bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple shock reverberations in a layer structure observed by particle-velocity and pressure gauges
Authors: Kondo K. , Yasumoto Y. , Sugiura H. , Sawaoka A.
Published: February 2003

Multiple reverberations of shock waves in a layer structure have been observed by means of a particle-velocity gauge using electromagnetic induction and a manganin pressure gauge. Changes in the particle velocity observed are in good agreement with estimates from the published Hugoniot data centered on the normal state. The shock pressure measured indicates that there are significant differences from the usual estimate, above. Attenuation of shock pressure and the suppression of thermal pressure accompanying the shock reverberations are considered to explain the differences. The reverberation shock pressures calculated using the Mie-Grüneisen equation of state, which correspond to the recentered Hugoniot values for the previous state, are in good agreement with the observed ones.
Attraction and repulsion of solid particles by solidification fronts I. Thermodynamic effects
Authors: Omenyi S. N. , Neumann A. W. , van Oss C. J.
Published: February 2003

This paper presents and discusses particle behavior at solidification fronts from a thermodynamic point of view. Engulfing or rejection of particles embedded in a melt by solidification fronts depends on whether such quantities as the free energy of adhesion or of engulfing are positive or negative. As the relevant energy balances contain solid-liquid interfacial tensions which are difficult to determine, these studies may also be viewed as tests for the validity of such data and the underlying theories used to determine them. In this paper, solid-liquid interfacial tensions are derived from contact angle data and the equation of state approach for interfacial tensions [Neumann et al., J. Colloid Interface Sci. 49, 291 (1974)]. The thermodynamic predictions obtained in this way for approximately 60 systems agree very well with microscopic observations with particles in the range of 10–200 mm in diameter.
Stability and pinning points in substrate-confined liquids
Authors: McCaldin J. O. , Kuech T. F.
Published: February 2003

Confinement of liquid by concavities in a substrate surface is treated with reference to contemporary interest in growing semiconductor crystal on inert substrates. Instabilities that occur during or after filling of simple concavity shapes are considered, with particular attention to the influence of discontinuities of slope in the substrate.
Al diffusivity as a function of growth rate during the formation of (GaAl)As heterojunctions by liquid phase epitaxy
Authors: Small M. B. , Ghez R. , Reuter W. , Potemski R. M.
Published: February 2003

We have analyzed the heterojunctions formed on different parts of a wafer of GaAs which was exposed to a Ga-Al-As solution in the presence of a small temperature gradient. The effect of the temperature gradient was to cause growth over part of the wafer and dissolution over the remainder. Analysis of the profiles has demonstrated the diffusion coefficient of Al in the solid to be strongly dependent upon whether growth or dissolution is occuring. This result may explain an earlier discrepancy between measurements of the diffusion coefficient, which were made under different conditions. It also suggests reasons for the observed morphological instability during dissolution in such systems.
Interface states and electron spin resonance centers in thermally oxidized (111) and (100) silicon wafers
Authors: Poindexter Edward H. , Caplan Philip J. , Deal Bruce E. , Razouk Reda R.
Published: February 2003

Interface states and electron spin resonance centers have been observed and compared in thermally oxidized (111) and (100) silicon wafers subjected to various processing treatments. The ESR Pb signal, previously assigned to interface ⋅Si≡Si3 defects on (111) wafers, was found to have two components on (100): an ⋅Si≡Si3 center oriented in accord with (100) face structure, and an unidentified center consistent with ⋅Si≡Si2O. The quantitative proportionality of Pb spin concentration to midgap interface trap density Dit is maintained on (100), and both are lower by a factor of about 3 compared to (111). This correlation persists over the range of oxidation temperatures 800–1200°C, for both n- and p-doped silicon, cooled by fast pull in oxygen, and cooled or annealed in nitrogen or argon. The correlation is independent of doping level. In samples with different oxide thickness, neither Pb nor Dit varied significantly over the range 100–2000 A, but Pb was smaller at 50 A. In general, ESR is judged to offer promise for further studies of specific interface features.
Correlation of chemical and electrical properties of plasma-deposited tetramethylsilane films
Authors: Szeto R. , Hess D. W.
Published: February 2003

Thin films of tetramethylsilane (TMS) were formed using rf-glow-discharge polymerization. The films were found to be pinhole free, chemically resistant, and adherent to silicon, aluminum, and glass substrates. Electron microprobe analyses and IR Fourier transform spectroscopy (FTS) demonstrated that small concentrations of oxygen (2–6 at. %) were always incorporated into the polymer structure. Film density, refractive index, and dielectric constant were correlated with the chemical composition of the films. Capacitance-voltage studies of metal-polymer-silicon structures indicated that charge trapping and polarization instabilities existed in the films, and FTS suggests that these charge effects originated at SiO and C = 0 sites. The polymer films were found to be sensitive to moisture and to oxygen. Electron transport was enhanced in films which were exposed to water vapor.
Radiation detection with superconducting granular thin films
Authors: Fujimaki N. , Okabe Y. , Okamura S.
Published: February 2003

Superconducting granular thin films are considered to be an array of Josephson junctions and can be used as fast, sensitive detectors of microwave and submillimeter wave radiation. This paper describes the experimental results on detection of 10 GHz and HCN laser radiation with tin granular thin films. In order to investigate the relationship between the granular structure and the sensitivity, several kinds of tin granular thin films are made with changing background pressure and substrate temperature which is controlled by a Peltier refrigerator. Optical microscope photographs show that the evaporation at lower background pressure from 10−7 to 10−8 mm Hg makes the tin granules more separate (they are connected to one another by narrow bridges) and that the evaporation with lower substrate temperature makes tin granules smaller. The films having high responsivity are obtained under the condition that the background pressure is 10−4–10−5 mm Hg and the substrate temperature is lowered about 10 K from room temperature. The responsivity values obtained are 9×106 V/W at 10 GHz and 270 V/W at 891 GHz.
Ferroelectric-to-paraelectric phase transition of vinylidene fluoride-trifluoroethylene copolymer
Authors: Yamada Takeshi , Ueda Toshinobu , Kitayama Toyoki
Published: February 2003

The ferroelectric properties of vinylidene fluoride-trifluoroethylene copolymer were studied. The infrared absorption spectra and x-ray diffraction patterns of the melt-crystallized film suggested the similar crystalline form to the polar form I of polyvinylidene fluoride. It was found that the ferroelectric-to-paraelectric phase transition occurred at 70 °C and was the first order in the melt-crystallized copolymer film by studying the dielectric constant, piezoelectric constant, D-E hysteresis loop, and DSC measurement. The Curie constant was 2200 K. The phase transition was accompanied by the expansion of the crystal lattice.
Excited-state absorption in the pump region of alexandrite
Authors: Shand M. L. , Walling J. C. , Morris R. C.
Published: February 2003

Excited-state absorption in alexandrite has been measured from 420 to 680 nm by using pulsed flash lamp pumping and a dye laser probe. The excited-state absorption cross section is generally of the same order of magnitude as the ground-state absorption cross section (10−19 cm2) and therefore may represent a large loss of energy from the pump source in a laser system. The results were confirmed at two wavelengths with a cw experiment in which 568- or 590-nm radiation was used for pumping and probing.
Measurements of Raman intensities and pressure dependence of phonon frequencies in sapphire
Authors: Watson G. H. , Daniels W. B. , Wang C. S.
Published: February 2003

Absolute Raman cross sections and mode Gruneisen parameters of the Raman-active optical vibrational modes of sapphire (a = Al2O3) were measured. Intensity measurements show that magnitudes of the Raman tensor components agree very well with group theoretical expectations. Pressure dependence of the frequencies has been measured over a range from 1 to 10 kbars and mode Gruneisen parameters have been calculated.
Dependence of secondary-electron emission from amorphous materials on primary angle of incidence
Authors: Salehi M. , Flinn E. A.
Published: February 2003

A series of measurements on the secondary-electron emission properties of a range of amorphous materials have been carried out under very stringent experimental conditions for various angles of incidence, over a wide range of primary energies. For these amorphous materials the effects of varying the angle of incidence of the primary beam agree with the predictions of simple theory. The measurements indicate that the rate of energy loss of a primary electron within the solid is reasonably well described over a limited range of energies by a power law. The value of the power-law exponent is slightly higher than the value of 1.35 suggested by Young and appears to vary with the atomic number of the target material. The inelastic reflection coefficient for these amorphous materials increases slightly with increasing angle of incidence.
Measurement of the sound velocity difference in two liquids by using interdigital transducers
Authors: Toda Kohji
Published: February 2003

The theory and experimental results for a method of measuring the sound velocity difference in two liquids are described. The compressional wave is radiated into a liquid from an interdigital transducer. The substrate surface without the interdigital electrodes is not in contact with the liquid. The phase difference between two delayed signals passed through two liquid cavities, which is converted to a dc voltage via a phase comparating circuit, corresponds to the sound velocity difference. An experimental confirmation of the propriety of the values obtained by the method is given in water with different temperatures.
Subkilovolt x-ray radiation from an argon plasma
Authors: Perez J. D. , Chase L. F. , McDonald R. E. , Tannenwald L. , Watson B. A.
Published: February 2003

The x-ray spectrum between 55 and 600 eV from an argon plasma produced in the PITHON high-voltage generator has been measured using the Lockheed grating spectrograph. Below 100 eV, line shapes show a deep depression at line center. This is most likely due to Doppler shifts during implosion. Above 100 eV, broad continuous bands of radiation are observed. A simple calculational model shows that these are closely spaced, bound-bound transitions which reflect the time history of the plasma temperature.
Some fundamental properties of zirconiated W(100) field-emission cathode
Authors: Yamamoto S. , Hosoki S. , Kawase S. , Hirai Y.
Published: February 2003

Fundamental properties of zirconiated tungsten field-emission cathodes are examined in order to clarify their high current stability mechanism. High stability is found to be restricted to (100) faces, on which a Zr-O complex is formed, preventing adsorption of gases such as H2, CO, and CO2 at moderate temperatures (1200–1500 °C). As the Zr-O layer is immobile, current fluctuations induced by Zr-O migration are minimum. In order to maintain high stability, especially long-term stability, a well controlled oxygen supply is necessary.
Molecular beam epitaxial growth of uniform In0.53Ga0.47As on InP with a coaxial In-Ga oven
Authors: Cheng K. Y. , Cho A. Y. , Wagner W. R. , Bonner W. A.
Published: February 2003

Epitaxial layers of In0.53Ga0.47As lattice matched to InP substrates have been grown by molecular beam epitaxy. The (100) InP substrate surfaces were first oxide passivated and then thermally cleaned under 1.5×10−6 Torr of arsenic moleuclar beam exposure (i.e., 1.24×1014 As4/cm2 sec). When they were heated to 500 °C, damage-free surfaces without oxygen and carbon contamination were obtained. The surface chemical composition as a function of the thermal cleaning temperature was studied with Auger electron spectroscopy. In0.53Ga0.47As epilayers of highly uniform composition were grown over a 7-cm2 InP substrate using an In/Ga coaxial oven design. Reproducible In and Ga beam fluxes to obtain lattice-match condition were achieved by adjusting the aperture ratio of the In and Ga reservoirs, and the oven temperature. Net electron concentration as low as 3×1015 cm−3 has been achieved for the In0.53Ga0.47As layers.
Theoretical and experimental efficiency of the conversion of heat into mechanical energy using shape-memeory alloys
Authors: Mercier O. , Melton K. N.
Published: February 2003

The efficiency of the conversion of heat into mechanical energy of shape-memory alloys has been obtained from experimental data and compared with the theoretical efficiency. Using a specially constructed torsion apparatus, the work produced by both the one-way and two-way-memory effects was measured. The theoretical efficiency was computed from the heat capacity and the enthalpy of the martensitic transformation, obtained from the same alloys by calorimetry. For NiTi based alloys a theoretical efficiency of up to 13% was found compared with 1–6% from measurements, depending on how the work was computed. For CuZnAl based alloys a theoretical efficiency of 3.4% was found, compared with 0–3% from measurements. The lower measured efficiencies are explained in terms of a nonideal martensitic transformation associated with the shape-memory effect.
Limitations on the open-circuit voltage imposed by P+ and N+ regions in silicon solar cells
Authors: Shibib M. Ayman , Fossum Jerry G.
Published: February 2003

It is shown theoretically and experimentally that the emitter recombination current, which limits the open-circuit voltage of silicon solar cells, can be more easily suppressed in P+N cells than in N+P cells. This result is due to fundamental effects that occur in heavily doped silicon: degeneracy of the majority charge carriers, Auger recombination, and energy-band-gap narrowing. Cell designs to suppress the emitter current are discussed, and experimental data supporting our theoretical analysis are presented.
Silicon solar cells realized by laser induced diffusion of vacuum-deposited dopants
Authors: Fogarassy E. , Stuck R. , Grob J. J. , Siffert P.
Published: February 2003

A technique for solar cell preparation based on vacuum deposition of thin films of dopants on silicon, followed by irradiation with a high-energy (∼1.5 J/cm2) ruby laser pulse is described. Several dopants like phosphorus, antimony, bismuth, aluminium, gallium, and indium have been investigated. Electrical and Rutherford backscattering measurements indicate that the dopant is dissolved in the silicon and becomes electrically active, as a result of the irradiation. The P-N junctions which are formed are shallow (depth <4000 Å) but heavily doped, since after the laser treatment the solubility of the dopant is generally higher than after a thermal diffusion. Therefore good diode characteristics can be achieved by this simple method, and solar cells up to 14 % efficiency under AM1 (air mass 1) illumination have been realized using dopants like phosphorus, antimony, bismuth, aluminium, or gallium.
Edge dislocation trapping by a cylindrical inclusion near a traction-free surface
Authors: Stagni L. , Lizzio R.
Published: February 2003

The force on an edge dislocation located near a cylindrical inclusion and a traction-free surface is calculated within the framework of linear elasticity. It is shown that the glide equilibrium positions are very sensitive to the orientation a of the slip plane with respect to the surface; in particular, the trapping effectiveness is monotonically reduced by increasing a from 0 to 90°. It is also found that a trapping action is exterted mainly by inclusions more rigid than the matrix, whereas in the bulk it is exterted mainly by inclusions less rigid than the matrix. Possible physical implications of the obtained results are discussed.
Oxidation precipitates in silicon
Authors: Salisbury Iain G.
Published: February 2003

In a recent paper [J. Appl. Phys. 50, 7996 (1979)] Leroy discussed the kinetics of growth of oxidation stacking faults. It is here suggested that it is unlikely that a self-interstitial stacking fault on {111} in a diamond structure crystal would have the form proposed by Leroy, since it does not preserve even nearest-neighbor bonding. An alternative structure, which preserves both nearest- and next-nearest-neighbor relationships, is described. It is further suggested that, since self-interstitials in silicon and germanium are known to aggregate on the low-energy {113}, any model for oxidation precipitates on {111} which assumes a simple self-interstital growth mechanism is unlikely to be correct.
cw argon laser annealing of anodic oxide on GaAs
Authors: Chakravarti S. N. , Das P. , Webster R. T. , Bhat K. N.
Published: February 2003

Anodic oxide films (850±50 Å thick) grown on n+(100) bulk GaAs were subjected to selective area annealing using a cw argon laser operating at an output power of 1.2 W. Capacitance-voltage (C-V) measurements performed on Al-anodic oxide-GaAs MOS capacitor structures show that laser-annealed capacitor dots have greatly reduced field-induced hysteresis effects in their capacitance-voltage characteristics compared to the unannealed ones. The oxide leakage current also shows a significant improvement—the leakage current magnitude of MOS capacitors in laser-annealed oxide island is over four orders of magnitude less than the oxide region which was not exposed to the laser radiation. Dielectric breakdown measurement indicates that laser-annealed capacitors have considerably higher breakdown voltages, about a factor of 2 higher than the unannealed capacitors.
Using prolate spheroidal magnetization distributions for magnetic modeling
Authors: Nixon D. A. , Baker F. E.
Published: February 2003

Coefficients for the prolate spheroidal solution of Laplace’s equation are derived in terms of a line of magnetization extending between the focal points of a spheroid. The present paper applies Havelock’s formula to obtain the magnetization corresponding to terms of a prolate spheroidal inverse model. Knowledge of the relationship of the prolate spheroidal coefficients to the equivalent magnetization distribution is required when mathematically modeling distinctly nonspherical static magnetic sources in the near field.
Passive feedback stabilization of the levitated coil by means of superconducting loops
Authors: Tran M. Q. , Lee A. , Bollens R.
Published: February 2003

Passive feedback stabilization of levitated coils is often considered in connection with the design of internal ring devices (Multipole or Surmac). A novel method using short-circuited superconducting coils as stabilizers has been proposed. We present here a numerical calculation of the stability of one levitated coil in the field of two other levitating coils. The stability is provided by a set of superconducting short-circuited loops placed around the floating ring. Stable configuration does exist. We also found that for a given magnetic configuration there exists a minimum current in the levitated coil below which it is unstable.
The chromatic and spherical aberration of round electron optical lenses with spatially periodic electrostatic fields: cone-edge and cone focusing
Authors: van der Merwe J. P.
Published: February 2003

Whereas conventional foilless electrostatic lenses without axial electrodes or space charge show positive spherical Cs and chromatic Cc aberration for paraxial rays, results presented here show that for periodic or quasiperiodic electrostatic fields, low or negative values of Cc and Cs can occur if the rays pass through zonal regions. Not only can cone-edge focusing occur, but cone focusing can be found at several values of the emission angle. As a possible application, charged particles of sufficiently high velocity originating from a weak point source, for instance, Auger or internal conversion electrons, can be focused onto a small spot by utilizing an annular rather than a circular aperture.
Inverse ion diode experiment
Authors: Miller P. A. , Halbleib J. A. , Poukey J. W. , Verdeyen J. T.
Published: February 2003

An experimental test has been performed of a novel ion diode intended for inertial confinement fusion applications. The diode is a small thin-walled evacuated glass sphere (nicknamed a ’’light bulb’’) which is irradiated by relativistic electron beams transported to the sphere via plasma channels. The virtual cathode formed by the electrons in the light bulb accelerates ions radially inwards from the walls of the sphere. The ions are focused on a levitated central target. Qualitative aspects of one-dimensional theoretical analyses of the light bulb are supported by the experimental results reported here. However, the overall ion beam generation efficiency in the experiment is evidently substantially below that of the simple theory, probably owing to two-dimensional effects.
High-energy (Visible-red) stimulated emission in GaAs
Authors: Vojak B. A. , Laidig W. D. , Holonyak N. , Camras M. D. , Coleman J. J. , Dapkus P. D.
Published: February 2003

The high-energy (visible-red) photpumped laser operation (6345 Å at 77 K, 6785 Å at 300 K) of AlxGa1−xAs-AlAs-GaAs quantum-well heterostructures (QWH) grown by metalorganic chemical vapor deposition (MO-CVD) is described. The QWH active regions are alloy-free and consist of GaAs quantum wells and AlAs barrier layers. The effect of the AlAs barrier-layer thickness on the energy banding of the confined-carrier states and transitions is demonstrated. The laser operation of the coupled GaAs quantum wells is observed as high as 400–445 meV above the bulk-GaAs band edge, which agrees with the calculated locations (Lz∼30 Å) of the lowest (n = 1) electron, heavy-hole, and light-hole confined-particle states or energy bands.
A potential scattering formulation for mode couplings of electromagnetic waves in waveguides
Authors: Guo Theodore C. , Guo Wendy W.
Published: February 2003

A formulation for the propagation of electromagnetic waves in waveguides is developed in the mathematical frame work of quantum mechanics. Mode-coupling problems are then treated as potential scatterings. In particular, an interacting Hamiltonian with scattering potential is analytically derived for the mode couplings due to a bend in a waveguide. The formulation can be generalized to thin-film waveguides and waveguides of arbitrary geometry.
Study of two-crystal acousto-optic signal processors
Authors: Waxin G. , Rouvaen J. M. , Bridoux E. , Torguet R.
Published: February 2003

A general two-crystal optical processor is analyzed here. The processing characteristics are analyzed versus the acoustic wave slownesses and the arbitrary internal optical magnification factor. The feasibility of convolution, correlation, ambiguity function, or Fourier transform display is demonstrated. Some experimental results are also reported.
Third-order elastic constants of erbium
Authors: Jiles D. C. , Palmer S. B.
Published: February 2003

The third-order elastic constants (TOEC) of single-crystal erbium have been determined from measurements of selected uniaxial and hydrostatic pressure derivatives of the second-order elastic constants (SOEC). The changes in SOEC were measured using an ultrasonic sing around system capable of resolution of ±2 parts in 106 for changes in acoustic velocity. Values for the TOEC are in fair agreement with the theoretical calculations of other workers.
rf superconducting properties of reactively sputtered NbN
Authors: Isagawa S.
Published: February 2003

rf properties of superconducting niobium nitride (NbN) have been studied for the first time by using C-band (6.5 GHz) TE011 mode cavities. NbN films have been deposited on inner surfaces of the cavities made of Nb by the reactive sputtering method. From the temperature dependence of the surface resistance the superconducting energy gap of NbN has been determined. Although Tc remains high, the energy gap is apparently very small [2D(0)?1.7] or 2.0 kBTc. It recovers, however, to a value 2D(0)?2.7 or 2.8kBTc with a dc magnetic field applied parallel to the cavity axis. Measurements have been made on both rf and dc field dependences of the surface impedance. Different behaviors have been observed between Nb and NbN cavities. A columnar structure model well accounts for these behaviors of NbN films. The NbN cavity is more stable against several gases and more insensitive to trapped dc field than Nb. The field is, however, limited purely thermally at relatively low levels probably owing to the weak superconductivity around the columns and to the poor thermal conductivity of NbN.
Surface binding energy shifts, mixed valence and localization of 4f electrons: Ce vs. Sm (invited)
Authors: Gudat W. , Campagna M. , Rosei R. , Weaver J. H. , Eberhardt W. , Hulliger F. , Kaldis E.
Published: February 2003

Synchrotron radiation and x-ray photoemission studies of ’’divalent’’ SmS, SmSe and ’’trivalent’’ SmSb as well as Sm metal strongly suggest the existence of a surface induced binding energy shift EsB (?0.5 eV to greater EB) of the 4f6 configuration in SmS and SmSe. The divalent surface component of Sm metal has been resolved spectroscopically and has EsB (4f6,6H) ∼0.8 eV relative to the Fermi energy EF. Resonance enhanced 4f emission has been used to determine EB for the 4f1 configuration in the metallic chalcogenides CeS, CeSe and CeTe as well as in the pnictides CeAs and CeN. A resonant two-peak structure located at EF and at EB∼1 eV indicates a 4f surface binding energy shift of this magnitude in this fascinating ’’mixed valent’’ nitride. No shift could be resolved in the other Ce compounds having EB (4f1) between 1.8 and 2.6 eV. This is assigned to the more ’’band-like’’, delocalized behaviour of 4f states in CeN. Constant-final- and initial-state spectra of CeN differ significantly from those of the other Ce compounds having f-count near to unity. We take this as a further indication of the mixed valent character of CeN. Resonance enhancement of the cross section of bonding levels (other than 4f states) is also observed, allowing to identify 5d mixing in the valence band. The results of these studies will serve as a novel basis for understanding the exact nature of the 4f state and related anomalous (magnetic) properties of these Ce compounds as well as in Ce itself and its intermetallic compounds.
Crystalline electric fields in mixed valent systems (invited)
Authors: Shapiro S. M.
Published: February 2003

The inelastic neutron studies of rare-earth-based mixed valent systems have all shown remarkably similar results: a broad quasielastic line with half width on the order of 10 meV. This width exhibits a strong temperature dependence in those systems which undergo a valence transition and is only weakly temperature dependent in those systems which show no transition. A surprising result was the absence of crystalline electric field (CEF) excitations. Recent measurements on the alloy Ce.9−xLaxTh.1 have revealed the existence of CEF excitations. For x = 0, the valence transition is strongly first order and occurs near To?150 K. The inelastic spectra exhibit the typical broad quasielastic scattering. As x increases, To decreases, due to internal pressure effects, and a well-defined, but broad, excitation appears near E = 15 meV. This is interpreted as a CEF excitation between the Γ7 and Γ8 levels of the Ce3+ ion. For x = 0.40, the valence transition is almost completely suppressed and the excitation becomes even sharper.
The periodic Anderson model for intermediate valence within the coherent potential approximation
Authors: Schweitzer J. W. , Graham R. L.
Published: February 2003

The periodic Anderson model for a lattice of magnetic ions as applied to the description of intermediate valence in rare-earth compounds is investigated within the coherent potential approximation.
Calculations for 4f atoms using new exchange-correlation schemes
Authors: Cole L. A. , Harmon B. N.
Published: February 2003

Local spin density, self-interaction corrected, and average density approximation calculations have been performed for La, Ce, Gd, and Lu as a function of 4f occupancy. Techniques are described and implications for band calculations discussed.
NMR and spin/charge fluctuations in intermediate-valent SmB6
Authors: Peña O. , MacLaughlin D. E. , Lysak M. , Fisk Z.
Published: February 2003

Information on spin and charge fluctuations in the non-metallic intermediate-valent compound SmB6 has been obtained via 10B and 11B NMR between 2 and 300 K. Both the isotropic shift and the quadrupole coupling constant are temperature independent over this range, as expected if the fractional valence mixing is also temperature independent. Below 4.2 K the boron spin-lattice relaxation rate T1−1 varies linearly with temperature, and yields a spin fluctuation rate τs−f1∼1013 sec−1, which corresponds to a spin fluctuation temperature Tsf∼ 50 K if characteristic of the stoichiometric compound. An increase of T1−1 above 20 K indicates the onset of Sm-spin relaxation by thermal excitations. The results are also consistent with relaxation by impurity-band states associated with vacancies, but the Korringa constant obtained on this assumption is unrealistically small. Comparison between data obtained from 10B and 11B resonances yields no indication of a contribution from electric field gradient fluctuations to the relaxation; an upper bound on the charge fluctuation time τcf≲3τsf is obtained. It is shown that correlations between Sm spin and charge fluctuations, if present, do not affect the nuclear relaxation in the extreme narrowing limit.
Magnetic properties of Eu substituted SmS
Authors: Hedman L. , Rao K. V. , Yeshurun Y.
Published: February 2003

Our magnetic measurements on Sm1−xEuxS alloys in the temperature range 2–340K, indicate that the ferromagnetic transition temperature, TC, dependence on the concentration of Sm follows the expectations from a simple dilution phenomenon. In the paramagnetic state the measured magnetic susceptibility and its temperature dependence can be described, at least to a first approximation, by a simple linear combination of the susceptibility due to Eu in its S = 7/2 state and the non-collapsed SmS.
Transport and magnetic properties of carbon doped EuB6
Authors: von Molnar S. , Tarascon J. M. , Etourneau J.
Published: February 2003

We report resistivity, magnetoresistance, Hall effect, specific heat, and magnetic measurements on small single crystals having the nominal compositions EuB5.97C0.03(ao = 4.183 Å) and EuB5.95C0.05(ao = 4.182 Å). We find that these materials are degenerate semiconductors in which both the carrier concentration and antiferromagnetic interactions increase with increasing carbon content. These results agree qualitatively with earlier work and confirm that pressure and chemical doping have opposite effects on the magnetic behavior of EuB6.
Tm1−xEuxSe: New narrow gap magnetic semiconductors
Authors: Boppart H. , Wachter P.
Published: February 2003

In the Tm1−xEuxSe alloy system the compounds are semiconductors in the composition range 0.5?x?1. The 4f13 level of divalent Tm is 0.1 eV (for x = 0.5) and 0.3 eV (for x = 0.85) below the 5d6s conduction band. On single crystals we have measured the initial susceptibility, the magnetization in fields up to 100 kOe and the electrical conductivity as a function of temperature. For the semiconducting Tm0.15Eu0.85Se, the temperature dependent photoconductivity was also measured.
Superconductivity and magnetism in the series R2Fe3Si5 by Mössbauer and magnetization measurements
Authors: Cashion J. D. , Shenoy G. K. , Niarchos D. , Viccaro P. J. , Aldred A. T. , Falco Charles M.
Published: February 2003

Members of the R2Fe3Si5 series become either superconducting or magnetically ordered depending on whether the metal atom R( = rare earth, Y or Sc) is diamagnetic or paramagnetic respectively. We have taken Mössbauer effect and magnetization measurements to determine the magnetic state of the iron and the nature of the superconducting electrons. 57Fe Mössbauer measurements on the Sc, Dy and Er compounds all showed two partially resolved, quadrupole split spectra at all temperatures from 300 K to 1.5 K, indicating that there is no resolvable magnetic interaction at the iron site. No major change in the spectrum of Dy2Fe3Si5 was observed in passing through its antiferromagnetic ordering temperature of ∼4 K. Measurements in an applied field of 5.6 T set an upper limit of 0.03 μB for the iron moment in Sc2Fe3Si5. However, measurements at 4.2 K in fields up to 7 T for the Dy compound gave an internal field ∼9% smaller than the applied field and linear with applied field. This corresponds to an induced moment at the iron site of ∼0.07 μB at 7 T applied field. The 161Dy Mössbauer resonance clearly showed the onset of magnetic order around 4 K and the magnetic moment Dy at 1.5 K was found to be 7.0±0.2 μB consistent with the magnetization measurements. The nature of the superconducting electrons in the R2Fe3Si5 series is discussed in the light of available measurements.
Neutron scattering studies of the magnetic superconductor (Ce1−xTbx)Ru2
Authors: Fernandez-Baca J. A. , Lynn J. W.
Published: February 2003

Neutron scattering measurements have been carried out on polycrystalline specimens of (Ce1−xTbx)Ru2, for x = 0.07, 0.18, 0.44, in order to study the inelastic magnetic scattering as well as the development of magnetic correlations at low temperatures. At small wavevectors the intensity in each sample increases with decreasing temperature indicating the development of ferromagnetic correlations at low temperatures, but the intensity saturates at low temperature with no peak in its temperature dependence. There is also no evidence of any magnetic Bragg peaks, which indicates that there is no long range ferromagnetic order. For x = 0.44, inelastic scattering measurements show a distribution of magnetic scattering from low energies up to 4.5 meV, with a relatively well defined maximum at 3.3 meV. At T = 20 K additional scattering appears at 6.6 meV, while the scattering which peaked at 3.3 meV appears to shift to lower energies.
Magnetic properties and Hall effect of amorphous Gd-Au films
Authors: Gambino R. J. , McGuire T. R. , Fukamichi K.
Published: February 2003

Amorphous alloys of GdxAu1−x have been studied in the range x = 0.26 to 0.72, T = 4.2 to 300 K and fields up to 80 kG. The Hall conductivity ρH/ρ2 is found to be linear in Tc suggesting that conduction electron spin polarization determines the magnitude of the spontaneous Hall effect.
The Hall resistivity of sputtered amorphous Fe-B films
Authors: Fukamichi K. , Gambino R. J. , McGuire T. R.
Published: February 2003

Amorphous Fe-B films were prepared by sputtering in a wide composition range. The magnetization curves at 4.2 K of these amorphous alloys are not saturated easily and the apparent high-field susceptibility drastically increases with a decrease in boron content. The concentration dependence of magnetization exhibits a broad maximum around 14 %B. The Hall resistivity (ρH) as a function of applied magnetic field is also not saturated easily, and this behavior tends to become more significant with decreasing boron content. Such behavior may be correlated with the Invar effects and the stress retained in the amorphous films. The spontaneous Hall coefficient (Rs) calculated from ρH has a marked concentration dependence at low boron content, indicating a decrease in the value. The apparent ordinary Hall coefficient R*o increases dramatically with decreasing boron content, and also the ordinary Hall coefficient Ro is estimated to exhibit a similar tendency. The present results suggest that the electronic structure of amorphous Fe-B alloys is analogous to that of crystalline Fe-Ni Invar alloys.
Anisotropic magnetoresistance in transition metal-boron amorphous alloys
Authors: Yamasaki J. , Fukunaga H. , Narita K.
Published: February 2003

Anisotropic magnetoresistance ratio (AMR) was measured for binary and ternary (Fe,Co,Ni)-B amorphous alloys over the temperature range from 77K to room temperature varying the composition systematically. The largest AMR at room temperature was 0.45% for (Fe0.95Co0.05)84B16 alloy, which is smaller by about one order in magnitude than those in crystalline binary transition metal alloys. It was found that AMR in Co-Ni-B alloys exhibits a maximum similar to crystalline Co-Ni alloys. The maximum values were obtained for the alloys having magnetic moment of 0.56μB regardless of composition, meaning that the rigid band model is applicable to the anisotropic magnetoresistance in Co-Ni-B amorphous alloys.
Magnetic and transport properties of Fe-Au and Co-Au films
Authors: McGuire T. R. , Aboaf J. A. , Klokholm E.
Published: February 2003

Thin film cobalt-gold and iron-gold alloys have been prepared by sputtering onto water cooled substrates. These alloys are crystalline with residual electrical resistivity (ρ) a factor of five greater than bulk alloys. For FexAu100−x the X-ray diffraction patterns are characteristic of fcc structures (high Au content) and bcc structures (low Au content); CoxAu100−x shows mixed fcc and hexagonal diffraction patterns. Fe-Au exhibits a constant magnetic moment per Fe of μB = 2.2 over the range 26 to 92% Fe. The resistivity of Fe-Au at 4.2°K is about 40μΩcm and is independent of composition. The Hall effect expressed as Rs/ρ2 where Rs is the spontaneous Hall coefficient increases with Fe dilution. Co-Au shows a concentration dependent magnetic moment which decreases with increasing Au and a Hall effect as given by Rs/ρ2 which increases in magnitude as the Co moment decreases. In addition the resistivity at 4.2 °K of Co-Au is composition dependent increasing with decreasing Co content. The anisotropic magneto-resistance in both Fe-Au and Co-Au behave similarly with the interesting feature that Δρ(Δρ = ρ∥−ρ⊥) has a maximum at about the same average magnetization as found for other alloys such as Ni-Fe and Ni-Co2. At the same composition of maximum Δρ the saturation magnetostriction becomes almost zero.
Kondo effect on the resistivity of Au:Gd and on the ESR of Au:Yb
Authors: Tsang E. , Baberschke K.
Published: February 2003

The resistivity of 5000 ppm atomic Gd in Au is observed to decrease with decreasing temperature from 4.2 to 1K, a behavior typical of ferromagnetic (Jeff≳0) Kondo effect. The scaling parameter TK is found to be ∼108K and N(EF)Jo is compared to ESR result. Spin-spin interaction is also evident in the resistivity below 2K. ESR measurements on dilute Au:Yb alloys from 100 mK to 4K and at microwave frequencies of 3 and 9 GHz show for the first time a logarithmic temperature dependence for both the g-shift and the relaxation rate. The results yield a Kondo temperature TK∼10μK and a degeneracy of d∼3 for the local moment-conduction electron interaction channels.
Low-field galvanomagnetic properties of nickel
Authors: Hurd C. M. , Shiozaki I. , McAlister S. P.
Published: February 2003

Measurements of the Hall effect, transverse and longitudinal magnetoresistance have been made for Ni in the range 4.2–300 K in applied fields up to 6T. The aim is to improve the understanding of spin-orbit coupling, particularly the side-jump and skew components of the Hall effect. The results are described by a two-band model corresponding to s↑ and s↓ itinerant electrons. Below ∼20 K, where s-d scattering is precluded, the s↑ and s↓ electrons have unequal relaxation times due to the magnetisation. The transverse magnetoresistance is large. There is no skew scattering. Increasing temperature in the range 20–100 K equalises the s↑ and s↓ lifetimes; the transverse magnetoresistance goes to zero. The Hall effect indicates a field-dependent relaxation time for s↑, s↓ electrons. Only at the highest temperatures (≳∼150 K) does a side-jump component appear.
Neutron studies of the magnetic phase transition in UAs
Authors: Shapiro S. M. , Sinha S. K. , Lander G. H. , Vogt O.
Published: February 2003

Uranium arsenide undergoes a first-order phase transition to a type-I antiferromagnetic (AF-I) structure at TN∼124 K. Above TN, UAs exhibits strongly anisotropic critical scattering suggestive of pseudo two-dimensional behavior. The temperature dependence suggests a tendency to orders with an incommensurate wave vector but then suddenly the system orders with the AF-I structure. A mean-field theory is proposed based on an anisotropic Hamiltonian and provides a reasonable description of the results.
Neutron scattering study of spin waves in the antiferromagnet RbMnCl3
Authors: Alperin H. A. , Melamud M. , Horowitz A.
Published: February 2003

The magnetic structure of the antiferromagnet RbMnCl3 (TN = 94K) consists of ferromagnetic planes stacked in the sequence A(+), B1(−), B1(+), A(−), B2(+), B2(−) along the C-axis. The two kinds of sites, A and B for the Mn2+ ions contain respectively, ’’lone spins’’ and (much closer) spin pairs. This study of the spin wave spectrum was undertaken with the objective of determining whether the principal magnetic interactions JAB and JBB are of the same order of magnitude (conventional Heisenberg type) or whether a strong coupling model (JBB≳≳JAB) applies. Two distinct optic branches observed in the [qoo] direction immediately ruled out the strong coupling model. A fit to the data was then performed using the conventional spin wave model with excellent results. We find JBB/JAB = 1.65 (±.1). With spin values SA = 2.4 and SB = 2.5, JBB = 0.73 meV and JAB = 0.44 meV.
Temperature dependence of the magnetic excitations in Gd
Authors: Cable J. W. , Wakabayashi N. , Nicklow R. M.
Published: February 2003

We have made inelastic neutron scattering studies of the magnetic excitations in gadolinium above and below the Curie temperature (Tc = 293 K). The constant Q measurements were made out to the Brillouin zone boundaries in the [001] and [100] directions in the temperature range from 9 to 593 K. The small q spin-wave energies renormalize in approximate proportionality to the net magnetization and approach zero at Tc. There is very little broadening of these peaks except at temperatures very near Tc. At large q, however, there is appreciable broadening but a much slower decrease of spin-wave energies with increasing temperature. The large q peaks do not vanish at Tc; instead, they persist as broad shoulders in the magnetic excitation spectra up to about 1.2 Tc.
Single crystal magnetization and susceptibility studies on CuCl2⋅DMSO, a salt with quasi 1-d ferromagnetic interactions
Authors: Landee C. P. , Willett R. D.
Published: February 2003

CuCl2⋅DMSO is one of a series of linear chain spin 1/2 compounds recently shown to have predominantly ferromagnetic interactions in the paramagnetic state. Initial studies1 conducted on powders showed the exchange interaction J to be relatively large (J/k = 45 K) with rather large interchain interactions (J′/J = −0.04). The present paper reports the first single crystal susceptibility and magnetization studies on this compound. The monoclinic compound has been found to order antiferromagnetically at 4.80 K with the easy axis the a axis. The two χ⊥′s are nearly equal, indicating uniaxial anisotropy. A spin-flop transition has been observed when an external field was applied along the easy axis. The magnetic field phase diagram for this transition has been measured down to 2 K in fields up to 9.5 kOe. Using a molecular field model, effective fields have been estimated for the antiferromagnetic coupling between chains and for the spin anisotropy. The antiferromagnetic exchange field is 23 kOe, 3.6% of the effective ferromagnetic exchange field within the chains (Hfm). The anisotropy field was found to be only 6×10−4Hfm, indicating nearly perfectly Heisenberg-type intrachain exchange.
Kinematic consistency in ferromagnets with single-ion anisotropy: Application to FeCl2
Authors: Rastelli E. , Tassi A. , Pini M.G. , Rettori A. , Tognetti V.
Published: February 2003

We have developed a theory which makes the expression for temperature-dependent magnon energies, obtained by means of boson representations of spin operators, kinematically consistent. The theory is applied to FeCl2, a S = 1 ferromagnet with rather large anisotropy, to calculate the temperature dependence of the energy gap of the uniform mode. Both a self-consistently renormalized spin-wave theory and an exact calculation at low temperatures by a T-matrix approach seem to indicate the presence of an anisotropic exchange in addition to easy-axis single-ion anisotropy. Comparison with experimental data shows the fundamental role of the correct treatment of the anisotropy.
The temperature dependence of the transmission of 24 GHz radiation through electrolytically formed nickel single crystals
Authors: Myrtle K. , Heinrich B. , Cochran J. F.
Published: February 2003

The temperature dependence of the 24 GHz anomalous FMR transmission peak previously observed in nickel specimens has been studied over the range 4 to 300 K using nickel single crystals deposited electrolytically on copper single crystal substrates. The experimental results have been compared with a calculation which includes magneto-elastic coupling between the lattice and the magnetization. In general, the theory gives a good account of the observed lineshapes and amplitudes, and an estimate can be made of the phonon mean free path and its temperature dependence.
Ferromagnetic anti-resonance in non-saturated magnetic metals
Authors: Rachford F. J. , Vittoria C.
Published: February 2003

We have developed a theoretical formulation for calculating electromagnetic reflection and transmission coefficients in magnetically non-saturated metals foils. For in plane magnetic fields two ferromagnetic anti-resonance (FMAR) transmission peaks are calculated in the non-saturated region for both bubbles and stripes domain structures. One anti-resonance occurs at frequencies higher than the ferromagnetic resonance (FMR) frequencies for non-saturated media and the other occurs between the two FMR resonances. The latter anti-resonance displays structure which is due to the presence of electromagnetic standing modes coinciding with a rapid variation in propagation constant near FMR. For perpendicular magnetic fields the FMAR peaks split in two reflecting the differences in permeability for alternate domain regions.
Magnetic multi-domain resonance in single crystal ferrite platelets
Authors: Rachford F. J. , Lubitz P. , Vittoria C.
Published: February 2003

We have observed ferromagnetic resonance (FMR) on single crystal platelets of Zn and Co substituted M-type hexagonal ferrites. FMR was observed with both swept field and swept frequency measurements. The results were compared, and agreed well, with calculations of resonance frequencies based on periodic arrays of stripes and bubble domains. In addition to the resonance parameters necessary to describe the results in the magnetically saturated regime, our calculations take into account the wall energy, which results in a field dependence of the domain spacing, which in turn strongly affects the resonances near saturating fields.