bluuebunny/crossref_metadata_2025 huggingface dataset:
Edge-closed laminated structures for thin-film heads
Authors: Herman D. A. , Argyle B. E. , Lee H.-P. , Trouilloud P. O. , Petek B.
Published: July 2002

Magnetic film laminations containing nonmagnetic spacers have been explored with the hope of eliminating domain walls to diminish Barkhausen instabilities. Such laminates have limitations however, which originate in their ‘‘edge-curling walls’’ (ECWs).1 We have developed a new structure, free of ECWs, in which flux closure at opposing edges occurs via edge-shorting material added to circulate the easy-axis flux of the flat layers. We show experimentally with Kerr-effect imaging that (1) this edge-closed laminated (ECL) structure can support an (ECW-free) ‘‘easy-axis’’ (EA) magnetic state under conditions as modeled recently by Slonczewski,2 and (2) that this EA state is quite robust in the face of imperfect structure fabrication. This is, if the imperfections are not too severe, the resultant states depart minimally from the pure EA state and conduct hard-axis-driven flux nearly as well. Flat-film ECL elements in diamond, stripe, and recording-head-yoke shapes, plus experimental heads with ECL top yokes, were fabricated. Our domain images verify some key predictions from Slonczewski’s static equilibrium modeling; additional results taken in applied magnetic fields extend the micromagnetic understanding. The sketch shows a typical domain pattem for a yoke-shaped element. The most stable state in the open portion of the yoke is the single domain shown. This remanent pattern was stable in the face of (slowly varying) external fields up to the 150 Oe that could be applied. The pole tip region contained a few 180° walls as indicated. On close inspection, these walls were seen to end in vestigial, nontouching, closure domains as predicted by the model when only partial flux closure occurs via the edge shorting material. The wall spacing in the tip varied somewhat following saturation–demagnetization cycles. The dynamic stability of this EA state was investigated in the experimental heads having ECL top yokes. The pseudodynamic LAMOM technique3 was applied using ‘‘write’’ pulsations. The EA state was stable up to twice typical write currents. A movie of dynamic results will be shown.
Bond-orientational anisotropy and anelastic deformation in sputter-deposited amorphous TbFeCo films
Authors: Yan X. , Egami T. , Marinero E. E.
Published: July 2002

Results of a synchrotron x-ray-scattering study on the structural anisotropy of sputter-deposited amorphous Tb26Fe62Co12 thin films are described, and the mechanisms which lead to the observed structural and magnetic anisotropies are discussed. The observed structural anisotropy is characteristic of bond-orientational anisotropy and is incompatible with the atomic pair-ordering model.
Side-writing phenomena in isotropic film media
Authors: Su James L. , Ju Kochan , Gallagher Timothy J. , Vo Lang
Published: July 2002

The isolated readback pulses of magnetoresistive (MR) heads on isotropic film media have been reported to exhibit base-line shifts. We have further observed that for piggyback MR (PMR) heads with thick pole-tip write elements operating at high write currents, an additional base-line shift occurs, thereby producing dual-base-line shifts. This second base-line shift results in anomalous signal-amplitude variations as the transition density increases. Moreover, the onset of the second base-line shift occurs ahead of the readback pulses at a distance equal to the trailing-pole thickness. We attribute the second base-line shift to the trailing-pole side writing, which modifies the magnetic dipole distribution along the track edges prior to the transitions at a distance equal to the trailing-pole thickness.
On the susceptibility of ‘‘ultrasoft’’ magnetic films (abstract)
Authors: Bouchaud J. P. , Zérah P. G.
Published: July 2002

It has been shown1 that after suitable annealing, some amorphous films, e.g., Co61B39 exhibited ‘‘ultrasoft’’ properties: a very small value of the anisotropy field, and a highly damped dynamical susceptibility. We interpret the experimental susceptibility in the framework of the effective medium theory in two dimensions, which predicts that the transverse susceptibility goes from √μ in the disordered case, to μ in the completely magnetized case, where μ=M/(Ha+H). To interpret the dynamical susceptibility, we generalize the LL equation, and find a large damping parameter α. In both cases the agreement with experimental data is excellent. It is conjectured that such a value of α might be due to strong fluctuations of the local anisotropy.
The influence of atmosphere on hysteresis loss and eddy current loss of low loss Mn-Zn ferrites (abstract)
Authors: Chen S. H. , Tung M. J. , Shu W. B. , Liu C. S. , Ke M. Y.
Published: July 2002

The working frequency of Mn-Zn ferrites in switching power supply has been increased recently. Therefore, the manufacturing Mn-Zn ferrites with low loss at high frequency is very important. However, there were few reports concerning the core loss of Mn-Zn ferrites.1 It is beneficial to study the parameters affecting the core loss of Mn-Zn ferrites. Therefore, we studied the influence of atmosphere on the hysteresis loss (Wh) and eddy current loss (We) for different compositions in this work. Three compositions, Mn0.70Zn0.21−xFe2.09+xO4 (x=0, 0.01, 0.02), were prepared by traditional ceramic process. The sintering condition is 1385 °C for 4 h. Then, the samples are annealed at 1100 °C for 24 h in different oxygen partial pressure (0.015–1.0 vol %). Experimental results show that both We and Wh have minimum value at different oxygen partial pressure for samples with different composition. Increasing Fe content which raises the Fe++ concentration shifts the We and Wh minimum point to higher annealing oxygen partial pressure. It is mainly due to the oxidation of Fe++ and the transition of conduction mechanism, and it will be further discussed later. We can obtain the lowest core loss for using 10 and 100 kHz are samples with composition x=0 annealed in 0.07 and 0.2 vol % oxygen partial pressure, respectively. Summarily, for application to low loss at different working frequency, it is found that different optimized atmosphere should be controlled during annealing for different composition.
Garnet film rotator applied in polarizing microscope for domain image modulation (abstract)
Authors: Wakabayashi K. , Numata T. , Inokuchi S.
Published: July 2002

A garnet film polarization rotator placed before the analyzer in a polarizing microscope was investigated to obtain the difference image of a positive and a negative one of magnetic domain in real time along with an image processor. In the difference image, a nonmagnetic image can be reduced and hence the weak magnetic contrast enhanced. Theoretical calculation of S/N and contrast C of the domain image as a function of the rotation shows they take maxima at the rotation angle of 2.6° and 0.1°, respectively, with the extinction ratio of e=4×10−6 of a polarizing microscope. Thus, since the thickness of the garnet film required is 1 μm or so, the absorption by the garnet rotator does not bring a serious problem even in a visible region for the domain observation. The optimum rotation of the rotator for a high quality observation was obtained by a quantitative study of images obtained experimentally as well as by a visual evaluation. A magnetically unsaturated garnet film with perpendicular magnetization (i.e., multidomain) was employed as a rotator, in which the polarization rotation angle θm of the undeflected beam with respect to the light diffraction could be continuously varied by an applied magnetic field. The dependences of S/N and C on θm were measured, resulting in a well agreement between the measured and the calculated. The visually best image was obtained at θm=0.5° which made the product of S/N and C maximum. The domain image of the Kerr rotation angle of θk=0.22° was observed in S/N=47 dB and C=0.4 when Ar+ laser (λ=515 nm) of tenths of a watt was employed as a light source. Since the domain image with 47 dB S/N does not need an image summation for a noise reduction, a garnet film rotator makes it possible to invert the contrast of a domain image in a real time for an improved domain observation.
MO determination of domain wall polarity and location of VBL by spatial filtering with phase correction (abstract)
Authors: Peterson V. K. , Iljicheva E. N. , Mushenkova I. V. , Fedyunin Y. N. , Shishkov A. G. , Il’yashenko E. I.
Published: July 2002

We have developed a new technique1 for direct optical observation of domain wall (DW) polarity (direction of midwall magnetization M) in order to determine the location of vertical Bloch lines (VBL) in LPE bismuth based garnet films with perpendicular anisotropy. A polarizing light microscope with slope illumination of the sample (one-side dark-field observation technique) and a quartz quarter wave plate, placed behind the objective, were used for phase corrections so that some DW (or segments) are shaded. Equations describing intensity distributions of the light diffracted by magnetic inhomogeneities were obtained from diffraction theory.1 The phase relations between complex amplitudes Ep and Es of the diffracted wave were shown to be a function of the DW polarity. According to this theory, the diffracted light from domain walls of opposite polarity will exhibit a dark light for suitable conditions of polarizer and quarter wave plate orientation. The theoretical results were experimentally verified. The proposed magneto-optic (MO) technique where the image contrast depends on the polarity of DW segments differs from that of Refs. 2 and 3 since we used the phase correction (plate λ/4) and an electronic or computer processing of the image were not needed.
Effect of interfacial microstructure on magnetic properties of dysprosium multilayers
Authors: Shan Z. S. , Jacobsen B. , Liou S. H. , Sellmyer D. J.
Published: July 2002

Nanostructured multilayers of Dy/M (M=Ta, Cu, Y, and Co) have been investigated. Correlations between the microstructure and the magnetic properties, in particular the effects of interfacial structure, are discussed. The temperature and layer-thickness dependences of anisotropy of these Dy/M multilayers can be interpreted reasonably in light of the model previously developed for the perpendicular anisotropy in amorphous multilayers.
Magnetic properties and structure of Al/Fe-N periodic multilayer thin films
Authors: Barnard J. A. , Tan M. , Waknis A. , Haftek E.
Published: July 2002

Periodic multilayer thin films of the form (xAl/yFe-N)n were grown by sequential dc-magnetron sputtering. The thicknesses of the individual Al and Fe-N layers are given by x and y, respectively, and the total number of bilayer units is n. For this set of experiments, x was fixed at 3.5 nm and y was varied systematically from 3 to 135 nm. Magnetic properties were studied by vibrating sample magnetometry and crystal structure by x-ray diffraction for both as-deposited and annealed films. A strong enhancement of the saturation magnetization was found in multilayers containing the thinnest Fe-N layers which was further strengthened by annealing. The coercivity was found to decline monotonically with decreasing Fe-N layer thickness in the as-deposited films. Annealing produced nonsystematic changes in coercivity. The evolution of magnetic properties with decreasing Fe-N layer thickness was correlated with complex changes in iron-nitride crystal structure. For the thinnest layers of Fe-N (less than 12 nm) the multilayers exhibited an essentially amorphous structure.
Magnetism of ultrathin films of Fe on Cu(100)
Authors: Pappas D. P. , Kämper K.-P. , Miller B. P. , Hopster H. , Fowler D. E. , Luntz A. C. , Brundle C. R. , Shen Z.-X.
Published: July 2002

Magnetism in ultrathin (1–10 ML) Fe films grown on Cu(100) has been studied by spin-polarized secondary electron emission spectroscopy. The variation of the magnetization with temperature and oxygen adsorption was investigated for various film thicknesses. The orientation of the magnetization for films between 5 and 6 ML thick switches reversibly between perpendicular (at low temperature) to in-plane (at high temperature). The switching transition temperature decreases with increasing film thickness, and is accompanied by a loss of long-range order over a range of 20–30 K. The transition is attributed to the temperature dependence of the perpendicular anisotropy. The effect of oxygen adsorption onto films with perpendicular remanence is to first suddenly turn the magnetization into the plane at a critical coverage, and then to kill the magnetization gradually with continued exposure. This indicates that the uniaxial surface anisotropy at the Fe-vacuum interface plays a major role in the magnetization of the film.
Possible giant surface magnetostriction in amorphous Co76Cr4B20 (abstract)
Authors: Sun S. W. , O’Handley R. C.
Published: July 2002

We have made preliminary measurements of magnetostriction at the surface (∼5 Å) of sputter-cleaned, amorphous ribbon in uhv (3×10−10 Torr). The value obtained λsurfs≂−14.8×10−6 is nearly four times the magnitude of the bulk saturation magnetostriction λbulks=−3.8×10−6 of this material Co76Cr4B20. The measurement was based on the spin polarization of the true secondary electrons emitted normally from the surface by a grazing incidence, 2 keV primary electron beam illuminating an area of a few mm2. Most of the low energy secondary electrons are believed to come from a depth of less than 0.5 nm. The spin polarization was measured using a thin film, diffuse-spin-orbit-scattering polarimeter. High quality, reproducible polarization vs. field (P–H) loops were obtained after repeated sputter cleaning and annealing in situ. Magnetostriction is determined by λ(H)= ∫H0d(H)dH where d(H)=4π∂M/∂σ]H is the magnetostrictivity, i.e., the stress sensitivity of magnetization at constant field. The latter was measured by bending the sample in situ to achieve tensile or compressive stresses at the front surface up to 107 Pa. The present effect is in no way related to the stress induced changes in bulk magnetostriction measured by Barandiaran et al. which are three orders of magnitude smaller in Δλ/Δσ.
The four dimensional Ising spin glass: A Monte Carlo study (invited)
Authors: Bhatt R. N. , Reger J. D. , Young A. P.
Published: July 2002

We describe results of Monte Carlo simulation studies on the Ising spin glass in four dimensions on a hypercubic lattice with nearest neighbor bonds. Studies of the equilibrium static properties show that the system undergoes a genuine phase transition to an ordered spin glass phase. Critical dynamical behavior is analyzed to obtain the dynamic exponent. Finally, we describe results on the spin glass phase, in particular the finite size scaling of the order parameter distribution function, and compare it with existing models of the spin glass phase, namely the droplet model and the Parisi solution for the low temperature phase of the infinite range spin glass.
Vortex liquids in high-temperature superconductors (invited)
Authors: Marchetti M. Cristina
Published: July 2002

Recent work on the hydrodynamic theory of vortex liquids in high-Tc superconductors is reviewed. Weak microscopic pinning centers are described within the flux-flow model of Bardeen and Stephen, while strong macroscopic pins set the boundary conditions for the flow. Entanglement and intervortex interactions can yield an exceptionally large intrinsic viscosity for the vortex liquid. This large viscosity allows the effect of a few strong pins to propagate over large distances and choke off the flow. As a new and experimentally relevant example of spatially inhomogeneous pinning on macroscopic scales, we consider the response of the flux liquid to an alternating current within a simple model that incorporates viscoelastic properties of the vortex liquid.
The dilute quantum Heisenberg antiferromagnet
Authors: Wan C. C. , Harris A. B. , Adler Joan
Published: July 2002

Series expansions are used to treat the randomly diluted spin-1/2 Heisenberg antiferromagnet at zero temperature. A series is obtained at zero temperature in powers of the concentration for many correlation functions and for the correlation length from which static, dynamic, and crossover exponents are estimated. The correlation length exponent is found to be 0.77±0.10 in two dimensions. The critical concentration for the appearance of long-range order is indistinguishable from the percolation threshold.
Magnetic properties of crystalline random anisotropy TbxY1−xAl2 magnets
Authors: Joven E. , del Moral A. , Arnaudas J. I.
Published: July 2002

The magnetic phase diagram of the crystalline dilute magnets TbxY1−xAl2 has been determined, showing spin-glass reentrance into a quasiferromagnetic (QF) phase for xt ≥ 0.27 and T ≤ 8.6 K, the tricritical point. The effective percolation limit is xp=0.16 with a critical line separating the paramagnetic and QF regimes of exponent φp=1.1. No signs of saturation magnetization are found, nor of any clear divergence of the dc zero-field susceptibility. On the spin-glass side of these series (x<0.27), the order parameters q (frozen local moment) and Δ (irreversibility parameter) have been determined from the field- and zero-field-cooled measured susceptibilities.
Thin-film recording media: Challenges for physics and magnetism in the 1990s (invited)
Authors: Johnson K. E.
Published: July 2002

Thin-film recording media introduced commercially to rigid disk drives in the early 1980s revolutionized the rigid disk industry. By the end of the decade, particulate disk technology accounted for less than half of the worldwide shipped disks and is expected to disappear from rigid disk drives altogether in the 1990s. The implementation of thin-film technology required entirely new disk fabrication processes and new insights into magnetic materials and microstructures. A review of the fundamental magnetic reasons for implementing thin-film technology will be given, followed by a discussion of the physics and magnetics of thin films. The technology is not completely understood and needs to be examined because of the continued increase of recording densities in rigid disk drives. Discussion will concentrate on thin films suitable for horizontal recording. Topics to be considered are those deemed important from a disk product development view and include thin-film media noise, anisotropy, and magnetic alloys and microstructures.
Co/Pt and Co/Pd multilayers as new magneto-optical recording media (abstract)
Authors: Zeper W. B. , van Kesteren H. W. , Jacobs B. A. J. , Spruit J. H. M. , Carcia P. F.
Published: July 2002

In this paper we will discuss Co/Pt and, to a lesser extent, Co/Pd multilayers optimized for magneto-optical storage applications. Perpendicular magnetic anisotropy and square hysteresis loops are achieved for multilayers with a total thickness below about 200 Å if they consist of very thin (≂4 Å) Co layers alternated with 10–20-Å Pt layers. Multilayer made by evaporation show a high coercivity (≳100 kA/m) and have proven to be suitable as magneto-optical recording medium. Recently we showed that Co/Pt layers with high coercivity can be made by sputtering as well, if not Ar but Kr is used as sputter gas.1 We will discuss the properties of Co/Pt multilayers in relation to the preparation technique and will present magneto-optical recording results for both evaporated and sputtered Co/Pt multilayer films. The written domain patterns can be very regular, as observed by scanning magnetic force microscopy, and a CNR as high as 55 dB (1 MHz carrier, 5 m/s, 30 kHz BW) is observed. The good oxidation and corrosion resistance together with increasing Kerr effect towards shorter wavelengths, where higher storage densities are possible, make that Co/Pt multilayers are attractive new magneto-optical recording media.
Magnetic properties of some tetravalent rare-earth perovskites
Authors: Bulman J. B. , Kuric M. V. , Guertin R. P. , Foner S. , McNiff E. J. , Cao G. , O’Riely J. , Crow J. E. , Wise P. P. , Yuen Tan
Published: July 2002

The temperature dependence of the magnetic susceptibility for 1.5<T<300 K, the field dependence of the magnetization M(H), for 0<H<23 T and 1.5<T<15 K, and the temperature dependence of the heat capacity C(T), for 5<T<95 K are reported for the insulating distorted-perovskite systems PrBaO3, TbBaO3, TbSrO3, and CeBaO3, and the pseudoternary system (Pr,Ce)BaO3. X-ray analysis at room temperature indicates single-phase structures for all materials. PrBaO3 shows magnetic ordering below TN=11.7 K, possibly due to a canted antiferromagnetic structure. TN is nearly independent of applied field up to about 12 T. High-field M(H) isotherms show a well-defined upward sloping kink at 12.7 T, which is independent of temperature for T<9.5 K. This is indicative of a spin-reorientation transition. The pressure dependence of TN is negligible: dTN/dP<0.1 K/kbar. TbBaO3 and TbSrO3 both show antiferromagnetic ordering, but with low- field hysteresis effects below 34 K. Clear C(T) anomalies at TN=11.7 and 34 K are seen for PrBaO3 and TbBaO3, respectively. CeBaO3 is paramagnetic, but shows no magnetic order down to 1.8 K, although M(H) is field dependent at 4.2 K. The results in the Pr-based system are compared with previous work in high-Tc-related Pr-based systems.
Fe-site occupancy and superconductivity in Y1−zCazBa2(Cu1−xFex)3O6+y
Authors: Smith M. G. , Taylor R. D. , Oesterreicher H.
Published: July 2002

X-ray diffraction and 57Fe Mössbauer spectroscopy studies show that partial substitution of Ca for Y in Y1−zCazBa2(Cu1−xFex)3O6+y (0.05≤z≤0.15, 0.003≤x≤0.20) result in increased Fe solubility and a larger percentage of Fe occupancy of the Cu(2) plane site (prepared conventionally). Materials with z≳0.00 have a slightly depressed superconducting transition onset temperature Tc relative to the z=0.00 compounds. It is also shown that Fe occupancy of the Cu(2) site in Y1−zCazBa2(Cu1−xFex)3O6+y can be substantially increased when these materials are treated at high temperatures in inert atmospheres followed by oxygenation at low temperatures. Tc decreases more rapidly in these latter materials compared to the conventionally prepared ones. Implications concerning ordered Fe-cluster formation and superconducting pair breaking in the Cu(2) site are drawn.
The effect of random coercivity on domain growth processes in rare earth–transition metal alloys (abstract)
Authors: Weng Robert S. , Wu Jiin-Chuan , Kryder Mark H.
Published: July 2002

In the present investigation, we show that local fluctuations of the magnetic properties in amorphous alloys, specifically the fluctuating anisotropy, can cause irregularity in the domain shape which has been attributed to causing writing noise.1 We propose a model for coercivity based on the pinning of domain walls by the randomly fluctuating anisotropy constant. This model is believed to be particularly suitable for materials containing non-S-state rare-earth ions like terbium, because the 4f electrons of these ions, through the spin-orbit coupling, interact strongly with the random local electrostatic fields. A computer model developed to simulate dynamic domain wall motion2 is used with a new coercive force model to predict the domain growth process. The effects of the random coercivity on the shape of the written domain were studied for two different processes: (a) thermomagnetic writing by a laser beam and (b) wall motion by thermal activation at a constant temperature. It is shown that domain shape distortion becomes more pronounced as the percentage of the random anisotropy relative to that of the constant anisotropy is increased, particularly in the case of thermal activation.
Dynamic vector Preisach models of hysteresis
Authors: Mayergoyz I. D.
Published: July 2002

Dynamic vector Preisach models of hysteresis are developed, and the identification problem for these models is posed. It is shown that some experimentally measured relaxation times can be used for the solution of the identification problem for the dynamic vector Preisach models. Moreover, it is shown that the identification problem can be reduced to a specific integral equation, and analytical techniques for the solution of this integral equation are discussed.
Noise characteristics of Co-Ni obliquely evaporated tape
Authors: Sato Kenichi , Chiba Kazunobu , Ito Takuya , Sasaki Toshikazu , Hokkyo Jiro
Published: July 2002

In Co-Ni obliquely evaporated tape, the magnetic properties and the microstructure are greatly affected by the oxygen gas introduced during the evaporation phase. When the oxygen flow rate is low, the dc-erased noise which is caused by the inhomogeneous structure of the magnetic layer, is greater than the ac-erased noise. The modulation noise level is also high and increases as the carrier frequency increases, as in longitudinal thin-film media having zig-zag transitions. As the oxygen flow rate increases, the signal output level increases to a maximum and the ac-erased, dc-erased, and modulation noise levels decrease. Tape prepared using the optimum oxygen flow rate does not show any increase in the modulation noise as carrier frequency is increased. Analysis of the three noises in the normal and reverse head transport directions made it clear that the ac-erased noise can be affected by the inhomogeneousness of the microstructure in the column, the modulation noise by the irregularity of the magnetic transition region which includes the microstructure, and the dc-erased noise not only by the inhomogeneousness of the microstructure but also by the partial switching caused by the magnetic field of the trailing edge of the Sm-Co magnet. Co-Ni obliquely evaporated tape prepared using the optimum oxygen flow rate is a particlelike medium with a high signal output level and low-noise characteristics.
Localized behavior of f electrons in CeAg: A theoretical study
Authors: Fraizzoli Samuele , Monachesi Patrizia , Moroni Elio G.
Published: July 2002

We perform self-consistent linear muffin-tin-orbital local-density-approximation (LMTO-LDA) electronic structure calculations for paramagnetic CeAg in the cubic phase to study the hybridization of the Ce f states which is found particularly effective with the Ce d and Ag p states. We also make self-consistent calculations of the electronic structure of LaAg and use it as the f-less analog of CeAg to determine quantitatively the localized part of the Ce 4f charge. The latter is identified with the average f-occupation number nf of the Anderson model.
Anisotropic magnetoresistance in magnetostrictive Metglasa) 2605SC for strain gage applications
Authors: Restorff J. B. , Wun-Fogle M. , Hathaway K. B. , Clark A. E.
Published: July 2002

The magnetoresistance of transverse-field-annealed Metglas 2605SC (Fe81B13.5Si3.5C2) ribbons has been measured as a function of both applied field and imposed strain. A maximum magnetoresistance of 0.3%, obtained with applied magnetic field agrees with previous measurements of unannealed samples. The magnetoresistance changes with imposed strain are slightly smaller, and indicate the presence of inhomogeneities in the sample or the imposed strain.
Pressure-induced electrical and magnetic properties in CeAs, CeSb and CeBi
Authors: Môri N. , Okayama Y. , Takahashi H. , Kwon Y. S. , Suzuki T.
Published: July 2002

Electrical resistance of single-crystalline CeAs, CeSb, and CeBi has been measured under hydrostatic pressure. In CeAs and CeSb, pressure enhances the change of overall features in the resistance-temperature R(T) curves. Resistance anomalies associated with magnetic phase transitions are observed and are found to be sensitive to pressure. It is noted that the R(T) curve of CeAs at ∼3 GPa is similar to that of CeSb at ambient pressure.
Pulsed nuclear magnetic resonance of 59Co in Co3S4
Authors: Nishihara H. , Kanomata T. , Kaneko T. , Yasuoka H.
Published: July 2002

Nuclear magnetic resonance of 59Co in Co3S4, which had been considered to be a simple Pauli paramagnet, has been reinvestigated by a pulsed method. Free-induction decay or spin-echo signals from A and B sites in the spinel structure have been observed. The signal from the magnetic A site shows a temperature-dependent Knight shift, and disappears suddenly at 58 K with decreasing temperature, suggesting the onset of a magnetically ordered state. The hyperfine coupling constant is roughly estimated to be −10 kOe/μB from the K-χ plot. The signal from the nonmagnetic B site, which shows a textbooklike quadrupolar powder pattern, is strong at low temperatures but the effect of the magnetic A site on the B site was not detected. The nuclear spin-lattice relaxation shows the Korringa-type behavior with (T1T)−1=13±2(s K)−1 for 59Co at the A site.
NMR studies of the electronic and magnetic properties of the 123 compounds (invited)
Authors: Alloul H.
Published: July 2002

A good knowledge of the magnetic properties of cuprates, from their insulating AF state to their metallic state, is required prior to a clarification of the origin of high temperature superconductivity. NMR techniques have proven to be quite successful in studying the magnetic properties on a local scale. The 89Y NMR, which can be detected even in the AF and paramagnetic phases of YBa2Cu3O6+x, allows one to study the influence of oxygen content or impurity substitutions on the 3D AF ordering. The associated changes of spin correlation length and interlayer exchange couplings will be discussed. In the metallic state of YBa2Cu3O6+x, NMR shift data taken on the various nuclear sites, 89Y, 17O, and 63Cu have allowed one to conclude that the covalency between Cu(3dx2−y2) and O(2pσ) holes result in a spin system which behaves as a single spin fluid. The large decrease of the susceptibility of the CuO2 planes at low T for oxygen depleted samples, as well as the different T dependencies of the 89Y, 17O, and 63Cu relaxation rates, is attributed to the existence of AF correlations at the wave vector Q of the AF structure of YBa2Cu3O6. However, the 89Y and 17O relaxation rates, which filter the Q component of the dynamic susceptibility, exhibit a behavior similar to that of a Fermi liquid, for large enough hole doping. The T variations of the spin susceptibility and of the AF correlations are discussed.
Sol-gel silicate thin-film electronic properties
Authors: Warren W. L. , Lenahan P. M. , Brinker C. J. , Ashley C. S. , Reed S. T. , Shaffer G. R.
Published: July 2002

We have explored the effects of various processing parameters on the dielectric and electronic integrity of sol-gel-derived silicate thin films and have identified several factors that strongly affect the thin-film electronic properties. We find that sol-gel dielectrics can exhibit excellent dielectric integrity: viz., low interface trap densities and fairly good insulating properties approaching those of a thermally grown silicon dioxide film on silicon.
Numerical and experimental studies of the intrinsic performance of AlInAs/GaInAs heterojunction bipolar transistors
Authors: King H.-X. L. , Woo J. C.-S. , Jensen J. F. , Stanchina W. E. , Ferro R. J. , Metzger R. A.
Published: July 2002

This paper discusses selected design issues important to the operation of high-speed AlInAs/GaInAs heterojunction bipolar transistors (HBTs). Simulation results reveal that velocity overshoot is an important effect in AlInAs/GaInAs HBTs. It is found to first order that the electron average speed through the base and base/collector depletion region is near 5×107 cm/s. Introduction of a built-in electric field in the base region improves the ft. However, the resultant improvement of the cutoff frequency in the AlInAs/GaInAs HBT is not as significant as in the AlGaAs/GaAs HBT because of the already larger electron velocity in the GaInAs base. Compositional grading in the emitter is not suggested in AlInAs/GaInAs HBTs because it degrades the dc and ac characteristics. The effects of a base setback layer at the emitter/base junction on dc current gain and cutoff frequency have also been studied. It is found that both the doping density and the thickness of the setback layer affect the cutoff frequency, and that the setback layer always degrades the intrinsic performance. The intrinsic setback layer has the lowest cutoff frequency while p-doped setback layer has the highest one.
Refractive index and electro-optic effect in compressive and tensile strained quantum wells
Authors: Pamulapati J. , Loehr J. P. , Singh J. , Bhattacharya P. K. , Ludowise M. J.
Published: July 2002

The effects of biaxial compressive and tensile strain on the excitonic resonances and associated changes in refractive index and electro-optic effect in quantum wells have been calculated and measured. Theoretical calculations include the important heavy-hole–light–hole band mixing effects. It is seen that the excitonic contributions dominate near the band edge. With increasing compressive strain the linear electro-optic effect is slightly increased, while the quadratic effect is greatly enhanced. The effects are reversed in quantum wells under tensile strain.
Plasma-grooved, buried contact silicon solar cells
Authors: Chong C. M. , Davies K. E. , Wenham S. R. , Gross M. , Horwitz C. M. , Green M. A.
Published: July 2002

Solar cells with less than 1% front-surface metal shading loss have been made with a deep-grooving hollow cathode dry etching process. Compared with standard laser-grooved cells, a 4% relative increase in short-circuit current density has been demonstrated. Open-circuit voltages of over 640 mV (air mass 1.5, 25 °C), a fill factor of almost 79%, and the application of an antireflection coating have resulted in a one-sun efficiency of 19.2%. This is one of the highest efficiencies yet reported for a cleaved 4 cm2 silicon solar cell.
Characterization of a dual-segment cylindrical surface discharge
Authors: Beverly R. E.
Published: July 2002

A cylindrical surface-discharge device was developed to study photolytically pumped and photoinitiated gas laser schemes. The discharge plasma plasma produces intense ultraviolet and vaccum-ultraviolet (vuv) broadband irradiation of a 3-l active volume. Homogeneous, large-area (≥103 cm2) plasma shells are formed adjacent to the interior surfaces of dielectric cylinders by an electric discharge. Although the device resembles a Z-pinch, the plasma shells do not collapse to the axis and operation with various gases at high pressure (≤2× 105 Pa) is possible. Initial experiments have emphasized electrical, gasdynamic, and radiative characterization of the device. Current wave forms are oscillatory, indicating an impedance mismatch between the surface-discharge source and capacitor-bank driver. A radially converging shock wave is launched by the discharge while the expanding plasma shells remain tightly pressed against the dielectric surfaces. Operation at a peak current of 94 kA produced approximately 45 J of radiated energy within the vuv spectral band from 170 to 210 nm in a 1.7-μs full-width-at-half-maximum pulse, which represents a conversion efficiency for stored electrical energy into radiation of 2.7% and an equivalent brightness temperature of ≂13 500 K. The effective optical pulse width decreases as one moves from the visible into the vuv spectral regions. vuv radiation is only efficiently produced during the initial current half-period, i.e., during the gap breakdown process.
Influence of partial ionization on the energy loss of fast ions in high-Z material
Authors: Peter Th. , Kärcher B.
Published: July 2002

Analytical and simple numerical calculations of the stopping power of partially ionized high-Z targets are presented. Up to now such calculations are difficult, mainly because of lacking precise average ionization potentials of the target ions. The aim of this paper is both to clarify the importance of a suitable treatment of target ions in different ionization stages and to show by means of general scaling laws and explicit examples, that high-Z plasmas of high density and low ionization degree may have smaller stopping powers than cold matter. The resulting range lengthening of the projectile ions might be of crucial importance for a proper design of pellets in inertial confinement fusion.
Solubility enhancement of metallic impurities in silicon by rapid thermal annealing
Authors: Mathiot Daniel , Barbier Daniel
Published: July 2002

We report on the results of a study of the influence of rapid thermal annealing (RTA) on the diffusivity and solubility limit of titanium and chromium in silicon. It is shown that RTA has no influence on the diffusion of the metal atoms as long as the treatment is performed with the metal silicide as the boundary phase, but that the diffusivity is decreased if silicidation occurs during RTA. On the other hand, a strong solubility enhancement is found to occur during RTA.
Determination of deep levels in gold-doped polycrystalline silicon
Authors: Fujita Y. , Masuda-Jindo K.
Published: July 2002

The deep acceptor levels associated with Au impurities have been investigated for single-crystal and polycrystalline silicon specimens with the use of electrical resistivity and Hall-coefficient measurements. The heat treatments related to possible grain-boundary segregation of Au impurities were performed for the polycrystalline specimens. Furthermore, in order to investigate the influence of lattice dislocations on the deep Au level, dislocation-free and dislocated single crystals were used and appropriate heat treatments were performed. It is shown that the activation energies for Au acceptor levels are strongly dependent on the presence of lattice imperfections such as grain boundaries and lattice dislocations in the Si crystal. A simple physical interpretation for these experimental findings is also given on the basis of tight-binding electronic theory.
Boron ion implantation through Mo and Mo silicide layers for shallow junction formation
Authors: Angelucci R. , Solmi S. , Armigliato A. , Guerri S. , Merli M. , Poggi A. , Canteri R.
Published: July 2002

Molybdenum silicide is investigated because of its possible application in a self-aligned process for ultra large scale integration technology. p+/n shallow junctions are fabricated by boron implantation through Mo films or MoSi2 layers and rapid thermal annealing. Both procedures enable us to obtain junctions as shallow as 130 nm with very good electrical characteristics (reverse current density 1 nA/cm2 at −1 V, ideality factor 1.05 and contact resistivity 1×10−6 Ω cm2). The influence of a surface preamorphization with different thicknesses on junction depth and electrical characteristics is reported.
Formation of single-phase MAsx films on GaAs by selective wet-hydrogen oxidation and etching
Authors: Weiss Eliezer , Keller Robert C. , Helms C. R.
Published: July 2002

A technique which shows promise for achieving stable contacts is reported. This technique involves the selective oxidation of Ga in H2O/H2 mixtures simultaneous with the reaction of the metal and As to form a metal arsenide compound. The oxidation step is followed by removing the Ga2O3 layer using an acid etch. The large free energy of formation of gallium oxide enables the adjustment of the partial pressure of H2O to H2 so that only gallium is oxidized, while the GaAs substrate, metal, and metal arsenide are not. This method is discussed for three metal contacts to GaAs: In, Pt, and Cr. The technique was applied to GaPt/PtAs2/GaAs structures. The GaPt phase can be oxidized completely, whereas the inner PtAs2 is left unoxidized. The oxide can be etched off to leave a structure consisting only of platinum-arsenide on the GaAs substrate.
Zero magnetic field ferromagnetic resonance properties of single-crystal YIG/GGG/YIG layers
Authors: Sun K. , Dorsey P. , Vittoria C.
Published: July 2002

This study is an extension of previous work dealing with single crystals of YIG/GGG/YIG grown in (110) layers. Ferromagnetic resonance (FMR) measurements for fields along the 〈111〉 axis were performed. The microwave measurements reveal hysteretic behavior as the FMR frequency is measured for positive and negative magnetic fields H. For H in which the magnetic moment is zero (spin flop) the FMR frequency goes through a discrete and measurable jump or change. This discontinuity in the FMR frequency at the spin-flop condition is attributed to the magnetostatic interaction between the two YIG layers.
Polydisperse analysis of absolute small-angle intensities scattered by activated carbons
Authors: Ciccariello S. , Benedetti A. , Polizzi S.
Published: July 2002

The absolute small-angle x-ray intensities, scattered by two activated carbons, are analyzed assuming that coals scatter as polydisperse distributions of uncorrelated layered cubic particles. The specific interphase surface areas and the densities of the samples are obtained by the particle populations resulting from the intensity best-fits. The values agree, within a factor two, with those obtained by different experimental techniques.
Near-surface effect for Ag and Au in lead-indium alloys
Authors: Huntington H. B. , Pacek Mario , Hall Charles
Published: July 2002

It has been observed in prior measurements of electromigration of noble metals in lead-tin and lead-indium alloys that the tracers tended to concentrate markedly with anneal near the surface. We observe an analogous anomaly when diffusing from heavy plates as for solubility measurements. Here we study both effects using refined sectioning by microtome and also an etching technique. The inward penetration from the ambient (oxygen or perhaps vacancies) appears to be responsible. The extent of its penetration is markedly increased by the inward diffusional flux of the noble metal tracer in the solubility-type measurements.
The effect of ion implantation and solute atoms on the interdiffusion in amorphous Si/Ge multilayers
Authors: Park B. , Spaepen F. , Poate J. M. , Jacobson D. C.
Published: July 2002

Amorphous Si/amorphous Ge multilayers were prepared by ion beam sputtering. Silicon, boron, gold, or oxygen atoms were introduced into the Si/Ge multilayers by ion implantation or during the sputtering deposition. Diffusion or ion mixing lengths were determined by measuring the decrease in the intensity of the first-order x-ray diffraction peak resulting from the composition modulation. Annealing of Si-implanted samples showed that after relaxation the diffusivity appeared unaffected by the implantation process. Annealing of the multilayers containing B or Au showed that the interdiffusion of Si and Ge in their amorphous phase can be enhanced by doping, while O implantation showed no effect. The enhancement factor is independent of the degree of structural relaxation, as observed by the decrease of diffusivity with annealing time, of the amorphous phase. A model is proposed that describes this behavior in terms of electronic effects, introduced by dopants, on the pre-existing structure defects governing interdiffusion.
Investigations of microstructure of thin TbFeCo films by high-resolution electron microscopy
Authors: Li Z. G. , Smith David J. , Marinero E. E. , Willett J. A.
Published: July 2002

High-resolution electron microscope observations confirm the presence of small crystallites in thin TbFeCo films protected by Si3N4 overcoats. Selected area electron diffraction patterns in top-view projection indicate that the crystals have a face-centered-cubic structure. Microscope analysis reveals grain growth following annealing of these protected thin films at 200 °C in vacuum, and Kerr measurements yield large reductions in coercivity relative to the room-temperature value. The typical grain size visible in top-view observations increases from about 3 nm in the as-deposited samples to about 30 nm after annealing at 200 °C for 36 h while the static coercivity, Hc, drops by about 40%. The fcc structure of the crystals is retained after annealing.
Ultraviolet induced transformation of polysiloxane films
Authors: Joubert O. , Hollinger G. , Fiori C. , Devine R. A. B. , Paniez P. , Pantel R.
Published: July 2002

We have studied the transformation of a polysiloxane film induced by high temperature annealing and by 248 and 193 nm excimer laser irradiation. Auger electron and x-ray photoelectron spectroscopy have been used to study the Si, O, and C profiles and the Si-O valence band structure before and after transformation. We suggest that laser induced transformation results from localized heating and oxidation of the Si-O chains coupled with a breakdown and oxidation of previously attached benzene groups into volatile gaseous products which diffuse out of the film.
Raman scattering of (GaAs)n(GaP)n short-period superlattices prepared by pulsed jet epitaxy
Authors: Kodama K. , Ozeki M. , Sakuma Y. , Ohtsuka N.
Published: July 2002

We have carried out the Raman-scattering measurement of (GaAs)n(GaP)n short-period superlattices (n=1–5) prepared by the atomic layer epitaxy technique called pulsed jet epitaxy (PJE). The zone-folding effects on the longitudinal-acoustic (LA) phonon were observed for all the samples. The Raman peak observed for the (GaAs)1(GaP)1 monolayer superlattice has also been tentatively assigned to the scattering from zone-folded LA phonons. If the assignment is correct, this is the first observation of the zone-folded LA phonon in a semiconductor monolayer superlattice. The present results suggest that the growth proceeds atomic layer by atomic layer in PJE.
Barrier structure for near unity transmission in double-barrier resonance tunneling
Authors: Lee Hong H.
Published: July 2002

A three-band model is used to draw conclusions on the barrier structure of double-barrier resonance tunneling under bias for an overall transmission of near unity. It is shown that contrary to what is generally believed, the barrier height and thickness of the two barriers should be essentially the same for near unity transmission even under bias. If the second barrier height is to be higher than the first barrier height, as is usually believed, the thickness of the second barrier should be smaller than that of the first barrier.
Localization of incident laser beam in the optical element by on-site photoacoustic detection
Authors: Tashiro Hideo , Suetsugu Yasushi
Published: July 2002

Weak photoacoustic signals generated spontaneously by a laser pulse proved usable for precise detection of the laser beam location on an optical element. Using a couple of acoustic emission sensors attached to the rear surface of a copper mirror, the displacement of a pulsed CO2 laser beam was measured with a precision of less than 0.1 mm. Characteristic features of such photoacoustic signals are also reported.
Optical properties of quantum wells grown upon gas source molecular-beam epitaxy low-temperature buffers
Authors: Shiralagi K. T. , Puechner R. A. , Choi K. Y. , Droopad R. , Maracas G. N.
Published: July 2002

GaAs/AlGaAs quantum wells are grown on gas source molecular-beam epitaxy (GSMBE) grown low-temperature buffers (LTB). Changes in LTB growth conditions produce noticeable changes in photoluminescence (PL) intensity and linewidths of the quantum wells. Layers grown at low temperatures (200–300 °C) incorporate excess arsenic which outdiffuses during subsequent quantum well growth. Reflection high energy electron diffraction and PL results are utilized to show strain and arsenic outdiffusion from the LTBs. Excess arsenic incorporation during the growth of GaAs at low temperatures is explained in terms of the association reaction of As2 to form As4 at the surface. The optimum V/III ratio for growth of LTB by GSMBE is discussed.
Magnetization and NMR study of the La-Al metallic glass system
Authors: Yang D. P. , Hines W. A. , Tsai C. L. , Giessen B. C. , Lu F. C.
Published: July 2002

In order to investigate the atomic and electronic structures of the melt-spun metallic glass system La100−xAlx (18≤x≤45), measurements of the 27Al NMR Knight shift and linewidth, as well as the magnetic susceptibility, have been carried out. The dependence of these quantities on the Al concentration shows a change in behavior at x=25, which corresponds to the equilibrium crystalline phase, La3Al, and is discussed in terms of a model previously introduced for the atomic structure. An analysis of the magnetic susceptibility indicates that the d-electron spin/orbital contributions dominate due to a large d-electron density of states at the Fermi energy. Values of 82 and 23 kOe per μB of s and d spin, respectively, were obtained for the hyperfine coupling.