bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetostress Effects in Evaporated Ni Films
Authors: Klokholm E. , Freedman J. F.
Published: January 2005

The residual stress in 1000-Å-evaporated Ni films has been measured as a function of substrate temperature Ts. For Ts < 100°C, the stress is tensile and decreases with increasing Ts; at about 100°C, the tensile stress changes to compressive stress. As Ts increases beyond 100°C, the stress becomes increasingly compressive. A maximum in the compressive stress is observed at about 150°C, and then the stress decreases. Planar hysteresis loops obtained from a vibrating sample magnetometer show severely sheared loops for specimens under tensile stress; for specimens in compression the hysteresis loops are almost square. It has also been observed that the saturation magnetic moment of the films depends on the vacuum during deposition. Films deposited at a pressure of 10−7 Torr have larger moments than those prepared at 10−5−10−6 Torr. Although the magnetic moment depends on the degree of vacuum, the stress does not. Magnetic resonance and torque measurements show that the resonance field for the uniform mode, and the perpendicular anisotropy constant, can be directly correlated with the stress in these films. Recent reports of the anomalous behavior of the perpendicular anisotropy constant of Ni films with Ts are, therefore, actually due to the variation of the stress with substrate temperature.
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.
A Basis for Some of the Variety of Magnetic Properties of the Heavy Rare-Earth Metals and Alloys
Authors: Wollan E. O.
Published: January 2005

A molecular field analysis has been made for the TbY alloy system, and the results relative to the initial magnetic ordering properties are discussed in terms of their implication for the heavy rare-earth metals and for alloys with Y, Sc and La. The results indicate that the similarities and differences in these magnetic systems can be closely correlated with the crystal parameters which determine the distances between magnetic atoms in a particular metal or alloy. Ordering temperature changes that result from atomic size effect and pressure-induced volume changes are compared and found to agree. Transition temperatures for alloys for which the axial ratios and atomic volumes are held constant are found to vary linearly with the effective spin variable. The over-all results are found to be qualitatively consistent with an RKKY type of interaction.
Computer-Aided Design of Ferrite Devices using Intrinsic Material Parameters
Authors: Allen J. L. , Taft D. R. , Hurd F. K.
Published: January 2005

A quantitative design procedure has been developed for a number of ``latching'' and analog ferrite devices which enables accurate prediction of both their loss and phase characteristics given the intrinsic material parameters and dimensions of the device structure. Radio-frequency magnetic properties of remanent state materials are represented by an ``averaged'' complex tensor permeability which takes into account the average effects of domain structure and permits loss and phase to be related to properties such as intrinsic linewidth, anisotropy field, and saturation and remanent magnetization. Phase and loss characteristics for each device are obtained by a computer-aided solution of the pertinent boundary value problem. Excellent agreement is obtained between analytical predictions and measured characteristics.
Effects of Heat Treatment on the Anisotropy Field of Hexagonal Ferrites
Authors: Greenwood R. E. , Rodrigue G. P.
Published: January 2005

The magnetocrystalline anisotropy field of aluminum-doped, hexagonal ferrites is varied and controlled through thermal quenching. This heat treatment is a fine control that can continuously vary the anisotropy field of finished, ground pieces by ∼10%. The change in anisotropy field arises from changes in site occupancy of the aluminum ions with quenching temperature.
Magnetic Loss in Remanent-State Toroids
Authors: Rodrigue G. P. , Allen J. L. , Taft D. R.
Published: January 2005

By characterizing remanent toroids as an assembly of saturated regions, an effective permeability tensor can be obtained that accurately predicts the loss in latching ferrite phase shifters. In this model, low power loss is directly related to the intrinsic linewidth of the material. Different domains experience differing effective bias fields, and this variation of effective field with saturation magnetization seems to accurately account for the observed dependence of threshold power on magnetization through conventional spin-wave arguments.
Utilization of Polycrystalline Antiferromagnetic Materials for Nonreciprocal Devices at Millimeter Wavelengths
Authors: De Meo E. A. , Heller G. S.
Published: January 2005

The components of the susceptibility tensor, including loss, for polycrystalline uniaxial antiferromagnetic materials are similar in form to the Polder tensor components, suggesting the feasibility of constructing nonreciprocal phase-shift or resonance-absorption devices at millimeter wavelengths using these materials. Plane-wave propagation in these materials has the same dependence on the susceptibility components as propagation in ferrite media. Using perturbation theory, figures of merit for both resonance isolators and phase shifters have been computed for typical material parameters. For a phase shifter the figures of merit are of the same order of magnitude as those for a ferrite operating at the usual microwave frequencies. For resonance isolators, the on-axis single-crystal linewidth of the polycrystalline antiferromagnetic will have to be an order of magnitude less than the linewidth of a polycrystalline ferrite to yield the same figures of merit.
Dependence of Ferromagnetic Resonance Linewidth on Structural Defects in Single Crystals of Lithium Ferrite
Authors: Lepore D. A. , Belt R. F. , Nielsen J. W.
Published: January 2005

Submicroscopic defects have been established as the major cause of linewidth in lithium ferrite single crystals. Over 100 highly polished lithium ferrite spheres showing no microscopic defects exhibited ΔH's ranging from 2 to 60 Oe. Spheres of low ΔH and high ΔH were chemically polished and etched. Low ΔH spheres had very few pits; high ΔH spheres were severely mottled and etched. X-ray topography and etching of (111) plates have confirmed that regions with defects >105 cm−2 exist near regions of only 102 cm−2. The regions are often separated by a sharp boundary along 〈110〉. Spheres prepared from very low-pit-count material repeatedly had ΔH's of <2 Oe before heat treatment. The defects appear to be dislocations and compositional variations. Heat treatment at 850°C caused no observable change in x-ray topographs. By careful selection of the crystals of low defect content, ΔH's as low as 0.87 Oe at 5.1 GHz and 25°C have been observed.
Properties of Manganese-Permalloy Films
Authors: Griest A. J. , Flur B. L.
Published: January 2005

Thin ferromagnetic films of Ni-Fe-Mn alloys with nominal manganese contents of 3%, 5%, 8%, and 12% have been prepared from alloy cathodes by bias sputtering. The resulting film compositions selected closely parallel the null magnetostriction contour in the ternary composition diagram. The effects of substrate temperature (100°−350°C) and film thickness (500–1200 Å) on wall-motion threshold H0, anisotropy field Hk0, dispersion α90, skew Δβ, and magnetostriction have been experimentally determined. The following conclusions can be drawn from the data: (1) There is a minimum-film bias potential at which uniform films exhibiting low dispersion of the easy axis are obtained. (2) For constant thickness and substrate temperature, H0 and Hk0 decrease with increasing manganese content. (3) For constant H0/Hk0 ratio, angular dispersion increases with increasing manganese content. (4) The alloys containing 3% and 5% Mn show the typical dependence of H0 and Hk0 on deposition temperature (i.e., H0 increases and Hk0 decreases with increasing deposition temperature). (5) For films of the 8% Mn alloy, H0 is relatively insensitive to deposition temperature. (6) For films of the 12% Mn alloy, H0 decreases with increasing deposition temperature.
The Microprobe Tester—An Instrument for the Local Evaluation of Magnetic Films
Authors: Zappe H. H.
Published: January 2005

The microprobe tester consists of two orthogonal loops wound around a nonconductive probe. One of these loops carries a sinusoidal, high-frequency current which causes a small local oscillation of the magnetization when the probe is held near the surface of the film. The resulting stray flux induces a voltage in the orthogonal loop. The second harmonic component of this voltage is filtered out and amplified. This second harmonic is used for a precise measurement of the main film parameters. Plots equivalent to B-H and cross-loops are obtained, and domain boundaries can be mapped. The instrument is basically inexpensive, insensitive to mechanical vibrations, and its measurements are independent of film reflectivity.
Electrodeposition of Thin Magnetic Films in the Ni–Fe–Cu System
Authors: Brownlow J. M.
Published: January 2005

A method for the electrodeposition of highly oriented thin magnetic film has been developed, with which it is possible to control, quite reproducibly, the composition of the film not only over large areas, but also throughout the film thickness. This is especially important in memory applications where magnetostriction must be carefully minimized to avoid skew effects and aging. 400- Å films have been electrodeposited on substrates of evaporated copper or silver on glass, such that they yield a coercive force of 5 Oe, anisotropy field of 4 Oe, and a dispersion of 3 deg (α90). At 1000 Å the dispersion is uniformly 1°. The properties and their thickness dependence are found to be very similar to those found in Ni–Fe evaporated films. A ternary alloy (68 Ni, 16 Fe, 16 Cu) is used to achieve control over the deposition process. The films are deposited from a highly buffered, dilute, nonagitated bath using a sequence of current pulses. 120 Å is deposited per pulse.
Magnetic Properties and Annealing Behavior of Electrodeposited NiFeS Thin Films
Authors: Luborsky F. E.
Published: January 2005

Zero magnetostrictive films of FeNi with sulfur contents up to ∼6.5% by weight were prepared by electrodeposition from electrolytes containing thiourea. The total sulfur content in the films increased linearly with thiourea coacentration. The Hc varied from about 10 Oe for no thiourea, down through a broad minimum of about 4 Oe at intermediate thiourea concentrations. The dispersion α90 also went through a broad minimum in this range; values as low as 1° were obtained. Hk was constant at 2.95±0.1 Oe above ∼1% sulfur. The effects of thiourea on Hc, Hk, and α90 are interpreted in terms of its influence on crystallite size and shape, on the smoothness of the film, on the impurity content, and on the planar stresses in the film. With this electrolyte, film compositions were constant throughout their thickness to ±0.2% Ni. Exposure of these films to 60°C in a saturating field parallel to their easy axis produced no changes in Hc, Hk, or α90 for times up to 2000 min. In a transverse field, the change in properties depended on the sulfur content of the films; the change in Hk with time followed ln(Hkt−Hk∞)/(Hk−Hk∞)=−(t/τ)1/2out to 6000 min, corresponding to (Hkt−Hk∞)/(Hk−Hk∞)≈0.1. The product Hkα90 was relatively independent of time. The rate constant τ at 60°C was 885 min, independent of sulfur content. The constant terms, i.e., the initial minus the final anisotropy and dispersion (Hk − Hk∞) and (1/α90−1/α90∞) were functions of the sulfur content. ``Stabilization'' reduced Hk − Hk∞ by a factor of about 5 without affecting the rate constant. The change in kinetics with sulfur content is attributed to the changes in isotropic stress, defects and impurities in the film. The higher impurity concentrations are believed to influence a larger fraction of the atom pairs, promoting their reorientation in the transverse annealing field by a lower-energy process.
Magnetic Properties of Substituted Ca2Fe2O5
Authors: Grant R. W. , Wiedersich H. , Geller S. , Gonser U. , Espinosa G. P.
Published: January 2005

The compounds, Ca2Fe2−xMxO5, with M=Ga3+ (0≤x≤1.5) or Sc3+ (0≤x≤0.5), have the Ca2Fe2O5 structure and exhibit antiferromagnetic order within both the tetrahedrally and octahedrally coordinated sublattices. Sc3+ substitutes almost exclusively in octahedral sites while Ga3+ prefers tetrahedral coordination. The Mössbauer effect has been used to measure both the Néel temperature and the distribution of nonmagnetic ions on the two sublattices for several substituted compounds.
Magnetic Behavior of the System Mn2O3–Fe2O3
Authors: Geller S. , Grant R. W. , Cape J. A. , Espinosa G. P.
Published: January 2005

Solid solutions of Fe2O3 and Mn2O3 with the bixbyite structure may be obtained to at least 50 mole % Fe2O3. Over the whole range, the lattice parameter is essentially constant. Mössbauer spectroscopy and susceptibility measurements indicate that these solid solutions become antiferromagnetic at much lower temperatures than does Mn2O3 itself. In fact, 2 mole % Fe2O3 causes a steep drop in TN, from ∼82° to ∼40°K. However, this value remains relatively unaffected by further increase in Fe2O3 concentration. The susceptibility measurements also indicate a second transition, at about 15°K below the antiferromagnetic ones, to apparently weak ferromagnetism with extremely low residual moments (∼0.01 μB/formula unit at 4.2°K). Mössbauer spectra of the 50 mole % powdered specimen at 55 kOe and at both 24° and 9°K exhibit a small polarization of the atomic spins, which in turn suggests either a small induced or small spontaneous moment.
Neutron-Diffraction Study of Antiferromagnetic Ba2CoWO6 and Ba2NiWO6
Authors: Cox D. E. , Shirane G. , Frazer B. C.
Published: January 2005

A number of ordered perovskite-type compounds A2BB′O6, in which B and B′ are, respectively, a 3d transition metal cation and a diamagnetic cation, undergo antiferromagnetic transitions. The latter have been interpreted in terms of antiferromagnetic ordering of the second kind arising from appreciable superexchange interactions over quite long distances involving two anions and one diamagnetic cation. A neutron diffraction study has been made of polycrystalline samples of two such compounds, Ba2CoWO6 and Ba2NiWO6. The crystal structures are cubic, and there is a slight displacement of the oxygen ions from the ideal perovskite positions towards the more highly charged W ions of about 0.1 Å. At 4.2°K the magnetic unit cell edge is double that of the crystallographic cell in both compounds and the observed magnetic peaks are consistent with ordering of the second kind. The spin direction in Ba2NiWO6 is perpendicular to the [111] axis, but in Ba2CoWO6 it appears to lie roughly 20° from the [111] axis.
Contribution of the Demagnetizing Field near the Spin-Flopping Field for CuCl2·2H2O
Authors: Terrell J. H. , Lawrence T. R. , Gooen K. , Naiman C. S.
Published: January 2005

A lack of symmetry in the susceptibility tensor χyx was found experimentally by Naiman and Lawrence over the spin-flopping region in CuCl2·2H2O when the external magnetic field was less than 10−3 rad away from the easy axis. This fact cannot be explained by considering the effective field acting on the two-sublattice system to be composed of exchange, anisotropy, and external magnetic fields. Additionally, the Dzialoshinski-Moriya interaction for CuCl2·2H2O appears analytically only as a shift in the critical field while the wander of the easy axis influences the shape but not the symmetry of χyx. The demagnetizing field has been included exactly using a 2×2 tensor, and it was found that for an ellipsoidal spin-flopping specimen the major effect on χyx is to shift the value of the critical field. According to Joseph and Schlömann, the demagnetizing tensor components for bodies with ``corners'' need not be constant, and this could possibly explain the observed asymmetry in χyx. To test this theory, single crystals were shaped into spheres and χyx was remeasured. The essential agreement between the results before and after shaping lead us to conclude that demagnetizing effects which depend on the crystal shape are not important. Possible crystalline inclusions and/or domain formation may play a significant role.
Low-Temperature Heat Capacity of NdCl3 and PrCl3
Authors: Colwell J. H. , Mangum B. W.
Published: January 2005

Heat capacities of PrCl3 and NdCl3 have been measured between 0.3° and 4°K. The dominant feature of the heat capacity curves is a broad anomaly indicating a region of extensive short-range magnetic ordering. The anomaly in NdCl3 has a maximum at 0.47°K and fits closely that of a linear Ising chain model. In addition, two small peaks appear at the same temperatures as the sharp spikes found in the magnetic susceptibility. PrCl3 has a sharp peak in the heat capacity at 0.4°K which is presumably associated with long-range ordering. The broad anomaly in PrCl3 has a maximum at 0.8°K. The magnetic entropy change for the temperature region of the measurements is approximately 80% of R loge2 for both salts.
Scattering of Light by Magnons
Authors: Shen Y. R.
Published: January 2005

Scattering of light by magnons has recently been predicted by calculations, and subsequently verified by experiments. In this paper, theoretical aspects of the problem are reviewed briefly. The spin-Raman effect is treated along the same line as ordinary Raman scattering by phonons. The order of magnitude of one-magnon Raman scattering is estimated from the rotatory power of the magnetic ions. The effect is smaller in antiferromagnets because of opposite spins in different sublattices. In ferrites and antiferromagnets, two-magnon Raman scattering can occur through exchange-type interaction. Raman scattering by magnetoelastic modes should also be observable. The possibility of constructing a tunable light oscillator is discussed.
Optical Diffraction by Magnetic Domains in Europium Chalcogenides
Authors: Suits J. C.
Published: January 2005

The transmission of light through single crystals of EuO and EuS has been measured as a function of magnetic field, temperature, and wavelength. Below the Curie temperature, the intensity of light reaching the photodetector abruptly diminishes to nearly zero as the applied field is decreased below a critical field Hcrit. This effect is caused by diffraction of light by magnetic domains. Photographs of the spatial distribution of transmitted light for H<Hcrit show that the light is rather uniformly distributed over large angles. This diffraction effect is largest near the optical band edge and diminishes at longer wavelengths. By measuring the temperature dependence of Hcrit one may determine the ferromagnetic Curie temperature in a novel manner. For EuO we find TC=69.5°K, which agrees well with a Curie temperature determination on the same sample by a more conventional magnetization method.
Far-Infrared Absorption by Two-Magnon Excitations in Antiferromagnets
Authors: Richards P. L.
Published: January 2005

Far-infrared spectroscopy has been used extensively for the study of antiferromagnetic resonance, that is, single-magnon excitations at the Brillouin zone center. The recent discovery of two-magnon excitations in antiferromagnets by Halley and Silvera now permits precise measurements of magnon energies at selected points on the Brillouin-zone boundary. The discovery and theoretical interpretation of the two-magnon effect is described in this review paper. Experimental results for the antiferromagnets MnF2, FeF2, and CoF2 and for the canted-spin weak ferromagnets NiF2 and MnCO3 are also presented. The experimental data are discussed in relation to the current theoretical understanding of the two-magnon effect.
Experimental Techniques with General Applicability for the Study of Magnetic Phenomena
Authors: Dwight K.
Published: January 2005

A review of the well-known magnetometer techniques for measuring magnetic properties is presented. Special attention is given to the peculiarities of each method which render it particularly attractive, or otherwise, for particular measurements. In addition, an attempt is made to estimate the investment in time and money required to implement the various techniques. Neutron diffraction methods and differential thermal analysis can also be used in the investigation of any magnetic material. Hence, they are included in this survey.
Special Magnetic Measurement Techniques
Authors: Foner Simon
Published: January 2005

Various magnetic measurement techniques, not generally applicable to all magnetic systems, are reviewed. Specific examples of direct measurement techniques considered include difference or differential magnetization measurements with static or pulsed fields and ac (periodic) variations of magnetization M or temperature T (∂M/∂T, ∂T/∂H, ∂M/∂H). Special emphasis is given to ac techniques, because commercial ac electronic processing equipment now permits a wide variety of sophisticated investigations to be readily accomplished. A number of indirect techniques are briefly discussed, such as the numerous magnetic resonances which permit microscopic local field evaluations. Limitations of these indirect techniques and some of the assumptions generally made when applying them to deduce magnetic properties are emphasized. A short review of the production of high magnetic fields in superconducting, high-power water-cooled, and pulsed-field solenoids is given, and production of very low fields is also briefly discussed. The last section considers measurement of magnetic fields, mainly high fields in low-temperature environments, and very low fields.
Crystal and Magnetic Structure of PbCrO3
Authors: Roth W. L. , DeVries R. C.
Published: January 2005

PbCrO3 has been synthesized in the high-pressure ``belt'' apparatus from PbO and CrO2 at 1150°C and a pressure in excess of 50 kbar. Single-crystal and powder x-ray diffraction at room temperature show the compound has the cubic perovskite structure with a0=4.00 Å. No deformation of the cubic structure was discerned in neutron diffraction patterns at 77° and 4.2°K. At low temperature the magnetic moments of the chromium atoms are ordered in the antiferromagnetic G-type structure in which the spins on each Cr are antiparallel to those of the six nearest neighbors. Assuming the magnetic form factor of chromium can be approximated by that of Cr3+, the magnetic intensities give a moment of 1.9 μB per chromium atom, approximately the spin value for Cr4+ (3d2). The temperature dependence of the (111) magnetic peak was measured and the results fitted to a Brillouin function with TN≈240°K. The magnetic susceptibility does not show a maximum at the Néel point but does obey a Curie-Weiss law above TN, consistent with the neutron-diffraction results.
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.
Growth of Single Crystals of Cadmium Chromium Selenide by Liquid Transport with Platinum Catalyst
Authors: Von Philipsborn H.
Published: January 2005

Single crystals of CdCr2Se4 were grown for the first time. Individual pills of CdSe and CrCl3, in close contact, were heated around 700°C for three days. Perfect octahedra up to 2 mm in size grew in the CdSe pill by liquid transport. Formation of CdCr2Se4 occurred only in the presence of platinum. The technique and its reactions are described in detail.
Giant Negative Magnetoresistance in Ferromagnetic Eu1−xGdxSe
Authors: Von Molnar S. , Methfessel S.
Published: January 2005

The NaCl-type compounds Eu1−xGdxSe form a continuous series of solid solutions between the ferromagnetic insulator EuSe and the antiferromagnetic metal GdSe. We have studied the temperature dependence of electrical resistivity ρ, in Eu1−xGdxSe single crystals and polycrystals between 2.5° and 300°K; we find, in qualitative agreement with earlier observations, for small x, an exponential increase in ρ similar to normal semiconductors but a very sharp drop in ρ below the magnetic transition temperature. The resulting peak in ρ decreases sharply with applied magnetic field strength and increasing Gd concentration. The temperature dependence of the Hall effect in single-crystal samples of Eu0.95Gd0.05Se indicates as origin of the resistivity anomaly an unusually large effect of the magnetic order on the carrier mobility. Preliminary thermoelectric power measurements support this conclusion. The possibilities of describing strong interactions between conduction electrons and localized spins by scattering theory and by magnetic self-trapping of electrons in the spin lattice are discussed.
Temperature Dependence of the 57Fe hfs in FeF2 below the Néel Temperature
Authors: Wertheim G. K.
Published: January 2005

The temperature dependence of the 57Fe hfs in FeF2 has been obtained with the Mössbauer effect in the region below the Néel temperature. In the low-temperature region (0°−50°K) the present measurements are in good agreement with the more precise determination of the temperature dependence of the 19F NMR by Jaccarino. In the region just below the Néel temperature the data were analyzed in terms of the equation H(T)=H(0)D(1−T/TN)β,yielding β=0.325±0.005 and D=1.36±0.03. This value of β differs slightly but not significantly from that found in MnF2 by Heller. D is larger than those previously reported in other materials because of the larger magnetic anisotropy in FeF2.
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 < 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.
Reflection of Electrons by Standing Light Waves: A Simple Theoretical Treatment
Authors: Bartell L. S.
Published: January 2005

The reflection of electrons by standing light waves, i.e., the stimulated Compton scattering proposed by Kapitza and Dirac, has been treated by applying the Born approximation. The probability that an electron will be reflected is derived, for light waves that are not too intense, as a function of the electron beam orientation and of the coherence properties of the light waves. It is shown, among other things, that the original formula of Kapitza and Dirac is not directly applicable to representative studies using lasers. More general formulas are given along with a discussion intended to serve as a practical guide in the design of experiments.
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 Crystallization of Vitreous Selenium as Induced by Chemical Vapors
Authors: Chiang Y. S. , Johnson J. K.
Published: January 2005

Crystallization of thin layers of vitreous Se induced by exposing the surface to various inorganic and organic solvent vapors, e.g., carbon disulfide, trichloroethylene, isopropyl acetate, has been studied at room temperature. It is noted that the morphology of the crystallites obtained and the various growth features observed are essentially the same for the different chemical vapors used and are similar to growth of Se crystals by evaporation. Different experimental conditions seem only to change the distribution of the relative abundances of the various morphologies and the time needed for achieving a certain extent of crystallization. The mechanisms of crystal growth in this case, as visualized through the various growth features at intermediate stages, are remarkably similar to growth by vapor deposition of Au and Ag films on single-crystalline substrates.
Striations on Copper Single Crystals Subjected to Torsional Fatigue. II. On the Mechanism of Fatigue Striation Formation and Fatigue Failure at Low Strain Amplitudes
Authors: Kuhlmann-Wilsdorf Doris , Nine Harmon D.
Published: January 2005

An analysis of the experimental evidence in Part I of this paper clearly indicates that for the case of copper crystals, striations in low-amplitude fatigue are suppressed by strong slip on intersecting slip planes, including the cross slip system, but are formed by interactions between dislocations on the primary glide system with dislocations on another glide system sharing the same slip plane. This observation is in obvious contradiction to any theory based on cross slip of the primary dislocations alone, since cross slip combined with glide and climb allows every conceivable rearrangement of the dislocations but cannot change the Burgers vectors. A model for the mechanism of striation formation is therefore developed which takes into account that dislocations with at least two different Burgers vectors on the primary slip plane cooperate, according to the experimental evidence. It is proposed that striations consist of sequences of ``cells,'' forming pairs of dense dislocation networks parallel to the primary slip plane, separated by narrow channels almost free of dislocations and debris. The networks consist of almost equal surplusses of dislocations with the three ½ 〈110〉 Burgers vectors in the active {111} slip plane, representing more or less well-developed twist boundaries with a greater or smaller neutral filling of other dislocations and debris. Once striations are formed, glide becomes concentrated in them and hardening proceeds at a much slower rate or comes to saturation. Extrusions and intrusions can arise in at least three different ways and it is believed that these mechanisms act singly or in combination, depending on conditions. It is shown that the model is in good accord with previous evidence. In particular, dislocation structures associated with striations in fatigued copper, observed by Laufer and Roberts, are very close to those described. A few simple numerical relationships are derived from the model which could be employed to test the theory presented. Much of the theory is believed to be applicable also to dislocation behavior in unidirectional work hardening of fcc single crystals.
Influence of Pump-Induced Material Inhomogeneities on Giant Pulse Evolution
Authors: Roess Dieter
Published: January 2005

In a giant-pulse laser rod an inhomogeneous excess inversion across the rod diameter will lead to a non-uniform growth rate of the photon avalanche, when the transverse modes are not tightly coupled. For a model inversion distribution the resulting giant-pulse elongation is calculated. The radial time dispersion can be compensated by a radius-dependent resonator feedback or by transverse mode coupling. The influence of thermal resonator curvature on the decoupling of transverse modes is discussed.
Vacuum Thermionic Work Functions and Thermal Stability of TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2
Authors: Wilson R. G. , McKee W. E.
Published: January 2005

Surfaces shown by x-ray diffraction measurements after fabrication to be TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2 were subjected to vacuum thermionic work function and thermal stability measurements. Subsequent x-ray diffraction stoichiometry checks showed that only ZrC and Mo2C remained stable after many hours at thermionic emission temperatures. TaB2 decomposed to TaB+B when a diffusion barrier of TaC was provided under the TaB2; the three disilicides decomposed to lower silicon content silicides. The vacuum work functions measured after outgassing were TaB2(4.32 eV), ZrC(3.70 eV), Mo2C(4.74 eV), MoSi2(4.73 eV), TaSi2(4.71 eV), and WSi2(4.62 eV), subject to some temperature dependencies, as described.
A Diffusion Model for Filamentary Crystal Growth
Authors: Schwoebel Richard L.
Published: January 2005

A surface diffusion model for filamentary crystal growth from the vapor phase is presented which accounts for extensive growth normal to the surface. The model is based on the mechanism by which adsorbed atoms are incorporated into surface steps and the anisotropy associated with the capture process. It is shown that filamentary crystals may be initiated at a variety of surface structures including dislocations or impurities but that neither of these is prerequisite. Rather, filamentary crystal growth depends on mobility differences of atoms adsorbed on various crystal planes and the mechanism of capture at surface steps. Results of computer calculations simulating filamentary crystal growth are presented.
Optical Properties of Epitaxial PbS Films in the Energy Range 2–6 eV
Authors: Rossi C. E. , Paul William
Published: January 2005

The reflectivity of epitaxial PbS films has been compared with the reflectivity of bulk PbS in the energy range 2.1 to 6.2 eV and found to agree in both magnitude and structure within a few percent at energies where interference effects can be neglected. The transmission of several films with thicknesses varying from 335 to 550 Å has been measured and the structure and shape of the spectra shown to be the same for the films with different thicknesses. The reflectivity of bulk PbS between 2.1 and 6.2 eV has been combined with measurements made by other workers outside of this range to compute optical constants from the Kramers Kronig relation. The optical constants obtained in this manner appear to agree quite well (within about 10% in most cases) with those obtained from the reflectivity and transmission of the films, considering the experimental difficulties experienced in measuring film thickness and the absolute magnitude of the reflectivity.
Mass-Scattering Cross Sections of Biological Specimens
Authors: Sarkar N. H.
Published: January 2005

Mass-scattering cross sections of biological specimens as determined by several authors are compared with the values calculated for carbon from the scattering theories of Lenz, Burge and Smith, and of Sarkar. It is found that the electron scattering theory of Sarkar for carbon gives a better representation of scattering by biological specimens.
Dislocation Damping in Aluminum at High Strain Rates
Authors: Ferguson W. G. , Kumar A. , Dorn J. E.
Published: January 2005

Impact shear tests of the Kolsky thin-wafer type were used to determine the effect of temperature and strain rate on the critical resolved shear stress for slip in aluminum single crystals at strain rates of 104 sec−1 and in the temperature range 20° to 500°K. The aluminum deformed in a viscous manner in that the flow stress was proportional to the plastic strain rate. The behavior was found to be temperature-dependent. The results are discussed in terms of dislocation damping models where the friction force acting on a dislocation results from, at cryogenic temperatures, electronic viscosity, and at higher temperatures, phonon viscosity. The theories predicted general agreement as to the magnitude of the observed damping but some discrepancy was found to exist between the observed and theoretical temperature dependence of the damping.
Electron Microscope Studies of the Structure of Opal
Authors: Cole Stephen H. , Monroe E. A.
Published: January 2005

Replication electron microscopy has confirmed that the microstructure of precious opal consists of spherical particles of amorphous silica, SiO2, packed in a cubic close-packed array. Twinning relationships have been observed obeying the spinel twin law. Regions related by twinning correspond to the bands or striations observed under the light microscope. A specimen of common opal displayed a unique topography upon etching.
Microwave Harmonic Generation from Josephson Junctions
Authors: Shapiro Sidney
Published: January 2005

An easily fabricated bulk form of Josephson junction has been used as a harmonic generator. Harmonically generated power emitted by these nonresonant junctions has been directly detected at about 12 Gc/sec, corresponding to the second or third harmonic of the input frequency. The harmonic output is sensitive to the bias point in the V-I characteristic and to the input power level as expected from Josephson's equations. The coupling to waveguide of the radiation emitted by the nonresonant junctions used in these experiments is superior to that achieved in earlier work using self-resonant junctions as microwave generators.
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.