bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties and superconductivity in Ce-doped (Nd1−xGdx)2CuO4 (abstract)
Authors: Jardim R. F. , Becerra C. C. , Paduan-Filho A.
Published: July 2002

Nd2CuO4 and Gd2CuO4 present antiferromagnetic ordering associated with the rare-earth ions at about 2 and 6.8 K, respectively. We report measurements of the ac susceptibility in polycrystalline samples of Gd2CuO4 and (Nd1−xGdx)2CuO4. The data in Gd2CuO4 in fields up to 30 kG show evidence of the existence of a spin-flop transiton around 2 kG at low temperatures. The samples of the (Nd1−xGdx)2CuO4 showed Néel temperature associated with the antiferromagnetic ordering of the rare-earth ions between 6.8<Tn(x)<2.1 K, 1<x<0.45, and Tn below 1.5 K for x=0.15 and 0.30. Our major interest in this work is to study Ce doping in (Nd1−xGdx)2CuO4 in order to explore the interplay between magnetism and superconductivity.
High-field magnetization process in randomly diluted metamagnet Fe1−xMgxTiO3
Authors: Kato H. , Nakagawa Y. , Hosoya S. , Kido G. , Nakagawa M. , Fukuda T.
Published: July 2002

The high-field magnetization process in the randomly diluted metamagnet Fe1−xMgxTiO3 has been investigated in single crystal samples with x≤0.3 by using dc magnetic fields of up to 300 kOe generated by a hybrid magnet. In contrast to the sharp metamagnetic transition along the hexagonal c axis observed in FeTiO3, the diluted compounds show a considerable smearing in the transition with increasing Mg concentration. When the field is applied along the a axis at 4.2 K, a sudden jump in magnetization occurs at 235 kOe in FeTiO3, while no anomaly is observed up to 300 kOe along the a* axis which is taken to be perpendicular to both c and a axes. The jump field is lower in the diluted compounds. For the sample with x=0.185 we have also observed an anomalous increase in magnetization along the a* axis at 270 kOe.
Some new ternary ferromagnets (abstract)
Authors: Webb David J. , Kuromoto Traci Y. , Kauzlarich Susan M.
Published: July 2002

A number of new ternary ferromagnetic compounds have been prepared1 which have the general formula A14MnX11 (A=Ca, Sr and X=As, Sb, or Bi) and are isostructural to the main group Zintl compounds Ca14GaAs11 (Ref. 2) and Ca14AlSb11.3 The Mn-Mn nearest-neighbor distances in these compounds are ≥11 Å. Each of the compounds containing Mn is a metallic ferromagnet with a Curie transition in the neighborhood of 40–60 K. From magnetization measurements in the paramagnetic regime it appears that the Mn has a valence of +3 and that there are good local moments associated with the four unpaired electrons. This is in contrast to the low-temperature state in which the ordered ferromagnetic moment is only about 2.5 μB/Mn. Since no structural change is found upon cooling the sample below the Curie temperature and resistivity measurements show a strong interaction between the conduction electrons and the local moments, we suggest that the ferromagnetic moment is reduced by coupling with the conduction electrons.
Frequency characteristics of the complex permeability and its application to the FEM solutions of hysteretic fields
Authors: Hayano S. , Miyazaki A. , Saito Y.
Published: July 2002

A complex permeability is derived from a Chua-type magnetization model. The frequency characteristic of the complex permeability is calculated and compared with those of experiments. This complex permeability is applied to obtain the finite-element solutions of hysteretic fields. Examination of the field distributions suggests that the frequency characteristic of the magnetic materials is mainly dominated by the essential feature of complex permeability not the field distribution effects such as a skin effect.
Side writing/reading in magnetic recording
Authors: Arnoldussen T. C. , Nunnelley L. L. , Martin F. J. , Ferrier R. P.
Published: July 2002

Side writing is a significant effect for narrow track widths used in high- areal-density magnetic recording. Lorentz electron micrographs can help to understand the nature of side writing and are used in this paper, in conjunction with analytical modeling, to characterize side writing in isotropic and strongly oriented recording media. Isotropic media exhibit a wide side-written fringe, including a strip often termed an ‘‘erased band,’’ although it is not truly erased. Strongly oriented media, however, show no erased band.
dc track edge interactions
Authors: Indeck R. S. , Reising S. C. , Hoinville J. R. , Muller M. W.
Published: July 2002

We have developed an experimental method for investigating the interaction between two dc track edges by studying the track edge noise. We conclude that two edges do not interact when they are several micrometers apart, but the noise reduces nearly to zero when their separation is less than about half a micrometer. There is a transition region that exists between these two limits. The net track edge noise power from two dc edges is quantized, implying that in our experiment track edges interact around the complete revolution of the disk or not at all.
Quasiperpendicular magnetic recording on a composite medium with Co-Cr perpendicular and Fe-Co longitudinal layers
Authors: Iwasaki Shun-ichi , Ouchi Kazuhiro
Published: July 2002

Quasiperpendicular magnetic recording on a perpendicular anisotropy Co-Cr medium with a very thin semihard back layer having longitudinal magnetization has been investigated. When the back layer was introduced, the Co-Cr media began to show single peak pulses and an enhanced output due to reduced demagnetization. A higher factor of improvement in the output was obtained for a Co-Cr layer with a lower coercivity. A dominant factor to determine the recording density limit was the head gap length. A recording density D50 of 125 kFRPI with overwrite of 30 dB can be achieved for a short gap of 0.15 μm when a MIG-type head was used. It is concluded that the composite medium has practical advantages for a hard-disk system as well as a video tape system.
Magnetic phase diagrams of (Cr1−xMox)0.986Si0.014 and (Cr0.97Mo0.03)1−ySiy
Authors: Smit P. , Alberts H. L.
Published: July 2002

The magnetic phase diagrams of two Cr-Mo-Si systems have been determined from electrical resistivity, ultrasonic wave velocity, and thermal-expansion measurements. The concentration dependence of the Néel temperature of (Cr0.97Mo0.03)1−ySiy was explained in terms of changes in the density of states and pair breaking effects on alloying. For (Cr1−xMox)0.986Si0.014 the magnetic phase diagram was explained by taking changes in the nesting parameter to be the dominant effect.
Linked-cluster expansion for the single-band Hubbard model
Authors: Pan Kok-Kwei , Wang Yung-Li
Published: July 2002

Using the linked-cluster expansion, we have obtained the free energy, uniform susceptibility, and staggered susceptibility of the s-band Hubbard model to the sixth order in terms of βt, where t is the hopping integral to the nearest neighbors and β is the inverse of temperature. We show that a special technique based on the multiple-site Wick reduction theorem is more convenient than previous perturbation calculations. Our linked-cluster expansion result is for an arbitrary value of the on-site repulsion U. It has made corrections of previous results of several papers (up to fourth order) and achieved the sixth-order term.
Magnetization and transport properties of Co-Ni-Pd alloys
Authors: Jen S. U. , Huang Y. R.
Published: July 2002

A series of Co15(NixPd1−x)85, Co25(NixPd1−x)75, and Co35(NixPd1−x)65 alloys was made. Different thermal treatments were performed on these alloys: (1) furnance cooling from 1000 °C with −3 to −5 °C/min, (2) annealing at 750 °C in high vacuum for 23 h, and (3) salt water quenching from 800 and 900 °C, respectively. Properties measured include magnetization, electrical resistivity, magnetoresistance, and lattice constant. An order-disorder transformation is suggested indirectly in CoNi3 by some changes in the measured properties for samples subjected to different thermal treatments. All the changes observed are explained from the viewpoints of order-disorder transformation, textural structures, impurities, and other phenomena. The physical effect of replacing Ni by Pd is discussed briefly.
Magnetic transition in thin wire of rare-earth metals (abstract)
Authors: Chin Arthur , Ali Naushad , Masden J. T.
Published: July 2002

Thin wires of several heavy rare-earth metals (Gd,Tb,Dy, and Ho) have been fabricated using a step lithographic technique with cross-section areas from 0.87 to 58×10−11 cm2. The thin films of each material were deposited in a UHV system by thermal evaporation and they have a room-temperature resistivity of 85, 145, 164, and 209 μΩ cm for Gd,Tb,Dy, and Ho, respectively. The electrical resistance of thin films and wires were measured by the four-probe method in the temperature range from 1.5 to 300 K. We also studied the isothermal magnetoresistance (MR) at temperatures below 30 K in a magnetic field up to 5.5 T. With decreasing temperature the resistivity of each material wires show (1) a decrease in ρ with a minimum at 55 K (Gd), 25 K (Tb), 6 K (Dy), 20 K (Ho), (2) a rise in ρ with a maximum at 30 K (Gd), 20 K (Tb), 5 K (Dy), 5 K (Ho), and (3) a sharp drop in ρ below the maximum. The minimum in the resistivity for each wires is associated with the localization effect. It is believed that the sharp drop in ρ after the maximum is due to a magnetic transition in the wire. This magnetic transition is possibly due to a large shift in the Curie temperature in thin wire. The field dependence of MR data above their magnetic transition temperatures, 20 K (Gd), 14 K (Tb), 4 K (Dy), are similar to that of paramagnetic metals. As the length of Tb wires are shorter than 30 μm, we do not see the sharp drop at low temperature.
Intermediate valences of Ce and electrical resistivity changes of Pd-Ce intermetallic compounds
Authors: Oki Kensuke , Saito Yasutoshi , Sato Hiroshi , Itakura Masaru , Kuwano Noriyuki , Yamashita Seiichi , Yamaguchi Toshio , Wakita Hisanobu
Published: July 2002

The changes in Ce valence and electrical resistivity have been studied for several intermetallic compounds of Pd-Ce. The Ce valence estimated from L3-XANES spectra varies smoothly with Ce concentration, with the exception of H-Pd5Ce. The extraordinarily low Ce valence of the H-Pd5Ce was interpreted in terms of the local configuration of Ce atoms in its crystal structure. The Ce valence of the Pd-Ce intermetallic compounds showed little variation with temperature. The resistivities of H-Pd5Ce and Pd3Ce have negative temperature coefficients below room temperature, suggesting that the dense Kondo effect becomes distinct in Pd-Ce alloys with the Ce valence close to 3.2.
Optical and magneto-optical characterization of TbFeCo thin films in trilayer structures
Authors: McGahan William A. , He Ping , Chen Liang-Yao , Bonafede Sal , Woollam John A. , Sequeda F. , McDaniel T. , Do H.
Published: July 2002

A series of TbFeCo films ranging in thickness from 100 to 800 Å have been deposited in trilayer structures on silicon wafer substrates, with Si3N4 being employed as the dielectric material. These films have been characterized both optically and magneto-optically by variable angle of incidence spectroscopic ellipsometry, normal angle of incidence reflectometry, and normal angle of incidence Kerr spectroscopy. From these measurements, the optical constants n and k have been determined for the TbFeCo films, as well as the magneto-optical constants Q1 and Q2. Results are presented that demonstrate the lack of dependence of these constants on the thickness of the TbFeCo film, and which can be used for calculating the expected optical and magneto-optical response of any multilayer structure containing similar TbFeCo films.
Experimental verification of a vector Preisach model
Authors: Vajda Ferenc , Oti John , Pardavi-Horvath M. , Della Torre Edward , Swartzendruber L. J. , Bennett L. H.
Published: July 2002

A vector moving Preisach model has been developed that describes partially oriented particulate media by pseudoparticles, consisting of a distribution of several basic particles with various orientations of easy axes. The model uses switching modes calculated by a micromagnetic simulation of physical particles. In order to test this model, the angular dependence of the magnetic properties was measured by a vibrating sample magnetometer for several samples of commercial recording media that had different degrees of particle orientation. The experimental results are in good agreement with the orientation dependence of the squareness and coercivity, as predicted by the model.
Exchange anisotropy in Ni80Fe20/CoxNi1−xO coupled films (abstract)
Authors: Carey M. J. , Spada F. E. , Parker F. T. , Berkowitz A. E. , Leroux C.
Published: July 2002

Single-crystal and polycrystalline thin films of antiferromagnetic CoxNi1−xO were prepared by reactive sputtering; films of Ni80Fe20 were deposited upon them without breaking vacuum. The objective was to produce antiferromagnetic oxide films with high magnetocrystalline anisotropy, K, at room temperature by alloying high-TN, low-K NiO with low-TN, high-K CoO. Although bulk CoO and NiO are immiscible below 750 °C, single-phase multilayer CoxNi1−xO films were produced by deposition onto substrates rotating above separate Ni and Co targets. Multilayers with periodicities of <1 Å and≳10 Å showed single-lattice parameters between those of pure NiO and CoO. Epitaxial oxide films were grown with (111) orientation on (0001) α-Al2O3 and with (100) orientation on (100) MgO. Polycrystalline oxide films on Si were also prepared. The Ni80Fe20 films showed enhanced Hc at 20 °C when coupled to the antiferromagnetic oxides, and displaced hysteresis loops were observed at 20 °C with polycrystalline or (111)-oriented oxide underlayers when the couples were cooled from 300 °C in a field. Both the enhanced Hc and the displaced loops disappeared upon heating to 300 °C. This behavior strongly indicates the existence of exchange coupling between the antiferromagnetic and ferromagnetic films.
Growth and characterization of new Bi14(Sr0.33Ca0.67)5O26 single crystals
Authors: Fujiwara Yasufumi , Hirata Satoshi , Kobayashi Takeshi , Min Eungi , Shibuya Kyouichi
Published: July 2002

New insulating Bi14(Sr0.33Ca0.67)5O26 layered single crystals have been grown by a flux method and their crystallographic properties have been characterized. The crystals exhibited a smooth cleaved surface perpendicular to [001] orientation. The x-ray precession camera analysis indicated the crystals have rhombohedral symmetry, belonging to a Laue group of 3̄m. Furthermore, some kinds of rare-earth elements have been successfully substituted for lattice sites of the crystal. The variation of the c-axis length reflected ionic radii of the rare-earth elements substituted. Radiant luminescence has been observed in visible and infrared regions in the Er-doped crystals, which was assigned to electron transition between spin-orbit levels of trivalent Er ions in the crystal.
Thermally activated dissipation and critical field H
c2 in c-oriented high-T
c Bi-Pb-Sr-Ca-Cu-O thin film
Authors: Wang Y. H. , Cui C. G. , Zhang Y. Z. , Li S. L. , Li J. , Li L.
Published: July 2002

A set of resistivity-temperature (R-T) curves measured under various applied fields in a high-Tc Bi-Pb-Sr-Ca-Cu-O thin film which has a zero-resistance temperature Tc0 of 110 K is reported. The remarkable broadening of the transition width is discussed under the flux-creep model, considering the very short coherence length of this oxide superconductor. The resistivity is thermally activated, which is consistent with the Arrhenius law with a magnetic field and orientation-dependent activation energy U0(H,Θ). The U0(H,Θ) has a very high value of 381.6 meV under a field of 0.1 T parallel to the c axis. The upper critical field Hc2 determined from these R-T curves shows high values and the effect of flux creep to the Hc2(0) is examined by the irreversible behavior with the ‘‘giant’’ flux-creep model.
Be, S, Si, and Ne ion implantation in InSb grown on GaAs
Authors: Rao Mulpuri V. , Thompson Phillip E. , Echard Richard , Mulpuri Savitri , Berry Alok K. , Dietrich Harry B.
Published: July 2002

Single- and multiple-energy Be, S, Si, and Ne ion implantations were performed at room temperature in InSb grown on semi-insulating GaAs substrates. The implanted material was subjected to both isochronal and isothermal annealing schemes. The as-implanted and annealed material was characterized by Hall, secondary ion mass spectrometry, and x-ray rocking curve measurements. The as-implanted material is highly n-type for all implant species used in this study. A maximum p-type activation of 90% and n-type activation of 16% was achieved for Be and S implants, respectively. Be activation depends on the thickness of the InSb layer. No in-diffusion of Be and S was observed even after 500 °C anneal. The Si implant has an amphoteric doping behavior.
Comment on ‘‘High-detectivity GaAs quantum-well infrared detectors with peak responsivity at 8.2 μm’’
Authors: Beck W. A.
Published: July 2002

Recent measurements of less-than-full shot noise in GaAs/AlGaAs quantum-well infrared detectors can be explained in terms of standard photoconductor generation-recombination theory. Therefore, more complex models are not yet necessary.
Reply to ‘‘Comment on ‘High-detectivity GaAs quantum-well infrared detectors with peak responsivity at 8.2 μm’ ’’
Authors: Janousek B. K. , Daugherty M. J. , Bloss W. L. , Lacoe R. , O’Loughlin M. J. , Kanter H. , De Luccia F. J. , Perry L. E.
Published: July 2002

The expression for the ratio between the noise current and full shot noise contained in our recent paper [J. Appl. Phys. 67, 7608 (1990)] is based entirely on standard generation-recombination noise theory, and does not represent a more complex model as Beck suggests [J. Appl. Phys. 69, xxx (1991)]. The equations presented by Beck contain errors, but once these errors are corrected, his equations and ours yield the same quantitative predictions.
Determination of the coherence length in high-mobility semiconductor-coupled Josephson weak links
Authors: Kleinsasser A. W.
Published: July 2002

A Nb-InAs-Nb superconductor-semiconductor-superconductor weak link based on a high-mobility homoepitaxial n-InAs film was reported recently [Akazaki, Kawakami, and Nittu J. Appl. Phys. 66, 6121 (1989)]. Measurements of the electron concentration, effective mass, and mobility allowed the coherence length in the normal link to be calculated. The mobility was high enough that the dirty limit was not applicable in the temperature range (∼2–7  K) over which the device critical current was measured. The temperature dependence of the critical current could not be fit by the usual theoretical form, even though an expression for the coherence length was used that should be applicable in both the clean and dirty limits. In this paper is demonstrated an excellent fit to the data, obtained by using the magnitude of the coherence length as a fitting parameter and assuming the dirty limit temperature dependence. This implies a coherence length proportional to T−1/2 but far shorter than that calculated from the known material parameters. It is suggested that a different scaling length may apply in high-mobility devices.
Electrical characterization of p-type ZnSe:Li epilayers grown on p+-GaAs by molecular-beam epitaxy
Authors: Marshall T. , Cammack D. A.
Published: July 2002

Small-signal ac admittance data are presented, and shown to provide accurate and unambiguous evidence of p-type behavior in Li-doped ZnSe epilayers grown on p+-GaAs. The devices measured are two-terminal vertical-transport structures, with unequal-area contacts in order to distinguish effects arising from the top metal Schottky barrier from those arising from the heterojunction. Qualitative features of the data alone are sufficient to determine the (positive) sign of the mobile carriers in the ZnSe. The data are analyzed using an equivalent-circuit model shown to be reliable for n-type ZnSe, from which the net doping and the ZnSe resistivity are extracted. Using these quantities, the ZnSe hole mobility is found to be about 28±4 cm2/V s. Schottky barrier and heterojunction barrier heights are also determined.
Electrochromism and thermochromism of LixVO2 thin films
Authors: Khan M. S. R. , Khan K. A. , Estrada W. , Granqvist C. G.
Published: July 2002

Thin films of LixVO2(0≤x≲0.43) were made by reactive sputtering and annealing post-treatment, followed by electrochemical cycling in an electrolyte containing LiClO4. The films showed electrochromism, and bleached under Li insertion. Weak thermochromism was observed with a drop of the transmittance, accompanied by a conductivity increase, at ∼60 °C.
Local plasmon modes of a semiconductor superlattice
Authors: Bloss Walter L.
Published: July 2002

The energy dispersion relation of the plasmon modes of an infinite periodic array of quantum wells where all the wells are doped with the same electron density except for one is calculated. In analogy to the local phonon modes of a vibrational lattice, we find that local plasmon modes exist. An explicit relation for the plasmon energy of the local mode is derived. Contrary to the surface plasmon mode of a semi-infinite superlattice predicted by Giuliani and Quinn [Phys. Rev. Lett. 51, 919 (1983)], these local modes exist at all values of the wavevector. A low-lying acoustic mode (ω≊qv) is found whose velocity is determined by the local density of the symmetry breaking well. Implications for obtaining amplification by drift instabilities in these structures are discussed.
Determination of deep-level parameters by a new analysis method of isothermal capacitance transients
Authors: Cola A. , Lupo M. G. , Vasanelli L.
Published: July 2002

A new method to analyze isothermal capacitance transients of Schottky barriers is proposed. Isothermal capacitance transients, recorded at different temperatures by an automatized measurement system, are analyzed by comparing the capacitance values at the same time but different temperatures. This method is similar to that used in the standard deep-level transient spectroscopy (DLTS), by inverting the role of time and temperature. The main parameters of the deep levels can be obtained as in the DLTS analysis. The analysis method is applied to Mo/GaAs Schottky barriers. Results have been compared with those obtained by standard DLTS analysis.
Influence of substrate temperature on lattice strain field and phase transition in MeV oxygen ion implanted GaAs crystals
Authors: Xiong Fulin , Tsai C. J. , Vreeland T. , Tombrello T. A. , Schwartz C. L. , Schwarz S. A.
Published: July 2002

A detailed study of the influence of substrate temperature on the radiation-induced lattice strain field and crystalline-to-amorphous (c–a) phase transition in MeV oxygen ion implanted GaAs crystals has been made using channeling Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and the x-ray rocking curve technique. A comparison has been made between the cases of room temperature (RT) and low temperature (LT) (about 100 K) implantation. A strong in situ dynamic annealing process is found in RT implantation at a moderate beam current, resulting in a uniform positive strain field in the implanted layer. LT implantation introduces a freeze-in effect which impedes the recombination and diffusion of initial radiation-created lattice damage and defects, and in turn drives more efficiently the c–a transition as well as strain saturation and relaxation. The results are interpreted with a spike damage model in which the defect production process is described in terms of the competition between defect generation by nuclear spikes and defect diffusion and recombination stimulated by electronic spikes. It is also suggested that the excess population of vacancies and their complexes is responsible for lattice spacing expansion in ion-implanted GaAs crystals.
The formation of decagonal and icosahedral phases in Al75−xPd25Crx (x <3 at.%) quasicrystals
Authors: Tsai An-Pang , Inoue Akihisa , Masumoto Tsuyoshi
Published: July 2002

An Al75Pd25 decagonal (D) phase changes to an F-type icosahedral (I) phase by the substitution of 3 at. % Cr for Al in a rapidly solidified state. The coexisting I and D phases in a rapidly solidified Al73Pd25Cr2 alloy have a close orientation relationship, in which a tenfold axis of the D phase coincides with a fivefold axis of the I phase.
Quantum inductance in resonant tunneling
Authors: Liu H. C.
Published: July 2002

An analytical high-frequency model for double-barrier resonant tunneling is formulated. An inductance due to the quantum mechanical resonant lifetime (τ) is confirmed theoretically. The magnitude of the anticipated inductance is τ/G, where G is the conductance of the device.
Analysis of correlation of magnetization and noise after ac erasing
Authors: Che Xiaodong , Suhl Harry
Published: July 2002

Normally, theories of magnetic noise after ac erasing take into account residual correlations among magnetic particles either through an ad hoc assumption or by numerical simulation of the erasing process [IEEE Trans. Magn. MAG 23, 1767 (1987); IEEE Trans. on Magn. MAG 20, 412 (1984); IEEE Trans. Magn. MAG 19, 899 (1983).] In this paper we present a theory for a particulate medium based on a pseudo-equilibrium calculation of the correlation, with the ac field acting as the heat bath. The results are compared with experiment.
Surface topography of ultrathin free-standing [100] gold films
Authors: Krakow William
Published: July 2002

Free-standing 40-Å-thick [100] Au films have been produced by vapor deposition which exhibited various types of surface topography when observed by transmission electron microscopy. Here, one surface can be attributed to surface terraces that are a replication of the underlying substrate. The other surface is a combination of a step-ledge growth mechanism and surface nucleation phenomena. It is the purpose here to report upon this expitaxial thin-film growth which has not been observed in thin vapor-deposited metal films.
Modeling the behavior of optical coatings in x-ray environments
Authors: Rhoades Clifford E. , Triplett John R.
Published: July 2002

Calculation of heating caused by the deposition of x rays in thin-film optical coatings is complicated because the mean free path of photo- and autoionization electrons is comparable to the thin-film thickness and thus electron deposition cannot be considered local. This paper describes the modeling in the computer code xrth of (a) x-ray deposition and transport, (b) electron production, deposition, and transport, and (c) thermal conduction and transport. X-ray transport is handled by multigroup discrete ordinates, electron transport is done by the method of characteristics, applied to the two-term spherical harmonics expansion approximation (P1) to the Spencer–Lewis transport equation, and thermal transport is computed by a Richardson extrapolation of a backward Euler solution to the heat conduction equation. Results of a few test cases and comparisons with other computer codes are presented.
Injection of an intense electron beam into a cyclic accelerator with solenoidal field focusing
Authors: Humphries Stanley , Terry R. L. , Frauenglass A.
Published: July 2002

This paper describes the injection and trapping of a high-current space-charge-dominated electron beam into a closed cyclic accelerator. A method has been developed to transport externally generated beams into a strong-focusing betatron using a pulsed E×B drift. The method requires modest electric fields, gives good trapping efficiency, provides continuous focusing of high-perveance beams, has tolerance to imperfections, and has the potential ability to maintain the emittance of the injected beam. The accelerator was a racetrack machine with an 8-m circumference. Forty solenoid coils with alternating field polarity provided strong focusing. The 220-A, 500-keV injected beam entered the machine through a 2.5-cm-diam shielded transport tube. A pulsed electric field captured a 30-ns slice of the beam− the system trapped most of the current that had completed a full circuit. The main problem encountered in the experiments was a rapid loss of beam electrons during and after trapping. Electrons traveled an average of only two revolutions (16 m). Experimental observations and theoretical studies implied that magnetic dipole field errors in the injector were the primary cause of beam loss.
Ferromagnetism and critical temperatures in dilute P
dMn alloys
Authors: Parra R. E. , González A. C.
Published: July 2002

Neutron-scattering and magnetization measurements on dilute PdMn alloys have been analyzed using a magnetic environment model of ferromagnetism, atomic short-range order, and Mn-Mn interactions. The analysis allows the calculation of several magnetic properties of PdMn, and the effects of Mn-Mn interactions and atomic short range order on the critical temperatures of ferromagnetism. These temperatures, which are small in dilute PdMn alloys in comparison with other typical giant moment systems such as PdFe, were calculated using the Monte Carlo simulation method, and the results were compared with experimental values, showing good agreement for the concentrations considered.
First-principles calculations of chemical and magnetic correlations in Fe-13.5% V (abstract)
Authors: Johnson D. D. , Staunton J. B. , Pinski F. J.
Published: July 2002

We have developed an ab initio method for calculating the static correlation functions in substitutional alloys, which, for example, describes their atomic short-range order (ASRO) as given by atomic diffuse scattering intensities. For magnetic alloys, a contribution to the total diffuse scattering intensities also results from the moment-chemical correlations (i.e., variations of local moments due to changes in the chemical environment). The response functions, which may be directly compared to single crystal neutron-scattering, are derived from a mean-field statistical mechanical description of compositional fluctuations in alloys. The statistical averages are performed via the Korringa–Kohn–Rostoker coherent-potential approximation, which incorporates the electronic structure of the high-temperature, chemically disordered state. For magnetic Fe-13.5% V alloys, we present results of first-principles calculations of the ASRO, which compare very well with the (quenched) single crystal data obtained by Cable et al.,1 and predict the structure of the moment-chemical correlations. Moreover, we determine the origin of the q-dependent structure in these correlations. In the future, this will allow direct comparison of neutron data with theory to understand more fully the underlying mechanisms which drive, e.g., ASRO.
Spin-wave theory of impurity states near the surfaces of ferromagnets and antiferromagnets
Authors: Chen Niu-Niu , Cottam M. G.
Published: July 2002

Calculations are presented for the influence of isolated magnetic impurities or defects on the spin-wave spectrum of semi-infinite ferromagnets and antiferromagnets. A Green’s-function theory and a Heisenberg model are used to study the spin-wave excitations associated with a defect at or near a magnetic surface, showing that there may be localized ‘‘defect modes’’ at energies outside the regions of bulk spin waves and surface spin waves. Applications are made to impurities in simple cubic ferromagnets and rutile-structure antiferromagnets.
The 57Fe Mössbauer spectra of oriented single-crystal and powder PbFe12O19 (abstract)
Authors: Evans B. J. , Thompson G. K.
Published: July 2002

The recent determination of the crystal structure of PbFe12O19 by means of single-crystal x-ray diffraction has made it possible to carry out a definitive and comparative analysis of the structure-property relationship of PbFe12O19, SrFe12O19, and BaFe12O19. We have therefore performed 57Fe Mössbauer measurements on oriented, single-crystal, and powder samples of PbFe12O19 at 298 K. For a single-crystal oriented parallel to the c axis, five distinct patterns are observed. The hyperfine fields, isomer shifts, and quadrupole interactions are as follows: 12k: Heff=413 kOe; δ=0.33 mm s−1; Δ=0.35 mm s−1; 4f1: 487 kOe; 0.24 mm s−1; 0.13 mm s−1; 4f2: 514 kOe; 0.39 mm s−1; 0.29 mm s−1; 2a: 496 kOe; 0.30 mm s−1; 0.11 mm s−1; 2b: 399 kOe; 0.30 mm s−1; 2.00 mm s−1. The relative magnitude of each of these parameters is in good agreement with and exhibits the same trend observed for high-purity SrFe12O19. The relative intensity of the 2b pattern for the crystal oriented parallel to the c axis is 8.2%, which approaches its theoretical value; of the total number of iron ions in the structure, 8.33% of them occupy the 2b site. The value for the polycrystalline sample is only 5.4% of the total intensity. However, for a single crystal oriented perpendicular to the c axis, the 2b pattern exhibits a negligible intensity within the experimental error. This result confirms the dynamic disorder in the position of the 2b iron ions and suggests a stronger anisotropy for the case of PbFe12O19 than for SrFe12O19 and BaFe12O19. Even though the trend in hyperfine parameters at 298 K is similar to Sr, Ba, and Pb hexaferrites, PbFe12O19 exhibits hyperfine fields that are consistently lower than those of the Ba and Sr analogues. This result is discussed in terms of the Curie temperatures, magnetic exchange interactions, and structural parameters.
Gallium phosphide junctions with low leakage for energy conversion and near ultraviolet detectors
Authors: Hughes R. C. , Zipperian T. E. , Dawson L. R. , Biefeld R. M. , Walko R. J. , Dvorack M. A.
Published: July 2002

There is a need for semiconductor junctions with very low leakage for energy conversion from low level radioactive or radio-luminescent sources, and low noise blue-green photodiodes. We report the properties of two types of GaP junctions; a Schottky barrier of Pd on liquid phase epitaxy grown n-type GaP and a p+ over n junction grown by metal-organic chemical vapor deposition. Both types of junctions show very low leakage currents and good efficiency for power conversion from low level beta particles, x rays, and blue-green light.
Effects of the magnetic field and negatively biased substrate voltage on TiN film deposition
Authors: Hwang Un-Hak
Published: July 2002

The cathode erosion rate in titanium arc experiments operated in a relatively weak magnetic field is measured. Formulas are derived for the time-dependent ion current density to determine the effect on TiN film deposition of negative bias voltage applied to the substrate
Numerical investigation of the intersubband and intervalley drift velocity by the Boltzmann integral equation method
Authors: Kiener C. , Vass E.
Published: July 2002

The influence of intersubband and intervalley scattering onto the drift velocity of hot 2D electrons in n-GaAs quantum wells and heterostructures is investigated numerically for the first time by means of the Boltzmann integral equation method. The dependence of the subband energy separation onto the drift velocity is analyzed systematically. The drift velocity in quantum wells having a thickness larger than 100 Å is found to be significantly reduced by intersubband transitions if the external electric field exceeds 1 kV/cm.
Lattice distortions in YBa2Cu3O7−δ thin films grown in situ by sequential ion beam sputtering
Authors: Kittl J. A. , Johnson W. L. , Nieh C. W.
Published: July 2002

We have analyzed epitaxial, c-axis oriented YBa2Cu3O7−δ thin films grown in situ by sequential ion-beam sputtering on (100) SiTiO3 and (100) MgO substrates. X-ray diffraction studies showed the presence of both homogeneous and inhomogeneous lattice distortions along the c-direction. The c-axis lattice parameters ranged from 11.72 to 12.00 Å. The broadening of the (00l) Bragg peaks in excess of the broadening due to finite film thickness was found to be due to inhomogeneous lattice distortions. The overall trend in the data shows an increase of the inhomogeneous strains with the enlargement of the c-axis lattice parameter. The inhomogeneous lattice distortions are interpreted as fluctuations in the c-axis lattice parameter. The resistive transitions were found to be correlated to the lattice distortions. We show correlations between the midpoint Tc and the c-axis lattice parameter and between the transition widths and the inhomogeneous lattice distortions.
Raman scattering of Si localized vibrational modes in InAs
Authors: Uematsu Masashi
Published: July 2002

Localized vibrational modes of Si have been investigated in Si-implanted InAs by means of laser Raman spectroscopy. Isotope ions 28Si, 29Si, and 30Si were implanted and the isotope shifts of spectrum peaks were used to assign the vibrations of Si-related lattice sites. Peaks at 359, 351, and 328 cm−1 are assigned to 28Si atoms on In sites (28SiIn), 28SiIn-28SiAs pairs, and 28Si atoms on As sites, respectively. The origin of the enhancement in the scattering of SiIn is likely to be near-resonance scattering with the E1-gap energy of InAs.
Sputter synthesis of modulated multilayer high-energy-product permanent magnet films
Authors: Chen K. , Hegde H. , Cadieu F. J.
Published: July 2002

Multilayered permanent magnet films with alternating layers differing vastly in anisotropy field and intrinsic coercivity have been sputter synthesized from Sm-Co-based TDK-type 2-17 bulk targets. The basic layer thickness range for which modulated properties can be observed has been investigated from <0.1 to ≳10 μm. The individual layers have been synthesized so as to exhibit high-static-energy product values of ≊15 MGOe. The alternating layers exhibited coercivities around 5 and 15 kOe, respectively, so that for applied reversed fields in the vicinity of 10 kOe the alternating layers have their in-plane magnetizations pointing in opposite directions, reducing the net magnetization to near zero. The magnetic property modulation was accomplished through modulation of the Sm content through sputter process control and the method of crystallization of the alternating layers, without changing either the sputtering targets or substrate positions. For such modulated layer films, the system magnetic energy density in the absence of external fields is a function of the reversed-field value applied after initial in plane saturation.
Suppression of Barkhausen noise in an MR head
Authors: Das Shyam C.
Published: July 2002

It is shown by the Bitter technique that magnetic domain walls nucleate at the ends of a long magnetoresistive (MR) element and propagate into the active central region as the transverse field is successively increased. A new technique utilizing current loops only at the ends of the element is used to apply longitudinal bias to suppress Barkhausen noise. Suppression of Barkhausen noise is also accomplished by minimizing longitudinal demagnetizing field using a high aspect ratio MR element, as well as minimization of the transverse demagnetizing field by overlapping two pieces of a yoke with the transverse edges of the MR element. These techniques are used to fabricate a Barkhausen noise-free yoke-type MR head.
Novel magnetic relaxation in single-crystal Tl2Ca1Ba2Cu2O8 superconductors
Authors: Zuo F. , Salamon M. B. , Datta T. , Ghiron K.
Published: July 2002

Magnetic relaxation in single-crystal Tl2Ca1Ba2Cu2O8 superconductors is reported. Typical logarithmic flux creep has been observed at low temperatures. At high temperatures and fields, different flux dynamics are observed: first, nonlogarithmic dependence followed by the appearance of reverse creep, i.e., increasingly negative magnetization. This latter effect begins after a temperature- and field-dependent wait time. To explain reverse creep flux-line roughening, driven by pinning randomness, is considered.
Metastable effects in high-voltage amorphous silicon thin-film transistors
Authors: Shaw John G. , Hack Michael G. , Martin Russel A.
Published: July 2002

We report on a high-voltage amorphous silicon thin-film transistor by which large drain voltages are controlled by a low gate potential. Under certain stress conditions, the output characteristics of these devices can undergo a parallel shift towards higher drain potentials. This phenomenon, which we call the Vx shift, has been analyzed by comparing numerical computer models to experimental data. Simulations show that the Vx shift is caused by negative charge located in the transistor’s amorphous-silicon layer near the edge of the gate. This charge resides in extra metastable deep traps which are generated by the equilibration of stressed amorphous silicon. As this equilibration mechanism is reversible, the Vx shift can be recovered.
Studies of InSb metal-oxide-semiconductor structure fabricated by photochemical vapor deposition using Si2H6 and N2O
Authors: Huang C. J. , Su Y. K. , Leu R. L.
Published: July 2002

Silicon oxide films (SiOx,0<x<2) have been prepared by photolysis of disilane (Si2H6) with nitrous oxide (N2O) at temperature below 200 °C using 2537-A ultraviolet light. Ellipsometric studies prove that the refractive index and etching rate of the photo-oxide films depend on the substrate temperatures and gas ratio. Composition and electrical properties of the interface (SiOx/InSb) are discussed by using Auger electron spectroscopy and metal-oxide-semiconductor capacitors. Hysteresis-free capacitance-voltage characteristics measured at 77 K are attained and the minimum interface state density is only 1.5×1011 cm−2 eV−1.
Thermoelectric phenomena in metals under large temperature gradients
Authors: Grigorenko A. N. , Nikitin P. I. , Jelski Daniel A. , George Thomas F.
Published: July 2002

Nonlinear contributions to thermoelectricity are studied when large temperature gradients are present in metals. A theory is presented to account for these phenomena in the case of monovalent metals obeying a parabolic dispersion law. Simple experiments are proposed in which nonlinear terms are relevant and produce measurable effects.
Picosecond third-order nonlinear optical susceptibility in nematic liquid crystals
Authors: Jiang J. P. , Rentzepis P. M.
Published: July 2002

We have measured the tensor components c1111 and c1221 of third-order nonlinear optical susceptibility of two nematic liquid crystals, MBBA (p-methoxy-benzylidene p-n-butylaniline) and EBBA (p-ethoxy-benzylidene p-n-butylaniline), in the picosecond regime. We observed that the molecule with ethoxy group (EBBA) has a larger third-order nonlinearity than the one with methoxy group (MBBA) and present a model to explain this effect.
Photoinduced paramagnetic centers in amorphous silicon oxynitride
Authors: Yount J. T. , Kraus G. T. , Lenahan P. M. , Krick D. T.
Published: July 2002

Room-temperature metastable paramagnetic point defects are created in plasma-enhanced chemical vapor deposited silicon oxynitride films by exposing the films to ultraviolet and vacuum ultraviolet illumination. We compare the response of films with low, intermediate, and high oxygen content. The defects include unpaired electrons on silicons bonded to nitrogen atoms (K centers), unpaired electrons on bridging nitrogens, and what appear to be overcoordinated nitrogen centers.
Electronic properties of epitaxial TiN/VN(001) superlattices
Authors: Hirashita N. , Greene J. E. , Helmersson U. , Birch J. , Sundgren J.-E.
Published: July 2002

Single-crystal TiN/VN superlattices with layer thicknesses lTiN=lVN and period Λ ranging from 0.96 to 12.4 nm have been grown on MgO(001) substrates at 750 °C by reactive magnetron sputtering. The superlattice structures had uniform layer thicknesses as observed by cross-sectional transmission electron microscopy and a comparison of x-ray superlattice diffraction spectra with calculated spectra indicated that any interfacial mixing had to be less than ± three atomic layers, (i.e., <±0.6 nm). Electrical resistivity and Hall measurements carried out as a function of Λ showed that the room-temperature electron carrier concentration n remained constant at 4.5×1022 cm−3 while the resistivity ρ increased and the electron mobility μ decreased rapidly with Λ<6 nm. For superlattices with longer periods, ρ∼30 μΩ cm, the expected value for bulk TiN and VN connected in parallel, and μ∼5 cm2 V−1 s−1. The temperature coefficient of resistivity between 80 and 300 K decreased with decreasing Λ but remained positive (i.e., metallic). A modified quantum size effect model accounting for diffuse and specular scattering of electrons at superlattice interfaces was used to explain the electronic transport properties. Best fit results showed that the fraction of specularly scattered electrons was ∼0.3.
Desorption spectra of laser ablation of Bi2Sr2CaCu2O8+x
Authors: Chen C. H. , Phillips R. C.
Published: July 2002

Quantitative measurements of desorbed ions and neutral molecules by a mass spectrometer from laser ablation of Bi2Sr2CaCu2O8+x were obtained. The results indicate that more neutral atoms and molecules desorbed than the corresponding ions. The ratio of neutral atoms to ions decreases when the laser power density increases.
The effect of surface recombination on surface photovoltage in semiconductors
Authors: Zhang Xiumiao , Song Jiatao
Published: July 2002

A numerical method is used to evaluate the surface photovoltage (SPV) in semiconductors as a function of surface recombination velocity, photon flux, substrate doping level, and oxide charge. It is found that SPV is reduced by the surface recombination. For a certain surface recombination velocity SPV increases approximately as the logarithm of photon flux. The effect of surface recombination on SPV is dependent on substrate doping level and oxide charge, to sum up, on the energy-band bend. SPV for depletion surface is more remarkably affected by surface recombination than that for strong inversion surface.
Silicon-on-insulator device islands formed by oxygen implantation through patterned masking layers
Authors: Bussmann U. , Robinson A. K. , Hemment P. L. F. , Campisi G. J.
Published: July 2002

Separation by implanted oxygen is recognized as a versatile technology to produce silicon-on-insulator substrates. The lateral isolation of device islands is achieved by subsequent local oxidation or mesa etching of the silicon top layer. In an alternative approach, implantation is performed through patterned masking layers leading to a continuous but nonplanar buried oxide. Thereby, total dielectric isolation (vertical and lateral) of the device island is achieved in a single implantation stage. The masking structures used in this investigation are thermal oxides and polycrystalline silicon layers with window openings as well as patterned wafers formed by local oxidation of the bulk silicon wafers. Oxygen was implanted with energies of 100 and 200 keV to doses up to 2.2 × 1018 O+ cm−2. The resulting structures are studied by cross-sectional scanning electron microscopy and transmission electron microscopy and the effects of mask material and implantation energy are discussed.
Boundary conditions for the heterojunction interfaces of nonparabolic semiconductors
Authors: Nag B. R.
Published: July 2002

Transmission probability curves are presented for InAs/Al0.4Ga0.6Sb/InAs tunnel diodes which show that for a 2-nm-barrier width, negative differential conductance (NDC) is indicated if the velocity effective mass is used to match the derivatives of the wave functions at the heterojunction interfaces, while the use of the energy-effective mass does not indicate an NDC. It is suggested that an experiment with such a diode may resolve the controversy about the effective mass, to be used for matching the derivatives.
Strain tolerance of Bi2Sr2Ca1Cu2O8−δ/Ag composites at high field
Authors: Li Qiang , Ostenson J. E. , Finnemore D. K.
Published: July 2002

Strain tolerance of Bi2Sr2Ca1Cu2O8−δ/Ag composites have been studied at fields up to 20 T and bending strains up to 2.6% in order to determine the factors that control the critical current density. The goal is to find the best way to distribute Ag such as to give both high strain tolerance and high critical current density. Partial melt processed samples prepared from micromilled mixtures containing 30% Ag by volume show a gradually decreasing critical current all the way out to 2.6% strain. Samples typically show about 1000 A/cm2 at 4.2 K, 20 T, and 0.75% strain. At 20 K, these values occur at 4 T and 0.75% strain.