bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser irradiation of compensation doped hydrogenated amorphous silicon
Authors: Al-Sabbagh S. K. , Wilson J. I. B. , Manookian W. Z.
Published: July 2002

A Q-switched ruby laser was used to study both reversible and permanent changes in the electrical conductivity of partially compensated n-type and p-type hydrogenated amorphous silicon (a-Si:H). This method of illumination provides an accelerated test of the magnitude of reversible photoinduced changes (known as the Staebler–Wronski effect) if the laser beam energy is insufficient to produce gross structural alterations in the samples. Compensated films are less susceptible to Staebler–Wronski changes than are single doped films. At energy densities above about 0.2 J cm−2, recrystallization of these thin films occurs, to an extent dependent on the energy. Energies above about 1.2 J cm−2 produced no further increases of conductivity. The total increase in conductivity over this energy range was 104–105 for p-type films and 103–104 for n-type films giving similar saturated conductivity values for both series of films. There were also large improvements in photosensitivity.
Homoepitaxial growth of ZnTe by low-pressure metalorganic vapor phase epitaxy
Authors: Ogawa Hiroshi , Nishio Mitsuhiro
Published: July 2002

Zinc telluride homoepitaxial layers have been grown on the substrates with different orientations by metalorganic vapor phase epitaxy method. Dimethylzinc and diethyltelluride were used as source materials. The substrate temperature was in the range of 385–470 °C. Relatively flat and smooth surface of the epitaxial layer was obtained only on the (100)ZnTe substrate. The in situ gas analysis using the quadrupole mass spectrometer was carried out during the growth.
Phase formation in a Bi-Sr-Ca-Cu oxide superconductor
Authors: Mei Yu , Green S. M. , Jiang C. , Luo H. L.
Published: July 2002

The formation of different superconducting phases in the Bi-Sr-Ca-Cu-oxide system sensitively depends on the preparation procedures, particularly the firing temperatures. The tangled x-ray powder diffraction patterns of coexisting Bi2Sr2CaCu2Oy and Bi2Sr2Ca2Cu3Oy have been completely identified. The basic unit cells are of approximate tetragonal symmetry. The lattice constants of the latter have been determined to be 5.40×5.40×37.09 Å3.
Noise equivalent power calculation: Application to Ga0.96Al0.04Sb avalanche photodiodes
Authors: Luquet H. , Gouskov L. , Pérotin M. , Jean A. , Magallon D. , Lahbabi M. , Bougnot G.
Published: July 2002

This paper presents a general method of calculation, allowing us to deduce the noise equivalent power in any type of avalanche photodiode. This method is checked by comparing numerical and analytical results for the case of a p-i-n junction. The calculation is applied to some Ga0.96Al0.04Sb diodes in order to estimate their performance and to deduce some trends for their optimization.
The effect of a valence-band offset on barrier formation in graded Hg1−xCdxTe heterojunctions
Authors: Madarasz Frank L. , Szmulowicz Frank
Published: July 2002

We use a highly accurate numerical computer model to solve the problem of equilibrium barrier formation in graded Hg1−xCdxTe heterojunctions including valence-band offsets. The present calculation is an extension of our previous work [J. Appl. Phys. 62, 3267 (1987)], which incorporated physical features designed to improve upon previous calculations, but employed the common anion rule. First, we analyze and compare our results to the recent work of Oda [Infrared Phys. 27, 49 (1987)] and find significant differences. Then, we make a comparison with the results of our previous work. We observe clear trends between our results with and without the valence-band offset. Unlike Oda, we do not make general predictions with regard to the conditions needed to support the formation and growth of a barrier in the conduction band, but instead find the band profiles to be a complex function of all the junction design parameters. For the present study involving narrow gap p on wide gap n heterojunctions, and the assumed: HgTe:CdTe 300-meV valence-band offset, the band profiles do not differ significantly from the profiles assuming the common anion rule.
Radiation-induced defect states in low to moderately boron-doped silicon
Authors: Awadelkarim O. O. , Monemar B.
Published: July 2002

Low to moderately boron-doped silicon crystals were irradiated at room temperature with a 2.0-MeV electron beam and studied by means of deep-level transient spectroscopy. New dominant hole traps H(0.12) and H(0.07) located, respectively, at 0.12 and 0.07 eV above the valence band, and an electron trap E(0.59) located at 0.59 eV below the conduction band are reported. The states H(0.12), produced directly after irradiation, and H(0.07), formed following 400 °C annealing, are observed in samples of low boron contents (∼1014 cm−3). The state E(0.59), on the other hand, is observed after 400 °C annealing in the moderately boron-doped samples (∼1015 cm−3). Based on the thermal stability and energy position of these states tentative defect identifications are proposed by correlation with published data. Other previously reported hole traps are observed at 0.22 and 0.34 eV above the valence band and are ascribed to the divacancy V2 (0/+) and the carbon interstitial-carbon substitutional pair, respectively.
A study of iron-related centers in heavily boron-doped silicon by deep-level transient spectroscopy
Authors: Awadelkarim O. O. , Monemar B.
Published: July 2002

Deep levels in iron-diffused heavily boron-doped silicon are investigated by means of deep-level transient spectroscopy (DLTS). For interstitial iron Fei a donor state is observed at 0.39 eV above the top of the valence band Ev. It is proposed that Fei exhibits charge-dependent annealing characteristics, and in its neutral charge state Fei is mobile at temperatures as low as ≊280–230 K. Three other Fe-related donor states are observed at Ev+0.53 eV, Ev+0.60 eV, and ≊Ev+0.63 eV. The latter two states, not reported in any previous DLTS study, are produced in comparable concentrations to that of Fei upon annealing at 100 °C, whereas the former state present directly after quenching is suggested to result from a complex defect containing Fei. It is also argued that the level observed in this study at Ev+0.60 eV is the same as the one reported earlier at 0.55 eV below the bottom of the conduction band, but that it corresponds to a donor state of an Fe-related defect, in contrast to previous suggestions of it being an acceptor state. The annealing behavior of the defect states observed is studied up to 300 °C, and possible interactions involving Fei are discussed.
The optimization of multipole magnetizing fixtures for high-energy magnets (abstract)
Authors: Lee J. Kelly , Furlani E.
Published: July 2002

Modern high-energy magnetic materials such as samarium-cobalt and neodymium-iron-boron require very large magnitizing fields to achieve full saturation. In some cases the recommended magnetizing field is as high as 40 kOe. Such a field is readily achievable in a large solenoid, and undirectional magnetization is easily accomplished. Many applications such as motors and linear actuators, however, require multipole magnets. The problem of designing custom fixtures for multipole magnetization has often been considered more of an art than a science. This paper shows that by mathematically modeling the capacitor discharge magnetizer and the fixture the problem can be solved with reasonable predictability. Two different multipole fixture designs are presented along with the experimental results. The basic equations are presented and used to predict the magnetic field intensity inside the fixtures. It is shown that optimum performance is achieved when the resistance of the fixture is equal to the parasitic resistance of the magnetizer. Finite element analysis is also used as part of the design process. The experimental results have been achieved using a high-voltage, low-energy capacitor discharge magnetizer and air core fixtures. The magnetization patterns that are produced are very sharp and well defined.
Very low loss ultrathin Co-based amorphous ribbon cores
Authors: Yagi M. , Sato T. , Sakaki Y. , Sawa T. , Inomata K.
Published: July 2002

Ultrathin Co-based amorphous ribbons with a thickness of 6–10 μm were fabricated by a single roller quenching method in vacuum. The compositions of the alloys were zero magnetostrictive: Fe4.7Co70.3Si15B10 and (Fe0.05Co0.95)71(Si0.5B0.5)29. The ribbons obtained had good smoothness and dimensional uniformity. The core loss of toroidal samples 15 mm in diameter was measured after annealing. The loss decreased with decreasing ribbon thickness. In the case of 6.4-μm-thick (Fe,Co)71(Si,B)29 amorphous ribbon, the values at 100 kHz and 1 MHz were 40 mW/cm3 and 1.8 W/cm3 for Bm=0.1 T, respectively. The former was 1/4 that of Mn-Zn ferrites or 1/2 that of 5-μm-thick Supermalloy tape wound core loss. The latter was (2)/(3) that of 5-μm Supermalloy tape wound core loss. In addition, the initial permeability beyond 100 kHz was also markedly improved by thickness reduction. The values of 6.4-μm-thick (Fe,Co)71(Si,B)29 ribbon measured at 1 and 10 MHz were about 7000 and 1000 for Hm=2 mOe, respectively.
Antiferromagnetic ordering in 2-1-4 copper oxides
Authors: Tang H. , Du Y-W. , Qiu Z-Q. , Walker J. C. , Morgan J. S. , Bryden W. A.
Published: July 2002

We have doped a small amount of Fe (0.5%) into the 2-1-4 superconducting oxides La2 CuO4−y and La1.85 Sr0.15 CuO4−y . Mössbauer measurements have indicated that the Fe dopants are in a high-spin Fe3+ state, but sharp differences have been found for samples before and after annealing in Ar, as well as with and without Sr. An antiferromagnetic transition at 292 K in the Ar-annealed La sample has been confirmed with both Mössbauer and magnetization measurements. The relevance of antiferromagnetism to the high-temperature superconductivity has been addressed.
Surface magnetism of epitaxial thin films by polarized electron scattering (invited) (abstract)
Authors: Alvarado S. F.
Published: July 2002

The development of spin-polarized spectroscopy techniques offers some of the most powerful probes to study the magnetic phenomena related to the interface region of free magnetic surfaces and multilayer systems. The study of the magnetic properties of surfaces and interfaces is relevant in the basic understanding of, e.g., the coupling in magnetic multilayer systems. By spin-polarized low-energy electron diffraction it has been possible to characterize such magnetic interfaces allowing to test the validity of recent theoretical models. Thus, depending on the strength of the surface magnetic coupling, different magnetic phase transitions can occur, the most spectacular one being the case when at the surface the ferromagnetic to paramagnetic transition occurs at a higher temperature than in the bulk. This phenomenon has indeed been demonstrated on Gr(0001)1 and on Tb surfaces.2 Furthermore, indications of anomalous behavior on Gd/3 leads now to consider an interpretation in the frame of the first-order phase transition predicted recently.4 The role of the interface region in the coupling between epitaxial ferromagnetic layers separated by an antiferromagnetic material has also been studied.5 Two Fe(001) films separated by a thin slab of Cr exhibit antiparallel coupling. The Cr(001) slab, however, shows no indications of the expected ferromagnetic surface sheet configuration.
Critical dynamics of dipolar ferromagnets (invited)
Authors: Schwabl F.
Published: July 2002

In real ferromagnets both exchange and dipolar forces are of importance. The crossover in the dynamics from isotropic to dipolar critical behavior has been a matter of debate for a long time. While neutron scattering experiments gave a dynamical critical exponent z= (5)/(2) and no crossover to z=2, the linewidth did not agree with the scaling function for isotropic ferromagnets. On the other hand, a crossover to dipolar critical behavior was found in hyperfine interaction experiments and the presence of the dipolar interaction also manifests itself in electron spin resonance experiments. We review a recent mode coupling theory for dipolar ferromagnets by means of which these phenomena all can be explained in a unified fashion. It turns out that the crossover in the transverse linewidth occurs at a wave number which is smaller than qD, the position of the static crossover. The dynamical scaling functions and the shape function are in agreement with experiment. Further experiments are proposed.
Excitations in the classical X
Y chain
Authors: Gerling R. W. , Landau D. P. , Challa M. S. S.
Published: July 2002

We have studied the time-dependent behavior of the classical XY chain in a symmetry breaking magnetic field using an ultrafast spin-dynamics method in which we integrate the equations of motion using starting configurations determined by Monte Carlo simulations. We calculated the three polarizations of S(q,ω) separately for temperatures from 0.1 to 1.0 J/kB and fields up to 1.5 J. The soliton contribution, the single-magnon peaks, and both the sum and difference two-magnon contributions are separated; we discuss them in detail and compare them with theoretical predictions.
Phenomenologies of ferromagnetism in metals (invited) (abstract)
Authors: Arrott A. S. , Heinrich B.
Published: July 2002

Magnetism remains mysterious 100 years after Ewing made his initial models of interacting compasses. Many aspects are seen clearly, but at each step from the spinning electron to the rotor of a motor complexity obscures. At the macroscopic level the difficulties in ferromagnetism start with magnetostatics, which in principle calls for the evaluation of sixfold integrals. At the quantum level one needs fully relativistic spin-polarized calculations that remain beyond the current state of the art in order to have a full description of the ground state of a homogeneous piece of material with periodic boundary conditions. While it is known in principle how to carry out such calculations, in practice an experimentalist relies on phenomenology for the interpretation of

data. The role of phenomenology is to create molds into which the experimental data is pressed. Theoretical analyses of critical phenomena are among the triumphs of modern magnetism. The picture is beautiful as long as one ignores anisotropies, dipole–dipole interactions, magnetostriction, and dynamic effects, all of which are the heart of micromagnetics, not to mention imperfections, inhomogeneities, and surface effects. Studies of the response, static and dynamic, of nearly perfect single crystals of Fe, grown from the decomposition of FeCl2 in the form of whiskers, provide examples where the

experiments attempt to approach the neatness of the theories. Interpretation of data requires understanding of the dominant magnetostatics, the underlying micromagnetics and the resulting magnetization patterns, and the major role of eddy currents in obscuring intrinsic loss effects. One combines these aspects of Maxwell’s equations with parametric formulations of the equation of state and the Landau–Lifshitz equations of motion to extract magnetizations, susceptibilities, anisotropies, and damping parameters as functions of internal fields and frequency. The micromagnetics of the ideally soft ferromagnetic material serves as a foundation for the phenomenology. Fifty years of progress

in understanding of phase transitions provides the critical phenomenology. The Landau–Lifshitz equations of motion developed for feromagnetism also describe the dynamic response in the transition from paramagnetism to ferromagnetism when allowance is made for the frequency, field, and temperature dependence of the damping. When the phenomenology and the data are not in full accord it is difficult to assign the source of the misfit. Yet one rejoices in the fact that they fit, sort of.
Paramagnetic anisotropy in high-T
c superconductors
Authors: Livingston J. D. , Hart H. R. , Wolf W. P.
Published: July 2002

Magnetic alignment of RBa2Cu3O7−x particles results from anisotropy in paramagnetic susceptibility, an anisotropy that differs in sign for different rare earths. Various factors contributing to this anisotropy are discussed, particularly the rare-earth single-ion anisotropy associated with crystal fields and second-order Stevens factors. For R=Eu, the observed anisotropy is consistent with that expected from the crystal-field splitting of J=1 excited levels.
Bi-Sr-Ca-Cu-O high T
C superconductors (abstract)
Authors: Sherwood R. C. , Tiefel T. H. , Jin S. , Davis M. E. , Kammlott G. W. , Fastnacht R. A.
Published: July 2002

A recent paper by Maeda et al.1 reported the discovery of a new 120 K superconductor based on a rare-earth–free ceramic material in the bismuth-strontium-calcium-copper-oxide system. We have confirmed the existence of the 120-K phase in the oxide system. The resistivity-temperature curve showed a fairly well-defined double-dip shape with the first dip starting at ∼120 K and the second at ∼95 K. The transition temperature, TC(R=0), was 84 K. This material appears to contain two superconducting phases with different TC’s. A pellet made from this superconductor levitates well at 77 K (liquid-nitrogen temperature) above a neodynium-iron-boron magnet with a surface magnetic field of ∼3000 Oe, thus indicating a nontrivial critical field in this material. The critical current density and its magnetic field dependence will be reported. The magnetic and mechanical behavior of the new superconductor will also be discussed.
Dynamical properties of magneto-optical effect in magnetic fluid thin films
Authors: Taketomi S. , Ogawa S. , Miyajima H. , Chikazumi S. , Nakao K. , Sakakibara T. , Goto T. , Miura N.
Published: July 2002

The dynamical properties of the magneto-optical effects of magnetic fluids thin films were investigated. The thin films, 12 μm thick, of magnetite colloidal particles in water solvents and alkylnaphthalene one were prepared. A pulsed magnetic field H(t) was generated in a single turn coil by discharging a 40-kV capacitor bank. The intensity I(t) of the transmitted light through the two crossed polarizers and the films located in the coil was measured. The relaxation process of the magneto-optical effect can be described in terms of a single relaxation time, τ=3 μs, for a water-based magnetic fluid, while the relaxation time constant for alkylnaphthalene one depends on the field strength. These dynamical properties can be interpreted by the time-dependent Ginzburg–Landau theory by introducing the order parameter of the colloidal particles.
Polarized neutron scattering of D2O-based magnetic fluids (depolarization)
Authors: Taketomi S. , Itoh S. , Endoh Y. , Ogawa S. , Miyajima H. , Chikazumi S.
Published: July 2002

Magnetite colloidal fluid with a carrier fluid of deuterium oxide (D2O) was prepared to eliminate the incoherent scattering by hydrogen nucleons and the depolarization of cold neutrons was measured. The magnetic fluid was cooled down to 17 K in an external magnetic field of 10 kOe. The sample exhibited a finite residual magnetization Mr, which decreases with increasing temperature from 17 K. With elevating the temperature from 17 to 300 K, the depolarization was measured in three cases in which the directions of the beam, Mr, and polarization are mutually changed. The polarized neutrons transmitting through the sample were depolarized by the magnetic moments in the colloidal particles. The polarizations as a function of the product of Mr and neutron wavelength λ at different temperatures reduce to the same functional form. The model which shows that no interactions exist among the ferrous colloidal particles succeeds partly in explaining the experimental results.
Study on the building factor of a stacked core made of amorphous sheets (abstract)
Authors: Matsubara K. , Nakata T. , Nakano M.
Published: July 2002

There are some factors increasing the building factor of a transformer assembled from amorphous sheets. One of the factors may be the localized irregularity of magnetization property. Such an inhomogeneity is caused by the localized mechanical stress or the inhomogeneous temperature distribution during annealing. Various stacked cores which are composed of amorphous sheets with inhomogeneous magnetic characteristics as shown in Fig. 1 have been investigated. Each half of the sheet is annealed uniformly at different temperature from the other half. The frequency characteristics of power losses are measured to clarify whether the main cause of the total loss increase is due to the hysteresis loss or the eddy current loss. The obtained results show that the incremental loss is mainly due to the increase of eddy current loss. The increase of eddy current loss may be due to the transverse flux across the interlaminar gap. Therefore, the relationship between power losses and gap length has been examined. The obtained results denote that the eddy current loss is increased by the transverse flux. The experimental results are also checked by numerical analysis of the flux distribution in stacked cores using the finite element method.
A new type of magnetic shield (abstract)
Authors: Haga A. , Kikuchi S. , Kimura H.
Published: July 2002

We propose a new type of magnetic shield which is made by piling the many U-shaped soft magnetic materials. We call it ♯-type shield because of its shape as shown in Fig. 1. The principle of magnetic shielding is based on the zero vector sum of the applied field and demagnetizing field outside the soft magnetic specimens. In this way a weak field region is produced inside the ♯-type shield which screen out the external field. Therefore, shielding effectiveness can be controlled by changing the demagnetizing factor which primarily depends on the shape of the specimen. It is hard for the conventional magnetic shield like a cylindrical shell to control its demagnetizing factor, therefore, the shielding effectiveness is based on only the permeability of the soft magnetic materials. However, it is easy for the ♯-type shield to control its demagnetizing factor by changing the length of U-shaped speciments. The shielding ratios S (external field/internal field) of the ♯-type shield have the maximum as the external field increases. The demagnetizing field due to U-shaped iron cancels perfectly the external field when the shielding ratio S is maximum. Therefore, S is extremely high (S=104). The critical field at which S is maximum optionally varies with the length L of U-shaped specimens. The shielding effectiveness of ♯-type shield using iron is as effective as that of the cylindrical shield using permalloy. The ♯-type shield is more economical. The shield is free from temperature rising because of the open structure. The ♯-type shield using iron can be applied to almost any device having magnetic structure or involving electron beam.
Low-temperature phase of yttrium iron garnet (YIG) and its first-order magnetoelectric effect
Authors: Kita Eiji , Takano Shunsuke , Tasaki Akira , Siratori Kiiti , Kohn Kay , Kimura Shigeyuki
Published: July 2002

A structural change in YIG is revealed by the observation of a first-order magnetoelectric effect at 77 K. The signal disappears at around 130 K. This indicates that a phase transition takes place at this temperature. Detailed field cooling experiments lead to the conclusion that the symmetry of YIG below 130 K is triclinic.
Study of weak magnetism effects in heavy-electron systems by μ+SR (abstract)
Authors: Barth S. , Gygax F. N. , Hitti B. , Lippelt E. , Ott H. R. , Schenck A.
Published: July 2002

We will present results from μ+SR investigations of the heavy-electron systems CeAl3, U2Zn17, UCu5, and UCd11. The latter three are known to order antiferromagnetically at low temperatures. The transition into the antiferromagnetic phase is clearly manifest in the μ+SR data, but also above the Néel temperatures some weak magnetism seems to persist as can be inferred from enhanced μ+ relaxation rates even in zero applied field. The involved effective moments are much reduced in comparison to the free-ion f moments, generally below 0.5 μB, and the magnetic order may be of the spin-glass or spin-density wave type. In nonmagnetic CeAl3 a spontaneous μ+ precession signal appears below 0.7 K in zero external field which implies the presence of even some coherent magnetic order of probably very short range in this system. These findings are consistent with other recent μ+SR and neutron scattering work, indicating that weak magnetic mechanisms seem to be a characteristic feature of heavy-electron systems.
Electronic structure and surface reactivity of Nd2Fe14B and related compounds
Authors: Jaswal S. S. , Langell M. A. , Ren Y. G. , Engelhardt M. A. , Sellmyer D. J.
Published: July 2002

Studies of electronic and magnetic structure and surface reactivity are reported for R2T14B compounds where R=Y, Nd, Gd, and T=Fe, Co. The calculations employed the self-consistent, spin-polarized linear-muffin-tin orbital method. Experiments included ultraviolet, x-ray, and Auger electron spectroscopy. Comparisons are made between the calculated and measured electronic densities of states, and the reactions of the surfaces with O2, H2, and CO gases are studied. The effects of heat treatment on surface segregation are also reported.
Theory of strong hybridization-induced relaxation in uranium systems
Authors: Hu Gong-Jia , Cooper Bernard R.
Published: July 2002

Commonly, for metallic uranium systems, sharp magnetic excitations are not observed in neutron inelastic scattering experiments, but rather there is a continuous spectrum of magnetic response. By extending our earlier theory for partially delocalized cerium systems, we can understand this behavior. The band-f hybridization is transformed to resonant scattering in our theory, where the exchange part of the scattering gives both a two-ion interaction (physically corresponding to cooperative hybridization, giving anisotropic magnetic ordering with unusual excitation dispersion for cerium systems) and a hybridization coupling of each ion to the band sea (giving relaxation and strong energy renormalization of the excitations for cerium systems). For uranium the f delocalization (and hence the hybridization) is much stronger than for cerium. The two-ion interaction (giving quasi-ionic energy level splitting) grows by an order of magnitude or more, as evidenced by greatly increased magnetic ordering temperatures. On the other hand, the single-site hybridization strength parameter 𝒥 characterizing the f-to-band-bath coupling grows more moderately as the f levels move toward the Fermi energy, because of the renormalizing effect of the direct scattering which broadens the f levels. The increased energy scale of the quasi-ionic level splitting for uranium as compared to cerium or plutonium is the major contributor to the greatly increased width of magnetic scattering distributions, while the moderate increase in coupling of each uranium quasi-ion to the band sea gives a lesser contribution. We apply this theory to UP and UAs and compare our results with experiment.
Calculation of the indirect-exchange interaction between nuclear spins in Cu and Ag
Authors: Miller D. J. , Frisken Steven J.
Published: July 2002

The indirect-exchange interaction between nuclear spins in Cu and Ag has been calculated using band structures based on two different methods: a self-consistent ab initio method and a semiempirical parametrized method. The results from the different band approaches agree with one another more closely than either of them does with the conventional result based on free-electron bands and constant matrix elements. The oscillatory nature of the interaction is similar in each case but the nearest-neighbor interaction is far more significant in the former cases. It is concluded that the simpler, parametrized approach gives satisfactory results but that there is insufficient evidence at this stage for any of the theoretical results to be chosen as the definitive one to be used in explaining the ordering of the nuclear spins in Cu.
The role of fluctuations in spontaneous metamagnetism
Authors: Tuszyński J. A. , Smith A. P.
Published: July 2002

A Landau–Ginzburg Hamiltonian involving coupled sublattice magnetizations as order parameters for spontaneous metamagnets is studied. A brief review of the mean field results is followed by an analysis of the role of fluctuations which arise due to the inhomogeneity terms in the Hamiltonian. Using a Gaussian approach the specific heat contribution from the normal modes is studied neglecting mode-mode coupling. A non-Gaussian approach to the problem is also outlined. While for finite sizes specific heat shows no anomalies, in the thermodynamic limit classical exponents are recovered. The kinetics of the transition is described by the Euler–Lagrange equations for sublattice magnetizations which result in two nonlinearly coupled nonlinear Klein–Gordon equations. Special solutions obtained from a particular ansatz include solitons and elliptic waves whose physical interpretation is provided.
Perpendicular magnetic anisotropy and magneto-optical properties of evaporated (Fe,Co)–rare-earth amorphous binary alloy films
Authors: Yoshihara A. , Takahashi M. , Shimamori T. , Wakiyama T. , Miyazaki M. , Yamaguchi S. , Hayashi K.
Published: July 2002

The dependence of perpendicular magnetic anisotropy on temperature and composition has been investigated for various (Fe,Co)–rare-earth amorphous binary alloy films prepared by evaporation. The temperature dependence of the perpendicular magnetic anisotropy is proportional to the third power of the rare-earth sublattice magnetization. The perpendicular magnetic anisotropy consists of two terms related to concentration. One is proportional to the rare-earth content and the other to its square. Both terms can be explained by a large rare-earth single-ion anisotropy.
Effects of annealing and periodic ion bombardment on the soft magnetism of FexN films by a double ion beam sputtering system
Authors: Naoe M. , Nagakubo M. , Yamamoto T.
Published: July 2002

Fe films with low nitrogen content have been prepared by using a dual ion beam sputtering apparatus. The effects of annealing at 300 °C for after-treatment of as-deposited films and the effects of periodic nitrogen ion bombardment onto growing Fe layers for growth process on their structure and magnetic properties have been investigated. The Hc of Fex N single layer films with nitrogen content of 2–3 at. % bombarded continuously by a mixture of argon and nitrogen ions decreased noticeably after annealing at 300 °C without significant decrease of saturation magnetization 4πMs. On the other hand , the Hc of the Fe/Fex N multilayered films bombarded periodically by the nitrogen ions at an accelerating voltage of 150 V decreased drastically, and took a minimum Hc of 1.5 Oe at proper cycle time tp. These results may be attributed to the relaxation of internal stress in films by annealing and the modification of microscopic morphology by ion bombarding, respectively.
Nanomagnetism: High-resolution magnetic surface studies using spin polarization of secondary electrons (invited) (abstract)
Authors: O’Handley R. C. , Woods J.
Published: July 2002

Intense scientific curiosity and the drive to increase information storage density have fueled extensive theoretical and experimental work on magnetic surfaces. Symmetry and bonding are reduced at surfaces and in magnetic materials this can cause changes in the moment and magnetic anisotropy over distances too small to probe optically. We have constructed and used a thin-film, spin-orbit scattering polarimeter (based on the NBS design) to measure the polarization of secondary electrons excited from magnetic surfaces. The low-energy secondary electrons come from the outermost atomic layers and carry a polarization proportional to valence polarization of the elements in the surface. Results on amorphous cobalt base alloys indicate a surface anisotropy in the outermost 2–5 nm pulling the magnetization away from the bulk preferred direction. High lateral resolution can be achieved by using the thin-film polarimeter to measure the polarization of secondary electrons excited from a magnetic surface by a high-resolution (25 Å), field-emission source, scanning electron microscope.
Magnetic properties of epitaxial bcc iron films on Ag(001) investigated by spin-polarized photoemission
Authors: Vaterlaus A. , Stampanoni M. , Aeschlimann M. , Meier F.
Published: July 2002

Epitaxial bcc Fe films, grown on Ag(001), ranging from 0.8 to 10 monolayers (ML), are ferromagnetic. At 30 K a remanent magnetization along the surface normal is observed for the 3–4-ML films. No perpendicular remanence is observed for the same films above 100 K and for films thicker than 5 ML or thinner than 2 ML. Above 5 ML the Curie temperature is around 1000 K as for bulk bcc Fe; for thinner films it is reduced and amounts to 400 K only for the 1 ML film.
Preludes to spin-wave chaos: Spin-wave instability processes, butterfly curves, kinks, flips, cusps, and shifts (invited) (abstract)
Authors: Patton C. E. , Srinivasan G. , Jantz W. , Wettling W. , Wilber W. D. , Booth J. G.
Published: July 2002

Manifestations of chaos1–3 above the threshold microwave field for spin-wave instability have brought this established topic in microwave magnetics back into vogue. This paper will review the nature of the instability onset and the factors which determine the variation of the threshold microwave field for instability (hcrit) with dc field, the so-called ‘‘butterfly curve.’’ A key factor here is the wave-vector k dependence of the spin-wave linewidth ΔHk. This k dependence leads to abrupt shifts in the wave number k for the unstable modes from large values (105 cm−1) to small values (103 cm−1) and a characteristic ‘‘kink’’ in the subsidiary absorption butterfly curve. Under certain circumstances, flips in the aximuthal spin-wave propagation angle are also predicted. Such flips show up experimentally in some of the expected circumstances, but not in others.
Ultrasonic shear-wave absorption in amorphous magnetic ribbons
Authors: Squire P. T. , Gibbs M. R. J.
Published: July 2002

Shear-wave propagation has been studied experimentally in samples of amorphous ribbon material of composition Fe40Ni38Mo4B18 (METGLAS 2826MB). The samples were in the as-received, stress-relieved, and transverse-field annealed states. Pulse-echo measurements have been made at frequencies between 0.5 and 2.5 MHz and at various applied fields. The frequency dependence of the absorption coefficient is consistent with the form af+bf 4 found in crystalline solids. In the case of amorphous material the second term is attributed to scattering from domains. As-received material has a higher loss than field annealed, especially at very low applied fields; this is thought to be due to magnetic damping associated with moment rotation. The implications of these results for shear-wave magnetometry are briefly considered.
Development of texture in extruded Fe-Nd-B magnets
Authors: Yang Choong Jin , Ray Ranjan
Published: July 2002

High-performance Fe-Nd-B magnets were prepared by consolidation of rapidly solidified melt-spun powders using a hot extrusion technique. The extrusion was carried out with various die openings to control the distribution of stresses and strains influencing the possible development of texture. A strong anisotropy in magnetic properties has been found in the extruded magnets. The highest remanence of 10.6 kG and the maximum energy product of 16.6 MGOe were achieved along the through-thickness direction of the magnet extruded with a rectangular cross section. A(001) [1̄20] texture was found to develop in the plane normal to the through-thickness direction. It is suggested that the enhanced remanent magnetization arises principally from the formation of a favorable texture.
Properties of NdFeB permanent magnets as a function of ribbon quench rate (abstract)
Authors: Carnegie David W.
Published: July 2002

The magnetic and structural properties of melt-spun NdFeB alloy depend in a sensitive way on the quench rate. These ribbon properties affect the process used in the fabrication of hot-pressed isotropic magnets and die-upset, aligned magnets. We present the results of an investigation into the nature of these process interactions. Melt-spun ribbon is produced for a series of substrate velocities to vary the quench rate. We discuss the magnetic properties of the resulting ribbon, hot-pressed MQ-II magnets and die-upset MQ-III magnets. The unique magnetic properties of melt-spun NdFeB material are due to the uniaxial anisotropy in the Nd2Fe14B1 phase and the process and composition-dependent microstructure consisting of very fine grains of the hard magnetic phase surrounded by NdFe eutectic. Microscopic study of ribbon and magnet samples reveals the nature of this structure and how it relates to the magnetic properties and processing parameters.
A theoretical model for the cathodoluminescence of granular phosphor screens
Authors: Giakoumakis G. E. , Lagaris I. E.
Published: July 2002

A theoretical model for the cathodoluminescence of a phosphor screen is presented. The model takes into account the granular structure of the screen and the random deposition of the phosphor grains on the screen substrate. It gives reliable predictions even in the case of the low thickness screens where the Hamaker–Ludwig [H. C. Hamaker, Philips Res. Rep. 2, 55 (1947); G. W. Ludwig, J. Electrochem. Soc. 118, 1152 (1971)] model is not applicable. Using this model we obtained results concerning the dependence of the screen efficiency on various parameters. These results are in close agreement with the experimental data already known for the cathodoluminescence of phosphor screens.
Transport critical current and magnetization measurements of melt-processed YBa2Cu3O7−x
Authors: Hermann A. H. , Sheng Z. Z. , Kiehl W. , Marsh D. , El Ali A. , Hambourger P. D. , Almasan C. , Estrada J. , Datta T.
Published: July 2002

We report magnetic field dependence of the transport critical current and dc magnetic susceptibility measurements on YBa2Cu3O7−x superconductors formed by melt-solid reactions at 950 °C between Ba-Cu-O (or Tb-Ba-Cu-O) and solid nonstoichiometric Y-Ba-Cu-oxide. Four-probe dc critical current measurements at 77, 64, and 4.2 K show strong depression of the critical current density with increasing magnetic field in agreement with a model of weakly linked superconducting regions. Diamagnetic shielding and Meissner flux expulsion measurements in the temperature range 10–300 K show about one third volume fraction of perfect superconductivity. Both shielding and flux expulsion were observed to be approximately temperature independent below 60 K indicating strong coupling between the grains throughout the entire volume below this temperature.
Formation and thermal stability of vapor-deposited amorphous Ni-Zr thin films
Authors: Minemura T. , van den Broek J. J. , Daams J. L. C.
Published: July 2002

The formation range and thermal stability of vapor-deposited, amorphous Ni1−xZrx thin films is studied and compared with previous results for melt-spun ribbons and also with a thermodynamic prediction. Crystallization temperature and glass transition temperature for films and ribbons turn out to be nearly the same; the glass formation range for films is larger than that for ribbons and agrees very well with the thermodynamic prediction.
Self-consistent calculations of tunneling currents in n+-GaAs/i- AlxGa1−xAs/n+-GaAs structures and comparison with measurements
Authors: Zimmermann B. , Marclay E. , Ilegems M. , Guéret P.
Published: July 2002

We present calculations and measurements of current as a function of voltage I(V), and conductivity at low voltage as a function of temperature, G(T), for n+ -GaAs/i- Alx Ga1−x As/n+ -GaAs single-barrier tunneling structures. The current is modeled by its tunneling and thermionic emission components. The shape of the conduction-band edge is obtained by solving Poisson’s equation self-consistently, together with two different models for the charge density. In the first model, the electron density is evaluated semiclassically, and in the second, the electron density is calculated from the electronic wave functions. Good agreement is obtained with both models between the experimental and the calculated I(V) and G(T) characteristics over the 4.2–200 K temperature range. The fits obtained are very sensitive to small variations (1%) in barrier width and effective barrier height, which allows one to determine these parameters within a narrower uncertainty range.
Deep acceptorlike recombination centers in bulk liquid encapsulated Czochralski GaP, studied with optically detected magnetic resonance
Authors: Godlewski M. , Monemar B.
Published: July 2002

The optically detected magnetic resonance technique is applied to determine the nature of broad, featureless emission bands observed in the near-infrared region in bulk GaP crystals grown by the liquid encapsulated Czochralski method. A broad emission band with maximum at ≊8000 Å (≊1.55 eV) was consistently observed in undoped and donor-doped (S, Te, Se, Ge) crystals, and is shown to be due to donor-acceptor pair (DAP) recombination. The analysis of the optically detected magnetic resonance experiments indicates that shallow donors and deep acceptors are active in the 8000-Å recombination. The identity of the ≊0.7-eV deep acceptor center active in this DAP transition could not be determined from the experimental results, but a single acceptor complex consisting of a Ga vacancy and two adjacent donors is proposed as a tentative model.
Variable angle of incidence spectroscopic ellipsometric characterization of TiO2/Ag/TiO2 optical coatings
Authors: Memarzadeh Kazem , Woollam John A. , Belkind Abe
Published: July 2002

Optical constants (3000–8000 Å) and layer thicknesses of TiO2/Ag/TiO2 optical coatings are determined using variable angle of incidence spectroscopic ellipsometry. Ellipsometrically determined silver layer thicknesses agree well with those obtained by cross-sectional transmission electron microscopy. Also, spectral characteristics, absent in bulk silver data, are observed in n and k spectra for the thin silver layers. It is suggested that these structures may be caused by plasmon effects from the silver layers.
Epitaxial growth of high T
c superconducting Y-Ba-Cu-O thin films on (001)MgO by a chemical spray pyrolysis method
Authors: Chu J. J. , Liu R. S. , Kung J. H. , Wu P. T. , Chen L. J.
Published: July 2002

A chemical spray pyrolysis method has been applied to grow epitaxial films of a high Tc Y-Ba-Cu-O compound (YBCO) on (001)MgO. Films as thin as 0.6 μm in thickness was found to exhibit excellent superconducting transition behavior. For films up to 2 μm in thickness, typical values of Tc onset, Tc zero and transition width (90%–10%) were measured to be 82, 76, and 1.5 K, respectively. Both plan-view and cross-sectional transmission electron microscopy revealed that the orientation relationships between the epitaxial films and the substrate are [001]YBCO//[001]MgO and (110)YBCO//(200)MgO. Twins, which may be perceived as domains that are rotated 90° along the c axis of the thin films with respect to the substrate, were found to be copiously present. The influences of the configuration of the oriented growth of overlayer thin films on the superconducting properties are addressed. The advantages of the chemical spray pyrolysis in producing superconducting thin films are outlined.
Deposition of high-quality a-Si:H by direct photodecomposition of Si2H6 using vacuum ultraviolet light
Authors: Fuyuki Takashi , Du Kai-Ying , Okamoto Shingo , Yasuda Sadayuki , Kimoto Tsunenobu , Yoshimoto Masahiro , Matsunami Hiroyuki
Published: July 2002

a-Si:H films were deposited by direct photochemical vapor deposition using vacuum ultraviolet lights emitted from deuterium (161 nm) and Xe (147 nm) discharge lamps. A source gas of Si2H6 was effectively decomposed, and a high deposition rate of 7.5 nm/min could be achieved in the case of the Xe lamp. The films had excellent electrical and photoelectric properties similar to ordinary films deposited by glow discharge, and showed very little degradation of photoconductivity under illumination.
Phase composition of sputtered Fe-SiO2 films (abstract)
Authors: Holtz R. L. , Edelstein A. S. , Lubitz P. , Volkening F. A. , Koon N. C. , Gossett C. R.
Published: July 2002

We report on some aspects of a wide-ranging study of the phase separation and properties of sputtered Fe-SiO2 films with Fe volume fractions of 5%–70%. Results of saturation magnetization, electron microscopy and diffraction, Mössbauer effect, and Rutherford backscattering measurements will be presented. We have identified four phases in our films: SiO2, α-Fe, a phase believed to be Si-stabilized amorphous Fe, and a few percent of an Fe compound. For Fe volume fractions below 40%, nearly all of the Fe is present as 10–40 Å particles of the amorphous phase. With increasing Fe content, the volume fraction of α-Fe increases, the fraction of amorphous phase decreases, and the particle sizes increase. Above 50%, α-Fe is the predominant phase. We believe that the relative amounts of crystalline and amorphous iron are related to the occurrence of excess silicon in the films that may arise under some sputtering conditions.
Ion energy analysis for sputtering-type electron-cyclotron-resonance microwave plasma
Authors: Matsuoka Morito , Ono Ken'ichi
Published: July 2002

This paper discusses discharge characteristics and ion energy analysis for sputtering-type electron-cyclotron-resonance microwave plasma. Sputtering discharge characteristics directly depend on the microparameters of the microwave plasma. Ionization efficiency of sputtered particles depends on the distance between resonance area and substrate, and ranges from 5% to 10%. The energy profile of ions extracted from the plasma broadens as the sputtering power increases. The application of a mirror field outside the resonance area suppresses the broadening in the energy profile of sputtered ions, and also suppresses the mean energy of the sputtered ion. Finally, the details of ion transport from the plasma to the substrate surface are discussed.
I
n s
i
t
u electron spectroscopy study of Si surfaces after Ar-ion-assisted Cl2 etching
Authors: Aoto Nahomi , Ikawa Eiji , Kurogi Yukinori
Published: July 2002

Si surfaces after Ar-ion-assisted Cl2 etching are studied with in situ observation methods. Low-energy electron energy loss spectroscopy (LEELS), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and reflection high-energy electron diffraction are employed for the analysis. Different primary electron energies are used on LEELS measurements to vary the probing depth from approximately 2 to 7 Å. Etched surfaces show two conspicuous LEELS peaks that present different depth profiles. One of these peaks is related to SiCl3-type surface reaction products detected with XPS, while the other peak is related to SiCl-type surface reaction products. The SiCl3-type reaction products exist at more superficial regions than those of the SiCl type. An amorphous reaction-product layer is formed through ion mixing on Cl-adsorbed Si surfaces by simultaneous supply of Cl2 molecules and an Ar-ion beam. The results of this study provide new information for the understanding of the Si dry-etching mechanism.