${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$${\mathrm{La}}_{\mathit{x}}$${\mathrm{Cu}}_6$ is known to have a γ [≡C/T (T→0)] per Ce mole that increases monotonically with increasing La concentration: γ of ${\mathrm{Ce}}_{0.1}$${\mathrm{La}}_{0.9}$${\mathrm{Cu}}_6$ is ∼2.3 J/Ce mole ${\mathrm{K}}^2$ while that for pure ${\mathrm{CeCu}}_6$ is only 1.6 J/Ce mole ${\mathrm{K}}^2$. To investigate this behavior, unusual in comparison with, e.g., ${\mathrm{UBe}}_{13}$ or ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$, the properties (including specific heat to 0.4 K, dc susceptibility to 1.8 K, and resistivity) of ${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$${\mathit{M}}_{\mathit{x}}$${\mathrm{Cu}}_6$, M=La, Th, Y, and Pr, 0≤x≤1, have been investigated, with the most extensive work being on La and Th. χ (1.8 K) remains essentially constant to x=0.4 for Th and La doping, and then rises (falls) for further La (Th) doping, with values for x=0.1 of 45.7 memu/Ce mole for La and 19.3 memu/Ce mole for Th versus 36.7 memu/mole for pure ${\mathrm{CeCu}}_6$. While the specific-heat γ values, as previously reported, increase essentially linearly upon increasing La doping, the γ values for Th doping remain essentially constant up to x=0.4, and then decrease monotonically upon further Th doping, reaching γ=500 mJ/Ce mole ${\mathrm{K}}^2$ for x=0.9.

This rather abrupt change in the behavior of γ versus Th doping, when compared to published results for specific heat under pressure for pure ${\mathrm{CeCu}}_6$, argues against a simple chemical pressure effect (${\mathrm{ThCu}}_6$ is smaller than ${\mathrm{CeCu}}_6$). Measurements reported here of the specific heat in field [C(H)] of ${\mathrm{Ce}}_{0.6}$${\mathrm{Th}}_{0.4}$${\mathrm{Cu}}_6$ and ${\mathrm{Ce}}_{0.8}$${\mathrm{Th}}_{0.2}$${\mathrm{Cu}}_6$, when compared to published C(H) data for ${\mathrm{CeCu}}_6$, ${\mathrm{Cu}}_{0.5}$${\mathrm{La}}_{0.5}$${\mathrm{Cu}}_6$, and ${\mathrm{Ce}}_{0.1}$${\mathrm{La}}_{0.9}$${\mathrm{Cu}}_6$, indicate that the large γ value of ${\mathrm{CeCu}}_6$, and its large field dependence, may be due to magnetic correlations and not, in fact, due to a correspondingly enhanced electron effective mass. This interpretation is consistent with known de Haas–van Alphen results and the known nearness to magnetism of ${\mathrm{CeCu}}_6$, where doping [${\mathrm{CeCu}}_{6\mathrm{-}\mathit{x}}$(Ag,Au${)}_{\mathit{x}}$] produces antiferromagnetism.

The Darwin theory of dynamical diffraction by crystals is extended to include the regions between Bragg peaks as well as situations of grazing and normal angles of incidence, i.e., the whole angular range extending from 0° to 90°. The modified theory reproduces the usual two-beam Laue dynamical theory in the close vicinity of the Bragg peaks, while in the regions between the Bragg peaks it predicts reflectivities in agreement with the kinematical theory. Many-beam effects due to all crystallographic planes parallel to the surface can be calculated in an extremely simple way making this approach particularly suitable to artificial multilayered structures. The weak scattering in the region where the far tails of two neighboring Bragg peaks interfere contains information about the phases of the structure factors.

Spin-polarized photoemission experiments on expitaxial Ag overlayers on Fe(001) have shown that a minority-spin surface state of the bare substrate evolves into an interface state, moves to higher energies, and crosses the Fermi level ${\mathit{E}}_{\mathit{F}}$ between 3 and 4 Ag monolayers. Application of a phase accumulation model shows that this state is a quantum-well (QW) state characterized by the quantum number ν=1, where ν=m-n, and where n and m are the number of wave-function nodes and number of layers, respectively. Higher members of the QW series cross ${\mathit{E}}_{\mathit{F}}$ with a periodicity Δm=(1-${\mathit{k}}_{\mathit{F}}$/${\mathit{k}}_{\mathrm{BZ}}$${)}^{\mathrm{-}1}$ identical with that in recent theories for the alternation between ferromagnetic and antiferromagnetic coupling in magnetic multilayers. The QW model fails at low coverages. A tight-binding model captures the behavior at low coverages while reproducing QW behavior at high coverages.

The ground-state spin configuration of antiferromagnetically coupled ferromagnetic thin films is determined by competition between anisotropies, interlayer exchange, and the applied field. A theory for spin waves is presented where both exchange and dipolar interactions are accounted for and it is shown how dramatic changes in the spin-wave frequencies can be observed by carefully choosing the experimental geometry. Also, many details of the ground-state spin configuration can be obtained by studying the behavior of the spin-wave frequencies as functions of propagation direction and applied field strength in these geometries. The results are summarized from the point of view of possible light-scattering experiments.

Low-temperature specific heat and magnetic susceptibility for ${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Th}}_{\mathit{x}}$RhSb alloys, 0≤x≤0.6, have been investigated. CeRhSb, identified previously as a Kondo insulator, has C/T>30 mJ/${\mathrm{K}}^2$ mol at T→0 K. Above 6 K, C/T is proportional to ${\mathit{T}}^2$ yielding a high-temperature γ of 90 mJ/${\mathrm{K}}^2$ mol. Th substitution for Ce causes large, but non-Kondo-like enhancement of the specific heat. Alloys corresponding to 0.3≤x≤0.4 belong to the heaviest Ce-based heavy fermions.

A finite-temperature theory of magnetism in amorphous magnetic alloys with strong environment effects is developed on the basis of the functional integral method for thermal spin fluctuations and the distribution-function method for random distribution of local magnetic moments. The theory drastically simplifies numerical calculations by means of the geometrical-mean model for amorphous structure as well as electronic structure, and allows us to investigate the magnetism in amorphous transition-metal alloys with large difference in atomic size via average coordination number which depends on the type of central atom. Numerical example is given of the amorphous Fe-Zr alloys. It is demonstrated that the theory reproduces quantitatively the local densities of states obtained from the first-principles calculations, and describes the magnetic phase diagram, in particular, the itinerant-electron spin glass. It is also shown that the atomic-size effects play an important role in the formation of ferromagnetism in concentrated Fe-Zr amorphous alloys. The reentrant spin-glass behavior around 90 at. % Fe is shown to be due to the thermal spin fluctuations of amplitudes of local magnetic moments.

The Boltzmann equation is solved for a system consisting of a ferromagnetic–normal-metallic multilayer. The in-plane magnetoresistance of Fe/Cr and Fe/Cu superlattices is calculated for (1) varying interfacial geometric random roughness with no lateral coherence, (2) correlated (quasiperiodic) roughness, and (3) varying chemical composition of the interfaces. The interplay between these three aspects of the interfaces may enhance or suppress the magnetoresistance, depending on whether it increases or decreases the asymmetry in the spin-dependent scattering of the conduction electrons. Properties of the interfaces relevant to the giant negative magnetoresistance are discussed.

Ising models on the plane square lattice with an arbitrary variation of the bond strengths, ${\mathit{J}}^{\mathrm{\parallel }}$(z) and ${\mathit{J}}^{\mathrm{\perp }}$(z), with one of the two axial coordinates, z, are considered. The total entropy is exactly represented as a functional of contributions ${\mathrm{\varepsilon }}_{\mathit{q}}$(z) to the local energy density arising from the Onsager fermions with wave vector q parallel to the layer axis, y. The resulting explicit local expression provides an effective variational principle for the free energy and energy-density profiles. In the scaling limit the problem reduces to a set of independent second-order differential equations for each ${\mathrm{\varepsilon }}_{\mathit{q}}$(z). The power of the method is demonstrated by application to an interface between two uniform but distinct regions; this includes the problem of a wall with a surface field, ${\mathit{h}}_1$, as a special case. Previous results for the bulk and surface exponents and for the energy-energy correlation function are easily recovered. Near criticality the method yields, in addition, universal, scaled energy-density profiles, ɛ(z;T), which exhibit rich crossovers and nonmonotonic variation with z.

X-ray-absorption near-edge structure (XANES) spectra at the Pr ${\mathit{L}}_{\mathrm{III}}$ threshold were studied for tetravalent ${\mathrm{PrO}}_2$ as a function of external pressure up to ≃117 kbar. The observed spectral changes of the double-peaked white line reflect an increase of the Pr 4f/O 2p covalency with pressure, in analogy to previous results for tetravalent ${\mathrm{CeO}}_2$ and ${\mathrm{CeF}}_4$. A splitting of the white-line component at the highest energy into two peaks, revealed in the second derivatives of the measured XANES spectra, is interpreted as arising from crystal-field interaction of the 5d states.

The renormalization scheme recently proposed by White is applied to the Ising model in a transverse field. It is found that this scheme is a significant improvement over standarad techniques as far as the computation of the ground state is concerned. It is shown that the errors in the ground-state energy are the largest in the neighborhood of the phase transition. Thus, this method has no special virtue in predicting the location of the phase transition and its associated critical exponents.

We have investigated the pinning of the spin-density wave and the low-frequency damping of the phase excitations in the solid solutions (TMTSF${)}_2$(${\mathrm{AsF}}_6$${)}_{1\mathrm{-}\mathit{x}}$(${\mathrm{SbF}}_6$${)}_{\mathit{x}}$ (0≤x≤1). The pinning is strongly enhanced by the weak nonmagnetic disorder introduced by the alloying. The damping is characterized by the nonlinear dc conductivity and by the dielectric relaxation. In a broad but limited temperature range we describe a temperature-independent damping with a strong dependence on defect concentration, suggesting elastic scattering of phasons by defects.

We calculate the Néel temperature ${\mathit{T}}_{\mathit{N}}$ for two-dimensional isotropic dipolar Heisenberg antiferromagnets via linear spin-wave theory and a high-temperature expansion, by employing the method of Callen. The theoretical predictions for ${\mathit{T}}_{\mathit{N}}$ for ${\mathrm{K}}_2$${\mathrm{MnF}}_4$, ${\mathrm{Rb}}_2$${\mathrm{MnF}}_4$, ${\mathrm{Rb}}_2$${\mathrm{MnCl}}_4$, and (${\mathrm{CH}}_3$${\mathrm{NH}}_3$${)}_2$${\mathrm{MnCl}}_4$ are in good agreement with the measured values.

The spectral densities of dynamical spin autocorrelation functions at infinite temperature are studied for the S=1/2XXZ model (with exchange couplings ${\mathit{J}}_{\mathit{x}}$=${\mathit{J}}_{\mathit{y}}$≡J,${\mathit{J}}_{\mathit{z}}$) on the linear chain, the square lattice, and the simple cubic lattice. The low-frequency behavior of a given spectral density is inferred from certain characteristic properties of its continued-fraction coefficients as determined from computed frequency moments. The analysis yields estimates for the ${\mathit{J}}_{\mathit{z}}$/J dependence of the infrared-singularity exponent. In the d=1 case, the exponent for spin fluctuations perpendicular to the O(2) symmetry axis responds sensitively as the anisotropy parameter sweeps across the O(3) symmetry point ${\mathit{J}}_{\mathit{z}}$/J=1, while the exponent for the parallel fluctuations shows little variation. In the cases d=2 and d=3 the same observations are made for autocorrelation functions of aggregate spins in chains and lattice planes, respectively.

We determine the influence of the Kosterlitz-Thouless transition on the stability of doubly spin-polarized atomic hydrogen adsorbed on a superfluid helium film and find that the lifetime of the gas is enhanced dramatically in the superfluid phase. Moreover, the relevant rate constants have a discontinuous behavior at the critical point. The observation of these effects is an unambiguous way to establish the achievement of the phase transition experimentally.

We present experimental observations at low temperature of subharmonic gap structures in high-quality Nb/${\mathrm{AlO}}_{\mathit{x}}$/Nb tunnel junctions, with relatively low critical current density. Samples having small, though appreciable, differences in the energy gaps show split structures which permit an interpretation in terms of the multiparticle tunneling (MPT). A detailed analysis and discussion of the experimental data in terms of the MPT theories is presented. In particular, the amplitudes and the temperature dependence of the subgap structures and the voltage dependence of the multiparticle current are investigated. Finally, a model that considers the tunnel barrier as consisting of randomly distributed thicknesses is proposed to overcome the failure of the theoretically predicted structure amplitudes for a uniform barrier. Within this framework, the experimental data of this work and those recently obtained by other groups are discussed.

In this paper we compare a set of atomic calculations of interfacial crack structure and properties with the predictions of an augmented elastic theory. Our intent is to critique the elastic predictions, especially the mode conversion and displacement closure oscillation features of the elastic theory. A simple physical picture is developed based on a crack stability diagram, using two sets of stress intensity axes. The first set is the normal applied stress intensity K and the second is a local stress intensity factor k, defined to describe the physics of the core region. The Griffith condition and dislocation emission criterion are defined in terms of the local k, and its associated effective core size parameter. Unfortunately, the physical core size is not a unique parameter in the problem, but varies directly with the amount of shear in the core. Thus, the effective core size for the Griffith condition is different from that for dislocation emission. In each case, the effective core size is much smaller than the physical core size, which means that the mode shift at the crack tip is considerably larger than would be expected on the basis of linear elasticity. However, with appropriately defined effective core size parameters, the Griffith condition is well satisfied, and the emission criterion based on the Rice unstable-stacking-fault condition is also surprisingly well satisfied in the mode-II emission configuration. The crack is found never to exhibit displacement oscillations, in part, because of the necessary condition that the Griffith condition be satisfied at the crack tip, and in part because the amount of shear in the core is limited by dislocation emission.

We report on a detailed study of superconducting critical temperatures ${\mathit{T}}_{\mathit{c}}$ and critical fields ${\mathit{H}}_{\mathit{c}2}$ of V/Fe multilayers. The thickness of the V layers (${\mathit{d}}_{\mathrm{V}}$) and Fe layers (${\mathit{d}}_{\mathrm{Fe}}$) as well as the total number of layers in the multilayer (N) were varied systematically. For ${\mathit{d}}_{\mathrm{Fe}}$≥0.6 nm, at constant ${\mathit{d}}_{\mathrm{V}}$, ${\mathit{T}}_{\mathit{c}}$ and the critical fields for parallel (${\mathit{H}}_{\mathit{c}2\mathrm{\parallel }}$) and perpendicular (${\mathit{H}}_{\mathit{c}2\mathrm{\perp }}$) orientation do not depend on either ${\mathit{d}}_{\mathrm{Fe}}$ or N, and a two-dimensional (2D) temperature dependence for ${\mathit{H}}_{\mathit{c}2\mathrm{\parallel }}$ without 3D-2D crossover is observed for small values of ${\mathit{d}}_{\mathrm{V}}$. The predicted oscillatory behavior of ${\mathit{T}}_{\mathit{c}}$ as a function of ${\mathit{d}}_{\mathrm{Fe}}$ is not found. We conclude that the superconducting V layers are completely decoupled by only 0.6 nm Fe, in conflict with previous reports. Upon decreasing ${\mathit{d}}_{\mathrm{V}}$ at constant ${\mathit{d}}_{\mathrm{Fe}}$, a strong decrease of ${\mathit{T}}_{\mathit{c}}$ is found. This, together with the temperature dependence of ${\mathit{H}}_{\mathit{c}2\mathrm{\parallel }}$ and ${\mathit{H}}_{\mathit{c}2\mathrm{\perp }}$ for all samples can be described by existing theory.

For values of r greater than the coherence length ξ, the axially symmetric Ginzburg-Landau equations are solved for a flux vortex carrying a longitudinal current. The field is not force free, and it is shown that there are no regular solutions to the force-free field equations that decay exponentially with increasing penetration into a superconductor. It is also shown, in this approximation, that in the case of a vortex carrying a nonzero longitudinal current, the Ginzburg-Landau equations are equivalent to the radial pressure-balance equilibrium relation in ideal magnetohydrodynamics. The techniques developed in this field to address stability issues can then be used to answer questions related to vortex stability.

In this paper we consider the possibilities for producing a dense gas of N≃${10}^5$ triplet positronium (Ps) atoms in vacuum contained in small cavity V≃${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^3$. We then consider the scenario where this dense gas of polarized Ps atoms may cool through a weakly interacting Bose transition. The rates for thermalization with the wall, equilibrium in the bulk, and loss of polarization by exchange collisions are calculated. A method for observing the transition is also discussed.

We have numerically studied dynamical behaviors of Josephson-junction ladders consisting of ${\mathit{N}}_{\mathit{p}}$ plaquettes, where the 2(${\mathit{N}}_{\mathit{p}}$+1) superconducting islands are coupled by resistively shunted Josephson junctions with negligible capacitance. When a ladder is subjected to a current of the form ${\mathit{I}}_{\mathrm{dc}}$+${\mathit{I}}_{\mathrm{ac}}$sin(ωt) in the [10] direction the dc I-V curve, in the presence of a transverse external magnetic field, becomes a devil’s staircase for ${\mathit{N}}_{\mathit{p}}$=1, and exhibits hysteresis and a transition to chaos for ${\mathit{N}}_{\mathit{p}}$≥2. We have identified the ‘‘symmetric state,’’ where the phase variables of the junctions satisfy symmetry relations and motion of the system is constrained to the phase space of smaller dimension than the original one. The dynamic behavior of each junction in the ladder depends very sensitively on whether the number of the plaquettes in a ladder is odd or even. However, the averaged dc I-V curves of the whole ladders with ${\mathit{N}}_{\mathit{p}}$≥3 turn out similar to one another, enabling one to understand the dynamical behavior of a large ladder from that of a three-plaquette ladder.