bluuebunny/crossref_metadata_2025 huggingface dataset:
Amplitude-Modulated Magneto-optic Readout
Authors: Smaller P. , Treves D.
Published: February 2004

In order to reduce the noise due to surface imperfections in a magneto-optic readout system the following scheme was developed: the recording medium consists of a high-coercivity storage film on top of which is deposited a low-coercivity readout film. The leakage field of the bits stored in the storage film magnetizes the readout layer in a similar pattern. An rf field that is weak enough not to erase the storage film but strong enough to switch the soft film is applied. The rf field is biased in such a manner that it switches only ``1'' bits but not ``0'' bits. Only the rf component of the photomultiplier output is detected, rejecting essentially all light fluctuations due to surface imperfection. The realization of such a system and experimental results will be described.
Magnetization Reversal in Multilayer Film-Device Structures
Authors: Chang H. , Genovese E. R. , Flur B.
Published: February 2004

While magnetization reversal in a large film sheet under uniform-field excitation is determined by the macroscopic anisotropy property and microscopic magnetization ripple structure, the magnetization reversal in miniaturized multilayer devices, in addition, depends strongly on the geometry of the device structures. Earlier papers reported the study of coupled-film strips using a nanosecond microscopic Kerr apparatus and simultaneous inductive and magneto-optic-measurement techniques. The present paper describes the reversal behavior in two coupled-film structures, in which the easy axis of each Permalloy layer may be aligned parallel to the strip length (closed hard axis or CHA) or perpendicular to the strip length (closed easy axis or CEA). The Permalloy layers may also be mismatched in thickness. When a Permalloy backing is added to the external drive line as a keeper, the reversal phenomena in both the storage layers and the keeper have been observed.
Detailed Spin-Echo Spectra of Ferromagnetic Fe–Al Alloys
Authors: Murphy J. J. , Budnick J. I. , Skalski S.
Published: February 2004

We have studied the application of the spin-echo technique of NMR to the problem of determining the detailed distribution of hyperfine interactions in a ferromagnet. The resonances of both solvent and solute nuclei have been studied in the helium temperature range for concentrations up to 6 at.% Al in Fe. For both nuclei we find appreciable structure in the spectra on the low-frequency side of a main line (the only line visible at the lowest concentration studied, 0.5%). Attempts have been made to fit consistently the observations on both Fe and Al in terms of a single conduction electron polarization model by explicitly considering effects out to the third neighbor shell. We find two features common to both spectra: (1) a concentration-dependent linewidth for the main line of each, and (2) a concentration-dependent field shift of the maximum of the main line which is equal for both nuclei. The Al linewidth (in kOe) is found to be ½ the Fe width which suggests that the hyperfine field shifts should be scaled by a factor of approximately ½ rather than unity when comparing the solvent and solute spectra.

The variation of the hyperfine interaction at both the Al and Fe sites for particular near-neighbor configurations are presented.
Magnetic Properties and Nuclear Magnetic Resonance of Diluted (Gd, Zr)Zn2
Authors: Asanuma M. , Yamadaya T.
Published: February 2004

The magnetic and NMR properties of Zr1−xGdxZn2 (0≤x≤0.05) have been investigated to clarify the influence of localized magnetic moments on conduction electron ferromagnet ZrZn2. The dependence of magnetization intensity of Gd concentration shows that the Gd atoms are S states and the spin polarization of conduction electrons by a localized Gd moment does not take place. Moreover, ferromagnetism would disappear above x=0.025. The hyperfine field of Zr in ZrZn2 is −38 kOe, and is remarkably less than usual for transition metals. This result is explained by assuming mixing of the 4d and 5s wavefunctions.
Exchange Interactions in Rare Earth Iron Garnets
Authors: Atzmony U. , Bauminger E. R. , Einhorn B. , Hess J. , Mustachi A. , Ofer S.
Published: February 2004

The exchange magnetic fields at Eu ions inside various rare earth iron garnets were estimated from measurements of the splittings of the 103-keV Mössbauer line of 153Eu. Mössbauer sources of the composition (M0.975 153Sm0.025)3Fe5O12 were prepared with radioactive Sm2O3 and an absorber of Eu2O3 was used. The splittings for diamagnetic Lu and Y were the same although the atomic cell sizes of YIG and LuIG differ by ∼1%. This indicates that the rare-earth iron-exchange interaction in the garnets is not very sensitive to the cell sizes of the garnets. For Gd the splitting was (8.0±1.5)% smaller than for Lu or Y, showing that the exchange field (at the Eu ions) produced by the Gd ions is about 8% of the field produced by the Fe ions. The Eu3+-rare-earth exchange interactions were found to be approximately proportional to 〈S〉 = (gJ−1) 〈J〉.
Hyperfine Structure of 57Fe in RbFeF3
Authors: Wertheim G. K. , Guggenheim H. J. , Williams H. J. , Buchanan D. N. E.
Published: February 2004

In magnetization and Mössbauer effect (ME) studies the cubic perovskite RbFeF3 exhibits magnetic phase changes at 39°, 87°, and 102°K. Above 102°K the material is paramagnetic. From 87° to 102°K the ME yields well-resolved hfs showing the combined effects of magnetic-dipole and electric-quadrupole interactions. Both are consistent with an exchange splitting of the low-lying, spin-orbit triplet of Fe2+. However, the sublattice magnetization if proportional to (TN−T)1/3, indicating that a molecular-field treatment is not applicable. Absence of remanence indicates that the crystal is antiferromagnetic in this region.

Below 87°K remanence is observed and the ME spectra exhibit two magnetically inequivalent iron sites. The details of the transition to this state show that it is not obtained by a canting of the antiferromagnetic spin system. Below 39°K all iron atoms are again equivalent in the ME spectra. These yield Heff=252 kOe and quadrupole splitting of 0.27 cm/sec with the axis of the EFG tensor at 40° to the direction of the magnetization.
Magnetization Distributions in Diluted Systems
Authors: Kitchens T. A. , Trousdale W. L.
Published: February 2004

In magnetic systems which have been substitutionally diluted there exist a large number of different magnetic sites the diversity of which is determined by the nature of the magnetic interaction and the statistical fluctuations in the distribution of the magnetic atoms. We have calculated the magnetic and exchange field distributions from the magnetic atom concentration, the lattice structure, and the magnetic interaction potential in a self-consistent way for any temperature below the transition temperature. The calculation has been applied to the case of the hyperfine field distributions observed by nuclear magnetic resonance and by the Mössbauer effect in magnetic random substitutional alloys where the interaction is long range.
Hyperfine Field Distributions in (ZrCo2)x(ZrFe2)1−x Alloys
Authors: Swartzendruber L. J. , Bennett Lawrence H.
Published: February 2004

Mössbauer-effect measurements in the cubic Laves-phase pseudobinary magnetic alloys (ZrCo2)x(ZrFe2)1−x yield complex spectra. Magnetization curves on these alloys have been previously reported. ZrFe2, with a saturation moment at 4°K of about 1.6 μB per Fe atom and a Brillouin-type magnetization curve, displays a Mössbauer spectrum consisting of two six-line patterns, each with a hyperfine field of about 200 kOe. ZrFeCo has been reported to show only a quadrupole splitting at 78°K, although this is well below the Curie temperature. We have observed resolved hyperfine splitting in this composition at 78°K and at 4°K. The magnetization curves in (ZrCo2)x(ZrFe2)1−x for x=0.2, 0.4, 0.5, and 0.6 imply magnetic-moment distributions. The Mössbauer spectra for these alloys show hyperfine field distributions that are strong functions of temperature over a wide range below the Curie temperatures. Discrete static distributions of hf fields may explain the spectra, but relaxation effects cannot be ruled out.
Magnetic Properties of fcc Rare Earth-Thorium Alloys
Authors: Child H. R. , Koehler W. C. , Millhouse A. H.
Published: February 2004

A neutron-diffraction study of rare earth-thorium alloys having the (fcc) structure has been carried out at temperatures ranging from room temperature to 1.3°K. For alloys of the heavy rare earth metals Tb, Ho, and Er, the fcc field starts at approximately 50 at.% Th. In a typical case the diffraction pattern at low temperatures exhibits broad diffuse maxima, due to magnetic scattering, which are centered at scattering angles and are 0.3 and 0.8 of that of the (111) nuclear reflection. The pattern can be interpreted in terms of short-range antiferromagnetic correlations. These results are to be contrasted with those previously found for the rare earth-rich hcp alloys, in which dilution by thorium stabilizes the ferromagnetic phase. For alloys of the light metals, Pr and Nd, the fcc structure is found in alloys containing 20 at.% Th. The magnetic scattering from such an alloy with Nd is similar to that observed for a polycrystalline specimen of the pure metal in which half the atomic sites have local symmetry which is cubic. It is probable that the magnetic structure of the fcc alloy is similar to the arrangement of moments on the cubic sites in the pure metal. The corresponding Pr-based alloy showed no magnetic ordering to 1.3°K.
Magnetic Properties of Rare Earth-Lanthanum Alloys
Authors: Koehler W. C. , Child H. R. , Wollan E. O. , Cable J. W.
Published: February 2004

Alloys of the heavy rare earth metals with La have been studied by neutron-diffraction methods. For alloys with 15 at.% or less of La the alloys have the simple hcp structure. The influence of La on the magnetic structures of the metals is such as to enhance the stability of a ferromagnetic configuration relative to an oscillatory one. The transition temperature is lower and the initial turn angle (when it exists) smaller in a lanthanum alloy than in the corresponding yttrium alloy. In the lanthanum-rich region, the system La–Tb has been most extensively studied with five compositions ranging from Tb0.10La0.90 to Tb0.75La0.25 having been investigated. Of these, the compositions Tb0.20La0.80, Tb0.40La0.60 and Tb0.50La0.50 formed a single phase alloy with the double hexagonal lanthanum structure (dhcp). The 4.2°K diffraction patterns of these three alloys exhibited a number of broad diffraction maxima rather similar to those found for Nd in the antiferromagnetic region. Néel temperatures of approximately 50°, 68°, and 75°K, respectively, were estimated for the three specimens. The specimen Tb0.75La0.25 exhibited lines from the hcp and dhcp structures as well as of a third phase which is probably the δ phase. In the Tb0.10La0.90 alloy both a dhcp and fcc phase were observed at room temperature; the low-temperature pattern exhibited magnetic reflections characteristic of the dhcp alloys. The La-rich Tb alloys thus are antiferromagnetic, rather than ferromagnetic as had been proposed previously.
Spatial Distribution of the Magnetic Moment in MnSi
Authors: Brown P. J. , Forsyth J. B. , Lander G. H.
Published: February 2004

Recent measurements1 of the magnetic properties of the monosilicides of some 3d transition metals have shown that MnSi has a small ferromagnetic moment (≈0.4 μB/formula unit) at temperatures below 30°K. Neutron-diffraction measurements have been made on both powder and single-crystal specimens. The powder data show that there is no ordered antiferromagnetic component to the moment, so that the total moment is that derived from the saturation magnetization. This result may be compared with the value of 1.4 μB/Mn obtained1 from the Curie-Weiss dependence of the susceptibility above 30°K.

The integrated intensities of the (hk0) reflections from a single crystal at room temperature were measured and the corresponding nuclear scattering amplitudes derived. A comparison of these values with those calculated from Pauling's2 structure (B20) confirmed the two positional parameters and indicated a 5% deficiency of manganese in the sample. This latter observation can be correlated with the lower saturation magnetisation of this sample (0.34 μB/Mn atom). Furthermore, the measurements showed the presence of a small amount of secondary extinction in the strongest reflections. Using the same crystal in a magnetic field at 4.2°K and the polarized neutron technique, measurements of the polarization ratios were made for the same set of reflections; the secondary extinction parameter derived from the room-temperature measurements enabled corrected magnetic scattering amplitudes to be deduced. The results indicate that the spatial distribution of magnetic moment around the Mn atom deviates significantly from spherical symmetry and that a significant negatively polarized moment is associated with the silicon atom.
Magnetic Anisotropy of Rare Earth Metals
Authors: Bly P. H. , Corner W. D. , Taylor K. N. R. , Darby M. I.
Published: February 2004

Torque measurements have been made to determine K1 on single crystals of Tb, Dy, and Ho. This constant has been measured as a function of field and temperature in the antiferro- and paramagnetic regions. For Dy and Ho, κ1 decreases with decreasing T between TN and TC, changing sign in Ho and becoming large and negative again when ferromagnetism appears. The results are used to estimate critical fields which agree well with those derived from magnetization measurements. In the paramagnetic region K1=βH2 as predicted by Callen and Callen and β∝ (T−TC)−2 where TC is the paramagnetic Curie temperature.

The basal plane constant, K4, has also been obtained for Gd, Tb, and Ho. There is no detectable anisotropy above TC. For Gd the value of K4 varies with T as (σ/σ0)21 and for Tb a good fit is obtained with a function of the form Î13/12[£−1(m)] as suggested by Callen and Callen. The magnitude of K4 extrapolated to 0°K for Gd is −800 erg·g−1; the value for Tb is about 500 times larger. A twelvefold symmetry is obtained with Ho and a further constant, K5, is required to describe the results.
Temperature Dependence of Magnetocrystalline Anisotropy
Authors: Birss R. R. , Wallis P. M.
Published: February 2004

A well-known theoretical treatment of the temperature dependence of magnetocrystalline anisotropy predicts the equality of the reduced first anisotropy constant and the nth power of the reduced spontaneous magnetization where n=10 at low temperatures. To allow for the effect of thermal expansion, the experimental values of this anisotropy constant should be corrected, according to Brenner (1957), by an amount dependent on b3, the third magnetoelastic coupling constant of Becker and Döring (1939).

Measurements of the temperature dependence of magnetostriction constants and of elastic constants are used to calculate b3 as a function of temperature for nickel and it is then found that the experimental value of n is effectively reduced, from about 50 at low temperatures (Carr 1958), to much nearer the theoretical value of 10. A critical examination of possible errors is presented, particularly with reference to experiments in which the pressure dependence of anisotropy is measured.
Time-Dependent Spin-Correlation Function in Ferromagnet and Antiferromagnet
Authors: Oguchi Takehiko , Ono Ikuo
Published: February 2004

A statistical theory of the localized model of ferromagnetism is developed by considering the effective density matrices for a single spin, and two nearest-neighbor spins, respectively. The Ising Model and the Heisenberg model, and even the case of the anisotropic exchange interaction, are treated within a unified mathematical scheme. The result is reduced to that of the Bethe approximation in the case of the Ising model, and the constant coupling approximation in the case of the Heisenberg model. The method is generalized to calculate the static spin-correlation function. It is obtained in Ornstein-Zernike type. In the nonequilibrium state, the expectation value of the spin decays by the homogeneous damping as well as the spin-diffusion process. This relaxation equation is different from that by Van Hove because of the existence of the homogeneous damping. The diffusion constant does not vanish even at the Curie point TC, contrary to Van Hove's result, although the damping constant vanishes at TC. The latter fact causes the critical slowing down of the regression of fluctuation. The solution of this relaxation equation gives the time-dependent spin-correlation function. The method can be applied to the antiferromagnetic case, too.
Magnetic Ordering of Terbium in Some Perovskite Compounds
Authors: Mareschal J. , Sivardière J. , De Vries G. F. , Bertaut E. F.
Published: February 2004

Four perovskite compounds ATbO3 (A = Fe, Cr, Al, Co) are studied by means of neutron diffraction. Three Nèel temperatures are distinguished. When A is magnetic and T < TN1, the A sublattice orders in a G mode; when T < TN2, the Tb sublattice orders and is coupled with A in the same irreducible representation of the space group Pbnm; finally when T < TN3, Tb orders in another mode which is decoupled from A, i.e., Tb orders in a different irreducible representation. The order in the latter case is the only one observed one if A is diamagnetic, and its origin is mainly dipolar. The Néel temperatures are given; the metamagnetism of Tb is studied for T < TN3.
Exchange Constant in Fe–Cr Films from Spin-Wave Resonance Spectra
Authors: Rossing Thomas , Phillips T. G.
Published: February 2004

Spin-wave spectra at 34 GHz have been observed in a series of iron-chromium films of varying composition. The spacing of the modes generally varies with the square of the spin wavevector k with the usual small distortion towards a linear spacing of the first few modes. In addition there is a region at the high mode number end of the spectrum which contains dependence on k4 or higher powers. The magnitude of these higher-order terms in the dispersion relation appears to be correlated with increasing chromium content.

The value of D determined from the k2 portion of the spectrum decreases with Cr content in approximate agreement with the value of D found by neutron-scattering experiments. The decrease of D and the increase of the k4 term with Cr content appear to be in qualitative agreement with the predictions of the itinerant electron model of spin waves in the iron group metals.
Motion of the Magnetic Moment of Thin Magnetic Films in a hf Rotating Field
Authors: Salanskii N. M. , Polskii A. I.
Published: February 2004

This paper is devoted to some spectral investigation of the signal induced by the magnetic-moment motion of thin anisotropic Permalloy films. Film switching was carried out by a rotating field of frequency f=6 Mc/sec. The signal induced by magnetic-moment motion was detected by a measuring coil. Three spectral signal regions may be marked out, depending on the magnitude of the constant and hf rotating fields in the film plane: rotation frequencies, subharmonic oscillations, and higher harmonics.

Rotation-frequency signal-amplitude measurement settled three kinds of magnetic-moment motion depending on the field magnitude: oscillating, partial, and full rotation. There is a continuous spectrum noise near the rotation frequency in the case of partial rotation. A physical model of this spectrum is discussed.

Subharmonic oscillations with ¼, ½, ¾ frequency rotations were also detected. These oscillations arise in the presence of the constant field when the rotating field corresponds to partial rotation.

In the experiments with rotating fields corresponding to full magnetic-moment motion, amplitude harmonic relations are nearly with coherent rotation theory.
Rare Earth Metal Single Crystals. II. Magnetic Properties of Tm, Eu, Sm, and Yb
Authors: Schieber M. , Foner S. , Doclo R. , McNiff E. J.
Published: February 2004

Magnetic-moment measurements are presented for single-crystal Tm, Eu, Sm, and Yb along principal axes. The 4.2°K data for Tm and Eu extend to 140 kG, and the Sm and Yb results, at low field, range from 4.2° to ∼300°K. Almost complete ferromagnetic alignment in Tm is attained for 140 kG along the [101̄0] direction. A value of almost 7 μB is observed. Eu is antiferromagnetic, shows a linear variation of σ vs Bo up to 140 kG (in disagreement with earlier data), and appears to be isotropic. The susceptibility for Yb shows a small isotropic paramagnetic component, possibly caused by impurities. Single-crystal data show that Sm is a uniaxial antiferromagnet with spins aligned along the c axis and TN=14°K.
Variation with Pressure of Magnetic-Ordering Temperature of Rare Earth Single Crystals
Authors: Bartholin H. , Bloch D.
Published: February 2004

The variation with hydrostatic pressure of the magnetic-ordering temperature of rare earth single crystals has been determined under pressure up to 6 kbar. This effect is determined from the thermal variation of susceptibility in an alternating field. A difference between the variation with pressure of the magnetic ordering temperature of the polycrystal of Gd and that of the single crystal is observed. The variation with pressure of the Curie temperature of polycrystalline Gd is (−1.48±0.02)×10−3 °K bar−1 to be compared to (−1.40±0.02)×10−3 °K bar−1 for the single crystal. The variations with pressure of the Néel temperature of Tb and Dy are, respectively, (−0.84±0.02)×10−3 °K bar−1 and (−0.41±0.01)×10−3 °K bar−1. An attempt to analyze these variations leads to the conclusion that the exchange energy is dependent upon volume for the major part through the c dependence of exchange interactions between first-neighbors ferromagnetic planes.
Status of Magneto-optical Experiments on Ordered Rare Earth Compounds
Authors: Leask M. J. M.
Published: February 2004

Rare-earth compounds of interest in this field have ordering temperatures typically in the range 1°−4°K. This in turn implies internal fields of order 10 kOe, and therefore a potentially amenable experimental situation.

A number of such systems have been studied recently, where the magneto-optic effects due to the magnetic order have been studied for both the host rare-earth ion, and for small amounts of other rare-earth ions introduced as probes into the systems. The following are some of the general conclusions to be drawn from this work: (i) the relative sucess of a ``one-ion''-essentially molecular field-picture in explaining effects observed both as a function of temperature and as a function of externally applied field, (ii) the considerable difference between effects seen by host ions and effects seen by probe ions, (iii) observation of magnetic effects at temperatures above the ordering temperature, therefore attributable to magnetic short-range order in the system, and (iv) the considerable difference in detail between short-range-order effects seen in different systems.
Computer Calculations for the Classical Heisenberg Model: Magnetization and Pair Correlation Functions
Authors: Vineyard G. H. , Watson R. E. , Blume M.
Published: February 2004

A computer study has been made of the static and time-dependent behavior of a simple cubic lattice of classical spins interacting through nearest-neighbor Heisenberg forces. The initial conditions have been chosen by a Monte Carlo calculation which also yields the magnetization as a function of temperature. The classical equations of motion of the spins have then been solved numerically for arrays of varying sizes, up to 4096 spins and the pair correlation functions have been calculated using these solutions. The magnetization calculation yields a Curie temperature in good agreement with the prediction of Rushbrooke and Wood, which is based on an analysis of the series expansion for the free energy. Pair correlation functions for various temperatures and various separations show damped oscillatory dependence on time, and are generally complicated. Various special starting configurations not corresponding to thermal equilibrium have also been used.
Stress Dependence of the g-Factors of Yb3+ in ThO2 and Ho2+ in CaF2
Authors: Tachiki M. , Sroubek Z. , Zimmermann P. , Abraham M. M.
Published: February 2004

The changes of the spin-Hamiltonian parameters g and A have been measured for Yb3+ in ThO2 and Ho2+ in CaF2 (both in cubic sites) as a function of applied stress. The stress-induced crystalline field is calculated in point-charge approximation and the g-shifts are obtained from the second-order perturbation calculations of this crystalline field and the Zeeman energy. In the case of CaF2:Ho2+ stressed along [001] and in the case of ThO2:Yb3+ stressed along [111], the contributions of the second-order crystalline field coefficients to the g-shift are dominant, and very good agreements with experiment are obtained without any shielding of the crystalline field. In the case of CaF2:Ho2+ stressed along [111], the correct sign of Δg is obtained, but the absolute magnitude is four times larger than the experimental value. To get agreement with experiment, the contribution of the fourth-order crystalline field coefficient, which is dominant in this case, should be multiplied by 3. The oxygen polarization contribution to the second-order crystalline field coefficient in the case of ThO2:Yb3+ is six times larger than the point-charge contribution, and thus the calculated g-shift becomes five times larger than the observed one. The discrepancy is attributed to the inadequacy of the usually used oxygen polarizability.
Activation Energy and Annealing Kinetics of Remanence Growth Caused by Low-Temperature Magnetic Anneal of Electron-Irradiated Nickel-Iron
Authors: Sery R. S. , Gordon D. I.
Published: February 2004

Defect annealing studies were made on a nickel-iron alloy (79 Ni-16 Fe-5 Mo) irradiated at 35°±7°C with 6×1016 1-MeV electrons/cm2. Samples used were 10-mil thick polycrystalline rings. Magnetic remanence measured at 25°C following magnetic anneals in the 40°−140°C temperature range was the defect-sensitive parameter studied. Isochronal magnetic annealing for 1 h periods with 10°C steps showed a characteristic annealing temperature (Ta) of ∼80°C. Isothermal magnetic annealing curves at 75° and 95°C, used to obtain activation energy (E) by the cross-cut method, gave a value of E=1.07±0.15 eV. As a check on technique, the combined isothermal-isochronal method was used and gave E=1.15±0.2 eV. Second-order chemical-rate annealing kinetics was indicated from the isothermal curves. In a related experiment, Chamberod et al quenched a 50 Ni–Fe alloy and made annealing studies of time decrease of permeability. Their data show Ta between 70° and 110°C and E=1.1±0.15 eV. Because quenching is an established method of introducing monovacancies in metals, the values of E and Ta obtained from annealing the quenched samples can be associated with the migration of vacancies. In view of the fact that the values of E and Ta which we obtained for the electron-irradiated samples match those obtained for quenched samples of similar materials, we infer that the primary defect involved in the process of increasing magnetic remanence in the range of 40°−120°C is the sample vacancy. Its migration during magnetic anneal permits like-atom-pair directional ordering to increase uniaxial anisotropy and remanence.
Diffusion of Gold and Silver in Thallium
Authors: Anthony T. R. , Dyson B. F. , Turnbull D.
Published: February 2004

The diffusivities D of gold and silver in the bcc phase of thallium and in the c and a directions of hcp thallium have been measured by a radioactive tracer technique. The diffusivities of gold are described by  Dbcc=5.2×10−4exp(−6000/RT),Dhcpa=5.3×10−4exp(−5200/RT),and Dhcpc=2.0×10−5exp(−2800/RT) cm2/sec;and those of silver by  Dbcc=4.2×10−2exp(−11 900/RT),Dhcpa=3.8×10−2exp(−11 800/RT),and Dhcpc=2.7×10−2exp(−11 200/RT) cm2/sec. The diffusivities of gold and silver are thus about two orders of magnitude higher than the thallium self-diffusion in the bcc phase and four to eight orders of magnitude higher than the thallium self-diffusion in the hcp phase. These results suggest that gold and silver are dissolved at least partially in the interstitial state in both phases in agreement with a theory which predicts that d-d correlation forces should cause dissolved noble metals to favor interstitial sites in thallium. Moreover, the difference in diffusivities of the noble metals in the two thallium phases indicates that the interstitial solute population is higher in the hcp phase, which has larger interstitial sites, than the bcc phase.
Measurement of Viscoelastic Properties of Evaporated Se Films
Authors: Wronski C. R.
Published: February 2004

Viscoelastic properties of evaporated Se films were investigated at several temperatures between 25° and 40°C by measuring the relaxation of thermally applied stresses. The very large changes in the relaxation times of the stresses in this small temperature range were analyzed in terms of viscosity of the films. Values for the Young's modulus and viscosity were obtained for ∼4 μ Se films. Agreement was found in the temperature dependence of the viscosity of the films and bulk vitreous Se in this temperature range.
Padé Approximant Estimates of the Magnetic Properties of EuO and EuS
Authors: Patterson J. D. , Chen Peter C. Y. , Broz Alfred L.
Published: February 2004

A Padé approximant analysis has been made of the magnetic susceptibility (X) and magnetic specific heat (Cm) of EuS. A similar, less detailed, calculation has been made on EuO. All calculations are limited in accuracy because only a few terms are known in the appropriate power series. Our calculations indicate that the Curie temperature (Tc) for EuS appears to be in the range 14.5°–16.0°K with γ≃1.4, where γ is defined by X→(T-Tc)−γ as T→Tc+). Tc for EuO appears to be in the range 60°–70°K with γ≃1.4. In our calculations for EuS, the exchange integrals of Charap and Boyd (J1/k=0.20°K and J2/k=−0.08°K) were used. For EuO, the exchange integrals J1/k=0.65°K and J2/k=−0.05°K were used. Our results indicate that the exchange integrals of Charap and Boyd can be improved upon. In particular, the set proposed by Passenheim et al. (J1/k=0.20°K and J2/k=−0.06°K) appears to be better. Similar comments are true for EuO. It appears that the Curie temperature predicted by the Padé approximant method provide at least one rather sensitive test for any proposed set of two exchange integrals.
Mechanism of Single-Crystal Growth in InSb using Temperature-Gradient Zone Melting
Authors: Hamaker Raymond W. , White William B.
Published: February 2004

Temperature-gradient zone melting has been utilized to study growth kinetics in InSb. Indium and lead were used as zone metals. In the temperature region between 410° and 460°C, the rate of zone migration was observed to be dependent on both the thickness of the zone and the orientations of the solids at the bounding interfaces. Interface velocities as large as 2×10−6 cm/sec were observed during In:InSb growth runs for liquid zones having an average temperature gradient of 30°C/cm. During Pb:InSb growth runs, interface velocities as large as 0.9×10−6 cm/sec were observed for liquid zones having an average temperature gradient of 60°C/cm. Photomicrographs of growth surfaces obtained after In:InSb growth runs clearly indicated that growth proceeded by a two-dimensional nucleation mechanism. A best-fit comparison with theory of the observed dissolution interface velocity as a function of zone thickness also indicates a two-dimensional nucleation growth mechanism for both the In:InSb and the Pb:InSb systems.
Intrinsic Flux Limits for Continuous and Q-Pulse Gain for the 10.6-μ Line of CO2
Authors: Hotz David F. , Ferrer Joseph N.
Published: February 2004

The limits on flux gain for the 10.6-μ line of CO2 are discussed on the basis of saturation and spectral hole burning. Although an individual P transition is homogeneously saturable, the entire collection of rotational transitions provides a quasi-inhomogeneous character for single-transition operation, which is due to collisional coupling among rotational levels. The experimentally determined cross section for induced emission is shown to agree with the theoretical value upon assuming that approximately 100 rotational levels of the 10°0 vibrational state of CO2 are strongly coupled by collisions. Thus, the induced-emission cross section for a single vib-rotor P branch transition of the 10.6-μ line is found to be 2×10−16 cm2. Using experimentally determined collision cross relaxation rates the cw hole-burning flux is found to be of order 7×105 W/cm2. The hole-burning flux for Q-pulse amplification is estimated to be 1% of the cw value from which one can infer the saturation flux for a single vib-rotor transition to be approx 0.25 W/cm2.
Interacting Components in Beam-Generated Beam-Plasma Systems
Authors: Frey Jeffrey
Published: February 2004

The ratio of the density of plasma electrons or ions, in excess of those required for neutralization, to the electron density in the beam generating the plasma is calculated. It is assumed that ambipolar diffusion is the only mechanism by which these particles drain from the system once the beam is neutralized. Curves of the ratio, as a function of pressure and beam voltage, are given for hydrogen and nitrogen plasmas. Agreement of a result for an argon plasma with experiment is good. In hydrogen, the density of secondary electrons or ions becomes comparable to the beam density at pressures of the order of 10−3 Torr; in nitrogen, the densities are comparable nearer 10−5 Torr. However, since the wave interactions that occur in a system will depend on the relative magnitudes of the components' plasma frequencies, interactions between the beam and secondary plasma electrons may be of importance at pressures lower than those cited.
Instability of Coupled Longitudinal and Transverse Electromagnetic Modes of Wave-Propagation in Bounded Streaming Plasmas
Authors: Bhatnagar P. L. , Raghvachar M. R. , Uberoi C.
Published: February 2004

The instability of coupled longitudinal and transverse electromagnetic modes associated with long wavelengths is studied in bounded streaming plasmas. The main conclusions are as follows: (i) For long waves for which O (k2)=0, in the absence of relative streaming motion of electrons and ions and aωp/c<0.66, the whole spectrum of harmonic waves is excited due to finite temperature and boundary effects consisting of two subseries. One of these subseries can be identified with Tonks-Dattner resonance oscillations for the electrons, and arises primarily due to the electrons with frequencies greater than the electrostatic plasma frequency corresponding to the electron density in the midplane in the undisturbed state. The other series arises primarily due to ion motion. When aωp/c>0.66, in addition to the above spectrum of harmonic waves, the system admits an infinite number of growing and decaying waves. The instability associated with these modes is found to arise due to the interaction of the waves inside the plasma with the external electromagnetic field. (ii) For modes with comparatively shorter wavelengths for which O (k3)=0, the coupling due to finite temperature sets in, and it is found that the two series of harmonic waves obtained in (i) deriving energy from the transverse modes also become unstable. Thus, for these wavelengths the system admits three sets of growing and decaying modes, first two for all values of aωp/c and the third for (aωp/c) > 0.66. (iii) The presence of streaming velocities introduces various other coupling mechanisms, and we find that even for the wavelengths for which O (k2)=0, we get three sets of growing and decaying waves. The numerical values for the growth rates show that the streaming velocities enhance the growth rates of instability significantly.
Transfer Characteristics and Frequency Response of Wide-Band Amorphous-Solid Debye-Sears Light Modulators
Authors: Minkoff J. B. , Bennett W. R. , Lambert L. B. , Arm M.
Published: February 2004

The operation of fused-silica Debye-Sears light modulators is investigated for normal light incidence over a range of conditions such that the effect of amplitude modulation of the light beam by the acoustic wave, as well as phase modulation, must be taken into account. Using the approximations of Raman and Nath, for which the ultrasonic wave can be treated as a phase grating, the relationships between input electrical excitation and the resulting spatial modulation are determined for shear and compression waves. The effect of the length of the light path on the operation of the light modulator is then considered for a range of values for which Raman and Nath's simplified approach is no longer valid. From the results of Bhatia and Noble it is shown theoretically and verified experimentally that, for single frequency excitation, a value of this dimension can be specified such that the effective spatial modulation of the light beam can be maximized. The case of electrical excitation over a finite frequency band is also considered, and a simple expression describing the frequency response of the light modulator, in terms of the total spatial modulation of the light beam, is derived. Measurements of light-modulator frequency response under conditions such that the amplitude-modulation effects are not signficant are presented. These measurements are found to agree with theoretical predictions.
Thermal Stress Problems in Glass
Authors: Woo T. C.
Published: February 2004

The development of the residual stresses in a glass plate undergoing a heat treatment is discussed in the light of viscoelasticity. Emphasis is placed on the method in which measured material functions are used. Advantages are pointed out of such a method versus other existing methods and the extension to an asymmetric thermal stress problem is given for an illustration.
Soft X-Ray Spectroscopy of Alloys: TiNi and the Ni–Al System
Authors: Cuthill J. R. , McAlister A. J. , Williams M. L.
Published: February 2004

Meaningful comparisons can now be made between the soft x-ray spectra of pure metals and theoretical densities of states distributions. The comparison of the Ni-M3 spectrum with theoretical results is shown as an example. Also, useful information can now be obtained from alloy spectra although the analysis of alloy spectra involves all of the problems inherent in the interpretation of pure metal spectra plus additional problems. Overlapping spectra and more complex absorption corrections are two additional problems discussed. In fact, the soft x-ray spectroscopy technique should provide a crucial test of theoretical results on alloy systems. Spectra from a series of Al–Ni compositions and the Ni-M spectrum from TiNi are discussed.
Line Profiles in the Nuclear Magnetic Resonance and Mössbauer Effect of TiFe1−xCox Alloys
Authors: Swartzendruber L. J. , Bennett L. H.
Published: February 2004

The 57Fe Mössbauer effect (ME) and the 59Co nuclear magnetic resonance (NMR) have been investigated as a function of alloy concentration, temperature, and stoichiometry in TiFe1−xCox alloys over most of the range 0≤x≤1. At room temperature, in carefully prepared samples, a single 57Fe ME line was observed for all values of x. This line broadened somewhat at low temperatures, although the magnetic properties of these alloys would have led one to expect a larger broadening at certain compositions. The 69Co NMR linewidth was narrowest for x close to 0 or 1 and was a strong function of x as well as of temperature and magnetic field. The intermediate compositions displayed resolved satellite structures. Annealing reduced both the ME and NMR linewidths. Deviations from stoichiometry and internal oxidation were readily observable from their effect on the ME line profile. Comparisons are made with TiFe2 and stainless steel ME spectra. Both the ME and NMR results for TiFe1−xCox are consistent with a CsCl structure over the entire composition range. The NMR results indicate a lack of atomic ordering on the Co, Fe sublattice.
Isothermal Magnetocaloric Oscillations
Authors: Long Jerome R.
Published: February 2004

The absolute amplitude of entropy oscillations related to the de Haas-van Alphen effect has been measured in a single crystal of tungsten by a straightforward dc technique in which isothermal conditions are employed rather than the adiabatic conditions that exist in the closely related phenomena known as magnetothermal oscillations. The measured amplitudes are in good agreement with the usual theories of the de Haas-van Alphen effect, when previously determined details of the tungsten Fermi surface are assumed. Some arguments on the validity of amplitude measurements are discussed.
Vapor-Deposited Nb3Sn Ribbons
Authors: Schindler Henry C.
Published: February 2004

The electromagnetic performance of high-field type-II superconductors is significantly affected by structural factors such as crystal size, crystal orientation, or crystal strain. Because the vapor-deposition process for depositing single-phase, polycrystalline, stoichiometric Nb3Sn on a heated moving substrate permits control of these structural parameters, this technique is used for the deposition of continuously monitored layers of Nb3Sn on long lengths of ribbon substrate. The thickness of teh Nb3Sn layer is controlled and can be readily varied to meet specific magnet requirements. For small-bore, high-field, layer-wound magnets, a family of commerical 0.090-in.-wide ribbons has been developed. For larger-bore magnets, in which ``pancake''-type construction is desirable, a commercial line of ½-in.-wide ribbons is currently being offered. Custom-size ribbons have been made as narrow as 0.025 in. and niobium stannide has been deposited on wires as thin as 0.005 in. in diameter. This paper describes these different ribbons and discusses their electromagnetic performance. Normalized curves have been developed for calculation of short-sample critical currents as a function of volume of niobium stannide. For instance. from 20 to 95 kG, normalized critical current In (i.e., the ratio of critical current at any desired field to the critical current at 100 kG) can be expressed as follows: In=Ic/I100 kG=exp(−0.0152H+1.597). From 95 to 140 kG, the following approximate expression can be used: In=Ic/I100 kG=exp(−0.02581H+2.592),where Ic is the critical current at the desired magnetic field, I100 kG is the critical current at 100 kG, and H is the magnetic field in kG. The current density of the Nb3Sn layer in the various types of vapor-deposited ribbon remains essentially constant. When a constant current density at 100 kG is used for the various Nb3Sn layer thicknesses, the Nb3Sn thickness and the ribbon width can be incorporated into the expression for critical current from 20 kG to 95 kG as follows: Ic=(W/0.090)37.4×104(t−7.5×10−5)exp(−0.0152H+1.597). From 95 kG to 140 kG, the following expression applies: Ic=(W/0.090)37.4×104(t−7.5×10−5)exp(−0.02581H+2.592),where W is the ribbon width in inches and t is the Nb3Sn layer thickness in inches. These data are discussed in detail. The critical currents obtained in actual magnets are often lower than the short-sample performance. In many magnet applications, it is economically desirable to obtain the highest possible current density. To achieve these goals, it may be necessary to compromise the amount of normalized metal parallel to the superconductor. Specific examples of optimization of magnet current density as a function of silver plating and cooper cladding of the superconductor ribbon are described.
Mechanical and Electrical Properties of Diffusion-Processed Nb3Sn-Copper-Stainless Steel Composite Conductors
Authors: Benz M. G.
Published: February 2004

Diffusion-processed Nb3Sn has high current density at high magnetic fields. When combined with copper or copper and stainless steel in the form of a flat laminated tapelike conductor, it also has flexibility, low normal-state resistance, and the ability to withstand high tensile stress. This paper considers various laminated conductors that have been constructed, with emphasis on mechanical as well as electrical performance characteristics. Design methods and subsequent test evaluation for performance characteristics are discussed.
Peak-Effect Studies on Niobium Nitride
Authors: Maxwell E. , Schwartz B. B. , Wizgall H. , Hechler K.
Published: February 2004

Observations of the temperature dependence of the peak effect in Nb–N between 4.2° and 1.35°K indicate that the field at which pinning effects set in is independent of temperature in this range. It is suggested that the repulsion between neighboring flux bundles acts to enhance flux pinning in the peak region.
The Anisotropic Structured Cell: A Practical Cryoelectric Storage Element
Authors: Gange R. A.
Published: February 2004

The realization of a fast random-access memory through application of cryoelectric technology is an attractive goal. The substantially perfect diamagnetism which characterizes the superconducting state permits the design of storage elements of very high packing density. The very low power densities and the extreme nonlinearity in the transition between the superconducting and normal states promise very fast operation of these elements with no half-select or delta noise. In addition, the number of memory positions that can be sensed appears to be quite large. In this paper, I describe the design concepts and performance of a three-wire1 cryoelectric storage element called the Anisotropic Structured Cell. Included is a comparison of the performance of the ASC storage elements as compared to loop cells of earlier design, and a discussion of the sense amplitude, signal-to-noise ratio, cell-to-cell isolation, operating tolerance, and operating current levels of high-density (13 200 cells/in.2) ASC arrays of ¼ million bit capacity. The paper also contains a first-order analysis of the use of these ASC elements in a large and practical high-speed cryoelectric memory organized in accordance with the hybrid, a, b, system.2
Tunneling Cryotron Flip-Flop
Authors: Matisoo J.
Published: February 2004

We have constructed tunneling cryotron flip-flops, have observed current transfer from one leg to the other, and have measured the time required for current transfer to be 2 nsec. The results are in agreement with the model previously proposed.1 The tunneling cryotron flip-flop consists of two devices in parallel, linked by a wholly superconducting path. A current is fed to the parallel devices; the current is steered from one device to the other by application of a control pulse. The measurements have been made on a loop of 1.16 in. in length (L=1.08×10−10H), containing two 10 mil diam junctions, having zero-field critical currents of 21 mA and 29 mA, respectively (in operation these are biased to near maxima on the gain curves, at 33 mA and 42 mA). The measuring apparatus is similar to that previously described.1 In operation, a current of 20 mA is transferred from one device to the other by the application of a 2 mA control pulse, a gain of 10. The time required for this current to transfer, Δttransfer, is 1.4 nesc≤Δttransfer≤2.0 nsec, with an uncertainty of at most 0.4 nsec. According to the previously proposed model of a constant gap voltage driving the loop inductance and which does not include the junction transition times (Ref. 1), the transfer time for 20 mA of current should be 2 nsec. One implication of this excellent agreement is that the junction transition time is appreciably smaller than the previously measured upper bound of 800 psec.2 Additional operating details will be discussed.