Analysis of the high-temperature spin-glass susceptibility: Determination of the local magnetic exchange

New measurements are reported of the magnetic susceptibility above the freezing temperature T_f for noble-metal spin-glasses with $\text{1}\text{2}$ to 6 at.% Fe or Mn. The susceptibility for T_f<T?5 T_f is not Curie-Weiss, but local magnetic correlations manifest themselves and provide a key for the determination of the exchange interactions in spin-glasses. The exchange parameters J_n are resolved up to 5 neighbors for $\text{Au}$Fe, $\text{Cu}$Mn, $\text{Au}$Mn and $\text{Pt}$Mn through a configuration ensemble calculation which includes atomic short range order.     

Band model parameters for the parallel bands of linear triatomic molecules—I. Theory

Generalized equations are developed for computing the band model parameters ($\text{S}\text{d}$), ($\text{S}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{/D}$) and ($\text{1}\text{d}$) for the parallel bands of linear triatomic molecules. The convergence of these band-model parameters as a function of the number of quantum states included in a computation is discussed for the 4.3 μm CO₂ band at various temperatures and wavenumbers. Comparisons are made to previous theoretical calculations for the 4.3 μm CO₂ band, where it is shown that an insufficient number of quantum states was included in the earlier work to insure convergence of the band-model parameters.     

Distinct binding states in adsorption on a homogeneous surface: Te on W(100)

The adsorption of Te on a W(100) surface is studied by thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and work function change (Δ?) measurements. Three distinct binding states are observed in the first monolayer corresponding the coverages from 0 to $\text{1}\text{2}$ monolayers (ML), $\text{1}\text{2}$ to $\text{2}\text{3}$ ML and$\text{2}\text{3}$ to 1 ML. Within each state a coverage dependence of the desorption parameters is found. The three binding states are discussed in terms of heterogeneity induced by lateral interactions and in terms of inherently different adsorption sites.     

Microscopic determination of nuclear deformation energy surfaces at very high spins

The deformation energy surfaces of a number of rare-earth nuclei are calculated microscopically as a function of the Bohr-Mottelson deformation parameters (β,γ), for the very high spin states $\text{(30}\text{h}\text{?}\text{?J?70}\text{h}\text{?}\text{)}$ and compared with semiphenomenological Strutinsky based calculations. The possibility of rotational isomers (yrast traps) is discussed.     

The mass parameters for the average mean-field potential

Starting from a mean-field hamiltonian with pairing interaction, we use the generator coordinate method (GCM) and a generalized gaussian overlap approximation to derive a multidimensional collective hamiltonian for large-amplitude motion. Numerical calculations are performed for Nilsson and Woods-Saxon potentials with BCS pairing. The BCS wave function is taken as the generator function and the deformation parameters of the single-particle mean field are used as the generator coordinates. We find that the GCM mass parameters on the average are smaller than those of the cranking (+ BCS) model by a factor of $\text{～}\text{2}\text{3}$. In the present approach, the zero-point energy correction to the collective potential is shown to vanish identically.     

Formal solutions for response functions of superconductors and 3He(B): II. Applications to acoustic and quasihomogeneous regime

Formal solutions for the autocorrelation functions of density and the transversal current are discussed in the acoustic and quasihomogeneous regime. The poles of these functions are obtained without any restrictions imposed on Landau parameters. The formula for sound dispersion at T = 0 is generalized by the inclusion of terms of the relative order of $\text{(}\text{kv}\text{2Δ}\text{)}{}^2$, (k is the wave vector, v is the Fermi velocity, Δ is the energy gap, $\text{h}\text{?}\text{≡ 1}$). The dispersion formulae for transversal and longitudinal excitations with a gap for ³He(B) are also given, with an accuracy up to the terms of the order of $\text{(}\text{kv}\text{2Δ}\text{)}{}^2$, for 0 ? T ? T_c, and without any restrictions imposed on Landau parameters. Under these last assumptions our autocorrelation functions are calculated in the polar as well as non-polar regions. It is shown that if T > 0, the transversal function vanishes at some ω, such that $\text{0 ? ω}{}^2\text{? (}\text{12}\text{5}\text{)Δ}{}^2$. Moreover,the zero of the density autocorrelation function is distanced from its pole by an amount of the order of $\text{(}\text{kv}\text{2Δ}\text{)}{}^2$.     

The frequency dependence of the ac susceptibility of the PdMn spin glass

We have measured the frequency dependence of the ac susceptibility _X(T) for three alloys of $\text{Pd}$Mn in the spin-glass regime. A strong dependence of _X(T) on frequency is observed near and below the freezing temperature in contrast to the archetypal $\text{Cu}$Mn spin glass. We discuss possible reasons for these differences.     

AES,photoemission and work function study of the deposition of Cs on (100) and (111)B GaAs epitaxial layers

Work function, photoemission and AES measurements have been made on (100) and (111)B epitaxial GaAs layers as a function of caesium coverage. It has been shown that the photoemission maximum and work function minimum occur at a coverage of $\text{2}\text{3}$ of a monolayer. The reduction of the work function takes place in distinct stages with changes in the rate of fall occurring at $\text{1}\text{8}$ and $\text{1}\text{2}$ of a monolayer for the (111)B face and $\text{1}\text{8}$, $\text{1}\text{4}$, $\text{1}\text{3}$ and $\text{1}\text{2}$ of a monolayer for the (100) face. This indicates the presence of specific adsorption sites which have not been observed in previous work on these faces.     

Ground state of ferromagnet with antiferromagnetic impurity

The Heisenberg ferromagnet with an antiferromagnetic impurity and arbitrary spin is considered. The method is suggested for constructing the ground state of such a system, the method using the Jacobi matrix technique. As an example, there has been investigated the ferromagnet with a simple cubic lattice and the matrix spin $\text{S =}\text{1}\text{2}$, and the impurity spin S′ = 1. The energy and wave function of the ground state are found as dependent on the system parameters.     

TDHF equations of motion for algebraic hamiltonians in a coherent state representation

Time-dependent Hartee-Fock (TDHF) equations are derived for nuclear systems with internal dynamical group U(r). The coordinates which appear in the TDHF equations are the coordinates which parameterize the U(r) coherent states. The TDHF orbits for the hamiltonian $\text{H}$ are identical with equations of motion for a classical system described by the hamiltonian function 〈$\text{H}$〉 obtained directly from the operator $\text{H}$. This quantum-classical correspondence facilitates interpretation of TDHF orbits. The phenomena of coexistence and critical elongation are discusses, as is the relation between the critical points of the function 〈$\text{H}$〉 and the spectral properties fo the operator $\text{H}$.     

The law of corresponding states for metals

Using the similarity of the effective potentials seen by ions in metals a reduced phonon equation of state is derived. It is shown that the melting point T_m(0) and the atomic volume Ω₀ at T = 0 K and at p = 0 are suitable macroscopic parameters for scaling ? and σ characterizing the interatomic potentials of metals having similar structures. The temperature and pressure dependence of thermodynamical quantities reduced with the above parameters are discussed and the results are compared with the experiment. It is shown that the pressure dependence of the reduced thermodynamic quantities can be described by the pressure dependence of the scaling parameters T_m(p) and Ω₀(p).The general form of the reduced equation of state (containing the electronic contributions as well) obtained gives that the reduced pressure is a universal function of the following reduced variables: the volume, temperature, de Broglie wavelength, Gibbs free energy of electrons $\text{3}\text{5}\text{zE}{}_{\mathrm{fo}}\text{?}$ (E_fo is the Fermi energy at T = 0 K) and depe of the valence z as well. It is shown that $\text{E}{}_{\mathrm{fo}}\text{?}$ is a function of $\text{Ω}{}_{\mathrm{o}}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}$ and $\text{(}\text{E}{}_{\mathrm{fo}}\text{/?}\text{)Ω}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ is approximately constant within the same sub-group of the periodic table.     

A neutron scattering study of the low temperature modulated phases of the perovskite-type layer structure PAMC [= (C3H7NH3)2MnCl4]

Elastic neutron scattering experiments between 100 and 180 K show clearly that ?-PAMC is incommensurately modulated with the modulation vector being temperature-dependent and approaching $\text{1}\text{3}\text{b}{}^1$ at the ? → ζ phase transition. This displacive phase transition appears to be of the lock-in type. It is triggered by the freezing of dynamically disordered propylammonium ions.     

Semidirect model calculations of differential cross sections for some photonuclear reactions in 40Ca

Based on the principle of detailed balance the direct-semidirect model for fast nucleon capture was used to calculate photonucleon differential cross sections at several incident photon energies in ⁴⁰Ca. The reaction channel configurations obtained are compared with the experimental ones. Several approaches to the interaction function were used in order to see which one best reproduces experimental values. Calculations performed with Rosen optical model parameters give much more consistent results than calculations using Becchetti-Greenlees parameters. No evidence is obtained of any contribution to the cross sections from a compact isoscalar quadrupole resonance at an energy $\text{63A}{}^{\mathrm{<mtext>?1</mtext><mtext>3</mtext>}}\text{MeV}$.     

Spin density wave magnetism in copper—manganese alloys

The incommensurate magnetization waves (IMW) occuring at the wave vector $\text{Q = (1, 0.5 ? δ, 0)}\text{2π}\text{a}$ and equivalent positions in reciprocal space in Cu_1?xMn_x have been studied as a function of temperature, wavevector, frequency and composition, using high-resolution, unpolarized neutron scattering techniques. We find that the elastic component of the scattering cross section at these incommensurate wavevectors approaches zero in the vicinity of the “spin glass” freezing temperature, T_f, closely resembling that expected for an order parameter on approach to the critical point. We suggest that the interaction between Mn atoms is long-range and intimately connected to a spin density wave instability.     

Deconvolution method for composition profiling by Auger sputtering technique

Some of the sputter broadening effects on profile measurements using the Auger sputtering technique have been quantitatively investigated for $\text{Ag}\text{Au}$ and $\text{Cu}\text{Ni}$ systems. Two methods have been used to measure the resolution function as a function of the sputter distance for these two systems. The broadening can be separated into contributions from original surface roughness and sputtering effects, the latter amounting to about 7% of the sputter depth for $\text{Cu}\text{Ni}$ and 14% for $\text{Ag}\text{Au}$ interfaces. Based on the measured resolution function, a deconvolution method has been developed to facilitate the retrieval of the actual profile from the observed profile by reducing the sputter broadening. Using this method, we found that the measured interfacial profile can be substantially sharpened. The implications of using the deconvolution method for interdiffisuion studies in thin films are discussed.     

Two-dimensional decorated Ising model with classical vector spins and Ising spins of magnitude s

A two-dimensional decorated Ising model with ν-dimensional vector spins and Ising spins of magnitude s is considered. The partition function, magnetization and correlation functions are expressed in terms of the average of functions of the spins of the Ising model with effective exchange constants. These results, although derived for a two-dimensional lattice, are valid for a lattice of arbitrary dimensionality. The phase diagram is obtained exactly in the zero external field and two-dimensional lattice for arbitrary values of s and ν, and, as expected, three transition temperatures are obtained for some values of the parameters. It is also shown that for $\text{|}\text{S}\text{|=1, s>}\text{1}\text{2}$ there is an additional ordered phase (up-down/up-down), and for $\text{|}\text{S}\text{|=ν}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ this additional phase can be either up-down/up-down or up-up/down-down depending on the values of ν and s.     

Absolute determination of electronic band structure of copper by angle-resolved photoemission

Structures in the angle-resolved photoemission spectra from copper in the (1$\text{1}$0) and (001) mirror planes at fixed photon energy hν as a function of emission angle show discontinuities in energy position or slope as function of emission angle. These discontinuities are due to the appearance of specific interband transitions on zone boundaries. The appearance angle allow the absolute determination of momentum $\text{k}$ of the transition. E($\text{k}$) points have been determined for most d-bands and several conductions bands. Experimental data are in good agreement with Burdick's band calculation, as also are the E($\text{k}$) points which have been determined using the energy coincidence method.     

Dynamics of the infinite-range ising spin glass

The Glauber dynamics of an Ising spin glass with infinite-range interactions and additional static field, h, is investigated near the freezing temperature, T_f. We obtain critical slowing down at and below the de Almeida-Thouless instability line, h_c(T), to order (1?T/T_f)³ with algebraic decay of the spin correlations ～t^?ν, where $\text{ν=}\text{1}\text{2}$ at T_f and $\text{ν≤}\text{1}\text{2}$ for T<T_f.     

Hyperfine and isotopically invariant parameters of the GeS microwave spectrum

The complete set of microwave data for the nine isotopic species of the GeS molecule, available in literature, is reduced to molecular parameters by a nonlinear least-squares fit. All the hfs lines due to ⁷³Ge ($\text{I =}\text{9}\text{2}$) and ³³S ($\text{I =}\text{3}\text{2}$) are included in this fit. Watson's expressions of Dunham coefficients, including corrections to the Born-Oppenheimer approximation, are used. Contributions from off-diagonal terms are taken into account in the hfs Hamiltonian which is numerically diagonalized. A set of 12 hyperfine and isotopically invariant parameters is obtained and compared with previous determinations. It is shown that the accuracy of the hfs parameters is improved by one order of magnitude by the global treatment of all the data.