bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropy of Gadolinium Iron Garnet
Authors: Calhoun B. A. , Freiser M. J.
Published: April 2005

The ``one-ion'' theory of origin of anisotropy has been tested by comparing the calculated value of the gadolinium contribution to the anisotropy of GdIG at 0°K with experimental measurements. Crystal field, dipolar, and dipole—crystal field effects are included in the calculation. The median of the values obtained using the crystal field parameters for Gd3+ in four diamagnetic garnets agrees within 3% with the result of torque measurements on a pure GdIG crystal. The experimental value, −21.9×104 ergs/cc, is approximately 10% lower than previous values for the anisotropy of GdIG. The good agreement between the calculated and experimental anisotropies provides quantitative confirmation of the theory used in the calculations.
Surface Anisotropy Energies of Thin Magnetic Films
Authors: Soohoo R. F.
Published: April 2005

The shape of the surface anisotropy energy surface of a thin magnetic film is investigated. By generalizing the exchange boundary condition to include the cases of unequal spin pinning at the two surfaces of a film, calculations of the spin-wave resonance spectrum were made and compared with the results of surface oxidation experiments. It was found that the surface anisotropy is uniaxial with the easy axis perpendicular to the surface of the film: the surfaces of the film being hard planes of magnetization. In addition to the ordinary volume spin-wave resonance modes due to spin pinning, we found also a set of surface modes whose rf component of the magnetization decreases rapidly from the surface toward the interior of the film. Several surface spin-pinning mechanisms have been proposed. The implications of these proposals are examined in light of our theoretical and experimental results.
Aspects of Magnon Renormalization Near the Transition Temperature
Authors: Bloch Micheline
Published: April 2005

The temperature dependence of the magnon energy is studied, together with the magnetization, by a self-consistent treatment of the model hamiltonian obtained by keeping the Heisenberg hamiltonian up to the diagonal term of fourth order in magnon operators. In this formalism, the dispersion relation appears to have the same form as for free magnons, apart from an important temperature-dependent factor α(T). The calculations have been carried out for simple cubic ferromagnets and CsCl-type antiferromagnets, with due account taken of the Brillouin zone boundary effect. It is found that no solution for α(T) exists above a maximum temperature TM which is compared to the values of the Curie and Néel temperatures calculated by the methods of Kramers-Opechowski and Bethe-Peierls-Weiss. At TM the magnetization has about 25 percent of its value at absolute zero. The fact that α(T) is independent of k appears to be a property of the cubic geometry to which the following considerations have been limited.
Drive Current Margins for Magnetic Film Memories
Authors: Anderson A. H. , Crowther T. S. , Raffel J. I.
Published: April 2005

The effect of spurious fields on magnetic-film memory operation is to considerably reduce digit-current margins by lowering disturb and raising writing thresholds. These fields are generated by fringing from drive lines, closure flux of neighboring magnetic elements, and sneak currents in the word selection matrix. Margins for the 256-word 370-nsec memory of the Lincoln Laboratory FX-1 computer are described and the process of ``creep'' disturbing which occurs due to spurious transverse fields in combination with normal digit fields is examined as well as methods for improving margins.
Measurement of the Covalent Spin Distribution in Manganous Fluoride Using Polarized Neutrons
Authors: Nathans R. , Alperin H. A. , Pickart S. J. , Brown P. J.
Published: April 2005

The spatial distribution of the covalent spin density in MnF2 has been obtained from a measurement of the ``forbidden'' magnetic scattering in the nuclear reflections using polarized neutrons. A partial Fourier map of the projected covalent spin on the basal plane was prepared. A model representing the covalent spin by isolated spherical charges that is consistent with the experimental data indicates that the covalent spin density for a single bond undergoes a change in sign as we proceed from the Mn2+ to the F− ion. That part closest to the 3d unpaired electrons carries the same sign as the magnetic ion. The results are discussed in terms of the existing theory.
Atomic Magnetic Moments in Dilute Iron—Palladium Alloys
Authors: Cable J. W. , Wollan E. O. , Koehler W. C.
Published: April 2005

Neutron scattering and magnetization measurements were made on dilute iron—palladium alloys to determine the existence and magnitude of the magnetic moments of the constituent atoms. This determination was made by the combination of the difference in the aligned magnetic moments obtained from the ferromagnetic diffuse neutron scattering and the average ferromagnetic moment per atom obtained from the saturation magnetization measurements. Data were taken on two alloys which contained 3 and 7 at. % Fe. The following results were obtained: Pd0.97Fe0.03:  3.0±0.2 μB/Fe,  0.15±0.01 μB/PdPd0.93Fe0.07:  3.0±0.2 μB/Fe,  0.27±0.02 μB/Pd.
Effect of Hydrogenation on the Paramagnetic Resonance of Gd in Pd and Pd-Rich Alloys
Authors: Shaltiel D.
Published: April 2005

Paramagnetic resonance of Gd in Pd and rare-earth-doped Pd has been reported recently.1,2 It was shown that a strong interaction with a long range exists between the conduction electrons and the spin part of the localized rare-earth ions. This was exhibited via the g shift of the Gd in pure Pd, with respect to its ionic value, e.g., g = 1.992±0.001, and the additional shift of the resonance when additional rare-earth impurities were alloyed into the Pd. The interaction and its range are attributed to the high density of states of the unfilled d band of the Pd. In Pd-Ag alloys the Gd g value shifts continuously toward its ionic g value with the increase of the silver content. This shift has the same behavior as the decrease of susceptibility with the increase of Ag concentration.1 For 40% Pd 60% Ag the g shift, as well as the susceptibility, are almost zero. These results confirm the above statement.

When Pd is hydrogenated the g value of Gd changes from 1.88 for the pure sample to 2.00 for a sample with H:Pd ratio of 50%. Thus hydrogenation shifts the g of Gd back to its ionic value. Alloying rare-earth impurities into Pd broadens the Gd line but produces no g shift in the hydrogenated samples. These results show that the interaction between the Gd localized moment and the conduction electrons is largely suppressed. This is expected from the fact that hydrogen reduces the anomalously high susceptibility of Pd.

The Gd resonance in mixed α and β phases (H/Pd from 5% to 60%) shows two lines: one at g ≈ 2.00, the other at g ≈ 1.90 corresponding to the lines in the separated β and α phase, respectively. The line intensities are roughly proportional to the amount of each phase present. This result contradicts Mott's hypothesis that the linear decrease of the Pd susceptibility with the increase of the hydrogen concentration is caused by filling the holes in the Pd d band with the hydrogen electrons.3 If Mott's hypothesis were correct, a continuous shift of the Gd g value, as in the case of Pd-Ag alloys, would be expected. We, therefore, conclude that the linear decrease of the susceptibility with hydrogen content is due to the proportion of the α and β palladium.

The additional increase of the linewidth in β palladium with increase of Gd or other rare-earth concentration is mostly accounted for by dipole-dipole broadening. Even with signal-to-noise ratios of 2000:1 only one line was observed. Despite the fact that powdered samples were used, the shape closely approximates a Lorenzian line. Therefore, we have assumed that all the seven ΔM = ±1 transition lines of the Gd 8S7/2 state are included in this line. The extrapolated linewidth for zero Gd concentration was 80 G. This gives an estimated upper limit for the zero field splitting of Gd in β palladium of 5 10−4 cm−1.
Neutron Diffraction Study of NiS
Authors: Sparks Joseph T. , Komoto Ted
Published: April 2005

A powder neutron diffraction study of stoichiometric NiS has been made in the range 85–770°K. The NiAs-type structure can be obtained at room temperature by quenching from above 700°K. This NiAs form exhibits a paramagnetic-antiferromagnetic transition at 263°K. In the antiferromagnetic state the moments in a hexagonal layer are coupled ferromagnetically and point in the direction of the c axis. The coupling between adjacent hexagonal layers is antiferromagnetic. The sublattice magnetization goes from zero to full saturation on cooling through 263°K. The measured moment just below the transition is 2.1 μB. The a- and c-axis lattice parameters are also observed to increase abruptly at this temperature by ⅓% and 1%, respectively. The transition is 3–4°K wide and exhibits thermal hysteresis. This transition thus has several characteristics of a first-order transition.
Spiral and Concentric-Circle Walls Observed by Lorentz Microscopy
Authors: Cohen Mitchell S.
Published: April 2005

Thin Ni–Fe films specially prepared by vacuum deposition on thin carbon substrates supported on electron-microscope specimen grids showed inward-growing spiral, or concentric-circle walls when rotated in a constant field. For either configuration it was necessary to have a film which was thin enough to support 360° walls, and which possessed high easy-axis dispersion, particularly near the film edge. Whether spirals or concentric circles were exhibited depended on the value of the easy-axis dispersion in the center of the film.
Contrast Dispersion in Magneto-Optic Apparatus for Domain Studies
Authors: Brennan P. , Williams M.
Published: April 2005

A marked variation of contrast over the field of view has been discovered in apparatus for displaying domains by means of the Kerr longitudinal magneto-optic effect when convergent light is used to illuminate the sample. One of the effects seen is a rather dark central band parallel to the mean plane of incidence when polarizer and analyzer are crossed and one polarizes in the mean plane of incidence. Within this band there is no contrast between antiparallel domains, but on either side there is a region of strong contrast, and if a domain pattern is moved from one of these to the other its contrast reverses. The band of zero contrast moves at right angles to the mean plane of incidence if the polarizer is rotated, and tilting the sample gives a similar effect. Simple classical explanations of the effects are given, taking into account both metallic and Kerr ellipticities.
Possibility of Visual Observation of Antiferromagnetic Domains
Authors: Brown W. F. , Shtrikman S. , Treves D.
Published: April 2005

The optical properties of magnetic materials are studied using symmetry considerations. It is found that in addition to birefringence, Faraday rotation, and optical activity there should exist another effect, namely gyrotropic birefringence. This birefringence is of opposite sign for magnetic domains related to each other by time reversal, and can, therefore, in principle be used for observation of antiferromagnetic domains so related. The dependence of the optical properties on external agents such as electric and magnetic fields and stress is also considered.
Magneto-Optical Studies of Chromium Tribromide
Authors: Dillon J. F. , Kamimura H. , Remeika J. P.
Published: April 2005

Chromium tribromide is one of the few ionic ferromagnetic crystals known. It has a hexagonal layer structure, and its Curie point is at about 36°K. Thin sections are transparent from the near infrared up to a strong sharp band edge at about 20 000 cm−1. Below this band edge a number of broad bands and sharp lines are observed. Linearly polarized light passing through a magnetically saturated crystal experiences a rotation of the axis of polarization which varies with wavelength and is proportional to the magnetization component along the line of sight. Exceedingly large magnetic rotations are associated with the band edge near 20 000 cm−1 where values of over 500 000° / cm were measured. The detailed structure of the 2T2 absorption at about 19 000 cm−1 seems to involve the ferromagnetic exchange coupling. An assignment is given for the band edge. Microwave-optical experiments have been performed in which ferromagnetic resonance has been observed visually and light has been amplitude modulated at 23 and 46 kMc.
Effect of Fluoride-Compensated Co2+ on the Anisotropy of BaFe12O19
Authors: Robbins M. , Banks E.
Published: April 2005

Samples in the series BaCoxFe12−xO19−xFx were prepared by firing appropriate mixtures of oxides and fluorides in a carefully dried oxygen atmosphere at 1350°C, with values of x ranging from 0 to 2.0. Single crystals of mixtures having x values of 0.3, 0.4, 0.5, 1.0, and 2.0 were grown from a flux composed of equimolar quantities of Na2CO3 and Fe2O3. The crystals had the BaFe12O19 structure for x values below 0.5 and the BaFe18O27 (W) structure for higher values of x. The mixture with x=0.5 yielded both kinds of crystals. Previous measurements of saturation magnetization in the easy direction had indicated that the Co2+ ions were substituting for Fe3+ in the tetrahedral sites. The positive anisotropy of the crystals decreased with increasing cobalt substitution, reaching a minimum at about x=0.47. A crystal having approximately this composition appeared to have very little anisotropy by qualitative tests. Torque measurements indicated that this crystal has a cone of easy magnetization. Comparisons of the magnetization of powders at a constant field (6000 Oe) with the calculated saturation value indicated that the powders approached saturation most closely at x=0.47, again suggesting a minimum in anisotropy at that concentration. The strong effect of tetrahedral Co2+ on the anisotropy is believed to be related to the presence of a trigonal component in the local crystalline field, owing to the presence of one fluoride ion and three oxygen ions in the immediate vicinity.
Influence of Particle Size on the Coercive Force of Barium Ferrite Powders
Authors: Tenzer R. K.
Published: April 2005

The influence of milling on the intrinsic coercive force (Hci) of different ferrite powders has been studied recently by several investigators. These have ascribed changes of coercive force to dislocations which are introduced through milling and are removed through subsequent annealing.

In our own studies of barium ferrite powders we relate the changes of Hci to changes in particle size. This interpretation is supported by experimental data and electron micrographs. The large particles of barium ferrite material (calcined at 1300°C) change during ball milling from predominantly multidomain size (several microns) to nearly superparamagnetic size (0.02–0.5 microns). Accordingly, coercive force increases at first and then decreases as milling is extended.

Annealing of ball milled material between 800° and 1100°C results in slight sintering. Since the sintering reduces the number of nearly superparamagnetic particles, considerable increases in coercive force occur.

These interpretations are further supported by the temperature dependence of the coercive force. After short milling, when multidomain particles are still predominant, Hci decreases as temperature of powder is lowered. After extended milling, however, this effect changes sign which is attributed to thermal fluctuations of the magnetization in nearly superparamagnetic particles.
Extension of Coincidence Limiting Frequency Range in Ferrimagnets
Authors: Comstock R. L. , Dean W. A.
Published: April 2005

Power limiting using the first-order spin-wave instability has been observed in a ferrimagnetically coupled filter-limiter at higher frequencies than had previously been believed possible. For example, a filter-limiter, using orthogonal strip-line resonators coupled by the dipolar fields of a YIG sphere, was constructed at 4000 Mc. Output power was limited with the sharp break at the threshold and flat limiting curve characteristic of coincidence limiters. This result is in contrast with the operation of similar limiters at this frequency which use the second-order spin-wave instability in which the limiting characteristic has a much more gradual slope transition above the threshold. Coincidence limiters have previously been believed to have a maximum operating frequency ωc=2ωMNT (3.27 kMc for a YIG sphere) since, with an isolated sample, coincidence of the uniform precession resonance and the subsidiary absorption occurs only for ω<ωc.

These results are observed for a coupled mode resonance in these ferrimagnetically coupled circuits which occurs for dc magnetic field values in the subsidiary absorption region below the uncoupled uniform precession value (ω/γ). It is found that a minimum value of the circuit-sample coupling is required to observe this extension of coincidence type limiting. Limiting thresholds as low as −10 dBm have been observed with the strip-line circuit and lower levels are believed to be possible. Wide low-level bandwidths (>10%) are also obtained with these circuits, but with an increase in the limiting threshold.

The above results are explained by computing the normal modes of the microwave-ferrimagnetic resonator circuit. It is found for tight enough coupling that one of the branches of the normal mode spectrum is in coincidence with the subsidiary absorption at a higher frequency than the uniform precession resonance. The usual coincidence limiter operation (ω<ωc) is thus the small coupling case of the more general type of operation.
Longitudinal Pumping of Magnetoelastic Waves in Ferrimagnetic Ellipsoids
Authors: Morgenthaler Frederic R.
Published: April 2005

The instability threshold of parametrically excited magnetoelastic waves is derived, as a function of the dc magnetic field strength, for that region of field where the phonon and magnon spectra intersect. The case considered involves the longitudinal pumping (with an rf magnetic field of constant frequency 2ω), of a small ferrimagnetic single crystal having cubic symmetry. The crystal is ellipsoidal in shape and is magnetized along a [100] direction. (The analysis is also applicable to a uniaxial crystal magnetized along its principal axis.) In this instance, the unstable magnetoelastic waves are a mixture of transverse phonons (polarized in the longitudinal direction) and magnons (spin waves) which propagate at (or very near) right angles to the dc field.

If, as is usual, the two branches of the magnetoelastic wave spectrum are split by a frequency large compared to the phonon relaxation frequency, an approximate, and greatly simplified expression may be deduced from the general solution. In this case, it is found that the line shape of the phonon contribution to the threshold is asymmetric, and that the peak of the curve occurs for a smaller value of dc field than is generally believed. This shift in field is ∼b2(2ΔHk)Q (where b is the magnetoelastic energy coefficient, 2ΔHk is the appropriate spin-wave linewidth, and Q is the appropriate phonon Q) and must be taken into account for an accurate determination of the exchange constant (particularly at the lower microwave frequencies). The peak of the phonon contribution to the threshold curve is independent of this shift and also of b; it is ∼λω2Q−1, where ω is the frequency of the magnetoelastic wave and λ is the exchange constant. The width of the peak at half-height is essentially independent of Q (except at very low frequencies) and is ∼|b|M2ωλ½, where M is the value of the saturation magnetization.
Importance of Penultimate Grain Size and Solid Solution Impurities in Secondary Recrystallization in 50 Fe-50 Ni
Authors: Benford James G. , Lindsay Robert W.
Published: April 2005

Vacuum induction melting was used to prepare eight melts of 50 Fe-50 Ni containing principally three levels of silicon—0.028, 0.23, and 0.67 weight percent–as an impurity. After forging and intermediate annealing operations, slabs were cold reduced 95 to 98.7%. Gradient and isothermal anneals were used to study the effects of atmospheres, penultimate grain size, percent cold reduction, and impurities on the cube texture and the secondary recrystallization phenomenon. Penultimate grain size and solid solution impurities were found to be extremely important in the development of the cube texture and in the occurrence of secondary recrystallization, and they must be considered in conjunction with any possible effects of inclusions.
Instability of the Fine Particle Structure of Certain Electrodeposits
Authors: Sallo J. S. , Carr J. M.
Published: April 2005

The effect of cold-working and annealing on fine particle Co–P and Co–N–P electrodeposits is described. It is shown that the rod-type structure is sensitive to both cold-working and annealing while the platelet structure is sensitive only to annealing. Quantitative differences in response to annealing are discussed. It is suggested that both rod and platelet particles are coated with a thin layer of nonmagnetic cobalt-cobalt phosphide or nickel-nickel phosphide. This nonmagnetic coating explains both the high coercivity of the samples and the effect of annealing.
Magnetic Annealing and Directional Ordering
Authors: Neurath Peter W.
Published: April 2005

Evidence in support of the view that magnetic annealing is due to directional ordering in substitutional alloys has been obtained in experiments on a 3% Si-Fe alloy. In addition to the theoretical interest of this result, the improvement in properties of practical importance, such as the 60 cycle watt losses and the magnetostriction have been demonstrated.

3×28×0.03 cm strips of (110) [011] oriented 3% Si-Fe material were isothermally annealed in fields of the order of 10 Oe parallel to their long axis, and at temperatures from below 350°C to above the Curie point. It was found that the temperature dependence of the magnetic annealing expressed as a ratio of the maximum obtainable effect was linear when plotted against 1/T and could be interpreted as due to an activation energy of 46 000 cal per mol, which is in excellent agreement with the activation energy for diffusion of Si in ferrite. From the practical point of view, it was demonstrated that a 5-min magnetic anneal at only 510°C was very effective in reducing losses and particularly in lowering the magnetostriction in the [011] direction. The absence of any effects in pure iron samples, compared to similarly oriented Si-Fe samples, showed that the effect was really due to the diffusion of silicon only.
Thermal Fluctuations of a Single-Domain Particle
Authors: Brown William Fuller
Published: April 2005

A statistical ensemble of particles, with moment orientations (θ, φ), can be represented by a surface density W (θ, φ, t) of points on the unit sphere. The corresponding surface density J satisfies a continuity equation ∂W/∂t=−∇·J. With no thermal agitation, J=WṀ/Ms, where M is the vector magnetization (| M | = const = Ms); its rate of change Ṁ is assumed to be given by Gilbert's equation. To include thermal agitation, we may add to J a diffusion term −k′∇W; this gives directly the ``Fokker-Planck'' equation of a previous, more laborious calculation. When ∂/∂φ=0, the equation simplifies and can be replaced by a minimization problem, susceptible to approximate treatment. In the case of a free-energy function with deep minima at θ=0 and π, such treatment leads again to a result derived previously by a method adapted from Kramers and valid when v(Vmax−Vmin)/kT is at least several times unity (v=particle volume, Vmax and Vmin=maximum and minimum free energy per unit volume, k=Boltzmann's constant, T=Kelvin temperature). When the minima are not deep, a different treatment is necessary; this leads to a formula valid when v(Vmax−Vmin)/kT<<1.
Effects of Electrical Current and Tensile Stress on the Domain Structure in Polycrystalline Grain-Oriented 3.25% Silicon Steel
Authors: Gniewek J. J.
Published: April 2005

A Kerr magneto-optic apparatus has been used to observe the effects of an electrical current and tensile stress on the domain structure in commercial, 3.25% silicon steel. It is noted that a current density of 0.27 A/mm2 produces almost complete saturation in a favorably oriented grain. This effect of current should be considered in elastoresistance and low-field magnetoresistance experiments. Upon application of a tensile stress of only 0.57 kg/mm2, a domain pattern resembling the `lozenge' pattern is shown to occur in certain grains. This indicates that the lozenge pattern is associated with stress and will probably not occur in a completely strain-free crystal. The corresponding strain-free pattern is identified here as a `chevron' pattern.
New Method to Measure Directly the 180° Bloch Wall Energy
Authors: Aléonard Roland , Brissonneau Pierre , Néel Louis
Published: April 2005

Using the Bitter technique, the traces of a single 180° Bloch wall are observed by a device composed of two microscopes, one on each side of the sample. The wall is twisted by an inhomogeneous magnetic field. The measured displacements of the wall traces are related to the surface energy γ0 of the Bloch wall which in turn is related to the Heisenberg exchange constant A.

In an iron-silicon alloy with 3% Si we find γ0=1.48 ergs/cm2 and A=1.48×10−6 ergs/cm at room temperature, in fair agreement with the value A∼1.7×10−6 ergs/cm derived from Bloch's law and spin-wave theory at 0°K.
Magnetic Properties of Oriented 3% Aluminum Iron Sheets
Authors: Foster K. , Pavlovic D.
Published: April 2005

A study was made of the magnetic properties of 3% aluminum iron sheets which had been cold rolled and annealed to obtain a (100) [001]-type texture. Torque curve measurements as well as microscopic domain pattern observations indicated that approximately 70% (100) [001] texture was obtained in 0.025-in.-thick sheets. These sheets had induction values for a field of 10 Oe, of 16 000 and 15 300 G at 0° and 90° to the rolling direction, respectively, while a value of 13 900 G was obtained at 45° to the rolling direction, indicating the double orientation in the material. Oriented sheets were also obtained at thicknesses of 0.008, 0.012, 0.014, and 0.018 in. The degree of orientation decreased to some degree with decreasing sheet thickness, while 60-cps watt losses decreased considerably with decreasing sheet thickness.
Crystal Structure of Dysprosium at Low Temperatures
Authors: Darnell F. J. , Moore E. P.
Published: April 2005

The temperature dependence of the lattice parameters of Dy has been studied from room temperature to 30°K. The previously reported expansion along the c axis of the hexagonal close-packed structure below TN=179°K has been observed in detail and found to be in agreement with predictions of Kittel. At the first-order antiferromagnetic-ferromagnetic transition TS=86°K a crystal structure distortion to orthorhombic was observed. The ratio of orthorhombic axes changes from b/a=1.732=√3 to 1.720 just below TS and to 1.715 at 30°K.
Magnetic Properties of Compounds of Manganese with Rare-Earth Elements Having the Cubic Laves Phase Structure
Authors: Nesbitt E. A. , Williams H. J. , Wernick J. H. , Sherwood R. C.
Published: April 2005

In the present work, four cubic Laves-phase compounds containing manganese were investigated. All four compounds TbMn2, GdMn2, DyMn2, and HoMn2 were found to have antiferromagnetic coupling. At low temperatures and appropriate magnetic fields, sharp peaks in the magnetization versus temperature curves were obtained. In general, these peaks shifted to lower temperatures as the strength of the magnetic field was increased. In the compound TbMn2, the peaks strongly persisted even at a field of 14 400 Oe. In addition, the properties of TbMn2 were drastically affected by cooling in a magnetic field and under these conditions its hysteresis loop was unsymmetrical.
Magnetic Characteristics of Praseodymium, Neodymium, and Samarium Hydrides
Authors: Kubota Yoshio , Wallace W. E.
Published: April 2005

Magnetization-temperature data are presented for the hydrides PrH2.02 to PrH2.71, NdH2.02 to NdH2.75, and SmH1.99 to SmH2.88 and for the three parent metals from 4.2° to 300°K. Of the twelve hydrides examined only NdH2.02 and NdH2.03 exhibited magnetic ordering. These hydrides exhibited a Curie point at 9.5°K and the saturation moment measured at 4.2°K was 1.36 μB per Nd atom. Assuming the applicability of a Brillouin function with J=9/2 the moment extrapolated to 0°K is 1.51 μB. These values are considerably lower than the value for the free tripositive ion (3.27 μB) or the moment observed in the paramagnetic region (3.40 μB) but are in reasonably good agreement with the theoretical value (1.58 μB) computed for 4.2°K taking into account crystal field effects.

The susceptibility behavior of the four Sm hydrides studied is generally similar. The trend with temperature is in reasonably good agreement with theory which treats Sm as a free tripositive ion. Susceptibility of the Nd hydrides follow the Curie-Weiss law above about 100°K with the expected slope but deviate negatively from it at lower temperatures. The deviations are attributed to either incipient ferromagnetic ordering or crystal field effects or a combination of the two.

The susceptibility behavior of the Pr hydrides is very unusual. The highest hydrides exhibit Curie-Weiss behavior above about 80°K but show positive deviations from linearity in 1/χ vs T at lower temperatures. That the deviations may be due to crystal field effects is considered possible but unlikely. PrH2.03 and PrH2.04 exhibit essentially identical susceptibility behavior and do not follow the Curie-Weiss law. Their susceptibilities are anomalously high near room temperature, exceeding the values for the element and the saturated hydride by a factor of about five.
Magnetic Structures of TbD2 and HoD2
Authors: Cox D. E. , Shirane G. , Takei W. J. , Wallace W. E.
Published: April 2005

TbD2 and HoD2 have the calcium fluoride type of structure and become antiferromagnetic below 40° and 8°K, respectively. A powder neutron diffraction study of TbD2 at 4°K revealed a sinusoidal modulation of basic magnetic ordering of the first kind, in which ferromagnetic (001) layers are coupled antiparallel to the two adjacent layers. Both the magnetic moment and the wave vector are directed along the [001] axis, with a periodicity of about 24 Å. The moment associated with the Tb ion is 7.9 μB.

The diffraction pattern observed for HoD2 was quite complicated and attempts to index the magnetic reflections either with multiple cell dimensions or with simple modulation of a few basic antiferromagnetic structures have proved unsuccessful.
Magnetic Properties of Plutonium Hydride and Deuteride
Authors: Olsen C. E. , Sandenaw T. A. , Matthias B. T.
Published: April 2005

Magnetic investigations on plutonium hydride (PuH2.74) and deuteride (PuD2.74) have shown these compounds to be either ferromagnetic, like the corresponding uranium compounds, or ferrimagnetic. The Curie temperatures of plutonium hydride and deuteride are the same, within experimental error, and are 107°K. The magnetic moment for the hydride and deuteride are greater than 0.24 and 0.13 Bohr magnetons per mole of compound, respectively, at 76°K. In addition the cubic plutonium oxide PuO1.62 was found to be either ferro- or ferrimagnetic with a magnetic moment greater than 0.16 Bohr magnetons per mole of plutonium at 4°K and a Curie temperature of 96.7°K.
Heusler Alloys
Authors: Oxley D. P. , Tebble R. S. , Williams K. C.
Published: April 2005

The results are given of comprehensive measurements on the magnetic and crystallographic properties of the ferromagnetic Heusler alloys Cu2MnAl, Cu2MnIn, Cu2MnSn, Cu2MnGe, Au2MnAl, and the antiferromagnetic alloy Cu2MnSb. The alloys Cu2MnBi and Cu2MnGa are polyphase and the ferromagnetism may be due to binary phases present. The indirect exchange effects which may give rise to ferromagnetism and antiferromagnetism in Heusler alloys are discussed.
Superconductors as Permanent Magnets
Authors: Bean C. P. , Doyle Margaret V.
Published: April 2005

A unique property of a superconductor is the possibility of lossless current flow at temperatures below the critical temperature of the superconductor. Hence it is possible to make permanent magnets since fields will exist because of these persistent currents. The potentialities of superconductors in this respect may be distinguished by considering the supercurrent paths in different topological configurations. Experiments on solid and hollow cylinders of lead are reported and compared to theoretical predictions. While the singly connected soft superconductor is uninteresting as a permanent magnet owing to the Meissner effect of flux exclusion, the multiply connected sample has at least some theoretical interest in this application. Considerable improvement may be expected when using the hard or high-field superconductor, since several theories of its behavior imply a connectivity of extremely high multiplicity. It is shown that an energy product of over twenty-five million gauss-oersteds is obtained from Nb3Sn at 4.2°K. One possible approach to understanding this behavior derives from the Mendelssohn filamentary mesh model. A macroscopic theory of this model postulating that a critical current density as a function of field is the basic property of high-field superconductors is shown to be capable of accounting for the observations. It can be predicted on this basis that other materials or other experimental conditions will make possible much higher values of energy product than reported here.
Evidence for the Negative Surface Energy Models of Superconductivity in Nb3Sn, Nb3Al, V3Ga, and V3Si
Authors: Swartz Paul S.
Published: April 2005

The magnetization and hysteresis of Nb3Sn has recently been found to be size-dependent; when the sample size is reduced, the size-dependent contribution to the magnetization is diminished. The magnetization loops of powdered Nb3Sn, Nb3Al, V3Ga, and V3Si are found to converge with decreasing particle size to the form associated with the negative surface energy models of superconductivity, but with some intrinsic hysteresis.
High-Field Magnetoresistance in Nickel Single Crystals
Authors: Marcus S. M. , Langenberg D. N.
Published: April 2005

Measurements of transverse and longitudinal magnetoresistance in pure single crystals of nickel are reported. In the samples studied both the longitudinal and the transverse magnetoresistance tend to saturation at high fields and the transverse magnetoresistance is quite isotropic. Comparison of these data with that of other workers shows that Kohler's rule is not obeyed in nickel and indicates that the observed tendency to saturation and lack of gross anisotropy are not characteristic of the Fermi surface topology in nickel. It is suggested that impurity scattering mechanisms peculiar to ferromagnetic metals play a major role in determining the characteristics of the magnetoresistance even at the threshold of the high-field region.
Ferromagnetism of UFe2 and Comparison with the Ferromagnetic Theories
Authors: Lin S. T. , Ogilvie R. E.
Published: April 2005

The intermetallic compound UFe2 is ferromagnetic. A considerable number of magnetization isotherms have been obtained from 200°K down to 4.2°K with applied field up to 14 000 Oe. The Curie temperature has been determined to be 172°K and the Bohr magneton number 1.02 per UFe2 molecule. Several hysteresis loops at different temperatures have been obtained. The coercive force, the remanence and the loop area are all very small. These data have been compared with existing theories of ferromagnetism. The σ0T/σ00−T/Tc curve deviates considerably from the molecular field for curve J = ½. The experimental data fit the T32 law better than the T2 law. Dyson's formula is valid below T/Tc=0.52 while Bloch's formula is valid below T/Tc=0.35.
Magnetization Studies on Some Superconducting Transition Metal Solutions
Authors: DeSorbo Warren
Published: April 2005

Magnetic induction measurements have been carried out on a number of homogeneous solid solutions of the transition metals Nb, V, and Ta with solutes of column IV A and VI A. The hysteresis effects are large when the solute atoms are large correlating with increase in critical temperature, lattice parameter, and critical current. When the solute atom size is the same or smaller than the parent atom the hysteresis is small, similar to the magnetic behavior observed in all the alloys when in a finely divided state. This variation approaches that predicted by negative surface energy models.
High-Field Electron Emission from Gallium Arsenide
Authors: Savage William R.
Published: April 2005

High-field electron emission currents were drawn from a point cathode made from a single crystal of n-type gallium arsenide. Stable currents were observed for several cathodes over a wide range of voltage with an upper limit on the currents which could be drawn from the material.
Plastic Deformation of Germanium at and below Room Temperature
Authors: Rindner W. , Tramposch R. F.
Published: April 2005

It is found that Ge can be plastically deformed by indentation at temperatures down to 78°K without introducing cracks. Photomicrographs are presented which show the characteristic etch-pit pattern of dislocation half-loops resulting from annealing and etching of indented (111) surfaces.
Electron Density Distribution in Indium Antimonide
Authors: Attard Alfred E. , Azároff Leonid V.
Published: April 2005

The electron density of a pure InSb crystal has been synthesized using very accurate x-ray diffraction intensities. After subtracting the electron density of the palladium core from both kinds of atoms, the distribution of the valence electrons was determined. By this means it was established that, on the average, 0.45±0.05 electrons are transferred from the Sb atoms to In atoms, as compared to a transfer of 0.34 or 0.42 electrons deduced from infrared absorption measurements. The effective ionic charge to be used in polar-scattering calculations for InSb was calculated to be 0.17±0.02 e based on the electron density, as compared to 0.18 e or 0.16 e determined from electron mobility measurements.
High-Field Study of a Hall-Effect Microwave Converter
Authors: Chang K. K. N. , Hughes R. D.
Published: April 2005

Utilization of the Hall effect in the frequency conversion of microwaves with gain was investigated. A conversion gain which seemed to be feasible was found to be dependent on the control sensitivity of the conversion system. A high control sensitivity can be achieved through use of a high-mobility Hall sample, like InSb, an efficient coupling of a modulating field to the sample, and a suitable high-energy pump source.

The high-power test was performed by using a pulsed microwave pump. Conversion gains were measured as a function of the pumping power and showed some ``saturation'' effects. These effects were explored and explained, based on the behavior of carriers in the sample under high-power microwave fields. In particular, a breakdown field beyond which the saturation seemed to disappear was found.

The present S band experimental model still suffered a conversion loss of 25 to 30 dB. Results have, however, revealed the possibility of a practical microwave Hall converter with gain.
Transmission of Monochromatic Radiation in a Two-Level Material
Authors: Bellman Richard , Birnbaum George , Wagner William G.
Published: April 2005

A theoretical study has been made of the transmission of a monochromatic, well-collimated beam of radiation normally incident on idealized material containing only two energy levels. The nonlinear partial differential equations governing the variation of population and photon density in space and time have been solved exactly for arbitrary initial conditions under the assumption that spontaneous emission and thermal relaxation from the excited state can be neglected. These conditions are satisfied in practice when the radiation is in the form of a pulse whose duration is short compared with the characteristic times of these relaxation processes. Two cases are considered in detail: (a) when all atoms are in the ground state and the material absorbs; and (b) when there is a population inversion and the material amplifies. In case (a), the radiation, with a characteristic velocity, ``bores'' its way through an optically dense substance emerging delayed in time and leaving the material in a perfectly transparent or saturated state. In case (b), an incoming pulse is amplified and sharpened—to a degree determined by the gain of the medium. In addition to these cases, the dependence of the apparent spontaneous emission lifetime on the size and population distribution of the material is mentioned.
Some Causes of Resonant Frequency Shifts in Atomic Beam Machines. II. The Effect of Slow Frequency Modulation on the Ramsey Line Shape
Authors: Shirley Jon H.
Published: April 2005

The effect of slow frequency modulation of the exciting radiation on the Ramsey line shape observed in an atomic beam experiment is formulated theoretically. It is shown that the presence of second harmonic in the modulation can introduce measurable frequency shifts, whether observed directly or with a servo system.
Theory of the Phase Transition in a Cylindrical Superconductor
Authors: Swihart James C.
Published: April 2005

The theory of the transition of a macroscopic cylindrical superconductor from the superconducting to the normal state when induced by an external longitudinal magnetic field is considered. Iterative approximate solutions are found, and it is shown that a second-order solution previously derived by Faber is actually a poorer approximation than the first-order approximation from which it was obtained.
Double Barrier in Thin-Film Triodes
Authors: Davis R. H. , Hosack H. H.
Published: April 2005

The electron transmission coefficient for an asymmetric double barrier model of a thin-film triode is discussed. Two resonant terms appear in the transmission expression, one of which depends on the relative properties of the barriers and the other on the thickness of the base or control film. The results of a detailed calculation for a simplified model are given.
Conditions Existing at the Onset of Oscillistor Action
Authors: Larrabee R. D.
Published: April 2005

One of the major problems in oscillistor work is connected with the stability and reproducibility of the surface conditions of the oscillistor specimen. An empirical surface treatment has been found which enables one to prepare reasonably reproducible and stable oscillistors. By utilizing this surface treatment, it has been possible to measure the conditions existing at the onset of current oscillations. The quantitative dependence of the minimal applied magnetic field required for oscillistor action has been measured as a function of applied voltage and specimen size. Some qualitative information regarding the dependence of the minimal applied magnetic field on bulk and surface properties has been inferred from the experimental data. These data reveal that there is an optimum size for oscillistor specimens that will minimize the electrical input power required for oscillations, and by using such samples, oscillistors have been fabricated that will function continuously at room temperature. An experiment designed to interact with the magnetic field produced by the helical perturbation proposed by Glicksman has disclosed a new effect that may provide a way of constructing an oscillistor amplifier.

These experiments have revealed that the conditions necessary for oscillations in the current are quantitatively different from the conditions necessary for oscillation of the components of electric field that are transverse to the applied electric field. Since no quantitative theory of the mechanism of current oscillation has appeared in the literature, no direct comparison between theory and experiment is possible. However, the applied electric and magnetic fields required for current oscillations are of the same order of magnitude as those predicted by the existing helical instability theories.
Ag Ion Transport and Deposition in α Quartz
Authors: Vanfleet H. B. , Baker G. S. , Gibbs P.
Published: April 2005

Contact of a negatively charged microprobe to the (0001) face of a silver-backed Madagascar αquartz crystal at temperatures between 300–573°C produced four distinct types of visible decorations. The most prominent of these were conducting metallic platelets on the basal plane about 0.4 μ thick, with surface areas ranging up to the dimensions of the anode. The growth of these platelets appeared to take place only at the periphery, and to be thermally activated with dependence upon field ε of the form exp[−(H0−βε½)/RT], where β=0.32 kcal/[mole(V/cm)½] and H0=38 kcal/mole. Metallic platelets which formed deep within the crystal bulk, having relatively large surface area usually caused the crystal to fracture. The migration of silver through the crystal bulk was observed to take place only in the [0001] direction. Geometric patterns showing the sixfold symmetry of the basal plane were observed to form, at or near the crystal surface, within a fraction of a second upon the application of a negative probe to the (0001) face. Probe currents, both axial and equatorial, were found to be thermally activated with energies between 38 and 39 kcal/mole for conduction not involving the transport of silver ions. Platelet formation in synthetic quartz crystals differed markedly from that for natural quartz. Instead of a conducting metallic platelet, an irregular dendritic growth appeared.
Contribution of Thermal Diffuse Scattering to Integrated Bragg Reflections from Perfect Crystals
Authors: Chipman David R. , Batterman Boris W.
Published: April 2005

It is shown that the contribution of thermal diffuse scattering to integrated Bragg intensities from perfect crystals can be much greater than previously expected. Measurements on the (555) reflection of silicon are presented showing a thermal scattering contribution of about 70% of the true Bragg intensity. The special aspect of the effect in perfect crystals is discussed and methods of reducing it or correcting for it are included.
Microstructure of Thin Single Crystals of Copper
Authors: Brockway L. O. , Marcus Robert B.
Published: April 2005

Single-crystal films of copper of 700–800 Å thickness have been prepared showing high densities of wide stacking faults. Variations in the annealing treatment of the films affect the nature of the imperfections occurring in the film.
Pulse Method of Measuring Thermal Diffusivity at High Temperatures
Authors: Cowan Robert D.
Published: April 2005

Equations are derived giving the temperature distribution within a thin slab of material which has received a short pulse of energy on one surface, for the case in which energy loss at the surfaces (by radiation or convection) is not negligible. An analysis of these equations indicates that measurement of thermal diffusivity by the pulse method should be feasible even when losses are so large that the maximum temperature of the far face is only 10 or 20% of the no-loss value; this includes nearly all materials, and temperatures to 2500°K or higher.
Hollow Crystals of Hexagonal ZnS
Authors: Soxman E. J.
Published: April 2005

Zinc sulfide powder was heated in a double crucible arrangement at 1150°C for one to three hours. X-ray diffraction measurements showed the development of hexagonal sulfide (wurtzite) and some oxide (zincite). On a thin platinum ribbon introduced to aid the study of crystal growth, several well-developed hollow crystals were found. By transmission electron diffraction measurement, these unusual crystals were identified as hexagonal zinc sulfide.