bluuebunny/crossref_metadata_2025 huggingface dataset:
The electrical characteristics of degenerate InP Schottky diodes with an interfacial layer
Authors: Hattori K. , Izumi Y.
Published: February 2003

Degenerate Au-n+-type InP Schottky diodes are fabricated using anodic oxidation, etching with aqueous HCl and annealing in a N2 atmosphere. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics are measured and discussed. High barrier heights qφB are obtained even in degenerate samples; for example, qφB =0.76 eV. The observed increase in qφB is caused by an interfacial layer between the metal and semiconductor. It is found that annealing in a N2 atmosphere prior to the evaporation of the Au contact is effective to increase the effective interfacial thickness δ/ε*i, and therefore, qφB. Here δ and ε*i are respectively the thickness and relative dielectric constant of the interfacial layer. The intercept on the voltage axis of the 1/C2 vs V plot is found to be considerably large compared with φB. This is also explained by the effect of the interfacial layer. The interface state density is estimated as 0.2–1×1013 eV−1 cm−2. The volume charge within the interfacial layer is discussed and found to be negative.
A simple model for plasma temperature in imploded hollow plasma liners
Authors: Kloc David A. , Roderick Norman F. , Hussey Thomas W.
Published: February 2003

Existing theory for the Rayleigh-Taylor instability in imploding hollow plasma liners has assumed a constant electrical resistivity during most of the implosion. While this is qualitatively justified by the competition between joule heating and field-diffusion-driven expansion of the plasma shell; one, nevertheless, expects the temperature and, therefore, electrical conductivity to rise during the implosion. A simple model for plasma temperature as a function of time, based on the neglect of radiative losses and using approximate fits to equation-of-state information, is presented here. The results are used to compute the minimum allowed wavelength, a parameter used to assess instability effects, and agreement with magnetohydrodynamic calculations to well within a factor of 2 is obtained.
Diffusion of substitutional impurities in silicon at short oxidation times: An insight into point defect kinetics
Authors: Antoniadis D. A. , Moskowitz I.
Published: February 2003

Oxidation-enhanced diffusion of phosphorus, arsenic, and boron and oxidation-reduced diffusion of antimony in silicon have been studied as a function of oxidation time. Data for the early phase of oxidation in dry oxygen from 5 to 60 min have been obtained. Oxidation-enhanced diffusivities show a steady decrease with decreasing oxidation rate for phosphorus, arsenic, and boron, with enhancements at long oxidation times in agreement with previously reported results. Antimony shows a reduction in diffusivity during oxidation. A model allowing calculation of diffusivity enhancement or reduction for all elements and oxidation times has been developed. The present data support the theory of a dual vacancy-interstitialcy diffusion mechanism for all the elements studied. The fraction of interstitialcy diffusion fI has been calculated, yielding fI=0.38 for phosphorus at 1000 °C, fI=0.30 for boron at 1000 °C, fI=0.35 for arsenic at 1090 °C, and fI=0.015 for antimony at 1100 °C. It has also been shown that the oxidation-induced supersaturation of self-interstitials is accompanied by an undersaturation of vacancies during oxidation. This undersaturation can be explained by a rate-limited bimolecular annihilation mechanism. This theory yields, for the first time, values for the vacancy-interstitial recombination-limited intrinsic vacancy lifetime in silicon under near-equilibrium conditions at high temperature; it also indicates the presence of an energy barrier to this recombination of the order of 1.4 eV.
Ferroelectricity and coherent phonon generation in piezoelectric composition-modulated structures
Authors: Wong H. K. , Wong G. K. , Ketterson J. B.
Published: February 2003

In this paper we suggest an approach to making new metastable ferroelectric materials and piezoelectric transducers which should be efficient in generating coherent phonons with wavelengths approaching interatomic distances. This involves the fabrication of composition-modulated (layered) structures consisting of piezoelectric components. The coherency strain accompanying short wavelength composition modulation leads to ferroelectricity; the periodic modulation of the piezoelectric parameters leads to an anomalously strong coupling to far infrared light when the composition wavelength is an odd half-multiple of the wavelength of a phonon at the driving frequency. Such transducers can open a new dimension in the study of phonons in dielectrics at low temperatures.
Dielectric studies of amorphous polymers at high pressures
Authors: Questad D. L. , Oskooie-Tabrizi M.
Published: February 2003

It is known that application of hydrostatic pressure causes an increase in Tg at low pressures; however, some question has arisen as to whether the increase will continue indefinitely. Two possibilities exists: (i) Tg may level off to a constant value at high pressures, or (ii) Tg may continue to increase at all pressures. The former is suggested by thermodynamic theories of the glass transition; the latter by free volume theories. In this study dielectric methods have been used to measure the pressure dependence of the α-transition temperature, Tα, for a number of amorphous polymers and to relate this to the pressured dependence of Tg. The results indicate that at low pressures dTα/dP may decrease with increasing pressure (i.e., Tα may appear to be levelling off), but at higher pressures (greater than ∼2 kbar) dTα/dP reaches a constant, non-zero value (i.e., Tα increases linearly with pressure). In addition, the high pressure limiting value of dTg/dP appears to be roughly proportional to the atmospheric pressure Tg of the polymer tested.
Polymer crystallization: Proper accounting of a wider class of paths to crystallization—variations on a theme of Point
Authors: DiMarzio E. A. , Guttman C. M.
Published: February 2003

Point has suggested that during the polymer crystallization process, individual stems form by zippering of monomer segments onto the substrate and that at any time during the zippering process the stem can fold over, thus initiating a new stem. We augment the treatment of Point analytically by allowing each of the subsequent stems to fold any stage in the zippering process rather than only during the forming of the first stem. The problem is isomorphic to the mathematical problem of the growth of a Cayley Tree with infinite branching! Although there is net growth, the rules of growth (crystallization) are such that branches of the tree can be resorbed. By use of a simple renormalization technique, formulae are obtained both for the steady state growth rate and for the lamellar thickness, which for special cases reduce to the Point results. Classical nucleation theory remains valid at low to moderate supercoolings.
Theoretical equation of state for simple liquids at high pressures
Authors: Jones Hermenzo D. , Gray Michael V.
Published: February 2003

A perturbation technique which is particulary well suited for high pressures is used to calculate thermodynamic properties for a simple liquid whose molecules interact via a Buckingham (exp-6) potential. There is good agreement between computations and experiments for moderate temperature isotherms for liquid nitrogen. A calculation of the shock Hugoniot of liquid nitrogen exhibits excellent agreement with experimental data.
Deuterium separation by ultraviolet laser dissociation of formaldehyde
Authors: Mannik L. , Brown S. K.
Published: February 2003

Irradiation of natural isotopic abundance formaldehyde with a narrow linewidth ultraviolet laser has yielded high deuterium enrichments (>600 at 5 Torr, 303 K) at five wavelengths in the range 340 to 355 nm. The temperature and pressure dependence have been measured for both the enrichment and the selectivity, the latter being determined from high resolution spectra of deuterated and natural formaldehyde. In general, for the conditions investigated (293–343 K; 2–26 Torr), both selectivity and enrichment are decreasing functions of temperature and pressure, but in certain cases the selectivity is independent of pressure over a small range. The highest enrichment (1110) was measured at 2 Torr, 293 K, 352.061 nm. The results can be explained in terms of hot bands as well as Doppler broadening and pressure broadening of formaldehyde absorption bands. For all five high enrichment wavelengths, the enrichment is larger than the selectivity at low pressure (<6 Torr), yet the two are equal at higher pressure. This implies that at low pressure the quenching of electronically excited HDCO by collisions with H2CO is a relatively inefficient process.
Application of Ampere’s force law to railgun accelerators
Authors: Graneau Peter
Published: February 2003

This paper examines the question of where in the railgun accelerator circuit is the seat of the recoil force. It is explained that conventional electromagnetic field theory and the older Ampere electrodynamics disagree on this point. The former places the recoil force in the remote gun breach while the latter claims it resides in the railheads close to the projectile. An experiment is described which tends to confirm the Ampere prediction. The second part of the paper deals with the force distribution along the projectile branch of the accelerator. Finite current-element analysis has been employed to show that both theories give approximately the same acceleration force distribution and that the total acceleration force furnished by them agrees well with an experimental check. However, according to the Ampere law, the projectile branch of the circuit should also be subject to strut compression and not only to transverse acceleration. This aspect of the Ampere electrodynamics still awaits experimental confirmation.
Radar resonance reflection from sets of plane dielectric layers
Authors: Jackins P. D. , Gaunaurd G. C.
Published: February 2003

The prediction of the Resonance Scattering Theory (RST) for the reflection coefficient from a set of two contiguous plane dielectric layers separating two semi-infinite dissimilar nonconducting media, is constructed and compared to the exact classical model solution. The comparison serves to: (a) show the excellence, accuracy, and simplicity of the RST prediction, and (b) to underline the usefulness of the RST to produce clear physical interpretations of generally complex phenomena. In addition, the analysis serves to provide a systematic method for detecting the presence of a dielectric layer under another one covering it (possibly the situation caused by an oil spill in ice-covered Arctic regions), by certain modulation effects present in the ‘‘response surface’’ of the returned echoes, which we describe in the text. This method not only serves to detect, but also to characterize/identify, the material composition of the low or hidden layer in the bilaminar configuration. The process disentangles which resonance feature present in the radar reflection coefficient is caused by which of the two interacting layers. This, therefore, solves the inverse scattering problem for the composition and thickness not only of the top visible (ice) layer, but also of the substance (oil) hidden under that upper layer, via the radar resonances of the reflected echoes.
Direct observation of picosecond light pulses from a pulse-current pumped semiconductor laser
Authors: Tsuchiya Y. , Miwa M. , Koishi M.
Published: February 2003

The direct observation of a picosecond substructure in the 70-ps light pulses emitted from a GaAlAs diode laser pumped by a pulse current is described.
Diffusion of Au into Sn thin films studied by the attenuated total reflection method
Authors: Chang C. , Callcott T. A. , Arakawa E. T.
Published: February 2003

The diffusion of Au into Sn thin films has been measured from 20 to 40 °C. Diffusion rates were determined using the method of attenuated total reflection which measures the absorption resonance in the reflection spectrum caused by plasmon excitation on the dielectric-metal interface. By observing the incident angle at which the reflection is a minimum, the thickness of the unreacted Au layer can be determined, and thus the thickness of the alloy phase in each stage can be calculated. The diffusion rate at 20 °C is found to be D=1.9×10−14 cm2 s−1, and the activation energy for the formation of AuSn is 22.6 kcal/mole.
Structure of vapor-deposited Ge films as a function of substrate temperature
Authors: Evangelisti F. , Garozzo M. , Conte G.
Published: February 2003

The structure of Ge films grown by thermal evaporation has been studied as a function of the deposition temperature Ts by X-ray diffraction, Raman scattering, and EXAFS (Extended X-ray Absorption Fine Structure) analysis. It is found that there is a temperature range where the material is microscopically heterogeneous and consists of crystallites embedded in an amorphous connective tissue. The dimension and the percentage of the ordered domains are determined, and the nature of the amorphous to polycrystalline transition is thoroughly investigated. The data support the hypothesis of the instability of the diamond structure for small crystallites.ufoff
Numerical analysis of transient photoconductivity in insulators
Authors: Sokel R. , Hughes R. C.
Published: February 2003

The nonlinear partial differential equations which describe transient photoconductivity in insulators are solved numerically. Trapping and recombination are included which allows photoconduction to be studied in the presence of large space charge. Use of methods for ‘‘stiff’’ differential equations insures stable time dependent solutions even for problems which have widely different time constants. The program is applied to a thin film (1000 Å) of silicon dioxide to illustrate the salient features of the numerical solutions and the capabilities of the program.
Effects of capacitance on noise rounded current-voltage curves of a Josephson tunnel junction
Authors: Yoshida K.
Published: February 2003

A theoretical study is made of the effects of a finite shunt capacitance of a Josephson tunnel junction on the noise rounding of its dc current-voltage (I-V) curves. A steady-state solution of the two-dimensional Fokker-Planck equation with a reasonable physical implication has been obtained with a trial function method. The solution leads to an analytical expression for dc I-V curves, which includes as limiting cases both the expression by Ambegaokar and Halperin in the zero-capacitance limit and that given by McCumber in the zero-noise limit. It is shown that the obtained dc I-V curves are in reasonable agreement with the results by computer simulation.
Silicon-wafer-surface damage revealed by surface photovoltage measurements
Authors: Goodman Alvin M.
Published: February 2003

Anomalous results of surface photovoltage (SPV) measurements on Si wafers are shown to be associated with a damaged region beneath the illuminated surface of the wafer being measured. The anomaly is a concave-upward curvature of the I0(α−1) plot with an r2 value, derived from linear regression analysis, less than the normally observed minimum value (∼0.98). Removal of the damaged region by an appropriate etching procedure allows subsequent SPV measurements whose results are substantially free of the previously observed anomaly. The qualitative character of the anomaly can be reproduced by a simple theoretical model in which only one effect of the damage is considered; this effect is a diminished quantum efficiency for hole-electron pair generation by photon absorption in the damaged region. The results suggest the use of SPV measurements as a test procedure for revealing the presence of surface damage in Si wafers.
A relativistic magnetron with a thermionic cathode
Authors: Ballard W. P. , Self S. A. , Crawford F. W.
Published: February 2003

A 500-kV, S-band magnetron has been designed and tested. An oxide cathode was used in an attempt to achieve 1 μs pulse lengths by using the pre-pulse space charge to shield the cathode from vacuum dc breakdown. The magnetron was designed according to conventional, nonrelativistic scaling laws and is unstrapped, utilizing a symmetric, axial output into a circular vacuum waveguide. Initially, focus electrodes were used to prevent axial electron losses but arcing between these and the anode limited the voltage below the π-mode oscillation threshold. Operation occurred in various space harmonics, as predicted by the relativistic Buneman-Hartree oscillation threshold equation. Removal of the focus electrodes allowed π-mode operation at voltages of ∼400 kV, powers of ∼20 MW, and pulse lengths of ∼35 ns. It is believed that high energy electrons strike the anode, ejecting ionized copper which neutralizes the space charge and creates a low impedance plasma channel, thereby preventing operation at pulse lengths longer than ∼35 ns for this design. The pulse lengths correlate well with a simple estimate of the ion transit time across the anode-cathode gap rather than the 1–5 cm/μs plasma diode closure rate frequently observed. The low powers obtained are a consequence both of the reduced efficiencies characteristic of relativistic magnetrons and operation at voltages well below the relativistic optimum.
Optical bistability using a nematic liquid crystal film in a Fabry-Perot cavity
Authors: Khoo I. C. , Normandin R. , So V. C. Y.
Published: February 2003

We have observed optical bistability in a Fabry-Perot cavity with a nematic liquid crystal film. Switching phenomenon was observed with a low power single-mode cw laser of about 300 mW.
Diluted magnetic semiconductors: An interface of semiconductor physics and magnetism (invited)
Authors: Furdyna J. K.
Published: February 2003

This paper reviews the electrical, magnetic, and optical properties of diluted magnetic semiconductors (sometimes also referred to as ‘‘semimagnetic’’ semiconductors). These materials are ternary semiconductor alloys whose lattice is made up in part of substitutional magnetic ions. Cd1−xMnxTe and Hg1−xMnxTe are examples of such systems. As semiconductors, these alloys display interesting and important properties, such as the variation of the energy gap and of effective mass with composition. They also exhibit magnetic properties which are interesting in their own right, e.g., a low temperature spin glass transition and magnon excitations. Most importantly, however, the presence of substitutional magnetic ions in these alloys leads to spin–spin exchange interaction between the localized magnetic moments and the band electrons. This in turn has rather important consequences on band structure and on donor and acceptor states, leading to dramatic effects in quantum transport, impurity conduction, and magneto-optics. Specifically, the presence of exchange interaction results in extremely large and temperature dependent g-factors of electrons and holes; in gigantic values of Faraday rotation; in anomalously large negative magnetoresistance; and in the formation of the bound magnetic polaron.
Stress relaxation of vitreous silica on irradiation
Authors: Primak William
Published: February 2003

The radiation-induced stress relaxation which is observed on ion bombardment of vitreous silica is described as a viscoelastic behavior in which the apparent viscosity is reduced to ∼1014 Poise during irradiation and then increases rapidly by 4 or 5 orders of magnitude on cessation or interruption of irradiation. The bombarded layer appears to possess a viscosity ∼1019 Poise, lower than would be expected for normal vitreous silica. On electron bombardment the viscosity is also reduced, but not as greatly as an ion bombardment, yet sufficiently to result in the whole radiation-induced volume contraction being realized perpendicularly to the surface, as has been found for ion bombardment. The maximum elastic stored energy which can be realized is but a fraction of a calorie per gram, hence the reported values of 200 cal/g would seem to be associated with the fragmentation of the network responsible for the reduced viscosity.
Differences in magnetic properties between amorphous and crystalline alloys
Authors: Buschow K. H. J.
Published: February 2003

The magnetic properties of the following intermetallic compounds were determined: HFCo2, HfCo3, Hf6Co23, HfCo7, TaCo2, TaCo3, NbCo2, and NbCo3. Several amorphous alloys of the type Y1−xCox (in the concentration range x=0.30 to x=0.55) were prepared by melt spinning. Their magnetic properties have been compared with those of vapor-quenched alloys studied previously. The concentration dependence of the magnetic moments was studied in the following vapor-quenched amorphous alloys: Mg1−xNix, Hf1−xCox, and Nb1−xCox. In various binary systems the magnetic properties of crystalline and amorphous materials have been compared and their differences are explained in terms of a local environment model.
Smeared critical region in amorphous ferromagnets
Authors: Aharoni Amikam
Published: February 2003

It is shown that with a decreasing amount of short-range order in an amorphous system, a smearing in the low field magnetization is encountered long before such an anomaly may be seen in the high field data. Thus the difference between the normal and anomalous behavior in the critical region is just quantitative and not qualitative.
High-field magnetization studies on an amorphous alloy with para, ferro and spin-glass regions
Authors: Rao K. V. , Gerber J. , Halley J. W. , Chen H. S.
Published: February 2003

Recently, in the concentration–temperature plane, a number of amorphous alloys have been shown to exhibit para, ferro, and spin-glass regions with decreasing temperatures. In order to gain further insight into the role of competing interactions and the local anisotropy that may bring about spin-freezing at low temperatures, we have carried out high-field magnetization studies (in fields up to 160 kOe) between 4 and 120 K on an amorphous Fe15Ni60P16B6Al3 alloy. These results can be summarized as follows: 1) At all temperatures the magnetization does not saturate even at applied fields of 160 kOe; 2) For fixed field, the high field magnetization slowly decreases with temperature. To analyze these data, we first reanalyze earlier, low field data on this system to show that this material behaves in a way consistent with the prediction by Toulouse of a finite field, Ehrenfest second order transition to a mixed spin-glass–ferromagnetic phase as the temperature is reduced. This new analysis then suggests that the high field data is all taken in the paramagnetic phase, lying above this line of phase transitions. In this region, we develop a simple spin wave theory which accounts for points 1) and 2) in the high field data.
Disappearance of ferromagnetism in amorphous (Fe1−xMnx)75P16B6Al3 ribbons
Authors: Manheimer M. A. , Bhagat S. M. , Chen H. S.
Published: February 2003

We present low field dc magnetization (M) measurements on the amorphous alloys (Fe1−xMnx)75P16B6Al3 for x≲0.35. Analysis shows that the spontaneous M goes to zero as T→TC− and Tf+ while the dc susceptibility diverges with T→TC+ and Tf−. It is demonstrated that the ferromagnet–spin glass transition line is significantly different from that obtained by scaling analyses of high field M data.
Deep radiative levels in InP
Authors: Temkin H. , Dutt B. V. , Bonner W. A. , Keramidas V. G.
Published: February 2003

Results of a detailed photoluminescence study of deep radiative transitions in InP crystals prepared by the bulk and epitaxial techniques are reported. In order to understand the origin of the photoluminescence (PL) spectra, bulk samples were subjected to isothermal anneals at different partial pressures of phosphorus. Similarly, the liquid phase epitaxy (LPE) wafers were grown with and without phosphorus in the gas stream. The electrical nature of some of the species responsible for the PL emission was inferred by a study of Cd diffused bulk samples. Based on these experiments the following tentative assignments are proposed. The photoluminescence band at 0.99 eV, common to all samples, is due to emission from a donorlike level related to the P vacancy. Bands at 1.21 and 1.14 eV appear to be due to emission to native acceptor levels associated with the In vacancy. The 1.08-eV band is attributed to emission to a complex of the donor (0.99 eV) and acceptor (1.21 eV) species. The relationship between these bands and residual impurities is discussed.
Nitrogen-bearing amorphous Fe83−xVxB14Si3 alloys: Thermal and magnetic properties
Authors: Rao K. V. , Steinback M. , Liebermann H. H. , Barton L.
Published: February 2003

Magnetic properties of amorphous alloys Fe83−xVxB14Si3 containing 0.02–0.85 at. % nitrogen have been studied from 4 K to the crystallization temperatures. The effect of vanadium in these alloys is to decrease the ferromagnetic transition temperature TC at 23 K/at. % V, as well as the magnetization σ at 8.8 (emu/gm)/at. % V. This indicates loss of ferromagnetism in this alloy system for V concentrations greater than 26 at. %. The addition of nitrogen increases crystallization temperature Tx, saturation magnetization, and spin wave exchange stiffness constant D. The observed T-dependence of the magnetization over the entire temperature range 4–300 K, can be described only by taking into account both the T3/2 and T5/2 terms. This is unlike the normal extended T3/2 behaviour observed in amorphous alloys having TC above room temperature.
Electron and proton irradiation effects in amorphous Fe–Ni–P–B alloys
Authors: Donnelly T. A. , Fisher D. G. , Murray R. B. , Swann C. P.
Published: February 2003

The effect of 1.25-MeV electron and 2.25-MeV proton irradiations of amorphous, melt-spun Fe–Ni–P–B ribbons has been studied by measuring changes in Curie temperature TC and in room temperature relative permeability. TC results are analogous to those obtained by annealing the same type of material at two different temperatures. Annealing experiments support the interpretation that electrons and protons deposit energy at two different rates corresponding to two effective annealing temperatures. The increase in TC is interpreted as the result of structural relaxation. The range of 0.25-MeV protons in the materials studied is less than the thickness of the sample. Irradiations at that energy produce samples with two Curie temperatures. The lower TC is associated with the as-quenched portion of the sample. The higher TC is associated with the portion of the ribbon traversed by protons. Relative permeability measurements in the low field region show increasing permeability with 2.25-MeV proton fluence.
Scaling of susceptibility and the size of the critical region in an amorphous GdAl spin glass (invited)
Authors: Malozemoff A. P. , Imry Y. , Barbara B.
Published: February 2003

We extend our earlier SQUID magnetometry studies of the susceptibility of amorphous Gd37A63 spin glass to a temperature range 5≤T≤100 K and a field range 0.5≤H<50 000 Oe. This enables us to determine the size of the critical region around the spin glass transition at TG=15.5 K; it extends to approximately 22 K in temperature and 15 000 Oe in field. We show that the range of reduced temperature t=(T−TG)/TG for spin glass critical behavior is determined by the parameter 1/Z1/2, where Z is the number of interacting neighbors, in rough agreement with experiment, and that the field range can be estimated from a crossover relation Hαtφ/2. We also find that nonanalyticity in χ(H) as H→0 persists at all temperatures below TG and argue that this can cause apparent nonanalyticity above TG as well in the presence of sample inhomogeneity.
Electrical resistivity and magnetization of the intermediate valence compound CePd3
Authors: Thompson J. R. , Sekula S. T. , Loong C.-K. , Stassis C.
Published: February 2003

The electrical resistivity and magnetization have been measured for a high quality single crystal of the intermediate valence compound CePd3. The magnetization was measured in the temperature range 4–175 K. After correcting for a small Curie-like impurity contribution, the susceptibility χ decreased with increasing temperature from the 4 K value of 1.85×10−3 emu/mole of CePd3. The electrical resistivity ρ was measured from 1.2–300 K. A resistance ratio ρ(300 K)/ρ(4.2 K)=11.5 was obtained. At low temperature (T<8 K), ρ varied quadratically with temperature having an intercept of 9.3×10−8 Ω m at 0 K.
Magneto-optical properties of amorphous terbium–iron alloys
Authors: Connell G. A. N. , Allen R. , Mansuripur M.
Published: February 2003

The magneto-optical properties of rf sputtered amorphous TbxFe1−x alloys (with 0.17≤x≤0.32) were investigated using reflectivity and polar Kerr measurements from a surface overcoated in situ with SiO2. The concentration dependence of the Curie temperature, compensation temperature, and low-temperature polar Kerr amplitude were all derived and the results compared with a mean-field theory. The temperature behavior of the coercive force was also determined. While a considerable degree of agreement is obtained with earlier work, it appears that the low-temperature polar Kerr amplitude can only be determined by the iron sub-network alone, if the iron moment increases with terbium concentration. The extent to which this view is justified is examined in light of current ideas.
Magnetic and thermal expansion properties in hydrided Fe–Zr amorphous alloys
Authors: Fujimori H. , Nakanishi K. , Hiroyoshi H. , Kazama N. S.
Published: February 2003

The effect of hydrogenation on the Invar-like thermal expansion anomaly for Fe–Zr amorphous alloys has been investigated. Low temperature magnetization hysteresis has also been examined for the hydrided alloys. The Invar anomaly is changed slightly by hydrogenation only through the increase in the saturation magnetization at 0 K (Mso), since the spontaneous-volume-magnetostriction (ωm) for the anomaly increases in proportion to the square of the saturation magnetization (Ms)2. But, the coupling constant between ωm and M2s is not changed by hydrogenation. Field cooling down to 4.2 K makes the magnetization hysteresis asymmetric in the case of the nonhydrided alloys, while no longer any asymmetrical loop has been observed in the hydrided alloys. Thus, the observed large ωm is explained by the simple ferromagnetic effect, rather than by the concept based on a magnetically mixed state.
Domain studies on amorphous ribbons with transverse or oblique magnetic anisotropy
Authors: Livingston J. D. , Morris W. G. , Luborsky F. E.
Published: February 2003

SEM techniques are used to study domain structures in amorphous ribbons with transverse or oblique magnetic anisotropy. Domain widths are much finer than in ribbons with longitudinal anisotropy, and vary with ribbon dimensions and anisotropy constant. The effects of applied magnetic fields and applied stresses are also discussed.
Thickness dependence of magnetic hysteretic properties of rf-sputtered amorphous Tb–Fe alloy thin films
Authors: Malmhäll R. , Chen Tu
Published: February 2003

The variation in the magnetic hysteretic properties of rf-sputtered amorphous Tb–Fe thin films as a function of the nominal film thickness was investigated, using Kerr magneto-optic and Hall effect measurements. The results on the thickness dependence of coercivity, polarity of the hysteresis loop, and Curie temperature of films prepared at the same sputtering condition indicate that there is a change in the ‘‘effective’’ film composition. This composition change is believed to be due to microstructure-induced variations in the short-range order during the film growth.
Kinetics of magnetic annealing in amorphous Fe5Co75Si4B16
Authors: Ochiai Y. , Aso K. , Hayakawa M. , Hotai K. , Uedaira S. , Makino Y.
Published: February 2003

Kinetics of magnetic annealing in amorphous Fe5Co75Si4B16 were studied through the change in anisotropy field. Preliminary experiments on as-cast specimens revealed the irreversible and reversible processes. The reversible portions of isothermal kinetic data were well fitted to (Hk−H∞k)/(H0k−H∞k)=B−m log t where m=−0.6+1.4×10−3 T. The analyses of a single time of relaxation with first or second order were evidently unsuccessful. Although further analyses based on broad distributions of relaxation times, box or Gaussian type, give log t dependence in kinetics both distributions do not explain the linear temperature dependence (not proportional to temperature as expected from broad distribuion analyses) in the coefficient m of log t. The similar behaviors found in other alloys are also referred and discussed.
Random-field effects in Fe1−xMgxCl2
Authors: Wong Po-Zen , von Molnar S. , Dimon P.
Published: February 2003

We analyze in detail how random fields are generated in a site-random uniaxial antiferromagnet when a uniform magnet field is applied. Explicit expressions are given for the mean-square random field. We also report on a systematic specific heat study of two three-dimensional Ising systems, pure FeCl2 and site-random Fe0.682Mg0.318Cl2 (MG318), in constant applied fields. The contrasting behavior of the two provide a vivid demonstration of random-field effects. The unusual changes in the shape of the specific heat anomaly observed in MG318 are explained as crossover behavior and not a manifestation of new critical behavior. The crossover exponent φ associated with the random fields is determined from the shape of the magnetic phase boundary. We find φ=1.25±0.10, in excellent agreement with theoretical prediction.
Magnetic properties of compositionally modulated thin films
Authors: Flevaris N. K. , Ketterson J. B. , Hilliard J. E.
Published: February 2003

The magnetization density per cm3 of Ni-content of compositionally modulated Cu–Ni thin films at 5 K was found to depend on the modulation wavelength (λ) and amplitude (A) and reached ∼90% of that of pure Ni. Short-λ and low-T studies on Cu–Ni showed an inter-wavelength coupling of the moments of Ni-rich regions that may depend on the thickness of the latter relative to that of the Cu-rich regions. Evidence for xy-like two-dimensional ferromagnetism was also observed in Cu–Ni with λ containing only a few Ni-rich planes. Coercivity and anisotropy were found to depend strongly on the modulation characteristics; the former increased sharply with decreasing λ while the latter had an oscillatory dependence.
Superconductivity and magnetism in Y4Co3 (invited)
Authors: Sarkissian B. V. B.
Published: February 2003

Y4Co3 is the first itinerant band magnetic superconductor. Experimental results suggest that magnetism and superconductivity in this compound are strongly linked. This may be due to strongly hybridized Y–Co bands.
Magnetic and NMR investigation of RRh3B2 (R=La to Gd) compounds
Authors: Malik S. K. , Dhar S. K. , Vijayaraghavan R. , Wallace W. E.
Published: February 2003

Magnetization (4.2 to 300 K) and 11B paramagnetic NMR (77 to 300 K) studies have been carried out on ternary borides RRh3B2 (R=La to Gd). These compounds crystallize in the CeCo3B2-type structure. From cell volume considerations Ce is in a mixed valent/quadrivalent state while the rest of the rare earth ions are in a trivalent state. With the exception of La and Pr compounds, all other compounds are found to order magnetically. From the high values of the ratio of paramagnetic moment to ordered state moment, the magnetic ordering is inferred to be the itinerant type in CeRh3B2 and EuRh3B2. In Nd and Gd compounds, magnetization data reveal that magnetic ordering is associated with the rare earth sublattice. A complex behavior of magnetization is observed in SmRh3B2. A first order quadrupole split 11B NMR spectrum is observed in Ce, Pr, Nd, and Sm compounds. The boron Knight shift in all these compounds is small and, within the limits of experimental error, scales linearly with susceptibility in Pr and Nd compounds. A temperature independent Knight shift is observed in SmRh3B2, indicating the influence of strong crystal fields.
Critical behavior of semi-infinite magnets (invited)
Authors: Diehl H. W.
Published: February 2003

The local critical behavior of magnets is modified in the vicinity of free surfaces. These surface effects can be studied by using semi-infinite model systems. Recent theoretical work on the semi-infinite n-vector model is reviewed. When possible the theoretical predictions are compared with experimental results. The general new features which show up in the field-theoretical renormalization-group approach are explained. Systems with defect planes and n-vector films are also briefly discussed.
Experimental verification of spin-wave theory in high fields (invited)
Authors: Pauthenet R.
Published: February 2003

The magnetic moment of single crystals of nickel, iron, cobalt, and yttrium iron garnet have been measured between 1.6 and 288 K, in magnetic fields up to 180 000 Oe, along the different crystallographic axes with an accuracy of 0.01%. From these measurements are verified: (i) The H−1/2i Holstein-Primakoff test on the (∂M/∂Hi,Hi) curves, where Hi is the internal field. (ii) The isothermal magnetization M(Hi,T) is represented by the equation M(Hi,T)=Ms(T)+A(T) ⋅ H1/2i+B(T) ⋅ Hi. (iii) The spontaneous magnetization Ms(T) is determined by fitting the experimental points M(Hi,T) with the above equation. (iv) From the Ms(T) variation we determine the absolute saturation moment M=0.619 μB/atom for Ni, 2.226 μB/atom for Fe, 1.729 μB/atom for Co (Hi∥c axis) and 1.72 μB/atom (H⊥c axis), 10.062 μB/mole 5Fe2O3⋅3Y2O3 for YIG. (v) Writing a priori Ms(T)=M0(1−anTn−an′Tn′−an″Tn″) the variation of the spontaneous magnetization with the temperature, and plotting the variation of log [M0−Ms(T)]/M0 as a function of log T, one proves n=3/2, n′=5/2, n″=0 for nickel and iron; for cobalt n=3/2 from points above 100 K; for YIG, n appears to be 5/2. (vi) From the a3/2 values are determined the stiffness coefficients D of iron, cobalt, and nickel which are in reasonable agreement with those determined by neutron diffraction. (vii) By subtracting the theoretical contribution of the spin waves as a function of magnetic field and temperature from the M(Hi,T) data, we obtain an additional superimposed susceptibility for iron, cobalt, and nickel as a function of the temperature, due to their metallic nature.
Superconducting magnetometer for quality control of nuclear fuel rods
Authors: Landry J. D. , Schoenig F. C. , Grossman L. N. , Bernatowicz H. , Jacobs I. S.
Published: February 2003

A superconducting magnetometer is used to assay gadolinium in uranium dioxide nucear fuel rods. Less than 10 percent by weight gadolinium is present in solid solution in the fluorite phase to provide power flattening and to extend the time between refueling of nuclear reactors. The magnetometer is part of an automated rod scanner which provides quality inspection of more than 50 000 fuel rods per year. The magnetometer can resolve a single out-of-specification gadolinia pellet (10 g of UO2 with a maximum of 10% Gd) with as much as 0.2 percent by weight ferromagnetic impurity. The measurement techniques considered during development of the scanner were neutron methods, x-ray fluorescence spectroscopy, modulated-field magnetometry, and moving sample magnetometry. The latter technique was applied by moving the fuel rod at speeds of about 5 cm/sec through two regions of different static magnetic field in excess of 20 000 oersteds. Each region contains a sampling coil which detects changes in magnetization within a volume 1 cm3. Combination of the two signals permits separation of the gadolinium magnetization from the uranium magnetization and ferromagnetic magnetization. The choice of the moving-sample magnetometric method has resulted in a low maintenance, economical, stable inspection device which has performed reliably in the manufacturing environment since August 1977.
A sensitive and compact magnetometer using Faraday effect in YIG waveguide
Authors: Doriath G. , Gaudry R. , Hartemann P.
Published: February 2003

A new type of sensitive magnetometer with a very small probe is described. It is based on a novel hybrid configuration utilizing the Faraday effect in a ferrimagnetic optical waveguide. A linear polarized light generated by a semiconductor laser operating at 1.3 μm is coupled into a multimode magnetic plane waveguide made of a gadolinium gallium substituted YIG epi-layer. The YIG film is of ‘‘easy in plane magnetization’’ type with a low saturation magnetic field. The Faraday rotation is detected with an infrared photodiode by measuring orthogonal polarization component. A polarization modulation technique at a frequency of 100 kHz is used to provide a high degree of noise rejection. The unknown magnetic field projection on the light propagation direction is measured by a zero magnetic field method based on the cancellation of the output signal at the modulating fundamental frequency. Characteristics of this magnetometer are presented. A sensitivity better than 10−7 Oe/Hz1/2 has been obtained at a frequency of 100 Hz.
Magnetovolume effects in Fe–Ti sputtered amorphous alloys
Authors: Fukamichi K. , Hiroyoshi H. , Kaneko T. , Masumoto T. , Shirakawa K.
Published: February 2003

Magnetovolume effects in Fe–Ti amorphous alloys prepared by high-rate sputtering have been investigated. The Curie temperature decreases linearly with increasing Ti content, whereas the magnetic moment varies gradually at the low Ti contents. The spontaneous volume magnetostriction is about 4.5×10−3, being much smaller than that of Fe–B and Fe–Ni Invar alloys. On the other hand, the high-field susceptibility and the pressure coefficient of the Curie temperature are about two times larger than those of Fe–B and Fe–Ni Invar alloys. From the present results, the density of states at the Fermi surface seems to be high. The present alloys are expected to be inhomogeneous because the pressure dependence curves of the Curie temperature are convex downward deviating from the straight line and the large thermal expansion anomaly is observed even above the Curie temperature.
Detection of anomalous stresses in gas pipelines by magnetometer survey (invited)
Authors: Atherton David L. , Teitsma A.
Published: February 2003

Pipelines constructed on unstable terrain (e.g., permafrost), submarine lines, etc. may shift, producing stresses which can lead ultimately to rupture. We have used magnetometer surveys to detect bending stresses in buried pipelines and to monitor new construction. The perturbations to the earth’s field are large and complex; typically fluctuations of 5–10 kilogamma are found 2 m above 1 m diameter buried line. These signals record initial magnetisations, joints, construction history, etc. and include the results of stress induced magnetisation changes. The magnetostrictive effect in steel depends on field, stress, and cyclic history. There is little basic data on the inverse effect, stress induced changes in magnetization. In a pipeline the bending stress distribution is complex so that fringing field changes due to stress magnetisation changes are not calculable. However, experience now enables us to interpret some of the features of our magnetometer surveys. Since stress effects are large we are optimistic that we can eventually develop the technique for surveying pipelines for unusual stress concentrations.
Magnetocrystalline anisotropy and Fermi surface of Ni3Al
Authors: Sigfusson T. I. , Bernhoeft N. R. , Lonzarich G. G.
Published: February 2003

The first magnetocrystalline anisotropy constant K1(T,H) has been measured in stoichiometric single crystals of weakly ferromagnetic Ni3Al as a function of magnetic field in the range 1≲H≲48 kG at T=4.2 K and of temperature in the range 1.2≲T≲43 K at H=16 kG. At 4.2 K and 16 kG we obtain K1=−(9.6±0.7)103 erg cm−3, a value reproduced within experimental error in three samples investigated having residual resistivity ratios [ρ(293 K)/ρ(4.2 K)] 17, 18, and 34, respectively. The measured value of K1 has the same sign but is about one hundred times smaller in magnitude than in pure Ni at the same temperature and field. Within our experimental field and temperature ranges we observe a relatively weak field dependence above 5 kG but a rapid temperature variation of K1(T,H) which falls with increasing temperature in proportion to a high power of the relative magnetization M(T,H)/M(0,H). Qualitative interpretations of these results are suggested.
Electronic structure and magnetism in VPd3 and FePd3
Authors: Jaswal S. S.
Published: February 2003

The electronic structure of VPd3 and FePd3 is studied in the paramagnetic state using the method of orthogonalized linear combination of atomic orbitals. The Stoner criterion as generalized by Jarlborg and Freeman for compounds is employed to investigate the magnetic instability. For VPd3, the calculated density of states does not have any large peak near the Fermi level and does not satisfy the Stoner criterion for ferromagnetism; this is in agreement with the magnetic susceptibility data of Burmester and Sellmyer down to 1.6 K. The spin-polarized calculations of Williams et al. for the cubic phase of VPd3 predict a magnetic state. In the case of FePd3, our calculations give a large sharp peak at the Fermi level which is primarily due to Fe d orbitals. Our results are similar to those of Switendick and are in agreement with the observed ferromagnetism.
Resistivity and galvanomagnetic coefficients of iron group metallic glasses with chromium substitutions
Authors: Long J. R. , Hadjipanayis G. C. , Sellmyer D. J.
Published: February 2003

Magnetic field and temperature dependences of the electrical resistivities and Hall resistivities were measured for the metallic glass ferromagnets Fe13Ni60Cr5Si10B12, Fe37Ni36Cr5Si10B12, Fe81B13.5Si3.5C2, and Fe5Co75Si15B5. Resistance minima and magnetoresistivity of the FeNiCr glasses have been found to be consistent with a modified Kondo model of low temperature scattering. The Hall resistivities are positive and large. The spontaneous Hall coefficients of the FeNiCr glasses are in good agreement with previous magnetization measurements on the same glasses.
Biaxial magnetoelasticity in steels
Authors: Schneider C. S. , Richardson J. M.
Published: February 2003

The effects of stress coaxial, transverse, and biaxial relative to applied field on magnetization, susceptibility, and domain wall configurations are derived and confirmed using rod, hollow cylinder, and hollow toroid steel samples. The effective stress σ=σ∥−σ⊥ is linearly proportional to pressure on 90° domain walls below residual stress and to changes in reluctance above residual stress. The equivalent field, Hσ=6.0(5) A/m, per MPa of stress was measured in excellent agreement with 6.2(4) A/m calculated from material parameters. The quantity dχ−1/dσ=9.0(6)×10−6/MPa was measured in good agreement with 8.3(5) calculated. A lower limit of reluctance due to inhomogeneities was observed. Magnetization increases with tension and compression allow measurement of ±90° domain wall fractions, f±=0.30±M/Ms, below the coercive field. Net magnetization changes from both walls generate magnetization hysteresis loops with stress cycling.
The effect of forsterite coatings on magnetic properties and domain structure of grain oriented 3% Si–Fe
Authors: Washko S. D. , Shen T. H. , Morris W. G.
Published: February 2003

Magnetic properties and domain structures were obtained on commercial grain oriented 3% Si–Fe before, during, and after removal of the forsterite base coating. A 200 kV Scanning Electron Microscope (SEM) was used for static and dynamic domain observations. Magnetic properties were correlated to the observed domain structure. Forsterite coatings significantly reduce both 180° domain wall spacings and the density of supplementary flux closure domains. However, lower losses were not realized from such alterations of the domain structures. The increased core losses can be rationalized in terms of the behavior of the domain structure during cyclic magnetization. The formation of the forsterite base coating leads to nonuniform, irreproducible 180° domain wall movement and pinning of the domain walls at subsurface forsterite particles.