bluuebunny/crossref_metadata_2025 huggingface dataset:
Extremal dynamics: A unifying physical explanation of fractals, 1/f noise, and activated processes
Authors: Miller S. L. , Miller W. M. , McWhorter P. J.
Published: July 2002

The properties of physical systems whose observable properties depend upon random exceedances of critical parameters are quantitatively examined. Using extreme value theory, the dynamical behavior of this broad class of systems is derived. This class of systems can exhibit two characteristic signatures: generalized activation when far from equilibrium and noise with a characteristic power spectrum (including 1/f ) when in quasiequilibrium. Fractal structures can also arise from these systems. It is thus demonstrated that generalized activation, noise, and fractals, in some cases, are simply different manifestations of a single common dynamical principle, which is termed ‘‘extremal dynamics.’’ Examples of physical processes governed by extremal dynamics are discussed, including data loss of nonvolatile memories and dielectric breakdown.
Study of surface reflectivity and etch rates of polyimide (Kapton H) utilizing double-pulsed 308 nm laser radiation
Authors: Mihailov S. , Duley W. W.
Published: July 2002

Studies of the ablation of polyimide accompanying two rapid sequential pulses of 308 nm laser radiation are presented. Measurements of the change in surface reflectivity revealed that both transient and permanent changes in the surface reflectivity resulted when pulses above the ablation threshold irradiated the surface. The permanent change was due to physical modification of the polymer surface and redeposition of ablated material. The transient change was likely due to increased surface absorption of the incident radiation at subthreshold fluences. Above threshold, scattering and absorption of the incident probe radiation by particles in the plume is likely the dominant process. Double pulsed etch rate measurements are also presented.
Single trapped vortices induced in a superconducting film by laser switching
Authors: Park George S. , Cunningham Charles E. , Cabrera Blas , Huber Martin E.
Published: July 2002

Light pulses from an infrared laser can momentarily drive a superconducting strip of niobium normal. Under certain conditions, a single vortex may be trapped while the strip returns to the superconducting state. It was determined that the speckle pattern due to modal interference in the incident light is the most probable cause of vortex trapping. By changing the relative contrast of the speckle pattern, we can change the trapping probability from 0% to about 5% per pulse.
Magnetic properties of Fe-Zr-Co/Fe-Zr-Co-N multilayered films
Authors: Ono H. , Fujinaga M. , Yonemoto T. , Miyagawa T.
Published: July 2002

Fe-Zr-Co/Fe-Zr-Co-N soft magnetic multilayered films were alternately prepared by Fe-Zr-Co alloy sputtering and electron cyclotron resonance plasma nitridation, and their magnetic properties and thermal stability were investigated. Co addition to Fe-Zr/Fe-Zr-N multilayered films was effective in improving the magnetic properties of these films. The soft magnetic properties of these films demonstrated outstanding thermal stability, and it was observed that the hyperfine field Hint increased up to that for pure Fe-Co alloy by heat treatment. Under the optimum preparation conditions, values for saturation flux density Bs of 2.02–2.06 T, coercivity Hc of 75–90 A/m, and relative permeability μ′≥3100 (at 20 MHz) were obtained in Fe84Zr8Co8/Fe84Zr8Co8-N and Fe76Zr8Co16/Fe76Zr8Co16-N multilayered films after annealing at 873 K for 3.6 ks.
Fabrication and characterization of thin, self-supporting germanium single crystals
Authors: Grant M. W. , Lyman P. F. , Hoogenraad J. H. , Carlsward B. S. , Arms D. A. , Seiberling L. E. , Namavar F.
Published: July 2002

Thin Ge single crystals (≤1 μm) up to 4 mm in diameter have been fabricated from epitaxial Ge films grown by atmospheric pressure chemical vapor deposition on Si(100) wafers. The thin Ge windows are formed by chemically etching away both the Si substrate and the region of the Ge film near the interface that contains misfit dislocations associated with heteroepitaxial growth and relaxation of the Ge films. The resulting Ge films are comparable in crystalline quality to bulk Ge wafers, as indicated by ion channeling studies.
An in situ measurement of intergranular coupling in magnetic film media
Authors: Mian Guo , Indeck R. S. , Muller M. W.
Published: July 2002

We describe an in situ nondestructive method to measure the intergranular coupling in magnetic thin film recording media based on Stoner–Wohlfarth switching theory [Philos. Trans. Roy. Soc. London A 240, 599 (1948)]. The method uses recording write and read heads and a disk test stand to measure a medium’s remanence curves from saturation and demagnetization. Using this technique, we have measured Henkel plots [Phys. Status. Solidi 7, 919 (1964)] for single layer and multiple layer longitudinal media, as well as a Henkel plot for a perpendicular thin film with a highly permeable underlayer, which cannot be obtained by the conventional vibrating sample magnetometer method.
Annealing kinetics of a-Si:H deposited by concentric-electrode rf glow discharge at room temperature
Authors: Conde J. P. , Chan K. K. , Blum J. M. , Arienzo M. , Monteiro P. A. , Ferreira J. A. , Chu V. , Wyrsh N.
Published: July 2002

The irreversible isothermal annealing of the as-deposited defects of hydrogenated amorphous silicon, a-Si:H, deposited at room temperature by concentric-electrode radio-frequency glow discharge is studied using dark and photoconductivity, space-charge limited current, and time-of-flight. The photoconductivity increases as a power law of the annealing time with exponent 0.8. The density of states at the Fermi level, measured by space-charge limited current, is inversely proportional to the annealing time. These results are compatible with bimolecular annealing kinetics. The dark conductivity obeys a Meyer–Nelder rule during the isothermal anneal.
Effect of mechanical stress on current-voltage characteristics of thin film polycrystalline diamond Schottky diodes
Authors: Zhao G. , Charlson E. M. , Charlson E. J. , Stacy T. , Meese J. M. , Popovici G. , Prelas M.
Published: July 2002

Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament-assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current-voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diamond Schottky diodes not only are very stress sensitive but also have good linearity. This study shows polycrystalline diamond Schottky diodes have potential as mechanical sensors.
Evidence for weak-link and strong-link couplings in high Tc granular superconductors, detected from the geometric influence on Jc-H behavior
Authors: Fiscina Jorge E. , D’Ovidio Claudio A. , Esparza Daniel A.
Published: July 2002

The Jc vs H characteristics of several samples were studied in connection with their geometry. The onset decoupling field was compared and correlated with a characteristic field of the weak-link array already introduced in a previously developed model. It is concluded that this characteristic field coincides with the decoupling field H0 defined by the junction area, not dependent on the geometry but on the microstructure of the sample. The role of weak-link and strong-link junctions in the critical current density was established from the dependence of the Jc vs H curves on geometry.
Dielectric constant of two-component, two-dimensional mixtures in terms of Bergman–Milton simple poles
Authors: Liu Ce , Shen Liang C.
Published: July 2002

According to the Bergman–Milton theory [D. J. Bergman, Phys. Rep. 43, (No. 9), 377 (1978), and G. W. Milton, J. Appl. Phys. 52, 5286 (1981)], the effective dielectric constant or conductivity of a two-component mixture is a function of the ratio of the dielectric constants (or conductivities) of those components. The function has simple poles only at some negative values of the ratio, and positions of the poles and residues are dependent only on the microgeometry of the mixture. In this study, the location of the poles and the values of the residues are found for two-component, two-dimensional composite materials with periodic, simple-square lattice structures using the Fourier series expansion technique. With the locations of the poles and residues determined, the effective dielectric constants or conductivities of two-component composite materials may be expressed in practical forms and may be predicted for composite mixtures even when the dielectric constants of the component materials are complex.
Low and high electric field transport in CdIn2Te4
Authors: Couturier G. , Jean B. , Lambert J. F. , Launay J. C. , Joffre P.
Published: July 2002

Low and high electric field transport in the CdIn2Te4 electro-optical semiconductor were investigated. The conductivity, the carrier concentration, and the mobility were measured versus the temperature using Hall techniques. Nonlinear current-voltage characteristics in high fields are interpreted in terms of thermal effects, not in terms of space-charge-limited currents as usually encountered. The nonreversibility of I-V measurements is also discussed, diffusion of species are proposed to explain the change of activation energy of the conductivity.
Thermal stability of Ta/Ge superlattices studied by Raman spectroscopy
Authors: Kumar Sunil , Trodahl H. J.
Published: July 2002

The thermal behavior of Ta/Ge superlattices has been studied using Raman spectroscopy. The high-frequency Raman spectra, obtained as a function of annealing temperature, reveal no significant change in the superlattice structure up to an anneal temperature of 400 °C. The interlayer diffusion at the Ta/Ge interfaces occurs at 500 °C followed by complete crystallization of the superlattice at 600 °C. Raman scattering from the folded acoustic modes of the superlattices was also employed to study the thermal behavior of superlattices, and the results thus obtained corroborate the above findings.
A new numerical method for computing the optical characteristics of birefringent fibers
Authors: Fontaine Marie
Published: July 2002

In this article, we present a new numerical method for solving vectorial Maxwell equations which makes it possible to study the birefringence of any geometric pattern of isotropic optical fiber. The distinguishing feature of this method is its use of an iterative process to determine the modes of propagation. The major advantage is the ease of the procedure since the various mathematical steps required can be performed by commercially available software.
Spectral optimization of a pulsed HF chemical laser for efficient energy delivery through a low-loss fluoride glass optical fiber
Authors: Sumiyoshi Tetsumi , Kannari Fumihiko , Obara Minoru
Published: July 2002

Pulsed HF chemical lasers oscillating in the midinfrared region of the spectrum where water can strongly absorb are suitable for the organic tissue ablation. For such a medical application, a flexible energy delivery system using an optical fiber is indispensable. The fluoride glass optical fiber may be used for low-loss optical energy delivery of the pulsed HF laser. Using an intracavity CO2 absorption cell, we have optimized pulsed multiline HF chemical laser spectrum for low-loss energy delivery through a fluoride glass optical fiber whose transmission loss is theoretically estimated to be minimum around 2.5 μm. The fractional output energy of P1-0(3) and P1-0(4) lines, which are sitting in the lowest loss spectral region of the practical fluoride glass fiber, exceeded half the multiline output energy using a line selective intracavity CO2 gas cell. The P1-0(4) line extracted from the resonator with a diffraction grating was successfully delivered through a 3-m-long commercial fluoride glass fiber (core/cladding diameter=450/500 μm). The delivered energy of 11.9 mJ was achieved with the corresponding energy fluence of 12 J/cm2 and peak intensity of 22 MW/cm2 at the exit core surface without optical damage.
Thermal oxidation and electrical properties of silicon carbide metal-oxide-semiconductor structures
Authors: Singh N. , Rys A.
Published: July 2002

Fabrication processes of metal-oxide-semiconductor (MOS) capacitors on n-type, Si-face 6H-SiC, and its electrical properties, have been reported in this article. The effects of thermal oxidation conditions at temperatures between 1150 and 1250 °C on the electrical properties of MOS capacitors were studied. After oxidation, the wafers were annealed under argon ambient to improve the capacitance-voltage (C-V) characteristics. The C-V characteristics of the Al-SiO2-SiC metal-oxide-semiconductor capacitors were measured at high frequency in the dark and under illumination. Under dark conditions, inversion did not occur, probably owing to the absence of minority carriers due to the large band gap of 6H-SiC. The C-V measurements made under illumination for both wet and dry thermally grown oxides show accumulation, depletion, and inversion regions. The ac conductance method was used to determine the interface trap densities and emission time constants of fast states. From the analysis of the data a total of fixed charges and the slow interface traps, Not+NitSlow of 1.5–3.3×1012 cm−2, fast interface trap densities, NitFast of 0.5–1.7×1011 cm−2 eV−1, and an emission time constant of 0.3–1.4 μs were obtained for wet oxidation. For dry oxidation, Not+NitSlow of 3.5–11.2×1011 cm−2, NitFast of 0.7–1.25×1010 cm−2 eV−1, and emission time constants of 0.6–2 μs were obtained.
Pump and signal cross saturation in cw dye lasers
Authors: Casperson Lee W. , Wilson A. C. , Sandle W. J.
Published: July 2002

It is well known that the signal output intensity from a dye laser oscillator depends directly on the pump intensity. The opposite effect, the dependence of the transmitted pump intensity on the signal intensity, is studied in detail. The theoretical results are compared with experimental data obtained using an argon-laser-pumped rhodamine 6G dye laser.
The magneto-optical Kerr effect of multilayers Fe/Pt and Co/Pt
Authors: Zhou Shiming , Zhai Hongru , Song Jingtao , Zhang Hongyan
Published: July 2002

In this communication, the magneto-optical polar Kerr rotation spectra of multilayers Fe/Pt and Co/Pt are calculated based on two different assumptions. First, the spin polarization of the Pt layer is assumed to be negligible. The calculated results for Fe/Pt and Co/Pt multilayers with dCo(Fe)/dPt=1 showed the magneto-optical Kerr rotation in the region from 300 to 800 nm increased with increasing modulation wavelength, which is opposite to experimental results. Second, the Pt layer is assumed to be polarized and has a direct contribution to Kerr rotation in the multilayers. The results agree with experiments qualitatively. It is found that the spin polarization of the Pt layer increases with decreasing Pt layer thickness.
Effect of temperature gradient on concentration profile of hydrogen in a palladium lattice
Authors: Lee W. M. , Uhm Han S.
Published: July 2002

A thermodynamic calculation is conducted to determine the distribution of hydrogen atoms absorbed in a one-dimensional palladium rod, along which a temperature gradient is imposed. The rod is assumed to be completely sealed, so that the total number of the hydrogen atoms is conserved regardless of its thermal conditions. A model calculation based on a zeroth-order interaction model predicts that upon the imposition of the gradient, the hydrogen distribution will significantly change from its initial uniformity. The profile of the redistributed hydrogen can be discontinuous at one point on the rod. The concentration gap developed at this point of temperature T implies that the two-phase region in the palladium hydride phase under the thermal equilibrium is nonexistent under the nonequilibrium condition. Similar to the disappearance of the two-phase region above the critical temperature, the concentration gap is reduced with an increase of the temperature gradient.
Enhanced tunability of asymmetric three-section InGaAsP/InP distributed feedback lasers
Authors: Hillmer H. , Zhu H.-L , Burkhard H.
Published: July 2002

Wavelength tunability in three-section distributed feedback laser diodes has been studied under pulsed and continuous biasing. In both cases comparably large modejump-free tuning ranges (2.5 and 3.7 nm, respectively) were obtained for devices operated with two injection electrodes. Several effects are discussed in terms of a possible explanation of the enhanced tunability in these devices.
Hydrogen passivation of nonradiative defects in InGaAs/AlxGa1−xAs quantum wells
Authors: Lord S. M. , Roos G. , Harris J. S. , Johnson N. M.
Published: July 2002

The effects of diffusion of monatomic hydrogen and deuterium in InGaAs/AlGaAs quantum wells were studied using photoluminescence (PL) and secondary-ion-mass spectroscopy. The multiquantum-well structures were grown by molecular-beam epitaxy and hydrogenated with a remote plasma. A significant increase in 77 K PL integrated intensity of bound excitons was observed after hydrogenation. This is attributed to the passivation of nonradiative recombination centers within InGaAs/AlGaAs quantum wells. A series of studies demonstrating the increase in passivation efficiency with increasing Al concentration in the barriers, the stability of the hydrogenation upon annealing to temperatures of up to and above 450 °C, the ratio of the deuterium concentration for samples with different barrier thicknesses, and the comparison of strained versus relaxed quantum wells, all strongly suggest that the passivated nonradiative recombination centers are interface defects. The stability of this hydrogen passivation at temperatures commonly used in device processing is particularly promising for device applications.
Preparation and properties of electrodeposited indium tin oxide/SnO2/CdTe and indium tin oxide/SnO2/CdS/CdTe solar cells
Authors: Das S. K. , Morris G. C.
Published: July 2002

Cadmium telluride-based solar cells have been prepared as indium tin oxide (ITO)/SnO2/CdTe and indium tin oxide/SnO2/CdS/CdTe structures where CdS and CdTe were prepared by an electrodeposition technique. Both open circuit voltage and short circuit current of ITO/SnO2/CdTe cells were higher than that of ITO/SnO2/CdS/CdTe cells. The spectral response measurement showed that the current collection was higher in the ITO/SnO2/CdTe cell relative to the ITO/SnO2/CdS/CdTe cell. Current-voltage temperature measurements indicated that the junction transport could be controlled by recombination or thermally assisted tunneling in the ITO/SnO2/CdTe cell, whereas tunneling could be the dominant junction transport mechanism in the ITO/SnO2/CdS/CdTe cell. Activation energies of ITO/SnO2/CdTe and ITO/SnO2/CdS/CdTe cells were 0.60 and 0.76 eV, respectively. The values of the built-in potential, Vbi calculated from the measurement of open circuit voltage with temperature were 1.41 and 1.5 eV for ITO/SnO2/CdTe and ITO/SnO2/CdS/CdTe cells, respectively, whereas from Mott–Schottky plots they were 1.1 and 0.95 eV, respectively.
Effects of scattering on the dynamics of holographic recording and erasure in photorefractive lithium niobate
Authors: Maniloff Eric S. , Johnson Kristina M.
Published: July 2002

Absorption and scattering, or fanning, have a pronounced effect on the observed dynamics of the photorefractive effect. In this article these effects are included in the coupled wave equations for both recording and erasure, and a comparison is made with experimental observations. It is shown that a single recording and erasure time constant is necessary to fit the experimental measurements, whereas separate time constants would be required if absorption and scattering were neglected.
Extrinsic recombination processes in proton irradiated InAs/GaAs heterostructures grown by molecular beam epitaxy
Authors: Vodopyanov K. L. , Graener H. , Phillips C. C. , Tate T. J.
Published: July 2002

The dynamics of carrier recombination in proton bombarded high-quality single crystal thin films of InAs grown by molecular beam epitaxy on transparent GaAs substrates are studied using the picosecond pump-probe technique in the photon energy range 335–483 meV. The effects of extrinsic recombination at the InAs/GaAs interface and of point defects introduced by proton damaging are separated by studying samples ranging from 3.3 to 0.27 μm in thickness and with proton doses in the range 1011–1015 cm−2. The data indicate an interfacial recombination velocity of 2.7×104 cm s−1 and a defect capture time of 160 ps, and in the regime studied mobility limitations are found to have a negligible effect on the recombination dynamics.
Morphology and crystallography of single crystal precipitates on Al alloy films grown by the sputtering method
Authors: Niwa Hideo , Yamaguchi Ichiro , Yagi Haruyoshi , Kato Masaharu
Published: July 2002

When Al alloys such as Al-1%Si or Al-2%Cu are sputtered on Si substrates at elevated temperatures, extruded single crystal precipitates are observed on the alloy films. The morphology and crystallography of the precipitates are studied in detail using scanning electron microscopy and transmission electron microscopy. The precipitates on the Al-2%Cu films contain a few percent Cu and are single crystals with crystallographically low-index facet planes. The temperature profiles during and after the deposition for the favorable occurrence of the precipitation are also investigated.
Collector-up light-emitting charge injection transistors in n-InGaAs/InAlAs/p-InGaAs and n-InGaAs/InP/p-InGaAs heterostructures
Authors: Belenky G. L. , Garbinski P. A. , Luryi S. , Mastrapasqua M. , Cho A. Y. , Hamm R. A. , Hayes T. R. , Laskowski E. J. , Sivco D. L. , Smith P. R.
Published: July 2002

The realization of collector-up light-emitting complementary charge injection transistors is reported. The devices have been implemented in molecular-beam-epitaxy-grown n-InGaAs/InAlAs/p-InGaAs and n-InGaAs/InP/p-InGaAs heterostructures using a self-aligned process for the collector stripe definition. Electrons, injected over the wide-gap heterostructure barrier (InAlAs or InP) by the real-space transfer (RST) process, luminesce in the low-doped p-type InGaAs active layer. An essential feature of present devices, besides their self-aligned collector-up configuration, is a relatively heavy doping of the n-type emitter channel, with the sheet dopant concentration of 4×1012 cm−2. This ensures a higher uniformity of the electric field in the channel and provides a relief from RST instabilities at a high level of collector current (linear density ∼10 A/cm). Devices with InAlAs and InP barriers show rather different optical characteristics, mainly due to the different band lineups ΔEC/ΔEV in InGaAs/InAlAs and InGaAs/InP heterostructures, leading to different ratios between the RST current and the parasitic leakage of holes from the collector into the channel. At high RST current densities, the effective carrier temperature Te in the active collector layer, determined from the high-energy tails of the luminescence spectra, is strongly enhanced compared to the lattice temperature. This decreases the device radiative efficiency and leads to a thermionic emission of carriers out of the active layer.
Differences in the structure of amorphous hydrogenated silicon-carbide layers prepared with either methane or silylmethanes
Authors: Fölsch J. , Rübel H. , Schade H.
Published: July 2002

Using Fourier transform infrared spectroscopy, we investigated hydrogenated amorphous silicon-carbide (a-Si1−xCx:H) films, deposited in a standard rf glow discharge. Different gas mixtures in combination with silane (SiH4) were used, namely methane (CH4), disilylmethane, trisilylmethane, and tetrasilylmethane. Methane-based and silylmethane (SM)-based a-Si1−xCx:H films yield two different classes of material. SM-based alloys contain more SiC groups and more CH groups, but less CH3 groups than methane-based material. In SM-based material, hydrogen is mainly bonded to silicon atoms, whereas in CH4-based material hydrogen is chiefly bonded to carbon.
Criteria for Si quantum-well luminescence
Authors: Ren Shang Yuan , Dow John D. , Shen Jun
Published: July 2002

Criteria are developed for selecting a barrier material XY such that Si/XY superlattices should emit light from their Si quantum wells. GaAs is such a material for [001] superlattices. In many such superlattices, substitutional N on a Si site will be a shallow donor, not a deep trap.
Spin reorientation and crystal field in Tm2Fe17Cx
Authors: Zhao T. S. , Kou X. C. , Grössinger R. , Kirchmayr H. R.
Published: July 2002

The spin-reorientation transitions in Tm2Fe17Cx are analyzed in terms of the crystal field and the Tm-Fe exchange interactions. It is deduced that with increasing carbon concentration, the Tm-Fe exchange field decreases slightly, whereas the absolute value of the second-order crystal-field parameter increases dramatically. The carbon concentration and temperature dependence of the magnetic anisotropy of the Tm ions in Tm2Fe17Cx are discussed.
Magnetocrystalline anisotropy in some RENi5 intermetallics
Authors: Algarabel P. A. , Morellón L. , Ibarra M. R. , Schmitt D. , Gignoux D. , Tari A.
Published: July 2002

Measurements of the parallel M∥ and perpendicular M⊥ components of the magnetization to the applied magnetic field HA have been carried out for all directions in the (010) plane on single crystals of hexagonal NdNi5, TbNi5, and HoNi5. These measurements were performed using a steady magnetic field of 15 kOe, in the ferromagnetic phase down to 4 K. These kinds of experiments allow a detailed description of the magnetocrystalline anisotropy to be given. The polar dependencies of the M∥ and M⊥ isotherms have been explained using a microscopic single-ion crystal electric field (CEF) and a molecular-field approximation to describe the exchange interaction.
The d-d exchange interaction in the diluted magnetic semiconductor ZnFeS
Authors: Twardowski A. , Fries T. , Shapira Y. , Demianiuk M.
Published: July 2002

We measured the magnetic susceptibility of Zn1−xFexS (x≤0.03) and found typical Curie–Weiss behavior above 100 K. Based on the high temperature expansion series developed for Fe based diluted magnetic semiconductors, we estimated the exchange interaction constant between the nearest neighbors JNN=−37 K, which is the largest value for Fe-based diluted magnetic semiconductors studied so far.
Short period oscillation of the interlayer exchange coupling in the ferromagnetic regime in Co/Cu/Co(100)
Authors: Bloemen P. J. H. , van Dalen R. , de Jonge W. J. M. , Johnson M. T. , aan de Stegge J.
Published: July 2002

A unique sample was prepared on a Cu(100) single crystal, consisting of three Co layers separated by two Cu layers in the form of wedges oriented perpendicular to each other: Cu(100)/80 Å Co/Cu wedge A/30 Å Co/Cu wedge B/30 Å Co/7 Å Cu/30 Å Au. Position-sensitive magneto-optical Kerr effect measurements along Cu wedge B, at a fixed position on Cu wedge A corresponding to maximum antiferromagnetic (AF) coupling, enabled us to investigate not only the AF but also the ferromagnetic (F) coupling between the two 30 Å Co layers as a function of the Cu thickness. The measurements confirmed both long and short period coupling oscillations in the AF regime, and revealed the predicted extension of the short period through the F regime.
Surface roughness and long-range order of a semi-infinite ferromagnet
Authors: Erickson R. P. , Cullen J. R.
Published: July 2002

We consider the effect of random surface roughness on a semi-infinite ferromagnetic film. We calculate the magnetization as a function of distance from the surface and the spin-spin correlation as a function of lateral separation. We show that, even in the absence of crystalline anisotropy or an external field, the surface of the ferromagnet is stable against random torques created by the roughness. Near the surface, the magnetization reduction is inversely proportional to the square of a ‘‘healing’’ length λ0≡(D/2πM0)1/2, where D is an exchange stiffness and M0 is the saturation magnetization. The correlations in fluctuations of the magnetization orientation decay exponentially with distance parallel to the surface, λ0 being in the exponent. In contrast, fluctuations decrease only as the reciprocal of the square of the distance perpendicular to the surface. Results are discussed and compared with other calculations of the effects of random surface perturbations.
Magnetic and magnetotransport properties of (100)Fe/Pd superlattices (abstract)
Authors: Childress J. R. , Schuhl A. , Durand O. , Galtier P. , Cros V. , Ounadjela K. , George J.-M. , Fert A.
Published: July 2002

It has recently been reported that Fe layers can couple through Pd interlayers, with at least one region of weak antiferromagnetic coupling.1 This system, with coupling fields of only a few tens of Gauss, is potentially attractive for low-field device applications. Additionally, compared to the case of multilayer systems based on noble metal spacer layers, the high paramagnetic susceptibility of Pd and its tendency to ferromagnetic order are expected to lead to modified coupling mechanisms. We report on the growth, structural properties, magnetic properties, and magnetotransport properties of epitaxial (100)Fe/Pd superlattices. Samples consisting of 10 bilayers, with Fe layer thicknesses ≊20 Å and Pd layer thicknesses in the range 10–50 Å (including in ‘‘wedge’’ geometries), have been fabricated by molecular beam epitaxy onto (100)MgO substrates. The structure was characterized by reflection high-energy electron diffraction, x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The structural and magnetic properties of the multilayers are found to be highly dependent on the growth procedures. Optimized growth conditions, including in particular the absence of any buffer layers, result in overall coercive fields below 15 G and allow the detection of small coupling fields. Magnetization measurements unambiguously reveal the presence of a weak uniaxial anisotropy in the Fe layers, resulting in split hysteresis loops along one of the two in-plane 〈100〉Fe directions. These loops are similar to those normally associated with antiferromagnetic (AFM) coupling. No evidence of AFM coupling has been found in the present study. Magnetoresistance measurements show abrupt changes of resistivity of up to 1.5% at low temperatures, which can be well explained by anisotropy effects during rapid reversals of the Fe layers.
Microscopic investigations of overwritten data
Authors: Gomez R. D. , Burke E. R. , Adly A. A. , Mayergoyz I. D. , Gorczyca J. A. , Kryder M. H.
Published: July 2002

The magnetic field distributions of overwritten patterns on rigid thin film disk media have been imaged with submicron resolution by using the magnetic force scanning tunneling microscope. The capability of the device to measure fields locally is exploited to quantitatively understand the conditions under which portions of overwritten data can remain and be detectable. The persistence and retrievability of previously recorded data are related to the radial offset of the head during overwrite for patterns created at high and low recording densities. It is observed that at high densities, for offsets less than 2 μm, overwritten transitions affect the newly written patterns by inducing track width modulation along its edges. At low densities, the track width variations are less noticeable, but can be elucidated by examining the detailed geometrical structure of overwritten patterns.
A study of old information induced interpattern proximity shift (abstract)
Authors: Tang Yaw-Shing , Tsang Ching
Published: July 2002

This article presents a high precision measurement of the proximity shift on a magnetic transition due to the presence of an old transition in the background. Using peak detection electronics, we deduced this interpattern shift by measuring the distance between a reference and a test transition in a multibit pattern, with and without a background transition in the vicinity of the test transition. The measurement process was carefully designed to achieve high accuracy. We measured the proximity shift of a 3380-type write head on disks with different remanent-thickness product for cases of both easy and hard transition types for both the background and the data transitions. Results showed three distinct transition shift behavior depending on the background-to-test intertransition distance: a gradual decay in the far region (≳2 μm), a rapid rise in the intermediate region and asymptotic saturation at the near region when the two transitions are almost on top of each other. The asymptotic shift magnitude agrees well with independently measured hard transition shifts, and good agreements with theoretical modeling are obtained for shifts in the far and intermediate regions.
Structure and magnetic properties of Sm2(Fe1−xAlx)17Ny compounds
Authors: Li Xinwen , Tang N. , Lu Zhonghua , Zhao Tongyun , Lin W. G. , Zhao Ruwen , Yang Fuming
Published: July 2002

By means of x-ray phase analysis, it is shown that all the interstitial Sm2(Fe1−xAlx)17Ny nitrides and the parent compounds crystallize in Th2Zn17-type structure for x≤0.4. The lattice constants of the parent compounds increase linearly with Al concentration. The introduction of nitrogen leads to a further increase in lattice constants, but the amplitude of the increase decreases with increasing Al concentration. The introduction of nitrogen leads to an increase of Curie temperature Tc . The composition dependence of Tc of the parent compounds exhibits a maximum, whereas Tc of the nitride decreases monotonously with increasing Al concentration from 750 K for x=0 to 313 K for x=0.4. The mean magnetic moments of iron ions in both nitrides and parents decrease monotonously with increasing Al concentration.
Spin reorientation transition in some REFe10V2 intermetallics under hydrostatic pressure
Authors: Arnold Z. , Algarabel P. A. , Ibarra M. R.
Published: July 2002

The large effect of the applied hydrostatic pressure on the spin reorientation transition (SRT) temperature observed in Er2Fe14B has been associated with the modification of the intensity of the CEF interaction with pressure. We propose that mainly the second order CEF terms are sensitive to the pressure and also that the applied pressure influences only slightly the fourth and sixth order CEF terms and the intensity of the R-Fe exchange interaction. In the present article, we report a study of the thermal dependence of the ac magnetic susceptibility under hydrostatic pressure up to 10 kbar in intermetallic compounds of the series RFe10V2 (R=Nd, Dy, and Er). The results show no evidence of any change of the SRT temperature in the measured range of pressure, which constitutes a confirmation of the negligible influence that the external applied pressure has on high order CEF terms.
Hard magnetic properties in melt-spun Co82−xFexZr18 alloys
Authors: Shen Bao-gen , Yang Lin-Yuan , Cao Lei , Guo Hui-qun
Published: July 2002

The Co82−xFexZr18 (0≤x≤16) alloys melt-spun with vs=40-47 m/s exhibit a single phase for all x. The Curie temperature Tc and the room-temperature saturation magnetization σs increase monotonically with increasing Fe concentration x. The anisotropy field for x=0 is found to be about 3.13T. In the as-quenched samples at the optimal quenching rate, room-temperature coercive field Hc decreases almost linearly from 3.0 kOe for x=0 to 1.3 kOe for x=16. The maximum energy product (BH)max increases at first with increasing Fe concentration x, and goes through a maximum value of 4.2 MGOe at about x=5, then decreases with x.
Magnetically induced texturing during the sintering of strontium hexaferrite (abstract)
Authors: Wallace J. B. , King H. W. , Payzant E. A.
Published: July 2002

The hexaferrite SrO⋅6Fe2O3 exhibits pronounced ferrimagnetic anisotropy at room temperature, with the direction of easy magnetization lying parallel to the c axis of its hexagonal crystal structure.1–3 This magnetic anisotropy is used to produce highly aligned permanent magnets, by the application of a magnetic field during processing at room temperature. Since this material exhibits paramagnetic anisotropy at temperatures above 470 °C, it is possible that preferred orientation textures can be produced when samples of various shapes are sintered in a magnetic field4 at temperatures between 1150 and 1250 °C. The crystal structure, texture and microstructure of samples of strontium hexaferrite prepared in this manner have been determined by x-ray diffractometry and scanning electron microscopy. The significance of the observed textures is evaluated in terms of the anisotropy of the room temperature ferrimagnetic properties.
Remagnetization processes of ultrathin magnetic films with ‘‘islands’’ structure
Authors: Lyakhimets S. , Maziewski A. , Stefanowicz E. , Tarasenko V. V. , Ferré J. , Grolier V. , Renard D.
Published: July 2002

Magnetization delay recently observed in ultrathin ferromagnetic films has been discussed using the Fatuzzo theory assuming homogeneous magnet. However, the islands structure of ultrathin films is observed for small sample thicknesses. The ‘‘islands’’ model of magnet structure is proposed in the present work for the delay description. It is assumed that the sample is broken at magnetic clusters created by magnetic islands connected by magnetic ‘‘bridges’’ and remagnetization of each cluster undergoes independently. Function describing sample remagnetization is obtained as a sum Ψ(t)=pΨ∞(t)+(1−p)<Ψ(t)≳, where p is the concentration of infinite clusters; Ψ∞(t) is the function from the Fatuzzo theory, and <Ψ(t)≳ is the remagnetization function averaged for a different number of islands in finite clusters. The presented model could be used for analysis of magnetization processes in other magnets consisting of magnetically interacting ‘‘islands.’’
Application of the Bean critical-state model for superconductors to demagnetizing interactions
Authors: Moloni Katerina , Dahlberg E. Dan
Published: July 2002

In ferromagnetic systems, plots of the isothermal remanent magnetization Mr(H) versus the demagnetization remanence Md(H) have been interpreted as indicators of interactions. Although they may qualitatively indicate interactions, they are difficult to quantify. As a first step to quantify these plots the Bean model developed for superconductors is used. This model is shown to qualitatively describe the Md(H) vs Mr(H) plots for a ferromagnetic film where large demagnetization fields are present.
Physical interpretation of the hysteresis parameters in the theory of hysteresis (abstract)
Authors: Jiles D. C.
Published: July 2002

One of the most important remaining issues in the theory of hysteresis is a complete description of the physical meaning of the parameters that define the model equations.1 In common with the Stoner–Wohlfarth theory of rotational processes, the theory of hysteresis provides one of the few theories of hysteresis based on underlying physical mechanisms, rather than curve fitting models. In this paper, it is shown that the parameter a, which governs the orientation of the anhysteretic curve, is related to the density of domains and the absolute temperature a=kBT/μ0〈m〉, where 〈m〉 is the magnet moment of the average domain in the material, measured in A m2. In fact, the magnetic material can be treated thermodynamically as an assembly of pseudodomains, each with identical magnetic moment 〈m〉, and each interacting with all the other domains via the coupling coefficient α, leading to a mean coupling field of αM. The pinning coefficient k is simply a measure of the energy dissipation caused by movement of domain walls. The dissipation energy is proportional to the change in magnetization, dE=μ0kdM. Finally, the reversible component of magnetization is due principally to domain wall bending, and the bending coefficient c is related to the domain wall surface energy γ, the average domain magnetization 〈m〉, and the spacing between pinning sites l, according to the equation c=(〈m〉pl4/4γ)⋅Fmax, where Fmax is the maximum force exerted on the domain wall by a typical pinning site. This means that the amount of domain wall bending increases with the strength of pinning sites (Fmax) and decreases in inverse proportion to the domain wall surface energy. In conclusion therefore it is possible to give an exact physical meaning for all of the parameters used in the theory of hysteresis.
Neutron measurements of the vortex lattice in YBa2Cu3O7 (invited)
Authors: Mook H. A. , Yethiraj M. , Wignall G. D. , Forgan E. M. , Lee S. L. , Cubitt R. , Paul D. McK. , Armstrong T.
Published: July 2002

Neutron diffraction has been used to measure the vortex lattice scattering for YBa2Cu3O7. A square pattern is found when the field is applied along the c axis, while a triangular pattern is found when the field is applied well away from the c axis. High-resolution measurements for the square pattern show that the vortex lattice has long-range orientational order but only short-range positional order. The temperature dependence of the penetration depth is not that expected for a superconductor with a conventional s-wave BCS-type gap. Preliminary measurements for temperatures near the irreversibility line are consistent with the occurrence of melting of the vortex lattice or glass phase.
Indirect multipolar interactions in rare-earth metals and alloys (abstract)
Authors: Fazleev N. G. , Fry J. L.
Published: July 2002

The presence of large quadrupolar interactions was observed in some rare-earth conducting systems such as DySb, TmCd, TmZn, DyZn.1 In this work, we present the results of an extensive ab initio calculation of the indirect pair interactions between rare-earth ions in transition metals arising from the polarization of the electric-multipole distribution of the conduction electrons. The effective Hamiltonian of the indirect quadrupolar pair interactions is constructed self-consistently, taking into consideration antishielding and band-structure effects in the system of conduction electrons, as well as the crystal field splitting of the rare-earth ion. Slater–Koster fits to first principles energy bands are employed to accurately account for the band-structure effects. The peculiarities of each intraband or interband contribution to the Fourier transforms of the indirect couplings as well as the role played by each type of the d electrons in the conduction band are investigated. The experimental data are discussed.2
Mössbauer studies on Fe–W alloys synthesized by mechanical alloying (abstract)
Authors: Aning Alexander , Oliver Frederick W. , Courtney Thomas H. , May Leopold
Published: July 2002

Mechanical alloying in Fe–W alloys has been studied using Mössbauer, and magnetic susceptibility measurements. Mössbauer spectra show that during initial milling a six line pattern characteristic of magnetic ordering is present and with continued milling the spectrum transforms into a broad singlet, which is characteristic of nonmagnetic material. Experimental data show that after 7 h of ball milling, the iron component homogenizes and becomes amorphous. The Mössbauer results are qualitatively consistent with earlier Mössbauer reports on Fe–V powder,1,2 and more recent measurements on Fe–W using other characterization methods.3 Changes in the Mössbauer results agreed with the associated magnetic susceptibility measurements and there was a significant decrease in the magnetic susceptibility for milling times between 2 and 25 h. A discussion of the experimental measurements will be reported and compared with other experimental investigations on mechanical alloys.
Theory of magnetic excitations in thin-film ferromagnetic semiconductors (abstract)
Authors: Paczek I. D. , Cottam M. G.
Published: July 2002

This work is concerned with ordered magnetic semiconductors described by the s-f (or s-d) interaction model.1 In this case the localized spins (f or d) are described by an exchange Hamiltonian and the itinerant electrons (s) by a hopping Hamiltonian, and there is a contact interaction that provides the coupling between the two types of spins. In a ‘‘bulk’’ (i.e., infinitely extended) ferromagnetic sample it is known2 that in addition to the usual ‘‘acoustic’’ spin-wave branch of magnetic excitations, there is a higher-frequency (or ‘‘optical’’) spin-wave branch and the Stoner-like continuum. Here we present a Green-function analysis to study the bulk and surface spin-wave excitations in a ferromagnetic thin film, by employing the above model and allowing for the variation of the parameters at the film surfaces. The method is a generalization of recent calculations for a semi-infinite ferromagnetic semiconductor,3 except in the present thin-film case we show that there may be additional surface spin-wave branches and the bulk waves become quantized (‘‘standing’’ bulk spin waves), depending on the surface parameters. Results are deduced for both narrow-band and wide-band ferromagnetic semiconductors.
Initialization method for triple-layer exchanged coupled direct overwrite MO disk (abstract)
Authors: Hatwar T. K. , Genova D. J. , Palumbo A. C.
Published: July 2002

Increasing efforts are directed at the development of direct overwrite (DOW) capability for achieving higher data transfer rate in MO media. DOW by light intensity modulation on a triple-layer medium has shown great promise. The three layers consist of memory, reference, and intermediate layers that are weakly coupled to each other. This scheme uses an auxiliary magnet to initialize the reference layer in one direction in addition to the bias magnet. DOW is between high and low power levels. High power aligns the magnetization of the coupled layers in one direction, and low power aligns the magnetization in the opposite direction. These high (Ph) and low (Pl) powers are generally widely separated. Since the focused writing beam has a Gaussian profile, when the center of the spot does the high power writing, the ‘‘skirt’’ is actually doing the low power writing. As a result, if the background is initialized in the direction of the high power written mark, a chain-like domain pattern is observed. This leads to high writing noise. We found that such writing noise can be eliminated by initializing the background in the direction of the low power written marks. We will discuss the spin structure in exchanged coupled triple-layer films and the DOW characteristics of the disk with the two different initialization methods.