bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaling approach to heavy fermions: Pressure effects in CeAl3
Authors: Continentino M. A. , Japiassu Gloria M. , Troper A.
Published: July 2002

We discuss experimental results on CeAl3 under external pressure using a recently proposed scaling theory of heavy fermion systems. Specific heat, resistivity, and electron spin resonance (ESR) data at different pressures are examined to obtain relations between the critical exponents characterizing the quantum critical behavior of this system. We observe that the critical exponents governing the behavior of CeAl3 belong to the same class of universality of those obtained for CeRu2Si2.
Microscopic origin of marginal Fermi liquid in strongly correlated spin systems (abstract)
Authors: Protogenov A. P. , Ryndyk D. A.
Published: July 2002

We consider the consequences of separation of spin and charge degrees of freedom in 2+1D strongly correlated spin systems. Self-consistent spin and charge motions induced by doping in sites of ground and dual lattices form such a spectrum of quasiparticles which together with dispersionless character of the collective excitation spectrum and the chemical potential pinning in the band center yield the necessary behavior of charge and spin polarizability to support the theory of marginal liquid formulated by Varma et al. [Phys. Rev. Lett. 63, 1996 (1989)].
Microwave induced nonlinearity in low frequency biased YBCO superconducting weak link rings (abstract)
Authors: Huang Y. , Widom A. , Vittoria C.
Published: July 2002

We fabricated weak link rings using YBCO thin films deposited on the single crystal MgO substrate by laser ablation. The dimensions of the microbridges in the rings were between 0.5–1 μ in length and 500 Å–0.5 μ in width which were made by focused ion beam milling. We biased the ring by Faraday induction voltage while monitoring the voltage across the microbridge. The frequency of the input signal was varied between 10 kHz and 5 MHz. When we superimposed a microwave signal (2–18 GHz) to the ring, below the superconducting transition temperature (Tc), we observed strong nonlinearities in the voltage measured across the microbridge. The microwave frequency was chosen to be close to the ring natural electromagnetic resonance.
Nonlinear effect of small volume fraction on the coercivity for acicular particles
Authors: Chang Ching-Ray , Shyu Jyh-Pone
Published: July 2002

Origins of nonlinear dependence of the coercivity on the volume fraction for an assembly of acicular particles are investigated. For a very small volume fraction, the nonlinear relationship between the coercivity and the volume fraction is attributed to the nonuniform distribution of particles and the surface effects. Considering the influence of surface, we find the coercivity can be either increasing or decreasing for a small volume fraction with different surface anisotropy constant Ks. Observed results agree with predictions based on the present model.
The coercivity of particle arrays
Authors: Klik Ivo , Huang Huei Li , Chang Ching-Ray
Published: July 2002

Thermal effects in an array of nonidentical, noninteracting single domain ferromagnetic particles are studied. Two sources of stochasticity are recognized within the array: the intrinsic stochastic nature of thermal relaxation and variations within the particles’ volume and orientation with respect to applied field, both are discussed in turn. We use the log-normal volume distribution {∼(σV)−1exp[−ln2(V/V0)/(2σ2)]} and a cosν ψ angular distribution to calculate the mean coercivity B̄c of a particle array. We find that B̄c increases rapidly with increasing average volume <V≳=V0 exp(σ2/2) while for misaligned particles (ν≤∞) we observe a sudden decrease in B̄c accompanied by a gradual loss of frequency dependence.
Magnetic interactions in CoCr thin films
Authors: Skorjanec J. , Close J. , Kirchner N. , Iverson P. , Dahlberg E. Dan
Published: July 2002

Both the isothermal remanent magnetization and the dc demagnetization remanence were measured on thin films of CoCr with a perpendicular anisotropy energy suitable for perpendicular recording media. The measurements were made with two applied magnetic field geometries, parallel and perpendicular to the film plane. Plots of the dc demagnetization remanence versus the isothermal remanent magnetization were used to determine the presence of interactions for both applied magnetic field geometries. As expected, the perpendicular magnetization process is dominated by the demagnetization field. When the data are corrected for the demagnetization field, a residual negative interaction is found from the perpendicular data. This negative interaction was also observed in the parallel applied field geometry plots, where the demagnetization factor is negligible. The success of the analysis, using a mean-field approximation to model the interactions, which in this case is the demagnetization field, suggests a general technique to quantify interactions in magnetic systems.
High-energy magnetic excitations in Mn90Cu10
Authors: Fernandez-Baca J. A. , Hagen M. E. , Nicklow R. M. , Perring T. G. , Tsunoda Y.
Published: July 2002

The study of the magnetic excitations in Mn-rich alloys should be a good test of the multiband calculations of the spin dynamics of pure γ-Mn, which is a prototypical itinerant-electron antiferromagnet. In this paper we report the results of recent neutron inelastic scattering measurements performed on Mn90Cu10 at room temperature (T=0.63TN) and up to 300 meV of energy transfer. These measurements were performed using the high-energy transfer (HET) chopper spectrometer at the ISIS spallation neutron source, Rutherford Appleton Laboratory, U.K. The results are in agreement with calculations using a model scattering function convoluted with the full HET resolution function. In this model there is a steep linear spin-wave dispersion (D≊250 meV Å) for wave vectors up to ≊1/2 of the Brillouin zone and a strong damping which is linear in the wave vector q. For larger wave vectors the spin-wave energies are constant at about 190 meV. These features are qualitatively similar to the predictions of Cade and Young for pure γ-Mn.
High permeability of Fe–Al–Si alloys films deposited on plasma-free substrate by dc bias sputtering
Authors: Hirata Toyoaki , Naoe Masahiko
Published: July 2002

Soft magnetic Fe75Al10Si15 (Sendust) films were deposited on substrates separated from the high-energy plasma using the facing targets sputtering (FTS) apparatus. The Ar bias voltage VB was changed in the range of 0 to −150 V, and the substrate temperature Ts was adjusted in the range of 50∼400 °C. Films deposited at PAr of 1.0 mTorr and VB of −100 V possessed almost the same composition as that of the targets: Fe75Al10Si15. Films deposited at PAr=1.0 mTorr, VB=0 V and Ts=350 °C exhibited a saturation magnetization 4πMs=11.7 kG, a coercivity Hc=0.6 Oe, and a static relative permeability μrs=5000. On the other hand, films deposited at PAr=1.0 mTorr, VB=−100 V and Ts=50 °C exhibited 4πMS=12.0 kG, HC=0.4 Oe and μrs=8000. In addition, these films exhibited radio frequency relative permeability μrf of 2850 and 1050 at fM=10 and 50 MHz, respectively.
Propagation characteristic of a ferrite image guide
Authors: Kwan P. , Vittoria C.
Published: July 2002

The propagation of electromagnetic waves in a ferrite image line was theoretically formulated. The formulation was based upon the effective permeability approach. The ferrite image line consisted of an insulating slab of ferrite with a rectangular cross section overlaid on an electrical ground plane. The ferrite was purposely magnetically biased so that FMR coincided with the band of frequencies in which propagation is allowable in the waveguide structure. Insertion loss and phase shifts of the electromagnetic wave signal was calculated as a function of frequency. We suggest that ferrite phase shifters, isolators, filters, and switches operating at the millimeters wavelength may be feasible using this guided structure.
The microstructures and magnetic properties of some cast and annealed Pr-Fe-Cu-B alloys (abstract)
Authors: Mycock G. J. , Faria R. N. J. , Harris I. R.
Published: July 2002

This paper reports the results of investigations of the microstructures and magnetic properties of some cast and annealed Pr-Fe-Cu-B alloys represented by the formulas PrxFe94.3−xCu2.0B3.7, Pr20.5Fe75.8−xCuxB3.7, and Pr20.5Fe77.5−xCu2.0Bx. Microstructural examination of these alloys showed that most of them exhibited Pr2Fe14B plate-like grains with the c axis perpendicular to the plate surface and there was c-axis alignment in the plane perpendicular to the predominant cooling direction. SEM examination of the alloys showed that the copper was concentrated in the intercrystalline regions and only trace quantitiies (<0.4 at. %) of copper were detected in the Pr2Fe14B phase. A eutectic mixture and a needle-like phase were observed in the intercrystalline regions. The permanent magnetic properties of the alloys, subject to various casting conditions and heat treatments, were investigated and enhanced properties were observed perpendicular to the predominant cooling direction. The largest (BH)max value (70 kJ m−3) was achieved for the Pr20.5Fe73.8Cu2.0B3.7 alloy after annealing at 1000 °C for 5 h to remove the free iron. An improvement in the intrinsic coercivity of 73% was observed for this alloy on annealing for 3 h at 500 °C. Attempts have been made to correlate the permanent magnetic properties of the alloys with their corresponding microstructures.
Effect of the MFM tip on the measured magnetic structure
Authors: Aharoni Amikam , Jakubovics J. P.
Published: July 2002

The distortion of the measured magnetic structure by the measuring magnetic tip in a magnetic force microscope (MFM) is studied for the case of a spherical Ni or Fe tip in contact with an Fe film which contains one domain wall, or which is uniformly magnetized. The distortion is found to be negligibly small for this particular case.
Hall effect and resistivity in Y-3d (Fe, Ni) based amorphous films
Authors: Peral G. , Colino J. , Alameda J. M. , Vicent J. L.
Published: July 2002

We have studied the magnetic behavior of amorphous Y-3d based systems, using resistivity and Hall effect measurements. YxNi1−x metallic glasses show a very different magnetic behavior from Fe glasses, with a cross over (x=0.22) from weak itinerant ferromagnetism to paramagnetism. Two more magnetic metallic glasses have been studied, a typical ferromagnetic system Fe-Si-Y (with Fe content only 52%) and a noncollinear ferrimagnetic (sperimagnetic) system (Fe-Si-Tb). In spite of their very different magnetic mechanisms the resistivities all show low temperature minima with logarithmic dependence below the minima temperatures. This behavior is not magnetic field dependent, with applied fields up to 70 kOe. We show Hall effect measurements that easily distinguish the different intrinsic mechanisms.
Magnetic and transport properties of Fe-Mo and Fe-W alloys
Authors: Jen S. U. , Chang S. A.
Published: July 2002

Two series of polycrystalline Fe100−xMox and Fe100−xWx (0≤x≤10 at. %) alloys were made. In order to preserve a single bcc phase, alloy samples, depending on the x value, were quenched from various temperatures TQ. In general, TQ is higher than 850 °C, and increases with x. X-ray diffraction was used to check the phase and the lattice constant of each sample. Magnetoresistance, electrical resistivity, and magnetic moment were measured at 4 K. Those experimental data are analyzed for Fe-Cr, Fe-Mo, and Fe-W alloys, especially the effects of moving down along the VIB column from Cr to W on the transport and magnetic properties. Comparison is made with Co-based alloys, where the changes of the spin-up resistivity from Co-Ni to Co-Pd and from Co-Pd to Co-Pt are due to the increase in s-s scattering. For Fe-based alloys, however, because the spin-down d band is partially empty (the roles of spin-up and -down bands are reversed), the spin-down resistivity is from s-d scattering instead.
Mössbauer and x-ray investigations of oxidized ultrafine iron particles treated with high-pressure and electrodischarge pulses
Authors: Gavriliuk Alexander G. , Voitkovsky Vladimir S. , Tsiok Oleg B. , Sidorov Vladimir A. , Sadykov Ravil A.
Published: July 2002

Ultrafine iron particles with an average size of 30 nm were obtained by the levitation method in an inert gas flow. Electrodischarge experiments were carried out under a pressure of 3 GPa. The values of the parameters of electrodischarge pulses were sufficient to move defects (ions, atoms, dislocations) by conductivity electrons to destroy the metastable state of nanocrystals, but not sufficient to generate heat wave. This effect had threshold features. After the first pulse the relative resistance drop was more than five times. Next, electrical pulses slightly reduced resistance up to its saturation. Properties of ultrafine iron particles have been studied using Mössbauer absorption spectra and x-ray diffraction for three types of samples: (a) primary powder, (b) powder treated to 3 GPa in a ‘‘toroid’’ device, (c) powder treated by electrical pulses at 3 GPa. An x-ray diffraction pattern revealed seven slightly broadened iron reflexes as well as more broadened oxide film reflexes. Oxide film reflexes correspond to the most intense reflexes of a spinel structure. The integrated intensities of 220,311 spinel reflexes divided by integrated intensity of 110 iron reflex are equal to 0.12, 0.14, and 0.19 for samples (a), (b), and (c) respectively. Thus, the relative content of oxide iron phase increases from samples (a) to (c). The increase of relative content of the oxide iron phase was confirmed by a Mössbauer absorption experiment. This effect can be explained by the transformation of the metastable solution of oxygen in iron lattice to iron oxide with a spinel structure, under the action of high-density current pulses.
Characterization, transport, and magnetic properties of Co/Pd multilayers produced by pulsed laser deposition
Authors: Enrech M. , Skomski R. , Coey J. M. D. , Lunney J. G.
Published: July 2002

Metallic Co/Pd multilayers with equal layer thickness and periods ranging from 5 to 150 Å were deposited using pulsed laser deposition. They have an fcc (111) texture and the diffraction patterns give clear evidence of a modulated period structure. From the period dependence of the in-plane electrical resistivity a diffuse interface between cobalt and palladium of thickness b=6±2 Å has been deduced. Magnetic, magnetoresistance, and Kerr-effect measurements indicate in-plane magnetization. In low fields (B0≤10 mT) the magnetoresistance is highly anisotropic, varying by −2% in the transverse configuration and +1% in the longitudinal configuration due to orbital moment of cobalt in the interface region. The shape of the Kerr-effect major hysteresis loop can be explained by the in-plane component of the anisotropy of the cobalt layers.
Layer thickness dependence of magnetic properties in Mn/Al multilayers
Authors: Hirayama Y. , Takeuchi T. , Futamoto M.
Published: July 2002

Relationships between the magnetic properties and the film structure of Mn/Al multilayers are examined by changing the thicknesses of Mn and Al layers. X-ray diffractions show that the Mn lattice spacing measured vertical to the substrate becomes smaller by increasing the Mn layer thickness or by decreasing the Al layer thickness. Saturation magnetization and magnetic anisotropy vary depending on the change of the Mn lattice spacing. Ferromagnetism and magnetic anisotropy of Mn/Al multilayers are closely related to the strain in the Mn lattice.
Modification of magnetic properties of Fe/Mn multilayers with modulation of layer thickness (abstract)
Authors: Nakagawa Shigeki , Naoe Masahiko
Published: July 2002

It seemed to be possible to distort the Fe crystal lattice in Fe/Mn multilayers, because the atomic radii of α-Fe and α-Mn with cubic crystal lattice are 1.26 and 1.29 Å, respectively. It is very interesting to investigate how crystallographic and magnetic characteristics of the Fe/Mn multilayers were changed by modulating the thickness of Fe and Mn layers. In this study, 2000-Å-thick Fe/Mn multilayers with sharp periodicity were deposited on plasma-free substrate Si wafer by the facing target sputtering method. The Ar gas pressure pAr was set at 2 mTorr. Deposition rates of Fe and Mn layers were 5 and 2 Å/s, respectively. The thicknesses of Fe and Mn, δFe and δMn, were in the range of 20–200 Å and 5–100 Å, respectively. The crystallites in Fe and Mn layers revealed the distinct orientation of α-Fe(110) and α-Mn(411) planes, respectively. The Fe(110) interplanar distance dFe increases from value close to Mn(411) interplanar distance dMn to that close to dFe with increase of the Fe layer thickness δFe in the range of 10–100 Å. The distortion of Fe crystal lattice increased with decrease of δFe and increase of interface number. The difference between the saturation magnetization 4πMs measured for the specimen multilayers and that calculated for the single layer films of simply diluted alloy increased with increase of δFe. However, 4πMs of the Fe layers in Fe/Mn multilayers did not changed with δMn except for the films with δFe as extremely small as 20 Å. And 4πMs took the value of nearly zero at δFe of 10 Å. In the range of δMn of 20–50 Å, the Fe lattice distortion was most remarkable and the coercivity Hc increased highly due to the large in-plane uniaxial anisotropy. Hc took its maximum value of about 70 Oe at δFe and δMn of 50 Å. This result may imply that the distortion of both layers are most remarkable. Consequently, it was confirmed that dFe and the crystallite size in Fe layers were changed and Hc was modified by modulating both δFe and δMn.
Magnetic fluctuations in superconducting La2−xSrxCuO4 (invited) (abstract)
Authors: Mason T. E.
Published: July 2002

Studies of the magnetic dynamics of La2−xSrxCuO4 have been carried out with particular emphasis on a sample with x=0.14 that becomes superconducting at Tc=33 K. This material exhibits incommensurate peaks in the inelastic magnetic neutron scattering with the same geometry as found for a metallic (but not superconducting) sample with x=0.075. In both cases the peak in χ″(Q,ω) is shifted from the commensurate position, (π,π) (in the notation of the square lattice of the CuO2 planes), to (π,π)±δ(π,0) and (π,π)±δ(0,π). The magnitude of the incommensuration, δ, increases with doping, x, as δ≊2x. As the temperature is decreased below 100 K the peaks become sharper in Q space and more intense at low frequencies. This development is interrupted by the superconducting transition which suppresses the fluctuations at low frequencies (below about 6 meV). The loss of low frequency magnetic fluctuations is uniform over the region of reciprocal space where the response is present in the normal state.
A magneto-optic technique for studying magnetization reversal processes and anisotropies applied to Co/Cu/Co trilayer structures
Authors: Daboo C. , Bland J. A. C. , Hicken R. J. , Ives A. J. R. , Baird M. J. , Walker M. J.
Published: July 2002

We report the magnetization reversal and magnetic anisotropy behavior of ultrathin Co/Cu(111)/Co (dCu=20 and 27 Å) trilayer structures prepared by MBE on a 500-Å Ge/GaAs(110) epilayer. We describe an arrangement in which the magnetization components parallel and perpendicular to the applied field are both determined from longitudinal MOKE measurements. For the samples examined, coherent rotation of the magnetization vector is observed when the magnetic field is applied along the hard in-plane anisotropy axis, with the magnitude of the magnetization vector constant and close to its bulk value. Results of micromagnetic calculations closely reproduce the observed parallel and perpendicular magnetization loops, and yield strong uniaxial magnetic anisotropies in both layers while the interlayer coupling appears to be absent or negligible in comparison with the anisotropy strengths. An absence of antiferromagnetic (AF) coupling has been observed previously [W. F. Egelhoff, Jr. and M. T. Kief, Phys. Rev. B 45, 7795 (1992)] in contrast to recent results, indicating that AF coupling [M. T. Johnson et al., Phys. Rev. Lett. 69, 969 (1992)] and GMR [D. Grieg et al., J. Magn. Magn. Mater. 110, L239 (1992)] can occur in Co/Cu(111)/Co structures grown by MBE, but these properties are sensitively dependent on growth conditions. The absence of coupling in our samples is attributed to the presence of a significant interface roughness induced by the Ge epilayer. The uniaxial anisotropies are assumed to arise from strain or defects induced in the film.
Effect of sintering atmosphere on magnetic aftereffect in polycrystalline yttrium iron garnet samples
Authors: Torres L. , de Francisco C. , Muñoz J. M. , Zazo M. , Iñiguez J. I.
Published: July 2002

Time effects associated with domain-wall stabilization processes are investigated at temperatures ranging from 80 to 420 K, for yttrium iron garnet polycrystalline samples sintered in different atmospheres. A very different behavior for samples sintered in high and low oxygen partial pressures is found. Above 0.1 atm the isochronal relaxation spectra show a peak around 180 K that could be associated with an electron diffusion controlled domain-wall relaxation. The activation energy for the process is close to 0.4 eV. Below this pressure, the spectra show both positive and negative peaks as a result of the competition between disaccommodation and accommodation processes. These peaks are closely temperature spaced in the neighborhood of 130 K, and the relaxation mechanism responsible for this behavior is not yet clear.
Heat capacity data of doped NdBa2Cu3Ox
Authors: Allenspach P. , Lee B. W. , Gajewski D. , Maple M. B. , Yoo S. I. , Kramer M. J.
Published: July 2002

Low-temperature specific-heat measurements were performed between 0.4 and 4 K on Nd–Ba–Cu–O-samples doped with Ca and additional Nd. In these samples, the specific-heat anomaly due to magnetic ordering of the Nd3+ ions as a function of hole concentration behaves similarly to that of oxygen-deficient NdBa2Cu3Ox. In samples with 0<Tc<70 K, a broad anomaly due to short range magnetic interaction was found but no indication for long range magnetic ordering could be observed. In the semiconducting samples, 3D-Ising-like anomalies with TN around 1.6 K were measured. In order to explain the behavior of the magnetic anomaly in the oxygen-deficient undoped samples, one could assume that the magnetic interaction depends on lattice parameters or interatomic distances. Our newest results clearly show, however, that the position and shape of the anomaly is mainly controlled by the density of carriers in the superconducting CuO2 planes, and not by structural properties. Thus, the magnetic rare-earth ions are isolated enough from the CuO2 planes not to influence superconductivity (except for Pr), but are not totally decoupled from the rest of the unit cell and the carrier concentration.
Magnetic electron emission holography
Authors: Timmermans E. M. E. , Trammell G. T. , Hannon J. P.
Published: July 2002

In the recently developed technique of electron emission holography, the sources are electron emitting atoms, adsorbed on the surface or part of the substrate. The directly emitted electron serves as a reference wave and its interference with the elastically scattered wave is responsible for the hologram character of the angular resolved intensity pattern. A straightforward numerical transform of this pattern yields a holographic ‘‘image’’ of the emitter’s environment on the atomic scale. We show that the effect of exchange on the electron scattering process similarly allows imaging of the nearby magnetic environment from the angular resolved electron spin polarization pattern, the spin hologram. In the proposed experiment, the electrons are assumed to be emitted from inner-core levels in an unpolarized manner. Consequently, any atom, magnetic or not, can be used as a source. The transform of the spin hologram then gives a picture of the spin vectors of the neighboring atoms. This suggests a broad range of experimental applications in the field of surface magnetism, ranging from anisotropy to antiferromagnetically coupled layers. We present the physics of the method and discuss briefly potential problems, such as the influence of multiple scattering and self-imaging. To illustrate the technique, we present the results of model calculations.
Electroplated CoNiFe alloy for use in an integrated inductive magnetoresistive recording head
Authors: Chesnutt R.
Published: July 2002

An electrodeposition formula and operating conditions were developed and optimized for the high saturation magnetization Co80Ni10Fe10 alloy. The effects of magnetic field application during deposition and in subsequent process operations was investigated. The bulk film magnetic performance was compared to conventional Permalloy. Identical write heads, designed for a 300 Mbit/in.2 operating point, were fabricated and tested for a direct comparison of conventional NiFe and CoNiFe. The yoke thickness of the CoNiFe heads was scaled linearly by the difference in saturation moment. Overwrite performance on high coercivity media demonstrated that the CoNiFe heads performance was equivalent to the thicker NiFe heads. Heads fabricated with yokes deposited in an orthogonal switching field, annealed with no applied field, exhibited reduced Hk in the bulk film measurement and reduced saturation write currents. The addition of boron to the alloy reduced coercivity.
Corrosion resistive Fe-Si-B films with low H
c and λs by reducing the high energy of γ electrons in tetrode sputtering
Authors: Hirata Toyoaki , Naoe Masahiko
Published: July 2002

The thin films of the Fe-Si-B alloy have been prepared by using an rf tetrode sputtering system, which can deposit the amorphous films with smaller Si and B contents by reducing the high energy of γ electrons. The as-deposited films with a composition of Fe80Si12B8 on the water-cooled substrates at room temperature were amorphous and exhibited the saturation magnetization 4πMs of 11.5 kG, the coercivity Hc of 15 Oe, the relative permeability μr of 43, and the magnetostriction constant λs of 18×10−6. Some of them exhibited 4πMs as large as 15.0 kG, Hc as very low as 0.01 Oe, μr as high as 7,530, and λs as small as 1.5×10−7 after immersion in water for one day.
Ground-state properties for an easy-plane spin-one antiferromagnet— The coupled-cluster method (abstract)
Authors: Wong W. H. , Lo C. F. , Wang Y. L.
Published: July 2002

Using the coupled-cluster method we investigate the ground-state properties of an easy-plane spin-one antiferromagnet which has a critical point at zero temperature. This spin system represents a nontrivial system with the single-ion anisotropy. Single-ion anisotropies have a fundamental influence on the behavior of a magnetic system, and prevail in almost all physical systems with spin greater than one half. Because of the complexities caused by the single-ion anisotropy term, the mean-field approximation is commonly used in calculations of the thermodynamic quantities. However, in the mean-field approximation both quantum and spin fluctuation correlations have been neglected. Here we apply the coupled-cluster method to obtain the ground-state energy, staggered magnetization and critical point for both two and three dimensional lattices. In the coupled-cluster method the correlations of the quantum and spin fluctuations have been systematically included.
Faraday rotation of surface-oxidized metal fine particles clustered in dielectric matrix (abstract)
Authors: Abe M. , Gomi M.
Published: July 2002

Off diagonal terms (which give magneto-optical effects) of ‘‘effective dielectric tensor’’ of composite material with magnetic fine particles dispersed in a dielectric matrix have been derived by the authors.1 In this study, we extended the effective tensor to the composite in which surface-oxidized metal ferromagnetic fine particles are clustered in the matrix. We proposed ‘‘magnetic cluster model’’ as follows. The surface-oxidized metal particles of size d, which is much smaller than light wavelength λ (d≪λ), aggregate in the matrix to form the magnetic clusters of average size D which is much larger than the wavelength (D≫λ). The composite as a whole contains the magnetic clusters at a volume fraction of F(0<F<1). In the cluster the surface-oxidized metal particles are dispersed at an average volume fraction of f(0<f<1). The surface-oxidized metal particles contain metal at an average volume fraction of g(0<g<1). Since d≪λ, we can apply to the magnetic fine particle the effective dielectric tensor, in terms of which we can calculate the effective dielectric tensor of the magnetic cluster. On the contrary, we cannot apply the effective tensor to the composite as a whole, because D≫λ. However, Faraday rotation of the composite is given by F times the Faraday rotation of the magnetic clusters which is expressed in terms of the effective dielectric tensor of the cluster. Faraday rotation spectrum was measured at λ=0.5–0.8 μm for a composite film (0.25 μm in thickness) in which Ni fine particles (∼20 μm in size) were dispersed in PVC (polyvinyl chloride) matrix by spin coating. The result was successfully interpreted by our magnetic cluster model assuming parameters F=0.15, f=0.78, g=0.9, which conforms to our experimental conditions.
Stark shift of the interband transitions in asymmetric step InGaAs/GaAs quantum wells
Authors: Marcinkevičius S. , Olin U. , Ottosson M. , Treideris G. , Šimkiené I. , Lideikis T.
Published: July 2002

The Stark shift of the ground interband transitions has been studied by means of room temperature photoluminescence in asymmetric step InGaAs/GaAs quantum wells with different step widths. The shift magnitude is found to increase with increasing step width. It is shown that by a proper design of the well profile the Stark shift in the asymmetric step quantum well may be increased nearly twice as compared to the rectangular well of the same width.
Electroluminescence and forward bias current in p-i-n and p-b-i-n a-Si:H solar cells
Authors: Wang Keda , Silver Marvin , Han Daxing
Published: July 2002

We have studied the forward bias current and electroluminescence (EL) in 0.4 μm a-Si:H p-i-n and p-b-i-n solar cells in the temperature range of 80 K≤T≤300 K. For comparison, the data in 2 μm p-i-n samples are shown. The forward current shows little temperature dependence in the thin cells, while the current drops considerably with the decreasing of temperature in the 2 μm p-i-n. When the temperature is increased from 80 to 300 K, the EL spectra show an energy shift of 0.3 eV from 1.2 to 0.9 eV in the thin cells, and only shift by 0.12 eV in the thick sample. An increase of EL near 1.2 eV at T≥200 K is seen in the p-b-i-n cells where b is a buffer layer. The lifetime distribution peaks at 10−6 s in the thin cells rather than 10−3 s as normally observed in thick samples.
Metal/intrinsic diamond/semiconducting diamond junction diodes fabricated from polycrystalline diamond films
Authors: Miyata K. , Dreifus D. L.
Published: July 2002

The electrical properties of metal/intrinsic semiconductor/semiconductor junctions formed by Al, undoped polycrystalline diamond, and B-doped p-type polycrystalline diamond films were investigated. These results are compared with those of standard metal/semiconductor junctions formed by direct metallization of Al on p-type semiconducting diamond. Polycrystalline diamond samples were grown using a microwave plasma-assisted chemical vapor deposition technique. These diamond thin films were then annealed, and chemically cleaned in order to stabilize their electrical properties prior to metallization. Good rectifying characteristics, with rectification ratios of 106–107 at 5 V, were obtained for metal-intrinsic diamond-semiconducting diamond junctions. Reverse bias breakdown voltages in excess of 20 V were observed with increasing thickness of the undoped diamond layer. Rectification was observed at 300 °C with a ratio of forward to reverse current of 103 at 5 V. A first-order model has been proposed to explain the effects of the undoped layer on the electrical characteristics of this junction diode. Only poor rectifying characteristics were obtained for metal-semiconductor junctions.
Gain and saturation parameters of a multichannel large-area discharge CO2 laser
Authors: Yelden E. F. , Seguin H. J. J. , Capjack C. E.
Published: July 2002

Details of an experimental investigation of the gain and saturation intensity of a multichannel extended-area discharge CO2 laser are presented. Measurements were made as a function of several discharge parameters. The gain coefficient was found to be similar in each of the individual discharge regions, having a maximum value of 0.70%/cm. Effects of gas pressure, gas mixture, and input power on gain and saturation parameters were studied. The saturation intensity varied as the square of the total gas pressure. The central interelectrode region of the device, which contained no visible discharge, exhibited a significant level of gain. The investigation reported herein provided important data for the design and optimization of optical extraction configurations.
Formation and diffusion behavior of intermixed and segregated amorphous layers in sputtered NiCr films on Si
Authors: Lee Ju-Hyeon , Rozgonyi G. A. , Patnaik B. K. , Knoesen D. , Adams D. , Balducci P. , Salih A. S. M.
Published: July 2002

Sputter-deposited Ni80Cr20 films on sputter-cleaned Si substrates contain an amorphous layer at the substrate/film interface whose composition is a mixture of all the elements present at the interface. Subsequent thermal processing at 300 °C for 30 min produces a new segregated Cr-rich amorphous layer as Ni atoms preferentially diffuse through and react with the initial amorphous layer and the silicon substrate. Further annealing results in the growth of uniform nanoscale NiSi layers, as long as the segregated a layer is sustained. The amorphous layers eventually crystallize at ∼500 °C and Kirkendall voids are observed at 550 °C. Whereas the formation of intermixed amorphous layers from metal–metal or metal–silicon systems has been reported by several authors, the segregated amorphous layer arising out of the interdiffusion and reaction between a metal alloy and Si is of both fundamental and technological interest due to its thermal stability and ability to control the silicide growth. In this work, we describe the evolution of both kinds of amorphous layers, i.e., intermixed and segregated, so as to elucidate their origins. The evolution of the two a layers is also observed when monolayers of Pt are introduced prior to NiCr deposition. In this case, the growth of the segregated amorphous layer is retarded and it dissolves earlier during thermal annealing.
Disorder-induced flicker noise in high-T
c rf superconducting quantum magnetometers
Authors: Galperin Yu. M.
Published: July 2002

Low-frequency noise in a hysteric rf superconducting quantum interference device (SQUID) originating from fluctuations of critical current of a weak link is considered. Such noise can be due to trapping-detrapping processes within the tunnel barrier or to the presence of structural defects with internal degrees of freedom in the surrounding of the weak link. The defects can switch between two (or more) metastable states due to interaction with the thermal bath. On the other hand, elastic (and electric) fields created by defects act upon the critical current of the weak link inducing its fluctuations in time. Such noise is most important for high-Tc SQUIDs at high enough temperatures when defects are effectively interacting with the thermal bath. The dependencies of the intensity and statistics of flicker noise on the SQUID’s parameters and operating regime are analyzed. It is shown that higher correlation functions of output voltage at a given driving current can provide some information on the mechanism of 1/f noise in rf SQUIDs.
Compositional analysis of molecular beam epitaxy grown InyGa1−yAs/GaAs/AlxGa1−xAs quantum wells by determination of film thickness
Authors: Maier M. , Köhler K. , Höpner A. , As D. J.
Published: July 2002

The thickness of the individual layers of molecular beam epitaxy grown pseudomorphic InyGa1−yAs (0.1≤y≤0.35)/GaAs/Al0.3Ga0.7As quantum well structures has been determined by transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS) depth profiling, and reflection high energy electron diffraction (RHEED) with the aim of the compositional analysis of the ternary alloy films. Agreement between SIMS and TEM thickness data within 15% is found. Reliable RHEED data at y≥0.25, where the number of RHEED oscillations is drastically reduced by the three-dimensional growth of the InGaAs film, have been obtained by averaging repeated RHEED measurements. As compared with TEM, RHEED tends to lower values by 10% at maximum. The compositional data determined by the different methods including also photoluminescence (PL) agree within 20% in the technologically important region y≥0.2. At y=0.1, extreme accuracy requirements concerning the thickness determination limit the accuracy of SIMS and TEM to around 30%. Therefore PL and RHEED are superior at this concentration. An influence of the growth temperature on the In content at y=0.3 could be detected only by PL, demonstrating the excellent relative accuracy of PL.
The stability of growing or evaporating crystals
Authors: Ghez R. , Cohen H. G. , Keller Joseph B.
Published: July 2002

The linear stability of a Stefan-like problem for moving steps is analyzed within the context of Burton, Cabrera, and Frank’s theory of crystal growth [Philos. Trans. R. Soc. London Ser. A 243, 299 (1951)]. Asymmetry and departures from equilibrium at steps are included. The equations for regular perturbations around the steady state are solved analytically. The stability criterion depends on supersaturation and average step spacing, both experimentally accessible, and on dimensionless combinations of surface diffusivity, surface diffusion length, and adatom capture probabilities at steps, which can be estimated from bond models. This stability criterion is analyzed and presented graphically in terms of these physical parameters.
The stability of rapidly growing or evaporating crystals
Authors: Keller Joseph B. , Cohen H. G. , Merchant G. J.
Published: July 2002

Solutions for the growth rate of perturbations in the locations of moving steps on a growing or evaporating crystal are presented. They are obtained by solving an equation derived by R. Ghez, H. G. Cohen, and J. B. Keller [J. Appl. Phys. 73, 3685 (1993)] based upon the Burton–Cabrera–Frank theory of crystal growth. They agree with the results derived via the adiabatic approximation when the dimensionless growth rate is small, which shows that those results are correct. However, when the growth rate is large the present exact results differ from those of the adiabatic approximation, as might be expected.
Amorphous GeCu alloy for low temperature resistor fabrication
Authors: Wong T. K. S. , Ingram S. G.
Published: July 2002

Amorphous germanium–copper alloy films (a-Ge1−xCux, 0.01≤x≤0.3) have been deposited and characterized at temperatures down to 3.9 K. The sheet resistivities of these films can be controlled by varying their copper content and are substantially higher than common thin film resistor materials. The films can be readily patterned by either wet etching or lift-off and are potentially useful for fabricating the high resistances necessary for observing the Coulomb blockade in single tunnel junctions.
Analysis of the single-particle scattering spectra for spin-density fluctuations of electrons in n-GaAs at T=300 K
Authors: Tsen K. T. , Chia C. , Sankey O. F.
Published: July 2002

The line shapes of single-particle scattering spectra for spin-density fluctuations of electrons in n-GaAs with carrier concentrations ranging from 5×1015 to 7×1017 cm−3 have been analyzed. We have found that the Raman line shapes can be very well explained by a theory developed by Hamilton and McWhorter which takes into account both the band-structure effects in semiconductors and the effects of carrier collision in a relaxation time approximation. For carrier concentration n≥2×1016 cm−3, the effects of finite collision time has been demonstrated to be very important and these effects must be properly taken into account in order to satisfactorily interpret the line shapes of single-particle scattering spectra for spin-density fluctuations in n-GaAs at T=300 K. We show that although Lindhard–Mermin’s expression for dielectric constant as well as Hamilton and McWhorter’s theory fit the Raman line shapes equally well for carrier density n=7×1017 cm−3, neglect of band-structure effects of the former tends to underestimate the carrier collision time. An interpretation of the deduced collision time in terms of electron-electron, electron-impurity, and electron-phonon scattering is also given.
Electrochemical doping properties and electronic states of poly(3-phenylthiophene)
Authors: Onoda Mitsuyoshi , Nakayama Hiroshi , Morita Shigenori , Yoshino Katsumi
Published: July 2002

Electrochemical, optical, and magnetic properties in poly(3-phenylthiophene), as a function of doping and electronic states, are discussed in detail. The band gap of poly(3-phenylthiophene) was evaluated to be 2.0 eV, and similar to that of polythiophene. The evolution of localized states is evidenced by the spectral change with electrochemical doping. The spin density evaluated from the susceptibility was consistent with the polaron density assumed to be formed by a very small quantity of dopants. These results are interpreted in terms of the polaron and bipolaron models. The electronic band structure of poly(3-phenylthiophene) was determined. The top of the valence band of poly(3-phenylthiophene) is located at a higher energy state than that of polythiophene by about 0.1 eV and it became clear that the dopant in poly(3-phenylthiophene) is relatively stable compared with that in polythiophene. Successful n-type doping in poly(3-phenylthiophene) was also confirmed.
The role of the gate insulator in the defect pool model for hydrogenated amorphous silicon thin film transistor characteristics
Authors: Deane S. C. , Clough F. J. , Milne W. I. , Powell M. J.
Published: July 2002

We demonstrate that differing transistor characteristics in the most important material systems can be explained by the defect pool model applied to the defects near the interface of hydrogenated amorphous silicon thin film transistors. Gate dielectrics used include plasma deposited silicon nitrides, plasma deposited silicon oxides, and thermally grown silicon oxides. The most important property of the gate dielectric is not the chemical composition but the fixed charge. In particular, as-deposited plasma deposited silicon oxide transistors can be made with similar properties to plasma deposited silicon nitride transistors or thermal silicon oxide transistors, by varying the fixed charge. After correcting the effects of the fixed charge variation, some differences still exist between the interface qualities. We introduce the parameter Ndb(min), i.e., the minimum density of dangling bonds (cm−2), which is a measure of interface quality independent of the fixed charge of the gate insulator. We propose that the variations in Ndb(min) are due to differences in disorder, perhaps caused by interface strain, leading to slight variations (∼5 meV) of the valence-band tail slope.
Critical cooling rate of amorphous Pd40Ni40P20
Authors: Lau C. F. , Kui H. W.
Published: July 2002

The critical cooling rate of amorphous Pd40Ni40P20 was measured by applying a fluxing technique under a well controlled cooling environment. It was found that the critical cooling rate is ∼0.75 K s−1 for a ∼7-mm-diam specimen. This simply implies a steady-state nucleation frequency of ∼10−2 cm−3 s−1 which is the smallest ever found in a metallic system.
An efficient method to compute the maximum transient drain current overshoot in silicon on insulator devices
Authors: Korman Can E. , Mayergoyz Isaak D. , Gaitan Michael , Tai Gwo-Chung
Published: July 2002

We present an efficient method to compute the maximum transient drain current overshoot in silicon-on-insulator metal-oxide-silicon field effect transistors. The method is based on the physical idea that the number of majority carriers remains unchanged immediately after a change in the applied gate bias. The maximum overshoot is computed by solving the Poisson and the stationary minority carrier transport equations under the constraint that the number of majority carriers is conserved. Hence, the novel aspect of the method is that it allows one to compute the maximum drain current overshoot without resorting to a computationally costly transient simulation. The accuracy of the method is verified by comparing the value of the drain current computed by this method with the maximum value of the drain current computed by transient simulations. The comparisons show that, with this method, the maximum transient drain current overshoot can be computed quite accurately for fast changes in the gate bias.
Interfacial structure and dopant redistribution of a tungsten polycide/N+ silicon substrate
Authors: Dai C. M. , Tung C. H.
Published: July 2002

The morphology and redistribution of dopants at the interfaces between silicon-implanted, low-pressure chemical-vapor-deposited silicon films with an n+ single-crystal silicon substrate are described. Using high-resolution transmission electron microscopy, it is shown that silicon implantation definitely lowers the annealing temperature needed to break up the native oxide layer. A post annealing temperature of 900 °C for 30 min, which is acceptable for sub-μm processes, is sufficient to cause the break up of the native oxide layer and the subsequent epitaxial growth through it with the aid of silicon implantation. The depth profile obtained by secondary ion mass spectrometry shows that the implanted dopants were piled up at the interfacial layer after thermal treatment. The redistributed profiles of impurities depend on the concentration of oxygen. The junction depth of the silicon-implanted polysilicon films is shallower than that of the unimplanted films.
Effect of ion implantation on aluminum void suppression
Authors: Kikkawa Takamaro , Endo Nobuhiro
Published: July 2002

The effects of ion implantation on stress-induced voiding in aluminum films were investigated. Arsenic ions with doses ranging from 1×1015 to 2×1016 cm−2 were implanted into the Al film surface. It was found that Vickers hardness and the electrical resistivity of the implanted Al film increased with increasing implantation dose. The average residual tensile stress at room temperature and the hysteresis of the Al film stress during heat cycles decreased with increasing implantation dose. It was also found that Al voiding, due to thermal stress-induced migration, decreased as the ion implantation dose increased and no voids were observed in the high dose (≥1×1016 cm−2) implanted region. Consequently, arsenic ion implantation into the Al surface could suppress Al voiding as results of mechanical hardening and compressive stress in the implanted Al layer.