bluuebunny/crossref_metadata_2025 huggingface dataset:
GaAs pattern etching with little damage by a combination of Ga+focused-ion-beam irradiation and subsequent Cl2 gas etching
Authors: Sugimoto Y. , Taneya M. , Akita K. , Hidaka H.
Published: July 2002

Pattern formation on GaAs by Ga+ focused-ion-beam (FIB) irradiation and subsequent Cl2 gas etching was carried out. A higher etch rate at the FIB-irradiated area compared with that not irradiated under Cl2 gas allows pattern construction without a mask process. The degree of residual crystal damage was evaluated using photoluminescence (PL) intensity measurements. The PL intensity in the etched region was one order of magnitude stronger than that of FIB sputtering, and was several times stronger than that of Ga+ FIB-assisted Cl2 etching. Etch depths of the order of 100 nm, which is five times deeper than that obtained by FIB sputtering, were efficiently performed using moderate Ga+-ion doses.
Thermoelastic attenuation of surface-acoustic waves in coated elastic media
Authors: Mayer A. P.
Published: July 2002

The presence of an interface strongly affects the attenuation of surface-acoustic waves due to coupling to temperature fluctuations via the thermoelastic effect. This is demonstrated for Rayleigh waves propagating in a substrate coated by a thin film with thermal conductivity and heat capacity different from those of the substrate. Even if the thickness of the film is so small that its effects on the frequency and displacement field are negligible, the attenuation coefficient of the surface wave can be strongly enhanced.
Diamond growth in combustion flames
Authors: Yalamanchi R. S. , Harshavardhan K. S.
Published: July 2002

Diamond crystallites were synthesized using various oxygen-hydrocarbon flames. The flames have been profiled in real time using a nonintrusive diagnostic technique. Optical emission spectra for different zones have been recorded and the active species identified. Diamond growth was observed only in the thermodynamically unequilibriated primary combustion zone of the flames. Carbon-bearing species, atomic hydrogen, and atomic oxygen, noted to be critical for diamond growth, were observed in the flames. The diamond growth was confirmed by x-ray diffraction, laser-Raman analysis, and scanning electron microscopy. The study offers the first insight into the flame spectra in the context of diamond synthesis at atmospheric pressures.
Effect of light soaking on the short-wavelength photoresponse in hydrogenated amorphous silicon
Authors: Ghosh Sukriti , Ganguly Gautam
Published: July 2002

The spectrum of the values of ημτ, the product of quantum efficiency, lifetime, and mobility of photogenerated carriers, has been obtained in the wavelength range 300–900 nm, before and after light soaking. It has been shown that in the annealed state, these values are nearly independent of wavelength as well as film thickness. The values of ημτ have been found to decrease more drastically in the short-wavelength region after light soaking, similarly to that observed after moisture adsorption. Changes in band bending are not likely to be the cause of the decrease in response as the dark conductivity does not change on light soaking. The implications of the result are discussed.
Analysis of a low-pressure mercury rare-gas positive column with a dynamic two-temperature representation of electron energy
Authors: Wani Koichi
Published: July 2002

A method for analyzing the dynamic behavior of a low-pressure mercury rare-gas positive column is presented. An eight-state scheme analysis for mercury and argon mixture under a non-Maxwell distribution of electron energy is established. The computing time is shortened by using the two-temperature model for electron energy distribution which I have developed to give an analytical expression for the non-Maxwellian distribution. Two-temperature parameters Tt and Tb for the tail and bulk temperature, respectively, are determined from a two-term Legendre polynomial expansion of the Boltzmann equation. Then a useful empirical result is that the ratio rT=Tt/Tb is a function of a single variable of electron density times electric field strength. By storing rT calculated as a function of this variable, the electron energy distribution, which should be calculated from the Boltzmann equation at each iteration step of solving the rate equations, is found simply by a table-looking-up procedure, whereby the computing time is shortened. The examination of the eight-state scheme is done by comparing calculated and experimental results, discussing physical processes occurring among the eight states.
Generation of very short far-infrared pulses by cavity dumping a molecular gas laser
Authors: de Bekker R. E. M. , Claessen L. M. , Wyder P.
Published: July 2002

Very short far-infrared (FIR) pulses have been generated by cavity dumping an optically pumped molecular gas laser using optical switching techniques. The active element used is an intracavity semiconductor, which is placed under the Brewster angle with respect to the optical axes. This element is made highly reflective by the sudden increase of the free-carrier concentration, induced by above band-gap illumination. In this way high power (∝1 kW) FIR pulses with a duration less than 10 ns can be produced.
Electrical, magnetic circular dichroism and Raman spectroscopic investigations on the EK2 double acceptor (78/203 meV) in GaAs
Authors: Roos G. , Schöner A. , Pensl G. , Wagner J. , Meyer B. K. , Newman R. C.
Published: July 2002

The electrical and optical properties of liquid encapsulated Czochralski grown, Ga-rich (melt composed of 55% Ga and 45% As), p-type GaAs were studied by the Hall effect, capacitance-voltage measurements, magnetic circular dichroism, optically detected electron spin resonance, deep level transient spectroscopy (DLTS), and Raman spectroscopy. Two levels with ionization energies of 78 and 203 meV above the valence band edge were examined and fitted to the singly and doubly charged ground states of a double acceptor which is designated an EK2 center. The Raman scattering cross sections for electronic excitations were determined from the defect concentrations measured by DLTS. The EK2 center is electrically passivated via a remote microwave hydrogen plasma technique. It can be reactivated by heat treatments with an activation energy of Ea=1.4 eV. The concentrations of the two levels were equal to each other in four as-grown samples, in samples following passivation, and at all stages during the subsequent reactivation. The observations are inconsistent with previous suggestions that the levels are due to two separate defects.
Temperature and illumination intensity dependence of photoconductivity in sputter-deposited heteroepitaxial (100)CdTe layers
Authors: Das S. R. , Cook J. G. , Mukherjee G.
Published: July 2002

Sputter-deposited, heteroepitaxial (100)CdTe layers prepared at growth temperatures of 300–325 °C are found to be p-type with high dark resistivities on the order of 2×105 Ω cm. The epilayers are highly photoconducting and exhibit photoconductivity to dark conductivity ratios as high as 1×106 at around 200 K. The photoconductivity is observed to exhibit a sublinear dependence on illumination intensity and a thermally activated behavior. The model developed by Simmons and Taylor [J. G. Simmons and G. W. Taylor, J. Phys. C: Solid State Phys. 7, 3051 (1974); G. W. Taylor and J. G. Simmons, J. Phys. C: Solid State Phys. 7, 3067 (1974)] to explain photoconductivity in amorphous semiconductors is shown to be applicable to these epitaxial layers. Hole traps at 0.40 and 0.23 eV above the valence band have been determined from the temperature dependence of the photoconductivity. Acceptor levels at 0.62 and 0.07 eV above the valence band, determined from the temperature dependence of the dark conductivity, are discussed in relation with photoluminescence bands at 0.81 and 1.00 eV reported earlier [S. R. Das, J. G. Cook, N. L. Rowell, and M. S. Aouadi, J. Appl. Phys. 68, 5796 (1990)] in these epilayers.
Capacitance-voltage characteristics of grain boundaries in cast polycrystalline silicon
Authors: Suresh P. R. , Ramkumar K. , Satyam M.
Published: July 2002

This paper reports capacitance-voltage measurements of grain boundaries made on cast polycrystalline silicon wafers. It has been observed that unlike the case of symmetric grain boundaries, the capacitance-voltage characteristics measured at high frequency, depend upon the polarity of the applied dc voltage. This deviation has been attributed to the difference in conductivities in the grains forming the grain boundary. Based on this, capacitance-voltage characteristics of grain boundaries have been calculated. Carrier trapping and emission by the grain boundary states have been considered to calculate the change in the filled trap state density due to the applied bias. A monoenergetic trap level has been assumed. The computed capacitance-voltage curves justify the observed variations.
Epitaxial growth of GaAs films from elemental arsenic
Authors: Chu Shirley S. , Chu T. L. , Green R. F. , Cerny C.
Published: July 2002

The metalorganic vapor phase epitaxial growth of GaAs has been investigated using trimethylgallium (TMGa) or triethylgallium (TEGa) and elemental arsenic (As) in hydrogen under atmospheric and reduced pressures. The important process parameters include the substrate temperature and the composition and flow rate of the reaction mixture. Device quality GaAs films have been grown at substrate temperatures of 450 °C or higher using TEGa and As, as compared with 510 °C or higher required by the TEGa-arsine process. The GaAs films deposited from TEGa and As are n-type, and the Hall mobilities in GaAs films deposited at 490 °C with a net electron concentration of 5×1015 cm−3 were 7000 and 23 000 cm2/V s at 300 and 77 K, respectively. The carbon concentration estimated from the 4.2 K photoluminescence measurements and the Hall mobility data is on the order of 5×1015 cm−3. Epitaxial GaAs films have also been grown from TMGa and As at 600 °C. These films are always p-type with room temperature net carrier concentration of 1015 cm−3 and higher and have higher carbon concentrations. Thus, the use of elemental arsenic for epitaxial growth of GaAs provides a cost-effective technology for many, particularly large area, GaAs devices.
Characterization of lubricated states on carbon coated media by low energy photoelectron spectroscopy method in ambient atmosphere
Authors: Nishimori Ken-ichi , Tanaka Kohichi , Inoue Yasunobu
Published: July 2002

In this paper, we demonstrated the usefulness of low energy photoelectron spectrometer (LEPS) to characterize lubrication states on sputter carbon coated thin-film disk. The threshold of photoelectric emission from lubricated sputter carbon, which was obtained by LEPS, gave significant information of the surface state on lubricated sputter carbon, and it explained the experimental results on the tribological behavior between the slider and lubricated disk. Furthermore, the thickness of the lubricant above 5 nm can be evaluated by measuring the attenuation of photoelectrons. It is applicable to the in situ measurement of photoelectric surface states of disk samples in ambient atmosphere without destroying them. This has a great advantage over the conventional photochemical analysis such as x-ray photoelectron spectroscopy and Auger electron spectroscopy.
Study of point defect clusters produced by BF+2 implantation in silicon single crystals
Authors: Lal Krishan , Bhagavannarayana G. , Virdi G. S.
Published: July 2002

High-resolution diffuse x-ray scattering (DXS) measurements made with a multicrystal x-ray diffractometer have been used to characterize point defect clusters produced by 90-keV and 135-keV BF+2 implantations (fluence=1×1015 cm−2). The specimens were 50-mm-diam (100) silicon single crystals (n type; 4–6 Ω cm resistivity). A highly monochromated and collimated Kα1 is obtained by three-plane (111) silicon single crystals oriented in (+,−,−) setting. The DXS intensity around 400 reciprocal lattice point was measured along [100±] directions. Implantation produced a slight broadening of diffraction curves from ∼6 to ∼7 arcsec. From unimplanted regions diffuse scattering was primarily due to isolated interstitial point defects in the investigated volume of reciprocal space. Implantation was found to produce interstitial point defect clusters. Experimental data has been analyzed by using a phenomenological model for dislocation loops by using a curve fitting method. The values of loop size Rcl, volume of the loops Acl, and number of defects per loop Ncl have been determined. For implantation energies of 90 and 135 keV, these are, respectively, Rcl=1.47×10−4 and 1.29×10−4 cm, Acl=2.92×10−16 and 2.27×10−16 cm3, and Ncl=1.46×107 and 1.37×107.
Low-threshold InGaAs/GaAs strained layer single quantum well lasers with simple ridge waveguide structure
Authors: Chao C. P. , Hu S. Y. , Law K-K. , Young B. , Merz J. L. , Gossard A. C.
Published: July 2002

Double heterostructure InGaAs-GaAs strained-layer single quantum well ridge waveguide lasers grown by molecular beam epitaxy were fabricated by using in situ laser monitored reactive ion etching to form the ridges. Continuous-wave threshold current as low as 3.5 mA was obtained on a ridge laser diode of 3.3 μm wide and 215 μm long having cleaved mirrors. The lasing wavelength is at 0.988 μm and the measured differential external quantum efficiency is 61%.
The effect of annealing on resistivity of low pressure chemical vapor deposited titanium diboride
Authors: Choi C. S. , Xing G. C. , Ruggles G. A. , Osburn C. M.
Published: July 2002

The correlation between the resistivity of TiB2 and the chemical vapor deposition parameters and subsequent annealing temperature have been studied. The films deposited from TiCl4 and B2H6 above 600 °C are found to be nearly stoichiometric TiB2 with a resistivity of 250 μΩ cm±20%, while those deposited below 600 °C are found to contain excess boron, and exhibit a higher resistivity. The resistivity of the films is observed to be independent of thickness in the thickness range from 15 to 550 nm. After high-temperature rapid thermal annealing (≳1000 °C), the resistivity is reduced to as low as 36 μΩ cm. The grain size in annealed films increases exponentially with temperature. The conductivity and the Hall mobility of the samples increase linearly with the grain size. The activation energy of grain growth, conductivity, and Hall mobility was found to be the same, 1.6–1.7 eV. From these results, it is evident that the carrier mobility of TiB2 is dominated by grain boundary scattering. The lower limit for resistivity of chemical vapor deposited TiB2 films is expected to be attainable only after annealing at temperatures approaching 1300 °C.
Optical constants and electrical transport parameters of HfSi2
Authors: Borghesi A. , Marabelli F. , Guizzetti G. , Michelini M. , Nava F.
Published: July 2002

HfSi2 polycrystalline thin films, grown by coevaporation of Hf and Si and subsequently annealed at 850 °C, were studied by electrical resistivity measurements (from 10 to 900 K), Hall voltage (from 10 to 300 K), and optical reflectance (at room temperature) from 5 meV to 12 eV. Composition and structure of the films were investigated by Rutherford backscattering spectroscopy and x-ray diffraction. HfSi2 is metallic with (i) a high residual resistivity, (ii) a phonon contribution to the resistivity showing a negative deviation from linearity, and (iii) low-energy interband transitions. Transport measurements yielded a Debye temperature of 430 K, a free-carrier concentration of ∼4×1021 cm−3, and a mean free path of 139 Å. The reflectivity was Kramers–Kronig transformed to obtain the dielectric functions which, at low energies, are discussed in term of the Drude model. The optical parameters agree quite well with transport results, thus permitting one to obtain a reasonable value for the Fermi velocity.
The influence of the indium incorporation rate on the lasing wavelength of InGaAs lasers grown by molecular beam epitaxy
Authors: Mariella R. P. , Lehew S. , Guthreau W.
Published: July 2002

Lasing wavelengths have been measured from 871 to 966 nm for a series of graded-index separate-confinement-heterostucture lasers with single InGaAs strained-layer quantum wells which were grown by molecular beam epitaxy (MBE). These wavelength data are compared to the corresponding indium fluxes in order to determine the incorporation rate of indium as a function of the substrate temperature during the growths. Kinetic models based on a simple sticking coefficient or based on the Law of Mass Action can fit these data for MBE growth with substrate temperatures of 570 or 625 °C.
Research on the model for solute redistribution
Authors: Chen Kuiying , Li Qingchun , Guo Junqing
Published: July 2002

We research the Aziz model [J. Appl. Phys. 53, 1158 (1982); Mater. Sci. Eng. 98, 369 (1988)] for solute redistribution and extend it based on the fact that the detailed balance does not hold if a system is far from equilibrium. In addition, comparison is made with the Aziz model; the discussion on physical variables used in the Aziz model is undertaken. Since the detailed balance has broken down, the interface velocity predicted in our communication at which the solute trapping occurs is greater than that in the Aziz model.
Observation of anomalous resistive transition around 160–200 K in Y5Ba6Cu11Ox thin films
Authors: Ma Q. Y. , Chang Chin-An , Yang E. S.
Published: July 2002

A large resistive transition between 160–200 K has been observed in Y5Ba6Cu11Ox thin films. The films were deposited on MgO substrates by electron-beam evaporation and annealed through rapid thermal annealing. With 960–980 °C, 30–60 s RTA, the films showed a resistance drop about one order of magnitude around 160–200 K. This resistive transition was measured reproducibly over many samples. The preparations and measurements of the Y5Ba6Cu11Ox films were similar to those of the YBa2Cu3O7−x films. The x-ray diffraction pattern indicated that the films mainly contain the YBa2Cu3O7−x phase. The films were polycrystalline with grain sizes of a few μm and an average thickness of 0.4 μm.
Josephson tunneling and gap structure in Y1Ba2Cu3O7−y/oxide barrier/Pb planar junctions on tetragonal LaSrGaO4 (100) substrates
Authors: Wen Z. , Iguchi I. , Nakamura K.
Published: July 2002

The Y1Ba2Cu3O7−y/oxide barrier/Pb thin film tunnel junctions are fabricated on the (100) plane of new tetragonal LaSrGaO4 single-crystal substrates by an in situ electron-beam deposition technique. Reproducible Josephson behavior is observed for all fabricated junctions. Above a Josephson critical current, a premature switching voltage of about 1 mV appears. The I-V curve under an applied magnetic field exhibits low-leakage quasiparticle tunneling characteristic. Modulation of Josephson critical current by the applied magnetic field yields a reversible Fraunhofer-like pattern against flux direction.
Influence of composition of MgO-doped lithium niobate on phase-matching temperature for frequency doubling in the visible
Authors: Young W. M. , Feigelson R. S. , Jundt D. H. , Fejer M. M.
Published: July 2002

The dependence of the phase-matching temperature for second harmonic generation (SHG) of 1064-nm radiation on Li/Nb and Li/Mg ratios in MgO-doped lithium niobate crystals was investigated. Crystals studied were grown from melts with 0, 1, 2, and 5 mol % MgO and were equilibrated to different Li contents through a vapor-phase-transport process. Crystals with no MgO doping, equilibrated to the Li-rich phase boundary, had the highest phase-matching temperature. At room temperature (25.5 °C), this material phase-matched for SHG of 978.4-nm radiation to generate blue light.
Experimental study of the scattering of a compressional wave by an elastic wedge
Authors: Piet J.-F. , de Billy M.
Published: July 2002

We investigated the diffraction pattern of an acoustic beam produced by the edge of a dihedral angle. The incident beam is perpendicular to the edge, and the angular variations of the scattered field are recorded in a plane which is perpendicular to the edge. The frequency of excitation is 2.5 MHz, and the dimensions of the samples are much larger than the incident wavelength. The experimental measurements of the angular diagrams are discussed in terms of surface waves and conversion modes.
Aluminum-coated optical fibers as efficient infrared timing fiducial photocathodes for synchronizing x-ray streak cameras
Authors: Koch J. A. , MacGowan B. J.
Published: July 2002

The timing fiducial system at the Nova Two-Beam Facility allows time-resolved x-ray and optical streak camera data from laser-produced plasmas to be synchronized to within 30 ps. In this system, an Al-coated optical fiber is inserted into an aperture in the cathode plate of each streak camera. The coating acts as a photocathode for a low-energy pulse of 1ω (λ = 1.054 μm) light which is synchronized to the main Nova beam. The use of the fundamental (1ω) for this fiducial pulse has been found to offer significant advantages over the use of the 2ω second harmonic (λ = 0.53 μm). These advantages include brighter signals, greater reliability, and a higher relative damage threshold, allowing routine use without fiber replacement. The operation of the system is described, and experimental data and interpretations are discussed which suggest that the electron production in the Al film is due to thermionic emission. The results of detailed numerical simulations of the relevant thermal processes, undertaken to model the response of the coated fiber to 1ω laser pulses, are also presented, which give qualitative agreement with experimental data. Quantitative discrepancies between the modeling results and the experimental data are discussed, and suggestions for further research are given.
Ellipsometric study of variations on the interlayer in chemically prepared CuxS/CdS bilayer thin film
Authors: Vijayakumar K. P.
Published: July 2002

Ellipsometry has been used to study the variation in the irregularities at the interface of CuxS/CdS p-n junctions with annealing temperature. It is found that annealing of CdS films before chemiplating affects the structure of the layer at the interface drastically. The p-n junction prepared using CdS films annealed at 200 °C is found to have a rather smooth interface; but, as the annealing temperature is increased beyond 200 °C, the interlayer becomes rough again. This is explained on the basis of the difference in reaction rate in and outside the grains. It is found that for CdS films annealed above 200 °C, the reaction rate inside the grains is greater than that in the boundaries. This is verified by measuring the CuxS thickness for different CdS films annealed at different temperatures using ellipsometry. In situ studies on CuxS/CdS junctions revealed during heating that the interface remains rather smooth for a larger range of temperature (up to 200 °C) if the junction is prepared by chemiplating CdS films annealed at 200 °C.
Microstructure of Nd-rich phase in Nd-Fe-B magnet containing oxygen and carbon impurities (abstract)
Authors: Minowa T. , Shimao M. , Honshima M.
Published: July 2002

The microstructures of Nd-Fe-B magnet were examined by scanning electron microscopy (SEM) with wavelength dispersive x-ray spectrometer (WDS) specially equipped lead stearate crystal for lighter elements detection. Investigations were performed on the samples of (Nd0.9Dy0.1)15FebalB8 magnets with various oxygen and carbon content. Oxygen and carbon were added to the alloy, because magnetic properties were extremely influenced by these elements and commercial magnets could not be produced without these impurities. SEM observations revealed a complex microstructure of Nd-rich phase1,2 in grain boundary junctions. Nd-rich phase principally consists of two different phases. One is Nd-rich phase absorbing oxygen and the other is Nd-rich phase condensing carbon. Carbon content were quantitatively confirmed by WDS analysis for the first time. The enrichment of carbon into Nd-rich phases were accelerated by a heat treatment in the temperature range between 500 and 800 °C. Coercive forces have significantly decreased at the content more than 0.1 wt. % of carbon.
EMPA measurements of magnetic microstructure in ultrathin films (invited) (abstract)
Authors: Unguris J. , Hart M. W. , Scheinfein M. R. , Celotta R. J. , Pierce D. T.
Published: July 2002

Very little is currently known about domains and domain walls in ultrathin ferromagnetic films, i.e., films that are a few atomic layers to a few tens of layers thick. A major experimental difficulty is that these films must be grown and examined in situ with strict control over their atomic structure and elemental composition. Recently, scanning electron microscopy with polarization analysis (SEMPA) has been used to image domains in Fe1and Co2 films that were only a few monolayers thick. The structure and composition of the films were monitored during growth using RHEED (reflection high energy electron diffraction) and Auger electron spectroscopy. The magnetic structure of these films was then investigated in situ using SEMPA. SEMPA directly images the magnetization by measuring the spin polarization of secondary electrons emitted in the scanning electron microscope. This combination of surface sensitive techniques allows one to study the domain structure, anisotropy and magnetization of the films as a function of various growth parameters, such as, thickness, substrate roughness, and temperature.
A thermally stimulated process in magnetic complex permeabilities of light illuminated yttrium iron garnet with some degrees of oxygen vacancy
Authors: Hisatake K. , Matsubara I. , Maeda K. , Fujihara T. , Kawai Y. , Kimura S.
Published: July 2002

On warming the previously white light illuminated yttrium iron garnet with some deficiency of oxygen with a white light, an imaginary part of permeability μ″ below 10 kHz has been found to show the triple peaks as a function of temperature, the activation energies of which are 0.095–0.22, 0.50, and 0.81 eV, respectively. Furthermore, the height of each peak depends strongly on the illuminating time of exciting light. These features have been discussed and interpreted based on a modified ‘‘two-center’’ model.
Magnetotransport in magnetic epitaxial metal layers buried in (Ga,Al)As heterostructures (invited) (abstract)
Authors: Allen S. J. , DeRosa F. , Gilchrist H. L. , Harbison J. P. , Leadbeater M. , Miceli P. F. , Palmstro/m C. J. , Ramesh R. , Sands T. , Zrenner A.
Published: July 2002

Incorporation of magnetic, metallic quantum wells in semiconductors has added new dimensions to epitaxial heterostructures. Magnetotransport experiments explore the interplay of bandstructure, quantum confinement, dimensionality and magnetism. Rare earth monoarsenides, like ErAs, have been grown as buried layers in GaAs. The material is a semimetallic antiferromagnet that exhibits spin-disorder scattering at the Néel point. By diluting the ErAs with ScAs, lattice matching to GaAs can be achieved and these materials exhibit Shubnikov–de Haas (SdH) oscillations. The exchange interaction between the conduction band and the 4f spin deduced from SdH agrees with that derived from spin-disorder scattering. Surprisingly, down to 2 monolayers, quantum confinement does not convert the semimetal into a semiconductor. This is not understood. But, the Neel point can be seen to drop by a factor of two by following the spin-disorder scattering. In the few monolayer regime the magnetotransport can change its character and is more aptly described by bound magnetic polarons. More recently, ferromagnetic, metastable, τ-MnAl layers have also been grown on GaAs. Thin layers of τ-MnAl grow in such a way that the tetragonal axis is perpendicular to the interface. The extraordinary Hall effect and longitudinal magnetotransport confirm that the moment has the desired property of being oriented perpendicular to the interface.
Preparation and stability of NdDyFeCoTi magneto-optical amorphous films
Authors: Zhang Si Jun , Li Xiao Li , Yang Xiao Yong , Zhang Feng Ping
Published: July 2002

Because the light rare-earth element Nd makes a significant contribution to the Kerr effect and the heavy rare-earth element Dy can improve the coercivity and perpendicular anisotropy, NdDyFeCoTi magneto-optical material was studied. The alloy targets were prepared by a vacuumm melting method with compositions (NdxDy1−x)25(Fe0.65Co0.30Ti0.05)75 with x=0.2–0.3. Because of the addition of Ti, the mechanical strength of the target was improved. Amorphous NdDyFeCoTi films were prepared by rf magnetron sputtering onto glass substrates at zero bias, a low Ar pressure of 3–7 mTorr, and a low-input sputtering power of 100–300 W. The magnetic and magneto-optical properties of these films were studied by VSM, Kerr hysteresis tracer, and Auger electron spectroscopy. The Kerr angle θk of 0.3° and the coercive force Hc of 3–5 kOe have been found. The stability of the films was examined by exposure in air for one month and annealing at 100–250 °C. The magneto-optical properties of the films exhibit no obvious change after exposure in air, but after annealing at 200–250 °C the properties of NdDyFeCoTi with a SiO2 protective layer became poor. As a result, it is necessary to improve the stability of NdDyFeCoTi magneto-optical films by a protective layer without oxygen such as AlN.
Strong exchange coupling in lanthanide bis-(phthalocyaninato) sandwich compounds
Authors: Trojan Kathleen L. , Hatfield William E. , Kepler Keith D. , Kirk Martin L.
Published: July 2002

Bis(phthalocyaninato)lanthanide sandwich compounds, which have the formula Pc2-LnPc1-, have been synthesized for Ln=terbium, holmium, and lutecium. Low-temperature magnetic susceptibility data for Ho(Pc)2 and Tb(Pc)2 show a reduction in moment from that which is expected for the lanthanide free ion value, which correlates with an antiferromagnetic exchange between the lanthanide f electrons and the phthalocyaninato ligand radical electron. The g factors determined from least-squares fitting of the Curie–Weiss law to the magnetic data show excellent agreement to the g factors calculated for the strongly coupled state. Magnetic moments calculated from the experimentally determined Curie constants are also in good agreement with those expected for the strongly coupled state. Low-temperature magnetic susceptibility data for Lu(Pc)2 follows the Curie–Weiss law with a limiting moment of 1.8 μB at 100 K. Since lutecium has a 1S0 ground state, only the phthalocyanine(1-) ligand would be expected to contribute to the magnetic susceptibility in this system. Room-temperature electron paramagnetic resonance measurements show no transitions at or near g=2, indicative of a free radical, due to the strong antiferromagnetic coupling of the ligand radical electron with the lanthanide f electrons. In the case of LuPc2, where no unpaired f electrons exist, a transition at g=2.00 is present.
Fe3+-substituted silicate gels: Precursors for zeolite-based catalysts
Authors: Pannaparayil T. , Marande R. , Komarneni S.
Published: July 2002

In order to investigate the possibility of isomorphous substitution of Fe3+ for Si4+ in the tetrahedral silicate network, two Fe-substituted silicate gel samples with Si/Fe atom ratios of 50 and 25 were prepared by the solution–sol-gel processing technique. The samples were characterized by magnetization and Mössbauer spectroscopic measurements over the temperature range 293–4.2 K. The magnetic moment of the Fe ions and Mössbauer isomer shifts were used to determine the valence state and coordination symmetry of the Fe species present in these gel samples. It has been found that iron enters substitutionally into the tetrahedral silicate structure, especially at low concentrations. This result is of importance, since Fe substituted silicates can be used as catalyst precursors in several technologically relevant chemical reactions.
Effects of alternation in some quasi-one-dimensional magnetic materials
Authors: Kirk Martin L. , Hatfield William E. , Lah Myoung Soo , Kessissoglou Dimitri , Pecoraro Vincent L. , Morgan Larry W. , Petersen John D.
Published: July 2002

Exchange coupling in Cu(II) and Mn(III) compounds with unusual structures is discussed. {[Cu(bipyrimidine)(OH)(H2O)] (ClO4)}n has an alternatingly bridged structure with alternating ferromagnetic (+167.6 cm−1 through the hydroxo bridge) and antiferromagnetic (−79.8 cm−1 through the bipyrimidine bridge) interactions. Copper(II) phthalate monohydrate has alternating next-nearest-neighbor exchange with J=−12.3 cm−1 and α=0.06. This is the first member of this class. The compound K2[Mn(III) (salicylate)2][Mn(III) (salicylate)2]{CH3OH]2 has manganese ions in two environments alternating along the chain. A modified model for the chain is presented, and exchange coupling is found to be small since magnetic orbitals are not linked by the bridging ligand.
Magnetic and structural characterization of the 2D XY-ferromagnet Rb2CrCl2I2 (abstract)
Authors: Visser D. , Bramwell S. T. , Kremer R. K.
Published: July 2002

Rb2CrCl2I2 crystallizes with a Jahn–Teller deformed K2NiF4 structure. This results in a ferromagnetic behavior for this compound. Rb2CrCl2I2 orders ferromagnetically at Tc=56.9(2) K. Magnetization and magnetic susceptibility measurements, using a vibrating sample magnetometer, Faraday balance, and SQUID magnetometer, on polycrystalline samples were used for the magnetic characterization. Rb2CrCl2I2 shows a Curie–Weiss behavior between 150 and 300 K. The intraplanar superexchange constant J/k=5.8 K. The intra- and interplanar anisotropy have been obtained from the magnetization curves at 4.2 K and are estimated at Hintra=0.16(2) T and Hinter=4.5(2) T.
What happens to dense excess electrons in antiferromagnetic semiconductors, especially in EuTe?
Authors: Umehara Masakatsu
Published: July 2002

With the aim of understanding what happens to dense excess electrons coupled with localized spins (f spins) in Eu-rich EuTe, the Kohn-Sham density-functional method is applied to dense excess electrons bound to doubly charged donors in antiferromagnetic semiconductors. The following two cases are studied: one is a pseudocrystal model of He-like donors coupled with f spins by the s(d)−f exchange interaction, and the other is a kind of dense bound molecular magnetic polarons. The comparison between the calculated result and the experiment shows that the former seems quite likely for Eu-rich EuTe: a weakly inhomogeneous state, whose binding energy is primarily due to the gain in the s(d)−f exchange interaction, may be responsible for the semiconductive behavior with surprising small activation energies and the nonmetal-metal transition, observed at the carrier concentration of ∼1019/cm3. The direct consideration of the presence of the Te vacancy seems quite important for understanding the behavior of the excess electrons in Eu-rich EuTe.
A digitizer based on reflections in delay lines (abstract)
Authors: Hristoforou E. , Reilly R. E.
Published: July 2002

A new type of digitizer is proposed, based on the generation of an acoustic pulse reflection in a magnetostrictive delay line (MDL), at a point where a force is applied. A conductor wire C crosses an array of MDL positioned at a distance close to their end and carries a pulsed current. The measuring portion of the delay lines is under a flexible mat, so that they are not pressed at any point if no force is applied. The initial acoustic pulse in the line is detected by short coils between C and the end of each line. If a force is applied on the flexible mat above a delay line, the position and the amplitude of the applied force are respectively defined by the delay and the amplitude of the reflected pulse, with respect to the initial one. Experimental results are given for the function of the peak value of the reflected signal with respect to the applied input force under various values of pulsed current and dc bias field, for a 1-mm-wide and 150-cm-long Metglas 2605SC delay line. The resolution of this type of digitizer along the length of the delay line can be 0.1 mm, while in the other dimension it depends on the pitch of the flexible array channels (i.e., on the width of the delay lines) and can be improved by using two arrays of delay lines, orthogonal to each other.
Long wavelength dynamics in a 1D planar ferromagnet: Magnetostatic modes and soliton-induced damping in CsNiF3
Authors: Reich Daniel H. , Lévy Laurent P. , Hawthorne Dean L.
Published: July 2002

Above 2.6 K, CsNiF3 is an excellent example of a soliton-bearing spin-chain system. We have studied the long wavelength excitations in CsNiF3 by spin resonance, using a strip line technique that couples to finite q excitations. In addition to the uniform precession mode, we have observed a magnetostatic resonance. It lies at a lower energy than the uniform mode, consistent with the spectrum expected in linear response. The uniform mode, however, broadens much more rapidly with temperature. We propose that a dipolar magnon-soliton interaction is the dominant channel for the relaxation of long wavelength excitations in this quasi-1D system.
Magneto-optical properties of ion-implanted Fe films
Authors: Gondō Y. , Aoyagi K. , Kogure H.
Published: July 2002

Magneto-optical properties, along with the structural changes of Fe films induced by Tb-, Bi-, and Fe-ion implantations, are presented. The polar Kerr rotation in a static magnetic field up to 13 kOe and the Faraday rotation in a pulse magnetic field up to 43 kOe were examined. Enhancement of the specific Faraday rotation in the ion implanted Fe layer is generally found at low doses. It is found that this enhancement is attributed to the changes of the optical constants n and κ of the Fe films due to the implantation. From the saturation field determined by the Faraday rotation versus magnetic field loop, the internal stress in Fe films is estimated. It is also found that the observed changes of the optical constants in the Fe-ion implanted Fe films are caused by the structural changes induced at low implantation doses.
Bloch line propagation with film thickness modulation bit patterns (abstract)
Authors: Maruyama Y. , Fujimoto K. , Suzuki R. , Imura R.
Published: July 2002

Bloch line (BL) propagation with a field-access scheme is necessary for the memory with low power consumption and high storage density. Previously we reported the field-access propagation using Co-Pt bit patterns.1 In these propagation patterns, (a) the drive field margins depend on the BL propagating direction to the magnetized direction of Co-Pt patterns and (b) the operating bias field margins are different at each corner of the stripe domain. The purpose of this paper is to solve these two problems. A new propagation method has been investigated using film thickness modulation patterns.2 The materials used here were magnetic bubble garnet films with composition of (YSmLuCa)3(FeGe)5O12. Fundamental characteristics of the samples are as follows: saturation induction 4πMs 200 G, anisotropy field Hk 1700 Oe, stripe width w and thickness h 5 μm. The thickness modulation patterns with an amplitude of about 1000 A were fabricated with the ion milling method. The stripe domains were stabilized around the 100% etched grooves, and aligned with 18 μm period. BL pair was propagated in the all part of the stripe domain walls at 500 kHz frequency, applying the triangular bias pulsed field with 50 ns rise time and 1000 ns fall time. As the result of the experiments, it has been found that the drive field margins are independent of BL propagation direction and the difference in the operating bias field margins at the each corner of the stripe domain becomes smaller. The BL propagation around the stripe domain was achieved with 5% bias field margin at the drive field of 8.5 Oe.
Hysteretic model for Barkhausen noise and the magnetically induced velocity change of ultrasonic waves in ferromagnets under stress
Authors: Sablik M. J. , Kwun H.
Published: July 2002

The magnetomechanical hysteresis model of Sablik and Jiles is applied to Barkhausen noise and the magnetically induced velocity change (MIVC) of ultrasonic waves in stressed ferromagnets. Barkhausen noise is modeled as being proportional to the irreversible differential susceptibility (dMirr/dH), i.e., the rate of change of irreversible magnetization. The predicted dMirr/dH signal is shown to qualitatively agree with that of the experimental Barkhausen signal. The MIVC effect is modeled by adapting the single domain model of Kwun to a multidomain model. Qualitative agreement is seen with experimental behavior under both tension and compression. In formulating, the approach used by Sablik, Jiles, and Barghout to compute the magnetostriction is utilized.
Japan, magnetism, and technological competition (invited) (abstract)
Authors: Callen Earl
Published: July 2002

Magnetism has been the fountainhead of ideas for understanding cooperative phenomena and magnetics is at the foundation of $60 billion of annual trade (Mallinson). And yet, led by the National Science Foundation, the federal science contracting agencies years ago dropped support of magnetism and magnetics. A few months ago I returned from 3 years in Tokyo as an ONR scientific cooperation and exchange officer, monitoring magnetism and superconductivity. Unlike the Americans, the Japanese, traditionally very strong in magnetics, continue to concentrate resources there. World-wide sales of magnetically soft electrical steels come to $5 billion/year. The US is now the largest external buyer of Japanese electrical steel. One million tons (over $1 billion) of top grade, grain oriented (GO) silicon steel are shipped annually. Half the world’s GO steel is produced by Nippon Steel (25 000 tons/month) and Kawasaki Steel (15 000 tons/month). In perpendicular magnetic recording (PMR) the Japanese are pre-eminent. Of the 342 attendees at the first Conference on PMR last year, less than 50 were Westerners. Co-Cr and Ba ferrite are now Japanese stories. In magneto-optics the Japanese are dominant. Twenty-five universities have had Monbusho-funded programs in magneto-optical recording materials, and MITI is building industry/university cooperative R&D laboratories on the campuses. The U.S. can and has to learn some things from Japan. I will offer a number of suggestions in the talk.
Magnetic transition temperatures of the Sm-Gd alloy system
Authors: Rives Carol J. , Anderson Elmer E. , Arajs Sigurds
Published: July 2002

This paper presents the magnetic transition temperatures for samarium-gadolinium alloys with concentrations ranging from 8%Gd up to 97%Gd. Our results show a single magnetic transition for gadolinium-rich alloys with transition temperatures decreasing as the samarium concentration increases. This trend continues through alloys of intermediate concentration, although the nature of the transition is not clear. For the samarium-rich end of the alloy range, the samarium-type antiferromagnetic transitions are clearly seen. The transition temperatures decrease as the two-thirds power of the de Gennes factor until the atomic concentrations of the two elements become almost equal, at which point a steeper decline is seen.
First-order instability theory for magnetostatic modes in ferromagnetic spheres
Authors: Chen Ming , Patton Carl E.
Published: July 2002

A first-order instability theory for magnetostatic modes in ferromagnetic spheres has been developed. The analysis is based on the interaction of three modes: the uniform mode pumped at microwave frequency ωp and a pair of magnetostatic modes at lower frequencies which sum to ωp. The magnetostatic mode instability arises when the pump microwave field amplitude exceeds some threshold. The theory yields (i) selection rules for the magnetostatic mode pairs with a nonzero coupling to the uniform mode, (ii) a characteristic equation for the frequencies of these modes, and (iii) microwave field threshold amplitudes for the parametric excitation of the mode pairs. For each mode pair, one or more sharp threshold minima are found. The superposition of these sharp minima resembles the complicated structure observed in the subsidiary absorption butterfly curve for single-crystal yttrium-iron-garnet spheres.
Spin cluster excitations in the one-dimensional Ising ferromagnet FeTAC (abstract)
Authors: Ravindran K. , Waplak S. , Drumheller J. E.
Published: July 2002

The compound FeTAC, [(CH3)3NH]FeCl3⋅2H2O, has been reported to be a highly anisotropic, effective S=1/2, one-dimensional ferromagnet above the ordering temperature Tc=3.1 K.1 Our previous low temperature susceptibility measurements in the range of 4.2<T<20 K, and the analysis based on Johnson and Bonner theory, indicate that the susceptibility is almost entirely represented by spin-reversed clusters.2 Here we report our preliminary results of electron paramagnetic resonance measurements at 9.2 GHz on this compound at low temperatures. The most interesting feature of the data along the easy axis is the appearance of the resonance peaks corresponding to g values of about 3.2, 6.4, and 9.6 at 4.2 K (≳Tc). We identify these multiple g-values as an indication of reversal of clusters, of 1, 2, and 3 spins. Bound states have been observed in other Ising systems, such as CoCl2⋅2H2O, in the ordered state.3 To our knowledge, FeTAC is the first compound to show bound state resonance in the paramagnetic region.
Two-dimensional nonequilibrium dynamics of domain-wall motion
Authors: Patterson G. N. , Giles R. C. , Humphrey F. B.
Published: July 2002

The dynamics of magnetic domain-wall motion in two dimensions for materials of interest to vertical Bloch-line memory devices has been simulated on the Connection Machine. By use of a Fourier transform technique to evaluate the demagnetizing fields and explicit time integration of the Landau-Lifshitz-Gilbert equation, the equilibrium configuration of a domain wall and the dynamic structure of a wall in the presence of an external field has been studied. Horizontal Bloch-line (HBL) nucleation, propagation and ‘‘punch through’’ can be observed in moving walls. The domain-wall configuration for stripe chopping has been investigated and HBL motion is seen to be a dominant feature in this process.
Temperature-dependent conductivity of narrow-band metals (abstract)
Authors: Riseborough Peter S.
Published: July 2002

We calculate the temperature-dependent conductivity for an N-fold degenerate Hubbard model, using a 1/N expansion. The conductivity is calculated for the paramagnetic limit of the model. The vertex corrections are included, order by order, in powers of 1/N. The expansion converges rapidly everywhere, except for a small window of size 1/N around the critical point where the paramagnetic phase becomes unstable. In this critical regime, the fluctuations produce large renormalizations of the quasiparticle effective mass. The scattering time due to impurities is also subjected to the same type of renormalization as the effective mass. Due to the cancellation of these two renormalizations the zero-temperature resistivity is unrenormalized. At low temperatures, the resistivity shows a T2 variation characteristic of a coherent Fermi liquid. This is followed by a linear T variation, and at even higher temperatures the resistivity goes through a maximum and then saturates to a value typical of spin disorder scattering. This variation suggests that a temperature induced crossover occurs from a coherent Fermi liquid to an incoherent, local moment phase.
Reduction of noise from external sources for floppy disk heads
Authors: Murata Y. , Tanabe S. , Sugawara N. , Suzuki S. , Shibata H.
Published: July 2002

A novel measurement technique and an analytical model for the determination of externally induced noise in floppy disk heads have been developed. Floppy disk heads are generally susceptible to magnetic fields from, among other things, machinery and CRTs. When an alternating magnetic field is applied to a floppy disk head, a magnetic flux will penetrate into the head, inducing a noise voltage in its coil. Since the floppy disk head has a complex geometry, the magnetic-flux distribution in the head is complicated. The distribution has been studied by a three-dimensional finite-element analysis and effective methods for reducing the noise voltage have been found. New heads have been fabricated according to the analysis results and a noise voltage reduced by 50% has been obtained. The measured noise voltages agree well with the calculated values.