The nucleation and growth of two-dimensional islands during the submonolayer stage of epitaxial growth is studied with kinetic Monte Carlo simulations and mean-field rate equations. Previous work on irreversible growth is extended to include relaxation of island shapes by edge diffusion. Island morphologies range from ramified structures at low temperatures to compact, polygonal shapes at higher temperatures. Using a self-consistent calculation of the rate coefficients, quantitative agreement is obtained between the solution to coupled, mean-field rate equations and the simulation results for average quantities. The island size distribution function is described by a single universal ‘‘scaling function.’’ The average island size is the only important scale for determining island densities. It is shown that the general form of the scaling ansatz applies to wider range of coverages than anticipated previously. This scaling form is combined with the solution to the rate equations to explore explicitly the D/F dependence of the number density of islands (D is the surface diffusion coefficient and F is the deposition flux).

Within a two-dimensional Su-Schrieffer-Heeger-like Hamiltonian, the electronic and vibrational properties of poly(phenylene vinylene) (PPV) and its model oligomers are investigated systematically. The stable geometric and electronic configurations of this PPV series are determined within the Bogoliubov–de Gennes formalism, with good agreement with the observed variation of the electronic gap with chain length, and the observed spatial extent of the nonlinear excitations (polarons, bipolarons, etc.). The dynamics of lattice relaxation subsequent to electron dopoing is also analyzed, and suggests relatively weak e-ph coupling in this system. The two-dimensional vibrational spectra of the PPV series have been obtained in the random-phase and frozen-phonon approximations, and certain doping-induced localized modes are identified to be either ir or Raman active. The ir, Raman, and resonant Raman spectra of the pristine and charged PPV series are calculated and compared carefully with corresponding experiments, with overall good agreement.

The thermal conductivity of sputtered a-Si:H thin films for a hydrogen content of 1–20 % and a film thickness of 0.2–1.5 μm is determined in the temperature range 80–400 K using an extension of the 3ω measurement technique. The reliability of the method is demonstrated on 1-μm-thick a-${\mathrm{SiO}}_2$ thermally grown on Si. Scattering of phonons at the interface between the a-Si:H film and the substrate places a simple upper limit on the heat transport by long-wavelength phonons and facilitates the comparison of the experimental data to recent numerical solutions of a Kubo formula using harmonic vibrations.

The magnetoelectric effect in composites of piezoelectric and piezomagnetic phases is investigated theoretically. The magnetoelectric effect is totally absent in these two constituent phases, and so it is a new property of the composites. A generalized theoretical framework based on a Green’s function method and perturbation theory is proposed to treat the coupled magnetoelectric behavior in the composites. Explicit relations for determining the effective magnetoelectric effect in the composites are derived, and the different approximate expressions for the magnetoelectric coefficient of the fibrous composites with 1-3 or 3-1 connectivity of phases are given. To illustrate the technique, numerical calculations of the magnetoelectric coefficients of the ${\mathrm{BaTiO}}_3$-${\mathrm{CoFe}}_2$${\mathrm{O}}_4$ composites for various phase compositions and particle shapes are performed. The theoretical estimates are shown to be in agreement with available experimental results, and also show the interesting magnetoelectric behavior of the composites.

We discuss effects of in-plane magnetic domains on the magnetoresistance of magnetic multilayers. We find that the role of domains is similar to spin-flip processes. If one does not know the domain structure, nor the amount of spin-flip scattering, both mechanisms are equally plausible for producing spin diffusion which suppresses the magnetoresistance for the current perpendicular to the plane of the layers.

The angular dependence of the dispersion relation is calculated for a system consisting of two ferromagnetic layers exchange coupled through a nonmagnetic spacer layer. Special attention has been focused on the resonance behavior in the unsaturated state of an antiparallel coupled system. The variation of both the acoustic mode and the optic mode with the external-field orientation is significantly modified from that in a noncoupled system and can be used to accurately evaluate the interlayer exchange-coupling strength A(${\mathrm{\theta }}_{12}$) as a function of the angle between the magnetization vectors in the two magnetic layers. Based on the exchange-coupled resonance theory, the angular dependence of ferromagnetic resonance (FMR) measurements has been performed on several series of symmetrical and asymmetrical Co/Ru/Co structures at X-band and K-band frequencies with the temperature ranging from 10 to 300 K. Only the bilinear exchange-coupling coefficient ${\mathit{A}}_{12}$ was observed in these systems. The biquadratic contribution is more than two orders of magnitude smaller than ${\mathit{A}}_{12}$. For the symmetrical Co(32 Å)/Ru(${\mathit{t}}_{\mathrm{Ru}}$)/Co(32 Å) series, oscillatory interlayer exchange coupling was observed as a function of the Ru thickness ${\mathit{t}}_{\mathrm{Ru}}$. The oscillation period (∼12 Å) and phase do not vary with temperature. However, the oscillation amplitude is significantly enhanced at low temperatures, following roughly the relationship ${\mathit{A}}_{12}$∝(T/${\mathit{T}}_0$)/sinh(T/${\mathit{T}}_0$) predicted by the theoretical models. For the asymmetrical Co(32 Å)/Ru(${\mathit{t}}_{\mathrm{Ru}}$)/Co(${\mathit{t}}_2$) structures, variation of the exchange coupling strength as a function of ${\mathit{t}}_2$ has also been observed for several series within which ${\mathit{t}}_{\mathrm{Ru}}$ is constant. The variation length Δ${\mathit{t}}_2$ between maximum and minimum coupling strength is rather large (about 10 Å) and consistent from series to series.

Using magnetoresistance measurements at 4.2 K, the magnetic transitions of Fe/Gd multilayers have been studied. At low field and low temperature, this system is in an aligned state where all the Gd spins (or Fe spins) are in the field direction and all the Fe spins (or Gd spins) are antiparallel to the field because of the antiferromagnetic coupling of Gd and Fe spins. We show that a phase transition from a Gd-aligned state to a twisted state is a surface-induced transititon which occurs at low field when the outermost layer is iron. This surface effect extends relatively far in the sample (several thousands of angstroms). These results are in good agreement with theoretical studies.

Magnetic multilayers [Fe(20 Å)Pd(${\mathit{t}}_{\mathrm{Pd}}$)${]}_{\mathit{n}}$ grown by electron-beam evaporation were studied by x-ray small-angle reflection and high-angle diffraction. Structural parameters such as the superlattice periods, the interfacial roughness, the interplanar distances, and the grain sizes were obtained. The experimentally measured superlattrice periods deviated from the nominal ones by a considerable amount. We found that the density of the multilayers had changed abruptly with a Pd layer thickness increase as revealed by the changes of the critical angles and superlattice periods around ${\mathit{t}}_{\mathrm{Pd}}$=30 Å. We also found that the crystal structure of the Fe layer changed from bcc to fcc when the Pd layer thickness ${\mathit{t}}_{\mathrm{Pd}}$≥36 Å. Comparison of the saturated magnetization ${\mathrm{\sigma }}_{\mathit{s}}$ and the structural perfection showed that the magnetic properties of the Fe/Pd multilayer are strongly structure dependent.

In this paper we have applied the coupled-cluster method to investigate the ground state of the spin-1 Heisenberg antiferromagnet with anisotropic exchange interaction and easy-plane single-ion anisotropy. A coupled-cluster approximation up to the second level has been performed to evaluate the ground-state energy and staggered magnetization for various lattices such as linear chain, honeycomb, square, simple cubic, and body-centered-cubic lattice. The convergence of our results is fairly rapid, and thus the coupled-cluster method seems to be a practical tool for calculating ground-state energy of a spin system since only the first few levels of approximation will be needed in actual practice.

Co-Nb/Pd multilayered films with amorphous Co-Nb layers were prepared by rf sputtering. Magnetic measurements showed that the Pd atoms near the Co-Nb layers are polarized by Co atoms. The total magnetically active thickness per bilayer contributed from the polarization of Pd atoms is about 3.2 Å. A perpendicular easy axis of films can be obtained when the Co-Nb layers are thinner than 7 Å. The interface anisotropy ${\mathit{K}}_{\mathit{s}}$ is about 0.25 erg/${\mathrm{cm}}^2$. An oscillatory variation in saturation magnetization versus the thickness of the Pd layers with a period of about 10 Å is obtained. It is related to the structure changes in the Co or Pd layers. When the thickness of the Pd layers is around 14 A,̊ an antiferromagnetic polarization of Pd atoms is induced in the center of the Pd layers.

Brillouin light scattering (BLS) and the polar magneto-optic Kerr effect (MOKE) have been used to determine the interlayer exchange coupling strength at room temperature in an epitaxial wedge sample of nominal structure Pd/Fe(20 Å)/Pd/Fe(10 Å)/MgO(100) in which the Pd interlayer thickness varied between 14 and 30 Å. The constituent Fe layers were chosen to have different thicknesses and hence possessed different perpendicular anisotropy fields. This allowed both acoustic and optical spin-wave modes to be observed in the BLS experiment and also meant that the polar MOKE experiment could in principle be used to determine both antiferromagnetic and ferromagnetic interlayer coupling strengths. In order that the magnetic parameters of the individual Fe layers be independently determined, superconducting-quantum-interference-device (SQUID) magnetometry, in-plane MOKE, polar MOKE, and BLS measurements have also been made upon reference samples of nominal structure Pd/Fe(20 Å)/Pd(150 Å)/Fe(10 Å)/MgO(100) and Pd/Fe(10 Å)/MgO(100). Comparison of BLS and polar MOKE for the reference samples revealed different values for the effective demagnetizing fields in the two experiments. This is discussed in terms of a possible weakened surface exchange interaction at the Fe/Pd interface. For the wedge structure, ferromagnetic interlayer exchange coupling was observed for the entire range of Pd thicknesses studied.

The infinite-range Ising spin glass in the presence of a Gaussian random field is investigated by means of the replica method. The replica-symmetric solution and its instability are discussed; it is shown that the Almeida-Thouless instability regions are always reduced by the random field. The crossover exponent φ associated with the irreversibility line is shown to be nonuniversal in the presence of a random field, varying in a range from 1 to 3. Some of our results are compared with recent experimental measurements performed in the diluted antiferromagnet ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{F}}_2$.

Detailed bulk magnetization (ac susceptibility) measurements on the amorphous ${\mathrm{Fe}}_{16}$${\mathrm{Ni}}_{64}$${\mathrm{B}}_{19}$Si alloy have been performed in the temperature region 0.95${\mathit{T}}_{\mathit{C}}$–1.5${\mathit{T}}_{\mathit{C}}$ (0.95${\mathit{T}}_{\mathit{C}}$≤T≤1.05${\mathit{T}}_{\mathit{C}}$) before and after it had undergone isothermal annealing at 400 K for 60 and 120 min. An elaborate analysis of the data so obtained, besides yielding accurate values for the asymptotic and leading ‘‘correction-to-scaling’’ (CTS) critical exponents and amplitudes, reveals that the structural relaxation consequent upon isothermal annealing does not have any influence on the asymptotic and CTS critical exponents and on the universal amplitude ratios ${\mathit{m}}_0$/${\mathit{M}}_{\mathit{s}}$(0) and ${\mathit{Dm}}_0^{\mathrm{\delta }}$/${\mathit{h}}_0$, whose values are close to those theoretically predicted for a three-dimensional Heisenberg ferromagnet, but has profound effect on the ratio ${\mathrm{\mu }}_0$${\mathit{h}}_0$/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{C}}$ and the Curie temperature, ${\mathit{T}}_{\mathit{C}}$. The fraction of spins actually involved in the transition at ${\mathit{T}}_{\mathit{C}}$ is small and reduces slowly with increasing annealing time. Consistent with the theoretical expectations, nonanalytic corrections (originating from the nonlinear irrelevant scaling fields) to the singular behavior at ${\mathit{T}}_{\mathit{C}}$ dominate over the analytic ones (arising on account of the nonlinear relevant scaling fields) in the critical region but the reverse is true for T≫${\mathit{T}}_{\mathit{C}}$. Regardless of whether the sample is annealed or not, the initial susceptibility follows the generalized Curie-Weiss law for as wide a temperature range as ${\mathit{T}}_{\mathit{C}}$≤T≤1.5${\mathit{T}}_{\mathit{C}}$. The present results provide a strong evidence for weak itinerant ferromagnetism in the glassy alloy in question.

The ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$ NQR and ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ NMR spin-lattice relaxation times, ${\mathit{T}}_{1\mathit{Q}}$ and ${\mathit{T}}_{1\mathit{M}}$, respectively, in paramagnetic Ni(${\mathrm{H}}_2$O${)}_6$${\mathrm{SnCl}}_6$ crystals were measured as a function of temperature. Their temperature variations depend on the correlation time ${\mathrm{\tau }}_{\mathit{e}}$ of the unpaired electron spins in the paramagnetic ${\mathrm{Ni}}^{2+}$ ions, and ${\mathrm{\tau }}_{\mathit{e}}$ was found to be governed mainly by the electronic spin-lattice relaxation originating from the spin-phonon interaction above approximately 250 K and by electron-spin flips caused by the exchange interaction below approximately 150 K. The temperature dependence of ${\mathit{T}}_{1\mathit{Q}}$ and ${\mathit{T}}_{1\mathit{M}}$ at high temperatures shows that the electronic spin-lattice relaxation time is determined by the Raman process. The correlation time of the electron flips was evaluated to be 1.8×${10}^{\mathrm{-}10}$ s from ${\mathit{T}}_{1\mathit{Q}}$. The exchange parameter between the nearest electronic spins and the paramagnetic Curie temperature were estimated to be 0.013 ${\mathrm{cm}}^{\mathrm{-}1}$ and 0.075 K, respectively. It was shown that reliable information on the electron-spin dynamics can be obtained from ${\mathit{T}}_{1\mathit{Q}}$ and ${\mathit{T}}_{1\mathit{M}}$.

An experimental study of conventional x-ray absorption and of magnetic circular x-ray dichroism has been performed on La/Fe and on Ce/Fe multilayers at the ${\mathit{L}}_2$ and ${\mathit{L}}_3$ edges of La and Ce and at the K edge of Fe to characterize the impact of the interaction of La or Ce and Fe on the local electronic and magnetic structure of the interfaces. The spectra reveal that the interaction is particularly unusual for Ce/Fe, where two effects have been observed. First, on a depth scale of at least 15 Å near the interface, the Ce atoms adopt the electronic structure of the α phase, with itinerant 4f states. Second, these α-phase-like Ce atoms are magnetically polarized and carry an ordered magnetic 5d spin moment. This moment is antiferromagnetically coupled to the Fe 3d moment. Interface mixing on a length scale of the magnetic polarization can be excluded. For the La/Fe system, a similar magnetic polarization is effective, but in contrast to Ce/Fe it is restricted to the immediate interface with Fe. The results are discussed with reference to recent measurements of the macroscopic magnetization and Mössbauer spectra. Comparison with intermetallic compounds of rare-earth and late transition-metal elements points to the importance of hybridization effects for the Fe and Ce or La electronic states near the interfaces in the multilayers.

A method is described of reducing the nuclear spin-lattice relaxation time in a polycrystalline solid without the introduction of any paramagnetic impurities. It relies on the fact that the relaxation times of nuclei on a surface are usually much shorter than those in the bulk due to greater freedom of movement. Simply reducing the particle size by grinding or other methods is shown to be effective in markedly reducing the spin-lattice relaxation time of all the nuclei in the specimen because of the good thermal contact between like nuclei in the interior and surface of small particles. The nuclear quadrupole resonance (NQR) of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^2{}_{}{}^{}\mathrm{D}$, or ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ was measured for the same specimens with different particle sizes by nuclear quadrupole double resonance to ensure that the chemical structure of the compound did not alter due to the grinding. In all samples studied, except sodium thiosulphate, the NQR spectrum was unaffected by the grinding except that the time necessary to collect the data was reduced. In the case of sodium thiosulphate a marked change in the NQR spectrum was observed despite the fact that no change in chemical composition could be detected. Data is presented which demonstrates the effectiveness of the technique and a simple model of the underlying mechanism is described.

A finite-temperature theory of amorphous metallic magnetism has been proposed on the basis of the distribution-function method and the functional-integral technique. It improves the previous theory, and describes self-consistently the amplitude fluctuations of local magnetic moments on the nearest-neighbor shell by means of the distribution function of two variables, the local moment, and the local bandwidth parameter on the same site. Application of the theory to amorphous transition metals around Fe shows that the improved theory reduces the ferromagnetism, smoothes the d-electron number dependence of the spin-glass order parameter, and narrows the reentrant spin-glass region. Qualitative features of the magnetic phase diagram, however, is shown to be unchanged. The present theory supports the existence of spin glass in amorphous Fe.

A large thermal expansion anomaly has been observed in amorphous ${\mathrm{Y}}_{7.5}$${\mathrm{Fe}}_{92.5}$ and ${\mathrm{Y}}_{16}$${\mathrm{Fe}}_{84}$ alloys over a wide temperature range from the spin glass to the paramagnetic state. This anomaly fades away around 450 K, implying that the magnetic excitation to small amplitudes of local moments is saturated above this temperature. The inverse-magnetic susceptibility influenced by this excitation becomes convex upwards up to around 450 K and varies linearly above this temperature, obeying a new Curie-Weiss law.

We have calculated the circular dichroism associated with core-level photoemission using multiple-scattering photoelectron-diffraction theory. For C 1s emission in a chiral geometry from CO adsorbed on Pd(111), photoelectron-diffraction calculations predict the dichroism found in experimental results due to Bansmann et al. and also agree well with prior free-molecule calculations by McKoy and Stephens. Backscattering from the Pd substrate is also found to alter the dichroic asymmetries for different adsorption geometries. Analogous calculations for Fe 2p emission from a small Fe cluster also indicate that dichroism due to a chiral geometry can strongly affect measurements of magnetic circular dichroism in systems with net magnetization. With generalization to include spin-orbit and multiplet splittings in the initial state and spin-dependent scattering of the outgoing electrons, photoelectron-diffraction theory thus should provide a general method for modeling dischroism in core-level photoemission from both nonmagnetic and magnetic systems.

It is postulated that in nanostructured ferromagnets, e.g., Ni, Fe, and Co, exchange and magnetostatic energy dominate crystalline anisotropy energy and therefore the usual domain structure imposed via anisotropy is replaced by a structure consisting of topological defects. The defects are nonlinear solutions of the classical Heisenberg Hamiltonian of spins modified by magnetostatic energy, have the topological properties of disclinations, and are partly classified by the Hopf index. Coercive force is a consequence of entanglements of disclinations, pinning, and mutual obstruction during crossing processes correlated to local (spin) conductivity. Domain boundaries at surfaces are replaced by topological point defects of opposite topological charge generated pairwise.