe theCu, Fe alloys with more than 3,5 at % show an additional minimum at temperatures between 10 and 1 K, which disappears if the samples are annealed at 380 K.     

Electronic structure ofCuNi,CuCo andAgNi alloys

Summary The pseudo Green's function theory for dilute alloys ofd-band metals is used to study the electronic structure ofCuNi,CuCo andAgNi alloys. The calculated densities of state are found in agreement with other available results. The virtual bound states with double-hump structure are found at 0.514, 0.54 and 0.4 Ryd forCuNi,CuCo andAgNi alloys, respectively.

---

Riassunto La teoria della pseudo funzione di Green per leghe diluite di metalli nella bandad è usata per studiare la struttura elettronica delle legheCuNi,CuCo eAgNi. Si trova che le densità di stato calcolate sono in accordo con altri risultati disponibili. Gli stati legati virtuali con struttura a doppia sporgenza si trovano a 0.514, 0.54 e 0.4 Ryd per leghe diCuNi,CuCo eAgNi.

---

Резуме Используется теория псевдо-гриновских функций для разбавленных сплавов металловd-зоны, чтобы исследовать злектронную структуруCuNi,CuCo иAgNi. Получено, что вычисленная плотность состояния согласуется с другими имеющимися результатами. Обнаружены виртуальные связанные состояния, имеюшие структуру с двойным максимумом, при 0.514, 0.54, 0.4 Ry соответственно для сплавовCuNi,CuCo иAgNi.

     

Observation of a correlation between the dependences of the radiative decay time and intensity of the impurity core-valence luminescence on excitation energy in K1−x CsxCl and Rb1−x CsxCl mixed crystals

A study of the spectral and kinetic parameters of impurity core-valence luminescence (CVL) excited by synchrotron radiation in K_1−x Cs_xCl and Rb_1−x Cs_xCl mixed crystals is reported. The dependences of the intensity and radiative decay time τ of impurity CVL on exciting photon energy hν have been found to be correlated. It is concluded that the observed τ = f(hv) relation originates from nonradiative decay of core excitations near the surface, which govern also the excitation spectral features in this spectral region. Fiz. Tverd. Tela (St. Petersburg) 41, 1973–1975 (November 1999)     

Relaxation time measurements in zinc alloys

Relaxation times obtained by means of de Haas-van Alphen measurements have been investigated in dilute alloys ofZnMn andZnAg. In both series of alloys measurements have been made on the needle, monster and lens sections of the Fermi surface. In theZnMn alloys, which exhibit a Kondo resistance minimum, the results analysed followingPaton andMuir [2] give a value for the s—d interaction constant,J, agreeing with this previous work. Similarly, an analysis followingNagasawa [4] givesJ values in agreement with that work. The situation posed by the existence of these two approaches, concerned as they are with opposite extreme limits, is discussed. In addition, the behaviour found in the other periods ofZnMn is discussed; here the effects seen on the needles are completely absent. A preprint of this paper was introduced during the discussion at the Conference on Electron Mean Free Paths by the Chairman of the Session, Dr.D. Shoenberg.     

Electron momentum density in Cu<Subscript>0.9</Subscript>Al<Subscript>0.1</Subscript>

A reconstruction technique based on the solution of the Radon transform in terms of Jacobi polynomials is used to obtain the 3D electron momentum density, ϱ(p), from nine high-resolution Compton profiles (CPs) for a Cu_0.9Al_0.1 disordered alloy single crystal. The method was also applied to theoretical CPs computed within the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) first-principles scheme for the same nine orientations of the crystal. The experimental ϱ(p) is in satisfactory agreement with the theoretical ϱ(p), shows most details of the Fermi surface (FS) and exhibits electron correlation effects. We comment on the map of the FS obtained by folding the reconstructed ϱ(p) into the first Brillouin zone, which yields the occupation number density, ϱ(k). A test of the validity of data via a consistency condition (within our reconstruction algorithm) as well as the propagation of experimental noise in the reconstruction of both ϱ(p) and ϱ(k) are investigated. Received: 24 October 2001 / Accepted: 20 January 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +48-71/344-10-29, E-mail: samsel@int.pan.wroc.pl     

The activation energy for γ-Fe precipitates inCuFe

The precipitation of the fcc γ-phase of iron has been studied by a systematic series of isothermal and isochronal (0–48 h) heat treatments (300–800°C) on a supersaturated solution ofCuFe containing 3 at% Fe. The optimal conditions (450–600°C) for precipitation of the maximum fraction (90%) of iron attainable within 48 h in the form of γ-Fe have been delineated from analysis of the room temperature spectra. The time dependence for formation of γ-Fe precipitates is well described by the equation for long term annealing. An activation energyE _a ≈0.6 eV for the formation of γ-Fe in Cu is obtained. It indicates short range rather than long range diffusion in theCuFe sample studied.     

Analytic solution of the BCS gap equation inD dimensions (D=1, 2, 3), at finite temperatures

The Bardeen-Cooper-Schrieffer (BCS) gap equation is solved analytically in one, two and three dimensions, for temperatures close to zero andT _c. We work in the weak coupling limit, but allow the interaction widthν≡ħω _m/E _F to lie in the interval (0, ∞) Here,ħω _m is the maximum energy of a force-mediating boson, andE _F denotes the Fermi energy. We obtain expressions forT _c and ΔC, the jump in the electronic specific heat acrossT=T _c, in the limitsν≪1 (the usual phonon pairing) andν>1 (non-phononic pairing). This enables us to see howT _c scales with the mediating boson cut off. Our results predict a larger jump in the specific heat for the caseν>1, compared toν≪1. We also briefly touch upon the role of a van Hove singularity in the density of states.     

I. XPS study of 3d-metal ions dissolved in aluminium

The core and valence band spectra of diluteAlMn,AlNi andAlCu alloys have been investigated by x-ray induced photoemission spectroscopy (XPS). The 2p levels of Mn and Cu inAlMn andAlCu change only slightly compared to their properties in the pure metals, whereas those of Ni inAlNi lose both their asymmetry and the two hole satellite. The 3s spectra of Mn inAlMn show a splitting of 2.9 eV, as compared to 4.3 eV in Mn metal. This indicates that inAlMn the Mn ion is magnetic, at least in the time scale of the XPS measurement. The valence band spectra of the alloys (and ofAlFe andAlCo) show virtual bound states with a width of about 1.5 eV and a distance relative to the Fermi energy which increases with increasingd-occupancy. The energy of the Al plasmons increase with increasingd-metal content.     

Investigation of the kinetic characteristics of heavily doped compensated CdSnAs2(Cu)

The concentrational dependences of the Hall coefficient and of the resistivity were used to investigate the interaction of diffusively introduced copper impurity with an ensemble of intrinsic defects inn-CdSnAs ₂. The initial electron density and the concentrations of theV _As andCu _As defects were found to be of the same order. A study was made of the dependence of the electrophysical properties ofCdSnAs ₂ (Cu) on the population of the impurity band and it was shown that the features of the kinetic characteristics ofCdSnAs ₂ (Cu) are determined by the absence of an energy gap between the bands with a conductivity of opposite sign and by the fact that one of the bands is an impurity band. State Pedagogical University, Nizhegorod. Kh. I. Amirkhanov Physics Institute, Dagestan Scientific Center, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 62–66, May, 1997.     

Improved tau polarisation measurement

Using 22 pb⁻¹ of data collected at LEP in 1992 on the peak of the Z resonance, the ALEPH collaboration has measured the polarisation of the tau leptons decaying into ,πν, ρν and a₁ ν from their individual decay product distributions. The measurement of the tau polarisation as a function of the production polar angle yields the two parametersN _τ andN _e, where, in terms of the axial and vector couplingsg _Al andg _Vl,N _l=2g _Vl g_Al/(g _Vl ² +g _Al ² ). This analysis follows to a large extent the methods devised for the 1990 and 1991 data but with improvements which bring a better understanding of the systematic uncertainties. Combining the 1992 measurements with our previously published results yieldsN _τ=0.136±0.012±0.009 andN _e=0.129±0.016±0.005. Assuminge−τ universality, the measurements imply an effective weak mixing angle of sin ² θ _W ^eff =0.2332±0.0014. Deceased     

The OPERA experiment

The aim of the OPERA experiment is to provide unambiguous evidence for the ν _μ ↔ ν _τ oscillation by looking at the appearance of ν _τ in a pure ν _μ beam. This oscillation will be sought in the region of the oscillation parameters indicated by the atmospheric neutrino results. The experiment is part of the CNGS (CERN Neutrino beam to Gran Sasso) project. The ν μ beam produced at CERN will be sent towards the Gran Sasso underground laboratory, where the OPERA detector is under construction. The detector, the physics potential, and performance for neutrino oscillation studies including the subleading ν _μ ↔ ν _ε search are presented. The text was submitted by the author in English.     

Kondo effect in spin glasses: Electrical resistivity

We investigate the influence of the Kondo effect on the electrical resistivity of spin glasses. Our approximation reduces in the limit of vanishing impurity concentrations to the Suhl-Nagaoka theory for the Kondo effect. The magnetic impurity interactions are taken into account in the form of time dependent two-spin correlation functions which can be measured by neutron scattering. The dynamics of the impurity spins leads to a partial destruction of the Kondo effect. For the resistivity this can be described by a temperature dependent effective spinS _eff ² (T) withS _eff ² 0 forT0 andS _eff ² S(S+1) forT, and by a reduction of the Kondo temperatureT _K. Sufficiently strong interactions lead toT _K=0. We obtain a resistivity maximum at a temperatureT _m due to the interplay of the Kondo effect and the spin dynamics;T _m depends onT _K and on the excitation spectrum, and therefore on parameters such as impurity concentration or pressure. The ratioT _m/T_f (T _f is the freezing temperature) is calculated for a single relaxation time and for a square density of relaxation modes and is compared with experimental data forAuCr,AuMn,AgMn, andCuMn. The influence of other possible modes on various spin glass properties is discussed.SFB 125 Aachen-Jülich-Köln     

The magnetic susceptibility of AgPd alloys with Mn and Fe impurities

Measurements of the magnetic susceptibility of AgPd alloys with Fe and Mn impurities have been performed at temperatures from 1.4 K to 300 K. Alloys with 5 and 10 at.% Pd, 2 and 6 at. ppm Fe and with Mn concentrations in the range 10 to 7,000 at. ppm were investigated. The temperature variation of the impurity susceptibility was analysed according to a Curie-Weiss law. The effective moment for Fe varies with the Pd concentration, which is interpreted as due to interactions between near neighbour Fe and Pd atoms. These interactions tend to lower the characteristic temperature of single Fe impurities and induce a spin on the Pd atom ferromagnetically coupled to the Fe spin. InAgPdMn one finds no such induced moment on the Pd atoms. The effective momentµ _eff =(5.36±0.10)µ _B per Mn atom and the Curie-Weiss temperature=(0.08±0.09) K are independent of Pd as well as Mn concentrations.µ _eff is slightly higher than for Mn in very diluteAgMn, which may be due to a different polarisation of the conduction electron gas around the impurities.     

De Haas-van Alphen studies of conduction electron scattering in dilute alloys of copper

Measurements of the Haas-van Alphen Dingle temperatures per atomic percent solute have been obtained for seven different cyclotron orbits in dilute alloys of nickel, germanium and gold in copper. The measured values have been inverted using a Fourier series representation for _k ^–1 to determine the variation of the local scattering rate over the Fermi surface for each species of solute.