bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin- and angle-resolved photoemission study of (110) Fe films grown on GaAs by molecular beam epitaxy
Authors: Schröder K. , Prinz G. A. , Walker K.-H. , Kisker E.
Published: July 2002

Single-crystal Fe(110) films grown on GaAs by molecular beam epitaxy have been studied utilizing synchrotron radiation to obtain the first spin- and angle-resolved photoemission data from the (110) face of α-Fe. The data locates the Γ↑12 at 1.0 eV, Γ↑25′ at 2.6 eV, and Γ↓25′ at 0.6 eV below the Fermi level, in excellent agreement with recent minimum energy self-consistent band theory calculations. The variation of the magnetization with film thickness is seen to be reflected in changes in the photoemitted electron spectra for films less than 100 Å thick.
Low temperature magnetic properties of the NdxFe1−x amorphous thin films
Authors: Dai Dao-sheng , Fang Rui-yi , Tong Li-tai , Lui Zun-xiao , Zhou Zeng-jun , Lin Zhao-hua
Published: July 2002

The magnetic properties of NdxFe1−x (0.04≤x≤0.09) amorphous thin films were studied in the temperature range 1.5–300 K at H=7 T. It was found that in these films the asperomagnetic and speromagnetic structures existed. The effective magnetic moment per Nd atom varied from 1.2 μB to 1.06 μB, and the distribution angle 2ψ0 of neodymium moment from 210° to 222° corresponding to x=0.04 to 0.90. The magnetic moment of iron atom also varied from 2.1 μB to 1.2 μB.
Spin-polarized photoelectrons and Auger electrons from magnetic materials (invited)
Authors: Kotani A.
Published: July 2002

Spin polarization of photoelectrons and Auger electrons plays an important role in the study of electronic states in magnetic materials. After reviewing the effects of electron correlation on the photoemission spectra in Ni, we present our theory of spin-polarized photoelectrons in the resonant photoemission of Ni. The agreement of the calculated results with experimental data supports the 3d electron correlation picture based on the two-d-hole bound state formation. The spin polarization of L23M23M23 Auger electrons from ferromagnetic materials is also calculated and compared with a recent experimental result.
Two-level systems and FMR near the ferromagnet spin-glass transition
Authors: Manheimer M. A. , Bhagat S. M. , Webb D. J.
Published: July 2002

We report temperature variations of the linewidth and resonance field for FMR in the reentrant ferromagnets a-FexNi80−xP14B6, x=11, 13, and 15. Microwave frequencies vary from 35 to 2 GHz and it is found that the anomalies, attendant upon approaching the FM-SG transition temperatures, are reduced when frequency is lowered. The results find satisfactory explanation in terms of a model coupling the resonating spins to magnetic two-level systems.
Defects in amorphous ferromagnets: Effects of ion implantation
Authors: Garoche P. , Gambino R. J.
Published: July 2002

The effect of boron implantation on the magnetic properties of Fe85B15Ni2 amorphous alloys has been investigated. The magnetization of thin film samples (3800 Å) obtained by rf sputtering has been studied before and after implantation of 1% atomic boron by using a SQUID magnetometer with magnetic fields up to 2 T. In this highly magnetostrictive material (λ≂30 ppm) the saturation process and coercive field are presumably dominated by the stress field due to the defect structure. Our analysis of the saturation process reveals that the vacancies introduced by boron implantation transform at room temperature into more stable defects: linear defects. These results are compared with computer simulations and model structures of amorphous metals.
Spin-glass properties in the dilute semiconductor Sn1−x MnxTe
Authors: Escorne M. , Godinho M. , Tholence J. L. , Mauger A.
Published: July 2002

Sn1−xMnxTe is known to be a ferromagnetic semiconductor for x>0.03. We have investigated more dilute samples and found a spin-glass state for x<0.03 as well as a double transition para→ferromagneticlike→reentrant phase for x>0.03. These properties can be explained by RKKY-like interaction between Mn moments (surrounded by their polarization cloud).
ac susceptibility of thermally annealed and neutron irradiated Cu-Ni alloys
Authors: Catchings III R. M. , Borg R. J. , Violet C. E.
Published: July 2002

The effect of thermal annealing and high flux neutron irradiation on the ac susceptibility of Cu-Ni alloys of composition 40, 50, and 60 at. % Ni have been studied. In this compositional region the short-range order and cluster changes introduced by the annealing and irradiation can greatly effect the magnetic state of the Cu-Ni system. Neutron diffraction studies on the Cu-Ni system have indicated the possibility of a miscibility gap forming in this system. The ac susceptibility of samples quenched from high temperature (900 °C), annealed at low temperature (350 °C), or irradiated at the LLNL, RTNS-II 14-MeV neutron source were measured as a function of temperature. The quenched 60 at. % Ni alloy exhibited a ferromagnetic transition near 195 °K that remained unchanged under neutron irradiation. The low-temperature annealed sample gave a transition occurring over a wider temperature range. The quenched 50 at. % Ni alloy exhibits a ferromagnetic transition at a lower temperature with a χ(T) curve that is peaked near 40 °K. The thermally annealed and irradiated sample exhibits a greatly broadened χ(T) curve. The quenched 40 at. % Ni alloy gives a paramagnetic behavior. The low-temperature annealed sample gives a χ(T) curve having a broad plateau that decreases at low temperatures. This behavior is suggestive of a ferromagnetic to spin-glass transition. The irradiated sample gives a χ(T) curve having a peak indicating a spin-glass transition at 2.4 °K.
A comparison of the systematics of the spin-glass susceptibility peaks in P
d Mn with an effective-field model
Authors: Zastre E. , Roshko R. M. , Williams Gwyn
Published: July 2002

We present new measurements of the ac susceptibility of two PdMn alloys containing 5.0 and 5.5 at. % Mn in approximately 50 static biasing fields up to 1 kOe, as well as a survey of previous data on more concentrated samples, in an attempt to establish the details of the field suppression of the spin-glass peaks in this system. These results are compared with the predictions of an arbitrary spin effective-field model. Both the experimental data and the theoretical predictions indicate that the rate of this suppression increases dramatically as one approaches the ferromagnetic–spin-glass critical point (i.e., as η=J̄0/J̄→1, where J̄0 and J̄ refer to the center and width of the exchange distribution).
Coexistence of antiferromagnetism and spin-glass ordering in the Ising system Fe0.55Mg0.45Cl2
Authors: Wong Po-zen , Yoshizawa H. , Shapiro S. M.
Published: July 2002

Fe1−xMgxCl2 is a diluted Ising antiferromagnet with competing first- and second-neighbor exchange interactions. For x≊45, the system undergoes a Néel transition at TN ≊7.4 K and a reentrant spin-glass transition at Tsg ≊3.0 K. From neutron scattering experiments we find that (i) the antiferromagnetic Bragg peak persists down to 1.2 K, well below Tsg; and (ii) the diffuse scattering becomes temperature independent below about 6.0 K, with the correlation length frozen at about 2.8 lattice spacings. These results suggest that long-range antiferromagnetic order and spin-glass-like short-range order coexist. Such a behavior is predicted by the infinite-range model for spin glasses with strong uniaxial anisotropy.
Linear chain antiferromagnetic interactions in Cs2CuCl4
Authors: Carlin Richard L. , Burriel Ramon , Palacio Fernando , Carlin Rachel A. , Keij S. F. , Carnegie David W.
Published: July 2002

The magnetic susceptibility of polycrystalline samples of Cs2CuCl4 has been measured over the temperature interval 1.1–30 K. A broad maximum in the data, centered around 2.6–2.7 K, is consistent with the existence of lower-dimensional antiferromagnetic interactions in this compound. The model used for fitting the data is the Heisenberg linear chain of Bonner and Fisher, with a small molecular-field correction. The parameters resulting from the data analysis are 〈g〉=2.20±0.02, −J/k=2.0±0.1 K, and −zJ′/k=0.10±0.05 K.
Towards equilibrium in spin glasses (invited)
Authors: Lundgren L. , Nordblad P. , Svedlindh P. , Beckman O.
Published: July 2002

New nonequilibrium features of the magnetic susceptibility of spin glasses are reviewed. Experimental observations on the time variation of the zero-field-cooled (ZFC) and field-cooled (FC) susceptibilities indicate that the same equilibrium value is obtained after the same characteristic time teq(T). ZFC and ac susceptibility measurements on metallic spin glasses unambiguously reveal the existence of aging of the zero-field spin-glass state. The possibility to probe the aging process from these measurements is outlined. The aging of the zero-field state ends at the characteristic time teq(T), where a spin-glass state at dynamic equilibrium is retained.
Theory of electron spin resonance in the insulating spin glass: Europium strontium sulfide
Authors: Raghavan Raghu , Levy Peter M.
Published: July 2002

We have extended nonlinear mode coupling calculations of electron spin resonance (ESR) line shape parameters, previously applied to a metallic spin glass, to the insulating spin glass Eu0.4Sr0.6S for temperatures above the freezing transition. The spectrum due to short-range exchange interactions is broadened by magnetic dipole coupling. The decoupling approximations are similar to those of Levy, Morgan-Pond, and Raghavan [Phys. Rev. B 30, 2358 (1984)]. In contrast to the metallic glass we obtain agreement, without adjustable parameters, for the high-temperature limit of the linewidth seen for a 40% concentration of europium. For finite temperatures, with the density of states of the exchange interaction obtained numerically, the temperature dependent linewidth and line shift so obtained agree semiquantitatively with experiment.
Small-angle neutron scattering evidence for the absence of long-range magnetic order in amorphous Fe91Zr9
Authors: Rhyne J. J. , Fish G. E.
Published: July 2002

Small-angle neutron scattering (SANS) studies of an amorphous Fe91Zr9 alloy have shown that there is no transition to long-range magnetic order in contrast to previous bulk magnetization results which indicated a transition to a ferromagnetic state at 220 K followed by a reentrant spin-glass state near 60 K. The scattering line shape is Lorentzian in Q down to below 150 K and yields a spin correlation length which reaches a maximum of only 27 Å at the transition T C=210 K and exhibits an essentially constant plateau of 23 Å down to helium temperature, with no evidence of a second transition in the 60–80 K range. The line shape departs from Lorentzian below about 120 K and can be represented by a Lorentzian plus Lorentzian-squared cross section as appropriate for a system in which long-range order has been replaced by a frozen cluster configuration. The absence of ferromagnetic order in Fe91Zr9 at Fe concentrations far above the percolation threshold suggests the presence of a very broad distribution of exchange fields arising from the random Fe site coordinates.
Mössbauer studies on LaNi4.7Sn0.3 and its hydride
Authors: Oliver F. W. , Morgan W. , Hammond E. C. , Wood S. , May L.
Published: July 2002

Mössbauer measurements were made on LaNi4.7Sn0.3 at room and liquid nitrogen temperatures. Experimental data yielded a singlet at room temperature and a doublet at liquid nitrogen temperature. Spectra of the hydrided sample yielded a doublet at liquid nitrogen temperature with an increase in the quadrupole splitting compared to the unhydrided spectra, but no change in the isomer shift. These data indicate that there is no significant interaction between the tin and the hydrogen. The magnetic character remained the same down to liquid nitrogen temperature as evidenced by the Mössbauer data. X-ray diffraction measurements on the hydride showed an expanded lattice with the same structure as found for the unhydrided sample. A decrease in particle size was observed upon hydriding.
Mössbauer and magnetization studies in Fe3−xRuxSi
Authors: Mishra S. N. , Rambabu D. , Grover A. K. , Pillay R. G. , Tandon P. N. , Devare H. G. , Vijayaraghavan R.
Published: July 2002

Magnetization and 57Fe Mössbauer studies have been made in Fe3−xRuxSi for 0≤x≤2. Up to x=1.35, the alloys behave like collinear ferromagnets and μ/f.u. and HF (Fe) values do not show any appreciable change, thus suggesting that Ru replacing magnetic Fe (A,C) atoms also possess a large moment of ∼1 μB. For x>1.35, the approach of magnetization to saturation becomes progressively slower and the system acquires an inhomogeneous magnetic structure. In the region 1.45 ≤x<1.8, Tm and Thf, the HF (Fe) evolution temperature, fall rapidly, with Thf≪Tm resulting in a behavior a la RuFeSi. For x>1.8, majority of the Fe atoms are on B site and they presumably undergo AF/random freezing. Even though Tm and magnetization behavior show considerable variation across the region 1≤x≤2, the character of Mössbauer spectra does not change and 〈HF (Fe)〉av measured at 4.2 K remain ∼250 kOe.
Dynamical effects and the critical behavior of random-field systems (invited)
Authors: Shapir Yonathan
Published: July 2002

A variety of phenomena is observed experimentally in random-field (RF) systems realized by the application of an external field to diluted antiferromagnets. At low temperatures, infinitely long hysteretic effects are manifested by the history dependence of the final states: long-range order is observed if the field is applied after cooling, while domain states are reached when field cooled. While no indications for critical fluctuations are detected in 2-D systems, scaling behavior, for both the correlation length and the specific heat, is observed in 3-D systems over an intermediate range of temperatures. The related critical properties seem to be well described by the corresponding ones in the 2-D pure Ising model. The renormalization-group approach, which yields for the equilibrium critical exponents their values of the pure model in d−2 dimensions, is reviewed. A generalization of the dimensional-reduction approach, which accounts self-consistently for renormalized responses of the RF system, is presented. The dynamical effects are implicitly incorporated through the variation in the critical response between the local and the global regimes, associated with short- and long-time scales, respectively. In both regimes the lower critical dimension is found to be d=2 in accordance with stability arguments. The short-time critical behavior indicates a dimensional reduction by one for the 3-D thermal exponents, in agreement with the experimental results.
Localization and magnetic properties in cerium compounds
Authors: Tholence J. L. , Haen P. , Jaccard D. , Lejay P. , Flouquet J. , Braun H. F.
Published: July 2002

Magnetic and transport measurements on heavy fermion compounds CeAl3, CeCu2Si2 and CeRu2Si2 are reported. Transport properties show that in CeRu2Si2, the f electron is more delocalized than in CeAl3 or CeCu2Si2. Magnetic data show the apparent cancellation of magnetic correlations for the CeAl3 and CeRu2Si2 compounds which have a nonmagnetic normal ground state; by contrast antiferromagnetic correlations lead to the decrease of the low temperature susceptibility of CeCu2Si2 which has a superconducting ground state.
Peltier heat of a small polaron in a magnetic semiconductor
Authors: Liu Nai-Li H. , Emin David
Published: July 2002

For the first time the heat transported with a small polaron in both antiferromagnetic and ferromagnetic semiconductors is calculated. This heat, the Peltier heat, π, is obtained from the change of the entropy of the total system upon introduction of a charge carrier. We explicitly consider both the intrasite and intersite exchange interactions between a small polaron and the interacting spins of a spin-1/2 magnet. There are two competing magnetic contributions to the Peltier heat. First, adding the carrier increases the spin entropy of the system. This provides a positive contribution to π. Second, the exchange between the carrier and the sites about it enhances the exchange binding between these sites. This reduces the energetically allowable spin configurations and provides a negative contribution to π. At extremely high temperatures when kT exceeds the intrasite exchange energy, the first effect dominates. Then π is simply augmented by kT ln 2. However, well below the magnetic transition temperature the second effect dominates. In the experimentally accessible range between these limits both effects are comparable and sizable. The net magnetic contribution to the Peltier heat rises with temperature. Thus, a carrier’s interactions with its magnetic environment produces a significant and distinctive contribution to its Peltier heat.
Large magnetic field effect on the heavy fermion superconductor U1−xThxBe13 just above T
c
Authors: Willis J. O. , Smith J. L. , Fisk Z. , Ott H. R.
Published: July 2002

Magnetic fields as small as 4 kOe substantially increase the resistivity of U1−xThxBe13 for x=0.0175 and 0.0378 between 1.4 K and Tc, the superconducting transition temperature of this heavy fermion material. At the intermediate value of x=0.026, Tc reaches a local maximum, and no normal-state field dependence is observed up to 4 kOe. At x=0.0603, away from the region of nonmonotonic dependence of Tc on x, again no field dependence is seen. The observations are discussed with regard to specific-heat measurements and in terms of the interaction of superconductivity with narrowband features.
Magnetic field induced superconductivity in the Chevrel phase compounds EuxSn1−xMo6S8 (invited)
Authors: Rossel C. , Meul H. W. , Decroux M. , Fischer O/. , Remenyi G. , Briggs A.
Published: July 2002

The experimental evidence for a new magnetic field induced superconducting state in the pseudoternary Eu-Sn molybdenum chalcogenides is presented. This state results from the Jaccarino–Peter compensation mechanism which accounts correctly for the observed Hc2-T phase diagrams. Using a multiple pair-breaking theory to analyze the data, we discuss the critical parameters needed to observe this phenomenon under different conditions, in these materials and at higher temperatures.
Magnetic-field-dependent susceptibility of single-crystal Ho-Mo-S Chevrel phase at very low fields
Authors: Holtzberg F. , Webb R. A. , McGuire T. R. , La Placa S. J.
Published: July 2002

We report measurements of the temperature dependence of the ac and dc susceptibility of single-crystal HoMo6S8 oriented both parallel and perpendicular to the magnetic axis in static magnetic fields varying from 0.005 to 100 Oe. We find Tc1 ≂1.70 K and Tc2 ≂0.65 K with significant supercooling in low fields at Tc1 and very long time effects associated with cooling through Tc2 but not on warming. We find a significant difference between the ac and dc susceptibility changes at both transitions. The lower critical field Hc1 is determined to be ∼20 Oe.
Theories of itinerant magnetism (invited)
Authors: Korenman Victor
Published: July 2002

Fluctuating mean-field theories of itinerant magnetism are extensions of Stoner theory which give a better account of temperature dependencies. They include the effects of spin-wave excitations, and allow for substantial magnetic behavior in the paramagnetic state. I discuss these theories and how well they are supported by thermodynamic data, and by recent neutron scattering and photoemission experiments, particularly in the cases of iron and nickel.
Transition-metal monoxides: Band or Mott insulators? (invited; abstract)
Authors: Williams A. R.
Published: July 2002

We argue that the widely held view that the transition-metal monoxides are Mott insulators is incorrect. Self-consistent spin-polarized energy-band calculations indicate that MnO and NiO are ordinary band insulators, and that FeO and CoO, while conducting in the local-spin-density approximation, satisfy the condition required for insulating behavior due to the development of an orbital magnetic moment. Our picture of the monoxides is supported by a variety of experimental data. The fundamental question raised by this work is the importance of charge fluctuations, or equivalently, of ionic configurations. The distinction between our band picture and the conventional picture based on ionic configurations (the energy price for which is the Coulomb integral ‘‘U’’) is particularly clear for the variation of the Néel temperature across the monoxide series. Perturbation theory indicates that T(Néel) varies inversely with U in the conventional theory, but inversely with the exchange splitting in the band picture. Since the exchange splitting tends linearly toward zero across the series, whereas U is constant or increases, the increase by a factor of five of T(Néel) across the series is more naturally explained by the band picture.
Superconductivity and magnetism in heavy-electron U intermetallics (invited)
Authors: Ott H. R. , Rudigier H. , Fisk Z. , Smith J. L.
Published: July 2002

Recent work intended to investigate a Fermi-liquid-type low-temperature state in uranium intermetallic compounds is reviewed. In form of a comparison of physical properties with those of CeAl3, the prototype heavy-electron system, some details concerning the occurrence of this heavy-electron state are discussed. Special attention is then given to experimental data giving evidence for superconductivity or magnetic order, both involving these heavy electrons. The possibility of unconventional superconductivity in these systems is supported by increasing experimental evidence.
Heavy fermion superconductors and some associated problems (invited)
Authors: Varma C. M.
Published: July 2002

Some of the problems posed by superconductivity in the heavy fermion solids and the more difficult problems of the heavy fermion state itself are qualitatively discussed.
Magnetism and superconductivity in Eu(Ho)Mo6S8
Authors: Capone II D. W. , Lai Fook M. S. , Guertin R. P. , Hinks D. G. , Dunlap B. D. , Foner S. , Abou-Aly A. I. , Brooks J. S.
Published: July 2002

A variety of ambient and high-pressure experimental results reveal the interplay between magnetism and superconductivity in Ho-doped samples of the pressure-induced superconductor, EuMo6S8. Ho concentrations up to 50 at. % of the rare-earth ions were used. High-resolution magnetic measurements are consistent with the crystalline electric field ground state for the Ho3+ ions being a magnetic doublet consisting largely of Jz =±8. The results of high-pressure magnetization experiments reveal negligible effects of reduced lattice constant on the rare earth-rare earth interactions. Resistivity in a 10 at. % sample for P=10 kbar shows the suppression of a P=0 structural transition, metallic conductivity down to low temperatures, and finally superconductivity at 8 K. The upper critical field, Hc2(T), for this sample was measured for P=7, 10, and 12 kbar and showed strong reentrant behavior [dHc2(T)/dT >0 as T→0 K]. A minimum with field in the resistivity above Hc2 was also observed at lowest temperatures. The Hc2(T) data are compared with those of EuMo6S8 at high pressure, which show positive curvature, and HoMo6S8, in which superconductivity is quenched by ferromagnetism at low temperatures.
Determination of recombination center position from the temperature dependence of minority carrier lifetime in the base region of p-n junction solar cells
Authors: Bhattacharya D. K. , Mansingh Abhai , Swarup P.
Published: July 2002

The minority carrier lifetime (τ) in the base region of n+-p silicon solar cells has been measured in the temperature range ∼77–400 °K using the open-circuit voltage decay technique. The injection level has been maintained constant in the entire temperature region. Experiment and theory agree in a small temperature region if τn0 (minority carrier lifetime in heavily doped p silicon) is assumed to be temperature independent. However, an excellent fit between experimental and theoretical results is obtained if τn0 is assumed to vary as exp[−(Eτn0/kT)].
Computer simulation of thin film nucleation and growth
Authors: Salik Joshua
Published: July 2002

Some of the processes involved in thin film nucleation and growth were simulated by means of a digital computer. The main conclusions drawn from the simulation results are (1) Because of the random nature of the processes involved, a large variation in results is obtained. (2) Upon impingement, clusters are formed up to a coverage of ca. 0.2, and from there on growth of existing clusters, rather than formation of new ones, takes place. (3) Surface migration is responsible for the formation of most of the clusters at coverages smaller than 0.1, whereas at higher coverages most clusters are formed upon impingement. (4) Surface migration accelerates the growth and causes reduction in cluster density. (5) Reevaporation slows the growth and reduces the cluster density dramatically.
Turn-on delay analysis of current-injection Josephson logic circuits
Authors: Sone Jun’ichi
Published: July 2002

A turn-on delay, during which the output voltage of a Josephson logic circuit is very small, is of prime interest for the design of high-speed Josephson digital integrated circuits. We have derived an analytical formula for the turn-on delay of the current-injection logic circuits, which is in good agreement with computer simulations. Analysis of the circuit equations shows that the nonlinear inductance of a current-summing Josephson junction plays an important role for the turn-on delay. Dependences of the turn-on delay on circuit parameters and operating conditions are calculated. For parameter values typical of 5-μm current-injection circuits, the turn-on delay is on the order of 10 ps. The turn-on delay and operating margin are compared in various types of current-injection logic circuits. The higher sensitivity of the threshold gate current to the input current is found to be desirable not only to reduce the turn-on delay but to operate in a wide margin.
New experimental method to investigate the renewal epochs in non-Markov processes
Authors: Faraci Giuseppe , Pennisi Agata R.
Published: July 2002

In order to describe exactly the renewal epochs of nonsimple Markov processes, a new experimental method has been developed which allows one to draw out of the sequence data which can be directly compared with exact formulas. The analyzed process has been obtained by superimposing an ordinary Poisson distribution with periodic signals when the whole train is processed by a device introducing a finite width (dead time) of nonextended type. Excellent agreement with the theoretical predictions has been found.
Comparative study of Fermi energy pinning and adatom bond character: Antimony versus the column 3 elements (Al, Ga, In) on GaAs (110) and GaSb (110)
Authors: Skeath Perry , Su C. Y. , Lindau I. , Spicer W. E.
Published: July 2002

New results which probe the nature of a defect mechanism responsible for pinning the Fermi energy within the band gap on the (110) surfaces of the 3-5 compounds are presented. From these results it is concluded that to first order the Fermi energy pinning position is independent of the fundamental difference between the Sb-GaAs chemical bond and the column 3 metal-GaAs bond. Furthermore, based on the defect mechanism for the Schottky barrier formation proposed by Spicer and Lindau, the present data can be most easily understood if the defect is more complex than a single surface lattice vacancy. Previously, investigations of column 3 metals on both n- and p-type GaAs, by photoemission electron spectroscopy, revealed a systematic difference in surface Fermi energy stabilization in the gap, with p-type samples pinning 0.25 eV below n-type samples. In the present work, it is shown that antimony, a column 5 element, yields essentially the same Schottky barrier height as the column 3 metals when adsorbed on GaAs (110). A strong similarity in the barrier height is also noted when Sb adsorption is compared to Ga adsorption on GaSb (110). The observed tendency for n-type GaSb to pin closer to the valence-band maximum than GaAs is consistent both with the Spicer/Lindau defect mechanism and with the ‘‘anion rule’’ of McCaldin, McGill, and Mead. These results are important for the theory of Schottky barrier formation and for Schottky barrier device fabrication.
Oblique, off-specular, linear, and nonlinear observations with a scanning micron wavelength acoustic microscope
Authors: Tan M. R. T. , Ransom H. L. , Cutler C. C. , Chodorow M.
Published: July 2002

We have constructed a micron wavelength acoustic microscope having a novel geometry which accentuates detail in acoustic imaging while providing ease in focusing, enhanced resolution, and the observation of third-order nonlinear products (2F1-F2). Convergent, acoustic beams generated by curved transducers provide very high power densities at the acoustic lens and focus. Oblique acoustic illumination of surfaces gives directionality to the image and the use of a second transducer position, removed from the specularly reflected beams, reduces undesired nonlinear interaction in the intervening liquid (water) medium. Increased resolution and sharper images are obtained by observing the second harmonic via the difference frequency (third-order product 2F1-F2) which falls back into the initial frequency range, ∼600 MHz. However, significant effects due to nonlinear interaction identified with the object have not yet been observed.
Pyroelectric anemometers: Experimental geometric considerations
Authors: Frederick J. R. , Zemel J. N. , Goldfine N.
Published: July 2002

The role of geometric factors in the operation of a modified design of the pyroelectric anemometer is examined. The two major variables were chip thickness d (133 and 205 μm) and the separation between the heater and the measuring electrodes (25≤ΔHE≤250 μm). The overall flow response varied as (flow) 0.48±0.02 for almost four orders of magnitude. No evidence of saturation was observed at either the high or low flow rates. One of the more interesting results obtained was the relative independence of the response at fixed flow rate on ΔHE for d=133 μm. Even for d=205 μm, the response was relatively independent of ΔHE, though some variation was observed.
Heat transfer model for the pyroelectric anemometer
Authors: Hesketh P. , Gebhart B. , Zemel J. N.
Published: July 2002

A resistor-capacitor analog heat transfer model is used to calculate the thermal pyroelectric anemometer (PA) response. This is compared to the data of Frederick et al. [J. Appl. Phys. 57, 4936 (1985)] in the accompanying paper. Steady-state gas flow conditions are assumed, and the calculations apply in the regime where the transit time of the gas over the device is much less than the time period of the heat input from the ac-driven heater. Since the pyroelectric substrate is thin, the analysis is simplified to one dimension and excludes edge effects, heat losses due to the support, and thermal radiation. Further, no temperature difference is assumed at the interface between the gas and substrate, i.e., no temperature jump. The calculated dynamic response is in excellent agreement with measurements. However, the calculated level of response is 240  μV at a gas flow of 10 m/min, much lower than the 570  μV measured by Frederick et al.
Profile of tracer Si in silicide when Si diffuses by vacancy mechanism
Authors: Lien C.-D.
Published: July 2002

A mathematical model is constructed to interpret the profiles of radioactive Si tracers during silicide formation. This model assumes that only Si moves in the silicide during silicide formation and that the moving Si diffuses in the Si sublattice of the silicide in terms of vacancy mechanism. Analytical solutions of the model for long-time annealing (i.e., asymptotic profiles) are given. The analytical asymptotic profiles are very accurate for the annealing period generally used in experiments. It is shown that the profiles of the Si tracer in the silicide are almost flat. This thus proves that self-diffusion of the tracer atoms cannot be neglected as assumed in some published papers. In fact, several experimental tracer profiles are found to be flat in the silicide. Some numerical solutions for short-time annealing are also given to show how the tracer profile evolves. The result given here can also be used for many intermetallic reactions.
Photo-Hall analysis for inhomogeneously excited semiconductors
Authors: Meyer J. R. , Bartoli F. J. , Hoffman C. A.
Published: July 2002

A more rigorous numerical method for determining bulk semiconductor transport properties from photo-Hall data is presented and is used to determine compensation densities in narrow-gap HgCdTe. Previous studies have treated carrier density inhomogeneities by means of a two-layer approach, assuming a photoexcitation layer of constant thickness associated with either the absorption depth or the ambipolar diffusion length. Here, we show that this approximation can lead to significant error. For arbitrary optical intensities a more detailed integration over depth is required, properly accounting for the variation in the optical and transport of the material with carrier density and optical intensity. In the present technique, the spatial profile of the carrier density, n(z), is calculated as a function of optical intensity Φ0. The electron mobility μ is expanded in known functions of the carrier density. By using this n(Φ0,z) and μ(n), integral expressions for the net conductivity and Hall coefficient are then evaluated. The unknown coefficients in the mobility expansion are varied parametrically to obtain the best fits to the measured Hall coefficient and conductivity as a function of optical flux. From this fit, the electron mobility is determined as a function of carrier density. Detailed sample calculations are performed for the case of narrow-gap, n-type Hg1−xCdxTe at low temperatures assuming 10.6 μm CO2 laser excitation. Analysis of the photo-Hall data using the improved method leads to a reliable determination of compensation densities in this material.
Excitation of sodium atoms by electron impact
Authors: Ganas P. S.
Published: July 2002

A semiempirical analytic central potential model is used to calculate optical oscillator strengths, generalized oscillator strengths, and integrated cross sections up to 5 keV for electrons colliding with sodium atoms. The excitations 3s-np are discussed, and the results for 3s-3p are compared to experiment.
Extraction of microwave pulses from a superconducting cavity by gas discharge switch
Authors: Kobayashi Osamu , Minami Kazuo , Saeki Koshiro , Awano Mitsuru
Published: July 2002

Microwave energy stored in a superconducting cavity is released to an output circuit in a short time by a gas discharge switch which is different from previous works. Output pulse of 350 times the input cw power fed to the cavity is obtained. A cw microwave is incident on a superconducting lead cavity of TE011 cylindrical mode with resonant frequency 2.868 GHz and unloaded Q of 3.8×106. A small semicircular glass tube with two electrodes and with rarefied helium gas is set inside the cavity. Pulsed discharge current of the order of 100 A and time width 0.4 μsec produces high-density plasmas which may be equivalent to a metal loop antenna. Large microwave output pulses of time width 0.17 μsec are produced. It is suggested that the apparatus may be extended to millimeter microwave pulse production.
Measurement of a piezoelectric d constant for poly(vinylidene fluoride) transducers using pressure pulses
Authors: Bur Anthony J. , Roth Steven C.
Published: July 2002

The hydrostatic piezoelectric coefficient dh has been measured for biaxially-oriented poly(vinylidene fluoride) transducers using pressure pulses having peak values of 1.8×107 Pa (2600 psi) and a pulse width of approximately 10 ms. For these measurements, the sample was placed in an oil pressure chamber at room temperature and the pressure pulse was initiated by dropping a 16-kg mass onto a plunger in the chamber. Since adiabatic compressional heating accompanies the pressure pulse, temperature compensation of the transducer was necessary. This was achieved by incorporating a thermocouple in the bilaminate configuration of the transducer and by amplifying the thermocouple signal appropriately to account for the pyroelectric response due to adiabatic heating, which was approximately 15% of the transducer signal. The calculation of dh shows that the response of the bilaminate transducer is linear up to 1.8×107 Pa (2600 psi).
Fine-grained Au-Pb-Bi counterelectrodes for lead alloy Josephson junctions
Authors: Suzuki H. , Imamura T. , Hasuo S.
Published: July 2002

Fine-grained Pb-Bi films with smooth surfaces have been investigated for application to the counterelectrodes of lead alloy Josephson junctions. We have observed that reduced grain size and a smooth surface can be achieved by forming a 2-nm-thick Au seeding layer prior to the deposition of a 400-nm-thick Pb-Bi film. Experimental junctions have been made using Pb-Bi counterelectrodes with the ultrathin Au layer; and their I–V charcteristics have been evaluated. The quality of the junctions has been observed to be slightly reduced; however, they have exhibited excellent initial yield compared to junctions with the conventional Pb-Bi counter electrodes.
Use of electron beam techniques to study ion deposition in secondary ion mass spectrometry sputter craters
Authors: Brown J. D. , Rüdenauer F. G.
Published: July 2002

Electron beam techniques have been used to examine the topography and composition of sputter craters formed by an indium primary ion beam from a liquid metal ion source during secondary ion mass spectrometric analysis. Secondary electron images in a scanning electron microscope revealed the crater topography but the presence of implanted In from the primary ion beam could not be detected using an energy dispersive x-ray detector. Auger electron spectroscopy was used to detect the presence of In in the craters, and to establish the qualitative distribution of elements in and around the craters at the surface. Surface contamination of the specimens prevented quantitative interpretation. The total indium concentration distribution across the craters was measured in an electron probe microanalyzer with a crystal spectrometer. The technique can be used to measure total In in the bottom of the crater from which total sputter yield can be obtained.
Effect of annealing on the optical properties of ion-implanted Ge
Authors: Wang Kou-Wei , Spitzer William G. , Hubler Graham K. , Donovan Edward P.
Published: July 2002

Infrared reflection and transmission measurements are used to study (111)- and (100)-oriented Ge samples which were implanted with sufficient fluences to produce a continuous amorphous layer. Two optical states of amorphous Ge are identified: (i) as-implanted, amorphous state which has an infrared refractive index about 8% larger than that for single crystal Ge, nc=0.92 nI; (ii) thermally stabilized amorphous state with an intermediate refractive index, nII=(0.963±0.002)nI. A shift of the fundamental absorption edge to higher energy occurs with the transition from the as-implanted to the thermally stabilized, amorphous Ge state, but no change in the density is observed for the transition. Annealing at about 300 °C for 2 h produces the thermally stabilized state. Annealing for longer time or at higher temperatures causes measurable epitaxial regrowth. The regrowth rates and activation energies for both orientations are also determined and compared with values measured previously by another method. With the regrowth rate ∝e−Ea/kT, Ea =2.0 eV for both orientations and the regrowth rates at 350 °C are 46 Å/min for (100) orientation and 4.0 Å/min for (111) orientation, respectively.
Effects of growth temperature on optical and deep level spectroscopy of high-quality InP grown by metalorganic chemical vapor deposition
Authors: Pudensi M. A. A. , Mohammed K. , Merz J. L. , Kasemset D. , Hess K. L.
Published: July 2002

Deep level transient spectroscopy and photoluminescence were used to study the effect of growth temperature (TG=550–650 °C) on high-quality InP (ND−NA=1.5×1015 cm−3; μ77=41 000 cm2 V−1 s−1) grown by low pressure metalorganic chemical vapor deposition. A close relationship between deep levels and acceptor concentrations was found. Four electron traps were observed; not all of these traps have previously been observed in InP grown by metalorganic chemical vapor deposition. A metastable defect was detected in one of the samples.
Thermally stimulated scattering in plasmas
Authors: Dysthe K. B. , Mjo/lhus E. , Pécseli H. L. , Stenflo L.
Published: July 2002

A theory for stimulated scattering of a laser beam is formulated where the dominant nonlinearity is the ohmic heating of the plasma. The analysis is carried out with particular reference to experimental investigations of CO2 laser heating of a linear discharge plasma. In the conditions characterizing this experiment local heat conduction is of little importance and the dynamic evolution for the electron temperature is dominated by heating and energy exchange with the ion component. These features are incorporated in the analysis. The resulting set of equations gives a growth rate and characteristic scale size for the filaments, which agrees well with the experimental results.
Relationship between beam and junction parameters in ion beam processed Josephson devices
Authors: Kleinsasser A. W.
Published: July 2002

Planar and edge-defined niobium-lead alloy Josephson junctions were fabricated using an ion beam tunnel barrier process consisting of Ar cleaning and Ar/O2 oxidation, with ion energies as low as 50 eV in the oxidation step, during which the ion energy and flux, oxygen fraction, and process time control junction critical current density. The effect of these process parameters on junction properties was studied using a 30-mm ion source and 57-mm wafers. Both run-run and on-wafer spatial variations were measured. Comparison of ion flux profiles with distributions of junction critical current densities revealed that the Ar preclean step, as well as the oxidation step, is important in controlling process uniformity. The results indicate that uniformity adequate for large scale integrated circuit applications should be attainable.
Nondestructive surface testing method using focused ultrasonic surface and Lamb waves
Authors: Nongaillard B. , Ourak M. , Logette P. , Rouvaen J. M. , Gazalet M. G.
Published: July 2002

A very sensitive method for detection of surface defects is presented. This technique relies on the utilization of good quality focused surface ultrasonic sources. Experimental results on ceramic samples with artificial defects are reported. Using this method, a precise positioning and dimensioning of the defects may be performed.
The effect of local domain wall pinning variations on the energy dissipation in ferromagnetics
Authors: Lorenz Bryen E. , Coren Richard L.
Published: July 2002

Domain wall behavior is examined, including the effect of variations of the local pinning energy. By applying a sampling technique to the wall energy curve the local pinning force, equal to the negative gradient of the sampled function, is reduced to a series of weighted impulses. These weights are taken to have a statistical distribution. The equation of motion of the wall is solved using the Ritz–Galerkin averaging method and the average dissipated energy per cycle is computed as a function of the statistical distribution and the usual wall motion descriptors. The inclusion of pinning emphasizes the differences of wall kinetics and loss calculations made assuming sinusoidal field or sinusoidal induction. The cyclic loss is greater than that calculated ignoring the pinning; it is not proportional to frequency but approaches linearity at high frequencies.
Reduction of cell size in hybrid bubble memory devices (abstract)
Authors: Suzuki R. , Takeuchi T. , Takeshita M. , Ikeda T. , Umezaki H.
Published: July 2002

Hybrid bubble memory devices using ion-implanted and Permalloy bubble propagation tracks have been proposed and developed. In this paper, the reduction of the cell size from 4 to 3 μm will be discussed. In the hybrid devices, the minor loops are composed of ion-implanted tracks and the functions are composed of Permalloy tracks. To reduce the cell size, therefore, both of the tracks should be improved. For the 3-μm-period ion-implanted tracks, the bubble diameter is reduced from 1 to 0.8 μm. According to the reduction of a bubble diameter, magnetostrictive anisotropy Δλ=λ100−λ111 is increased from 5 to 8×10−6 because the Sm content is increased to increase the anisotropy field Hk. The large Δλ affects the characteristics of inside and outside turns in the ion-implanted tracks. To get a good margin for the turns, the anisotropy field change induced by ion implantation ΔHk should be larger than in 4-μm-period tracks. There is a new problem in 3-μm-period hybrid devices. In the hybrid devices, there is no deep ion implantation in the Permalloy track region, while there is a deep ion implantation in the ion-implanted track region. The effective bubble height is, therefore, different in the ion-implanted and Permalloy track region, and the bias field region where bubbles exist stable is different. In the typical 3-μm-period devices, the bias field region of the ion-implanted tracks is 20–30 Oe lower than that of the Permalloy tracks. The operating bias field adjustment (OBA) is needed. We have checked some OBA methods and found that the thinning of the garnet film in the Permalloy track region is a good method. Thinning the garnet film partially, the operating bias field can be adjusted easily and there is no harmful effect.
Surface acoustic wave attenuation in magnetic bubble garnet films
Authors: Hanna S. M. , Friedlaender F. J.
Published: July 2002

The magnetic field dependence of the surface acoustic wave (SAW) attenuation in magnetic bubble garnet films has been experimentally investigated. SAW delay lines have been fabricated on magnetic bubble garnet films. Interdigital transducers on a piezoelectric layer (zinc oxide film sputtered on top of the garnet film) have been used for acoustic wave generation and detection. Results of the attenuation measurements for different magnetic field orientations with respect to the SAW propagation direction are presented. The maximum increase in the SAW attenuation was observed when the applied dc magnetic field H was parallel to the surface wave propagation vector k. Minimum change in the SAW attenuation was observed when the magnetic field was applied perpendicular to k.
Energy storage of the atomic carbon laser in an electrical discharge
Authors: Zediker M. S. , Prelas M. A. , Miley G. H.
Published: July 2002

An experimental investigation of the atomic carbon laser’s energy storage was conducted with a rotating back mirror. The high rotational speed of the mirror allowed the laser cavity to be switched to a high Q configuration for various time delays after the discharge. This study, which combines results from experiments and computer simulations, revealed a short upper laser level lifetime of about 2 μsec. Thus, the lifetime of the upper laser state is too short to account for the delay observed (∼5 msec) in previous experiments on the atomic carbon nuclear-pumped laser.
Fluctuations and quantum domains in solid-state microdevices
Authors: Liboff Richard L.
Published: July 2002

The validity of employing classical macroscopic equations of motion to describe degenerate plasma domains is examined. It is argued that such analyses are inconsistent when fluctuations in charge-carrier number grows comparable to mean values. The following expression for relative mean-square fluctution of charge-carrier number away from the mean was applied to micro-solid-state samples. δN=(κe/n5/6) (m̄*T/ 300 V)1/2. In this expression n is number density of charge carriers, m̄* is effective mass divided by electron mass, V is volume, and κe is a constant. Employing this formula it was concluded that for n-type GaAs and InP at charge-carrier density=1017 cm3 and temperature 300 K, classical equations fail at dimensions less than ≂0.15 μm. For p-type GaAs and InP, under the same conditions, the critical length is ≂0.29 μm.