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.     

Ion implantation as a tool for studying the Kondo-systemZnMn

In the case ofZnMn alloys it is shown how low temperature ion implantation can be used for the production of dilute magnetic alloys. The Kondo effect in the resistivity (T) was studied between 1.1K and 20 K. The phonon part of the resistivity was subtracted using (T)-curves from Zn-Films with similar disorder produced by self-ion implantation. A logT-dependence with a slope proportional to the Mn-concentration was found below 200 ppm. The influence of disorder on the specific Kondo slope is discussed.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthday.     

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.     

Critical behavior in radiation damaged systems

Perturbed angular distribution (PAD) measurements of Bleck et al. of the critical behavior of⁶³NiNi,⁶⁶CuNi, and⁶⁷ZnNi have been reanalyzed, and shown to be insufficiently asymptotic to permit deduction of meaningful critical exponents. Via experiments on implanted¹¹¹InNi, done with and without annealing of radiation damage, and by comparison to diffused¹¹¹InNi, it is suggested that unannealed radiation damage can produce serious systematic errors in critical exponents.This work has been supported in part by DMR 01250 from the U.S. National Science Foundation to Clark University, and in part by the Stichting voor Fundamenteel Onderzoek der Materie, the Netherlands     

The Hall coefficient and other transport properties of dilute alloys of copper and silver

The low field Hall coefficient of a number of polycrystalline foils of dilute (2%) alloys of copper and silver has been measured in the temperature range 1.5–50°K, and at room temperature. The alloys chosen wereCu-Au andAg-Au (uncharged impurity),Cu Ge andAg-Sn (charged impurity), andCu-Ni andAg-Pd (transition metal impurity). At 20°K and below, the Hall coefficients of the different copper alloys differ widely from each other,Cu-Ge giving the highest (negative) values (up to twice the room temperature value for pure copper), andCu-Au the lowest (down to 0.7 of this value). There are also significant concentration dependences. The silver alloys show corresponding but smaller changes. A relationship, due to Tsuji, gives the Hall coefficient as a function of the Fermi velocityν and the mean curvature 1/ϱ of the Fermi surface, for the case of an isotropic relaxation time. The integrals over the Fermi surface have been numerically estimated using the known Fermi surface and electron velocities. For both Cu and Ag the results agree with the experimental room temperature values, which we take as evidence thatτ(k) for phonon scattering is here close to isotropic. On the other hand, to account for the Hall coefficients of the alloys, it is necessary to assume that the relaxation timeτ varies over the Fermi surface. It is seen that in Cu and Ag the neck regions contribute relatively little toR since both 1/ϱ andν are small there. The main change inR in different alloys arises from the variation in the relative weighting given to the belly regions by different kinds of impurity scattering. A closer analysis shows that the bulges in the Fermi surface of copper in the 〈100〉 directions contribute relatively heavily because of their high positive curvature. The anisotropy ofτ deduced from the Hall coefficient is compared with that deduced from other measurements.     

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.     

LMR quadrupole interaction measurement on69mGe and71mGe in Zn

A new experimental set-up to perform in-beam LMR (Level Mixing Resonance) measurements is briefly outlined. The first results are reported here. The quadrupole interaction of^69mGeZn is measured and in good agreement with earlier measurements:v _Q=80.6(4) MHz; for^71mGeZn, the valuev _Q=33.1(30)MHz is found. In addition, the relaxation behaviour and radiation damage of Ge recoil implanted in Zn is studied.     

The effect of temperature and concentration on the electric field gradient in binary indium alloys

The concentration and temperature dependence of the quadrupole hyperfine interaction of¹¹¹Cd in InTl (hcp),InPb (fct),InTl (fct) andInCd (fct and fcc) alloys were studied using the perturbed angular correlation technique. The change in the observed quadrupole interaction frequency with concentration can be described by a linear dependence on the axial ratioc/a in all cases. In the alloys with identical crystal structures the strength of thec/a dependence is independent of the solute, in contrast to the strength of the concentration dependence. In all cases where no phase transition occurs, the change in the electric field gradient with temperature follows the empirical relationV _zz (T)=V _zz(0) · (1–B·T ^3/2), where the coefficientB depends on the lattice structure, on the solute-solvent combination and on the concentration. The phase transitions ofInCd alloys at 293 K could clearly be seen as discontinuities in the temperature curves. A similar series of discontinuities observed around 116 K suggests the existence of a cubic low temperature phase.     

The representations of the oscillator group

Using the Mackey theory of induced representations all the unitary continuous irreducible representations of the 4-dimensional Lie groupG generated by the canonical variables and a positive definite quadratic hamiltonian are found. These are shown to be in a one to one correspondence with the orbits underG in the dual spaceG to the Lie algebraG ofG, and the representations are obtained from the orbits by inducing from one-dimensional representations provided complex subalgebras are admitted. Thus a construction analogous to that ofKirillov andBernat gives all the representations of this group.The research reported in this document has been sponsored in part by the Air Force Office of Scientific Research OAR through the European Office Aerospace Research, United States Air Force.     

Unstable systems and repeated measurements

In this part of the paper we treat two examples. In the first one the chamber structure is assumed only to be periodic andP(t) is an exponential. In the second example no specific assumption is made about the primary decay law and the measuring device is structured as an idealized spark chamber. This example contains results ofBeskow andNilsson as a special case.We follow the program formulated in the first part of this paper (referred hereafter as [I]). In the introduction of [I] we mentioned three examples; here we give two of them.     

Preparation and critical currents of vapour-deposited Nb3Sn compound

Conclusion The presented results have shown that by optimizing some of the basic technological parameters of the chemical vapour-deposition process it is possible to increase substantially the critical currentI _c and the Nb₃Sn layer thickness of the produced superconductor without any other technological treatment.The critical currentI _c reported byEnstrom et al. [7] concerning the pure reaction atmosphere without doping gases, is about 13 A/mm (per 1 mm of the tape width), in our case it is 62 A/mm in transverse magnetic field of 5 T. We have shown that as far as the Nb₃Sn tape length of the order of 100 m is concerned, it seems more advantageous to work with Nb/Sn chlorides ratio for the region of 0·55 to 0·87 in contrast to the value of 0·33 reported byEnstrom et al. [7]. As we have already mentioned, further increase of theI _c andJ _c values may be achieved by means of doping gases injection into the reaction atmosphere or by additional heat treatment [11] etc.As it is also reported byEnstrom et al. [7], by doping the gaseous ambient with 0·1% CO₂, the increase ofI _c from 13 A/mm to 84 A/mm in the magnetic field of 5 T may be obtained. As the preliminary results of our investigation have shown, an increase from 32 A/mm to 106 A/mm by using the doping gases may be achieved for the tape travelling velocity of 4 m/h, the Nb/Sn chlorides ratio equal to 0·55 and the substrate heating current of the value of 4 A.We expect that by optimizing the technological parameters mentioned above together with following doping and additional heat treatment, we may obtain a substantial increase in theI _c andJ _c values.     

Numerical mean field studies of the site disordered spin glassCuMn

Numerical mean field studies ofCuMn alloys have been performed for different concentration and external magnetic field strengths in a wide temperature range using a cube with 12*12*12 lattice points and periodic boundary conditions. The calculations include only RKKY interaction based on hyperfine field measurements by Slichter and coworkers. They result in realistic values for the spin glass transition temperturesT _f . The temperature was varied from the paramagnetic regime down to the deeply frozen state far belowT _f . The exchange and hyperfine field distributions have been calculated. The copper NMR spectra of the main line and the satellites are shown. Moreover, the temperature behavior of the order parameter, the probe magnetization, the magnetic heat capacity and the NMR line width are given.     

Nuclear resonance studies of95NbFe

Dilute alloys of 35-day⁹⁵Nb in polycrystalline iron have been studied by nuclear magnetic resonance on oriented nuclei (NMR/ON) using frequency modulation and fast passage techniques. Comparison of resonance frequencies with nuclear orientation results confirms the spin 9/2 for the⁹⁵Nb ground state. The zero-field resonance frequency is 275.29(9) MHz, leading to ag-factor of 1.3653(25) if the hyperfine field from spin-echo measurements on⁹³NbFe is used. Relaxation times, line shapes, and the frequencyversus field behavior are discussed. A summary of data for CoFe alloys, used here for calibration purposes, is also given.A preliminary report of this work was given at the International Conference on Low Temperature Physics (LT 14), Helsinki, 1975. The work was supported in part by the Deutsche Forschungsgemeinschaft (SFB 161).     

Nuclear magnetic resonance on oriented76,77,82Br in Fe

Nuclear magnetic resonance on oriented^76,77,82BrFe has been measured using recoil-implanted samples. The magnetic hyperfine splitting frequency of⁸²BrFe in a zero external magnetic field has been determined to be 201.90(3) MHz. The resonances of⁷⁶BrFe and⁷⁷BrFe were also observed in an external magnetic field of 0.2 T asv(⁷⁶BrFe)=340.9(3) MHz andv(⁷⁷BrFe)=403.5(2) MHz. With the known values of theg-factors, the hyperfine fields have been deduced:B _HF(⁸²BrFe)=81.397(27) T,B _HF(⁷⁶BrFe)=81.38(7) T. Theg-factor of⁷⁷Br was determined to be |0.6487(4)|.     

Mössbauer and X-ray study of rapidly quenched and mechanically alloyed Al-Fe alloys

Mössbauer spectroscopy and X-ray diffractometry were used to study the effect of the cooling rate as well as of the milling time on the structure of rapidly quenched Al-6.8% Fe, Al-0.5% Fe and mechanically alloyed Al-8% Fe alloys. The main phase of the rapidly quenched alloys was identified as Al _m Fe besides Al₆Fe andAlFe solid solutions. In the mechanically alloyed samples (with milling time between 1.5–43 hours), we have found -Fe, AlFe solid solution and a third phase characterized by a doublet with Mössbauer parameters which are not so far from those of clusters inAlFe alloys. We have observed a continuous increase of the quantity ofAlFe solid solution, together with a significantly less increase of the third phase as a function of the milling time. Simultaneously, the quantity of alpha-iron has gradually decreased.     

The hyperfine magnetic field of172Yb in Fe and Ni

Time-differential perturbed angular correlation measurements have been performed on the 91–1095 keV -ray cascade emitted by¹⁷²Yb nuclei in the capture decay of¹⁷²Lu, using implanted sources of¹⁷²Lu in Fe and Ni. From these measurements hyperfine field valuesB(YbFe)=–1253±83 kG andB(YbNi)=–143±12 kG follow at room temperature. From the modulation amplitude of the spectra it follows that only about 20% of the ytterbium nuclei participate in the precession.     

Superconducting properties of ion implantedIn Mn alloys

Annealed Indium films have been implanted with 150 keV-Mn ions at low temperatures. TheT _c -depression and the low temperature part of the resistivity exhibit the Kondo effect, the Kondo temperature being strongly influenced by lattice defects. The lattice disorder has been increased by pre-implantation of In ions. The influence of lattice disorder on the magnetic properties ofIn Mn alloys is explained by applying the strong coupling theory of superconductors.It is found that the main effect results from a shift of the Fermi energy relative to the virtual bound state, due to a variation of the effective massm ₀·(1+).     

Electron tunneling into ion implanted PbMn and SnMn alloys

Tunnel junctions ofPb-I-Al andSn-I-Al were implanted at low temperatures with Mn ions in the ppm region. The tunnel characteristicdI/dV was measured on the pure sample and on the alloy with different concentrations. A bound state is found in both systems at an energy 0.7 ₀. Comparison with theory confirms, that the Kondo effect is not necessary for the existence of a bound state.     

The magnetic hyperfine field at181Ta impurities in the 4f-ferromagnets Ho and Er

The magnetic hyperfine fieldH _hf at¹⁸¹Ta impurities in the ferromagnetic Rare Earth metals Ho and Er has been determined by time differential perturbed angular correlation measurements at 4.2 K. The results |H _hf(TaHo)|=101(8)kG |H _hf(TaEr)|= 94(8)kG together with the previously determined values ofH _hf(TaGd) andH _hf(TaDy) show that the magnetic hyperfine field at Ta impurities in the Rare Earth metals is predominantly due to the conduction electron polarization of the hosts.     

Magnetic hyperfine fields of Nb andMo in nickel by NMR-ON of90Nb and93mMo

The magnetic hyperfine splitting frequencies of⁹⁰NbNi and^93mMoNi in an external magnetic field of 0.2 T have been determined by the NMR-ON method to be 18.52(7) and23.73(10) MHz, respectively. With the assumption of Knight shift factorK=0 and with the knowng-factors, the hyperfine fields of⁹⁰NbNi and^93mMoNi were deduced asB _HF(⁹⁰NbNi)=-4.118(16) T andB _HF(^93mMoNi)=-3.491(33) T. The rather long spin-lattice relaxation time of 32(5) min was observed for⁹⁰NbNi at an external magnetic field of 0.2T and8 mK.