bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anomalous Behavior of the Negative Magnetoresistivity in Au-Fe Alloys
Authors: Rohrer H. 
Published: January 2005

The magnetoresistivity of dilute Au-Fe alloys containing 0.1 at.% to 1 at.%Fe has been measured in the temperature range 2° to 77°K and in magnetic fields up to 200 kOe. Although the residual resistivity ρ is proportional to the Fe concentration, the negative magnetoresistivity Δρm/ρ, due to the freezing out of the contribution of the exchange scattering, drops rapidly with increasing Fe concentration. We find Δρm/ρ = − (A + Bc)−1, where c is the Fe concentration in at. % and A and B are parameters which depend on temperature and magnetic field. At low temperatures A and B are positive and of comparable magnitude; B is decreasing with both increasing field and increasing temperature. Above 22°K, B is small and negative.
At low temperatures, two anomalies of the magnetoresistivity are observed: First, in the highest fields applied no saturation of Δρm is obtained and second, below a certain temperature T0, Δρm is no longer a function of μH/kT only, as theoretically expected [except for very slowly varying terms of the form ln (EF/μH)]. These anomalies become more pronounced with increasing impurity concentration. T0 increases from 10°K for 0.1 at.%Fe to about 50°K for 1.01 at.%Fe. By extrapolating Δρm/ρ to zero Fe concentration these anomalies remain. Therefore, they seem to be intrinsic and are merely enhanced by correlation effects between the impurities.
Further, from the temperature dependence of the zero-field resistivity and the high field resistivity, the s-d interaction parameter, J, was obtained to be 0.064 eV &lt; J &lt; 0.1 eV. This value of J is considerably smaller than previously reported for similar alloy systems like Cu-Mn, Y-Ce and others. It is shown that the reason for such high values of J is an incorrect application of Kondo's expression for the exchange resistivity.
Dependence of Magnetic Anisotropy on the Crystal Structure of Ni–Fe Thin Films
Authors: Suzuki T. , Wilts C. H. 
Published: January 2005

The induced magnetic anisotropy of Ni–Fe films has been shown to be related to the crystal structure of the film. By use of electron diffraction, the crystal structure of vacuum-deposited films was determined over the composition range 5% to 85% Ni, with substrate temperature during deposition at various temperatures in the range 25° to 500°C. The films were deposited on single-crystal NaCl substrates. The phase diagram determined in this way has boundaries which are in fair agreement with the equilibrium boundaries for bulk material above 400°C and deviate markedly below 300°C. The (α+γ) mixture phase disappears below 100°C. Although epitaxial growth occurs at high temperatures, the existence or absence of epitaxy has no significant effect on the type of crystal growth.
Comparison of these data with measured values of the anisotropy energy indicates that the anisotropy is strongly sensitive to structure. The anisotropy energy for γ structure is about 2½ times larger than for α structure at the composition where the anisotropy can be measured for the α structure and extrapolated with reasonable confidence for the γ structure. Others have proposed pair ordering as an important source of anisotropy because of an apparent peak in the anisotropy energy at 50% Ni composition. The present work shows that there is no such peak, and therefore pair ordering cannot be a dominant contributor.
Magnetic Properties of the Systems HgCr2S4–CdCr2S4 and ZnCr2Se4–CdCr2Se4
Authors: Baltzer P. K. , Robbins M. , Wojtowicz P. J. 
Published: January 2005

The distribution of magnetic ions and the crystallographic parameters remain essentially constant throughout the system Hg1−xCdxCr2S4. A study of the magnetic properties of this system was therefore undertaken in order to further elucidate the origin of the large difference in the magnetic properties already reported on the endpoints. The Curie temperature was found to increase nonlinearly from 36.0° to 84.5°K as x varies from 0 to 1. The low-temperature F-AF (ferromagnetic-antiferromagnetic) transition and metamagnetism of HgCr2S4 penetrate well into the system, up to x≃0.37 at which the F-AF transition temperature approaches 0°K.
The distribution of magnetic ions remains constant, but the crystallographic parameters vary in the system Zn1−xCdxCr2Se4. Nevertheless, since ZnCr2Se4 is an antiferromagnetic with large positive θ, while CdCr2Se4 is a ferromagnet, a magnetic study of this system provides further evaluation of the theory of the ferromagnetic spinels. In addition, the evaluation of the nonlinear variation of ferromagnetic Curie temperature from 22° to 129.5°K, observed for x=0.35 to 1, permits qualitative evaluation of the exchange parameters of ZnCr2Se4. The Néel temperatures were found to be ≃20°K for the whole antiferromagnetic region of the system x=0 to 0.35. F-AF transitions in zero field and/or metamagnetism are also observed over a large compositional region.
Magnetic Critical Point Exponents—Their Interrelations and Meaning
Authors: Fisher Michael E. 
Published: January 2005

The definitions and determination of the thermodynamic magnetic critical point exponents α, α′, β, γ, γ′ and δ are reviewed, and ``gap exponents'' Δ and Δ′ for the divergences of higher derivatives of the free energy with respect to the field are introduced. The rigorous inequalities relating the exponents are discussed.
The ``microdomain'' or ``cluster'' model of ferromagnetism leads to relations between these exponents since it expresses them in terms of two underlying exponents σ and τ. The exponent σ is directly related to the effective surface free energy of a large microdomain and thence to the dimensionality. This yields some insight into the meaning of the observed exponent values and of the differences between the critical behavior of the Ising and Heisenberg models. The recently developed homogeneity and scaling arguments are presented. These generate the same thermodynamic exponent relations and further ones for the correlation exponents η, ν and ν′. They also indicate that a general law of corresponding states might hold in the critical region. Theoretical and experimental evidence on the validity of these various ideas is briefly reviewed.
Concentration Profile of Superparamagnetic Precipitates
Authors: Kneller E. , Trippel G. 
Published: January 2005

According to previous work the temperature variation of the initial susceptibility, χ0, of superparamagnetic Cu–Fe–Ni alloys deviates from Curie's law, Ms2/χ0 = CT (Ms = spontaneous magnetization). After tentatively correcting for magnetostatic interaction effects with the first order Debye term, the data could be analyzed quantitatively in terms of a temperature-dependent ferromagnetic particle volume which follows from a gradual concentration transition (interface) between precipitates and matrix. Based on this analysis the interface thickness, Δρ, was determined on 74Cu2Fe24Ni for the aging temperature Θ≡TA/TS≃0.95 (TS = critical temperature of the precipitation); Δρ≃12 Å.
In this work the variation of Δρ with TA was studied. For 71Cu3Fe26Ni, Δρ decreases from 17A for Θ = 0.97 to 6.5 A for Θ = 0.915, following the theoretical relation Δρ ∝ (TS−TA)−1/2. For Θ = 0.85, Ms2/χ0 nearly follows Curie's law. This explains why no interface effect was detected on other alloys for Θ &lt; 0.6. Furthermore, it is shown that the Debye interaction correction is applicable in all of the above mentioned work. Finally, it is indicated how the actual concentration profile of precipitates may be determined from experimental data of χ0(T).
On the Coercivity of γFe2O3 Particles
Authors: Eagle D. F. , Mallinson J. C. 
Published: January 2005

Over the temperature range −180° to 300°C, measurements have been made of the coercivity of 5:1 acicular γFe2O3 particles. Samples of two different lengths, 2000 and 6000 Å, were included in the study. The coercive force is linearly dependent upon two terms, shape (αM) and magnetocrystalline (βK/M). These may be separated by reducing identical particles to Fe3O4 and measuring their coercive force at the isotropy point −143°C, yielding the shape factor α. It is found that the shape term accounts for approximately 67% of the observed room-temperature coercive force. The shape term is almost independent of particle diameter and fits well with the ``chain-of-spheres'' reversal model. The remaining 33% of the coercivity has the same temperature dependence as the coercive force of cubic γFe2O3 particles, thus confirming its magnetocrystalline origin.
The room-temperature coercivity of cobalt-doped cubic particles was measured as a function of particle diameter. Over the diameter range 300–1000 Å the data again fits the linear addition of shape and magnetocrystalline terms. The shape term is diameter-dependent and fits the micromagnetic ``curling'' reversal model which has been found previously only in metallic whiskers.
Effects of Applied and Residual Stress on the Magnetoresistance of Nickel
Authors: Bagchi D. K. , Cullity B. D. 
Published: January 2005

The magnetoresistance of annealed nickel was measured under both tensile and compressive stresses up to 10 000 lb/in.2 (7.0 kg/mm2). The zero-stress value of ΔR/R (1.88%) was increased to 2.48% by tension and decreased to 0.29% by compression.
The magnetoresistance was also measured after increasing amounts of plastic elongation; the values of ΔR/R measured at 550 Oe were found to decrease with increasing amounts of plastic strain. This result is compatible with a residual microstress distribution in which the volume fraction of the specimen in compression equals or exceeds the volume fraction in tension.
The elastoresistance ΔR/R of annealed nickel was found to be 1.46% at 8000 lb/in.2 compression (5.6 kg/mm2) and −0.60% for the same stress in tension. Elastoresistance measurements on deformed specimens do not lead to any conclusions about the residual stress state.
Dislocation Mobility and Motion under Combined Stresses
Authors: Baker G. S. , Carpenter S. H. 
Published: January 2005

Measurements of dislocation damping as a function of static biasing stress and during deformation have been carried out on single-crystal, high-purity tantalum. The results show that the dislocation mobility for small periodic stresses is orders of magnitude greater than for large constant stresses. The change in flow stress Δσ due to the application of a small periodic stress σv is proportional to σv2. This second-power dependence of Δσ on σv is shown to result from thermal activation of the deformation. Calculations of activation energies and volumes using the point-defect theories of Gilman and Fleischer give reasonable values.
The large difference in dislocation mobility between the periodic type motion and the unidirectional motion indicates that the thermal component of the flow stress is not due to a Peierls-type mechanism, but to discrete dispersed barriers to dislocation motion.
Surface Self-Diffusion of Nickel and Platinum
Authors: Melmed Allan J. 
Published: January 2005

The surface rearrangement of nickel and platinum due to (1) an electric field (build-up) and (2) surface tension (annealing) as the net driving force, has been studied by field-electron emission microscopy over the temperature range 510°–750°K for Ni and 550°–850°K for Pt. An Arrhenius-type relationship between temperature and time was found in both cases, so that an activation energy could be associated with each process. It is assumed that this is an average activation energy for surface diffusion.
The results of the field build-up experiments gave an activation energy of Qf=19.1±1.9 kcal/mole for Ni over the negative field range (28–38)×106 V/cm, and Qf=26.3±2.6 kcal/mole for Pt over the negative field range (27–39)×106 V/cm. It was possible to measure the effect of the electric field using a method devised earlier by Bettler and Charbonnier. This gave calculated zero-field activation energies of 20.6±2.1 kcal/mole for Ni and 29.7±3.0 kcal/mole for Pt. The results of the annealing experiments (no electric field) gave an activation energy of Q0=21.4±2.1 kcal/mole for Ni and 29.5±3.0 kcal/mole for Pt. (The foregoing indicated uncertainties are estimated over-all limits of error.) It is concluded from the agreement between the results of the two different types of measurement that either type of measurement (for fcc metals) may be used to determine the same quantity within a 10% uncertainty.
Effect of Contamination on the Adhesion of Metallic Couples in Ultra-High Vacuum
Authors: Johnson K. I. , Keller D. V. 
Published: January 2005

The present work is concerned with determining the factors controlling the adhesion of metal couples. Most previous studies have been done in the presence of contaminants and, under these conditions, an energy barrier for adhesion has always been observed. This barrier has been ascribed to various factors: the need to disperse the contaminants so that metal-metal contact and, consequently, adhesion, can occur; the energy required to realign the surface metal atoms to form an interfacial bond; and, for lightly loaded conditions, the necessity to overcome the elastic relief stresses which may break any bond formed during the unloading of the couple. A further condition for adhesion which has been postulated, is that the metal couples must be mutually soluble.
The present adhesion experiments show that contaminant dispersal is the major barrier to adhesion. Thus, spontaneous adhesion occurred under vacuum conditions for the three systems studied when the surfaces were sufficiently clean, whereas subsequent contamination resulted in nonadhesion. Substantial amounts of contamination could, however, be tolerated. The contaminants may be divided into two classes, stable surface films and mobile gaseous or liquid films. While both are barriers to adhesion, the latter may be removed by application of a vacuum, whereas the former requires a more rigorous treatment.
Because adhesion occurred for clean surfaces under vacuum conditions, even where elastic deformation predominated, the postulated energy barrier of adhesion due to the realignment of the surface atoms is considered of minor importance, at least for the softer metals studied here. Further, no evidence for rupture of the bonds by the elastic relief forces on unloading such lightly loaded clean couples has been observed. The latter effect, however, is thought to become more important whenever stable surface films are present, because of the limited metal-metal contact.
Since the one immiscible system studied here showed as great a tendency to adhesion as the miscible systems, the condition of bulk miscibility is considered no criterion per se for adhesion.
Domain-Wall Motion in Barium Ferrite Single Crystals
Authors: Asti G. , Colombo M. , Giudici M. , Levialdi A. 
Published: January 2005

The 180° domain-wall motion in barium ferrite single crystals has been studied by the pulsed-magnetic-field technique described in a previous article.
The domain-wall velocity has been measured as a function of the internal magnetic field in a range from 50 to several hundred Oe and at temperatures of 80° and 293°K. The rate of increase of the applied magnetic field dHa/dt has no apparent effect if it does not exceed 1.6 kOe/μsec. Reasonable agreement is found between the wall velocities as measured and values foreseen on the basis of the model proposed by Hagedorn and Gyorgy to explain wall mobility in YIG.
An accurate analysis of the dependence of the wall velocity on the magnetic-field intensity suggests the existence of a threshold field Ht, which depends on the value of the damping constant α and defines the point of transition from one motion mechanism to another. We think that Ht may be identified with the critical field H0=2παMs which appears in a solution given by Walker to the domain-wall equations, and that the model proposed by Hagedorn and Gyorgy simply applies to the case H&gt;Ht. This means that, rather than the damping constant α alone, the quantity k=H/2παMs is to be taken as a suitable parameter to distinguish between different motion mechanisms.
Simultaneous Occurrence of and Competition between Stimulated Optical-Scattering Processes in Gases
Authors: Minck R. W. , Hagenlocker E. E. , Rado W. G. 
Published: January 2005

Using the gain coefficients for individually stimulated Brillouin and Raman transitions in gases, we have been able to predict the pressure and temperature at which the gain coefficients for various transitions are equal. The competition between simultaneously stimulated optical-scattering processes has been studied in the vicinity of these predicted intersections. Within a limited range of parameters, two processes can be stimulated simultaneously. The experimentally observed gain for the weaker process is affected by the presence of the intense Stokes beam associated with the dominant process in some instances, but not in others. Using idealized models, the enhancement of the gain coefficients due to the presence of additional intense-frequency components and the reduction of gain due to depletion of laser power have been considered, but neither effect yields a consistent explanation of the observed behavior.
The competition between vibrational Raman-vibrational Raman, vibrational Raman-rotational Raman, Raman-Brillouin, and forward-reverse propagating Raman were studied. In all of these experiments, no evidence for enhancement of gain, but several examples of reduction in gain, were observed.
Observations of Sub-Unit-Cell Stacking Elements in Mixed-Layer Structures by Electron Microscopy
Authors: Cook C. F. 
Published: January 2005

The ``hexagonal ferrites'' comprise a quasipolytypic series of ferrimagnetic oxides containing Ba, Fe3+, and a divalent metal cation (Me2+). These encompass a family of hexagonal and rhombohedral mixed-layer structures derived by the c-axis stacking of two complex invariant building blocks, mainly ``M'' and ``Y''. The M stacking element is a 5-anion-layer block, 11.6 Å in height with the composition BaFe12O19, and the Y stacking element is a 6-anion-layer block, 14.5 Å high with the composition Ba2Me22+Fe12O22. The largest series, M2Yn(n=0 to 21), involves the stacking of two M blocks and a variable number of Y blocks. Permutation of the M and Y elements allows mixed-layer polytypism within a given stoichiometry, i.e., M to Y ratio. More than twenty (20) mixed-layer structures and their polytypes have been examined by electron microscopy after direct replication of the basal face.
Basal faces which were etched with dilute hydrochloric acid exhibit etch steps of sub-unit-cell heights. The specific M and Y stacking sequence of a mixed-layer structure may be obtained by measuring the step-height ratio, MYx/MYn−x, of two adjacent steps, provided either the shadow angle or the x-ray c-axis dimension is known. In addition it has been found that the c-axis dimension and the specific stacking sequence may be uniquely determined by counting the individual M and Y building blocks which are replicated as separate and distinct etch-planes on a crystal surface that has been process-etched.
Double Magnetic Resonance of Coupled Spins
Authors: Bates Clayton Wilson 
Published: January 2005

A perturbation procedure is introduced to solve for the probability amplitudes of a system of coupled spins under the action of two rf magnetic fields; one a large saturating signal, the other a relatively weak one. The power absorbed when the saturating signal connects two states in the system is affected by the presence of the second signal connecting two other states especially if both signals have one state in common. The mixing of these states by the saturating signal can become large enough in some instances that it becomes meaningless to speak in terms of population differences and rate equations for these levels. It is further shown that the effect of the intermediate levels is to cause a shift in the resonance frequency for these levels. For widely spaced levels this ``intermediate'' effect may be neglected, but for closely spaced levels it can become appreciable.
A four-level system is used to illustrate the method. Relaxation effects are neglected.
X-Ray K Absorption Edges of Alloys. II. Nickel-Cobalt and Nickel-Iron Solid Solutions
Authors: Donahue Raymond J. , Azároff Leonid V. 
Published: January 2005

Changes taking place in the fine structure of the cobalt K edge in Ni-Co solid solutions indicate a decline in the 3d-4s hole density at cobalt atom sites. Changes in the Ni K edge in the same alloys suggest that the hole density at nickel atoms increases, thus supporting the rigid-band model for these alloys.
Significant changes in the Ni K edges of fcc (gamma) Ni-Fe solid solutions suggest that the rigid-band model may be valid for these alloys also. It does not appear to be applicable, however, to bcc (alpha) solid solutions. In both alloy types, the fine structure at the Fe K edge remained unchanged. Good agreement was obtained with magnetic measurements on bcc Ni-Fe alloys.
Breakdown Conduction in Al-SiO-Al Capacitors
Authors: Budenstein Paul P. , Hayes Paul J. 
Published: January 2005

Destructive breakdown has been studied in Al-SiO-Al capacitors using transmission electron microscopy and electron diffraction, while the capacitors were subjected to controlled electrical stresses. Extensive electrical measurements were made outside the electron microscope on other capacitors. The purpose is to describe destructive breakdown and to relate it to prebreakdown conduction, conditions of fabrication, and capacitor structure.
It is found that breakdowns originate at inhomogeneities in the dielectric which appear in electron micrographs as irregularly shaped dark spots about 0.5 μ in diameter. The structure of these dark spots has not been determined. Breakdowns are not concentrated at pinholes, dust spots, or fissures. Breakdown is accompanied by the growth of crystalline silicon. Electrical measurements with a given capacitor reveal two well-defined polarity-sensitive threshold voltages, one for the onset of breakdown and one for the cessation of breakdown. Both are virtually independent of temperature from 80° to 380°K. The voltage threshold for the onset of breakdown varies approximately as w1/2, where w is the dielectric thickness, while the voltage threshold for the cessation of breakdown is found to be independent of dielectric thickness. The diameter of a typical breakdown is 10 to 100 μ. The conductivity of the breakdown site at the onset of breakdown changes by a factor of about 1010 in a time less than 0.1 μsec. Duration of a breakdown is usually about 1 μsec.
A breakdown mechanism is proposed that is based upon an electrochemical solid reaction in the presence of the breakdown electric field: Si−O−Si+(breakdown electric field)→Si−Si++O+e,where the term Si−Si+ means the two silicon atoms are in crystalline form and one is singly ionized. A description of the breakdown process is given using this reaction.
Flash Evaporation and Thin Films of Cuprous Sulfide, Selenide, and Telluride
Authors: Ellis S. G. 
Published: January 2005

Films of Cu1.8S have been made by flash evaporation. They have a resistivity of 6.2×10−4Ω·cm and an absorption coefficient to 1.5 eV radiation of 1.13×103 cm−1. The corresponding quantities for Cu1.8Se are: 1.6×10−4Ω·cm, and 1.18×103 cm−1. The resistivity of Cu1.8Te films increases with time.
It is found that if during flash evaporation the ratio of partial pressures of Cu and Se at the substrate fluctuates then the film does not have the composition of the charge.
Cu1.8S has potential applications for producing transparent conducting coatings on substrates which cannot be heated above room temperature.