bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic phase diagram and spin-glass behavior of Co1−xMnxCl2 ⋅ 2H2O (abstract)
Authors: DeFotis G. C. , Mantus D. S.
Published: July 2002

Magnetization and susceptibility measurements have been made on the title system in order to determine the phase diagram (T vs x plane) and to investigate hysteretic and time-dependent effects. The pure constituents are rather isotropic (Mn) and rather anisotropic (Co) isomorphous antiferromagnets which order at 6.7 and 17.2 K, respectively. The ordered spin arrangements are of different periodicity, and competing ferromagnetic and antiferromagnetic interactions can be anticipated in mixtures. Anomalies in susceptibility versus temperature reveal the presence of paramagnetic- (antiferromagnetic) phase boundaries. The transition temperatures lie on curves Tc(x) which descend fairly sharply from the two sides of the phase diagram; i.e., the pure component ordering temperatures are not connected by a continuous phase boundary. In all mixtures lower transitions are observed as well. Below these transitions more significant hysteresis in magnetization versus field is observed than above them, and in certain mixtures pronounced time dependences also. The thermoremanent magnetization and the isothermal remanent magnetization as a function of field in a 54%-Co/46%-Mn sample exhibit maxima, and have a general appearance typical of spin glasses. The time dependence, followed long enough, appears to be neither logarithmic nor algebraic in form, but rather more nearly that of a ‘‘stretched’’ exponential.
Nature of the reentrant spin-glass-like state in Ni-Mn
Authors: Abdul-Razzaq W. , Kouvel J. S.
Published: July 2002

The reentrant state of the disordered alloy Ni77Mn23 below ≊60 K was studied by magnetization (M) measurements for various fields (Hcool) applied during cooling to 4.2 K. The locus of time-independent M(Hcool) points indicates that the state at equilibrium is characterized by a spontaneous ferromagnetic moment. The spin glassiness of the state is evidenced by displaced hysteresis loops measured for nonzero Hcool. From the loops for Hcool≥2000 Oe, the sample appears to act essentially as a single domain with a net M and a undirectional anisotropy oriented along Hcool. For lower Hcool (especially zero), the loops suggest that the sample is subdivided into similar but smaller domains with different anisotropy directions. This simple domain picture is model-tested against our data and its detailed validity is shown to require some additional considerations.
Spin-glass and double-transition behavior in Gd-La glasses
Authors: O’Shea M. J. , Sellmyer D. J.
Published: July 2002

We report studies of high-field magnetization, field-cooled magnetization, thermoremanent magnetization, and isothermal remanent magnetization as a function of temperature in the metallic glass sytem GdxLa72−xG28 where G28=Ga18B10 for the compositions x=72, 68, 64. The first two compositions show double-transition behavior and the last one shows only a paramagnetic to spin-glass transition. The approach to saturation at intermediate fields (up to 40 kOe) is of the form 1/H1/2 as predicted by a mean field model which incorporates a small random anisotropy. The field-cooled magnetization in these samples is independent of time and is reversible, suggesting it is the equilibrium magnetization. This field-cooled magnetization in the double transition samples (and spin-glass sample) goes smoothly to zero with applied field, indicating the absence of an equilibrium macroscopic moment in zero applied field. The thermoremanence shows a maximum which becomes progressively more pronounced as x decreases.
Ferrimagnetic Heisenberg chain; influence of a random exchange interaction
Authors: Drillon M. , Coronado E. , Beltran D. , Georges R.
Published: July 2002

We report on the magnetic behavior of ‘‘rigid’’ ferrimagnetic chains isolated in bimetallic complexes of the EDTA and ‘‘flexible’’ ones obtained in the amorphous variety. As shown by LAXS, the only noteworthy difference in the amorphous state is the random distribution of bond angles between nearest neighbors within chains. The ‘‘rigid’’ bimetallic chains in CoNi(EDTA)6H2O are described in terms of Heisenberg model with an exchange coupling J=−7.5 K. The behavior of the amorphous variety somewhat differs, following the law X=AT−0.8 typical of REHAC. A classical spin chain model involving a J distribution and alternating g factors allows to explain successfully the temperature dependence of the susceptibility.
Analysis of high temperature susceptibility using a generalization of the Curie–Weiss law
Authors: Arrott A. S.
Published: July 2002

The Curie–Weiss Law is generalized to take into account differences among lattices, spin values, and range of exchange interactions. Several forms of the generalization are given for the purpose of facilitating the abstraction of magnetic moments from susceptibility data. A parameter γp is introduced that describes exactly the behavior in the high temperature limit and correlates well with the behavior nearer to the critical temperature.
Ground state of the 1-dimensional antiferromagnetic Heisenberg model (abstract)
Authors: Borysowicz J. , Kaplan T. A. , Horsch P.
Published: July 2002

We have calculated the 2-point correlation functions ωil(N)=(4/3)〈Si ⋅ Si+l〉 and their averages over i, ωl(N), in the ground state of the 1-dimensional antiferromagnetic Heisenberg model for N=4(2)16 spins. Both periodic (rings) and free-ends (chains) boundary conditions are considered. Surprisingly tight lower and upper bounds have been obtained for ωl(∞) under reasonable assumptions. In addition to showing the rather strong even-l-odd-l alternation in ‖ωl(N)‖, already known, our bounds indicate a smooth behavior in l‖ωl(∞)‖ for l odd and for l even, with, surprisingly, a broad maximum attained within the odd-l values at l≂6 to 8. The bounds obtained from the chain results were essential to seeing this maximum (because the l-values available for given N are larger than for rings). The quantity l‖ωl(N)‖ for chains with fixed N also shows such a maximum, and in addition shows a similar maximum for even l’s. If the trends for large l and N which we have found continue in ωl(∞) and in SN, the structure factor at wave vector π, then finite-size contributions to ωl(N) will have to contribute to the (seemingly) logarithmic divergence of SN as N→∞. We are not aware of any models where a similarly weak divergence shows such a finite-size contribution. Earlier results, including ‖ωl(∞)‖≊A/l for l→∞, gave no hint of the decrease in l‖ωl(∞)‖ described above. Recently ‘‘logarithmic corrections’’ have been mentioned, wherein ‖ωl(∞)‖≊(A/l) (ln l+B)−1. This might be related to the decrease in l‖ωl(∞)‖ which we found. If finite-size corrections are neglected, then this 1/l ln l behavior would predict SN≊ln ln N for N→∞, as opposed to the trend SN∼ln N that we found; continuation of the latter trend would then have to be due entirely to the finite-size contributions. Some insight into various surprising aspects of ωil(N) is gained by considering a single-band model of noninteracting electrons, which is a special case of the Hubbard model, as is the Heisenberg model.
Renormalization theory for spin glasses based on eigenstates of the J matrix (invited)
Authors: Hertz J. A.
Published: July 2002

We propose a renormalization scheme for spin glasses based on localized clusters associated with the eigenstates of the exchange matrix. These clusters are chosen as the block spins of the renormalization procedure and their interactions estimated. The interaction matrix of this new spin glass problem is then diagonalized to find clusters of clusters, and so on. The simplest estimate of the interactions predicts a phase transition for d>2. The successive levels of slow modes or clusters provide a direct description of the relevant metastable states and spin dynamics on a hierarchy of time scales.
Low-field susceptibility of GdAl spin glass: Cooling-rate dependence and field dependence of peak temperature
Authors: Matsui M. , Malozemoff A. P. , Gambino R. J. , Krusin-Elbaum L.
Published: July 2002

We use SQUID magnetometry to extend dc susceptibility measurements on GdAl spin glasses to 10 mOe, two orders of magnitude lower than previously reported. We confirm that if the temperature is lowered too quickly, a nonequilibrium susceptibility may be observed, but for sufficiently slow cooling, an equilibrium, erogodic susceptibility may be determined down to a few degrees below the susceptibility peak. The field dependence of this peak is incompatible with a T=0 phase transition model but supports a finite temperature-phase transition.
Random anisotropy and phase diagram of spin glasses
Authors: Fert A. , de Courtenay N. , Campbell I. A.
Published: July 2002

Torque measurements on CuMn, CuMnAu, and AuFe alloys confirm the phase diagram predicted by Kotliar and Sompolinsky for Heisenberg spin glasses with random anisotropy in the presence of an applied field. At low fields the transition is Ising-like. High enough fields restore the behavior expected for Heisenberg glasses without random anisotropy.
Magnetic properties of the FeAl1−xCux system
Authors: Saleh A. S. , Mankikar R. M. , Yoon S. , Okpalugo D. E. , Booth J. G.
Published: July 2002

The substitution of a 3d transition metal (T) for Al in the equiatomic intermetallic compound FeAl results in the onset of ferromagnetism beyond a certain critical concentration of (T). The system appears magnetically and structurally similar to the equivalent Co(GaT) alloys for which the critical concentration appeared to be related to an average electron concentration parameter. The present paper discusses Cu substitution in FeAl, i.e., the series FeAl1−xCux. It was found using x-ray and neutron diffraction techniques that the alloys remain single phase up to x=0.35 and that the crystallographic order remains B2 throughout. The site occupancy has also been determined and compared with the predictions of theoretical models. Ferromagnetism is observed to occur in the alloys with x>0.2. For these ferromagnetic alloys the inverse susceptibility against temperature curves (for T>TC) all have the same slope independent of composition suggesting an interpretation in terms of an itinerant model. This interpretation is also supported by a Rhodes–Wohlfarth plot. A region of superparamagnetism presages the onset of ferromagnetism and from this the size of the magnetic clusters is estimated to be 20–25 Å in radius.
Magnetic and Mössbauer investigation of REFe4B (RE=Er, Tm, Lu) compounds (abstract)
Authors: Vaishnava P. P. , Kimball C. W. , Umarji A. M. , Malik S. K. , Shenoy G. K.
Published: July 2002

Magnetic and Mössbauer studies have been carried out on a series of ternary borides REFe4B(RE=Er, Tm, Lu) crystallizing in hexagonal CeCo4B-type structure1. These compounds are found to be magnetically ordered at room temperature. Magnetization studies in the temperature range 5–300 K reveal the presence of compensation temperatures in Er and Tm compounds indicative of antiferromagnetic coupling between the rare-earth and Fe moments. Room-temperature 57Fe Mössbauer studies yield values of hyperfine fields of 246, and 185 kOe in LuFe4B. The 166Er Mössbauer studies give an almost free ion hyperfine field at the Er site, indicating that exchange interaction in ErFe4B is much stronger than the crystal field effects.
Numerical results for the random field Ising model (invited)
Authors: Pytte E. , Fernandez J. F.
Published: July 2002

We have performed numerical calculations for the random field (H) ferromagnetic Ising model in two dimensions. To study equilibrium properties, we have used the transfer matrix technique, thus bypassing serious equilibration problems which would arise in a Monte Carlo calculation for random systems. We have calculated the structure factor S vs H. Our results are consistent with S∼exp(c/H2) as predicted by theories which yield a lower critical dimension dc=2, whereas the expected behavior for dc=3, S∼H−4, is inconsistent with our results. To study dynamic properties we have used Monte Carlo simulations to determine the equilibration of Ising systems in random fields at low temperatures T following a quench from high T. The rate at which domains grow with time is determined as a function of the random field strength H, the linear dimension of the system L and temperature T. Domains are found to grow logarithmically with time. For small systems, L≤L*=(4J/H)2, the exponents a and b of the exponential equilibration time τ∼exp[(H/T)aLb] are found to be a≂1.0 and b≂0.5, in agreement with recent calculations based on approximate interface models. We tested the L and H/T dependence of τ in 3D and found a≂1.0, b≂0.5 also in 3D.
Thermal renormalization of the order wave vector in Heisenberg helimagnets
Authors: Rastelli E. , Tassi A.
Published: July 2002

In spite of a great deal of experimental and theoretical work on the helimagnetism, the actual possibility of evaluating the temperature dependence of the helical-order wave vector arising from the magnon-magnon interaction is quite unsatisfactory, in particular for Heisenberg helimagnets. For Heisenberg ferromagnets with planar anisotropy and for XY helimagnets, the self-consistent harmonic approximation (SCHA) of Villain provides an efficient tool which reduces to the well-known self-consistent renormalized (SCR) spin-wave approach in the ferromagnetic case when no anisotropy is present. If we try to extend the SCHA to Heisenberg helimagnets, we face a serious shortcoming: for zero anisotropy the Goldstone theorem is violated at the helix wave vector and zero-point motion contributions are certainly overestimated. This failure arises because the SCHA takes into account the four-operator potential but neglects at all the three-operator potential that has been recently proved to give contributions of the same weight in 1/S. So we have modified the SCHA in order to bypass the above shortcoming and we fit this approach on NiBr2: elastic and inelastic neutron scattering data meet our theory in a satisfactory semiquantitative way but some qualitative features, as, for instance, the observed first-order helix-antiferromagnet phase transition, claim further theoretical effort.
The magnetic field dependence of the specific heat of CeAl3 (abstract)
Authors: Edelstein A. S. , Brodale G. E. , Fisher R. A. , Lisse Carey M. , Phillips Norman E.
Published: July 2002

Specific heat measurements have been performed on four polycrystalline samples of CeAl3 in the temperature range 0.32≤T≤20 K and in magnetic fields H up to 8 T. Though the samples were contaminated by 4–15% of CeAl2 and/or Ce3Al11, the specific heat of CeAl3 is so much larger than that of the other compounds below 1 K that their contribution to the specific heat can be neglected. Normalizing our data by the amount of CeAl3 that we estimated to be present, the specific heats for all four samples are in good qualitative agreement with one another for all T<1 K and for all the magnetic fields investigated. In this temperature range the specific heat C decreases approximately linearly with increasing H for H<8 T. It should be noted that Bredl et al. observed a more complex magnetic field dependence in their investigation of the specific heat of CeAl3. The slope of the decrease in C we observed with increasing H in the purest sample is approximately independent of T. In addition the ratio C/T is temperature dependent at low temperatures. All of these properties of the Kondo compound CeAl3 are different from what one would expect on the basis of a simple resonant level model (RLM). For example, RLM predicts that C should decrease with increasing H, but instead of a linear decrease it predicts that C should decrease as H2. A model, which incorporates crystal field effects as well as the Kondo effect, predicts the observed approximately linear magnetic field dependence of the specific heat and also the observed magnetization. In the model the component of the magnetization perpendicular to the c axis is computed by ignoring the Kondo effect and using only the effect of the crystal field splittings. The component of the magnetization parallel to the c axis is computed using RLM to treat the ground state J=±3/2 doublet but also includes contributions from the excited state J=±1/2, ±5/2 doublets which become important at higher fields. The magnetization is found by performing the appropriate average over angles that is required for polycrystalline samples. This magnetization is then used in a thermodynamic relationship for the magnetic field dependence of the specific heat. The generalized form of the RLM predicts the correct magnitude of the decrease in C in an applied field of 8 T.
Self-consistent band calculations for an Anderson Hamiltonian treatment of anisotropic f-electron systems
Authors: Wills J. M. , Cooper B. R. , Thayamballi P.
Published: July 2002

The unusual magnetic ordering, magnetic excitation behavior, and anomalous crystal-field splitting in CeBi and CeSb can be explained using a model Hamiltonian obtained by applying the Schrieffer–Wolff transformation to the Anderson Hamiltonian. It is highly desirable to obtain a first principles prediction of the parameters of the theory in order to extend this understanding quantitatively to other cerium and light actinide materials. To this end, we have calculated the electronic structure of CeBi and CeSb with the linear muffin-tin orbital (LMTO) method, using a self-consistent fully warped potential, and have obtained the coupling between non-f band states and f states localized in the sense of the Anderson Hamiltonian. This is applied to a calculation of the anomalous crystal-field splitting in CeBi and CeSb, and application to calculating the anisotropic two-ion interaction is discussed. We find that the dominant contribution to the anomalous crystal-field effect (about two thirds) comes from hybridization with d bands.
Concentration and temperature dependence of the Hall resistivity in FeZr glasses
Authors: Cochrane R. W. , Trudeau M. , Strom-Olsen J. O.
Published: July 2002

Hall resistivity measurements are reported for amorphous FexZr1−x alloys near the critical concentration, xc =0.37, for the onset of ferromagnetism. At room temperature, the Hall coefficient RH is positive and grows systematically with Fe concentration as xc is approached from the paramagnetic side. The temperature dependence of RH follows a Curie-like variation whose coefficient diverges at xc. In the ferromagnetic regime, the spontaneous Hall coefficient is extremely large, leading to the conclusion that the side-jump mechanism is responsible for the magnetic contribution. Furthermore, the dependence of RH on susceptibility in the two regimes suggests that this same side-jump term is also responsible for the positive Hall coefficient in the nonmagnetic glasses.
Ferrons versus bound magnetic polarons in the antiferromagnetic semiconductors (abstract)
Authors: Mauger A. , Mills D. L.
Published: July 2002

In antiferromagnetic semiconductors, an excess electron may self-localize by inducing a ferromagnetic moment in its near vicinity via the s-f exchange interaction, thus creating a potential well. The resulting entity is the ‘‘ferron,’’ or self-trapped magnetic polaron. This has been the topic of numerous theoretical papers since Vitins and Wachter proposed that large ferrons were responsible for ferromagnetic cluster found in EuTe. We investigate this possibility in the present paper. We find that ferrons of large radius, where the electron spin density within a single unit cell fails to fully saturate the ferromagentic moment of the cell, cannot exist in three dimensions. For strong s-f coupling and small ferron radii, its core saturates and ferrons can exist in principle in three dimensions, but our variational calculation yields no self-trapped state for experimental parameters appropriate to EuTe. However, electrons localized on donors induce a ferromagnetic moment within their sphere of influence (the bound magnetic polaron). We calculate this moment, and conclude its accounts quantitatively for the experimental magnetization data on EuTe. We conclude that the magnetic properties of n-type EuTe are thus dominated by bound magnetic polarons, rather than ferrons, and the latter are of potential importance only in quasi-one-dimensional antiferromagnets.
Transport and magnetic measurements on UPt3
Authors: Jaccard D. , Flouquet J. , Lejay P. , Tholence J. L.
Published: July 2002

Experiments on the normal phase of UPt3 show a large positive magnetoresistivity, almost temperature-independent, linear in field, and a positive thermoelectric power which is not linear in temperature as T→0. The superconducting phase is characterized by a high thermal conductivity with a strong T2 term, by a coherence length smaller than the mean free path, and by lower and upper critical fields H(0)c1∼60 Oe and Hc2(0)∼26 kOe.
Low temperature resistivity of Ce-La-Th under pressure
Authors: Lawrence J. M. , Thompson J. D. , Fisk Z. , Batlogg B.
Published: July 2002

The low temperature resistivity of Ce0.9−xLaxTh0.1 alloys is known to vary as ρ0+αT2. We have investigated the variation of ρ0 and α with pressure for several concentrations x. An unusually strong nonlinear decrease of the residual resistivity with pressure occurs; the magnitude of the decrease is an order-of-magnitude larger than in the isostructural nonmagnetic alloy La0.8Th0.2. The temperature coefficient α(P) also decreases strongly. These results are in qualitative accord with recent theories of the resistivity of disordered valence fluctuation compounds.
Conductivity and magnetic properties of TmSe and TmS: Comparison to the dilute cases
Authors: Holtzberg F. , Flouquet J. , Haen P. , Lapierre F. , Lassailly Y. , Vettier C.
Published: July 2002

Magnetization, neutron diffraction, and resistivity measurements performed on the compounds TmSe and TmS are compared to those on the dilute alloys (Tm,Y)Se and (Tm,Y)S. In the paramagnetic regime, major differences exist between a regular array of Tm ions (TmSe and TmS) and the dilute systems. Localization (TmSe) or magnetic correlations (TmS) appear clearly in the conductivity behavior or in the dependence of the static susceptibility. A low content of Y atoms in TmSe has a drastic effect on the conductivity and on the magnetic order. We will discuss the connection between the degeneracy of the ground state with the opening of a gap.
Electronic configuration of cerium in amorphous alloys (invited; abstract)
Authors: Durand J. , Malterre D. , Marchal G. , Krill G. , Ravet M. F. , Kappler J.-P.
Published: July 2002

We have investigated the effect of structural disorder on the valence of cerium in different families of amorphous alloys prepared by coevaporation on to cryogenic substrates. The Ce electronic configuration was characterized by LIII x-ray absorption spectroscopy and bulk magnetization measurements. Special attention was paid to the amorphous analogs of prototypic Kondo and strongly mixed valent compounds in the crystalline state, such as Ce Si2 (TK≂200 K), CemNin, CemCon. The cerium was found to be purely trivalent in amorphous CexSi1−x (0≤x≤0.75) alloys over both the metallic and nonmetallic concentration ranges, so that the weakly mixed valent state in crystalline CeSi2 is believed to rely on details of the crystalline symmetry and band structure. In contrast, the cerium was found to remain mixed valent in amorphous CexCo1−x (0.15≤x≤0.75) and CexNi1−x (0.30≤x≤0.60) alloys, without any significant effect of the structural disorder. The concentration dependence of the Ce valence anomaly was found to be different in the Ce Ni and Ce Co alloys. This different behavior is discussed in terms of electronic band structure.
Green’s function solution of the Kondo problem and universality of the thermodynamic properties (invited)
Authors: Arai Tadashi
Published: July 2002

Using a functional derivative approach, we derive, for the nondegenerate Anderson model of dilute magnetic alloys, a Green’s function, which is valid at all temperatures and which accurately exhibits the Kondo effect. This is made possible by explicitly satisfying the Baym criterion for the macroscopic conservation of particle-number, momentum and energy—a criterion not satisfied by any of the earlier Green’s function treatments of the Kondo model or the Anderson model. The free energy of the system is calculated and the universality of all the thermodynamic properties including resistivity is analytically demonstrated. The temperature-dependent susceptibility χ(T) and specific heat C(T) thus calculated are found to be almost indistinguishable from the results of the renormalization group theory.
Paramagnetic neutron scattering from Ni (invited)
Authors: Böni P. , Shirane G.
Published: July 2002

New polarized beam measurements have been carried out in the paramagnetic phase of 60Ni in order to enlarge the (q,ω) range previously studied by Steinsvoll et al. Magnetic scattering has been detected up to halfway to the zone boundary. The results can be successfully interpreted in terms of a diffusive-type scattering function over an unexpected wide (q,ω) range q<0.5 Å−1 and ω<80 meV. The neutron data are also compared with the predictions of the very recent band model by Callaway. Finally, we point out important similarities and differences in the paramagnetic scattering from localized systems, such as EuO, and itinerant systems and discuss the universality of the paramagnetic scattering function.
Self-consistent electronic structure of disordered Fe0.65Ni0.35
Authors: Johnson D. D. , Pinski F. J. , Stocks G. M.
Published: July 2002

We present the results of the first ab initio calculation of the electronic structure of the disordered alloy Fe0.65Ni0.35. The calculation is based on the multiple-scattering coherent-potential approach (KKR-CPA) and is fully self-consistent and spin polarized. Magnetic effects are included within local-spin-density functional theory using the exchange-correlation function of Vosko–Wilk–Nusair. The most striking feature of the calculation is that electrons of different spins experience different degrees of disorder. The minority spin electrons see a very large disorder, whereas the majority spin electrons see little disorder. Consequently, the minority spin density of states is smooth compared to the very structured majority spin density of states. This difference is due to a subtle balance between exchange splitting and charge neutrality.
Interpretation of temperature variation of exchange splitting of Fe and Ni
Authors: Stearns Mary Beth
Published: July 2002

In recent years, several angle-resolved and spin-polarized photoemission experiments on Fe and Ni have concentrated on measuring the exchange splitting as a function of temperature with special emphasis on the behavior near and above TC. As is well determined, a considerable fraction of the moment of both Fe and Ni is of local character. For temperatures not too far above TC, the photoemission time (∼ℏ/Γ∼4×10−15 s) is much shorter than the spin flip time of the local moments (∼ℏ/kTC∼2×10−14 s) and much longer than the itinerant d electron hopping time (∼1/ωp∼10−16 s). Thus in this region relaxation effects are not important, so that the photoemission spectra can be simply interpreted in terms of the behavior of the localized and itinerant contributions to the total spin moment. Since the intraband exchange energy is ∼1 eV per spin, the exchange splitting due to the local part of the moment μl remains constant over the temperature range that can be studied. In contrast, the splitting due to the itinerant part of the moment μi is due to an average over several local spins and therefore varies as the net magnetization. Thus the exchange splitting Δ(T), as seen in photoemission studies, varies as Δ(T)=Δ(0)[μl+μi{Ms(T) /Ms(0)]}/μs. Of all the analyses in the literature the two component, equal integrated intensity analysis is contended to be most correct. It gives results which are in agreement with the fraction of local moment obtained from dHvA measurements and band structure calculations, i.e., ∼85% for Fe and ∼60% for Ni. The two other types of analysis, which appear in the literature, are discussed.
Electron-beam-induced current determination of minority-carrier diffusion length and surface recombination velocity in mercury-cadmium-telluride
Authors: Artz B. E.
Published: July 2002

A method is presented for determining the minority-carrier diffusion length and surface recombination velocity in passivated, shallow junction semiconductor devices. The method is particularly useful with devices where the minority-carrier diffusion length is comparable to the diameter of the electron beam interaction volume. A gaussian beam profile is convoluted with a theoretical model for electron-beam-induced current and the results used to determine the minority-carrier diffusion length from measured data. The surface recombination velocity is estimated from the dependence of the measured minority-carrier diffusion length on the electron beam accelerating voltage. The technique is applied to a photovoltaic infrared sensor device made in mercury-cadmium-telluride.
Model for a thin-film silicon-on-sapphire bipolar junction transistor
Authors: Benumof Reuben
Published: July 2002

A silicon-on-sapphire lateral thin-film bipolar junction transistor is unique in that recombination on the interface between the overlying silicon dioxide layer and the silicon semiconductor underneath must be taken into account. A simplified model of recombination is developed and then applied to determine the recombination currents in the bulk of the base of a bipolar junction transistor and in adjacent space-charge regions. The expressions for these currents are used to modify the conventional Gummel–Poon model to include recombination on the top surface of a lateral bipolar junction transistor. In the modified form essential constants retain their original meanings.
High-resolution electron-microscopy studies on laser-annealed unsupported amorphous germanium films
Authors: Cesari C. , Nihoul G. , Marfaing J. , Marine W. , Mutaftschiev B.
Published: July 2002

The first results on high-resolution electron-microscope observations of unsupported amorphous germanium films, crystallized in situ by pulsed laser irradiation, are presented. They provide new information on structure and perfection of the as-grown crystals and on the morphology of the crystal-amorphous interface. It is shown that, after crystallization, amorphous regions can exist as inclusions among dendrites. The structure of the crystal-amorphous interface depends on its crystallographic orientation and is probably related to the degree of relaxation of the amorphous phase in its immediate vicinity.
Laser scan registration for lateral epitaxy of silicon-on-insulator stripes on silicon substrates
Authors: Zorabedian P. , Kamins T. I. , Drowley C. I.
Published: July 2002

An improved technique for seeded laser recrystallization of silicon-on-insulator stripes has been developed using a slanted elliptical beam and a computer-controlled system to register laser scans to alignment marks on the silicon wafer. After the wafer position is automatically determined by searching for alignment marks with a low-power beam, a raster is generated parallel to the device features, and the aligned laser beam is swept across the wafer. The dependence of the defect structure of the recrystallized films on the parameters used for scanning and the resulting thermal gradients are described. With the proper choice of parameters, defect-free, single-crystal silicon films over oxide stripes up to 65 μm wide have been obtained.
Performance of laser dye solutions under high signal fluxes: An analysis of signal propagation and excited-state energy extraction in mobile and rigid media
Authors: Hammond Peter R.
Published: July 2002

As a continuous-wave signal builds up in an energized laser dye solution, the lifetimes for the excited state of the molecules become shorter than their orientational relaxation time. Physical consequences of the phenomomenon are considered for two extreme situations—transmission through pure mobile and pure rigid media continua, respectively. The dye is treated as a linear oscillator and spectral properties are assumed to be unchanged between the media. Two problems are examined, namely signal propagation and the extraction of energy at a point in the medium for a number of configurations of pump and signal polarizations, transverse or longitudinal excitations. Signal gradients and steady-state conversion efficiencies are presented algebraically and graphically. A mobile medium has one of the steepest gradients, the largest energy storage, and one of the highest conversion efficiencies. Nevertheless, performance of a transversely excited, single-pass amplifier for the commonly used configuration where pump and signal are plane polarized and have a shared polarization axis (Configuration C) shows little difference between rigid or mobile media, according to this analysis. For a rigid Configuration C, only about 21% of the dye molecules carry most of the signal load, in contrast with a mobile medium where all molecules work equally, and such a restricted distribution undergoes rapid turnover of its excited state. Twisting of the signal plane of polarization in a dye amplifier is confirmed.
Electrical characterization of plasma-grown oxides on gallium arsenide
Authors: Hshieh F. I. , Bhat K. N. , Ghandhi S. K. , Borrego J. M.
Published: July 2002

Plasma-grown GaAs oxides and their interfaces have been characterized by measuring the electrical properties of metal-oxide-semiconductor capacitors and of Schottky junctions. The current transport mechanism in the oxide at high electrical field was found to be Frankel–Poole emission, with an electron trap center at 0.47 eV below the conduction band of the oxide. The interface-state density, evaluated from capacitance and conductance measurements, exhibits a U-shaped interface-state continuum extending over the entire band gap. Two discrete deep states with high concentration are superimposed on this continuum at 0.40 and 0.70 eV below the conduction band. The results obtained from measurements on Schottky junctions have excluded the possibility that these two deep states originate from plasma damage. Possible origins of these states are discussed in this paper.
Resistance stability of AuIn2 thin-film resistors for Pb-alloy Josephson integrated circuits
Authors: Hasumi Yuji , Arai Kunihiro , Waho Takao , Yanagawa Fumihiko
Published: July 2002

The influence of In diffusion on resistance stability of AuIn2 thin-film resistors was studied and the mechanism for resistance change was clarified. When resistors with In concentration below that of AuIn2 were in contact with Pb-In-Au alloy interconnection lines, In diffused from the Pb alloy into the resistors. This diffusion caused grain growth in the In-diffused zone, in addition to a phase change from an AuIn and AuIn2 mixture to AuIn2 single phase. The In-diffusion-induced grain growth decreased film resistivity because resistivity is mainly determined by grain-boundary scattering. When the resistor was preannealed before being connected to interconnection lines to saturate grain growth, excellent resistance stability was obtained even though In concentration shifted by ∼2 wt. % below AuIn2 stoichiometry.
Effects of fissures in the brain on electroencephalograms and magnetoencephalograms
Authors: Cuffin B. Neil
Published: July 2002

The electroencephalogram and magnetoencephalogram maps measured on the head can be used to estimate the location, orientation, and amplitude of electrical sources in the brain. It is known that differences in the electrical conductivities of the various tissues in the head can affect these maps and estimates, e.g., the low conductivity of the skull ‘‘smears’’ electroencephalogram maps and makes sources appear deeper in the head than they actually are. Since fissures in the brain are filled with cerebrospinal fluid, which is several times more conductive than the brain tissue in which the sources are located, and since fissures are close to many of the sources, they may have significant effects on the maps and estimates of source parameters. However, little or no information is available about these effects. This study uses a spherically-shaped computer model of the head which contains fissures to determine these effects. It is found that even a fissure as large as the interhemispheric fissure has a maximum effect on location estimates of 0.75 cm and a maximum effect on orientation estimates of 15°. The maximum effect of this fissure on amplitude estimates is 28% with the estimates being larger than the actual source for sources perpendicular to a fissure and smaller for sources parallel. In general, there are no significant differences in the effects of the fissures on estimates using electroencephalogram and magnetoencephalogram maps. The fissures cause a radial source in the spherically-shaped head model to produce only a small magnetic field with a map like that of a source perpendicular to the fissure; a radial source in a sphere with no fissures would produce no magnetic field. Since most fissures in the brain are smaller than the ones in this head model, it is concluded that actual fissures in the brain have little effect on electroencephalogram and magnetoencephalogram maps and source estimates using these maps.
Optical properties of cobalt-doped amorphous aluminum oxide
Authors: Niklasson G. A.
Published: July 2002

Co-Al2O3 composites were prepared by dual electron beam evaporation. When the volume fraction of cobalt is lower than 0.07, the metal is almost completely dispersed as ions in the amorphous oxide matrix. Due to the local ordering of amorphous aluminum oxide, absorption bands caused by crystal field effects are seen in the visible wavelength range. The features of the spectra are consistent with cobalt ions located in tetrahedrally coordinated sites in the oxide. Thus optical absorption measurements can be used to determine whether the metal is present as ions or as particles in various cermet materials.
X-ray lasing in a Na/Ne plasma environment
Authors: Cochran F. L. , Davis J. , Apruzese J. P.
Published: July 2002

An investigation has been conducted to determine the feasibility of generating conditions favorable to population inversion, gain, and x-ray lasing in a two-component plasma consisting of sodium and neon. An intense laser beam is assumed incident on both sides of a Na/Ne slab target separated by a carbon thermal buffer. Temperature and density profiles of the laser target interaction are calculated using a Lagrangian hydrodynamics model. Level populations and radiative emissions are evaluated using a collisional-radiative equilibrium model including opacity effects. It appears possible to achieve measurable gain at 82, 58 and 230 Å from the 3-2, 4-2, and 4-3 transitions of heliumlike neon, respectively. Additionally, by pulse tailoring and target design, it should be possible to enhance the Na pumping power. off
Electrical conductivity of deuterated ethanediammonium tetrachlorocuprate
Authors: Drumheller John E. , Hoiness S. F. , Tigges C. P. , Lindbeck Martha J.
Published: July 2002

Electrical conductivity measurements have been made on deuterated ethanediammonium tetrachlorocuprate, [ND3(CH2)2ND3]CuCl4, in the temperature range from 287 to 386 K. The decrease in conductivity gives further indication that the charge carriers in these ionic semiconductors are protons.
Donor-acceptor pair scattering in compensated semiconductors
Authors: Rimbey P. R. , Mahan G. D.
Published: July 2002

The drift and Hall mobilities have been calculated for the scattering of electrons from donor-acceptor pairs in a nondegenerate semiconductor. The separation between donor and acceptor has been correlated via a nearest-neighbor distribution function and the impurity potentials modeled as screened coulomb interactions. By utilizing Alfred’s [Phys. Status Solidi B 82, 467 (1977)] temperature-dependent dielectric function, the mobility in the high- and low-temperature regimes is obtained and compared with the dipole approximation of pair scattering in the Born approximation. The random pair approximation exceeds the dipole mobility by orders of magnitude for moderate dopant levels of, e.g., the order of 1016 cm−3, and temperatures greater than 30 °K, indicating that the dipole approximation may be inadequate for most applications of interest.
Mobility and carrier density of rapid isothermally annealed antimony implanted (100) and (111) silicon
Authors: Jones R. E. , Li B. Z. , Oleszek G. M.
Published: July 2002

Sheet resistance and Hall effect measurements were made on graphite strip isothermally annealed antimony implanted (100) and (111) silicon. Although the (111) silicon annealed at lower temperatures, the (100) silicon achieved a lower sheet resistance (∼40 Ω/⧠ for a 3.8×1015 cm−3 dose) due to a greater activated carrier surface density. Supersaturated solid solutions were observed for both surfaces. At high active carrier concentrations (≳1×1020 cm−3), the rapid decrease of mobility with increasing carrier concentration is attributed to ionized impurity scattering.
ac magnetic characteristics of cores made from pressed, annealed, and repressed rectangular steel particles
Authors: Krause R. F.
Published: July 2002

This paper describes a material and new method of processing that yields pressed compacts magnetically suitable for a variety of ac applications. Small rectangular plain-carbon steel particles with dimensions 2.0×0.51×0.15 mm are decarburized, individually insulated and uniaxially pressed using typical powder-metallurgical techniques. In this condition the 60-Hz losses are somewhat higher than conventional carbon steel sheet while at higher frequencies the losses are lower. This loss behavior is due to the large hysteresis-to-eddy current ratio,>9. The permeability of the compacts is poorer than that of carbon steel sheet. Attempts to reduce the core loss by lowering the hysteresis loss component through a series of stress-relief annealing experiments resulted in exceptionally high losses. These high losses were attributed to large circulating eddy currents caused by local particle-to-particle sintering. Subsequent repressing, either uniaxial or cold isostatic, resulted in a dramatic reduction in the eddy current loss component and a total core loss superior to that of conventional carbon steel sheet. The variations in magnetic performance are related to the sample density, initial core pressing pressure, the annealing parameters, and the repressing method and pressure.
Magnetic properties of a new hard magnet alloy (Fe40Co40Mn20)98.6−xCxSi1.4 (x∼0.4)
Authors: Myohga O. , Igarashi H. , Kubo Y.
Published: July 2002

A new hard magnet alloy, (Fe40Co40Mn20)98.6−xCxSi1.4(x∼ 0.4) was developed. The alloy permits heavy cold-working wherein optimum magnetic properties can be obtained by a suitable heat-treatment after the cold-working, that is, bHc=54.9–63.7 kA/m, Br=0.24–0.47 T, and (BH)max=5.6–11.2 kJ/m3. The alloy retains its high temperature fcc form (nonmagnetic phase) by a quenching, whereas a cold-working produces a small volume of ferromagnetic phase which is transformed in a martensitic style. Heat-treatment at about 400–600 °C causes a bcc phase precipitation, resulting in a fine lamella mixture of magnetic and nonmagnetic phases.
Electronic and magnetic structure of ultrathin cobalt-chromium multilayers
Authors: Herman F. , Lambin P. , Jepsen O.
Published: July 2002

In order to study exchange coupling and spin distributions at atomically abrupt ferromagnetic/antiferromagnetic interfaces, we construct lattice-matched Co/Cr multilayer models. Here we consider strained-layer superlattices composed of alternating regions of ferromagnetic bcc Co and antiferromagnetic bcc Cr with repeat periods ranging from four to eight atomic layers. For computational simplicity, Cr is represented by a theoretically stabilized commensurate antiferromagnetic spin arrangement. The multilayer spin distributions are determined by carrying out first-principles self-consistent spin-polarized LMTO/ASA electronic structure calculations. We find that the magnetic properties of the Co/Cr superlattices are dominated by the ferromagnetic Co layers, though the antiferromagnetic character of bcc Cr is still evident. For multilayers containing one Co layer and three to seven Cr layers per repeat period, there is only one stable spin arrangement corresponding to ferromagnetic coupling across the Co/Cr interfaces. For superlattices containing thicker Co regions, e.g., three Co layers and five Cr layers, there are two distinct spin arrangements corresponding to ferromagnetic as well as antiferromagnetic coupling across the Co/Cr interfaces. The implications of these results for more complicated Co/Cr multilayers are discussed.
Optical and electronic properties of the electron beam resist poly(butene-1-sulfone)
Authors: Williams M. W. , Young D. W. , Ashley J. C. , Arakawa E. T.
Published: July 2002

The optical properties of thin films of poly(butene-1-sulfone), PBS, an electron beam resist, are presented for the range of photon energies from 2.5 to 39.0 eV. The density of these films is found to be (1.39 ± 0.02) g cm−3. A sum-rule calculation is used to demonstrate the overall consistency of the data obtained. The optical data are used to calculate inelastic electron mean-free paths in PBS as a function of incident electron energy from 100 to 10 000 eV.
Charge control and geometric magnetoresistance of a gated AlGaAs/GaAs heterojunction transistor
Authors: Harrang J. P. , Higgins R. J. , Goodall R. K. , Wallis R. H. , Jay P. R. , Delescluse P.
Published: July 2002

We have measured a series of low-temperature transport parameters of AlGaAs/GaAs heterojunction transistors. The techniques used provide direct measurement of the two-dimensional electron gas on the same sample in which standard device characterization tools are applied. This creates an environment for devising and testing realistic device models. The apparent charge density is measured via both Hall and capacitance-voltage measurements and is compared with the two-dimensional electron gas charge measured via Shubnikov–de Haas conductivity oscillations. From this comparison we interpret the charge control of these gated heterojunction devices. Geometric magnetoresistance, magnetotransconductance, and Hall measurements of the mobility are presented and complications arising from the layered structure of the heterojunctions are discussed.
Drag force acting on a kink moving uniformly in an atmosphere of paraelastic tetrahedral interstitials in a body-centered-cubic metal
Authors: Ogurtani Tarik Ö. , Seeger Alfred K.
Published: July 2002

The drag force acting on a rigid kink moving uniformly along a general dislocation line and in an atmosphere of mobile tetrahedral (light) interstitials is investigated numerically for anisotropic body-centered-cubic metals. It is shown by extensive computer modeling that the drag force versus normalized kink velocity plot goes through a maximum composed of six subpeaks, one acoustic and five optic in character, composing three distinct bands. The acoustic branch, and the upper optical band composed of modes 6 and 5, are associated with the isotropic and the pure shear parts of the elastic dipole tensor of the tetrahedral interstitial species, respectively. An extremely accurate and concise analytical expression is deduced that reveals a Navier–Stokes-type fluid viscosity regime; it shows also that decoupling of Snoek and Cottrell atmospheres is a reliable approximation.
Influence of magnetic field on 1/ f  noise in GaAs Corbino disks
Authors: Song Myong-Ho , Min H. S.
Published: July 2002

The influence of magnetic field on 1/ f  noise in GaAs Corbino disks is investigated experimentally. It is clearly shown that the experimental results can be explained by the number fluctuation model but not by the mobility fluctuation model.