bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of ion-implantation damage on two-dimensional boron diffusion in silicon
Authors: Marchiando J. F. , Albers John
Published: July 2002

Model two-dimensional distributions of implanted boron and implantation-induced displacement damage near a mask edge are used to calculate the two-dimensional redistribution of boron resulting from a typical short-time anneal. The damage is removed during annealing by releasing vacancies which enhance the diffusion of boron. The effect is that boron preferentially redistributes further into the bulk. Such considerations become increasingly important as metal-oxide-semiconductor field-effect transistors become smaller.
Neutral and ionized states of group III acceptors in silicon
Authors: Cerofolini G. F. , Bez R.
Published: July 2002

The deep dopant description of group III acceptors in silicon explains in a simple way their chemical shifts as well as new experimental evidence, such as acceptor neutralization by atomic hydrogen or the ‘‘supershallow’’ levels observed in Si : Ga, Si : In, and Ge : Ga. In the deep dopant description, thermal- and optical-ionization processes are very different, and in turn differ from the neutralization process.
Diffusion of magnetic fields into conductors of nonuniform resistivity
Authors: Sprott J. C.
Published: July 2002

Solutions are obtained for the spatial variation of electrical resistivity of cylindrical and rectangular conductors such that the magnetic field external to the conductor maintains a constant spatial variation as the magnetic field diffuses into the conductor. Practical implementations of the ideal solution are described.
Diffraction efficiency of the gratings photoinduced in KCl:Li F
A center crystals
Authors: May Marie , Hong J. P. , Debrus Solange , Rzepka Edouard
Published: July 2002

We have studied the diffraction efficiency of a grating photoinduced by two perpendicular light vibrations in FA KCl:Li crystals at liquid-nitrogen temperature. We calculate the concentrations of centers parallel to each crystallographic axis after such an illumination. From these expressions, we derive the complex relative dielectric constants of the crystal. Finally, using the coupled-wave theory, we obtain a theoretical expression giving the diffraction efficiency. This expression is the sum of two terms: a term characterizing the amplitude contribution of the grating and a term characterizing the phase contribution of the grating. We show that for some wavelength of the visible spectrum, the diffraction efficiency of such a grating may be high enough in spite of the strong absorption of the crystal.
Effects of laser-driven shocks on silicon single crystals
Authors: Webb A. W. , Skelton E. F. , Nagel D. J. , Qadri S. B.
Published: July 2002

Damage of single-crystal Si induced by 25-ns pulses from a ruby laser (694 nm) has been studied after retrieval of the samples. Macroscopic evaluation was made using optical microscopy and measurement of the surface profiles. Microscopic study techniques included Laue and topographic x-ray methods as well as x-ray rocking curves. Cleavage affected both spallation and front surface damage. Some surface fracturing takes place after the environment has cooled below the melting point of Si, while other instances seem to be controlled by the shock geometry rather than cleavage planes. The impact zone remains single crystal with narrowly oriented mosaic structure noted occasionally. Material around the impact site is polycrystalline, evidently redeposited from the plasma.
Electron trapping in thin gate insulators prepared using a two-step silicon oxidation procedure
Authors: Jackson Daniel B. , Bolkhovsky Vladimir , Gildenblat Gennady Sh.
Published: July 2002

A two-step process for oxidation of silicon results in an improvement in thin silicon dioxide breakdown voltage distributions. This conclusion, previously demonstrated for approximately 8-nm-thick oxides, is shown to be valid for thicker oxides as well. However, no information was previously available concerning the trapping characteristics of gate insulators formed using the two-step oxidation process. In this work, we used the substrate hot electron effect to investigate the trapping characteristics of new insulators. Based on the degradation rate of both threshold voltage and linear transconductance of metal-oxide-semiconductor transistors, we conclude that the two-step oxidation process reduces the rate of substrate hot carrier induced degradation, in addition to improving the gate insulator integrity. We also observed a strong correlation between the degradation in linear transconductance and threshold voltage. This correlation is explained by the generation of, and trapping at, interface states and bulk oxide traps. Under our experimental conditions, the interface state density increases sublinearly with the number of electrons injected into the gate insulator. Investigation of the trapping kinetics indicates the presence of two trap species, only one of which influences the degradation in linear transconductance.
Raman determination of the composition in semiconductor ternary solid solutions
Authors: Saint-Cricq N. , Landa G. , Renucci J. B. , Hardy I. , Muñoz-Yague A.
Published: July 2002

The use of Raman spectrometry for the precise determination of the mole fraction in semiconductor solid solutions is presented. It is shown that if the frequency difference between the modes related to the two binaries involved is used, the scattering of the results due to various experimental conditions (temperature, spectrometer calibration, ...) is avoided. In addition, the method is rapid, nondestructive, reliable, and allows to probe the composition at different depths into the layer.
Field-enhancement calculations for a field-distortion triggered spark gap
Authors: Pashaie B. , Schaefer G. , Schoenbach K. H. , Williams P. F.
Published: July 2002

We present the results of numerical field calculation which supplement a recent article in which we described a new design concept for field-distortion triggered spark gaps. The calculations verify the shielding and field enhancement assumptions made in the article, and they provide insight into the interaction of the design tradeoffs associated with simultaneously maximizing the holdoff voltage and the triggering capability of the gap.
A computational study of laser-supported detonation waves propagating up an oblique incident beam
Authors: Bohn C. L. , Crawford M. L.
Published: July 2002

We conducted a series of numerical experiments to study the propagation of laser-supported detonation waves (LSDWs) in the case that a CO2 laser beam strikes an aluminum surface obliquely in air. A reflected shock formed at the aluminum surface was more prominent at higher angles of incidence θ of the beam, but otherwise the hydrodynamics of the plasma and the LSDW were insensitive to θ. Furthermore, the total impulse delivered to the aluminum varied approximately as 1/cos θ, a result that can be modeled with elementary blast-wave theory.
A multiple scattering theory for current-access magnetic bubble devices
Authors: Keister B. D. , Smith R. L.
Published: July 2002

The problem of currents and magnetic fields arising from a conducting sheet perforated with a distribution of holes for current-access magnetic bubble memories is investigated using a multiple-scattering formalism. The case of two circular holes is examined in detail. The results suggest that currents and fields for more complicated arrays of noncircular holes can be calculated reliably by a superposition of isolated hole solutions, ignoring the presence of all but extremely close neighboring holes.
A phenomenological model of the red luminescence kinetics in ZnTe:O
Authors: Hjalmarson Harold P. , Norris C. B.
Published: July 2002

We previously described an efficient red luminescence in ZnTe:O which dominates the emission spectrum from liquid nitrogen to room temperatures; this luminescence has been attributed to recombination at isoelectronic O centers. Frequency-domain luminescence measurements on this band have revealed complex kinetics corresponding to fast and slow decay processes. In this paper, these kinetics are compared with the predictions of a two-step electron capture model in which recombination occurs by electron capture at the O center followed by hole capture. Although the slow decay component of the luminescence is consistent with the electron capture model, the fast transient is shown to be in qualitative disagreement with that model. It is argued that more sophisticated versions of the basic two-step capture model will not fit the data. Parallel processes in which two mechanisms contribute to the luminescence are proposed to explain the data. In particular, it is proposed that direct capture of free excitons by the O impurities together with two-step electron capture may explain the data.
Temperature dependence of hydroxyl formation in the reaction of hydrogen with silica glass
Authors: Wiesenfeld J. M. , Stone J. , Marcuse D. , Burrus C. A. , Yang S.
Published: July 2002

The formation of hydroxyl due to reaction of a silica glass made by the modified chemical vapor deposition process with hydrogen has been studied for temperatures between 200 and 900 °C. The glass is treated under 1 atm of hydrogen, which diffuses into and reacts with the glass. For treatment temperatures between 900 and 500 °C, spatial hydroxyl concentration profiles are measured. For treatment at 400 °C and below, only equilibrium OH concentrations are measured. Three temperature regimes are identified for the reaction: T>700 °C, 700 °C>T>400 °C, and T<400 °C. A simple model combining H2 diffusion with chemical reaction explains the profile data for temperatures above 500 °C. The model assumes a finite number of preexisting reactive sites in the glass, which does not depend on treatment temperature. Assuming the same net reaction over the entire temperature range, enthalpies and entropies of reaction are derived from the data. The reaction at 800 °C of H2 with the glass Suprasil W has also been studied. For this glass the reaction is extremely rapid compared to H2 diffusion, and the kinetics are described by a tarnishing model. These results demonstrate that OH formation in silica glass due to reaction with H2 depends on preexisting defects in the glass, and therefore depends strongly on the nature and thermal history of the glass.
Enhanced electron-beam-induced current contrast of grain boundaries in silicon-on-insulator films
Authors: Kuper F. G. , De Hosson J. Th. M. , Verwey J. F.
Published: July 2002

The direct electron-beam-induced current (EBIC) observation of electrical properties of grain boundaries in silicon-on-insulator (SOI) structures has always been hampered by the insulated structure to be measured. In this communication a new structure is proposed with which EBIC images of grain boundaries in as-grown SOI layers can be obtained. Implantation of fluorine in the layer causes an enhanced contrast of these boundaries.
Native defect related inhomogeneity in characteristics of GaAs field-effect transistors fabricated on annealed dislocation-free substrates
Authors: Inada Tomoki , Fujii Takashi , Fukuda Tsuguo
Published: July 2002

The EL2 distribution showed a clear correlation to both the resistivity and the characteristics of field-effect transistors. It was observed that the nonuniformity of the characteristics of field-effect transistors was not improved by annealing, though those of both EL2 and the resistivity were improved by annealing. It is probable that the nonuniformity is related to the grown-in inhomogeneity in the distribution of native defects other than EL2. The importance of minimizing such an inhomogeneity in the growth process has been confirmed.
Electrical properties of ion-implanted polyacetylene films
Authors: Koshida Nobuyoshi , Suzuki Yoshiyuki
Published: July 2002

Ion-implantation studies of (CH)x films were carried out with ∼10-keV sodium ions. The temperature dependence of the sheet resistance of the implanted layer exhibited a thermal-activation-type behavior. Its activation energy decreased with increasing the ion dose. A long-term observation of the capacitance-voltage characteristics of an implanted p-n junction showed that a step junction was formed long after implantation as a result of the competition between defects annealing and dopants diffusion. These results ensure that low-energy ion implantation is a useful process for the n-type doping of (CH)x.
Hot-hole injection probabilities into the insulator of metal-insulator-silicon devices
Authors: Hellouin Y. , Chehade F. , Garrigues M.
Published: July 2002

The probability of hot-hole injection has been measured both on metal nitride-oxide silicon (MNOS) and metal-oxide-semiconductor (MOS) structures in the case where the silicon electric field is one dimensional and normal to the interface. The experiment uses the effect of optically induced hot carrier injection as proposed by Ning et al. [J. Appl. Phys. 48, 286 (1977)]. In the case of MNOS structures, the hot-hole injection currents can be readily measured because the Si-Si3N4 interface barrier is lower than the Si-SiO2 interface barrier. Measurements on MOS structures were carried out using heavily doped silicon. The measurements have been interpreted using the lucky carrier model with some modifications: the hot-hole mean-free path has been found equal to 41±5 Å in the case of MOS structures. Taking into account the accuracy of the measurements, this value is compatible with the value derived in the case of MNOS structures and also with the value derived from ionization measurements.
Space-charge conduction and relaxation in dielectric films
Authors: Henisch H. K. , Manifacier J.-C.
Published: July 2002

The single-carrier transport equations which apply to conduction in a semi-insulator, with and without traps, are solved numerically, in the static case as well as during subsequent relaxation, with and without light, for low and high fields. Diffusion is taken into account, and the significance of the boundary conditions is illustrated. The results imply, inter alia, a ‘‘reverse reciprocity failure.’’
A potential fall produced by a space-charge dipole layer moving in an oxygen glow discharge
Authors: Nobata Kanehiro , Kakishima Tokuichi
Published: July 2002

A potential fall created by a space-charge dipole layer that moves as a solitary wave with a velocity close to that of an electron in the positive column at higher pressure in oxygen is shown. Sometimes only one potential fall exists between electrodes. The number of the potential fall changes with discharge current, by which the hysteresis phenomenon is found. Since the width of a potential fall is much larger than the electron mean-free path, both ionization and attachment play an important role in the potential fall for the formation of a dipole layer. The shape of the small current change when a dipole layer arrives at an anode is examined, suggesting what is existent in a dipole layer. The nature of the self-excitation of a dipole layer in the positive column cannot be found. The reason why a dipole layer appears and how it is maintained in the positive column of the oxygen glow discharge are explained.
Deposition of new piezoelectric Ta2O5 thin films and their surface acoustic-wave properties
Authors: Nakagawa Yasuhiko , Gomi Yasuo , Okada Takashi
Published: July 2002

A new technique for the deposition of the crystallized Ta2O5 thin films is described. Crystallized Ta2O5 thin films have been deposited on fused quartz substrates by reactive dc-diode sputtering. Crystalline structure and piezoelectric properties of the Ta2O5 thin film were investigated. Surface acoustic-wave properties, including a phase velocity, coupling coefficient, temperature coefficient of delay, and propagation loss, were measured.
Characteristics of a Nd-doped yttrium-aluminum-perovskite picosecond laser
Authors: Portella M. T. , Montelmacher P. , Bourdon A. , Evesque P. , Duran J. , Boltz J. C.
Published: July 2002

We report on the temporal characteristics of a Q-switched and mode-locked Nd-doped yttrium-aluminum-perovskite laser. The emission at the 1.0795-μm line shows up a 16-ps coherence time and an overall 200-ps pulse duration. This last one can be reduced to 70 ps by adjusting the laser cavity length to an accuracy better than 1 μm.
Annealing effect for heavily Sn-implanted GaAs
Authors: Shim Tae Earn , Itoh Tadatsugu , Yamamoto Yasuhiro
Published: July 2002

Rutherford backscattering spectrometry, transmission electron micrography, and the Hall measurement have been used to investigate the lattice site location, residual defects, and activation behavior of Sn-implanted GaAs. Undoped GaAs (100) wafers were implanted with 150-keV Sn+ ions to doses of 5×1014–3×1015/cm2 at room temperature and annealed at 850 °C for 15 min with a Si film cap. Transmission electron micrographs for annealed samples showed that the residual defects were dislocations. The precipitation of Sn was observed in 1×1015 and 3×1015/cm2 implanted samples. The electrical activation efficiency has been measured to be 1.1%–2.6% by Hall measurement, and the peak carrier concentrations for all the annealed samples were 1×1018/cm3. The channeling Rutherford backscattering showed that 35%–88% of implanted Sn atoms were located in the substitutional lattice sites. It was found that only about 3% of substitutional Sn atoms in GaAs were activated as donors.
Fe-doped semi-insulating InP grown by chloride vapor-phase epitaxy
Authors: Tanaka K. , Nakai K. , Aoki O. , Sugawara M. , Wakao K. , Yamakoshi S.
Published: July 2002

Fe-doped semi-insulating (SI) InP layers have been grown using chloride vapor-phase epitaxy for the first time. Fe-doping was carried out by introducing FeCl2 to the growth region, bypassing the source region. The FeCl2 was formed by etching a pure metallic Fe source by HCl vapor. The resistivity of the SI-InP epitaxial layers was evaluated by measuring current-voltage characteristics, and a high value of 4×108 Ω cm was obtained. The semi-insulating current blocking was maintained up to an applied voltage of nearly 30 V, even at 110 °C, with a layer 4.3 μm thick.
Dynamic Monte carlo simulation of depinning of domain walls
Authors: Mon K. K. , Binder K. , Landau D. P.
Published: July 2002

We present preliminary results of a Monte Carlo study of the relaxation for a ferromagnetic, single spin-flip Ising model of surface-field-induced depinning transitions of domain walls. The relaxation of the first layer is reported for L×L×40 lattices, with L from 8 to 20, and interpreted in terms of the diffusion of the wall.
Anomalous temperature dependence of the effective susceptibility exponent in amorphous Fe-Ni-Zr alloys (abstract)
Authors: Puźniak R. , Rao K. V.
Published: July 2002

It is well known that the effective exponent γ(T) for the paramagnetic susceptibility in amorphous ferromagnets exhibits an unusual temperature dependence over a wide range. In sharp contrast to the monotonic behavior observed for ‘‘pure’’ magnetic systems, with increasing temperatures γ(T) for amorphous ferromagnetic materials increases from the critical Heisenberg value of 1.38 near TC to much larger values (≥2) and after a maximum eventually approaches the Curie-Weiss behavior. Such a crossover behavior in χ(T) has been explained as being due to a noncritical interplay between the magnetic correlations and the spatial fluctuations of the exchange interactions. With this point of view a recent Monte Carlo simulation1 of the phase transition in random ferromagnets predicts that site disorder has a much stronger influence on χ(T) than bond disorder. In order to study the consequences of site, and bond disorder and also the possible role of competing exchange interactions on γ(T) behavior we have measured the low-field ac and dc susceptibilities for melt-spun amorphous Fe-rich (Fe-Ni)90Zr10 alloys over an extended range of temperature. In these ‘‘ferroglasses’’ substitution of Fe with Ni is found to suppress the low-temperature ‘‘spin-glass phase’’ completely for Ni conc. above 8 at. %, while at the same time increasing TC. Thus Ni substitution in these alloys results in a material where γ(T) behavior exhibits progressive change from a nonmonotonic to conventional behavior. We find that the dynamics of correlated spins and its sensitivity to local inhomogeneities in an amorphous material can thus be well resolved near the percolation threshold for the loss of long-range ferromagnetic order.
Magnetic anisotropy in the UxTh1−xZn8.5 system
Authors: Willis J. O. , Fisk Z. , Aikin R. M. , McElfresh M. W. , Thompson J. D. , Zirngiebl E. , O’Rourke J. A. , Smith J. L.
Published: July 2002

We have investigated the source of the anisotropic susceptibility of UZn8.5 by preparing single crystals of UxTh1–xZn8.5 for small x. Preliminary indications are that anisotropic exchange, rather than crystal field effects, are responsible for the anisotropy, but possible impurity contributions to the (anisotropic) susceptibility of the ThZn8.5 do not permit a stronger statement. Further measurements for small x show that both the electronic specific heat and the susceptibility at low temperature are strongly enhanced, and that Kondo-type resistivity minima are observed. The enhancements are somewhat reduced in the concentrated system UZn8.5.
Voltage dependence of dc resistance in polycrystalline ferrimagnetic materials
Authors: Kunar Bijoy K. , Singh P. K. , Kishan Pran
Published: July 2002

The voltage dependence of dc resistance of polycrystalline GdtY3−tFe5O12 (t=1.0, 1.1, 1.6, and 2.2) is experimentally studied at different temperatures. The data is explained on the basis of Krausse’s theory. It is found that gadolinium substitution in YIG does not affect the grain-boundary potential barrier height (φ0). The temperature, however, affects φ0. The parameter z, in Krausse’s model, which is found to be temperature independent, increases with the increase in the gadolinium substitution in YIG.
Anisotropic magnetoresistance of Co-Fe thin films
Authors: Freitas P. P. , Berger L. , Silvain J. F.
Published: July 2002

The ferromagnetic resistance anisotropy Δρ/ρ0=(ρ∥−ρ⊥)/ ρ0 of Co91Fe09 films with thickness t between 5 and 113 nm has been measured at 4.2 and 295 K. Here, ρ∥ and ρ⊥ are the resistivities when the magnetization is parallel and perpendicular to the current, and ρ0 is the zero-field resistivity. Δρ/ρ0 is equal to 2.7% for t>40 nm at 4.2 K, but decreases fast for thinner films. This decrease is associated with an increase of surface scattering and grain-boundary scattering. We plot Δρ/ρ0 vs ρB/ ρ0 where ρB is the resistivity of a bulk sample. This is the appropriate version for thin films of the ‘‘Parker plot,’’ based on Matthiessen’s rule. Our data form a straight line on this plot, in accordance with theory. Films of thickness ≂80 nm have been annealed at 300 °C, causing a reduction of lattice defects and an increase of Δρ/ρ0. The Parker plot shows that different scattering centers are important in annealed and unannealed samples. We also measured the compositional dependence of Δρ/ρ0 in thick CoxFe100−x films.
Coherent-state Hall effect in the heavy fermions CeCu6 and U2PtC2 (abstract)
Authors: Penney T. , Milliken F. P. , Holtzberg F. , Fisk Z. , Meisner G. P.
Published: July 2002

The Hall effect is found to set the scale for coherence in the normal state of CeCu6 and U2PtC2. CeCu6 is a nonmagnetic, nonsuperconducting heavy fermion system.1–4 Its resistivity at high temperature is like that of a collection of incoherent Kondo scatterers. At low temperature the resistivity smoothly decreases to a very small value, indicating that scattering has become coherent. The Hall effect has two strong extrema in its temperature dependence which define a high-temperature incoherent scattering region, a transition region, and a low temperature coherent region. Although U2PtC2 is superconducting below 1.5 K,5 the Hall results in the normal state show two extrema similar to those of CeCu6. However, these features are scaled to higher temperatures, consistent with the smaller low-temperature electronic specific heat and higher Fermi temperature.
Scanning electron microscopy with spin polarized electrons (invited) (abstract)
Authors: Unguris J. , Hembree G. G. , Celotta R. J. , Pierce D. T.
Published: July 2002

The recent joining of scanning electron microscopy and electron spin polarization analysis has greatly improved the ability to study magnetic microstructure.1,2 By measuring the spin polarization of secondary electrons, scanning electron microscopy with polarization analysis (SEMPA) can directly measure the magnitude and direction of the magnetization and direction of the magnetization in the region probed by the incident electron beam. This region is defined by the diameter of the incident electron beam (∼10 nm) and the escape depth of the secondaries (∼5 nm). In addition to the purely magnetic image SEMPA also simultaneously and independently measures the usual topographic image, thereby making comparisons between magnetic and topographic structures easier. We have successfully used SEMPA to study magnetic structures in Fe crystals, permalloy films, CoNi recording media, and metglasses. Examples from this work will be given in order to demonstrate the unique capabilities of SEMPA.
Imaging domains in transmission electron microscopy (invited) (abstract)
Authors: Mishra R. K.
Published: July 2002

Magnetic domain walls and domains inside thin electron transparent specimens of ferromagnetic materials can be imaged using the Fresnel and Focault techniques in a transmission electron microscope. Combined with the diffraction, microstructural and microchemical capabilities of modern microscopes, Lorentz microscopy offers one of the most powerful tools to study structure-property relationships in magnetic materials. In addition, using this technique, it is possible to deduce the local magnetization distribution around inhomogeneities and complex Bloch and Néel walls. Lorentz images can be used to quantitatively measure domain wall thickness and estimate domain wall energy. With modified sample holders and pole pieces, one can study in situ domain wall motion and the interaction of domains with microstructural features such as second phases, grain boundaries, structural defects, etc. All these will be illustrated with examples of Lorentz images from soft and hard magnets with special emphasis on the Nd-Fe-B hard magnets. Finally, the limitations of the Lorentz imaging technique utilizing the deflected electron intensities will be outlined and a new technique which utilizes the phase changes in the electron beam as it passes through the material in a scanning transmission microscope will be reviewed.
Examination of epitaxial (111)Ag/(110)Fe heterostructures (abstract)
Authors: Stern G. P. , Walker J. C.
Published: July 2002

We have spent a number of years growing (110) Fe films on (111) Ag substrates. This is a well-known epitaxial system and there is little or no diffusion at the Ag/Fe interface. Furthermore, no alloys or intermetallic compounds form. The disadvantage is that (110) Fe grows on (111) Ag in three possible directions so that single crystal growth is difficult to achieve. Despite this we consider this system to be a good candidate for producing high quality metallic superlattices. Our earlier work1 indicates that the magnetic properties of such superlattices may depend critically on the relative thicknesses of Fe and Ag. Toward this end we have begun to make high quality structures consisting of two or more cycles of Fe and Ag of differing thicknesses. We report here on samples of Ag/Fe/Ag with the (110) Fe layer approximately 4–10 layers in thickness. Magnetic measurements on the samples are made by Mössbauer spectroscopy and SQUID magnetometry. Preliminary results indicate that for the thinnest Fe layers (∼4 layers) the magnetic hyperfine field and SQUID magnetometry measurement shows anomalous temperature dependence, indicating a noncontinuous island growth of the Fe. This island growth of the Fe can be prevented by cooling the Ag substrate to 100 K during the Fe deposition. Comparisons to samples in which two or more Fe layers are separated by very thin (∼5 layer) Ag films are made. In this case hyperfine fields are measured whose temperature dependence is different from that measured for single isolated Fe films. These results will be discussed in terms of conduction electron polarization transmitted through the Ag layers.
Confirmation by SQUID magnetometry of FMR measurements of magnetization in ultrathin Fe-B amorphous films
Authors: Zhang Lu , Rado George T.
Published: July 2002

Direct measurements were made by means of SQUID magnetometry of the magnetization of ultrathin Fe50B50 and Fe70B30 amorphous films at room temperature. The film thicknesses used included most of those investigated in the authors’ recent ferromagnetic resonance (FMR) determinations of the surface anisotropy Ks and the magnetization M of such films. The directly measured values of M confirm adequately the M values obtained by computer fitting of a theory to experimental FMR data. Thus, the present experiments offer substantial support for the reliability of the FMR method for measurements of Ks and M in ultrathin films.
Chaotic motion of domain walls in soft magnetic materials
Authors: Suhl H. , Zhang X. Y.
Published: July 2002

We have studied numerically one-dimensional rf driven motion of domain structures. The equation of motion solved has Landau–Lifshitz damping and includes all the basic phenomenological magnetic interactions: demagnetizing field, anisotropy field, and exchange field. We have found that for a large range of parameters, the spatial average of the magnetization is chaotic in time, and the spatial pattern at fixed time itself is likewise chaotic. The power spectrum of the chaotic time series has a 1/f shape. The phase boundary between chaotic and nonchaotic motion is described, and a limited analytical insight into this problem is discussed.
An anomalous magnetic effect in the Pt1Co1 order–disorder alloy system
Authors: Orehotsky J. , Orehotsky J. Larsen
Published: July 2002

The saturation magnetization (Ms) of an atomically disordered, quenched Pt1Co1 alloy was measured at 25 °C as a function of annealing time for various annealing temperatures between 418 and 513 °C. Previous results in the ordering temperature range of 615–719 °C indicate the existence of a rapid transient response that occurs before the initiation of ordering. The transient was found to cause a 5% decrease in the saturation magnetization of the disordered alloy. Measurements of the room temperature saturation magnetization for the annealing temperature range of 418–513 °C where the ordering kinetics are sluggish succeeded in isolating the transient, and showed that the transient occurs by a thermally activated process whose kinetics obeyed the time-dependent power law Ms=2.4t−n+38.9, where the power law coefficient (n) exhibited an Arrhenius temperature dependence characterized by an activation energy of 9 kcal/mol. These kinetic response characteristics were employed to determine the mechanism responsible for the transient behavior in terms of phase stability and nucleation and growth concepts.
Where are the iron atoms and iron moments in RFEmAl12−n? A Wigner-Seitz analysis
Authors: Melamud M. , Bennett L. H. , Watson R. E.
Published: July 2002

The ternary compounds RFenAl12−n (n=4,5,6; ThMn12 structure) form an extensive family of alloys having complicated magnetic structures, with the rare earths (R) and Fe ordering at different temperatures. This magnetic ordering has been inferred from magnetization, Mössbauer and neutron diffraction measurements. X-ray results are in disagreement with the magnetic measurements as to which sites are occuped by the Fe, and it is not clear at which of the sites iron has the largest magnetic moment. Recently, we have suggested that the occurrence of a substantial magnetic moment at an atomic site in certain magnetic systems can be related to the occurrence of −72° disclination lines connection atoms on this site. These disclinations are bond lines joining two near-neighbor atoms which have six nearest neighbors and can be recognized by a sixfold face appearing on the Wigner-Seitz polyhedra of the two atoms. The Wigner-Seitz construction and its use in the analysis of this and related problems is presented.
Ferromagnetic transition in Pd-Fe and Pd-Co alloys (abstract)
Authors: Pilipowicz A. , Claus H.
Published: July 2002

New low-field dc magnetization measurements on dilute Pd-Fe and Pd-Co samples between 0.2 and 1.0 at. % Fe(Co) are presented. It is demonstrated that defects produced during plastic deformation and surface inhomogeneities produced during strain relieve annealing (by either preferential Pd evaporation and/or surface segregation) have a dramatic effect on the low-field response of the samples. Plastic deformation increases the Curie temperature by as much as 20%. Strain relieve anneal produces a well-defined surface layer of the order of 0.02 mm thick with a Curie temperature slightly higher than that of the bulk. This surface layer couples via dipolar forces to the bulk of the sample significantly altering the low-field response of the latter. Both effects considerably ‘‘smear’’ the magnetic transition of the samples. This explains, for example, why the low field susceptibility of ferromagnetic Pd-Co alloys never reach the demagnetization limit.1 A systematic study of the two effects will be presented and new conclusions about the ferromagnetic properties of homogeneous Pd-Fe and Pd-Co will be drawn.
Magnetostatic wave ring resonator exhibiting a single resonance
Authors: Poston T. D. , Stancil D. D.
Published: July 2002

A magnetostatic surface wave ring resonator is described which employs a new transducer configuration for exciting a single resonant mode. The configuration consists of one three-element grating array and one three-element meander array. The predominant resonance is 10 dB above adjacent resonances and exhibits a loaded Q as high as 890 with 13 dB insertion loss at approximately 1.86 GHz.The device is tunable over the range of 1.5–2.1 GHz, although suppression of unwanted resonances is reduced near the edges of this range.
A design theory of a single stage YIG-tuned impedance transformer/filter
Authors: Tang Sing-Ye
Published: July 2002

A single-stage YIG-tuned impedance transformer/filter is the fundamental unit of YIG-tuned filters. In this paper a design theory of this unit has been developed, by which the values of the geometrical, electrical, and magnetic parameters determining its electric characteristics can be calculated. Some important inferences are given. Experiments have supported the design theory.
Flux growth and magnetic properties of hexagonal ferrite single crystal (abstract)
Authors: Zhao Chun , Wang Tianjin
Published: July 2002

Using a new tenary system flux Bi2O3-BaO-B2O3, the growth of hexagonal ferrite single-crystal BaM and ZnW has been investigated. The flux has a lower melting point and wider growth temperature range. The shape characteristic of the crystals grown has changed from thin platelets to columns. The substitution of diamagnetic ions in hexagonal ferrite has been studied. In order to discuss the origin of magnetic anisotropy in hexagonal ferrites BaM and ZnW, the magnetic anisotropy at each sublattice has been calculated by a well-known H. B. Callen and E. Callen anisotropy model which is given by K1(T)/K1(0) =I1+1/2[Zi(T)]/I1/2[Zi(T)] with Zi(T)=2KT∑nm=1N imSiSmJimσm(T). The magnetization σi(T) and the exchange parameters Jim in different sublattice has been fitted by a least-squares method to the experimental values of the saturation magnetization, according to the molecular field theory. The results show that the contributions of Fe3+ in different sublattices to magnetic anisotropy are different. The strong uniaxial magnetic anisotropy in hexagonal ferrites is attributed mainly to the contribution of ferric ions located in trigonal bipyramidal sublattices 2b BaM and 2b 2b in ZnW. The influence of diamagnetic ions Zn, In, Al substitution for Fe3+ to magnetic anisotropy can be explained by the calculated resultant.
Spin-wave resonance in single-crystal epitaxial iron films (abstract)
Authors: Vittoria C. , Jonker B. T. , Krebs J. J. , Prinz G. A.
Published: July 2002

We have made ferromagnetic resonance measurements on single-crystal films of iron on ZnSe/GaAs substrates using field and frequency swept techniques. For field swept measurements the magnetic field was applied normal to the film plane and the frequency was fixed at 9.50 Hz. We find that spin-wave resonance (SWR) modes are excited in addition to a localized surface mode.1 The SWR modes obey an n2 law, where n is the spin-wave order number and a value of A/M=1.28×10−9 Oe cm2 (where A is the exchange stiffness constant and M the magnetization) is deduced from the data. This value is in reasonable agreement with that obtained1 on iron films grown directly on GaAs substrate. The fact that higher-order spin-wave mode linewidths increase only slightly from the main line linewidth of 30 Oe implies that these films are of improved quality in comparison to previous films. For the frequency swept measurements2 the frequency was swept from 0.01 to 20 GHz continuously. Ferromagnetic resonance was measured in zero field at 14.8 GHz. The measured resonance frequency compares reasonably well with the calculated value of 14.2 GHz using only measured3 static field values of 4πM=20.9 kG, g=2.10, 2k1/M=560 Oe, and 2ku/M =460 Oe. The inclusion of ZnSe epilayer in between the iron film and GaAs substrate have improved the quality of the iron film as manifested in our FMR measurements. The linewidth of each spin-wave and main mode excitations are the narrowest values measured to date in iron films.
Electrical detection of end point in polishing process of thin-film heads (invited)
Authors: Kawakami K. , Suda M. , Aihara M. , Fukuoka H. , Hagiwara Y. , Takeshita K.
Published: July 2002

A novel method for detecting the polishing process end point was developed for thin-film heads to achieve a gap depth (throat height) of smaller than 1.5 μm. Special thin-film heads whose magnetic paths are closed at the front end of the gap films were used. As the throat height of these gap films are much the same as the maximum tolerable value of the gap depth, the end point can be detected by monitoring the opening of the magnetic paths of the thin-film head themselves. Electrical detection of the opening was studied, utilizing the bias current dependence of the head inductance. Both inductance values of the head, with and without the bias current, Lb and Lnb, change when the magnetic path opens. The Lnb and Lb values at 3-mA bias current are 250 and 95 nH for the head having a closed magnetic path, and 180 and 155 nH for an open one, respectively. The difference Lnb−Lb decreases to about 1/6 when the magnetic path is opened. An apparatus was developed to measure the amplitude of Lnb−Lb. It utilizes a Wheatstone bridge circuit, excited with a 10-MHz sinusoidal signal for measuring inductance, and a 0.2-Hz rectangular pulse train as a bias current, respectively. Experimental results indicate that polishing can be stopped within 0.6 μm of the front edge of the gap films.
The magnetic structure of Cu0.9Pd0.1MnSb (abstract)
Authors: Noor S. S. Abdul , Murasik A.
Published: July 2002

The CIb-type intermetallic Cu0.9Pd0.1Mn Sb has been investigated by neutron diffraction and inelastic scattering techniques. Below 42 K, both antiferromagnetic and ferromagnetic contributions were detectable in neutron diffractograms while pure ferromagnetism was detectable at up to 453 K. A canted spin structure was proposed to explain the coexistence of both components. However, no sudden enhancement in the ferromagnetic contribution was detected at around TN (42 K) when the assumed canted spins are supposed to flip into a purely ferromagnetic ensemble. An inelastic incoherent scattering measurement was performed in order to investigate exchange interaction by observing transitions due to Zeeman levels at 5 and 80 K. The discrepancy between experimentally observed magnetic parameters and those calculated using molecular field theory was explicit. Suggesting that the material is magnetically inhomogeneous and the coexistence of two magnetic phases might be appropriate for this compound. This may emphasize the importance of the role played by the electron concentration in deciding the magnetic behavior of the material as supported by the Ruderman–Kittel–Kasuya–Yoshida RKKY model.
Critical exponents for Ising spin glasses through high-temperature series analysis
Authors: Singh Rajiv R. P. , Chakravarty Sudip
Published: July 2002

We present estimates of the critical exponents ν and η for the three-dimensional ±J distribution Ising spin glass based on high-temperature series analysis. The method of star graph expansion is used to obtain the series for two different susceptibilities to order W17 (W=tanh2 J/kT). The series are analyzed through first-order inhomogeneous differential approximants. Assuming Tc =1.175, we find the exponents to be ν=1.3±0.2 and η=−0.25±0.2.
Time-domain model for noise from particulate recording media
Authors: Veeravalli V. V. , Katti R. R. , Kumar B. V. K. Vijaya , Kryder M. H.
Published: July 2002

A stochastic theory apprach is used to characterize the noise from particulate recording media, which has been established to be signal dependent and nonstationary. It is indicated that the media noise is completely characterized stochastically by determining its autocorrelation function. The inadequacy of power spectrum measurements, obtained from a spectrum analyzer, in determining the autocorrelation function of nonstationary noise is discussed. The nonstationary media noise is then modeled in the time domain in terms of two stationary stochastic processes, and one deterministic function of time. The consistency of this noise model with experimental observations of background noise and modulation noise is demonstrated. The deterministic function of time in this model is calculated from the signal, and the autocorrelation functions of the component stationary stochastic processes are determined from spectrum analyzer measurements. From these, the autocorrelation function of the nonstationary media noise is deduced. The advantages of this technique, as opposed to time-domain measurements, in deducing the autocorrelation function are discussed.
Magnetic and structural characterization of Dy-Y superlattices
Authors: Borchers J. , Sinha Shantanu , Salamon M. B. , Du R. , Flynn C. P. , Rhyne J. J. , Erwin R. W.
Published: July 2002

Single-crystal superlattices of dysprosium and yttrium with bilayer thickness ranging from 70 to 105 Å have been grown using molecular-beam epitaxy techniques. Detailed x-ray analysis of these samples shows them to be coherent structures with abrupt interfaces between the alternating layers. These superlattices differ magnetically from pure Dy with properties that show distinct dependence on the thickness of the intervening Y.
Magnetic tape recovery and rerecording of data (invited)
Authors: Kalthoff C. H. , Bradshaw R. L. , Bartkus E. A. , Finkelstein B. I.
Published: July 2002

Degraded magnetic tapes and data were recovered from damaged reels through a series of chemical, mechanical, and rerecording processes. This paper describes the procedures used on three reels recovered from the space shuttle Challenger after being immersed in the ocean for six weeks.
New universality classes in one-dimensional antiferromagnets
Authors: Affleck Ian
Published: July 2002

New universality classes in two-dimensional critical phenomena have recently been discovered using methods of quantum field theory and conformal invariance. These can equally well describe classical two-dimensional systems at their critical temperature or one-dimensional gapless quantum systems at (or near) zero temperature. (The two types of systems are related by the transfer matrix or Feynman path integral.) It is argued that isotropic one-dimensional antiferromagnets are realizations of these new universality classes. Exact predictions for the low temperature specific heat, susceptibility, correlation length, and other critical properties are made. These agree exactly with exactly solveable models and well with experimental results on CuCl2⋅2(NC5H5).
Soft magnetic materials—17 years after electron irradiation
Authors: Sery R. S.
Published: July 2002

During the period 1963–1966 about 175 flat ring samples of Supermalloy, Unimag, Mumetal, 65 Ni-Fe, and pure iron were irradiated with electrons. Energies and integrated fluxes varied from 0.5 to 2.0 MeV and (0.2–1.0)×1017 e/cm2, respectively. Some samples were irradiated in the Earth’s magnetic field and the rest were irradiated with applied circumferential fields of 0.22 Oe. Temperatures of irradiation varied from about 80 to 125 °C for most samples. In the course of time most of the original samples were lost, discarded, damaged, or annealed. In 1983 the remaining 55 were retested to see what changes in magnetic properties may have occurred. The properties and characteristics checked included Hc,Br, and the magnetization curves and hysteresis loops. The main findings with respect to changes in properties after about 17 years of storage are the following: (1) The properties measured showed, at most, slight changes. (2) The small changes that did occur in Hc were consistent increases of up to 20% for some samples.
Electronic magnetic relaxation in manganese ferrites (abstract)
Authors: Brabers V. A. M. , Scheerder A. A. A.
Published: July 2002

In soft magnetic ferrites, the dispersion of the dynamic magnetic susceptibility and the maxima in the loss factor are known to be caused by the electron hopping between Fe2+ and Fe3+ ions.1 However, in the manganese ferrite system MnxFe3−xO4, two distinct electronic relaxation phenomena are reported for the compositions x=0.8, the first with an activation energy of about 0.015 eV and the second with Ea =0.06 eV.2 The elementary processes of these two relaxations are not well established; inter- and intra-atomic electron transitions between the iron ions are claimed as an interpretation,2 whereas electron transitions between iron and/or manganese ions are another interpretation.3 In the present paper, we report a detailed investigation of the magnetic relaxation effects in the manganese ferrite system, in combination with electrical conductivity measurements. The obtained results are interpreted on the basis of electronic hopping between Fe2+ and Fe3+ ions only, taking into account the effect of ionic disorder on octahedral sites, which is also the cause of the Coulomb gap formation at the metal-semiconductor transition in pure Fe3O4.4
High-field torque magnetometry measurements on Y1.8Er0.2Fe14B (abstract)
Authors: Williams C. M. , Koon N. C. , Das B. N.
Published: July 2002

Y1.8Er0.2Fe14B is an interesting system in that the tendency of the Er ions to order in the basal plane is almost exactly canceled at low temperatures by the uniaxial anisotropy of the iron sublattice.1 We have performed torque magnetometry measurements in all three principal planes of a single crystal of this material at temperatures from 4 to 300 K in magnetic fields up to 60 kG, which is adequate to produce near saturation even in directions away from the principal axes, thus allowing us to determine the magnetocrystalline anisotropy free energy as a function of orientation and temperature. The free energy data were compared with calculations using the full set of crystal field parameters allowed by symmetry.
Magnetostrictive response of metallic glasses
Authors: Gibbs M. R. J. , Squire P. T. , Brugel D. , Hardy S. C. , Willson J.
Published: July 2002

The ultimate response of sensors employing the magnetostrictive properties of metallic glasses depends on efficient transfer of strain between the system under investigation and the transducer. In this paper the effect on magnetostriction of applying bonding agents is studied using a model system, which takes account of application to a fiber-optic magnetometer. Measurements are presented of the dc M-H, λ-H, and λ-M loops. Results for as-received and stress-relieved samples are compared, and are discussed in terms of the domain and spin geometry of the specimens. The implications for fiber-optic magnetometers are considered.