bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation-Induced Recombination Centers in Germanium
Authors: Curtis O. L. , Cleland J. W. , Crawford J. H.
Published: April 2005

An attempt has been made to provide a better understanding of minority carrier recombination processes in irradiated germanium. To this end, studies have been made of the minority carrier lifetime of both n- and p-type material, following fast neutron and Co60 γ irradiations. The effect of carrier concentration and temperature has been determined. The primary conclusion drawn from these investigations is that the recombination process is associated with an energy level located 0.20 ev below the bottom of the conduction band. From measurements of the lifetime in n-type specimens, the hole capture cross section has been calculated and found to be σp=3×10−15 cm2 and σp=4×10−16 cm2 for neutron and γ-induced centers, respectively. If a second, lower lying level is associated with the second ionization of the defect responsible for recombination, then the effective number of recombination centers is reduced in p-type material as the Fermi level approaches the valence band, due to this ionization. Such a process is in qualitative agreement with the observed data.
On the Nature and Location of Bubble Nuclei in Boiling from Surfaces
Authors: Bankoff S. G. , Hajjar A. J. , McGlothin B. B.
Published: April 2005

In the pool boiling of pure organic liquids from a reproducible platinum surface, an initial temperature overshoot is observed before the surface breaks into nucleate boiling. A logarithmic plot of heat flux vs temperature excess has a slope of 3.5 for the first traverse but subsequent traverses give a reproducible line having a higher slope and surface temperature. Vigorous heating in air restores the surface to its original condition. These results are explained in terms of the trapped-bubble hypothesis by assuming that many potential vapor traps on the surface are filled with liquid initially, and fill with vapor once boiling commences. The gradual increase in surface temperature for a given flux is attributed to the progressive deaeration of the nucleating centers by dilution with vapor. To reconcile the fact of surface aeration with the existence of an initial temperature overshoot, it is necessary to assume that the temperature drift is due primarily to the removal of sorbed air, resulting in decrease in contact angle, corresponding to improved wetting of the surface. These experiments also indicate that the bulk of the active nuclei are on the heating surface, rather than on dust particles in the liquid.
Polarization Reversal in Tri-Glycine Fluoberyllate and Tri-Glycine Sulfate Single Crystals
Authors: Pulvari Charles F. , Kuebler Wolf
Published: April 2005

Time and field dependence of switching current at room temperature was studied for tri-glycine fluoberyllate as well as for tri-glycine sulfate. It is shown that the theory describing polarization reversal in BaTiO3 c-domain crystals based on observed time and field dependence of polarization P=f(E,t) developed by the authors is applicable. Activation field α and mobility μ appearing in the basic equation were determined for tri-glycine fluoberyllate (TGFB) as well as for tri-glycine sulfate (TGS). For both materials, α, as well as μ was found to be independent of crystal thickness indicating that no skin properties are involved. The value of α for TGFB and TGS is lower by a factor of at least 2.5 and 3, respectively, than for BaTiO3. Compared to values for BaTiO3, the value of μ for TGFB and TGS is lower for thick crystals and higher for relatively thin crystals (δ<8×10−3 cm). Switching conductivity for both materials is given. Both TGFB and TGS were investigated under various pulsed conditions and no fatigue effect was found. The hysteresis losses in both materials are less by a factor of about 10 than those for BaTiO3.
Effect of Neutron Irradiation on the Curie Temperature of a Variety of Ferrites
Authors: Salkovitz E. I. , Bailey G. C. , Schindler A. I.
Published: April 2005

A variety of commercially available ferrites were irradiated in the Brookhaven reactor to a total integrated flux of 1.2×1017 nvt (fast), at a temperature of 50°C. None of the samples showed a significant change in the Curie temperature.
Microwave Method for Measuring the Probability of Elastic Collision of Electrons in a Gas
Authors: Hirshfield Jay L. , Brown Sanborn C.
Published: April 2005

A plasma in a dc magnetic field has a transverse conductivity component whose reactive part depends, as to both magnitude and sign, on the strength of the magnetic field. By measuring the value of magnetic field that is necessary for bringing this reactive part to zero—and hence removing any resonant-frequency shifts of a TE011 mode of a cylindrical cavity containing the plasma—determination of the probability of elastic collision of electrons in helium is obtained as a check on the method. The value of Pm=20±1 cm−1 mm Hg−1 for the electrons at room temperature thus obtained agrees substantially with the value obtained by previous workers. Sources of error in the measurement are discussed.
Solution to the Equations of Space-Charge Flow by the Method of the Separation of Variables
Authors: Kirstein P. T. , Kino G. S.
Published: April 2005

The equations for irrotational, electrostatic laminar space-charge flow (no thermal velocities or normal magnetic field at the cathode) are set up in terms of the action function. The resulting nonlinear partial differential equation is first reduced, by the method of the separation of variables in cylindrical polar coordinates, to the solution of a set of first-order, nonlinear, ordinary differential equations in one coordinate. It is shown that it is possible to predict axially symmetric, electrostatic, hollow beams from the inside of hollow cylindrical cathodes with space-charge-limited emission which asymptote, theoretically, to other extremely thin cylinders—though thermal velocities would, in practice, limit such a convergence. The characteristics of a particular beam, and the electrode system to produce it are shown.

The beams which result from the separation of variables in other coordinate systems are described. In spherical polar coordinates one obtains hollow axially symmetric beams from a conical cathode, which may asymptote to other cones; in a less familiar coordinate system, spiral coordinates, sheet beams from equiangular spiral cathodes result.

Finally, it is shown how the method may be extended to include magnetic fields transverse to the cathode. Some new solutions to space-charge flow in crossed electric and magnetic fields from a space-charge-limited cathode are mentioned.
Optical Theory of Thermal Velocity Effects in Cylindrical Electron Beams
Authors: Herrmann Gabriel
Published: April 2005

Most previous treatments of long high-density electron beams have assumed laminar flow. Recent experiments show that in many cases this assumption is unjustified. The present theory is based on a non-laminar optical model which treats thermal velocities as an integral part of the motion. A Maxwellian distribution of initial transverse velocities is assumed at the cathode, and a first-order focusing theory is applied in order to calculate trajectories at any point in the beam. It is shown that whenever a long beam is confined by a focusing field, images of the cathode are formed repeatedly along the axis.

When applied to uniform magnetic focusing fields, the theory predicts the periodic formation along the axis of cathode images and crossovers, and a relative rotation of successive images. Such effects have been reported. Values of required focusing fields are derived for given space-charge and thermal-velocity conditions, and relations are established between beam spread and transverse velocities. The resulting picture differs radically from the laminar model of beam flow.
Analog Multiplier Based on the Hall Effect
Authors: Löfgren Lars
Published: April 2005

The Hall effect is shown to be well fitted for electronic multiplication of voltages—one of the most cumbersome operations in analog computation. The use of this effect yields a very simple instrument with good accuracy and speed. The rise time—corresponding to a 0.2% error in amplitude—for the response of a step voltage of maximum value (100 volts) applied to the slower of the two inputs, can be kept down to about 1 msec. This time is dictated only by the feeding circuits and is linearly dependent on the amplitude of the step. Thus a step of 5 volts gives a rise time of 50 μsec. Most semiconductors are investigated with respect to their capabilities of accurate multiplication. Silicon is found to be the best choice. The choice of dimension of the semiconductor crystal is discussed from the solution of a potential problem with skew boundary conditions which determines the Hall voltage. The output of a silicon crystal may be as high as about 0.5 volt for an applied magnetic induction of 5000 gauss, a current through the crystal of about 5 ma, and with a simple thermal contact between the crystal and the core of the magnet, without having errors greater than 0.1%. The output voltage is amplified with a chopper amplifier to 20 volts.
Explosive-Induced Shock Waves. Part II. Oblique Shock Waves
Authors: Drummond William E.
Published: April 2005

The explosive production of oblique shock waves in solids is analyzed in the approximation that third and higher order terms in the shock strength can be neglected, and a procedure is developed for calculating the attenuation of the shocks. Application is made to the problem of determining the equation of state of the burned explosives gas.
Method for Measuring Magnetostriction Corrected for Initial Domain Distribution and its Application to Nickel and Iron
Authors: Stauss H. E.
Published: April 2005

A method has been developed for the measurement of magnetostrictive strain that overcomes the effect of initial domain distribution in isotropic materials. A cubic specimen is used, placed between two iron rods of the same cross section. The combination is put along the common axis of two like solenoids connected in series. Strain is measured with a resistance strain gauge, once parallel to the magnetic field, and a second time normal to the field after the specimen has been rotated 90°. At saturation the algebraic difference gives 3/2 of the saturation magnetostriction. Use of the difference eliminates or reduces a number of experimental errors in addition to that arising from nonrandomness of initial domain distribution.

The method has been applied to grade A nickel and armco iron.
Thermally Precipitated Phases and their Distribution in an Aluminum-Silicon-Cadmium Alloy
Authors: Marburger R. E. , Schluchter A. W.
Published: April 2005

X-ray and electron diffraction and electron microscopy have been used to study the composition and distribution of the precipitated phases in an aluminum—4% silicon—1% cadmium alloy as a function of thermal history. Thin precipitated crystallites are detected in extraction replicas of specimens tempered above 400°F and have been identified by selected area electron diffraction as elemental silicon. The amount of silicon remaining undissolved after solution treatment at 1000°F can easily be distinguished from that precipitated upon tempering, and the amount of silicon observed to dissolve and reprecipitate after solution and tempering treatment is in agreement with reported equilibrium data. The aluminum oxide replica was found to be unsuitable for this investigation. A direct carbon replica technique, however, was found to be satisfactory. The extent of precipitation of the minor phases as a function of tempering temperature, as determined by quantitative x-ray diffraction studies, was found to correlate with a mechanical property of the alloy.
Intrinsic Bulk Viscosity in Monatomic and Diatomic Gases
Authors: Nettleton R. E.
Published: April 2005

The Born-Green theory, employing the Kirkwood superposition approximation, is investigated as a means of calculating the intrinsic bulk viscosity—a bulk viscosity due solely to Van der Waals interactions—in a monatomic gas. In the framework of the Born-Green Theory, it is found that the Kirkwood approximation does not introduce irreversibility and leads to homogeneous integral equations with no normalizing conditions. By the neglect of terms of the order of contributions from triple collisions, expressions for the bulk viscosity are derived in terms of other thermodynamic quantities which yield rough values of the order of one micropoise for argon and nitrogen at 0°C, 1 atmos.
Etching of Germanium Crystals by Ion Bombardment
Authors: Wehner G. K.
Published: April 2005

A study is made of the etch effects produced by sputtering germanium crystals and bicrystals under normal incident low-energy (100 ev) Hg+-ion bombardment in a low pressure plasma (1 micron gas pressure). The surfaces show preferentially etched pits which readily reveal the crystal orientation. These pits become more abundant at lower target temperature and truncated at higher target temperature or at higher energy of the bombarding ions. A sequence of micrographs from the same surface area reveals that these pits cannot be correlated with the pits which are persistently developed by CP-4. A 6° tilt boundary however always develops into a sharply indented furrow just as was the case with a CP-4 etchant.
Time Decrease of Permeability in Iron
Authors: Rathenau G. W.
Published: April 2005

Measurements on iron containing interstitial nitrogen are discussed. Relaxation phenomena with different relaxation times can be resolved. Unequal initial stiffness of the domain walls gives rise to satellites of the main relaxation. The activation energy of the main relaxation and its satellites coincides with that known for bulk diffusion. Short demagnetization of the relaxed material prior to time decrease results in wall movement during the measurement and in apparent longer relaxation times. The method has been applied for the determination of the activation volume for interstitial diffusion. Preliminary results of measurements on single crystals are given.
Structure and Ferrimagnetism of the Ilmenite Compound MnNiO3
Authors: Bertaut E. F. , Forrat F.
Published: April 2005

MnNiO3 is a ferrimagnetic compound, belonging to the ilmenite type. The sublattices of Mn4+ and Ni2+ are coupled antiferromagnetically as the sublattices of Fe3+ in hematite. The saturation magnetization at T=0°K is 0.76μB.
Analogy between Directional Ordering and the Magnetic Diffusion Aftereffect
Authors: Brissonneau Pierre
Published: April 2005

The preferential distribution of carbon atoms among three different interstitial sites of α iron, depending on the direction of the spontaneous magnetization, has a close formal resemblance to the directional order induced by a field cooling. The measurement of the hysteresis loops of α iron and with carbon content 0.0046% by weight actually revealed such close resemblance to those of the Perminvar type alloys and those of certain ferrites containing cobalt oxide.
Uniaxial Magnetic Anisotropy Induced in Fe–Ni Alloys by Magnetic Anneal
Authors: Ferguson Eric T.
Published: April 2005

The uniaxial magnetic anisotropy induced in iron-nickel alloys by a magnetic anneal has been determined as a function of the composition, annealing temperature and duration. It was found that the result is consistent with the Néel-Taniguchi theory.
Magnetic Resonance of Ferrites with a Compensation Temperature
Authors: Pauleve Jean
Published: April 2005

Calculations of the resonance fields as a function of temperature and of resonance frequency as a function of field for temperatures near the compensation temperature for lithium-chromium ferrite and gadolinium garnet are given. For the latter case, a comparison is made between the assumption of zero anisotropy and an assumed negative anisotropy.
Rotational Model of Flux Reversal in Square Loop Soft Ferromagnets
Authors: Gyorgy E. M.
Published: April 2005

The present paper analyzes a rotational model of flux reversal in ferromagnetic materials. A brief review of the experimentally established details of the flux reversal process in square loop ferrites is given. The discrepancies between the experimental results and the predictions of the domain wall motion theory are discussed. The switching coefficient, Sw, is examined in detail.

The rotation model is based on the solution of the modified Landau and Lifshitz equation, but does not assume that the magnetization rotates uniformly throughout the sample. The model predicts the shape of the output voltage pulse, the relationship between the flux reversal time and the applied field, and the minimum switching coefficient that can be obtained for a given ferrite. The switching coefficients determined experimentally for ferrites, permalloy tape, and thin evaporated metal films (with zero transverse field) are within a factor of three of the minimum value of Sw predicted by this model.
Effects of Heat Treatment of Thin Ferromagnetic Films at Intermediate Temperatures
Authors: Mitchell E. N.
Published: April 2005

Iron-nickel films deposited in vacuo in the presence of a magnetic field have been annealed in an inert environment. It has been established that, when the annealing is performed in an orienting field of 30 oe, initial magnetic properties of these films can be altered provided that the initial temperature is high enough. If a field is applied at right angles to the original preferred direction and in the plane of the film, the magnitude of the magnetic anisotropy can be reduced without changing the preferred direction; the preferred direction of magnetization can be changed if the anneal temperature is sufficiently high. This last effect confirms the observations of Williams and Sherwood.
Steady-State and Pulse Measurement Techniques for Thin Magnetic Films in the vhf-uhf Range
Authors: Smith D. O. , Weiss G. P.
Published: April 2005

A vhf-uhf bridge consisting of two loops placed symmetrically in a rectangular coaxial cavity has been used to study steady-state and pulse relaxation in thin (∼1000 A) Permalloy films. For steady-state measurements a coaxial transformer converts the bridge output from balanced-to-ground to unbalanced-to-ground; measurements from 100 to 1500 Mc are currently possible. Pulse measurements utilize the ungrounded deflection plates of a wide-band traveling-wave oscilloscope; pulse response to 2 mμsec can be resolved. Drive-pulse calibration is accomplished unambiguously by using some of the unique switching properties of films which have uniaxial anisotropy.
Phase Analysis of Alnico V Based on Temperature Effects
Authors: Tenzer R. K. , Kronenberg K. J.
Published: April 2005

A magnetic analysis of the composition of the two Alnico V phases is tried. Structure-independent properties, like saturation magnetization and temperature coefficient, serve to indicate the correctness of alloys supposed to represent these phases. A model of the two-phase structure of Alnico V is derived from electron micrographs. The combined saturation magnetization and the combined temperature coefficients are calculated with this model using the measured properties of the single alloys. The two alloys whose combined properties come closest to those of Alnico V consist mainly of NiAl and Fe2Co, respectively.
Magnetic Measurements on Some Precipitating Systems
Authors: Berkowitz A. E. , Flanders P. J.
Published: April 2005

In the systems Au–Ni and β-brass-Fe, ferromagnetic precipitate particles develop in a nonmagnetic matrix. Single crystal samples of these alloys have been examined by measuring saturation magnetization, torque curves, rotational hysteresis, and remanence.

The data on the Au–Ni system have been analyzed to infer particle anisotropy distributions, orientation of the ``easy'' axes of the particles, and other features of the precipitate particle system. Electron micrographs of the precipitate particles are in general agreement with this analysis. The measurements on the β-brass-Fe system indicated that the precipitate particles were single crystals with the same crystal habit as the matrix, and were elongated in the 〈111〉 directions. The temperature dependence of the torque curves was identified with the temperature dependence of shape and magnetocrystalline anisotropy.
Precipitation and Magnetic Annealing in a Copper-Cobalt Alloy
Authors: Becker J. J.
Published: April 2005

In an alloy containing 2% cobalt, balance copper, it is possible to quench a nonmagnetic solid solution from 1000°C and then produce a ferromagnetic precipitate in a nonmagnetic matrix by aging at several hundred degrees. The magnetic properties of this precipitate can be correlated with the size and shape of the precipitate particles. Considerable information about the precipitation process can be obtained in this way. In these experiments, saturation magnetization, torque, rotational hysteresis, remanence, coercive force for zero magnetization, and coercive force for zero remanence (which behaves in a surprising fashion) have been observed during the course of aging. In particular, the effect of a field during aging in producing magnetic anisotropy (``magnetic annealing'') has been studied and is shown to occur entirely during the growth of the particles, after the precipitation is complete.

The precipitation process is viewed as one in which the particles as they grow are first superparamagnetic, then stable single domains, and finally multidomain. This point of view is consistent with all of the varied phenomena observed.
Ferromagnetic Resonance and Nonlinear Effects in Yttrium Iron Garnet
Authors: LeCraw R. C. , Spencer E. G. , Porter C. S.
Published: April 2005

A study of ferromagnetic resonance at 9300 mc and 3000 mc in single crystals of yttrium iron garnet is described. Cavity perturbation techniques are used with polished spherical samples 9 to 11 mils in diameter. The line widths along the hard axis [100] are found to be 2.3 and 5.7 oe, respectively, at 9300 mc and 3000 mc. It is believed the 2.3 oe is the narrowest resonance line yet observed on spheres of ferromagnetic material at room temperature. Because of the narrow line widths, the nonlinear behavior of these crystals is of particular interest. At 9300 mc the rf field, hcrit, for saturation of the main resonance line is 46 millioersteds. Using Suhl's spin wave theory of nonlinear effects in ferromagnets, the 46 millioersteds (associated with a z-directed spin wave) predicts a spin-lattice relaxation time T1 of 7.4×10−8 sec, in good agreement with the 7.0×10−8 sec measured by other independent methods. This T1 then predicts an ``intrinsic'' line width of 1.54 oersted. Thus the observed line width of these crystals at 9300 mc is within a factor 1.5 of its theoretical limiting value. At 3000 mc, where the subsidiary resonance coincides with the main resonance, hcrit is 5.0 millioersteds (associated with spin waves not z directed). As the temperature is increased toward 340°K, an interesting effect is observed. The hcrit rises quite abruptly; in fact it changes by 10.5 db between 335°K and 340°K. This and other observations are compared with Suhl's nonlinear theory with good results.
Ferromagnetic Dynamical Response
Authors: Callen Herbert B.
Published: April 2005

A dynamical equation, describing the response of the magnetization to an applied field, is proposed. The analysis is based on a spin-wave picture. The dynamical equation contains three parameters, defined in terms of particular magnon-magnon and magnon-phonon transition probabilities. A more detailed theory for one of these parameters is developed. The resultant size and shape dependence of the magnetic loss is suggestive of experimental observations.
Origin of Ferromagnetic Resonance Line Broadening in Manganese-Rich Manganese Ferrites
Authors: Harrison S. E. , Belson H. S. , Kriessman C. J.
Published: April 2005

Ferromagnetic resonance line widths in dense polycrystalline and single crystal specimens, the magnetic moment and the anisotropy field (K1/Ms) have been measured as a function of temperature. Between room temperature and the Curie point the excess resonance line width, which is given by ΔH(excess)-ΔH(polycrystal)—ΔH (single crystal), is found to have the same temperature dependence as the saturation magnetization. This result is obtained even though the polycrystalline density (>98%) is sufficiently high to be in the range where the excess line width has usually been attributed to anisotropy broadening. In the region below room temperature ΔH(excess) becomes dependent on the anisotropy field. An approximate criterion, that is suggested by the data, to determine whether the anisotropy field or the magnetic moment is responsible for the broadening is the ratio K1/Ms2≷0.25. The compositions measured were Mn1.24Fe1.76O4 and Mn1.49Fe1.51O4. The polycrystalline g factor (gp) is greater than the single crystal g factor (gs) and both g factors are functions of the temperature. The shift in the polycrystalline resonance peak is discussed with reference to the Standley Stevens theory and limited agreement is found. The anisotropy constant, K1, has been found to vary as the fifth power of Ms for these ferrite compositions.
Effects of Composition and Processing Variables on the Magnetic Properties of the 50% Nickel-Iron Alloy
Authors: Savitski M. J.
Published: April 2005

In a factorial experiment, a study has been made of the effects of small amounts of alloying elements and processing variables on the magnetic properties of the 50% nickel-iron alloy. The composition variables were: three levels of manganese, two of silicon, two of sulfur, and two of oxygen. The processing variables were: hot rolling at two temperature levels, annealing or not annealing after hot rolling, and final annealing at six temperature levels. The ingots were processed to tape from which toroidal cores were made.

The results of magnetic tests made with a constant current, flux-reset core tester indicate that certain elements need to be added to the melt to produce a grain-oriented alloy with satisfactory magnetic properties, and that the processing must be compatible with the additions made. The binary manganese-oxygen addition was most beneficial. In general, hot rolling at a high temperature level was beneficial, and annealing after hot rolling was detrimental to the magnetic performance.
Orientation Study of Ultra-Thin Molybdenum Permalloy Tape
Authors: Koh P. K.
Published: April 2005

Quantitative pole density stereograms of {111}, {220}, {200}, and {113} poles of ⅛-mil molybdenum permalloy tape were developed in order to establish its cold rolled deformation texture and annealed textures.

Cold rolled the tape induced multiple slip common to all face-centered-cubic metals and developed (110) [3̄35] and (110) [33̄5] end orientations which deviate 5° about [110] from the recognized {110} 〈112〉 brass deformation texture.

On annealing at 771°C the cold rolled tape was found to develop (120) [001]+(210) [001] and (113) [7̄8̄5] +(113) [785̄] orientations as components of the annealed texture which bear in general at 35°-45° rotation orientation relationship about 〈111〉 with the cold rolled end orientations.

Annealing at 1160°C developed the same texture as that obtained after 771°C annealing.

From the pole figures made on 927°C annealed tape, the same annealed texture prevailed whether the pole figure was made on its full ⅛ mil thickness or on its central 0.00005 in. section.

Hysteresis loop tracings made on the cold rolled tape revealed an apparent direction of easy magnetization along the rolling direction. No easy magnetization direction was revealed in the rolling plane on the annealed tapes. These findings support the deductions from the corresponding pole figures.
Development of Preferred Orientations in Silicon Iron
Authors: Brown J. R.
Published: April 2005

The (110) [001] texture in silicon iron arises by a process of secondary recrystallization after cold reduction of the strip in two stages separated by an anneal. It is possible to produce the same texture by a one-stage or a three-stage reduction process. The rolling textures and primary recrystallization textures for each of these processes have been experimentally determined and are all different. In spite of this, the (110) [001] secondary orientation develops in each case. It is tentatively suggested that impurities in the steel, already known to be important in controlling grain growth in silicon iron, also supply the directional forces leading to the (110) [001] texture.
Cube Texture in Body Centered Magnetic Alloys
Authors: Wiener G. , Albert P. A. , Trapp R. H. , Littmann M. F.
Published: April 2005

Cube oriented, (100) [001], iron silicon alloys have been prepared in thickness ranging from 0.8 mil to 11.0 mils. Both ac and dc magnetic properties are given for the alloys. The data show that comparable properties to commercial singly oriented steel of the (110) [001] texture are obtained both parallel and perpendicular to the rolling direction. The magnetic properties are sensitive to both the amount of cube oriented grains and the distribution of the directions about the rolling direction of the sheet.
Preferential Volatilization of Cations from Ferrites During Sintering
Authors: Brownlow J. M.
Published: April 2005

The abnormal plots of reduced magnetization vs temperature for ferrites containing zinc are found to be associated with a concentration gradient in zinc that is generated by the preferential loss of zinc during sintering. The variation of the gradient in samples of zinc-iron spinels is correlated with sintering and annealing treatment and with sample dimensions.
Ionic Valences in Manganese-Iron Spinels
Authors: Eschenfelder Andrew H.
Published: April 2005

Because both manganese and iron assume multiple valences in oxide structures, it is possible to fabricate spinels over a continuous range of composition from Mn3O4 to Fe3O4. Magnetic-moment data for samples fabricated within this range are reported and an interpretation of the data in terms of the distribution of ions of manganese and iron is presented.

The data agree with previous indications that manganese ferrite, MnFe2O4, is an almost completely normal spinel with Mn2+ on A sites and Fe3+ on B sites. In addition, the usual assumption that excess iron replaces manganese as Fe2+ on B sites is substantiated. However, the data are not compatible with the previously held assumption that Fe3+ is replaced by excess manganese as Mn3+. Instead, the variation of magnetic moments and Curie temperatures with composition is interpreted in terms of a model in which excess manganese replaces Fe3+ as Mn4+ and an equal amount of iron is converted to Fe2+. When the manganese content gets so high that all the iron is Fe2+ (Mn2FeO4), manganese then replaces the iron as Mn3+ and reconverts an equal amount of Mn4+ to Mn3+, and the Mn3+, because of its tetragonal nature, introduces spinel twinning.

It is proposed that the Mn4+–Fe2+ pair in octahedral coordination is stabilized with respect to a Mn3+–Fe3+ pair because of the interaction of the manganese orbitals with the 2p orbitals of the surrounding oxygen anions.
Measurement of the Properties of Various Ferrites Used in Magnetically Tuned Resonant Circuits in the 2.5–45 Mc/sec Region
Authors: Lombardini Pietro P. , Schwartz Richard F. , Doviak Richard J.
Published: April 2005

An investigation was conducted directed toward securing data for choosing the best ferrite to be used in the Penn-Princeton 3 Bev high intensity proton synchrotron now being built at Princeton University. The ferrite samples tested were from American and European manufacturers and were in the form of small rings 2 inches or less in diameter. Measurements were required of μ and Q under varying magnetic bias, at various rf flux levels, in the band frequencies 2.5 to 45 megacycles per second. At the beginning of this research no clear method existed for a proper choice of ferrite, and generally speaking the manufacturers' data were inadequate. Therefore a novel technique of measurement was devised, and an effort was made to establish a minimum number of parameters for defining ferrite properties for this application. The present paper includes a description of the techniques used and a resume of the results obtained.
Factors Limiting a Magnetic Suspension System
Authors: Breazeale J. B. , McIlwraith C. G. , Dacus E. N.
Published: April 2005

A magnetic suspension apparatus is reported which is capable of operating in any attitude in space, or under reasonable accelerations in any direction. The device may be used as a low-friction bearing or as a force-measuring balance. Limitations of both of these useful properties exist because of physical and magnetic properties of the materials used. These limitations are discussed and their order of magnitude reported for several common magnetic materials. As a low-friction bearing, hysteresis torques as low as 3×10−5 dyne-cm, and eddy current torques as low as 9×10−7 dyne-cm per radian/sec are reported. As a force-measuring balance hysteresis errors and deviations from linearity of as little as 0.1% of full-scale force may be obtained. The maximum force under which support can be maintained, is about five times the weight of ferromagnetic material in the supported object. Displacement of the supported object under an applied force can be made as small as 10−6 cm/dyne.
Origin and Use of Instabilities in Ferromagnetic Resonance
Authors: Suhl H.
Published: April 2005

An outline is presented of the behavior of ferromagnetic materials in large high-frequency fields. It is shown that, because of the collective behavior of the electronic spins, instabilities set in beyond a certain critical field amplitude. Finally, the application of such effects to the construction of ferromagnetic amplifiers is discussed.
Ferrimagnetic Resonance in Gadolinium Iron Garnet
Authors: Calhoun B. A. , Smith W. V. , Overmeyer J.
Published: April 2005

Ferrimagnetic resonance in single crystals of gadolinium iron garnet has been observed at 9479 and 23 725 mc. Crystals from two different preparations have different compensation points (13° and 32°C). The resonance behavior is discussed in terms of a two sublattice theory. gGd is equal to 2.006 above −90°C and increases at lower temperatures. The gadolinium ions contribute to the anisotropy below −40°. An extra resonance observed near the compensation point is attributed to inclusions in the crystals. The gadolinium apparently contributes substantially to the total damping of the magnetization.
Effect of Cation Vacancies on the Magnetic Annealing of Cobalt-Substituted Magnetite
Authors: Bickford L. R. , Brownlow J. M. , Penoyer R. F.
Published: April 2005

Five crystals of nominal composition Co0.1Fe2.9O4, grown from the melt under different partial pressures of oxygen, were subjected to magnetic annealing at 100°C. The relaxation time characterizing the annealing process is shown to increase from several minutes for crystals known to contain cation vacancies to a value too large to be determined for a crystal essentially stoichiometric with respect to oxygen content. The observed changes in relaxation time and magnitude of the anneal-induced anisotropy are interpreted as the effect of cation vacancies on the ease of movement of cobalt ions between equivalent cation sites during the annealing process.
Preparation and Properties of Crystal-Oriented Ferroxplana Samples
Authors: Stuijts A. L. , Wijn H. P. J.
Published: April 2005

Samples of the hexagonal ferroxplana materials, with a preferential plane for the magnetization, show an increased resonant frequency compared to samples of cubic ferrites with the same permeability. It appeared possible to use the large stiffness for rotation of the magnetization out of the preferential plane, in order to orientate the single crystal particles of a ferroxplana powder in a magnetic field. In this way samples with two different textures have been obtained. In one case the basal planes of the crystals have one direction more or less in common (fan texture); in the other case all basal planes lie more or less parallel to each other (foliate texture). In both cases the permeability is appreciably increased, while the resonant frequency is only slightly decreased. Permeabilities of 56 at 90 Mc/sec and 28 at 230 Mc/sec, both for tanδ=0.1, have been found. This large increase in permeability is caused mainly by an elimination of the effect of the anisotropic permeability of the crystals.
Rigorous Approach to the Theory of Ferromagnetic Microstructure
Authors: Brown William Fuller
Published: April 2005

Current ``domain'' theory relies heavily on Bloch walls and the Landau-Lifshitz method of assembling them. A rigorous attack on the same problem leads to a nonlinear boundary-value problem; with electronic computers available, this problem is now less formidable than when it was first formulated. Numerical calculations have been carried out for an infinite cylinder that reverses its magnetization by ``magnetization curling.'' The conditions under which this process occurs can be determined by means of a linear theory, similar to the theory of elastic stability, developed independently by the author and by Frei, Shtrikman, and Treves. To follow the process beyond its initial stages, a nonlinear differential equation must be integrated by numerical methods. The calculations show that the only stable states are ones of uniform positive or negative longitudinal magnetization; the transition between them occurs in a single jump, and only during the jump is the magnetization nonuniform. Thus a particle with no stable states other than ``single-domain'' ones may be ``multidomain'' during transitions. The results suggest that stable nonuniform states will be found in a finite body, and even in an infinite cylinder if imperfections are present.
Model for Nonlinear Flux Reversals of Square-Loop Polycrystalline Magnetic Cores
Authors: Haynes M. K.
Published: April 2005

The theory of the reversal wave forms of polycrystalline magnetic cores proposed by Goodenough is based on the growth of ellipsoidal domains of reverse magnetization which originate from nucleating centers at grain boundaries. The present model extends this theory with the assumption that the nucleating centers are randomly distributed throughout the core volume. Radial field variations are neglected.

The rate of change of reversed magnetization area of the irreversibly moving and colliding walls is calculated as a function of their position, starting from a Poisson distribution of nucleating centers, and then converted to a function of flux. The equation derived for rate of flux change is dxdt=4.82Sw(H−H0)(1−x)(−ln1−x2)23,where Sw is the switching coefficient, H0 is the threshold field, H is the applied field, and x is the ratio of flux density to retentivity.

This nonlinear differential equation is solved for the simple case of constant current drive. For more complicated circuit conditions, solutions of the core equations require numerical methods. Programs have been written for the IBM Type 704 DPM to calculate the behavior of circuits containing many such cores interacting and switching together. Results obtained check reasonably well with experimental evidence.
Switching Properties of Permalloy Cores of Varying Coercivity
Authors: Rossing Thomas D. , Korkowski Vincent J.
Published: April 2005

In attempting to develop a 4–79 molybdenum Permalloy core for use in a memory with nondestructive readout, studies have been made of switching properties of Permalloy tape cores with coercivities ranging from 0.1–1.0 oe, corresponding to heat treatments over a temperature range of 300–900°C. The switching time of a core can be shortened by means of auxiliary field pulses which help to nucleate domains of reverse magnetization, but have little effect on their rate of propagation. In general, auxiliary field pulses applied perpendicular to the direction of remanent magnetization are more effective than those applied antiparallel to it provided the latter are not large enough to cause switching by themselves. The timing of the auxiliary pulses is important. Many of the cores have a ``preferred'' direction presumably caused by small domains of extremely high coercivity. The experimental results are interpreted in the light of domain wall motion theory.
New Concept in Large-Size Memory Arrays—the Twistor
Authors: Bobeck Andrew H.
Published: April 2005

Three methods have been developed for storing information in a coincident-current manner on magnetic wire. The resulting memory cells have been collectively named the ``twistor''. Two of these methods utilize the strain sensitivity of magnetic materials and are based on the century old Wertheim or Wiedemann effects; the third utilizes the favorable geometry of a wire.

The effect of an applied torsion on a magnetic wire is to shift the preferred direction of magnetization into a helical path inclined at an angle of 45° with respect to the axis. The coincidence of a circular and a longitudinal magnetic field inserts information into this wire in the form of a polarized helical magnetization. In addition, the magnetic wire itself may be used as a sensing means with resultant favorable increase in available signal since the lines of flux wrap the magnetic wire many times.

An experimental transistor-driven 320 bit twistor array has been built. The possibility of applying weaving techniques to future arrays makes the twistor approach appear economically attractive.
New Magnetic Core Loss Comparator
Authors: Tompkins R. E. , Stauffer L. H. , Kaplan A.
Published: April 2005

A new method has been developed for the rapid measurement of magnetic flux density and power loss in single sheet steel specimens. In use the sheet specimen is inserted into an exciting unit which generates an ac magnetomotive force to provide the required flux density. A measuring head is then pressed against the surface of the specimen and the power loss and flux density are read directly on an indicating instrument. Localized measurements in areas as small as 1 sq in. are possible.

Simultaneous pickup of the emf induced in the specimen by the time varying flux, and the mmf generated by the exciting unit is accomplished by a pair of probes and a modified Chattock coil. Specially designed amplifiers, integrating circuits and switching arrangements enable the operator to observe the hysteresis loop or to read the power loss directly. Specimens of varying shapes and sizes may be employed without cutting or stacking and power loss distributions are readily observed.
Magnetometallurgy—Applications and Techniques
Authors: Arrott Anthony
Published: April 2005

The use of measurements of intrinsic magnetic properties—susceptibility, saturation magnetization, and transition temperature—in solving problems in metallurgy is discussed. Applications to phase-diagram determinations, precipitation studies, kinetics, detection of inhomogeneities, and quantitative analysis are considered. Methods of measurement requiring little capital investment are pointed out in the hope of stimulating metallurgy graduate students to apply magnetic analysis to their problems.
Unusual Magnetic Behavior of Disordered Ni3Mn
Authors: Kouvel J. S. , Graham C. D. , Becker J. J.
Published: April 2005

Measurements were made of the magnetization of disordered Ni3Mn for various fields between 945 and 7550 oe and at many temperatures between 1.5 and 300°K. The magnetization vs temperature curve for any given field is found to have a pronounced maximum at about 25°K and a long concave-upward section extending from about 140°K to temperatures above 300°K. By means of a new method of analysis, the Curie point is deduced to be 132°K. An abnormally large induced magnetization, greatest at about 50°K, is also found. All the experimental results are consistent with the occurrence of a ferrimagnetic-ferromagnetic transition at low temperatures.
Further Magnetic and X-Ray Diffraction Studies on Iron-Rich Iron-Aluminum Alloys
Authors: Taylor A. , Jones R. M.
Published: April 2005

Lattice parameter determinations of body-centered cubic iron-rich α-phase iron-aluminum alloys have revealed anomalies in the region of Fe3Al which can be associated with magnetic properties and order-disorder transformations. In particular, it has been discovered that by severely cold-working nonmagnetic alloys in the region of 35 atomic percent aluminum, an extremely large increase in lattice volume is induced. This is of the order of 3% and is of a much larger order than that to be expected from dislocation theory. At the same time the alloys develop a high degree of ferromagnetism. Annealing the alloys for a few minutes at 150° to 200° causes the magnetism to disappear and restores the lattice parameter to its original value. The breadths of the main lattice lines after the anneal and the re-emergence of superlattice reflections seem to indicate that the loss of ferromagnetic properties is associated with lattice ordering and not with the removal of microstresses.
Magnetic Moments and Apparent Molecular Fields in Some Rare Earth Metals and Compounds
Authors: Henry Warren E.
Published: April 2005

A study has been made of the absolute magnetization of some rare earth metals (gadolinium and cerium) and some compounds (ytterbium oxide, neodymium oxide, erbium oxide and yttrium iron garnet) as a function of magnetic fields up to 60 000 gauss and temperature down to 1.3°K. The saturation magnetization of ferromagnetic gadolinium is 7.05±0.10 Bohr magneton per atom of gadolinium and its molecular field is 1.3 megagauss. The average magnetization of cerium is only 0.17 Bohr magneton per atom of cerium even at 1.3°K and 60 000 gauss. It is ferrimagnetic with an estimated antiferromagnetic molecular field of one-half megagauss. Ytterbium sesquioxide has an antiferromagnetic molecular field of about 35 000 gauss and becomes antiferromagnetic at about 3°K in zero field. Yttrium iron garnet (YIG) has been studied and the saturation magnetization has been determined at 100°K and in the helium range. The saturation magnetization is 0.83 at 1.3°K as compared with 1.25 Bohr magnetons per atom of iron in gamma iron (III) oxide studied previously. A ballistic method was used for measuring the magnetic moment and the calibration was made using metallic iron.
Antiferromagnetic Domain Walls and the Magnetization Process in α−Fe2O3
Authors: Jacobs I. S. , Bean C. P.
Published: April 2005

The magnetic properties of α−Fe2O3 are of interest since it is a prototype of the class of antiferromagnetic substances possessing a weak ferromagnetism superimposed on the normal antiferromagnetic susceptibility. Two possible sources of the weak ferromagnetism, i.e., moment bearing antiferromagnetic domain walls and special ferrimagnetic forms of Fe2O3, are considered from the standpoint of their magnetization processes. It is noted that moment bearing or nonmoment bearing domain walls may be required by the presence of certain edge and screw dislocations. The net moment of a domain wall may reverse by a wall displacement process or by the motion of a boundary within the domain wall, i.e., a Bloch line. Measurement of the rotational hysteresis in α−Fe2O3 proves that the weak ferromagnetism is not caused by a nonepitaxial second-phase ferrimagnetic impurity. It is concluded that the behavior of α−Fe2O3 at room temperature can be ascribed to moment bearing domain walls magnetizing by Bloch line motion, and/or ferrimagnetic Fe2O3 basal intergrowths in exchange contact with the antiferromagnetic lattice (Meiklejohn effect). The low-temperature state can also be qualitatively understood with this model.
Size Dependence of the Wall Characteristics in a Two-Domain Iron Particle
Authors: Amar Henri
Published: April 2005

The study of the energy per unit volume versus wall width in a cubic two-domain iron particle leads to the following results: (1) The width and energy per unit area of the wall have values considerably different from their values in bulk iron. (2) The width of the wall slowly rises with increasing size of the cube while the energy decreases. (3) The two-domain configuration is energetically unstable when the cube edge is less than 200 A, in fair agreement with current single domain criteria.