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.     

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.     

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.     

Applied field Mössbauer spectra of low-spin mononuclear and binuclear iron(III)phthalocyanines

Well characterized low-spin Fe(III)phthalocyanine complexes have recently been synthesized. Two six-coordinate examples, a binuclear -oxo bridged complex [((-picoline)FePc)₂O],1, and a mononuclear bis-azido complex (PNP)[FePc(N₃)₂],2, display typical S=1/2 Fe(III) parameters (1, =0.20 mm/s, E_Q=1.79 mm/s;2, =0.22 mm/s, E_Q=2.47 mm/s at 4.2K). As an applied longitudinal magnetic field is increased to 32kOe the corresponding splittings in1 and2 indicate very small effective fields at the Fe nuclei. This is due to an S=O ground state in the weakly antiferromagnetically coupled complex1. The small hyperfine splitting in2 contrasts with the well resolved hyperfine splitting reported for various S=1/2 Fe(III)porphyrins and Fe(III)heme proteins.     

Long-range order in the XXZ model

The existence of long-range order is proved under certain conditions for the antiferromagnetic quantum spin system with anisotropic interactions (XXZ model) on the simple cubic or the square lattice. In three dimensions (the simple cubic lattice), finite long-range order exists at sufficiently low temperatures for any anisotropy(0) ifS1, and for 0<0.29 (XY-like) or>1.19 (Ising-like) ifS=1/2. In two dimensions (the square lattice), ground-state long-range order exists under the following conditions: for any anisotropy (0) ifS3/2; 0<0.032 (XY-like) or 0.67<<1.34 (almost isotropic) or>1.80 (Ising-like) ifS=1;>1.93 (Ising-like) ifS=1/2. We conjecture that the two-dimensional spin-1/2XY model (=0) has finite ground-state long-range order. Numerical evidence supporting this conjecture is given.     

Unstable Particles, Gauge Invariance and the Δ++ Resonance Parameters

The elastic and radiative ⁺ p scattering are studied in the framework of an effective Lagrangian model for the ⁺⁺ resonance and its interactions. The finite width effects of this spin-3/2 resonance are introduced in the scattering amplitudes through a complex mass scheme to respect electromagnetic gauge invariance. The resonant pole ( ⁺⁺) and background contributions ( ⁰, , , and neutron states) are separated according to the principles of the analytic S-matrix theory. The mass and width parameters of the ⁺⁺ obtained from a fit to experimental data on the total cross section are in agreement with the results of a model-independent analysis based on the analytic S-matrix approach. The magnetic dipole moment determined from the radiative ⁺ p scattering is nuclear magnetons.     

Temperature dependence and input optical power tolerance of an InGaAsP electroabsorption modulator module

We report the temperature dependence and input optical power tolerance of an InGaAsP electroabsorption (EA) modulator module. Thermal stability of the module was found to be very high. The optimum E _g at 20°C has been estimated to be 48–55 meV. At E _g of 53 meV, the insertion loss was almost independent of the temperature, while the driving voltage was strongly dependent on the temperature. The breakdown phenomena were investigated in detail; these occurred under conditions of very high input power and/or high bias voltage. Input power for breakdown was smaller for higher bias voltage or smaller E _g. Allowable maximum input optical power has a large margin (>5 dB) for the conventional input level in practical systems.     

Deep levels related to transition metals in Si under hydrostatic pressure

The influence of hydrostatic pressure up to 5×10⁸ Pa on deep levels related to transition metal impurities in silicon is determined by means of an isothermal capacitance method. Under pressure, donor levels of isolated Fe, V, Ti, and Mn shift towards the valence band in contrast to earlier results for deep chalcogen donors. This behavior is contrary to what is expected by considering only effects of hybridization. Quantitative differences between Fe, Ti, V, and, on the other hand, Mn suggest a different microscopic structure of these defects. The Fe-acceptor pairs FeB, FeAl, and FeGa move towards the valence band with a rate comparable to that of the ₁ conduction band. The thermal capture coefficients of isolated Fe, V, and Ti are found to be pressure independent up to 5×10⁸ Pa.On leave from Sony Corp., Research Center, Yokohama, Japan     

Wavevector scaling,surface critical behavior,and wetting in the 2-d, 3-state chiral clock model

The controversial 2-d, 3-state chiral Potts model is studied using transfer matrix finite size scaling. at =0, we find dq _N/dN ^–4/5, whereq is the wavevector, the chiral field, andN the strip width (N=4–10). The result is consistent with den Nijs's crossover exponent =1/6. With surface fields on the infinite free boundaries, exponents associated with bulk magnetizationy _H, surface magnetizationy _H, and surface susceptibility are computed vs. ; results are similar for or to the infinite direction. Preliminary results are given for the bulk specific heat critical amplitudes, to test the universality of amplitude ratios. The interface wetting line is located for 01/4 using simple transfer matrix calculations of surface tensions in the solid-on-solid approximation. Overhangs or bubbles seem relatively unimportant at all temperatures.     

Activation energy for elastic interaction between Frank dislocation loops and glide dislocations in f.c.c. Metals

The activation energyG for the thermally activated passing of glide dislocations close to Frank dislocation loops which do not intersect the slip planes is calculated by means of the linear theory of elasticity as a function of the applied stress, of the distances loop centre-slip plane, and of the orientations and radii of the loops. The influence of anisotropy onG is investigated for some f.c.c. metals, especially for copper. For sufficiently high stresses the dependence ofG on stress is shown to approach theG-stress expression suggested by Seeger in his theory of radiation hardening.On leave fromFaculty of Mathematics and Physics, Charles University, Praha, Ke Karlovu 5, Czechoslovakia.     

Magnetic relaxation spectrum of ferrites Mn x Fe3−x O4+γ

The initial permeability disaccommodation in ferritesMn _x Fe₃–xO₄₊ , 0·5x1, was studied in a temperature range around –200°C to +180°C. Four separate bands were found in the relaxation spectrum of these ferrites.

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Mn _x Fe_3–x O₄₊

Mn _x Fe_3–x O₄₊ , 0,5x1, –200°C +180°C. .

     

Transition temperature and gap anisotropy of pure and impure superconductors

The algebraic structure of linearized Eliashberg theory atT=T _c is exploited to derive expressions for the anisotropic gap(k, i _n ) and theT _c-enhancement. These formulas are exact to second order in the anisotropy, and require as input the isotropic gap(k, i _n ), the anisotropic spectral function ² F(k, ), and the impurity scattering rate 1/ _k . Approximate formulas based on a square well model are also given. The formulas for impurity effects are new and very simple.     

Micromagnetic Description of the ΔE-Effect in Amorphous Ferromagnets

Dependences of the magnitude of the E-effect in Fe_81.5B_13.5Si₃C₂ amorphous metal alloys on the external magnetic field and the temperature of thermomagnetic treatment are investigated. Four characteristic regions are distinguished in the dependence of the E-effect on the magnetic field strength. The experimental results are explained in the context of micromagnetism theory.     

Optimum profiles for dispersive multimode fibres

A simple closed-form expression is given for the index profile of multimode fibres with arbitrary dispersion providing transmission capacities as large as 1.6/ ² Mbit/s km, wheren/n. Our result reduces to a previous result of Marcatili for the special case of circularly symmetric fibres. A transmission capacity of 150 Mbit/s over a 10 km long fibre appears possible with LED sources operating at optimum wavelengths for the medium.     

Relationship between field shift and phase constant change in two-dimensional three-layered dielectric or hollow waveguides due to uniform bends

It is shown theoretically that the field shift x and phase constant change in two-dimensional three-layered dielectric or hollow waveguides bent uniformly with large bending radiusR are related by x = 2R/ ₀, where ₀ is the axial phase constant. The relationship predicts that the field distributions of the TE₀ or TM₀ mode shift toward the outward direction of bending, whereas those of other TE _n or TM _n (n=1,2,...) modes shift inward in a hollow waveguide. Characteristic features in dielectric waveguides are also described.     

Dependence of the steepness of the exponential absorption tail on the chemical composition of materials

The quantity characterizing the steepness of the exponential tail of the fundamental absorption edge is studied. It is shown, that the magnitude of of binary compounds can be roughly estimated from their chemical composition in a way described in this paper.Boní II, Praha 4, Czechoslovakia.The author thanks Ing. D. Leal, CSc for his valuable discussions concerning this work.     

The theory of neutron scattering from mixed harmonic solids

In the intermediate valent cerium alloys Ce_1–xY_xPd₃, Ce(Pd_1–xRh_x)₃ and Ce(Pd_1–xAg_x)₃ the Gd³⁺-ESR shows a non-linear increase of the linewidth H(T) in the temperature range 4.2KT300K. The deviation from the linear Korringa law can be described by a reduced conduction electron density of states at the Gd site (which is a Ce lattice site) in the energy range E _4f (=width of the Ce 4f states). This supposition allows a determination of E _4f from the H(T)-data. For CePd₃:Gd³⁺ we find E _4f=(650±100) K. E _4f increases with Y- and Rh-concentration and decreases with Ag-concentration.     

Orthogonalization of channel spaces in the quark resonating group model

A recently developed coupled-channel resonating group method with orthogonalized function spaces is tested. As test example a six-quark three-channel resonating group model is used. The channels are theNN-, - andCC- (hidden colour) channels. In earlier calculations without orthogonalization of channel spaces the relative motion function of theNN-channel had a node in theS-wave at approximately 0.5 fm. In the new treatment, in which the - andCC-channels are only orthogonal corrections to theNN-channel, this node is no longer present. The newNN wave function is very similar to the one of the single-channel approximation. Thus, in the one- and three-channel approximation, we consistently find that the six-quark resonating group model does not support the notion of a short-distance node in theNN wave function.     

Spin-glass dynamics determined from muon spin relaxation and neutron spin echo measurements

Muon spin relaxation (SR) and neutron spin echo (NSE) measurements of magnetic ion correlation times and correlation functions in the spin glass systemsCuMn,AgMn, andAuFe are compared. It is found that theSR and NSE measurements are in excellent agreement both above and below the spin-glass freezing temperatures. The experimental results are compared to recent theories of spin-glass dynamics.We are grateful to D.L. Huber and R.E. Walstedt for stimulating discussions. This work was performed under the auspices of the U.S. Department of Energy, and was also supported by the U.S. National Science Foundation, Grant No. DMR-8115543.