bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical and electronic properties of microcrystalline silicon as a function of microcrystallinity
Authors: Han Daxing , Yue Guozhen , Lorentzen J. D. , Lin Jing , Habuchi H. , Wang Qi
Published: July 2002

Films were prepared by hot wire chemical vapor deposition at ∼240 °C with varied hydrogen dilution ratios R=H2:SiH4 from 1 to 20. The optical and electronic properties as a function of microcrystallinity were studied. We found: (a) At low H dilution R⩽2, there is no measurable crystallinity by Raman spectroscopy and x-ray diffraction in the a-Si:H matrix, but an optical absorption peak at ∼1.25 eV appears; when R=2, the film shows the lowest subgap absorption, the highest photosensitivity, and the largest optical gap. (b) When R⩾3, the c-Si phase is measurable by Raman and a low-energy photoluminescence (PL) band (0.84–1.0 eV) appears in addition to the high-energy band (1.3–1.4 eV). Meanwhile, all the absorption spectra show a featureless line shape. (c) An energy redshift is observed for both PL peaks as the film grows thicker. Finally, (d) the conductivity activation energy first decreases from 0.68 to 0.12 eV, then increases with increasing microcrystallinity. A mode of two sets of energy bands of electronic states for these two-phase materials is suggested.
Radiative deformation
Authors: Arpaci V. S. , Esmaeeli A.
Published: July 2002

An infinitesimal change δQ in heat flux Q is shown, in terms of entropy flux Ψ=Q/T, to have two parts, δQ=TδΨ+ΨδT. The first part being the thermal displacement and the second part being the thermal deformation. Only the second part dissipates into internal energy and generates entropy. Thermodynamic arguments are extended to transport phenomena. It is shown that the thermal part of the rate of local entropy generation is related to the local rate of thermal deformation by s′′′=−ψi/T(∂T/∂xi), where ψi=qi/T, ψi being the rate of entropy flux vector, and qi the rate of heat flux vector. The part of this generation related to radiation is illustrated in terms of an example.
Fabrication of refractive index grating into azo-dye-containing polymer films by irreversible photoinduced bleaching
Authors: Hattori Toshiaki , Shibata Tomoaki , Onodera Sinji , Kaino Toshikuni
Published: July 2002

We report on the direct fabrication of refractive index gratings by irreversible photoinduced bleaching (photobleaching) into azo-dye-containing polymer films with a large second-order optical nonlinearity. Gratings were formed into azo-dye-doped or attached polymer films upon exposure to an interference pattern of two laser beams from second harmonic light at 532 nm of a mode-locked Nd: yttrium–aluminum–garnet laser. To investigate whether the refractive index grating is formed into the azo-dye-containing polymer films by the two-beam interference exposure, IR spectroscopy was examined. Absorption strength from an azo bond in the exposed polymer film reduced selectively as compared with that of unexposed film. Although surface relief structure with a few nanometers depth on the polymer film was observed by using atomic force microscopy, the modulation depth of the grating was very small. So, we considered that the effect of the relief structure to diffraction efficiency obtained here is negligible. Furthermore, the grating could not be erased by light. From these results, we confirmed that the grating obtained here was mainly caused by photobleaching, not by photoinduced birefringence and/or optically induced surface relief grating. In addition, highly efficient gratings, 20% or more, could be formed by using the azo-polymer film.
Microstructure of epitaxial Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films grown by metalorganic chemical vapor deposition
Authors: Stemmer S. , Bai G. R. , Browning N. D. , Streiffer S. K.
Published: July 2002

Epitaxial, perovskite Pb(Mg1/3Nb2/3)O3–PbTiO3 films were grown by metalorganic chemical vapor deposition under various deposition conditions and characterized by x-ray diffraction and transmission electron microscopy. Pyrochlore free films were obtained under all deposition conditions used in this study. Magnesium-rich growth conditions lead to the formation of a Mg-rich impurity phase in the films, embedded as coherent lamellae parallel to the growth direction. Depending on the growth conditions, a wide variation in the stoichiometry and volume fraction of this impurity phase was found between samples, whereas morphology and crystal structure were found to be very similar.
Oxidized ultrathin Fe films on Cu(001)
Authors: Koveshnikov Alexey N. , Madjoe Reginaldt H. , Karunamuni Jeevenanda , Stockbauer Roger L. , Kurtz Richard L.
Published: July 2002

We report photoemission studies of ultrathin films of the minority-spin conductor, Fe3O4 on a Cu(001) substrate. Fe films are deposited at room temperature and oxidized at 810 K in 10−6 Torr O2. For Fe films less than 2 ML thick, LEED and STM measurements show that oxidation produces mostly an FeO(111) while thicker Fe layers give Fe3O4(111). Photoemission reveals that there is a distinct electronic structure for these two phases. There are also significant differences between the electronic structures of ultrathin oxide films and those of corresponding bulk oxides.
Magnetic excitations in tetragonal HoCr2Si2
Authors: Moze O. , Rosenkranz S. , Osborn R. , Buschow K. H. J.
Published: July 2002

Magnetic excitations in tetragonal HoCr2Si2 have been measured by neutron spectroscopy. The temperature and Q dependence of the excitations measured at 8 K confirm that they can be attributed to crystal field (CF) dipolar transitions experienced by the Ho ion. The analysis of the neutron spectroscopy data for HoCr2Si2 is simplified by the fact that the CF coefficients have already been determined for the series RX2Si2 (R=rare earth, X=Cu, Ni) by neutron spectroscopy. In addition, electronic band structure calculations and experimental determinations of the electric field gradient for numerous compounds of the type RT2Si2 (T=Cr, Cu, Ni) show that the first-order CF coefficient, A20, changes sign when passing from the series RX2Si2 (X=Cr, Ni) to RCu2Si2. In the light of this information, the available neutron spectroscopy data for HoCr2Si2 are presented and discussed.
Time-dependent transport effects in CoFe/Al2O3 discontinuous multilayers
Authors: Kakazei G. N. , Lopes A. M. L. , Pogorelov Yu. G. , Santos J. A. M. , Sousa J. B. , Freitas P. P. , Cardoso S. , Snoeck E.
Published: July 2002

Discontinuous multilayered metal-insulator Co80Fe20(t)/Al2O3(30 Å) thin films with different values of nominal thickness t of metal layer were prepared by ion beam deposition. At t<14 Å, a new phenomenon of slow electric relaxation was found, suggesting formation of highly nonequilibrium electronic states in the process of tunnel transport in such systems. An extension of the well-known Sheng–Abeles approach on the case of finite concentrations of charged granules is proposed. Within mean-field approximation, it gives a general picture of this phenomenon, though the corrections due to correlation between charges can be essential.
Monte Carlo studies of the spin-glass-like phase in Fe0.25Zn0.75F2
Authors: Barbosa Paulo H. R. , Raposo E. P. , Coutinho-Filho M. D.
Published: July 2002

Monte Carlo results on the three-dimensional randomly-diluted Ising antiferromagnet FexZn1−xF2 indicate that its spin-glass-like phase at x=0.25 and zero magnetic field is characterized by the presence of finite antiferromagnetic domains, separated by random vacancies, but strongly correlated in time. The glassy behavior is a consequence of the combined action of short-range interactions and the presence of strong density fluctuations in the highly diluted regime, close to the percolation concentration. By studying the aging of the system, we also find that its dynamics is much alike that of theoretical spin-glass models.
Insulating ternary magnetic Co1−xMnyFex−yCl2⋅2H2O
Authors: DeFotis G. C. , Beveridge A. C. , Wilkens M. J. , Fuller Z. J. , McMahon J. G. , Wallo C. D.
Published: July 2002

The title system is the first mixed insulating magnet to be examined composed of three separate magnetic components. Each of the three possible binary mixtures based on the same isostructural MCl2⋅2H2O components has been examined. The Co/Fe mixture has competing orthogonal spin anisotropies, the Co/Mn mixture competing ferromagnetic and antiferromagnetic exchange interactions, and the Fe/Mn mixture both competing anisotropies and competing exchange interactions. Hence various pairwise competitions will occur in a ternary mixture of these components. Four different compositions are examined, with (x,y)=(0.830,0.681), (0.623,0.464), (0.539,0.377), and (0.366,0.272). These provide representative coverage of several interesting regions in the three binary T−x phase diagrams, specifically in terms of a relative binary composition (rbc) which can be defined for a ternary mixture in pairwise fashion. High temperature susceptibilities follow a Curie–Weiss form χM=C/(T−θ) rather well. Curie constants are approximately as expected based on fractions of different metal ions present, and both C and θ are closest to values characterizing the Co/Mn binary mixture. Low temperature susceptibilities exhibit features suggesting phase transitions. The temperatures at which these occur are often close to what might be anticipated from the binary T−x phase diagrams for the appropriate rbc. In certain cases, however, transitions anticipated on such a basis do not seem to be present. The ternary mixtures also exhibit behavior suggestive of spin glass properties.
Numerical analysis of magnetic field diffusion in ferromagnetic laminations by minimization of constitutive error
Authors: Fresa R. , Serpico C. , Visone C.
Published: July 2002

In this article, the diffusion of electromagnetic fields into a ferromagnetic lamination is numerically studied by means of an error-based numerical method. This technique has been developed so far only for the case of nonhysteretic constitutive relations. The generalization to the hysteretic case requires a modification of the technique in order to take into account the evolution of the “magnetization state” of the media. Numerical computations obtained by using this approach are reported and discussed.
Soft x-ray magnetic circular dichroism investigation of the spin reorientation transition in Nd2Fe14B
Authors: Garcı́a L. M. , Chaboy J. , Bartolomé F. , Goedkoop J. B.
Published: July 2002

A temperature dependent x-ray magnetic circular dichroism (XMCD) study at the Fe L2,3 and Nd M4,5 edges through the spin reorientation transition of a Nd2Fe14B single crystal is presented. Direct comparison of XMCD data with values of the magnetic moments derived from Mössbauer spectroscopy allows one to independently determine the evolution of the titling angle between Fe and Nd moments and the c axis. The experimental results evidence a strong noncollinearity between Fe and Nd magnetic moments in the low-temperature phase. A new result is the observed delay in the reorientation of the Fe sublattice with respect to that of the Nd sublattice by around 10 K.
Effect of degree of die upset on magnetic behavior in Nd13.9(Fe0.92Co0.08)80.3B5.3Ga0.5
Authors: Crew D. C. , Lewis L. H. , Welch D. O. , Panchanathan V.
Published: July 2002

DC demagnetization (DCD), isothermal remanent magnetization (IRM), and reversible magnetization measurements were used to examine the magnetic reversal behavior in melt-quenched samples of composition Nd13.9(Fe0.92Co0.08)80.3B5.3Ga0.5 subjected to different levels of thermomechanical deformation (die upsetting). The reversible magnetization measurements indicate that in the thermally demagnetized condition domain walls are present within the material for all levels of deformation. During demagnetization from a saturated state, domain walls are present in a minority of grains at low levels of deformation but these domain walls disappear at higher levels of deformation. This behavior is explained in terms of changes in the relative strengths of nucleation and pinning fields. Comparison of these results to previous results obtained on similar materials indicate that changes in the magnetization behavior with degree of deformation are more marked in samples which are free of Ga, indicating that Ga additions act to suppress the nucleation of new domain walls, presumably in the grain boundaries.
Phase formation and magnetic properties of SmFe7Nx+αFe composite thin films
Authors: Song J. M. , Nakano M. , Ogawa N. , Fukunaga H.
Published: July 2002

Sm(Zr)Fe 7 N x +α Fe composite thin films were prepared on various substrates with differing values of thermal expansion from SmxFebalZry (11.3≦x≦17.8,0≦y≦3.2) targets by the rf sputtering method followed by annealing and nitrogenation. Their phase formation and magnetic properties were studied. All of the as-deposited films were amorphous, and the only films synthesized from the target with x=84 were crystallized into a composite of Sm(Zr)Fe7+αFe by annealing. Successive nitrogenation of the films with x=84 formed Sm(Zr)Fe7Nx+αFe composites whose grain diameter was estimated to be 30–50 nm. Despite the small coercivity of the prepared films, their recoil curves showed a remarkable spring-back phenomenon which originates in the exchange coupling between Sm(Zr)Fe7Nx and α Fe grains. The addition of Zr decreased the lattice constant, and choice of substrate did not affect the grain size.
Bias study on seed-layered DSMR head
Authors: Guo Yimin
Published: July 2002

Bias profile of a DSMR head with conductive seed layers is studied by utilizing a transmission-line model. A closed-form analytical formula has been obtained as a function of head geometry and current shunting. It is found that if the two magnetic sensing elements are still symmetrically located between shields as before, the first MR element bias angle would be reduced while the second MR element bias angle would be increased by the same amount which is proportional to the shunting current if no saturation occurs at middle of bias profile. Studies also suggest that keeping the same total read gap length the bias angle difference is smaller when the two MR elements are designed to be closer to each other. Shifting both the two MR elements toward the top shield with a certain small distance is found to be more effective to compensate bias angle difference through introducing asymmetric image current fields.
Controlling garnet film composition by magnetic-field-controlled radio frequency magnetron sputtering
Authors: Furuya A. , Baubet C. , Yoshikawa H. , Tanabe T. , Hirono S. , Yamamoto M. , Tailhades P. , Bouet L. , Despax C. , Presmanes L. , Rousset A.
Published: July 2002

To find a way to control the compositional change in Bi-substituted garnet during sputtering, we studied the effects of controlling the cathode magnetic field. The magnetic-field-controlled rf magnetron sputtering method that we developed can create a garnet film whose composition is the same as that of the sputtering target. When we deposited a film of Bi-substituted Dy iron garnet–ferrite (Bi2DyFe4GaO12) by this method, there was no compositional change between the target and the film even after a long sputtering process. Therefore, this sputtering method is effective at suppressing compositional change during the film formation process.
Anomalous low temperature magnetoresistance in polycrystalline CeFe2
Authors: Radha S. , Roy S. B. , Nigam A. K.
Published: July 2002

Results of magnetoresistance measurements on a polycrystalline sample of CeFe2 are presented. The sample has been characterized as a ferromagnet below 230 K. A fairly large positive magnetoresistance is observed below 50 K that is indicative of the presence of an antiferromagnetic interaction over the mean free path length. At higher temperatures the magnetoresistance is characteristic of a ferromagnet. The study suggests the existence of stable antiferromagnetic correlations in high fields at low temperatures in this compound.
Magnetic, Mössbauer and magnetostrictive studies of amorphous Tb(Fe0.55Co0.45)1.5 films
Authors: Danh T. M. , Duc N. H. , Thanh H. N. , Teillet J.
Published: July 2002

The Tb(Fe0.55Co0.45)1.5 films were fabricated by rf magnetron sputtering from a composite target. Samples were investigated by means of x-ray diffraction, vibrating sample magnetometer, conversion electron Mössbauer spectra, and magnetostriction measurements. The as-deposited film is an amorphous alloy with a perpendicular magnetic anisotropy and an intrinsic magnetostriction λ=1080×10−6 in an applied field of 0.7 T. In this state, it was determined that the hyperfine field Bhf=23.5 T and the cone-angle between the Fe moment direction and the film-normal direction β=12°. After annealing in the temperature range of TA=250–450 °C the amorphous structure still remained, however the anisotropy was changed to a parallel one. The soft magnetostrictive behavior has also been improved by these heat treatments: the parallel magnetostriction λ∥=465×10−6 was almost developed in low applied fields of less than 0.1 T and, especially, a huge magnetostrictive susceptibility χλ=dλ∥/d(μ0H)=1.8×10−2 T−1 was obtained at μ0H=15 mT.
The effect of Pd coating on electron emission from silicon field emitter arrays
Authors: Lee Jong-Lam , Oh Sang Pyo , Youn Han Sang , Kang Seung-Youl , Lee Jin Ho , Cho Kyoung Ik
Published: July 2002

Uniform silicon tip arrays were fabricated using the reactive ion etching followed by the reoxidation sharpening, and the effect of Pd-coated layer on electron emission characteristics was studied. The electron emission from Si field emitter arrays (FEAs) was a little improved by removing surface oxide on the FEA, but pronounced drastically by coating 100-Å-thick Pd metal layer. The turn-on voltage in the Pd-coated Si FEAs reduced by 30 V in comparison with that in noncoated ones. This is resulted from the increase of surface roughness at the tip apex by the Pd coating on Si FEA, via the decrease of the apex radius at which electrons are emitting. The Pd-coated emitters showed superior operating stability over a wide current range to that of the noncoated ones. This suggests that Pd coating enhanced the high temperature stability and surface inertness of Si FEA.
Influence of annealing ambient on oxygen out-diffusion in Czochralski silicon
Authors: Yamazaki Hideyuki , Matsushita Hiroshi , Sugamoto Junji , Tsuchiya Norihiko
Published: July 2002

The out-diffusion of oxygen in Czochralski grown silicon (100) wafers annealed at high temperature under a hydrogen or an argon ambient has been investigated by secondary ion mass spectrometry (SIMS). The wafers were annealed with three successive process: loading of wafers into furnace at 850 °C then ramping up, annealing at 1200 °C for 1 h, and ramping down from 1200 to 850 °C. It was found that oxygen diffusivities obtained from the above two kinds of samples showed almost the same values. Also, no difference in the oxygen concentration of the subsurface region in Si was observed between the above two kinds of samples within SIMS detection limit of 2×1016 atoms/cm3. The result indicates that there is no significant difference in oxygen diffusivity between the two annealing ambients of hydrogen and argon gases.
Comment on “Hydrogen–oxygen interaction in silicon at around 50 °C” [J. Appl. Phys. 83, 2988 (1998)]
Authors: Herring Conyers , Johnson N. M.
Published: July 2002

In a study of the kinetics of binding of presumed H2 complexes in silicon to monatomic oxygen impurities, Markevich and Suezawa [J. Appl. Phys. 83, 2988 (1998)] were able to infer a diffusion coefficient for the isolated H2 species. We point out here that to within experimental accuracy this diffusion coefficient agrees both in magnitude and in temperature dependence with the diffusion coefficient measured by us in 1991 for a neutral, spinless hydrogen species commonly found in plasma-hydrogenated n-type silicon. The agreement not only supports the validity of both types of measurements, but also encourages the interpretation that the same hydrogen complex (presumably H2 at or near a tetrahedral site) was dominant in both experiments and diffuses by a single mechanism dominant from 305 to 473 K and independent of concentration over a wide range.
Response to “Comment on ‘Hydrogen–oxygen interaction in silicon at around 50 °C’ ” [J. Appl. Phys. 87, 4635 (2000)]
Authors: Markevich V. P. , Suezawa M.
Published: July 2002

Experimental results related to investigations of the hydrogen (deuterium) molecule diffusivity in Si crystals are discussed.
Comment on “ZnGeP2 birefringence and its temperature dispersion using polarized interference” [J. Appl. Phys. 81, 425 (1997); 77, 5942 (1995)]
Authors: Bhar G. C. , Kumbhakar P.
Published: July 2002

Fischer and Ohmer [J. Appl. Phys. 81, 425 (1997); 77, 5942 (1995)] could not explain the paradox concerning the anomalously low phase matching angle for second harmonic generation of CO2 laser radiation in ZnGeP2 crystal by their measured birefringence and its temperature dependence. Based on their measured birefringence and its temperature dispersion we have shown that a temperature rise of such crystal by 150 °C or so, is enough to explain this anomaly.
Time and orientation dependence of ordering in anodized aluminum for self-organized magnetic arrays
Authors: Lu Bin , Bharathulwar Shravan , Laughlin David E. , Lambeth David N.
Published: July 2002

Anodization experiments to create alumina pores were performed using pure Al and hard disk Al–Mg substrates. A single step anodization was employed for up to 40 h to determine the time dependence of pore ordering. The pores formed from the Al–Mg substrate were unordered, while ordered-pore domains as large as 3 μm form in both the as-rolled and annealed pure Al samples. The effect of the aluminum grain crystallographic orientation was investigated via orientation-imaging microscopy for the pure Al surface with both order and disordered pores. It was found that neither heat treatment nor crystallographic orientation played a large role in the pore ordering.
Magnetic anisotropy of transition-metal and rare earth compound Nd2BaNiO5
Authors: Okazaki Makoto , Tanaka Norikazu , Motizuki Kazuko
Published: July 2002

The origin of magnetic anisotropy of each Ni2+ and Nd3+ ion in the antiferromagnetic Nd2BaNiO5, which is a related compound with the one-dimensional Haldane system Y2BaNiO5, is studied. First, we calculate the energy splitting of the orbital state of the Ni2+ ion (3F state) and that of the degenerated J state of the Nd3+ ion (4I9/2 state) due to the crystalline electric field. For the Ni2+ ion, Pryce’s spin Hamiltonian is derived and the single-ion type anisotropy constants are evaluated. The result indicates that the easy direction of the spin of the Ni2+ ion is parallel to the a axis. For the Nd3+ ion, the ground state is given by a doublet. To discuss the easy direction of the magnetic moment −gJμBJ, we calculate the magnetic susceptibility. As the result the easy direction of the magnetic moment of the Nd3+ ion is found to be parallel to the c axis. Furthermore, an effect of the magnetic dipole-dipole interaction on magnetic anisotropy is investigated.
Magnetic anisotropy in antiferromagnetic layers affecting exchange bias of Ni–Fe/Mn–Ir bilayers
Authors: Yagami Kojiro , Tsunoda Masakiyo , Takahashi Migaku
Published: July 2002

The magnetic anisotropy of antiferromagnetic layers (KAF) was estimated for Ni–Fe 50 Å/Mn–Ir dAF bilayers using Mauri’s method (dAFcr=JKs/KAF), where JKs is the saturation value of the unidirectional anisotropy constant (JK). The critical thickness of the antiferromagnetic layers (dAFcr), at which JK took half the value of JKs, was determined from the dependence of JK on dAF. The dAFcr was found to be almost constant (35±2 Å) independent of JKs. Thus, the relation of JKs∝KAF was derived, suggesting that the variation in JKs is due to a change in the value of KAF. JKs, however, was found to vary considerably for various Mn–Ir films possessing an almost identical Ir content, and thus probably the same value of KAF. In addition, studies by x-ray diffraction, transmission electron microscopy, and electron diffraction revealed that the change in JKs was independent of the microstructure and phase of the antiferromagnetic (AF) Mn–Ir films, both of which control KAF. Thus, JKs was found to be independent of KAF contradicting the relation, JKs∝KAF. This contradiction results from the assumption by Mauri that the coupling energy (J) is equal to JKs even in the polycrystalline exchange-coupled bilayers. A model that took account of the distribution of KAF axes of AF grains in the plane of the AF film successfully explained the behavior of JK. JKs was found to change independent of both J and KAF, and furthermore, it has been shown that the dependence of JKs on the sputtering conditions for Mn–Ir films is probably due to the effective temperature of the films during deposition.
Single-crystal YIG phase shifter using composite stripline structure at X band
Authors: How Hoton , Shi Pin , Vittoria Carmine , Kempel Leo C. , Trott Keith D.
Published: July 2002

A tunable phase shifter at X band using single-crystal YIG film material grown on GGG substrates is fabricated. The phase shifter is a quarter wavelength in the absence of a bias magnetic field. The phase can be tuned 120° by varying the bias magnetic field from 3440 to 3720 Oe. The resultant variation in insertion loss was 0.5 dB. Measurements compared very well with calculations.
Hybrid transmission line-micromagnetic model for MR heads
Authors: Wang Lei , Giusti James H. , Fernandez-de-Castro Juan
Published: July 2002

A hybrid transmission line-micromagnetic model for a shielded MR read head is described. In this model, the magnetostatic potentials and magnetization orientation angles in the magnetic films of a sensor stack satisfy the transmission line and micromagnetic equations. This coupled system of partial differential equations is solved by a finite difference method with nonuniform mesh. The magnetic flux entering the sensor from the media or permanent magnets are calculated by reciprocity. The hybrid model is found to agree closely with a conventional micromagnetic model for magnetization distributions in the sensor.
Screened exact exchange functional calculations of the spin-wave dispersion in transition metals
Authors: Zein N. E. , Antropov V. P. , Harmon B. N.
Published: July 2002

The screened “exact” nonlocal exchange approach is applied to the calculation of magnetic susceptibility of transition metals, particularly to the calculation of spin-wave dispersion. We discuss the choice of an appropriate approach and aspects of linear muffin-tin orbital-atomic sphere approximation (ASA) calculations, in particular calculation of the Green function in the three-center approximation. We calculated transverse spin-wave frequencies in Fe with the local density approximation and with the nonlocal functional using both the “frozen” magnon method and calculation of bound state energies (corresponding to spin-wave excitations).
Spatial and spatiotemporal self-focusing of spin waves in garnet films observed by space- and time-resolved Brillouin light scattering
Authors: Büttner O. , Bauer M. , Demokritov S. O. , Hillebrands B. , Kivshar Yu. S. , Grimalsky V. , Rapoport Yu. , Kostylev M. P. , Kalinikos B. A. , Slavin A. N.
Published: July 2002

A new advanced space- and time-resolved Brillouin light scattering technique is used to study diffraction of two-dimensional beams and pulses of dipolar spin waves excited by strip-line antennas in tangentially magnetized garnet films. The technique is an effective tool for investigations of two-dimensional spin wave propagation with high spatial and temporal resolution. Nonlinear effects such as stationary and nonstationary self-focusing are investigated in detail. It is shown that nonlinear diffraction of a stationary backward volume magnetostatic wave (BVMSW) beam, having a finite transverse aperture, leads to self-focusing of the beam at one spatial point. Diffraction of a finite-duration (nonstationary) BVMSW pulse leads to space–time self-focusing and formation of a strongly localized two-dimensional wave packet (spin wave bullet).
Giant magnetoresistance of Fe/Cu/Fe(001) trilayers grown directly on GaAs(001)
Authors: Monchesky T. L. , Urban R. , Heinrich B. , Klaua M. , Kirschner J.
Published: July 2002

The giant magnetoresistance of crystalline Fe/Cu/Fe(001) epitaxial structures characterized by scanning tunneling microscopy are presented. Fe/Cu/Fe(001) trilayers capped with Au are grown directly on GaAs(001) using a new procedure for producing pure Fe layers with As-free Fe surfaces on GaAs(001). The temperature dependence of the magnetoconductance and sheet resistance measured from 4 to 300 K is modeled by the Boltzmann equation assuming that the mean free paths in the crystalline epitaxial layers are equal to those in bulk materials. The results of the simple model suggest that the coefficient of the specular scattering at the Fe/GaAs interface is R=0.45, while the scattering at the outer Au interface is diffuse. Spin asymmetry scattering at the metallic interfaces is ΔT=|T↑−T↓|=0.34, Tavg=(T↑+T↓)/2=0.79. The sheet resistance was best modeled using a low temperature mean free path of 25 nm in the Fe layer.
Ab initio calculations of giant magnetoresistance
Authors: Binder J. , Zahn P. , Mertig I.
Published: July 2002

We present ab initio calculations of the giant magnetoresistance in magnetic multilayers. The electronic structure of the multilayers is calculated by spin density functional theory using a screened Korringa–Kohn–Rostoker method. The scattering of nanostructural defects in the multilayers is described by means of a Green’s function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasiclassically solving the Boltzmann equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the Boltzmann equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). Since we consider ferromagnetic systems a two current model is applied. Trends of residual resistivities and giant magnetoresistance ratios are discussed for Co/Cu multilayers with 3d transition metal defects.
Effect of Ga addition to the Pr3(Fe,Co,Ti)29 (3:29) system
Authors: Sirisha K. , Huang M.-Q. , McHenry M. E. , Chen Q. , Ma B. M.
Published: July 2002

Polycrystalline Ga-substituted Pr3(Fe1−xCox)27.5Ti1.5 (x=0.3,0.4) magnets have been studied for high temperature permanent magnets. Using x-ray diffraction, in addition to the majority 3:29 phase, the presence of the minority 2:17, 1:12 and α-Fe phases was observed. An increase in TC was observed with increasing Co content. A TC as high as 572 °C was observed for x=0.4. Magnetic measurements at room temperature showed an increase in the anisotropy field HA with increasing Co and Ga concentration, while the coercivity decreased. Scanning electron microscopy and energy dispersive x-ray analysis measurements indicated the 3:29 phase as the majority phase.
Temperature dependence of anomalous currents in worst-bit cells in dynamic random-access memories
Authors: Yamaguchi Ken
Published: July 2002

Anomalous currents (I) in worst-bit cells in high-density dynamic random-access memories are theoretically analyzed with temperature (T) as a parameter. And activation energy (Ea) is evaluated from the slopes of (log I) versus (1/T) plots. It is found that the anomaly in Ea as a function of applied bias (V), i.e., a steep decrease and saturation in Ea–V curves, can be clearly explained by introducing spatial locality in the deep-trap distribution. Moreover, it is shown that the anomaly in Ea–V curves occurs synchronously with an anomaly of current; i.e., a steep increase and saturation in I–V curves. Simulated electron-hole distributions clarify the physical mechanism of these anomalies; that is, when applied reverse bias is low and the spatially localized deep traps are outside of the depletion layer, Ea is near Eg because of electrical nonactivity of deep traps. And when applied reverse bias is high and the deep traps are spatially included in the depletion layer, carriers generated from deep-trap centers dominate the carrier transport and Ea is around the energy level (Et) of deep traps located near the midgap. The steep decrease in Ea is thus a result from mixing of the two energy levels (Eg and midgap). Further, it is found that deep-trap-assisted tunneling under a high-field condition reduces Ea. The activation energy defined by the slope in the (log I) versus (1/T) plots is therefore not considered a direct indicator of real Et.
Charge separation technique for metal–oxide–silicon capacitors in the presence of hydrogen deactivated dopants
Authors: Witczak Steven C. , Winokur Peter S. , Lacoe Ronald C. , Mayer Donald C.
Published: July 2002

An improved charge separation technique for metal–oxide–silicon (MOS) capacitors is presented which accounts for the deactivation of substrate dopants by hydrogen at elevated irradiation temperatures or small irradiation biases. Using high-frequency capacitance–voltage measurements, radiation-induced inversion voltage shifts are separated into components due to oxide trapped charge, interface traps, and deactivated dopants, where the latter is computed from a reduction in Si capacitance. In the limit of no radiation-induced dopant deactivation, this approach reduces to the standard midgap charge separation technique used widely for the analysis of room-temperature irradiations. The technique is demonstrated on a p-type MOS capacitor irradiated with Co60 γ rays at 100 °C and zero bias, where the dopant deactivation is significant.
Structure of randomly cross-linked networks. A theoretical relationship between the molecular weight between cross links and the cycle rank, and its comparison with experiment
Authors: Queslel J. P. , Mark J. E.
Published: July 2002

Randomly cross-linked networks have a complex topology. The determination of their cross-link density is still a challenge since no definitive relationships have been established between Mc, the molecular weight between junctions, and macroscopic characteristics such as the modulus or volume fraction of polymer present at swelling equilibrium. It is shown here that a simple relationship exists between Mc, Mn (the number average molecular weight of the primary chains), and ξ, the cycle rank for regular networks having no defects other than chain ends. Specifically: ξ/V0=(ρ/2Mc)(1−3Mc/Mn), where V0 and ρ are the network volume and density, respectively. Since the cycle rank is directly related to the phantom modulus, it is also shown that the later Flory–Erman theory treating entanglements as restrictions on junction fluctuations can be successfully used to determine Mc. Some experimental results are given. The Flory–Erman proportionality constant I is calculated and found to be in good agreement with values reported in the literature.
Laser induced fluorescence of the MgCa molecule
Authors: Atmanspacher H. , Scheingraber H. , Vidal C. R.
Published: July 2002

Using the radiation of several ion laser lines and of a tunable dye laser, the first gas phase spectra of the MgCa molecule have been obtained. The laser induced fluorescence spectra have been assigned to the A 1Σ+–X 1Σ+, B 1Π–X 1Σ+, and the C 1Σ+–X 1Σ+ systems. The quantum numbers of the levels belonging to the X 1Σ+ ground state were determined using a quantum mechanical, variational method. The vibrational quantum numbers of the excited levels and the assignment to the different electronic states were obtained from a comparison of the measured and calculated Franck–Condon factors which are in very good agreement.
Dynamics of polymeric fractals
Authors: Muthukumar M.
Published: July 2002

We present an effective medium theory of the viscosity of a solution containing polymeric fractals. Both the intra- and interfractal hydrodynamic interactions and the excluded volume effect are included. Suppressing the entanglement effects, we have obtained explicit formulas for the viscosity at arbitrary frequencies and polymer concentrations. The concentration dependence of the screening length of the hydrodynamic interaction is also derived. The dependence of the viscosity of the solution on the fractal and spectral dimensions of the suspended fractals is also discussed.
The bound and quasibound levels of 6Li2 a 3Σ+u
Authors: Xie Xingbin , Field R. W.
Published: July 2002

Rotationally resolved 6Li2 2 3Πg→a 3Σ+u fluorescence spectra have been obtained by perturbation facilitated optical–optical double resonance spectroscopy. Principal molecular constants for the a 3Σ+u first excited state of 6Li2 are (2σ uncertainties): Te =8180.9±5.4 cm−1, ωe =73.0±1.4 cm−1, ωexe =3.95±0.14 cm−1, Re =4.13±0.08 Å, and De =336.0±5.4 cm−1. Transitions into 0≤v≤6 and N=18, 20, 31, 33 were observed and the total number of bound rotation–vibration levels was computed to be 193 for the a 3Σ+u state of 6Li2.
A
b i
n
i
t
i
o pseudopotential study of the first row transition metal monoxides and iron monohydride
Authors: Dolg M. , Wedig U. , Stoll H. , Preuss H.
Published: July 2002

Spectroscopic constants for the ground states of the first row transition metal monoxides and iron monohydride have been determined from SCF and CI(SD) calculations using energy-adjusted ab initio pseudopotentials representing the Ne-like X(Z−10)+ cores of the transition metals. For iron monoxide and iron monohydride excited states have also been investigated and electron affinities have been determined.
Kinetic theory of inhomogeneous fluid: Tracer diffusion
Authors: Davis H. Ted
Published: July 2002

Enskog’s kinetic theory of dense hard sphere fluids, modified to allow long-ranged attractive interactions in a mean field sense, is used to derive the friction and tracer diffusion coefficient tensors for strongly inhomogeneous fluid. The kinetic equation yields the exact Yvon–Born–Green equations for the density distributions at equilibrium. Resulting formulas for the friction and diffusion coefficients are similar to the Enskog formulas for homogeneous fluid except that in inhomogeneous fluid they are tensors and they are computed as local averages of the product of the local density and pair correlation function. With a suitable closure approximation for the pair correlation function, such as that introduced by Fischer, the theory provides for the first time a tractable, unified approximation for computing density distributions and tracer diffusion coefficients in fluids in interfacial regions, microporous solids, and external fields.
Fluctuation-based computer calculation of partial molar properties. I. Molecular dynamics simulation of constant volume fluctuations
Authors: Debenedetti Pablo G.
Published: July 2002

Partial molar volumes, energies, and enthalpies are calculated via the (N,U,V) molecular dynamics implementation of their corresponding operational definitions in terms of constant volume fluctuations. The method is exact for the former property but only approximate for the latter two. The partial molar volume operational definition satisfies Euler’s homogeneous function theorem identically. The corresponding energy definition is based upon a differential equation and does not, therefore, satisfy the homogeneity constraint identically. A numerically unimportant but conceptually profound correction to the recently derived partial molar energy operational definition is incorporated and its theoretical implications discussed.
A
b i
n
i
t
i
o calculations on the energy of activation and tunneling in the automerization of cyclobutadiene
Authors: Čársky Petr , Bartlett Rodney J. , Fitzgerald George , Noga Jozef , Špirko Vladimír
Published: July 2002

Results of ab initio two-configuration CI-SD/[3s2p1d/2s], MBPT(4), CCSD+T(CCSD), and CCSDT-1 calculations are reported for the rectangular D2h equilibrium and square D4h transition structures of cyclobutadiene. The latter is a classic example of a multireference correlated method. The optimum CC and CH bond lengths found for the D4h transition structure are 1.448 and 1.093 Å, respectively. The activation barrier for the automerization is 9.0 kcal/mol at the two-reference GVB-CISD level while the single reference CCSD gives 19.9, 14.4 for CCSD+T(CCSD) and finally a dramatic change to 9.5 at the highest CCSDT-1 level. The importance of triples in overcoming the multireference character at the transition state is apparent. On the other hand, GVB-CISD is simpler than CCSDT-1 which attests to the importance of a qualitatively correct multireference starting point for this example. A less sophisticated computational method, GVB/4-31G, which also gives a reasonable barrier of 10.2 kcal/mol was used for the construction of the two-dimensional potential surface of automerization. The following lowest vibrational energies were obtained for this surface (v1 and v2, the symmetric and antisymmetric CC stretches in D4h symmetry, are given in parentheses): 0 and 4.2 cm−1 (00+; 00−); 1526.1 and 1607.6 cm−1 (01+; 01−), 1480.9, and 1485.5 cm−1 (10+; 10−), and 791.6 cm−1 for the zero-point energy (00+). The computed splitting of the vibrational ground state implies the rate of automerization is k=2.5×1011 s−1 for temperatures close to absolute zero.
Laser spectroscopy of NiO: The 3Σ− ground state
Authors: Srdanov Vojislav I. , Harris David O.
Published: July 2002

The results of the first rotational analysis of NiO are reported. Several bands in the green spectra region were resolved and analyzed using laser induced fluorescence (LIF). It was found that the symmetry of the well behaved ground electronic state is 3Σ− as was predicted by ab initio calculations. Moreover, the analysis showed that the angular momentum coupling scheme can be described as intermediate between Hund’s coupling cases (b) and (c). A least-squares fit of the ground state combination differences gave re=1.627 Å.
Normal mode analysis of surface adsorbed and coordinated pyridine molecule
Authors: Mizutani G. , Ushioda S.
Published: July 2002

We have carried out a normal mode analysis of the molecular vibrations of pyridine adsorbed on silver surfaces or coordinated to various molecules and ions. There are two types of bonding that result in distinct shift patterns of the normal mode frequencies upon adsorption or coordination. ‘‘Metal ion-type bonding’’ is characterized by a strong pyridine–substrate bond which results in large frequency shifts, while ‘‘halogen-type bonding’’ causes comparatively smaller shifts due to weaker bonding. Adsorption on silver surfaces corresponds to weak halogen-type bonding, and the major cause of the observed frequency shift is the electron transfer (back donation) into the aromatic ring upon adsorption.
Cross sections and photoelectron asymmetry parameters for photoionization of H2O
Authors: Machado L. E. , Brescansin L. M. , Lima M. A. P. , Braunstein M. , McKoy V.
Published: July 2002

The iterative Schwinger variational method is used to obtain cross sections and photoelectron asymmetry parameters for photoionization of the three outermost valence orbitals (1b1, 3a1, and 1b2) of H2O for photon energies from near threshold to 50 eV. A comparison of these calculated results with available experimental data is encouraging.
New method in time-dependent quantum scattering theory: Integrating the wave function in the interaction picture
Authors: Zhang John Z. H.
Published: July 2002

A new approach for solving the time-dependent wave function in quantum scattering problem is presented. The conventional wave packet method, which directly solves the time-dependent Schrödinger equation, normally requires a large number of grid points since the Schrödinger picture wave function both travels and spreads in time. Also, since the Schrödinger picture wave function oscillates in time with frequency ω=E/ℏ, a very small time increment is required to integrate the Schrödinger equation, especially for high energy collisions. The new method presented in this paper transforms the Schrödinger picture wave function into the interaction picture and carries out the integration in it. The new approach is superior to conventional one in that (1) a smaller numerical grid is required due to the localized nature of the interaction picture wave function, since it is not a traveling wave and does not spread appreciably in coordinate space, and thus behaves like a bound state wave function. (2) The interaction picture wave function varies slowly with time and is essentially independent of energy, permitting the use of a large time increment in the numerical integration. Because of these two features in this new approach, we are able to integrate the time dependent wave function once and obtain an accurate S matrix over a wide range of energy efficiently.
Efficient state-specific preparation of highly vibrationally excited NO(X 2Π)
Authors: Yang X. , Wodtke A. M.
Published: July 2002

Vibrational levels of nitric oxide (NO) X 2Π from v″=8–24, whose energies vary from 1.76 to 4.61 eV, have been produced using the stimulated emission pumping (SEP) technique. A narrowband tunable argon fluoride laser is used to access the B 2Π state which provides good Franck–Condon overlap with many vibrational levels of the ground electronic state. Saturation of the transitions is achieved at low pulse energies providing high pumping efficiency. Both spin–orbit states of NO are accessible with this scheme. Accurate molecular constants for v″=23 and 24 are given for the first time. The feasibility of an optically pumped infrared laser is discussed.
On the dissociation energy of Mg2
Authors: Partridge Harry , Bauschlicher Charles W. , Pettersson Lars G. M. , McLean A. D. , Liu Bowen , Yoshimine M. , Komornicki Andrew
Published: July 2002

The bonding in the X 1Σ+g state of Mg2 is investigated using near-complete valence one-particle Slater and Gaussian basis sets containing up to h functions. Full configuration interaction (FCI) calculations are used to calibrate four-electron correlation treatments. We show that the four-electron complete CI limit can be approached using a sequence of either second-order CI (SOCI) or interacting correlated fragment (ICF) calculations. At the valence level, our best estimate of the dissociation energy (De) is 464 cm−1. We show that this is a lower limit and probably within 5 cm−1 of the complete basis value. The inclusion of core–valence correlation using a model operator approach decreases De by about 35 cm−1 and increases the bond length by 0.03 a0, thereby yielding spectroscopic constants in good agreement with experiment. Attempts to compute the core–valence effect accurately by expanding the CI treatment were unsuccessful.