bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for Impurity Bands in La-Doped EuS
Authors: Chen C. W. , Carter F. , Heikes R. R.
Published: April 2005

A study has been made of the effect of La doping on the electrical conductivity of EuS. The doping has been observed to cause considerable decreases of the resistivity at all temperatures between 4.2° and 300°K. In the paramagnetic state, the electrical data are well represented by a straight line of the form ρ/T=ρ0 exp (ΔE/kT),where ΔE is the activation energy for conduction. The resistivity reaches a maximum value at a temperature which is closely related to the Curie temperature (Tc). A decrease of resistivity of approximately three orders of magnitude in each case is observed at the magnetic transition. Resistivities below Tc display a metallic-type temperature dependence. The resistivity anomaly may be attributed to a change of the conduction mechanism from an activated hopping process to that involving impurity bands. It is shown that for temperatures below Tc the existing ideas concerning impurity banding are valid of one properly takes into account the effects of the magnetization of the host lattice. Above Tc the excess electrons are in localized states and the conduction process resembles that of Li-doped NiO. A full account of this work will be published in Physics.
Magnetic and Crystallographic Study of the Phase Transition in Copper Ferrite
Authors: Levinstein H. J. , Schnettler F. J. , Gyorgy E. M.
Published: April 2005

The cubic-to-tetragonal phase transformation in copper ferrite has been studied by x-ray diffraction and metallographic techniques. The temperature at which the transition occurs and the degree of tetragonality existing at room temperature depend upon the relative distribution of the copper ions between the tetrahedral and octahedral sites. The transformation is diffusionless and occurs by a double shear mechanism. This results in a lamellar microstructure in which the orientation difference between adjacent lamellae are functions of the degree of tetragonality. Tetragonal copper ferrite exhibits a rotational hysteresis, the magnitude of which is also dependent upon the degree of tetragonality. The temperature dependence of the complex permeability has been measured at various frequencies.
Magnetic Properties of CuF2
Authors: Joenk R. J. , Bozorth R. M.
Published: April 2005

We have measured the moment of a pressed powder sample of monoclinic CuF2 from 4.2° to 300°K in fields to 25 kOe. χ(T) indicates an AFM transition at TN=69°K, and analysis gives ḡ≈2.3 and Θ≈−200°K. TN and Θ are consistent with magnetic ordering of the first kind with AFM exchange interactions J1(corner-bc)≈34°K and J2≈22°K. Weak ferromagnetism of anisotropic exchange origin is expected on the grounds of symmetry; the measured ferromagnetic moment is σ0≈1 G cm3/mole, corresponding to a canting angle φ≈0.01°. Assuming magnetic dipolar anisotropy and estimating principal axes and values for the anisotropic g tensor, we find the spin axis to be about 2° from c and 99° from a in the ac plane with anisotropy field HA∼2000 Oe, and the weak moment to be parallel to the monoclinic axis b with canting field HDM∼1000 Oe. Pseudodipolar anisotropy may be expected to change the orientation, but not the order of magnitude of these fields. The uniform mode AFM resonances are not degenerate in general, but both would be expected to occur at v/c∼9 cm−1 using these values.
Mössbauer Studies of Spin Flop in Antiferromagnetic Hematite
Authors: Blum N. , Freeman A. J. , Shaner J. W. , Grodzins L.
Published: April 2005

The antiferromagnetic sublattice magnetizations below the Morin transition temperature TM≈260°K, are parallel and antiparallel to the trigonal axis of rhombohedral α-Fe2O3. Experiments at 80°K, using the Mössbauer technique together with high external magnetic fields on both polycrystalline and single-crystal samples, show that the directions of the sublattice magnetizations flop from along the trigonal axis for the applied field H0Hc; Hc is found to be 67.5±3 kOe. In the polycrystalline sample this behavior is exhibited through the occurrence of a maximum in the width of the outer lines of the Mössbauer spectrum plotted as a function of H0. In the single crystal, which is oriented so that the gamma rays propagate along the [111] direction, the magnetic transition is clearly observed as a sudden qualitative as well as quantitative change in the appearance of the Mössbauer hyperfine spectrum; below the critical field the Δm=0 lines are the strongest components of the six-line spectrum.
Superconducting ac and dc Properties of Lead-Bismuth Films
Authors: Garbuny M. , Gottlieb M. , Conroy J.
Published: April 2005

Measurements have been made on the superconducting properties of thin films of lead-bismuth alloys ranging in composition from pure lead to 70% bismuth. These were deposited in 300-Å-thick layers on glass and polypropylene substrates. At T=4.2°K, Hc rises with increasing bismuth concentration to a maximum of 23 kG at 50% bismuth and then falls abruptly to zero for greater bismuth concentrations. At 1.9°K this maximum increases to 33 kG at 50% bismuth. Current densities of 107 A/cm2 were reached, corresponding to 7 A in a 2-mm-wide sample.

Measurements were made of the low-frequency ac superconducting losses by the L-C circuit Q method. Frequencies in the order of a few hundred cps were achieved by vacuum deposition of circuit elements several hundred feet long. The only dielectric material present was polypropylene whose dissipation factor was found to be 5.5×10−6 (Q=1.8×105). With this background loss the superconducting losses were barely detectable in lead-bismuth, with a lower limit on Q of about 106. Losses became large when currents were sufficiently high for the formation of normal regions. The onset of these losses correlated very well with dc resistance measurements. For the long circuit elements this resistive onset occurs at low current densities, about 104 A/cm2. Present work is aimed at raising the current-carrying capacity of the long circuits to that of the short samples, and measuring ac superconducting losses at high current densities.
High Critical Current Superconducting Titanium-Niobium Alloy
Authors: Vetrano J. B. , Boom R. W.
Published: April 2005

The stabilization of transport current in a high field Ti-Nb alloy by metallurgical heat treatment was investigated. Solid-solution annealing of the alloy, followed by nucleation and growth of a second-phase precipitate, was found to have a pronounced influence on the ability of the alloy to carry high transport current in high magnetic fields. The precipitate was most effective in the early stages of growth. Overaging resulted in reduced values of critical transport current density. Aging of a Ti-20.7 at. % Nb alloy for ¾ to 6 h at 400°C yielded a critical current density in excess of 105 A/cm2 at 4.2°K in a 30-kG applied magnetic field. The same alloy in a solid solution condition carried less than 104 A/cm2 at the same temperature and field. The upper critical field (Hc2) of the aged alloy was found to be 128 kG at 1.2°K.
Magnetic Annealing Experiments in Some Cu-Ni-Fe and Cu-Ni-Co Alloys
Authors: Becker Joseph J.
Published: April 2005

In a spinodally decomposing ferromagnetic precipitation alloy, magnetic annealing effects might be expected to occur if the precipitation in a field is carried out near the Curie temperature of the quenched phase. Cu-Ni-Fe and Cu-Ni-Co alloys are known to undergo spinodal decomposition. Several alloys in these systems were solution treated, quenched, and aged in a field applied along a diameter of the disk-shaped specimens. Torque curves were then measured. The Cu-Ni-Fe alloys showed no effect, but all three Cu-Ni-Co alloys investigated showed uniaxial anisotropy. The largest Ku, attained in an alloy of 50% Cu, 20% Co, and 30% Ni, was 5×104 erg/cm3. Nevertheless, the parallel and perpendicular remanence and coercive force were only a few percent different.
Critical Current Degradation in Wide Samples of High-Field Strip Superconductors
Authors: Hoag Ethan D.
Published: April 2005

Measurements of the magnetic anisotropy of critical current in samples wide enough for use in large magnets reveal a degradation effect in strip superconductors. The effect is manifested as a truncation or ``chopping off'' of the peaks of the anisotropy curves of these samples. With narrow samples the anisotropy curves (average critical current density plotted as a function of magnetic field direction) normally display a well-defined peak centered about the direction parallel to the rolling plane of the strip. With wide samples, however, this peak appears progressively more truncated as the width is increased, and the truncation level (i.e., maximum current density) is roughly inversely proportional to the width, so that the total current tends to remain constant, independent of width. For Nb-25% Zr strip 0.051 mm thick, this limiting current is approximately 125 A at a field of 4 Wb/m2 for widths between 1 and 10 mm. 1.32-mm-wide samples display little or no truncation and have maximum current densities of 1.8×105 A/cm2, whereas 10-mm-wide samples show severe truncation and have maximum current densities of 2.6×104 A/cm2.
Resistive Intermediate State for Thin Superconductive Films of Tin
Authors: English Thomas D. , Finzi Leo A.
Published: April 2005

An experimental study of the resistive transition state of vacuum-deposited films of tin has been performed in the temperature range extending from 3.7° to 2.0°K for various values of normally applied magnetic field H. In general, the relationship between the current through the film I and the voltage drop across the film V is not linear. However, over a broad range of the variables T, H, and I, the voltage drop V can be expressed in terms of the voltage drop which occurs when the sample is completely normal VnV=Vn(1−exp{−a[H−b(Tc−T)]Tc−T});  for  T<Tc,  b(Tc−T)<H,where Tc is the zero-field transition temperature. The constants have been found to be: a=0.12°K/G and b=64 G/°K.
Theory of Spin-Wave Resonance in Thin Films
Authors: Schlömann Ernst
Published: April 2005

A new theory of spin-wave resonance, based upon the assumption that the saturation magnetization varies linearly across the thickness of the film, is described. The characteristic equation for the normal modes has been solved both for free and for strongly pinned surface spins. According to this theory the lower-order modes are approximately equally spaced, their separation in magnetic field being given by δH≃1.5 (H0′)⅔D⅓, where H0′ is the field gradient and D=2A/M0 a phenomenological exchange constant (A = Landau-Lifshitz constant, M0 = saturation magnetization). The theory agrees remarkably well with the experimental data of Nisenoff and Terhune on Permalloy films.
Phonon Generation by Stripe-Domain Resonance in Permalloy Films
Authors: Seavey Marden H. , Kearns William J.
Published: April 2005

The generation of microwave phonons by stripe-domain resonance (SDR) in Permalloy films is described. The phonon polarization is mainly longitudinal and this is explained by the orientations of the precessing spins in the stripe domains. The phonon echo power behaves similarly to the SDR absorption with dc magnetic field when the field is in the film plane or at an angle to it. The ratio of the echo power out of the cavity to the input power can approach that for the main resonance but is usually from 5 to 10 dB less.
Ferrimagnetic Resonance Linewidth in Rare-Earth-Doped YIG at Low Temperatures
Authors: Clarke Barry H.
Published: April 2005

In order to test the ability of the longitudinal mechanism to explain the relaxation at low temperatures of rare-earth-doped YIG, we have measured linewidths ΔH in [111] directions at 9.3 Gc/sec for YIG doped with 5% Yb, 2.6% Er, and 1% Nd, from 1.5°–100°K. The measured linewidths are strongly temperature-dependent in this temperature range, decreasing (with decreasing temperature) by two orders of magnitude, from maxima of several hundred oersteds to only a few oersteds. After subtracting out a small line-width contribution associated with the host lattice, the remaining strongly temperature-dependent contributions, associated with the rare-earth ions, are in agreement with the predictions of the longitudinal mechanism at low temperatures (kT<δ/2): ΔH∝ {ωτ/[1+(ωτ)2]} (kT)−1 exp(−δ/kT), where ω is the measurement frequency and δ is the splitting of the doublet ground state by the anisotropic iron-rare-earth exchange interaction. If we assume that the rare-earth ion relaxation time τ is slowly varying with temperature (as is reasonable for Kramers ions at low temperatures where τ probably arises from a direct process) then we obtain the following estimates for δ in the [111] direction: 61.3 cm−1 for Nd; 21.0 cm−1 for Yb; and 18.3 cm−1 for Er. These results are in good agreement with the results of spectroscopic measurements where these are available, i.e., Yb and Er.
Control of Texture in Magnetic Material by Surface Energy
Authors: Walter John L.
Published: April 2005

Different crystallographic planes, at a gas-metal interface, have different surface energies. Although the energy difference is small (less than 100 erg/cm2), it is sufficient to cause migration of boundaries between grains of different (hkl) surfaces provided there is a sufficiently small restraint to boundary migration. Since the (110) plane is the plane of lowest surface energy γ in 3% silicon-iron, grains with (110) planes at the gas-metal interface are favored to grow at the expense of other (hkl) grains (γ110<γhkl) when the material and annealing atmosphere are free of impurities. In the presence of certain impurities, however, γ100 may be lower than γhkl and grains with (100) planes are favored to grow at the expense of all others.

With proper processing, sharp (110)[001] or (100)[001] textures may be obtained in sheets of high-purity silicon-iron.

Grain size and texture can be altered by deliberate additions of oxide film to the surface, by the amount of silicon in the alloy, and by the choice of annealing atmosphere.

The effect of improved texture and low impurity concentration on magnetic properties is discussed.
Effects of Local Atomic Order on the Magnetic Properties of Au-25 at.% Fe
Authors: Sundahl R. , Sivertsen J. , Chen T.
Published: April 2005

In a study of the effect of local atomic order on the physical properties of metallic solid solutions, the authors have measured changes in magnetic properties of a Au-25 at.% Fe alloy with heat treatment. Measurements of σ were made as a function of H between 9.0 and 18.5 kOe and T between 78° and 320°K. The Curie temperatures were determined from plots of H/σ vs σ2 and the magnetic moment at 0°K from an extrapolation of a plot of σ(18.5 kOe) vs T32. The local-order parameters were determined for the two states from x-ray diffuse scattering measurements. Application of the cluster-variation method to the calculation of the Curie temperatures from the order parameters gives quantitative agreement with the experimental measurements, while the use of a Curie-Weiss model gives values which are higher than experiment. The magnetic moments on the iron atoms are found to be higher than for pure iron and to increase with the change in order.
Ni-Fe-Nb-Ag, A New Square-Loop Alloy for Magnetic Memory Elements
Authors: Tolman E. M.
Published: April 2005

A new alloy composed of 79.4% Ni, 16.6% Fe, 3.0% Nb, and 1.0% Ag has been developed for use in magnetic memory elements. After heat treatment the material in flattened-wire form (0.003×0.00025 in.) has a rectangular hysteresis loop with a squareness ratio of 0.95, a coercive force of 1 Oe, and a switching coefficient of 0.3 Oe-μsec. In basic Ni3Fe alloys, uniaxial magnetic anisotropy as well as increase in coercive force result from cold working. Normally, the anisotropy is destroyed by the anneal required to lower the coercive force. Retention of magnetic anisotropy has been achieved by the addition of Nb and Ag to the basic alloy. This behavior is attributed to the presence of dislocations anchored in the slip planes. These dislocations are believed to result from the interaction between lattice strains arising from the oversize foreign atoms (Nb and Ag) and strains generated by plastic deformation.
Effect of Oxygen on the Magnetic and Long-Range Ordering Properties of Ni3Fe
Authors: Nesbitt E. A. , Batterman B. W. , Fullerton L. D. , Williams A. J.
Published: April 2005

Previously, it was shown that oxygen is a factor in the magnetic annealing of Permalloy (Ni-Fe alloys) and Perminvar (Ni-Fe-Co alloys). Electron-diffraction studies indicated that oxygen caused impurity faults by condensing on the (111) planes of the crystal. An intimate connection between the presence of these impurity faults and the ability to respond to heat treatment in a magnetic field was established. However, the orientation of these faults was not observed to be directly related to the direction of the field heat treatment. In the present work on single crystals of 76% Ni—24% Fe, it was found that those crystals which were heat treated in a purified hydrogen atmosphere did not respond to the magnetic annealing treatments when cooled at normal rates, whereas those that were heat treated in a slightly oxidizing atmosphere did respond. Furthermore, after subsequent heat treatment, x-ray investigations showed that the crystals which did not respond to magnetic annealing had substantially more long-range ordering present (4 to 1) than the crystals which did respond. Long-range ordering first appeared in both specimens after 475°C for 18 h. The specimens that did not respond to magnetic annealing also developed substantially higher values of crystal anisotropy than those that did respond. The uniaxial anisotropy which was developed by the slightly oxidized crystals could not be obliterated by ordering heat treatments. This work suggests that the oxygen inhibits the long-range ordering mechanism, and, therefore, it may aid in the formation of like pairs of atoms.
Alloys with Low Remanence and Low Coercive Force in the Region of 9% Aluminum Iron
Authors: Pavlovic D. , Foster K.
Published: April 2005

A material combining low remanence with a low coercive force has been developed by applying a high-temperature heat treatment to alloys in the region of 9 wt % aluminum iron. This material displays a large grain size with a predominantly (111) texture in the plane of the sheet. Epstein strips as well as rings of 9% aluminum iron had a remanence of 1.66 to 2.68 kG and a coercive force of 0.25 to 0.3 Oe. Other typical properties were a maximum permeability of 2700, inductions of 12.9 kG at 10 Oe and 16.1 kG at 100 Oe, electrical resistivity of 90 μΩ-cm, and Rockwell B hardness of 87. The properties of these alloys may be particularly suitable for application in relays, where a low residual induction would minimize or eliminate the air gap and good mechanical properties would reduce the wear of the relay pole faces.
Magnetic Aftereffects in Fe-Al Alloys
Authors: Maringer R. E.
Published: April 2005

Measurements of the decay of magnetic permeability with time after demagnetization have been performed on Fe—17 at.% Al. Measurements were obtained over the range of 360° to 475°C, with a wire specimen acting as the core of an open-end transformer. The decay curves could be separated analytically into two components, with relaxation times differing by about a factor of six. Relaxation times for the shorter of the two components agree well with relaxation times calculated from observations of the Zener peak (by internal-friction methods) in these alloys. Thus, as is the case for carbon in alpha-iron, this component results from an ordering process which can be either stress or magnetically induced. The activation energy for this process is about 56 kcal/mole. The longer of the two relaxation processes apparently involves directional ordering alone.
Effect of High Pressure on the Al-Mn Binary Alloy System between 40 and 100 at.% Mn
Authors: Ernst D. , Tydings J. , Pasnak M.
Published: April 2005

The effect of pressure on the aluminum—manganese binary system was investigated by preparing various Al-Mn alloys in a cubic multi-anvil pressure apparatus. Pressures of 40 000 and 60 000 atm were used in preparing the alloys from powdered Al and Mn mixes. Indirect heating was used to melt the specimens and to apply a variety of heat treatments (including a magnetic anneal) to the alloys while they were under pressure. The x-ray results indicate that pressures of 40 000 atm have little effect on the Al-Mn system, since the phases prepared under pressure were the same as those found at 1 atm by other investigators of this system. A new identification of the phases present in the η, η′ region was made. One phase is body-centered cubic (a0=8.9 Å), the other is face-centered cubic (a0=12.5 Å). It was not possible to ascertain to which phase, η or η′, the above a0 values belonged. The results obtained at a pressure of 60 000 atm differed from those found at 40 000 atm as follows: (a) when quenching alloys in the 50–60 at. % Mn region from 1550°C at 60 000 atm, the magnetic τ phase is formed in preference to the ε phase which is formed at 40 000 atm, and (b) a new phase, the structure of which is being determined, was formed from the η,η′ phases. Several specimen magnets were made by the high-pressure technique; their magnetic properties were comparable to as-cast AlMn magnets before they were given optimizing treatments.
Performance and Ferrimagnetic Material Considerations in Cryogenic Microwave Devices
Authors: Comstock R. L. , Fay C. E.
Published: April 2005

Circulators which can be operated at cryogenic temperatures are discussed. Both symmetrical Y-junction circulators using polycrystalline ferrimagnetic garnets and hybrid-gyrator circulators using single crystals are evaluated. The temperature dependence of the ferromagnetic resonance losses of polycrystalline aluminum-doped and undoped yttrium iron garnet is reported. Device performance is evaluated in terms of the measured material properties.
Square-Loop Garnet Materials for Digital Phase-Shifter Applications
Authors: Taft D. R. , Hodges L. R.
Published: April 2005

Materials from the garnet family 3[(1-x) Y2O3·xGd2O3]· 5[wAl2O3· (1-w) Fe2O3] have been investigated for use in latching-type digital phase shifters. At room temperature, as x and w varied from 0 to 0.30, the electrical properties of these materials varied in the following manner: saturation magnetization (4πMs)−1780 to 500 G, resonance linewidth (ΔH)−33 to 200 Oe, remanence ratio Rr(Br/Bs)−0.90 to 0.65, coercive force (Hc)−0.50 to 2.00 Oe, switching constant (Sw)−0.50 to 1.00 μsec-Oe. By proper choice of x and w, some of these properties can be made quite insensitive to temperature and power variations over wide ranges. It was found that, although Hc and Rr tend to undergo large unfavorable changes with x and w, they could be controlled by increasing the average size of the crystallites. A five-bit (180°, 90°, 45°, 22½°, and 11¼°) phase shifter was developed using material from the above family in a square toroid geometry. This device operated across the frequency band 5.4 to 5.9 Gc/sec with a switching rate of 5 kc/sec and a maximum switching time of 1 μsec. Phase-shift stability over the temperature range 50° to 125°F was better than 5%, losses were less than 0.80 dB and VSWR less than 1.25 across the frequency range. The unit performed equally well at peak power levels up to 10 kW and average power levels up to 300 W. The total energy required for continuous switching of the 180° bit at the above rates was slightly over 200 μJ.
Saturation Ion Currents to Langmuir Probes
Authors: Chen Francis F.
Published: April 2005

The parabolic variation of saturation ion current with probe potential observed in dense plasmas is fortuitous and is not directly related to the effects of orbital motion. Agreement between measured and computed saturation ion characteristics is illustrated. The discussion is in the framework of collisionless, magnetic-field-free theories; they apply to the experiments only if the ion Larmor radius is much larger than the probe radius.
Magnetization of Polycrystalline EuS as Determined by the Pyromagnetic Method
Authors: Argyle B. E.
Published: April 2005

Measurements of magnetization of polycrystalline EuS powder are obtained by the pyromagnetic method between 4.2° and 60°K in fixed applied fields ranging from 4 to 14 kOe. For fields sufficient to saturate (H0≥12kOe), the data, as analyzed by Weiss molecular field theory with a new graphical technique, specify Tc=16.5°±0.2°K, in good agreement with the specific heat anomaly at 16.2°K. The observed behavior of the approach to saturation suggests a preferred choice of mechanisms for the origin of the large saturation field.
Investigation of Hot Opaque Arc Plasmas by Microwave Cavity Techniques
Authors: Maloney W. T.
Published: April 2005

The behavior of a steady-state argon arc plasma flowing through a cold 1-cm circular copper pipe at pressures from 0.1 to 1 atm and gas flow rate of 2600 ml/min is studied by microwave cavity techniques. The high electron density (ne>1016 cm−3) and large density gradients in the arc preclude the usual simple interpretation of data. At this density it is however possible to interpret the cavity resonant frequency as a measure of the ``diameter'' of the arc column. Experimental results show the dependence of this diameter on pressure, arc current, and the presence of contaminant gases in concentrations as small as 10 ppm. A simple explanation of the influence of diatomic contaminants is given which attributes column contraction to enhanced thermal conductivity brought about by diffusion of dissociation energy. Dilation of column caused by krypton is attributed to enhanced electron concentration in the cooler regions of the plasma due to krypton's lower ionization potential. Calculations of thermal conductivity of argon-contaminant mixtures are shown to correlate well with the experimental results. The microwave technique appears in a new role as monitor and judge of the plasma behavior.
Ultraviolet Light Emission from Townsend Discharges in Hydrogen
Authors: Nygaard Kaare J.
Published: April 2005

The total ultraviolet radiation from self-sustained Townsend discharges in hydrogen has been measured by means of a sodium salicylate wavelength shifter and a photomultiplier tube. The excitation coefficient per unit pressure δ0/p has been determined for E/p=80−250 V/Torr-cm. δ0/p as a function of E/p passes through a maximum for E/p≈150 V/Torr-cm. The pressure dependence of the radiation can be ascribed to quenching with a quenching pressure equal to 20 Torr. An attempt has been made to evaluate separately the excitation coefficient for the 21πu radiation by subtracting other uv contributions from the total light intensities observed.
Impurity Distribution in Epitaxial Growth
Authors: Grove A. S. , Roder A. , Sah C. T.
Published: April 2005

A solid-state diffusion theory is developed giving the distribution of impurities in epitaxial growth. It is shown that for most practical cases this theory takes on a particularly simple form. Extensive experiments were performed in the study of the distribution of the most common acceptor and donor type substrate impurities in silicon: boron and antimony. It is shown that the impurity distribution in most of the epitaxial film is uniform corresponding to the impurity doping of the SiCl4 used in the epitaxial growth, and that the profile near the substrate—film interface is very close to the predictions of this simple theory. In addition, certain particular cases of interest were studied such as the spreading of a layer of impurities predeposited on the substrate surface prior to epitaxial growth, the effect of film growth rate on the impurity distribution, and the change in the impurity distribution during an additional high-temperature step. In all cases, experiments and the solid-state diffusion theory are in excellent agreement.
Effect of Impurities on the Hardening and Coloration of KCl Irradiated at Room Temperature
Authors: Sibley W. A. , Russell J. R.
Published: April 2005

Measurements of flow stress and F-band coloration have been made at room temperature on a number of ``pure'' and impurity-doped KCl crystals as a function of gamma and electron irradiation. As has been observed, the flow stress increase, for late-stage coloration, is proportional to the square root of the F-band absorption. However, it is found that the early-stage coloration does not contribute to the radiation hardening. These results suggest that the late-stage production mechanism for F centers involves interstitial formation and clustering, whereas no stable interstitials are formed during early-stage coloration. Moreover, even though it is known that certain impurities enhance early-stage coloration, it is found that the concentration of early-stage F centers is only a small percentage of the total impurity concentration. This suggests that only isolated positive-ion vacancies are involved in the F-center production mechanism for this stage.
Energy Distribution of Energetic Atoms in an Irradiated Medium
Authors: Kostin M. D.
Published: April 2005

A set of coupled linear integral equations for the energy distributions of rapidly moving atoms in an irradiated medium composed of many species is investigated. It is assumed that only binary collisions occur in which an energetic atom interacts with a thermal atom. Solutions are obtained for the case of two species where scattering is isotropic in the center of mass system and all collision cross sections have the same energy dependence. When the mass m1 of species 1 is much less than m2 the collision densities have the form f(E)=aE−2+bE−2+4(c1+c2)m1/m2, where c1 and c2 are related to the collision cross sections. When m1 = m2, then f(E)=aE−2+bE−1/(1+c1)−1/(1+c2). Similar solutions are found for intermediate mass ratios.
Magnetic Properties of Mixed Metal Oxides Containing Trivalent Cobalt
Authors: Blasse G.
Published: April 2005

In oxidic lattices the Co3+ (3d6) ion has been found both in the diamagnetic low-spin state and in the paramagnetic high-spin state. The factors influencing the equilibrium between high- and low-spin Co3+ ions are discussed.

New compounds are presented in which the change of the equilibrium distribution among these two states is measurable because the energy difference between the two states is small. It is then possible to change the equilibrium by varying the temperature. The temperature dependence of the magnetic susceptibility of such a compound is anomalous as has been derived by Ballhausen and Liehr.
Electrical Resistivity of Metals and Alloys Containing Localized Magnetic Moments
Authors: Dekker A. J.
Published: April 2005

In metals and alloys containing localized magnetic moments, an important contribution to the electrical resistivity can be associated with disorder of the atomic spin system. This contribution is ascribed to a scalar interaction between the spins of the conduction electrons and the atomic spins. Assuming a simple form for this interaction, the experimental and theoretical situation concerning the spin-disorder resistivity is reviewed for pure metals, dilute alloys, and concentrated binary alloys.
Spin Density Measurements and the Spin Susceptibility of the 4s Conduction Electrons in Fe
Authors: Stearns Mary Beth
Published: April 2005

It has been observed that the Mössbauer spectra of many ferromagnetic alloys can be analyzed to give the effect on the internal field at an 57Fe nucleus of a solute atom in any of the first six neighbor shells surrounding an Fe atom. The success of such an analysis indicates that the effects of many elements (e.g., Al, Si, Mn, V, Cr) are quite localized and, in particular, the results of the Al and Si alloys indicate that these atoms can be interpreted as acting like holes in the Fe lattice. From considerations of the various contributions to the hyperfine field in Fe, it appears that for the FeAl and FeSi alloy systems the observed changes can be attributed to changes in the spin polarization of the s conduction electrons as a function of distance from an Fe atom. The main features of the observed variation are: (a) an oscillating polarization whose amplitude of oscillation is much greater than that corresponding to a Ruderman-Kittel-Kasuya-Yosida type calculation and whose sign is such as to show that the indirect exchange interactions in Fe via the 4s conduction band are strongly antiferromagnetic; and (b) the period of the oscillation corresponds to a Fermi radius, kF∼0.95×108 cm−1, which yields a 4s conduction electron/atom ratio of about 0.3. With the assumption of a reasonable magnetic form factor for Fe (that from neutron diffraction measurements), the observed polarization can be Fourier inverted to give the spin susceptibility of the s conduction electrons in Fe. The results of such an inversion yield a spin susceptibility function which has a large peak at the Fermi diameter.
Some Systematics of the Core Polarization Hyperfine Field in 3d Ions
Authors: Geschwind S.
Published: April 2005

It was pointed out some time ago by Abragam and Pryce that there was an anomalous part of the hyperfine field (approximately −200 000 G per unit electron spin) that was essentially constant in the 3d ions. This anomalous field arises from admixture of configurations with unpaired s electrons. Alternatively, it has been viewed as a spin polarization of the inner core s electrons by the outer 3d electrons. Increased precision of measurement, aided by ENDOR in some cases, reveals some striking constancies with regard to this core polarization hyperfine field (cphf). First, it is found that the cphf within an isoelectronic sequence in the same type of ligand coordination is constant to within a few percent. It may change as much as 40% depending upon environment but in the same type of environment (same ligand number and ligand ion) it is constant, i.e., the cphf is independent of the charge on the nucleus. The second interesting fact is that the cphf is independent of ligand distance, i.e., it is the same within a few percent in MgO, CaO, and SrO. Aside from these two invariant features, there seems to be a monotonic increase across the 3d series in the cphf field in accord with the prediction of Freeman and Watson. These systematics will be illustrated in detail and some very tentative explanations for this behavior offered.
Very High Coercivity Chemically Deposited Co–Ni Films
Authors: Judge J. S. , Morrison J. R. , Speliotis D. E.
Published: April 2005

Films of Co–Ni, varying in composition from 30% Co to 100% Co, and ranging in thickness from 250 to 2500 Å, were prepared by chemical deposition. Small amounts of P were also included in the deposit. Their crystallographic and magnetic properties were studied as a function of composition and thickness. X-ray diffraction revealed a hexagonal structure for the Co films, with increasing presence of a cubic phase as Ni was introduced. The hexagonal crystallites of the all-Co films were randomly oriented, but in the Co–Ni films there was an increasing orientation of the hexagonal (002) and cubic (111) axes perpendicular to the substrate. The coercivity for a particular thickness increased as the Ni content of the films increased, reaching a peak of about 1300 Oe at 10% to 30% Ni depending on the thickness. Beyond this, the coercivity decreased rapidly to a value of 200 Oe as the Ni content of the films increased to 70%. In the Co films the coercivity decreases markedly with increasing thickness. This dependence on thickness becomes less and less pronounced as Ni is introduced, until the coercivity becomes independent of thickness in the vicinity of 20% Ni. Thereafter, the coercivity increases with increasing thickness, and this effect becomes more evident at higher Ni contents.
Causes of the Inhomogeneity in the Magnitude of the Anisotropy Field in Thin Nickel—Iron Films
Authors: Oredson H. N. , Torok E. J.
Published: April 2005

The inhomogeneity in the magnitude of the anisotropy field of vacuum-deposited nickel—iron films has been determined, from the data of Oredson and Torok, and from new data presented here, as a function of film composition. From this data, the contributions from the magnetocrystalline anisotropy of the randomly oriented crystallites, and from local uniaxial strains has been determined for various substrate temperatures and sources. For example, for evaporation from a ring source onto a substrate at 300°C, (δHb)2=(2.87×10−10)η2+ (1.25×10−8) K12+0.133. The constant term is attributed to shape anisotropy due to film-surface roughness and to the edge of the film and to variations in the magnitude of the anisotropy field due to temperature variations across the film during deposition. The contribution due to magnetocrystalline anisotropy and that due to magnetostriction plus local strain are roughly equal.

Hoffmann recently proposed a theory which gives the size of a domain, and shows that the effect of the randomly oriented crystallite anisotropies can be characterized by an effective anisotropy constant Keff=N−½K1 where N is the number of crystallites in a domain. Extending this theory, a similar relationship is found for the effective uniaxial strain due to the random strains. From this, a theoretical curve of δHb vs composition is obtained which is a fairly good fit to the data.
Origin and Effects of Local Regions of Complex Biaxial Anisotropy in Thin Ferromagnetic Films with Uniaxial Anisotropy
Authors: Torok E. J.
Published: April 2005

Besides the uniform field-induced anisotropy field in a thin ferromagnetic film, there are perturbation anisotropy fields due to the magnetocrystalline anisotropy of the randomly oriented crystallites, their shape anisotropy, the shape anisotropy of the film at the edge, and from the locally anisotropic strains on the crystallites. These perturbations are of great importance in determining the magnetic behavior of the film. Because of exchange and magnetostatic coupling, uniaxial perturbation anisotropy fields of great magnitude in crystallite-sized areas appear instead as complex biaxial perturbation anisotropy fields of small magnitude in areas the size of small domains. The size and shape of these regions are calculated. Most interactions between these areas are automatically included in the randomly oriented complex biaxial perturbation anisotropy fields. These fields can explain the various negative anisotropy effects, the internal biasing field, the relationship between the angular and magnitude inhomogeneity, the shape of the probability density function, the amount of ``negative'' anisotropy in a film, and the position of the negative anisotropy peak. The magnetization creep threshold is significantly larger in films with negative anisotropy than without. The susceptibility is explained quantitatively by including the magnetic stray field due to the net magnetic charge that builds up on the walls when the magnetization vector is rotated.
Uniaxial-Anisotropy Spectrum in Nonmagnetostrictive Permalloy Films
Authors: Smith D. O. , Weiss G. P.
Published: April 2005

The uniaxial-anisotropy spectrum in Permalloy films has been studied by: (1) deposition in H∥ on a substrate at temperature Ts, (2) annealing in either a dc field H⊥ or a circular rotating field Hr for specified time intervals, (3) quenching of the substrate holder by water-cooled coils. Significant aspects of this procedure are: (1) annealing is carried out before exposure to air (oxygen), (2) quenching gives well-defined annealing times, (3) each experiment involves freshly deposited samples which are in a well-defined and reproducible state. These experiments have led to the identification of five separate contributions to the anisotropy in nonmagnetostrictive Permalloy, namely: (1) and (2) two types of contributions due to lattice vacancies with rotational activation energies≤0.2 eV and which became locked after exposure to air (oxygen), (3) and (4) two contributions with rotational activation energies∼1 eV, thought to be due to half self-interstitials and carbon interstitials, respectively, and (5) directed Fe–Fe pairs.
Range of Ferromagnetic Exchange Interaction in Nonmagnetic Films on Iron Substrates
Authors: Trousdale W. L. , Lindgren R. A.
Published: April 2005

An experiment has been performed to measure the penetration of conduction electron spin polarization into nonmagnetic metallic films deposited on an iron substrate. The technique was to evaporate the metal in question on the iron and then to probe the effective exchange field, produced by the electron spin polarization, as a function of the distance from the substrate by evaporating an intermediate partial layer of 57Co. The hyperfine field of the 57Fe was measured by the Mössbauer method and the exchange was calculated from the hyperfine field under the assumption that the hyperfine field is related to the exchange field through the Brillouin function of the local spin. Measurements were carried out at 300°, 78°, 4.20°, and 1.22°K.

Samples using palladium on an iron substrate were investigated with the 57Fe placed from 20 to 120 lattice spacings away from the substrate with the following results: (1) The size of the exchange field varies from 0° to ∼150°K in the thinnest sample and from 0° to 25°K in the thickest. (2) For samples of given thickness, an empirical probability distribution function for the exchange field was found which gave a good fit to the hyperfine spectra at all temperatures. (3) The probability function is maximum at zero exchange field, decays initially quite rapidly, and then tails off slowly.

A few measurements have been made with copper and silver as the intermediate metal. The indication is that the effective exchange field in copper is greater than in silver but considerably less than in palladium.
Effects of Residual Deposition Atmosphere and Substrate Temperature on the Magnetic Anisotropy of Permalloy Thin Films
Authors: Lykken G. I. , Mitchell E. N.
Published: April 2005

In an attempt to determine the role of trapped impurity atoms in the magnetic anisotropy observed in Permalloy thin films, a specific, oil-free vacuum system was developed which allowed rapid, simultaneous deposition (1000 Å/min) of 82% Ni-18% Fe onto two glass substrates (one usually at liquid-helium temperature, the other at various temperatures above liquid helium) with a deposition pressure better than 2×10−9 Torr. In all cases the films deposited onto the heated substrates appeared anisotropic while those deposited onto the cold substrates appeared isotropic at liquid-helium, intermediate, and room temperatures (when examined in ultrahigh vacuum with a hysteresis loop tracer). It was found that an anisotropy could be introduced into the isotropic films by low-temperature annealing. The results of this investigation indicate that a sufficiently low substrate deposition temperature can inhibit the formation of magnetic anisotropy. It was not possible to eliminate the anisotropy in this experiment by reducing the residual atmosphere.
Study of the Magnetic Properties of the Actinide Metals: Th1−xUxPd3
Authors: Wernick J. H. , Williams H. J. , Shaltiel D. , Sherwood R. C.
Published: April 2005

ThPd3, with UPd3, forms a continuous series of solid solutions. These two intermetallic compounds have the hexagonal DO24 structure. We have studied the magnetic susceptibilities of eleven Th1−xUxPd3 alloys (0≤x≤1) at temperatures from 1.4° to 300°K in fields up to 15 kOe and at 4.2°K in fields up to 80 kOe. ThPd3 is diamagnetic and shows a temperature-independent susceptibility, but the addition of U, even in small amounts, gives rise to a strongly temperature-dependent paramagnetic susceptibility. The data analyzed in terms of T against 1/χ−χ∞ gives a Curie-Weiss behavior in the high-temperature region with 3.35 μB/U atom at low U concentrations; decreasing to 2.6 μB for UPd3. It appears that the U-5f electrons form a localized moment for low U concentrations. A deviation from a Curie law at around 100°K for all U concentrations is suggested to be due either to crystal field splitting of the U-5f levels or to the presence of a narrow 5f band. The lack of any indication of an antiferromagnetic transition in the temperature behavior of the susceptibility at high U concentrations and the linearity of the magnetic moment with magnetic field up to 80 kOe for the same alloys, favors the formation of a very narrow 5f band as the U concentration increases and lends support to previous EPR experiments of Gd in UPd3, where a similar conclusion was reached.
Magnetic Studies at the Research Institute for Iron, Steel and Other Metals
Authors: Hirone Tokutaro
Published: April 2005

A brief survey of several investigations is presented. (1) Spin-flopping magnetization measurements up to 80 kOe in α Fe2O3 in the low-temperature state are reported. The temperature dependence of the uniaxial anisotropy constant is obtained therefrom. Its magnitude is of the order of 104 erg/cc and increases with decreasing temperature. Measurements with the field perpendicular to the trigonal axis reveal that at a temperature in the transition region (240°K), the magnetic state moves first toward the high-temperature behavior with weak ferromagnetism, but above 60 kOe it returns to the antiferromagnetic low-temperature state. (2) Thermomagnetic measurements on CaFeO2.5 and CaFe4O7 indicate that a weak ferromagnetism appears at 400°C. From the crystal structure, a Dzyaloshinsky-Moriya canting is suggested to account for the weak moment. (3) High-field measurements of MnAu2 extend to low temperatures the previous data on its transition field (screw-type antiferromagnetism to ferromagnetism). The screw angle appears to be changing slowly even below 80°K. Longitudinal and transverse magnetostriction measurements in MnAu2 are reported through the transition and up to 80 kOe. Relative length changes of about 10−4 are observed and significant volume contractions during the screw-flopping and rotation stages are inferred. (4) Saturation moment and Curie point measurements of Pd-Fe alloys (near 30 at. % Pd) are reported and compared with similar Invar-type behavior in Ni-Fe alloys.
Magnetization of the Rare-Earth Manganese Compounds R6Mn23
Authors: DeSavage B. F. , Bozorth R. M. , Wang F. E. , Callen E. R.
Published: April 2005

Measurements have been made of the magnetic moments of compounds of the type R6Mn23, where R is a rare-earth ion. Determination of the saturation moments of Mn with nine of the rare earths (Sm, Nd, Gd, Tb, Dy, Ho, Er, Tm, and Lu) show that, with one exception, the rare-earth and manganese moments are antiparallel; only in the gadolinium manganese compound is there complete ferromagnetic coupling. From the moment of Lu6Mn23 one derives the moment of 0.4μB per manganese atom. The measured moments of the other compounds agree closely with those calculated assuming a moment of 0.4μB for Mn and the normal moment of gJ for the appropriate rare-earth atom.
Double Barrier Transmission Characteristics
Authors: Hosack H. H.
Published: April 2005

A general expression for the time-independent transmission coefficient of a double barrier is derived. Unity double barrier transmission is found possible for all energy levels above or below the double barrier potential energy levels. The conditions under which unity transmission occurs are obtained and discussed.

Application of the general theory to a piecewise constant potential model indicates that double barrier effects in thin film devices may be most noticeable for a majority of current carriers at energy levels near the maximum potential energy level of the double barrier. The small width of the transmission resonances in the examples considered indicates that double barrier effects would probably not be detected, and if they were detected would probably not be interpreted as such, unless investigation of this particular phenomenon was an objective of the research being conducted.