bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure Study of an Amorphous Electrodeposited Nickel-Phosphorus Alloy
Authors: Bagley B. G. , Turnbull D.
Published: February 2004

The radial distribution function for an electrodeposited amorphous nickel-phosphorus (14.9 wt% P) alloy has been determined. The atomic distribution was found to be similar to that in a liquid metal, and more disordered than that observed in an amorphous nickel-phosphorus alloy produced by chemical deposition. Two transformations (both exothermic) were observed in this alloy; the first of which occurred at 280°±2°C with an energy of 18.5 cal/g (960 cal/g atom) and the second at 410°±5°C with an energy of 6.0 cal/g (310 cal/g atom). As deposited, the alloy exhibits only a very weak small-angle x-ray scattering, apparently not due to the presence of the phosphorus.
Compression of Porous Copper by Shock Waves
Authors: Boade R. R.
Published: February 2004

Hugoniot data for porous copper of two initial densities, 6.052 and 7.406 g/cm3, are presented for compressive stresses ranging from 2 kbar to 1 Mbar. These densities respectively correspond to 67.8% and 82.9% of the density of solid copper. High explosives were used to generate the shock waves in the highstress region, and an air gun was used in the low-stress region. The profiles of the propagated distrubances in each porous copper at low stresses are characterized by three distinct waves. The first of these waves is a low-level wave (<0.5 kbar) traveling at about sonic velocity. The second wave, having an amplitude of ∼1.1 kbar in the 6.052 g/cm3 copper and ∼1.3 kbar in the 7.406 g/cm3 copper, travels at about one-half of the sonic velocity. The velocity and amplitude of the third wave increase with increasing input stress. The experimental Hugoniot data are compared with curves calculated from Hugoniot data for solid copper using the Mie-Grüneisen equation of state with the assumption that compaction of the porous copper is complete. At low stresses, the data approach the calculated curves asymptotically with increasing stress and indicate that compaction is essentially complete for stresses greater than about 21 kbar. At higher stress the experimental data agree very well with the calculated curves.
Anomalies of the Energy of Positive Ions Extracted from High-Frequency Ion Sources. A Theoretical Study
Authors: Benoit-Cattin Pierre , Bernard Louis-Christian
Published: February 2004

Starting from the hypothesis of the modulation of energy of ions extracted by the high-frequency voltage one calculates the width and the form of the energy spectrum of these ions. The variation of the energy deviation of the ions in function of the extraction voltage is obtained by applying to the extraction system the double floating probe theory. These results are in agreement with the experimental results.
Ejection Patterns in Low-Energy Sputtering of GaAs and GaP Crystals
Authors: Comas James , Cooper C. Burleigh
Published: February 2004

The angular distribution of particles sputtered from single crystals of GaAs and GaP has been studied. The (110), (111), and (1̄1̄1̄) faces of the crystals were bombarded normally with Ar ions with energies ranging from 100 to 600 eV. Crystal temperatures were varied between 50° and 525°C. From the (110) face a strong normal 〈110〉 spot appeared. From the (111) face, three strong 〈110〉 spots appeared, accompanied by less intense and less well defined 〈114〉 spots. From the (1̄1̄1̄) face no preferential ejection was noted. The clarity of the spots improved with increasing target temperature.
Experimental Approach to a Theory of Plasticity at Elevated Temperatures
Authors: Wray P. J. , Richmond O.
Published: February 2004

The problem of providing an experimental basis for an isothermal theory of plasticity of metals at elevated temperatures has been examined. The key objectives are considered to be the establishment of a steady-state function and the discovery of a nonsteady deformation law. Constant stress and constant strain rate are judged the best loading conditions for both of these tasks since they provide paths, under the simplest thermomechanical histories, to the steady-state deformation. The use of plots of strain rate and its time derivative for constant stress tests and plots of stress and its time derivative for constant strain rate tests is advocated as a means of best displaying the transient nonsteady behavior. It is even suggested that the functions represented by such plots may be independent of the loading history prior to the period of constant stress or constant strain rate applications. Constant stress and constant strain rate tests are limited in the early (nonsteady) period by lack of control of structure on initial loading, and generally in the later period by the nonuniformity of deformation. It is suggested that the former difficulty may be overcome by employing loading rates sufficiently rapid to permit sensible constancy of structure. Nonuniformity of deformation imposes a severe restriction on the examination of steady-state deformation.
Time-Harmonic Fields in Source-Free Bianisotropic Media
Authors: Cheng David K. , Kong Jin-Au
Published: February 2004

A bianisotropic medium is defined as one in which the field vectors D and H depend on both E and B, but may not be parallel to either. A moving medium appears bianisotropic to the laboratory observer, even if it is isotropic in its rest frame. It is shown that, for time-harmonic fields, a bianisotropic medium can be viewed as one which is electrically and magnetically anisotropic with properly defined dyadic operators. In particular, a moving medium can be characterized by a permittivity tensor and a permeability tensor for plane-wave propagation. This characterization simplifies the solution of electromagnetic problems in moving media. As illustrated, the dispersion relations in a moving uniaxially anisotropic medium are obtained, and the problem of a plane wave normally incident upon a moving uniaxial medium is solved.
Electrical Resistivity of Iron-Carbon Alloys
Authors: Wagenblast H. , Arajs Sigurds
Published: February 2004

The electrical resistivity of alpha iron-carbon solid solutions prepared from iron sources of two different general impurity levels has been studied as a function of applied longitudinal magnetic field up to 60 kOe at 4.2°K. It is demonstrated that the presence of interstitial carbon increases the resistivity of iron and drastically alters the shape of the magnetoresistivity curves, particularly at low fields. The residual resistivity contribution per at.% carbon in solution in high-purity iron is about 4.9 μΩ·cm. At 78°K the value is approximately 6.0 μΩ·cm/at.% carbon, indicating a positive deviation from the Matthiessen rule. In comparison, the residual resistivity of a lower-purity iron is about 6.5 μΩ·cm/at.% carbon at both 4.2° and 78°K. The magnetoresistivity data for the two iron materials containing carbon in interstitial solid solution are shown to obey the Kohler rule to a moderate approximation. In addition, some data are presented which demonstrate that the magnetoresistivity is dependent on the dispersion of the carbon in the iron.
Work-Function Measurements on Monolayer Films of Uranium on (100), (110), and (113) Oriented Faces of Tungsten Single Crystals by Photoelectric and Contact Potential Difference Techniques
Authors: Lea Colin , Mee C. H. B.
Published: February 2004

Uranium was evaporated on to (100), (110), and (113) oriented faces of tungsten single crystals at pressures of less than 5×10−10 Torr. The work function of each of the tungsten surfaces was monitored by photoelectric and contact potential difference (Kelvin and electron-beam) techniques as uranium was adsorbed on to it. The curves of work function versus coverage were fitted to the Gyftopoulos and Levine theory of monolayer adsorption. The constants of the curves gave a value for the density of uranium atoms in a monolayer on each tungsten surface: For the (100) surface one uranium atom is adsorbed for each unit cell in the two-dimensional lattice of surface tungsten atoms, on the (110) surface there is one uranium atom for every two unit cells, and on the (113) surface there are four uranium atoms to each unit cell. For film thicknesses of about two monolayers, the photoelectric technique gave work function values in excellent agreement with those from the Kelvin method, the values being 3.73±0.02 eV for the U/W100 system, 3.90±0.03 eV for U/W110, and 3.67±0.03 eV for U/W113. The electron-beam values were higher than those obtained by the other two methods, probably due to an increase in the electron reflection coefficient as uranium is adsorbed on to tungsten.
Electrostatic Waves in Inhomogeneous and Magnetized Plasmas
Authors: Lee Kai Fong
Published: February 2004

A formalism is presented for the study of electrostatic waves in inhomogeneous plasmas immersed in a finite magnetic field perpendicular to the direction of inhomogeneity. Based on the quasistatic approximation, the dispersion relation is found to depend on the geometrical factors through four quantities which possess certain general properties. The dispersion relation is solved explicitly for the case of cold plasma. It is found that, in stationary plasmas, the density inhomogeneity not only affects the frequencies of oscillation but also alters the propagation and evanescent bands of the two branches of electron plasma waves. For streaming plasmas, the inhomogeneity, the transverse boundary, and the finite magnetic field all contribute to the stabilization of the instability. It is shown that the concept of effective density, developed previously for the infinite magnetic field case, can be extended to the case of finite magnetic field. Various special cases studied previously are recovered by putting appropriate parameters to zero in this general formalism.
Compositional Inhomogeneities in GaAs1−xPx Alloy Epitaxial Layers
Authors: Ewing Richard E. , Smith Deane K.
Published: February 2004

Inhomogeneities in vapor-grown epitaxial layers of Ga(As, P) alloys on GaAs substrates were studied by the electron microprobe, the divergent-beam x-ray method, and x-ray topography. The epitaxial layers were prepared by growing a graded composition region between the substrate and the final GaAs1−xPx composition. The electron microprobe was used to determine the As/P ratio in the layer by scanning the cleaved edge of the epitaxial layer and substrate. The results showed two types of samples: those with composition steps in the graded composition region and those without these steps. Pseudo-Kossel patterns for the composition steps as well as for the GaAs substrate and the GaAs1−xPx alloy surface layer are seen in the divergent x-ray pattern photographs. The sharpness of the pseudo-Kossel lines indicates that the degree of crystalline perfection decreased with increasing phosphorus content of the epitaxial layer. Lang topographs show that the accommodation for the lattice mismatch between the substrate and epitaxial layer results in the formation of bunched edge dislocations which have [011] and[011̄] Burgers vectors. Finally the influence of the defect structures on the diffusion of zinc into the Ga(As, P) material is shown qualitatively by the nature of the diffusion front. The nature of the defect distribution directly controls the nature of the zinc diffusion front into the Ga(As, P). Increased electroluminescent efficiency of devices produced from the material is directly correlated with the flatness of the diffusion front.
Edge Emission Bands in Cadmium Sulfide
Authors: Kingston David L. , Greene Lawrence C. , Croft Lake W.
Published: February 2004

It is shown that there are five clearly defined series of edge emission bands in pure cadmium sulfide crystals. These series have their zero phonon peaks at 5128, 5140, 5163, 5179, and 5234 A at 4.2°K. The temperature dependence of the peak wavelengths and intensities of these series is discussed and a band model presented.
Circular Arrays of Tangential Dipoles
Authors: Hilburn J. L. , Hickman C. E.
Published: February 2004

The elements of the circular antenna arrays investigated in this paper consist of N identical center-fed cylindrical dipoles whose centers are equally spaced around the circumference of a circle. The elements are placed tangential to the circle and lie in the plane of the circle. The derivation of the integral equations defining the vector potential over the surfaces of the elements is presented first. The reduction of these equations to a single integral equation is then obtained by the introduction of sequence voltages for the terminal voltages. A numerical solution of this equation for each sequence is then obtained employing the Gaussian quadrature formula for numerical integration. Approximate values of the sequence terminal admittances are determined by obtaining a polynomial representation of the sequence currents. Experimental results of the current distribution and the terminal admittance on a driven monopole in a tangential array positioned on a ground plane are compared with the theoretical calculations. Finally, the radiation patterns are determined for the numerical currents and these are compared to the radiation patterns arising from the conventional sinusoidal currents.
Dispersion Relation of Long Transversely Magnetized Cylinders (Metal Boundary)
Authors: Sawado Eikichi
Published: February 2004

A theoretical study of the dispersion relation of transversely magnetized circular cylinder with metal boundary is discussed. In the present paper we show that the characteristic frequency generally increases with increasing wavenumber. This shows that the dispersion relation gives forward waves. This situation is closely similar to the independent study by Auld and Mehta for the theoretical results on the problem of transversely magnetized rectangular rods.
Nature of the Material Perturbations Responsible for Hysteresis in Magnetic Domain-Wall Motion
Authors: Baldwin John A.
Published: February 2004

Néel has attributed magnetic hysteresis to random perturbations of the properties of the magnetic material. There has been some question as to whether these properties should be regarded as varying more or less smoothly through the material or whether they should be thought of as highly localized ``pinning centers'' or ``defects.'' Most experimental results can be interpreted equally well using either point of view. However, for one experiment, the predictions of the two theories are distinctly different. This is the dependence of wall velocity on magnetic field when the wall is subjected to a step function of field. In this paper it is shown that the prediction of theory is at variance with experiment if the perturbation is a smoothly varying function of position whereas it is in agreement if the perturbations are localized. In this latter case, wall pinning and irreversible snapping free can occur. Account is taken of wall flexibility, including magnetostatic effects, in the calculations.
Atomic Displacements around Dislocation Loops
Authors: Keating D. T. , Goland A. N.
Published: February 2004

The displacement field around a ``penny-shaped'' inclusion or void in an isotropic elastic medium has been computed by the methods outlined by Sneddon. The boundary conditions for such a loop are that in the plane of the loop z = 0, the displacement is = ±| b |/2 for r less than the loop radius c, and zero outside the loop, and that the shear stress in the r direction across this plane is zero everywhere. We assume that the actual atomic displacements are represented by this displacement field beyond a few atomic diameters of the loop. The solutions for the r and z components of the displacment field are given in series from, and contour plots for these components have been generated by a CDC-6600 computer for Poisson's ratio, σ = 0.30. At large distances from the loop the series expressions for the displacement field converge to that of a single doublet force without moment oriented in the z direction plus a point singularity at the center of the loop. The strengths of these two singularities are expressed in terms of the dimensions of the loop, | b | and c, and σ. From these strengths the lattice dilatations including image effects have been calculated for a finite medium with a uniform distribution of loops. We obtain the results that the only dilatation is normal to the plane of the loop, and that the strain is simply the fraction of atoms contained in the loops.
Recovery Behavior of Si(Li) Junctions after Gamma Irradiation
Authors: Ammerlaan C. A. J.
Published: February 2004

An investigation was made into the room-temperature recovery behavior of lithium-drifted p+-i-n+ junctions in silicon after irradiation with 60Co gamma rays. In most cases, the effects due to irradiation were detected by measuring the capacity vs reverse voltage characteristics of the junctions. Negative space charge appears to be created by precipitation of lithium donors on irradiation defects. The relaxation time associated with this interaction is determined by a capture radius of (4±1) × 10−8 cm. In reversebiased junctions, space charge is neutralized by lithium-ion drift. This compensation process, also observed in lithium-diffused p-n junctions, is characterized by the ionic relaxation time. Expressions, relating both time constants to properties of the basic silicon, are given.
Formation of Hg1−xCdxTe by Hg Ion Bombardment of CdTe Single Crystals
Authors: Foss Norman A.
Published: February 2004

Layers of Hg1−xCdxTe have been formed by Hg+ ion bombardment of intrinsic CdTe single crystals. Spectral photoresponse measurements indicate a variation in x through the thickness of the Hg1−xCdxTe ranging from x≃0.2, at the surface, to x = 1 corresponding to a bandgap of 0.12 and 1.5 eV, respectively. The material has a conductivity of typically 10−5 (Ω·cm)−1 at 77°K and a 2 μ thickness in the region where x≤0.3.
Generation and Measurement of Ultrashort Light Pulses
Authors: Weber H. P.
Published: February 2004

An experimental arrangement for the generation of ultrashort light pulses by mode locking of a Nd:glass laser with a saturable dye and their half-width measurement is described. The pulses, being too short for determining their duration by conventional means, were studied by measuring their autocorrelation function with a method based on optical second-harmonic generation. Measurements were made for two positions of the dye cell within the resonator; first, at some small distance from one of the mirrors and second, with one mirror forming one of the walls of the dye cell. For the former dye cell position the output considered of two or more pulses with a half-width of approximately 30 psec, separated by about 120 psec. With the latter arrangement however, short single pulses were generated having a duration of 8–12.5 psec. In addition this arrangement greatly improved the reproducibility of the pulses and the stability of the output from flash to flash.
Mechanism for Laser Surface Damage of Glasses
Authors: Davit J.
Published: February 2004

A visible breakdown is produced on glass surfaces by high-intensity laser light. The mechanism believed to be responsible for this breakdown is discussed. The successive steps of the mechanism are: optical absorption, fluorescence, chemical reaction by quenching the fluorescence, and breakdown. The theory of this mechanism is in good agreement with our experimental data obtained with different glasses at wavelengths of 10 600, 6943, and 5300 Å.
High Photovoltages in Cadmium Sulfide Films
Authors: Brandhorst Henry W. , Acampora Ferdinand L. , Potter Andrew E.
Published: February 2004

Larger-than-bandgap photovoltages were observed in thin films of CdS which had high resistances and were not uniformly thick. The decay of the photovoltage after removal of light and the effects of temperature and light intensity on the photovoltage were studied and compared to a theoretical model. The results conform with the concept that the photovoltage is due to a space charge produced by a nonuniform distribution of trapped carriers in a multitude of series-connected elements. Analysis of the decay of the photovoltage showed the presence of at least four trapping levels at 0.08, 0.14, 0.26, and 0.41 eV.
Escape of Dislocations from Bound States by Tunneling
Authors: Gilman J. J.
Published: February 2004

At low temperatures stress-activated plastic flow occurs in solids. A quantum-mechanical tunneling model for this process is discussed which leads to an exponential dependence of the rate on the stress: rate ∼e−K/σ. The model can be applied either to locally bound kinks or to segments bound to point defects. The temperature dependence of the process is also discussed.
Mobility of Edge Dislocations in Single-Crystal Calcium Fluoride
Authors: Keig G. A. , Coble R. L.
Published: February 2004

The mobility ν of edge dislocations in calcium fluoride has been measured over an applied stress τ range of 0.1–1.0 kg/mm2 and from temperatures between 25° and 100°C. The data are fitted to the relationship v=6×104exp[−(0.54 eV/kT)−(0.89 kg/mm2/τ)]cm/sec. The activation energy observed for dislocation mobility agrees with that for migration of fluorine ion vacancies in CaF2. Oxygen impurity is observed to harden the crystals. Interactions between oxygen ion and fluorine ion-vacancy dipoles and the dislocation strain fields are considered responsible for some of the velocity-stress-temperature behavior.
Mössbauer Studies on the Superparamagnetic Behavior of Magnesioferrite Precipitates
Authors: Gonser U. , Wiedersich H. , Grant R. W.
Published: February 2004

Mössbauer spectroscopy has been used to study the superparamagnetic properties of small ferrimagnetic MgFe2O4 domains coherently precipitated in a MgO lattice. Different average sizes of precipitates were obtained by varying the annealing temperature and time. A technique is described to estimate the average particle size and relaxation time for the thermal reorientation of the net magnetization from the Mössbauer data.
Quadrupole Splittings and Paramagnetic Shifts in the NMR of 27Al in Rare Earth Aluminum Garnets
Authors: Edmonds D. T. , Lindop A. J.
Published: February 2004

The nuclear magnetic resonance of 27Al at both the a and d aluminum sites of dysprosium aluminum garnet (DAG), terbium aluminum garnet (TbAG), and ytterbium aluminum garnet (YbAG) have been measured at several temperatures between 4° and 290°K. The quadrupole coupling constants e2qQ/ℏ in MHz for the d and the a sites were temperature independent and equal to 5.731 and 0.320 in TbAG, 5.873 and 0.447 in DAG, and 6.300 and 1.053 in YbAG. The increase of the effective internal magnetic field at an aluminum nucleus expressed as a percentage of the externally applied field (the paramagnetic shift) which reaches values of 2% at 4.2°K for YbAG was calculated for YbAG assuming only magnetic dipole interaction and shown to be in excellent agreement with experiment at temperatures between 4.2°K and 290°K. For DAG and TbAG in which the paramagnetic shift reaches 4.8% at 100°K and 6.2% at 77°K, respectively, a similar calculation must await more accurate wavefunctions for the excited states of the magnetic ions.
NMR in Antiferromagnetic Complex Hydrated Manganese Chlorides
Authors: Spence R. D. , Casey J. A. , Nagarajan V.
Published: February 2004

Chlorine and proton zero-field NMR has been observed in three new antiferromagnetic materials CsMnCl3·2H2O, KMnCl3·2H2O, and Cs2MnCl4·2H2O. Their Néel temperatures are 4.8, 2.74, and 1.86°K, respectively. In KMnCl3·2H2O and Cs2MnCl4·2H2O at 1°K the chlorine lines lie in the range 6–21 MHz and the proton lines in the range 18–24 MHz. In CsMnCl3·2H2O they lie at half this value. CsMnCl3·2H2O contains linear Mn–Cl–Mn chains and this is apparently reflected in its high Néel temperature compared to Cs2MnCl4·2H2O in which no such chains exist. Presumably the potassium salt also contains such linkages and the Néel temperature and the grouping of the chlorine lines indicate their presence. The transfer hyperfine interactions between the magnanese and chlorines are all approximately equal in these salts, MnCl2·4H2O and Rb2MnCl4·2H2O for which values have been previously reported. The small variations can be accounted for by differences in Mn–Cl distances.
Proton Magnetic Resonance Study of Magnetic Ordering in Two Cupric Salts
Authors: Wittekoek S. , Poulis N. J.
Published: February 2004

The shifts and the widths of the proton magnetic resonance lines in two Cu2+ salts have been studied to obtain information about the antiferromagnetic short-range order in these crystals. In Cu(NH3)4SO4·H2O, where the Cui+ spins order in antiferromagnetic linear chains, the resonance lines show a strong broadening at decreasing temperatures. This is explained by the decrease of the fluctuations of the Cu2+ spins due to the forming of antiferromagnetic clusters. The experimental results are in agreement with a simple model, relating the fluctuations and the susceptibility of the Cui+ spins.

In Cu(NO3)2·3H2O measurements of the lineshifts show that the Cu2+ spins order antiferromagnetically in pairs. No broadening of the PMR lines is observed, which is explained by the absence of cluster forming.
Magnetic-Resonance Properties of Pure and Titanium-Doped Hematite
Authors: Searle C. W. , Wang S. T.
Published: February 2004

Pure and doped single crystals of hematite were investigated using microwave techniques. Our results show that both the field required for resonance and the linewidth increase with Ti doping, and that the linewidth of the Ti-doped samples favors a slow relaxation process. It is found that values of HD′, the canting field determined by resonance, and HD, the static canting field are related by HD′=HD+4HMHK0′/HD.However, Ti-doped samples must be treated by considering a three-sublattice model.
On the Behavior of CoF2 in a High Magnetic Field Normal to the c Axis
Authors: Ozhogin V. I.
Published: February 2004

A magnetization curve of the AF single crystal CoF2 (tetragonal, TN=37. 7°K) in the magnetic field applied perpendicular to the c axis along x ∥ [100], as measured earlier,1 displays an anomaly, consisting in the sudden drop of dm/dH at the field Hx=Hc∼160 kOe. The anomaly of this kind is anticipated in a great number of easy axis AF with a nonzero Dzyaloshinsky field HD and is connected with a rotation of sublattice moments around the field, which ceases at Hx=Hc= (2HAHE−HD2)/ (HA2+HD2)½. For CoF2 the experimental mx vs Hx curve lies close to the calculated one with HE=240 kOe, HA=75 kOe, HD=115 kOe. At the same field one of the AFMR frequencies turns to zero: ω10=ω0 (I−Hx2/Hc2)½, where ω0= γ(2HAHE−HD2)½, while immediately after Hc ω10 increases according to ω10=ω0(Hx/Hc−I)½. The g-factor anisotropy and magnetoelastic interaction do not influence the vanishing of ω10 at Hc (changing only the expression for Hc) and so should not prevent observation of AFMR near Hc at microwave frequencies. The ``linear'' magnetostriction of a shear type2 (reversed piezomagnetic effect) for CoF2 in the field H̄ ∥ [100] must follow the law uyZ=λHx (I−Hx2/H2)½ and should vanish at Hx>Hc. The maximum value uyZ∼10−4 is expected at Hx=Hc/2½.
Nonlinear Effects above the Spin-Wave Instability Threshold
Authors: Starobinets S. S. , Gurevich A. G.
Published: February 2004

An induction method at high-power level has been used to investigate effects above the first- and the second-order instability thresholds at ferromagnetic resonance. In the case of the first-order process a step on the hf magnetization pulse and low-frequency oscillations take place with a delay of about 30 μsec from the begining of the pulse. For the second order instability, the dependence of the uniform precession amplitude upon power level has three critical points, the first of which is the Suhl threshold, and the second the threshold of relaxation oscillations. The ``gap'' in the resonance curve suddenly arises in the third point. An attempt to explain some experimental results is made.
Magnetic Properties of Some Rare Earth-Aluminum Alloys
Authors: Barbara B. , Bècle C. , Lemaire R. , Pauthenet R.
Published: February 2004

The RAl alloys are orthorhombic; the structure can be described with a trigonal motif similar to a half-cell of CsCl. The R3Al2 alloys are tetragonal. The magnetic properties of the RAl alloys, where R is any rare earth from Ce to Tm, and those of the R3Al2 alloys, with R passing from Gd to Tm, have been measured in fields up to 25 kOe or 60 kOe and at temperatures between 1.4° and 400°K. The RAl alloys, with R from Pr to Tb, order antiferromagnetically at temperature between 20°K (PrAl) and 72°K (TbAl); the magnetic configuration of TbAl has been studied by neutron diffraction; HoAl is ferromagnetic with a Curie point at 26°K; DyAl, ErAl and TmAl exhibit metamagnetism at 4.2°K. Gd3Al2 is ferromagnetic with a Curie point at 282°K, close to that of Gd; Dy3Al2 shows an antiferromagnetic transition near 20°K in zero field and metamagnetic behavior induced by a field below this temperature; its Curie point is 76°K. All compounds exhibit a Curie-Weiss behavior above their transition points, with a paramagnetic moment close to that of the corresponding free tripositive rare earth ions.
Magnetic Properties of the Compound Series Y(MnxFe1−x)2 and Y6(MnxFe1−x)23
Authors: Kirchmayr Hans R.
Published: February 2004

The pseudobinary systems Y(MnxFe1−x)2 and Y6(MnxFe1−x)23 show complete solid solubility. The magnetization and the susceptibility from 80° to 1500°K have been measured.

The Curie temperature and the magnetization are lowered by the addition of Mn to YFe2 and Y6Fe23 and also by the addition of Fe to Y6Mn23. No magnetic ordering above 90°K is observed for Y(MnxFe1−x)2, if x>0.6 and for Y6(MnxFe1−x)23, if 0.4<x<0.8.

The change of the hyperfine fields with temperature is proportional to the magnetization. In Y(MnxFe1−x)2 compounds a distribution of hyperfine fields determined by Mössbauer measurements is present, which results from the randomly distributed Fe atoms at the neighboring sites. In the Y6(MnxFe1−x)23 series a twofold hyperfine field distribution is observed, arising from the four nonequivalent lattice sites and from the random distribution of Fe and Mn atoms on these sites.
Magnetic Properties of Sinusoidal Spin-Density Waves by the Band Model
Authors: Shimizu M.
Published: February 2004

Various properties of the sinusoidal spin-density waves observed in Cr are explained by the band model of a magnetic medium. By the method proposed before, the increase of the free-energy density due to a given distribution of the magnetization 2μBn(r) is written as a function of temperature, magnetic field, n(r) and its derivatives. In order to get a stable sinusoidal modulation of a simple antiferromagnetic ordering, the ordinary and higher-order exchange stiffness constants in the expansion of magnetic energy as a power series of n(r) and its derivatives are expected to be negative and positive, respectively. New interaction energies between elastic strains and derivatives of n(r), besides the ordinary magnetoelastic energy, are introduced in our model to explain the transition between transversal and longitudinal SSDW's and the anisotropies, relative to the directions of modulation and polarization, of the susceptibility and dilatation; the nature of the transition at the Néel temperature is also discussed. The temperature variations of the maximum moment of SSDW, specific heat, and susceptibility are calculated by our model. From the comparison between these calculated and experimental results it will be seen that our model of SSDW is very useful to explain various properties of the SSDW observed in Cr metal.
Temperature Dependence of the Magnetic Excitations of Uranium Dioxide
Authors: Dolling G. , Cowley R. A.
Published: February 2004

The magnetic excitations of UO2 have been measured by inelastic neutron- scattering techniques with the triple-axis crystal spectrometer at the C5 facility of NRU. On increasing the temperature, the neutron groups from the modes of higher (>1.5×1012 Hz) frequency decreased slightly in frequency, barely increased in width, but decreased markedly in intensity, and were not observable above TN[(30.5±0.5)°K for our specimen]. For example the results for the frequencies of the modes with scattering vector Q = (0.5, 0.5, 2.5)2π/a are (ν(T)×1012 Hz): ν(9) = 2.02±0.03, ν(21) = 2.00±0.04, ν(25.3) = 1.95±0.05, ν(27.0) = 1.75±0.05, ν(29.5) = 1.50±0.07. The neutron groups from the modes with lower frequencies decreased more markedly in frequency, but also showed little increase in width and were not observed above TN. The experiments indicate that the modes of lowest frequency which appeared to have almost zero frequency at TN are closely associated with the transition. These measurements, together with the strong magnon-phonon coupling in UO2 and the known temperature dependence of the elastic constants, suggest that the transition in UO2 is a Jahn-Teller distortion of the lowest-triplet state coupled to an antiferromagnetic ordering.
Observation of a Localized Magnon in Co-Doped MnF2
Authors: Buyers W. J. L. , Cowley R. A. , Holden T. M. , Stevenson R. W. H.
Published: February 2004

Measurements have been made with neutron scattering techniques of the spin-wave frequencies at 4.2°K in a doped single crystal of MnF2 containing 5% of substituted Co impurity. The triple-axis crystal spectrometer at the C5 facility of the NRU reactor was used throughout in its constant-Q mode of operation. The low-frequency acoustic spin-wave branches for the [110] and [001] directions agree closely with the measured dispersion for pure MnF2 and are largely unaffected by the presence of Co impurities. Additional scattering has been observed at a frequency of 3.57×1012 sec−1, which appears to be independent of the momentum transfer. This scattering is not observed above TN at 110°K and no mode of this frequency has been observed in pure MnF2. This additional scattering is believed to result from a localized spin-wave mode associated with the Co impurities. The frequency agrees closely with calculations of the energy of the first excited state of Co in MnF2 in the molecular-field approximation.
Spin Orientation and Magnetic Properties of Ca2FeAlO5
Authors: Grant R. W. , Geller S. , Wiedersich H. , Gonser U. , Fullmer L. D.
Published: February 2004

The Mössbauer effect has been used to determine the spin directions and magnetic space group of Ca2FeAlO5. At 5°K the spins on both the octahedral and tetrahedral sublattices are directed along the crystallographic a axis following the convention c<a<b. This is consistent with the magnetic space group Ic′m′m′ for Ca2FeAlO5. The sublattices are individually antiferromagnetically ordered. The crystal structures of Ca2FeAlO5 and Ca2Fe2O5 are apparently closely related but at 5°K as well as at room temperature, the spins in Ca2Fe2O5 are along the c axis. The Néel temperature of Ca2FeAlO5 is 60°±15°C. The internal fields at 5°K observed at the octahedral and tetrahedral iron sites of Ca2FeAlO5 are 502±10 and 454±10 kOe, respectively.
Mössbauer Study of FeCl2·4H2O in the Temperature Range 4.2° to 0.025°K
Authors: Ono K. , Shinohara M. , Ito A. , Fujita T. , Ishigaki A.
Published: February 2004

The Mössbauer spectrum of 57Fe in FeCl2·4H2O has been examined in the temperature range 4.2° to 0.025°K. The temperature dependence of the internal magnetic field indicates that the spin ordering starts at 1.3°K. The spectrum below the Néel temperature is well-explained with the parameters H = 266 kOe, e2qQ/2 = 3.10 mm/sec, η= −0.2 and ∠Hq = 25°, where H, e2qQ/2, and η have the conventional meanings and ∠Hq is the angle between the internal magnetic field and the electric field gradient at the iron nucleus. The spectrum for a single crystal with gamma rays being parallel to the monoclinic crystal axis b determines ∠Hb = 15°. Thus, below the Néel temperature the directions of the internal magnetic field at the two sites of iron nuclei in this material make an angle of 30° with each other.
Magnetic Properties of Rare Earth Hydroxides
Authors: Wolf W. P. , Meissner H. , Catanese C. A.
Published: February 2004

The rare-earth hydroxides, R(OH)3 with R–La to Yb and Y form a series of simple magnetic crystals isostructural with the hexagonal rare-earth trichlorides. Compared with most ionic rare-earth crystals they have relatively small lattice parameters, and one may therefore expect magnetic cooperative effects at readily accessible temperatures. In this paper we report the first series of magnetic measurements on small, hydrothermally grown single crystals (1 to 10 mg) which show that Tb(OH)3, Dy(OH)3, and Ho(OH)3 order ferromagnetically at 3.72°, 3.50°, and 2.55°K, respectively, while Nd(OH)3 and Gd(OH)3 undergo more complex antiferromagnetic transitions near 1.7° and 2.0°K. Er(OH)3 remains paramagnetic down to 1.2°K. Magnetization measurements on Tb(OH)3, Dy(OH)3, and Ho(OH)3 in fields up to 14 kG give saturation moments (corrected for Van Vleck temperature-independent paramagnetism) of 1350 emu/cc (9.0 μB/ion), 1418 emu/cc (9.6 μB/ion), and 1121 emu/cc (7.6 μB/ion) parallel to the c axis and almost zero perpendicular to the c axis. The correspondingly large and anisotropic magnetic dipole interactions account approximately for the observed Curie temperatures, suggesting that Tb(OH)3, Dy(OH)3, and Ho(OH)3 may be among the simplest examples of Ising-like systems studied so far, with dominant interactions along linear chains of nearest neighbors. Single crystals are found to be chemically stable with apparently good optical properties, suggesting useful applications to magneto-optic devices. These are discussed briefly.
Optical Spectroscopy of Rare Earth Perovskites
Authors: Schuchert H. , Hüfner S. , Faulhaber R.
Published: February 2004

High-resolution optical absorption spectra have been obtained on antiferromagnetic DyAlO3 and weakly ferromagnetic HoFeO3 and DyFeO3 at low temperatures. In DyAlO3 the absorption lines show a triplet structure which vanishes in Y(Dy)AlO3. From this it is concluded that the magnetic interactions take place for each Dy ion with only two neighbors. At 3.5°K the splitting of the absorption lines starts to increase with decreasing temperature yielding a Néel temperature of (3.5±0.1)°K. The magnetic moment of the ground state is determined to be μ = (8.6±1.0)μB. In DyFeO3 a Néel temperature of (4.5±0.3)°K is deduced from the temperature dependent lineshift, the magnetic moment of the ground state is found to be μ = (8.9±1.0)μB.
Correlation of Magnetic Susceptibility and Infrared Spectra of FeF2
Authors: Stout J. W. , Steinfeld M. I. , Yuzuri M.
Published: February 2004

Precise measurements of the magnetic susceptibility of single crystal FeF2 parallel and perpendicular to the tetragonal axis are reported. Measurements of the polarized infrared spectra of crystalline FeF2 show transition to electronic levels arising from the splitting of the 5D state of the Fe2+ ion by the ligand field of D2h symmetry. A magnetic dipole transition observed at 1115 cm−1 when the magnetic field of the light is polarized parallel to the tetragonal axis is tentatively identified with a transition from the ground orbital state of symmetry A1g to an excited level of symmetry B1g arising from the octahedral 5T2g levels. In the helium temperature range the magnetic susceptibility parallel to the tetragonal axis is (5.6±0.1) × 10−4 cm3 mole−1. This value is correlated with that calculated from the matrix element of the orbital angular momentum parallel to the tetragonal axis connecting the ground state with the excited orbital state.
Effects of Magnetic Ordering on the Optical-Absorption Transitions of the Co2+ Ion in Fluoride Salts
Authors: Holloway W. W. , Kestigian M.
Published: February 2004

The optical absorption spectra of the Co2+ ion have been studied in magnetic and nonmagnetic fluoride salts with perovskite structures. The temperature dependences of the Co2+ ion absorption band, e.g., 4T1g→4T1g (P), maxima show effects due to the ordering of these magnetic materials. These effects are observed as shifts in the band maxima in addition to changes of purely thermal origin. The magnetic effects occur in the vicinity of the Néel temperatures in both cobalt salts and in magnetic salts such as RbCo0.05Mn0.95F3, where the cobalt ion is an impurity. Magnetic effects have also been observed in the structure of the optical transitions.
Magnetic Neutron Scattering from Atoms Dissolved in Ferromagnetic Iron and Nickel
Authors: Low G. G.
Published: February 2004

Recent experimental results giving the distribution of the magnetic-moment disturbance associated with solute atoms in ferromagnetic iron and nickel are summarized. The disturbances around transition elements dissolved in iron are of two quite different forms dependent on whether the element concerned lies to the right or to the left of iron in the periodic table. This suggests a dependence on the sign of an electrostatic perturbing potential and a discussion of this possibility is given in terms of a simple electron gas model. The two types of magnetic disturbance observed are not related by a sign reversal and the nonlinearity thus demanded by experiment is thought to result from limitations on electron-density increases imposed in iron by the restricted number of orbitals available at any one site. Experimental results for iron alloys containing nontransition-element solutes are also examined. Measurements on a wide range of both transition and nontransition elements dissolved in nickel are reviewed. Zn, Al, Ga, Si, Ge, Sn, Sb, V, Cr, Nb, Mo, Ru, W, and Re all result in a widespread loss of magnetic moment from the nickel host surrounding a solute site. The magnetic disturbances corresponding to these impurities differ in magnitude but show an approximately invariant shape. These defects are discussed in terms of bound impurity states and a molecular-field treatment involving a nonlocal and nonlinear susceptibility to represent the magnetic properties of nickel.
Coupled Walls in Multilayer Films
Authors: Feldtkeller E.
Published: February 2004

If the thickness of an intermediate nonmagnetic layer separating two ferromagnetic layers is larger than the ferromagnetic wall thickness (order of 1 μ), only a magnetostatic interaction at the film edges exists. If the intermediate-film thickness is smaller than the wall thickness, the magnetostatic interaction of the domain walls is essential, yielding special multilayer wall configurations. If the intermediate film is thinner than that necessary for a complete exchange isolation (order of 10 nm), the wall configurations are modified by an exchange coupling between the local magnetizations of the layers. The wall configurations and their influence on the wall motion and switching behavior are reviewed in this paper.
Lorentz Microscopy of Weak Magnetic Flux Inhomogeneities
Authors: Wohlleben D.
Published: February 2004

The potential of Lorentz microscopy to give quantitative information about weak magnetic field inhomogeneities can be exploited fully only if the classical approximation to the electron contrast is abandoned in favor of the wave mechanical reality. The inhomogeneities cause coordinate dependent phase shifts Δφm in the coherent electron wavefunction which can be detected in principle by any electron optical method for phase contrast.

The transition from a classical to a wave-mechanical treatment of contrast is necessary if the inhomogeneity contains flux of the order of one fluxon h/2q or less.

Contrast formation in the defocused mode is discussed. The image space in this mode has sections with almost classical, low contrast (due to running lateral waves) divided by the caustic mantle from other sections with wave-mechanical, high contrast (due to standing lateral waves). The maximum contrast due to a given inhomogeneity can be predicted from its maximum magnetic phase shift Δφm = (q/ℏ) ΔΦI.

The differential and total scattering cross sections of an arbitrary flux distribution for particles with charge q are calculated. The total cross section does not depend on the kinetic energy.

In order to observe a flux inhomogeneity ΔΦI≪h/2q in principle, a minimum number Np min of particles must be passed through it. This number is Np min > 〈Δφ2〉−1 if the particles are recorded in pure scattered states (Fraunhofer diffraction, dark-field microscopy). The minimum number is Np min> 〈Δφ〉−2, if the detection is achieved in some optimum arrangement of interference between the scattered and an unscattered state (around the caustic mantle in the defocused mode; interference microscopy; Zernike phase contrast). In the case of detection by interference, the minimum number of scattered particles NS min necessary for observability is NS min> 〈Δφ〉−1. This relation shows that for observability of a total flux 〈Φ〉 a minimum amount of scattered charge QS min = NS min 2q is necessary, given by the relation QS min 〈Φ〉>ℏ. A full paper will appear elsewhere.
Anisotropic Magnetization of TmSb
Authors: Vogt O. , Cooper B. R.
Published: February 2004

We report the experimental observation, with pulsed field, of the anisotropy in magnetization theoretically predicted for single crystals of TmSb. Agreement with crystal-field-only theory is excellent at 1.5°K. At 20.4°K, agreement between isothermal theory and experiment is poorer. This discrepancy can be explained if spin-lattice relaxation effects cause the observed magnetization to be a mixture of isothermal and adiabatic effects.
Experiments on Two-Dimensional Heisenberg Systems
Authors: de Vries G. , Breed D. J. , Maarschall E. P. , Miedema A. R.
Published: February 2004

The crystal structure of the group of compounds with the general formula M2+M2+(Hal)4, where the magnetic ion may be Mn2+, Ni2+, or Cu2+ for instance, strongly suggests the possibility of studying the thermal and magnetic properties of almost isolated layers of magnetic atoms.

The susceptibility vs temperature curves have been obtained for K2NiF4, K2MnF4, and Rb2MnF4 single crystals for which the interaction within a layer has the antiferromagnetic sign. Below TN both the curve for the parallel susceptibility and the heat capacity are in agreement with spin-wave predictions for a two-dimensional layer taking into account the anisotropy field as derived from the observed field for spin flopping.

The values for kTN/J in K2MnF4, Rb2MnF4, and K2NiF4 agree with predictions from partition function series expansions.

In Cu(CH3NH3)2Cl4 and Cu(C2H5NH5)2Cl4 the nearest-neighbor interaction has the ferromagnetic sign. Two transition temperatures are found in the heat capacity, the higher ones probably corresponding to the Curie temperature of the isolated layer, the lower one the transition to long-range order in three dimensions. The values for kTC(2)/J observed, are about 1.1.
A Large Sharp Film NDRO Bit Organized Memory
Authors: Barker P. D. , Oredson H. N. , Torok E. J.
Published: February 2004

Sharp films are planar NiFe films shaped like a diamond with the easy axis along the long diagonal. They have very high nucleation thresholds, reversible limits 0.1 Oe less than Hk, and can be switched rotationally by the combination of two fields, HL = ⅔Hc and Hr = ⅔Hk, each of which is incapable of switching the film when applied separately. This is the report of a design for a 106 bit 60-nsec cycle time (time between successive reads or writes) memory. It uses four unpaired sharp films per bit; each film is 15 mil wide by 45 mil long and the digit lines are shaped like elongated U's. They are connected by infrared soldering from substrate to substrate. At the end of each sense line is an inexpensive low-level gate which allows sharing of sense amplifiers and prevents saturation of the sense amplifiers after a write. The same word current, 250 mA, is used for NDRO reading and writing. Digit current is also 250 mA.
Critical Scattering of Neutrons from Terbium
Authors: Als-Nielsen J. , Dietrich O. W. , Marshall W. , Lindgård P. A.
Published: February 2004

The inelasticity of the critical scattering of neutrons in terbium has been measured above the Neél temperature at the (0, 0, 2−Q) satellite position. The results show that dynamic slowing down of the fluctuations does occur in a second-order phase transition in agreement with the general theory. However, the detailed variation of the inelasticity with temperature is in disagreement with existing theories, and it is concluded that the conventional theory is invalid except at infinite temperatures.