bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Properties and Color-Center Formation in Thin Films of Molybdenum Trioxide
Authors: Deb S. K. , Chopoorian J. A. 
Published: April 2005

The optical absorption spectrum of thin films of MoO3 has been measured over the temperature range from 77° to 290°K. The fundamental absorption edge occurs at 3300 Å with an absorption coefficient of 105 cm−1. A stoichiometric film of MoO3 shows three absorption peaks at 3350, 2880, and 2700 Å, respectively, and these are suggested to be due either to exciton formation or to transitions involving a split valence band.
Values for the refractive index have been measured in the wavelength range 0.42–1.2μ. The low-frequency dielectric constant (18.0±1) has been measured and the comparison with the high-frequency dielectric constant (5.70) indicates that the bonding is predominantly ionic.
The electrical conductivity has been measured on a polycrystalline sample in the temperature range 298° to 900°K and the activation energies of conduction found to be 1.83 eV (intrinsic) and 0.56 eV (impurity).
On irradiating a thin film (0.2μ) of MoO3 with light of wavelength shorter than 3300 Å, three color-center bands having maxima around 5000, 6250, and 7700 Å are formed. The same type of color centers are also formed on heating the film in oxygen in inert atmosphere. The color centers thus formed cannot be bleached optically. However, they can be bleached thermally in oxygen at 300°C. The growth and decay of color centers has been studied in detail.
The formation of color centers is associated with increased dark conductivity of the MoO3. Very weak photoconductivity and photovoltaic effects with threshold energy corresponding to the fundamental absorption edge at 3300 Å have been observed.
An ESR signal characteristic of Mo5+ state has been observed in a film of MoO3. There is a small increase of ESR signal on color-center formation which disappears completely on heating in air at 300°C.
An energy-level diagram has been proposed to account for the optical and electrical properties as well as the color-center formation in MoO3.
Thermal and Optical Energy Gaps in PbTe
Authors: Tauber R. N. , Machonis A. A. , Cadoff I. B. 
Published: April 2005

The optical absorption edge (indirect energy gap) for PbTe was determined in the temperature range of 80°–520°K. It was found that dEg/dT had a value of 4.1×10−4 eV/°K in the temperature range from 80°–350°K, while above 400°K, dEg/dT was approximately zero. The low-temperature linear portion extrapolated to 0.19 eV at 0°K while the high-temperature portion extrapolated to 0.36 eV. This behavior is explained by a two-valence band model, one active at low temperatures, the other in the high temperature range.
A thermal energy gap of approximately 0.36eV was obtained from the temperature variation of resistivity and Hall coefficient in the intrinsic range, 500°–900°K. This value agrees with the high temperature optical data extrapolated to 0°K, thus correlating the optical and thermal energy gaps.
High-Pressure Phase-Equilibrium Studies of CdS and MnS by Static and Dynamic Methods
Authors: Miller R. O. , Dachille F. , Roy R. 
Published: April 2005

The P-T equilibrium of CdS polymorphs was studied in the range to over 50 kbar and 700°C in opposedanvil and hydrothermal pressure apparatuses. Use of CdS of diverse origins revealed important effects of structure, preparations, and mechanical treatment on polymorphic transitions, especially noticeable in electrical resistance discontinuities with pressure or temperature changes. A triple point was located at 425°±5°C and 16.5±0.5 kbar between the phase fields of CdS-I (wurtzite, and also CdS-I′, metastable sphalerite), CdS-II (rocksalt structure) and CdS-III (a new polymorph, presumably of B23 structure). The slopes of the I to II, I to III, and II to III phase boundaries are 130°, −47°, and 1.6°C/kbar, respectively.
Resistivity of the II phase was found not to be ``metallic.'' The large drop in resistance during the I–II reconstructive transformation is attributed to a grain boundary conduction mechanism.
The P-T-X of the system MnS-CdS was determined to 600°C and 40 kbar. A maximum of 80 mol % CdS was found in a quenchable II phase, but the III phase could not be quenched at any composition.
Ion Collection in the Bayard-Alpert Gauge
Authors: Comşa George 
Published: April 2005

A collecting factor for ions created at a given distance is computed on the basis of a simplified model and under the assumption of a Maxwell distribution of the initial velocities of ions. The factor is independent of the mass of the ion, but is a function of the temperature and takes values differing substantially from unity for usual dimensions of the collector.
The effect of the collector dimensions on the x-ray-limited pressure may be analyzed by using an approximate expression for the integral collecting factor.
Calculation shows that for very fine collecting wires the collecting factor is affected even by the extremely small momentum transferred to the helium ion from the electron during the ionizing collision. Experiments have confirmed the foregoing considerations, thus opening the way to the measurement of such momenta.
Tb3+ Fluorescence and Nonradiative Energy Transfer from Gd3+ to Tb3+ in Borate Glass
Authors: Pearson A. David , Peterson G. E. , Northover W. R. 
Published: April 2005

The fluorescence behavior of Gd3+ and Tb3+ has been studied with the ions dissolved together in a Calibo-1 glass host. The two ions form a coupled system so that energy absorbed by Gd3+ is transferred to Tb3+ by a nonradiative mechanism and is then emitted as Tb3+ fluorescence.
When Tb3+ is incorporated alone into this glass, concentration quenching effects are observable. These have been found to be due to the shortening of the Tb3+ 5D4 lifetime, which in turn is due to the Tb3+ ions being packed closer together as the concentration of Tb3+ is increased. It is proposed that this gives rise to ``chains'' of Tb3+ ions along which energy can migrate, by a nonradiative transfer mechanism, to sinks in the structure.
The rate of internal conversion from Tb3+ 5D3 to Tb3+ 5D4 has also been studied as a function of concentration. The results have been interpreted as being due to the formation of Tb3+-Tb3+ resonance-coupled pairs, which causes the rate of internal conversion to increase as the concentration of Tb3+ increases.
The effects of changes in temperature and base glass composition on the Tb3+ 5D4 lifetime have also been investigated and are reported.
Properties of InAs Lasers
Authors: Melngailis I. , Rediker R. H. 
Published: April 2005

Two different recombination mechanisms can be distinguished in the infrared radiation spectra of InAs. The photoluminescence of n-type InAs corresponds to a direct band-to-band (or weak exciton) transition. The photoluminescence of Zn-doped p-type InAs and the injection luminescence of most Zn-diffused diodes correspond to transitions between conduction-band states (not excluding shallow donors for p-type crystals with a heavy donor compensation) and acceptor states about 17 meV above the valence band. The diode emission, therefore, results from injection of electrons into the p-type side of the junction, although band-to-band radiation has also been obtained in some diodes under certain conditions of current density and magnetic field.
Present InAs diode lasers which emit near 3.1 μ (band-to-acceptor line) have external quantum efficiencies of about 12% and threshold current densities of about 300 A·cm−2 at 11°K, and they can be operated continuously with currents of several amperes. With magnetic fields of several kG applied perpendicular to the diode current the threshold has been further reduced and the efficiency increased to as much as 25%. This enhancement of emission is shown to be associated with a decrease of injected carrier diffusion in the magnetic field which produces a more compact active region. The threshold increases nearly exponentially with temperature up to 150°K, the highest temperature for laser action at present. The angular spread of the coherent radiation beam in the plane perpendicular to the junction plane is about 30°, which corresponds to a coherently emitting region of 6 μ at the junction. Angles as small as 7° were measured in the plane of the junction.
Coherent emission at 3.0 μ corresponding to a band-to-band transition is obtained from n-type (ND=2×1016 cm−3) InAs crystals at 11°K by exciting them with 0.84-μ emission of a GaAs p-n junction laser. The angular spread of the coherent radiation beam in the plane perpendicular to the optically excited plane is 9° which corresponds to a coherently emitting region of 20 μ, over three times larger than the 6 μ for the diode laser.
Thermoelectric Power and Electrical Resistance of Chromium-Iron Alloys from 125° to 625°K
Authors: Schröder Klaus , Yessik Michael J. , Baum Neal P. 
Published: April 2005

The Seebeck coefficient S of alloys with up to 23 at. % iron has been measured from 125° to 625°K. S of alloys with 10, 15, 19, and 23 at. % Fe was nearly temperature-independent and had values between 6 and 9 μV/°K. Pure chromium and alloys with up to 4 at. % Fe had a nearly temperature-independent S at temperatures above 375°K, with S ranging from 13 to 16 μV/°K. However, S exhibited a pronounced maximum below room temperature. The maximum values and the corresponding temperatures are: pure chromium: 21 μV/°K, 275°K; 1 at. % Fe: 27 μV/°K, 240°K; 2 at. % Fe: 40 μV/°K, 175°K; 4 at. % Fe: 34 μV/°K, 280°K. The resistance anomaly of chromium rich samples with maxima below room temperature was similar to that found by other authors. This anomaly has been attributed to the transition to antiferromagnetism.
It has been shown that the peak of the phonon drag term S (phon) in pure chromium occurs at 25°K. The observed peaks in our experiments above 125°K should be due to the electron-diffusion term S (diff). It can be deduced from S of alloys with 10 to 23 at. % Fe, that s-d scattering has only a small effect on the S (diff) and it is concluded that the structure change of the conduction band at the transition to antiferromagnetism is responsible for the maxima in S. The indicated energy dependence of the Fermi surface is in qualitative agreement with band models deduced from Hall-effect measurements in the same alloys.
Antiferromagnetism in Chromium Alloys
Authors: Mackintosh A. R. 
Published: April 2005

The antiferromagnetism of Cr and its alloys has recently been extensively studied by neutron-diffraction1–3 and transport-property measurements.2,4 The concentration dependence of the moment, the Néel temperature, and the periodicity of the magnetic ordering can be correlated with the theoretical band structures and the anomalies in the transport properties just below TN.
Magnetic ordering in Cr is a consequence of the localized nature of the d-functions, which give rise to a large intra-atomic Coulomb interaction; and the narrow d bands which favor the formation of a magnetic state.5,6 The magnetic form factor7 is in qualitative agreement with the relative occupancy of the d bands of different symmetry.8 Decreasing the electron concentration by the addition of V causes a decrease in magnetic moment and TN and also decreases the Q vector of the magnetization. It has been shown6,9 that in some cases, the magnetic periodicity of such a structure is determined by the extension of a prominent piece of the Fermi surface and it appears that, in this case, the distance between the octahedral faces of the electron jack at Γ and the hole surface at H determines Q.10 This hypothesis is in approximate agreement with the calculated Fermi surface dimensions,11 and the change in periodicity and moment with alloying can also be qualitatively understood. The transport properties provide evidence that the magnetic ordering destroys a significant proportion of the Fermi surface. Increasing the electron concentration by adding Mn causes the moment and TN to increase and, in addition, tends to make the magnetic periodicity commensurate with the lattice. This allows a maximum interaction between the magnetization wave and the d electrons. The addition of Mo or W causes a gradual decrease in the moment and TN, probably due to the less localized nature of the d functions in these metals.
In pure Cr there is a transition from a transverse to a longitudinal spin density wave on cooling through 121°K, due to the extra entropy associated with the former spin configuration. This transition is rapidly eliminated by the addition of impurities, for reasons which are not at present understood.
An Extremely High Power X-Band Three-Port Circulator
Authors: Wantuch E. , Lepore D. 
Published: April 2005

The modifications of typical ferrite materials by either hot-pressing or the addition of fast relaxing impurities are compared in a three-port circulator.
A standard MgMn ferrite with empirical formula Mn0.08Mg1.25Fe1.67O4± was tested in the three-port circulator model. It showed an onset of nonlinear behavior at 20 kW. By hot-pressing, the peak power level was extended to 200 kW with 0.1 dB rise in insertion loss, and to 500 kW with 0.25 dB increase in insertion loss.
A gadolinium-substituted garnet with empirical formula 3(Y0.6Gd0.4)·5(Fe)O12 was tested in the same geometry. It exhibited a threshold power level of 10 kW. A 4% substitution of dysprosium greatly extended the peak power handling capability of the three-port circulator. No increase in insertion loss over low-power readings was noted up to 500 kW peak.
Evidence by Lorentz Microscopy for Magnetically Active Stacking Faults
Authors: Zijlstra H. , Haanstra H. B. 
Published: April 2005

In the ordered MnAl crystal containing magnetic atoms which are coupled ferromagnetically, stacking faults are postulated through which an antiferromagnetic coupling exists between the atoms on either side of the fault. These account for the anomalous magnetic behavior1 of fine MnAl powder. Such faults give rise to a domain structure the walls of which are strongly pinned to these crystallographic defects. A direct evidence for the occurrence of these stacking faults is obtained by using Lorentz electron microscopy, whereby shadow patterns of opaque MnAl particles show a characteristic distortion of their contours when the microscope is used out of focus. The distortion is interpreted in terms of stray fields due to the domain structure. Experiments were carried out in a Philips EM 200 electron microscope.
By using the normal objective lens, the pattern can be studied with or without a strong applied field. Fields up to 9000 Oe could be applied. Domain structures were observed that showed a remarkable indifference for these fields. This rigidity is explained by assuming that the walls are pinned to stacking faults.
Domain structures with a high pole density on the walls were also observed. These structures are unfavorable owing to large magnetostatic energy. Their occurrence is also explained by the presence of stacking faults.
A full account of the method and the results will be submitted as a regular article to this Journal.
A Current Review of Lodex Permanent Magnet Technology
Authors: Falk R. B. 
Published: April 2005

The history of elongated, single-domain permanent magnets, commencing with the theoretical considerations of Stoner and Wohlfarth and others to the reduction to practice by Paine, Mendelsohn, and Luborsky, and final development of product (Lodex) manufacturing capabilities, is briefly reviewed.
The present Lodex permanent magnet is prepared by a relatively complex electrochemical and amalgam metallurgical process. A wide variety of magnetic properties may be obtained by altering the ratio of elongated particles to matrix material during processing. Isotropic and anisotropic permanent magnets having complex shapes and extremely close tolerances are formed directly by a variety of powder metal and extrusion processes. Such magnets consist of antimony-coated particles of iron-cobalt embedded in a metallic lead matrix.
The use of Lodex magnets in automotive, meter, communication, and control applications is discussed in detail. Current laboratory development work on oxide-coated iron-cobalt particles, coercive force improvements on existing particles, and physical property improvements of the present magnet structure is reviewed.
Stabilization Prediction for Permanent-Magnet Field Motors and Generators
Authors: Wentworth B. W. , Ellis E. L. 
Published: April 2005

A primary concern in the design of permanent magnet field motors is the interaction of the field flux and the flux produced by the armature current. An analytical model has been established to quantitatively predict the degree to which the permanent magnet field is demagnetized by the armature current. As an aid to analysis, the pole face opposite each armature tooth is treated as a separate section. The maximum amount of magnetizing or demagnetizing force is determined for each section from ΔH=−4π(K0−Ka)NI/50.8 lm,where K0 is the number of armature slots opposed to field flux; Ka, the number of armature slots aiding field flux; NI, the maximum ampere turns per slot (generally at stall current); and lm, the radial length of the permanent magnet in inches. The maximum demagnetizing force per section is then used to determine the stabilized flux densities per section, which in turn are used to determine the stabilized flux per pole for the machine. The effects of armature reversal can be included in the stabilization prediction.
The analytical model was compared with a static test model, and it was determined that the predictions were accurate to within a few percent. Employment of this method of field flux analysis with optimization of armature parameters, including tooth width and armature winding, provides the designer with competent design tradeoffs prior to committing expensive tooling operations.
Application of Modern Permanent-Magnet Materials to the Excitation of a Slow-Speed Power Servomotor
Authors: Lord W. 
Published: April 2005

The main requirements of low-speed, dc power servomotors used as drive members of director control systems are for fast speed of response coupled with optimization of size and weight for a given torque output. It can be shown that the over-all time constant of such a dc machine is inversely proportional to the gap density squared; thus, where physical size and temperature rise of the field windings are important design limitations, the use of modern, high-energy permanent-magnet materials becomes advantageous.
This paper describes the conversion of a conventional 6-pole, 1-hp, 100-rpm machine to one having permanent magnet excitation employing Columax (Alnico VB, DG) poles. Difficulties associated with machining, and magnetizing and demagnetizing the 6-pole stator in situ are discussed, and a study of the maximum demagnetization forces existing in such a machine, carried out with the aid of Hall plates, is given. A comparison of both the dynamic and the steady-state performance of the conventional machine and the permanent magnet machine, shows the feasibility of using modern permanent magnet materials for such an application.
ac Field ``Freezing'' and ``Melting'' of Magnetization in Fine-Particle Assemblies
Authors: Kneller E. , Friedlaender F. J. , Puschert W. 
Published: April 2005

Alternating-current-freezing curves Mf(H, H′) and ac-melting curves Mm(H, H′) represent a dynamic recording of the process of storing and erasing, respectively, of magnetic signals under the continuously equilibrating action of an ac-field H′.
The properties of such curves are discussed in connection with measurements on assemblies of acicular γ−Fe2O3 particles. Indication is made how these curves are calculated from simple particle models. It is especially shown that the extension of the pair model with equal volumes, equal critical fields, and negative interaction field to unequal critical fields accounts surprisingly well for most details found experimentally.
Linewidth Studies in Ordered Lithium Ferrite
Authors: Nilsen W. G. , Comstock R. L. , Remeika J. P. 
Published: April 2005

Linewidth measurements have been carried out in ordered lithium ferrite from 4.2°K to room temperature and at several microwave frequencies. Our purpose was to compare the linewidth characteristics of ordered lithium ferrite with those of YIG in the low-temperature range. We find that nominally pure lithium ferrite exhibits a small linewidth peak at about 19°K as compared to roughly 40° to 50°K for YIG. Of particular interest is the fact that in lithium ferrite the linewidth increases with microwave frequency both below and above the linewidth peak and that the peak occurs at the same temperature independent of microwave frequency. For YIG below the peak, the linewidth decreases with increasing microwave frequency.
In an attempt to determine the origin of the linewidth peak in lithium ferrite, several samples were made with small dopings of silicon and manganese. These samples also had a linewidth peak at 19°K, but the height of the peak was roughly the same for undoped and doped samples made at the same time. Chemical analysis and conductivity measurements showed that the pure samples did not contain significant amounts of Fe++ or manganese, that the silicon-doped samples contained Fe++, and that manganese probably enters the lithium ferrite lattice as Mn3+. Apparently, neither Fe++ nor Mn3+ is the primary cause of the linewidth peak in lithium ferrite. Also, calcium-doped YIG, which is known to contain Fe4+, did not show a linewidth peak. It appears that the linewidth peak in lithium ferrite is not due to an impurity ion.
SSWM in Thin Permalloy Films Prepared in Vacuums of 10−5 and 10−9 Torr
Authors: Lykken G. I. , Harman W. L. , Mitchell E. N. 
Published: April 2005

Standing spin-wave modes were measured in Permalloy films (82% Ni-18% Fe, thickness range 100–2800 Å, substrate deposition temperature 4.2°K &lt;T&lt;573°K) at room temperature and 12.2 Gc/sec. Two series of films were examined: series I made in an ultrahigh vacuum system (10−10−10−9 Torr) and measured prior to removal from this vacuum and later in air, series II made in an oil diffusion system (10−5 Torr) and subsequently measured in air. The absorption modes of all series I films shifted to higher magnetic fields as they aged in vacuum at room temperature, while aging in air generally shifted them to lesser fields; in both cases the relative intensities of the modes were unchanged. Annealing greatly altered the absorption spectra and shifted them to lesser fields. Most films exhibited a quadratic dependence on mode spacings supporting the surface-spin-pinning model. The series II films could also be fitted to the volume inhomogeneity model by changing the numbering of the modes.
It is shown that in most cases, the shifting of the spectra is due to changes in g, 4πM and (A/M) ⊥ and that the SSWM in the series II films are described best by the surface-spin-pinning model. It is concluded that there is strong spin pinning at the substrate-film interface and that this pinning is much greater than at the top surface, except in extreme cases such as highly oxidized films.