bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Temperature Spin-Wave Resonance at 3000 and 4000 Mc/sec in a Permalloy Having Nearly Zero Magnetocrystalline Anisotropy
Authors: Weertman J. R. , Rado G. T.
Published: April 2005

The observation of spin-wave resonance in Permalloy samples of extremely low anisotropy has been extended to liquid nitrogen temperature. Measurements at both room and liquid nitrogen temperature have been carried out at 3000 and at 4000 Mc/sec. At room temperature the complete experimental resonance curve can be explained at both frequencies on the basis of the spin-wave resonance theory of Ament and Rado by using an average exchange stiffness constant, A, of (3.3±0.5)×10−6 erg/cm and a g factor of 2.06±0.01. The agreement between experiment and theory would be destroyed if a Landau-Lifshitz or Bloch damping term were included. The theory of Ament and Rado predicts that as the temperature is lowered the exchange broadening of the resonance line increases and the resonance field decreases. Both effects have been observed qualitatively but neither is as large as would be expected from the theory. It has been found that at a given temperature the plot of the imaginary versus real part of the equivalent permeability at 3000 Mc/sec differs only by a scale factor from the corresponding plot at 4000 Mc/sec. At room temperature the above frequency increase causes a decrease in the permeabilities of 30% from the corresponding values at 3000 Mc/sec, as compared to a predicted 15% decrease. The discrepancy between theory and experiment at the low temperature is about the same at one frequency as at the other. Since the corresponding resonance fields differ by a factor of two, any effects due to incomplete saturation seem to be ruled out.
Effect of Electronic Mean Free Path on Spin-Wave Resonance in Ferromagnetic Metals
Authors: Rado George T.
Published: April 2005

It is suggested that under certain conditions the interpretation of ferromagnetic resonance phenomena in metals should not make use of Ohm's law because the electronic mean free path may not be negligible in comparison to an appropriately defined effective skin depth. Such conditions can exist even at moderately low temperatures provided the equivalent permeability is sufficiently large. The anomalous effects due to the mean free path are shown to be particularly important in spin-wave resonance, i.e., in a modified ferromagnetic resonance which is appreciably influenced by the exchange interactions existing in the skin depth. A suitable perturbation method is developed for calculating these anomalous effects on the basis of Maxwell's equations and the spin-wave equation. Using a relation proposed by Reuter and Sondheimer, as imple first-order result is then obtained for the surface impedance and for the equivalent permeability derived therefrom. The limitations of the underlying physical model are pointed out, and the applicability of the theory to existing experimental results is briefly discussed.
Inhomogeneous Broadening of Magnetic Resonance Lines
Authors: Clogston A. M.
Published: April 2005

An inhomogeneously broadened magnetic resonance line is narrowed by dipole fields. The theory of this effect is developed in terms of the classical equations of motion of a magnetized medium by expanding the magnetization and fields into Fourier series. An expression is obtained for the imaginary parts of the susceptibility tensor. In the applicable range of the theory, the line width decreases inversely as the magnetization, and is strongly shape dependent.
Ferromagnetic Resonance in Uniaxial Polycrystalline Materials
Authors: Morrison C. A. , Karayianis N.
Published: April 2005

A theoretical determination is made of the resonance curve of a nonconducting polycrystalline ferromagnetic material with uniaxial crystalline anisotropy. A finite intrinsic line width is assumed for the single crystal, and effects of grain boundaries, impurities, inhomogenieties, and volume and surface divergence of the magnetization are ignored. The results are compared qualitatively with experiment.
Magnetic Anisotropy Induced by Magnetic Annealing and by Cold Working of Ni3Fe Crystal
Authors: Chikazumi Sōshin
Published: April 2005

After a brief report on the experiments which have been made on magnetic annealing, recent investigations on the magnetic anisotropy which is induced by cold rolling are described. The local and the average anisotropy induced by rolling was observed by means of domain pattern and torque measurement for (110)[001], (001)[110], (001)[100] rolling of single crystals and rolling of polycrystals. It was shown that the anisotropy for individual cases was well explained by assuming the ``slip-induced directional order.'' Two types of the anisotropy i.e., long-range order (fine slip) type and short range order (coarse slip) type, were calculated. Dependence on the degree of order and its difference between single and polycrystals are also discussed.
(110) [001] Secondary Recrystallization Texture in Three Percent Silicon-Iron
Authors: Fiedler H. C.
Published: April 2005

The secondary recrystallization texture has been related to the structure developed during prior processing. The (110) [001] component of the primary recrystallization texture, from which secondary grains grow, develops from the (111) 〈112〉 doublet component in the prior recrystallization texture. If the material undergoes two rather than one prior recrystallization heat treatments (each separated by a cold reduction), the amount of the (110) [001] component in the primary recrystallization texture is in general increased, and as a consequence, the completeness of secondary recrystallization is promoted.
Magnetic Properties of Cube Textured Silicon-Iron Magnetic Sheet
Authors: Walter J. L. , Hibbard W. R. , Fiedler H. C. , Grenoble H. E. , Pry R. H. , Frischmann P. G.
Published: April 2005

Cube textured magnetic sheet containing approximately 3% silicon in iron has been developed in the General Electric Company Research Laboratory. The magnitude of the cube texture as determined by torque magnetometer tests is of the order of 90% or greater when compared to a single crystal with a (100) [001] orientation. The magnitude of the texture was confirmed by x-ray diffraction pole figures.

Static dc magnetic tests and 60 cycle ac w loss tests made on single strip samples taken both parallel to the rolling direction and at right angles to the rolling direction indicate nearly equal magnetic properties in both directions of the sheet. These properties are equivalent to the magnetic properties measured in the single good direction of the ``grain oriented'' transformer material. Finally, two transformers were made: one using laminations of the cube textured silicon iron, the other of the ``grain oriented'' material. It was found that transformer made of the cube textured material produced significantly lower energy losses at all inductions and at 17 000 gauss the losses were approximately 60% of the losses produced by the ``grain oriented'' transformer. Similarly the current required to produce 17 000 gauss in the cube textured transformer was again about half that required to excite the ``grain oriented'' transformer to the same induction.
Effect of Elastic Bending on Magnetic Properties of Oriented Silicon Iron
Authors: Cole R. W.
Published: April 2005

To determine how the ac and dc magnetic properties are affected by elastic strain, the magnetic properties in the rolling direction of Epstein strips of elastically bent grain-oriented 3% silicon iron were measured in an Epstein frame and in a Carr single-strip permeameter. As the degree of bending becomes more pronounced, the coercive force and the ac core loss increase and the permeability decreases. The domain theory gives a rather simple approximate interpretation of the permeability data for magnetic intensities between one and ten oersteds.
Effect of Hydrostatic Pressure and Temperature on the Magnetic Properties of a Nickel-Zinc Ferrite
Authors: Adams C. Q. , Davis C. M.
Published: April 2005

Magnetic properties of a nickel-zinc ferrite (15% NiO, 35% ZnO, 50% Fe2O3) were measured over a temperature range of 23°C to 110°C at hydrostatic pressures up to 40 000 psi.

The relation between the shift in Curie temperature, ΔTc, and the change in pressure, Δp, was empirically found to be ΔTc=0.078(Δp)0.316.

It is shown that if magnetic anisotropy and internal strains limit the magnetizing processes, the relation between coercive force, Hc, maximum flux density, Bm, and initial permeability, μ0, is given by Hc=δBm/μ0,

where δ is a proportionality constant. The experimental results obtained over the entire range of temperature and pressure verify the above relation. The value of δ is 2.56 for the ferrite investigated.
Substitution for Iron in Ferrimagnetic Yttrium-Iron Garnet
Authors: Gilleo M. A. , Geller S.
Published: April 2005

In yttrium-iron garnet, iron may be entirely replaced by aluminum and gallium; chromium, scandium, and indium may be substituted for iron to a limited extent. Substitution proceeds on a steric basis for the nonmagnetic ions: Al3+ and Ga3+, which are smaller than Fe3+, preferentially occupy the smaller, tetrahedrally coordinated positions, 24(d); the Sc3+ and In3+ ions, which are larger than Fe3+, preferentially occupy the larger, octahedrally coordinated positions, 16(a). The Cr3+ ion, though smaller than Fe3+, preferentially occupies the octahedral position, presumably because of its electronic configuration. The magnetic moment initially increases with octahedral substitution and decreases with tetrahedral substitution. The Curie temperature is decreased by the substitution of nonmagnetic ions for iron as a consequence of the decrease in the number of Fe3+–O2−–Fe3+ interactions.
Some Ferrimagnetic Properties of the System LixNi1−xO
Authors: Goodenough J. B. , Wickham D. G. , Croft W. J.
Published: April 2005

Crystallographic and magnetic measurements of the system Li+xNi++1−2xNi+++xO for the entire range 0≤x<0.5 are reported. For values of x≤0.3, the lattice appears to be antiferromagnetic and is cubic above the Curie temperature. For the range of compositions 0.3<x<0.5, the lattice is rhombohedral and apparently ferrimagnetic, a maximum magnetic moment per gram of 31 cgs cm3/g being observed at x=0.46. A maximum ferrimagnetic Curie temperature of 241°K was observed for the composition x=0.41. These properties are interpreted in terms of a partial ordering of Li and Ni ions into alternate sets of (111) planes which couple antiparallel to one another, the moments within any set being either ferromagnetically coupled or paramagnetic, depending upon the number of nonmagnetic near neighbors in the neighboring planes.
Effect of Thermal History on the Antiferromagnetic Transition in Zinc Ferrite
Authors: Grimes D. M. , Westrum Edgar F.
Published: April 2005

Quenched zinc ferrite is ferrimagnetic, annealed ferrite paramagnetic at 300°K. Although annealed zinc ferrite has a lambda-type heat capacity transition at about 9.5°K, quenched zinc ferrite retains only elementary vestigia of this transition. A similar effect exists in Li0.05Zn0.90Fe2.05O4 in which the transition temperature is slightly lowered relative to that of zinc ferrite. This temperature shift does not appear to exist for Ni0.1Zn0.9Fe2O4. The magnetic entropy at 300°K is essentially unaltered by lithium substitution or thermal history.
Magnetic Germanates Isostructural with Garnet
Authors: Tauber Arthur , Banks Ephraim , Kedesdy Horst H.
Published: April 2005

In order to study the magnetic interaction between the eightfold and the combined six- and fourfold sites in the garnet structure, several germanate garnets have been synthesized. If no magnetic cation is present in the fourfold site no spontaneous magnetization has been found in the temperature range 90° to 500°K. A partial substitution of the nonmagnetic cation in the fourfold site by magnetic cations, however, leads to a spontaneous magnetization.
Growth of Magnetic Garnet Crystals
Authors: Nielsen J. W.
Published: April 2005

Single crystals of magnetic garnets have been grown from solutions of molten lead oxied, iron oxide, and the oxides of yttrium, samarium, erbium, or gadolinium. The crystals are grown by slowly cooling melts from 1325°C to near 900°C. A convenient composition is 52.5 mole % PbO, 44 mole % Fe2O3, and 3.5 mole % M2O3 where M is Y, Gd, Er, or Sm. Crystals of yttrium-iron garnet have been grown which contain gallium partially substituted for iron.

The method may also be extended to the growth of nonmagnetic yttrium gallium garnets by using a melt which is 72.7 mole % PbO, 26 mole % Ga2O3 and 1.3 mole % Y2O3.

Bismuth oxide can be used as a solvent for the growth of magnetic garnet crystals but the substitution of bismuth in the garnet lattice makes it less desirable than lead oxide.
Measurement of Losses of Magnetic Materials at High Inductions at Frequencies up to 100 Megacycles
Authors: Bady Isidore
Published: April 2005

Methods for measuring ferrites at high inductions are given. For frequencies below 50 Mc, a conventional series resonant circuit is used, and coupled to a high power signal source through a variable capacitive attenuator. The test sample is in the form of a toroid with an appropriate winding. The Q of the test sample is determined with the aid of an air coil whose Q is known. Harmonics, sources of errors, and pulse modulation are discussed. For frequencies of 50 Mc and above, a short circuited coaxial slotted line is used. To get high currents into the slotted line, it is inductively coupled to a high power signal source and tuned to resonance by means of a capacitor. A method for determining the current in the line is given.
Behavior of the TE Modes in Ferrite Loaded Rectangular Wave Guide in the Region of Ferrimagnetic Resonance
Authors: Crowe W. J.
Published: April 2005

A computation is described which reveals the exact values of the propagation constants of the TE modes in rectangular wave guide loaded with a transversely magnetized ferrite slab over a frequency interval which includes resonance. Magnetic losses are included in the analysis. It is shown that the way in which the modes link through resonance depends upon the value of the magnetic damping parameter, and further that they generally link in such a way that an interference between two or more modes will occur.
Miniaturized Resonant Antenna Using Ferrites
Authors: Grimes D. M.
Published: April 2005

The radiation resistance and reactance of point source dipoles are profoundly affected by the surrounding medium. A radiator of length l in an infinite ferrite medium is electrically μl meters long if μ=ε (relative permeability and permittivity).

For very small ferrite spheres, the radiation resistance is determined by the relative permittivity, the effective reactance length by both the permittivity and the permeability. Thus it is possible to exchange length for resistance. Further work on linear radiators surrounded by ferrite in the form of a prolate figure of revolution is indicated.
Appraisal of Permanent Magnet Materials for Magnetic Focusing of Electron Beams
Authors: Glass Myron S.
Published: April 2005

In the magnetic focusing of electron beams there is a growing need for permanent magnets of higher coercive force than those which are easily obtainable. Special techniques in the design of compact tubular magnets for strong focusing fields enable the use of magnet materials of relatively low remanence. The low remanence of some materials suitable for this use has limited their general use and this has probably retarded their final development. There is a good potential demand for these materials for electron beam focusing which should stimulate increased development effort.
Microwave Frequency Conversion Studies in Magnetized Ferrites
Authors: Skomal E. N. , Medina M. A.
Published: April 2005

Frequency conversion studies conducted upon polycrystalline ferrites and yttrium iron garnets have established that microwave mixing displays a linear dependence upon input powers. Sum and difference signal powers generated in ferrites and garnets were examined as a function of rf power and sample shape. Conversion efficiencies of −14 db for sum signal output and −36 db for difference signal output were achieved for magnesium manganese ferrite at X band.
Spin-Lattice Relaxation Time in Yttrium Iron Garnet
Authors: Farrar R. T.
Published: April 2005

The spin-lattice relaxation time in yttrium iron garnet (YIG) has been measured by a pulsed ferromagnetic resonance method similar to that of Bloembergen and Wang and Damon, in which the z component of magnetization is directly observed.

A microwave pulse with 2×10−8 sec rise and decay time, 5×10−7 sec long, and 2 w peak power is applied to a TE102 rectangular cavity operating at 9300 mc sec. The z component of magnetization Mz changes at the beginning and at the end of the rf pulse. The time of decay of the changing Mz signal at the trailing edge of the pulse (at which time the applied rf field is zero) is a measure of the spin-lattice relaxation time.

A spherical sample of YIG, 0.03 in. diam, is placed in a quartz tube, 0.05 in. o.d., about which a five turn coil of No. 38 wire is wound. The coil with sample is inserted in the center of the cavity with the axis of the coil in the z direction. At this position, the rf magnetic field is maximum and the electric field is a minimum. The presence of the coil does not measurably change the properties of the cavity. The voltage induced in the coil is proportional to the change in Mz and is observed on a high speed oscilloscope. The time constant of the equipment is approximately that of the exciting pulse. Thus the spin-lattice relaxation time can be accurately determined directly if it is appreciably larger than this value.

The ferromagnetic resonance line width is 2.3 oersteds and the measured spin-lattice relaxation time is 7×10−8 sec. Discussion is given relating these measurements to those reported in the accompanying papers.
Microwave Properties of Polycrystalline Rare Earth Garnets
Authors: Sirvetz M. H. , Zneimer J. E.
Published: April 2005

A number of garnets including yttrium garnet, Y3Fe5O12, and mixed garnets of the forms (Y1−αSmα)3Fe5O12 and (Y1−βGdβ)3Fe5O12 have been prepared. X-band ferromagnetic resonance and saturation magnetization have been measured as a function of temperature. At room temperature samarium substitution for yttrium produces an approximately linear increase of line width with samarium content with practically no change in magnetization. Gadolinium substitution, on the other hand, has a much smaller effect on line width but produces an approximately linear decrease in saturation magnetization. Possible microwave application of these materials are discussed.
Ferrimagnetic Resonance in Single Crystals of Rare Earth Garnet Materials
Authors: Jones R. V. , Rodrigue G. P. , Wolf W. P.
Published: April 2005

The preliminary results of a study of the ferrimagnetic resonance properties of single crystals of rare earth iron garnet containing samarium, gadolinium, dysprosium, holmium, erbium, and ytterbium are presented. The measurements have been conducted in the temperature region from 77°K to 550°K at microwave frequencies in the x band. The effective g values and line widths are consistent with the previously reported measurements on polycrystalline samples. In this temperature region the anisotropy energy of the Sm, Gd, Er, and Yb crystals can be represented by the usual cubic form with a negative first order term. The line widths exhibit a large anisotropy which increases with decreasing temperature.
Temperature Dependence of Ferromagnetic Anisotropy
Authors: Carr W. J.
Published: April 2005

The temperature dependence of the crystalline anisotropy constants of iron, cobalt, and nickel is discussed.

It is shown that Zener's result for iron (i.e., the first anisotropy constant varies as the tenth power of the magnetization) also may be derived from molecular field theory.

In cobalt a satisfactory agreement with experiment is obtained by using Zener's results together with the postulate that the intrinsic anisotropy varies with thermal expansion in the manner recently calculated by the author.

For nickel also the temperature dependence of K1 seems to require, in addition to the tenth power of the magnetization, a multiplicative factor that is linear in the temperature. No explanation has been found for this latter term.
Magnetization Processes in Heat-Treated Single Crystal Cobalt Ferrite
Authors: Foner S. , Artman J. O.
Published: April 2005

The results of a series of magnetization measurements, ranging from 4.2°K to 300°K, on a heat-treated single crystal of cobalt ferrite are summarized. A simple domain picture accounts for the present results and agrees with many related experimental observations. Derived values of cubic anisotropy and induced uniaxial anisotropy are presented. Low temperature hysteresis and remanence observations are also described. A mechanism which could account for the unusual magneto-thermally induced uniaxial behavior is outlined briefly.
Theory of Magnetostriction and g Factor in Ferrites
Authors: Tsuya Noboru
Published: April 2005

A quantum mechanical theory based upon the Heitler-London approximation has been developed to explain the spatial variation of magnetostriction and g factor in ferrites. As a first step, the electronic wave functions of cations of transition elements in the crystal field were found, taking into account the crystal structure of ferrites. The g factors of various cations in ferrites were determined by a method similar to that of Abragam and Pryce, and g factors thus found were related to those of ferrimagnetic resonance absorption by the use of the theory of Wangsness and the author.

The magnetostriction was obtained by the perturbation method and it was concluded that there are four mechanisms predominant among those giving rise to magnetostriction. They are (1) the interplay of spin-orbit interaction with the strain potential, (2) classical dipolar interaction, (3) the interplay of anisotropic exchange interaction with the strain potential, and (4) the interplay of the potential with the intra-spin-spin interaction. Other mechanisms were estimated to be ineffective. The predominant mechanisms in Ni ferrite are (1) and (2); in Co ferrite, (1); in magnetite, (1), (2), and (4). In annealed Mn ferrite and Cu ferrite, the mechanism (2) is most effective. In quenched Cu ferrite, both mechanisms (2) and (3) are the most important.
Temperature Dependence of Microwave Permeabilities for Polycrystalline Ferrite and Garnet Materials
Authors: Nemarich J. , Cacheris J. C.
Published: April 2005

Measurements of the microwave permeabilities μ∥ and μ⊥ = (μ2−K2)/μ have been made at a frequency of about 9200 Mc using a cavity perturbation technique. Samples in the form of thin slabs were used. Both the static magnetic field and the temperature were varied. The temperature ranged from 25°C to 150°C and the internal magnetic fields were varied from zero to 1500 oersteds. A general qualitative agreement between theory and experiment is obtained for one of the ferrite materials. Both μ⊥ and μ∥ were found to increase with increasing temperature for the range measured.
Effect of Cobalt on the Relaxation Frequency of Nickel-Zinc Ferrite
Authors: Schnettler F. J. , Monforte F. R.
Published: April 2005

The complex permeabilities of a number of Ni–Zn–Co ferrites were measured as a function of frequency from 0.1 to 250 mc/sec. These ferrites were prepared under identical conditions from reagent grade chemicals. Their compositions differed in the relative amounts of cobalt, nickel, and zinc they contained, the amount of iron being held constant. A number of specimens of each composition were prepared at different firing temperatures, so as to include a variation in the degree of reaction.

An analysis of the data was made in which the initial permeability and relaxation frequency were correlated with certain composition and structure variables. They include the quantity of cobalt, the nickel-zinc ratio, the firing temperature, and the amount of shrinkage which occurred during firing. It was found that these variables would account for 88% of the variations of the initial permeability and 70% of the variations of the relaxation frequency. A further result of the analysis defines the conditions for obtaining maximum quality (μ0f0) at a given value of initial permeability.
Magnetic Fluctuations in Molybdenum Permalloy
Authors: Brophy James J.
Published: April 2005

Considerations of generalized noise and magnetic viscosity suggest the existence of magnetic fluctuations in ferromagnets. Magnetic fluctuations in molybdenum Permalloy tape ring cores have been detected by observing noise voltages at the terminals of a coil wound on the sample. For thin tape cores and at low frequencies, the observed magnetic noise spectrum is in excess of Nyquist noise and is characteristic of a slow relaxation phenomenon with an activation energy of 0.04 ev. For thick tape cores and at high frequencies, core losses yield noise voltages in agreement with Nyquist's law and provide a means of studying ferromagnetic loss with zero magnetic excitation.
Operating Range of a Memory Using Two Ferrite Plate Apertures Per Bit
Authors: Kaufman M. M. , Newhouse V. L.
Published: April 2005

In order to make use of all the structural and economical advantages which apertured ferrite plates may offer to a magnetic memory, techniques were developed to compensate for the nonuniformity from hole to hole found in experimental plates. An analysis is presented which indicates that storage of information using two holes per bit and allowing both holes to switch increases the operating range of a ferrite plate memory to a point where it is possible to drive it with a ferrite plate switch. A switch-driven ferrite plate memory has been operated successfully in the laboratory and confirms the results of the analysis.
Recent Advances in the Design of High-Field dc Solenoid Magnets
Authors: Kolm Henry H.
Published: April 2005

The art of dc solenoid design is re-examined with the objective of maximizing magnetic field at the expense of volume and homogeneity, while providing axial access at the largest feasible angular aperture. Solenoids of this type would provide higher fields for the investigation of cyclotron resonance and magneto-optical effects in thin specimens at far-infrared frequencies where limitations of source intensity and detector sensitivity require large-aperture optics and preclude the use of pulsed magnets. Heat transfer experiments indicate that under conditions of nucleate boiling it is possible to transfer heat across a copper-water interface at more than ten times the rate of 200 w/cm2 which served as the basis for Bitter's design some twenty years ago. Transfer rates of 2500 w/cm2 were achieved in a 0.010×0.20-in. rectangular flow channel and at a copper temperature of only 114°C. Two modified Bitter solenoids and a new, tape-wound wide-aperture solenoid were designed to dissipate the maximum power of 1700 kw supplied by Professor Bitter's generator at MIT through a considerably reduced transfer area and thus provide higher fields in smaller volumes. The design and preliminary performance data are described.
Further Development of the Vibrating-Coil Magnetometer
Authors: Dwight K. , Menyuk N. , Smith D.
Published: April 2005

The vibrating-coil magnetometer is a versatile and sensitive instrument, with greater freedom of sample environment than can otherwise be obtained. There are several practical factors which tend to degrade the performance of the instrument below theoretical expectations. These difficulties are discussed, and improved techniques for overcoming them are described. The resulting performance is compared both to that of the original instrument and to that theoretically obtainable. The present performance is shown to be within an order of magnitude of the theoretical limitation, which constitutes a marked improvement in the quality of the vibrating-coil magnetometer. The capabilities of the instrument are illustrated by several experiments.
Design of Optimum Inductors Using Magnetically Hard Ferrites in Combination with Magnetically Soft Materials
Authors: Ludwig J. T.
Published: April 2005

A new method is developed for the optimum design of inductors carrying unsymmetrical currents and having magnetically soft ferromagnetic cores biased with magnetically hard gaps. Techniques are given for obtaining designs to meet those specifications for which the optimum design has no air gap, and those specifications imposing limits on the maximum induction.
Pulse Generator Based on High Shock Demagnetization of Ferromagnetic Material
Authors: Kulterman R. W. , Neilson F. W. , Benedick W. B.
Published: April 2005

The shock wave from a pellet of high explosive is passed without attenuation through one leg of a closed ferromagnetic core which has been previously magnetized. The shock wave demagnetizes the core, reducing the flux from the remanent value to zero. This change in flux generates a voltage in any winding wound on the core. Idealized calculations indicate that the voltage pulse generated in this manner will be a squarewave with amplitude, in volts, given by eg = NBRvw, and a pulse width, in seconds, given by T = s/v, where N is the number of turns, BR the remanent magnetization (webers/m2) and v is the shock velocity (m/sec). It is also assumed that the core has a rectangular cross section, w being the width of the core (m) in the direction perpendicular to BR and v, and s being the thickness of the core (m) in the direction parallel to v.

Experimental tests have produced output pulses with an amplitude of 6400 v/turn-meter of w where the length of the pulse was in fair agreement with the known shock velocity of the material used. At the present time it is believed that the operation of the device can be explained by a transducer mechanism which converts some of the energy of the shock wave into electrical energy.
Skullcap Method for Magnetizing Bowl-Shaped Magnetron Magnets
Authors: MacDonough Francis X.
Published: April 2005

In the microwave field, magnetrons and backward-wave oscillators utilize permanent magnet material to establish magnetic fields transverse to the electron flow in the tubes. Bowl-shaped magnets, more efficient and less weighty than the conventional styles, are now in common use and are being magnetized by an external two-turn coil of a size and shape to enclose the tube with the magnets assembled thereon. This novel method, with the addition of an external magnetic ``keeper'' circuit, has given satisfactory magnetizing results to each type of tube to which it has been applied.
Transitions from Ferromagnetism to Antiferromagnetism in Iron Aluminum Alloys
Authors: Sato H. , Arrott A.
Published: April 2005

From a study of magnetic isotherms over the range of compositions from pure Fe to 40 atomic percent Al in Fe and over temperatures from 4°K to 300°K, we have produced strong evidence for the existence of super-exchange interactions between iron atoms separated by aluminum atoms. The iron rich alloys show ferromagnetism in the usual way, but, for concentrations approaching 40 atomic percent Al, the alloys behave as antiferromagnetic with Néel points near liquid hydrogen temperatures. There is a transition range of composition in which the stable state just below the Curie temperature is ferromagnetic but at low temperatures is antiferromagnetic.

The large changes in magnetic properties occur for the ordered structures and in composition ranges where the number of nearest neighbor iron-iron interactions is changing rapidly with composition, but where the number of next nearest neighbor iron-iron interactions remains practically constant. These considerations lead to a model where only the nearest neighbor direct positive exchange interactions between iron atoms, and indirect negative exchange interactions between iron atoms separated by an aluminum atom are taken into account. The treatment by a Bragg-Williams type calculation leads to a qualitative understanding of the observed magnetic effects in the iron aluminum system, including the differences between the disordered state and the two types of ordered states. The model also leads to a reinterpretation of neutron diffraction data.
Magnetic Properties of Dilute Magnetic Alloys and of the Rare Earth Metals
Authors: Pratt G. W.
Published: April 2005

Dilute alloys of paramagnetic atoms in Cu or the noble metals have been found to exhibit ferromagnetism as well as antiferromagnetism. This is of particular interest because the origin of the magnetic behavior cannot lie in the customary Heisenberg exchange interaction between nearest neighbors because of the large separation between the paramagnetic atoms in dilute alloys. A similar situation exists in the rare earths where nearest neighbor 4f−4f direct exchange is negligible. The spin coupling can be explained by taking account of the direct exchange interaction between the paramagnetic atoms and the conduction electrons and by superexchange. To describe the superexchange coupling it is necessary to know the energy levels of the paramagnetic atom in the solid. The results of a Hartree-Fock analysis of this problem are briefly discussed. A generalization of a previous molecular field treatment is also given.
Optical Properties of Several Ferrimagnetic Garnets
Authors: Dillon J. F.
Published: April 2005

All of the ferrimagnetic garnets studied to date have been found to be transparent to visible light down to wavelengths of about 5200 A. Thin sections (e.g., 0.005 cm) have been examined to determine the absorption and the specific Faraday rotation through that part of the visible spectrum where they transmit light. These measurements have been made at temperatures down to 4.2°K. They are interpreted as giving us information on electronic energy levels. A magnetic birefringence and a circular dichroism have been observed. The Faraday rotation permits observation of the domain structure in these crystals at any temperature below the Curie point. Possible microwave-optical experiments are discussed briefly.
Blunting of Tungsten Needles by Surface Diffusion
Authors: Boling J. L. , Dolan W. W.
Published: April 2005

Progressive blunting of tungsten needles heated in vacuum is made continuously or intermittently visible by a technique permitting needles to be heated while mounted in a conventional electron microscope. This technique permits the study of surfaces having small radii of curvature where detectable geometric changes due to diffusion occur in conveniently short periods of time. When the needle shape remains similar to its original geometry as its radius increases, a theory of Herring is applicable for distinguishing whether the transport process involved is volume or surface diffusion. Evidence is presented which indicates that surface diffusion predominates in the conditions of these experiments, i.e., for temperatures from 2600°K to 2900°K and radii from 3×10−6 cm to 3×10−5 cm.
Crystal Growth Mechanism in Cadmium Sulfide Crystals
Authors: Reynolds D. C. , Greene L. C.
Published: April 2005

Large cadmium sulfide crystals have been grown from the vapor phase. The crystal growth was studied by observing growth patterns, chemical etch patterns, and vaporization patterns. The studies reveal a layer or lamellar type growth, the layers resulting from the coalescence of monatomic steps into ledges of many atomic layers in height. The layers are generated at or near the crystal edge and move across the surface by edge nucleation. The exact mechanism by which the steps are generated is not known, however, it is believed that they result from screw dislocations or surface nucleation.
Low-Temperature Thermal Conductivity in Neutron Irradiated Vitreous Silica
Authors: Cohen Anna Foner
Published: April 2005

Measurements of the thermal conductivity, K, of vitreous silica have been made at low temperatures before and after fast neutron bombardment. The observed increase of K upon bombardment is in agreement with the prediction of Klemens. Over the exposure range used, K increases approximately linearly with dose to the level used (6×1019 n/cm2) whereas the density appears to have nearly saturated, suggesting that the two properties are not directly related. A possible explanation for the K increase upon bombardment is that the neutron bombardment relieves macroscopic strains. Alternatively, it is possible that bombardment causes an increase in local order in the vitreous material.
Small Signal Power Conservation Theorem for Irrotational Electron Beams
Authors: Klüver J. Wilhelm
Published: April 2005

The first-order linearized set of Maxwell-Lorentz equations are used as basis for the derivation of a power conservation theorem describing the balance between the rf kinetic power and the rf electromagnetic power in the electron beam. The theorem applies to laminar electron beams in which the electron flow is irrotational and the thermal velocity distribution at the cathode surface is neglected. The kinetic power flow is given in terms of the longitudinal rf kinetic potential or the Chu potential, the longitudinal part of the rf beam current and the equivalent longitudinal surface current on the beam boundary. This surface current embodies the effect of the transverse rf motion in the beam. A short discussion of the application of the theorem to thin beams is given.
Surface Motions of a Thick Plate
Authors: Knopoff L.
Published: April 2005

The motion of a thick elastic plate, infinite in two dimensions and bounded by air on the two parallel faces, has been studied. The plate is excited at a point on one face, as in Lamb's problem, by a force impulsive in time, and directed normal to the surface. The early motions of this surface have been described by Lamb. An exact solution, in closed form, for the motion of the opposite face is available only at the epicenter. The motions at all other points are evaluated by a seismic model. At the epicenter, the measurements and the calculations are in agreement; at this point a strong P pulse and a weaker S pulse are observed. This S phase has a wave form, for short pulses, which is the time integral of the wave form of the P phase. Off the axis of symmetry, the form of the S pulse is the same as that of the P pulse. The S pulse becomes quite strong away from the epicenter, attaining an amplitude of nearly four times that of the P pulse at about 45° in the Solenhofen limestone plate. A bodily S-surface P phase, whose existence is in agreement with predictions based upon geometrical arguments is discerned at angles exceeding the critical angle.

A simplified description of the early motion of the reverse face may be constructed. This simplified response is a useful tool which may be used to reduce the complexity of the calculations encountered in other boundary value problems.
Fast Neutron Attenuation in Graphite
Authors: Duggal V. P. , Puri S. M.
Published: April 2005

Spatial distribution of a fast neutron flux has been measured experimentally in graphite (density 1.62 g/cc) using threshold radioactivants. For these measurements neutrons were obtained from D-T and D-Be reactions. Assuming the neutron flux to vary as 1/R2e−R/L, the values of relaxation length L (between 50 cm and 70 cm) obtained with a phosphorous detector from D-T and D-Be neutrons are 23.5±1.5 cm and 19.7±1.0 cm, respectively. It is also seen that fast flux falls off less rapidly than resonance neutron (1.46 ev) flux after about 50 cm in graphite.

The spatial distribution of neutrons between the energies 1 Mev to 3 Mev from a plane monoenergetic source of 3-Mev neutrons has also been obtained using a Monte-Carlo calculation.
X-Ray Investigation of Perfection in Tin Whiskers
Authors: Smith H. G. , Rundle R. E.
Published: April 2005

Tin whiskers with elasticities far above that of bulk tin were examined for perfection by x-ray diffraction. Intensities were measured for several whiskers varying in diameter from 2 μ to 11 μ. Some of the data were obtained by means of a Geiger counter with CuKα radiation and some by photographic methods with MoKα radiation. The observed structure factors were corrected for extinction according to the dynamical theory of x-ray diffraction with the crystallite size as a parameter and then compared to the calculated structure factors. The agreement with dynamical theory for imperfect crystals is very good, yielding a crystallite size of 1.5 μ for a 5.5 μ whisker and 2.7 μ for whiskers of about 10 μ in diameter. The whiskers were observed growing in several crystallographic directions.
Adsorption of Activated Gases
Authors: Bills D. G. , Carleton N. P.
Published: April 2005

The adsorption of gases activated by electron bombardment has been investigated theoretically and experimentally. From postulates concerning probabilities of adsorption and deactivation for activated molecules in collision with surfaces an expression is derived giving the rate of adsorption in terms of these probabilities and of the amount of activated gas already adsorbed on the surfaces. This relation is also determined experimentally by a new method in which constant pressure is maintained in the adsorption vessel by admitting gas to it from a reservoir through a controlled leak, while the adsorption is taking place. The theoretical expression fits the experimental data, suggesting that the assumptions of the theory are essentially correct. From numerical values obtained under various experimental conditions some information is derived about the processes involved in adsorption of activated gases.
Neutron Production at High Energies
Authors: Crandall Walter E. , Millburn George P.
Published: April 2005

Neutron yields from several targets bombarded by deuterons, protons, neutrons, and He3 ions with energies of hundreds of Mev were measured by detecting the neutrons with MnSO4 solution. The effect of secondary targets of U and Th in multiplying the primary yield was investigated, and the energy dependence for Be and U targets bombarded by deuterons was measured for energies between 90 and 320 Mev. The data were analyzed in terms of the average number of neutrons produced in an inelastic collision; the largest number observed was 17 for 340-Mev protons bombarding U. The data are in reasonable agreement with evaporational theory and Monte Carlo calculations.
Polygonization of Copper
Authors: Young F. W.
Published: April 2005

It has been demonstrated that dislocations can be revealed as etch pits in copper crystals doped with a small amount of Te. The progress of polygonization of such copper after bending was followed with etch pits and x-ray diffraction. It was found that climbing occurred at 500°C and that polygonization was complete after 2 hr at 1000°C. In similar experiments with three samples of nominally 99.999% copper, the one which was probably purest did not polygonize, while the other two did so. This indicates that if impurity is necessary for polygonization, only a very small amount is required.
Thermal Restoration of Oxygenated Germanium Surfaces
Authors: Rosenberg A. J. , Robinson P. H. , Gatos H. C.
Published: April 2005

Cleaved germanium surfaces, oxygenated at room temperature, were heated under high vacuum and the restoration of their oxygen-adsorbing capacity was determined. No restoration was observed at 425°C. Above 575°C, however, the oxygen-adsorbing capacity of the surfaces was completely recovered. Discharge of GeO from the surface was associated with this process. The restoration process followed first-order reaction kinetics with an activation energy of 56 kcal/mole. Concurrently with restoration a pronounced decrease in the surface area was observed. The results are discussed in terms of the kinetic and energy requirements of the system.
Measurement of Shunt Impedance of a Cavity
Authors: Mallory Kenneth B.
Published: April 2005

The equivalent shunt impedance of a lightly coupled transmission cavity can be measured by inserting very small perturbing elements and using a simple bridge method to detect small shifts of transmission phase. A simple graphical procedure is developed for the interpretation of these measurements. It is shown that the procedure measures directly the shunt impedance R of the cavity, rather than the geometric quantity R/Q. Experimental results are presented for one such cavity, which show that phase information thus obtained is about 100 times as sensitive as amplitude information normally obtained from a transmission cavity.
Orthogonality Properties for Modes in Passive and Active Uniform Wave Guides
Authors: Bresler A. D. , Joshi G. H. , Marcuvitz N.
Published: April 2005

Orthogonality relations are given for the ``four-vector'' guided modes of anisotropic uniform wave guides and for the ``six-vector'' guided modes of uniform wave guides containing unidirectional electron beams with axially independent dc velocities. In general, these orthogonality relations involve both the modes of the given wave guide and those of an appropriate ``adjoint'' wave guide. A description is given for the adjoint wave guides associated with wave guides which contain media whose characteristics are restricted only by the requirement that they be axially independent and which, if bounded, are subject to a variety of boundary conditions arising from idealizations of actual boundaries.
Detection of Screw Dislocations in α-Al2O3 Whiskers
Authors: Dragsdorf R. D. , Webb W. W.
Published: April 2005

An x-ray method has been worked out for the detection of screw dislocations in whiskers and has been proved satisfactory on α-Al2O3 whiskers in which the screw dislocation is identified by an axial pore and the twist independently measured by optical methods.
Neutron Penetration in Infinite Media; Calculation by Semi-Asymptotic Methods
Authors: Holland Samuel S.
Published: April 2005

Application is made of the semi-asymptotic method of Spencer to the penetration and slowing down of neutrons in infinite media. This method can handle complete numerical input data, and is not restricted in distance. Calculations are carried out for the ideal constant cross section case, and a 1-kev point source in air. Complete flux spectra for the 1-kev point source are given for distances out to 100 mean free paths (mfp).
Measurement of Instantaneous Absolute Barium Evaporation Rates from Dispenser Cathodes
Authors: Rutledge W. C. , Milch A. , Rittner E. S.
Published: April 2005

A simple procedure for determining the ``instantaneous'' absolute evaporation rate of barium from dispenser cathodes is presented. The method entails exposing a clean tungsten wire to a stream of barium and noting the time required to reach maximum emission. The sensitivity of the wire as a detector of total barium is established on an absolute basis by chemical calibration. It has been found that the wire sensitivity is a function of the barium oxide content of the evaporant stream. This fact may be employed to determine the oxide composition of the evaporant from wire emission-time measurements and a single chemical analysis. It is also possible to obtain approximate, instantaneous values of total barium and the fraction BaO at any time during tube life from wire emission-time measurements only. Calibration data are presented for almost the full range of Ba–BaO compositions.
Note on Positive-Ion Effects in Pulsed Electron Beams
Authors: Senise José T.
Published: April 2005

Positive-ion effects have been observed in pulsed electron beams of short duration (0.5 to 5 microseconds), under conditions of operation normally encountered in high-power microwave tubes. Three different aspects of ion effects were studied; (1) beam focusing, (2) ion oscillations, and (3) ion trapping at scallop minima. Experimental results are given and correlated with previous work on ion effects by other authors.