bluuebunny/crossref_metadata_2025 huggingface dataset:
Results of Magneto-Optical Investigation of Rare-Earth Iron Garnets
Authors: Krinchik G. S. , Tjutneva G. K.
Published: April 2005

The fine structure of the 7F0→7F4 absorption line of the Eu3+ ion in single crystals of europium iron garnet has been studied. The magneto-optical method allows us to evaluate the contributions of magnetic and electric dipole transitions to the absorption coefficient of the garnet. Anisotropy in the structure of the line was observed, the intensities of individual components depending on the relative orientation of the plane of the polarized light and on the magnetization vector of the crystal. The main components of the line are shown to arise from an exchange Zeeman effect. From the magnitude of the splitting the exchange field acting on the Eu3+ ion is found to be 220 000 Oe. Certain components of the fine structure are interpreted in terms of combination lines involving spin-wave modes in the garnet.

Measurements of the Faraday rotation in europium, dysprosium, terbium, and samarium garnet in the infrared are described and used to calculate the g factor for the ground state of the rare-earth ion.
High-Power Effects in Flame-Sprayed and Hot-Pressed Nickel-Aluminum-Gallium Spinels
Authors: Zneimer J. E. , Kaplan B. , Lehman K. , Lepore D. A.
Published: April 2005

Significant improvements on high-power handling capability of ferrites in the nickel-aluminum-gallium spinel system (NAGS) have been obtained by hot pressing these materials. The materials investigated were NiAlxGayFe2−(x+y)O4, where x+y was 0.975. The x/y ratio was varied from 2.24:1 to 2.95:1. Cavity measurements were made on these samples at S band to approximately 2 MW peak which is equivalent to approximately 35 rf Oe. Nonlinearity was determined by observing the decrease in the peak of susceptibility χ″ at an applied field required to maximize χ″. Results are compared to samples prepared by conventional ceramic techniques in this system and in the magnesium-manganese-iron system. Conventionally prepared and flame-sprayed materials in the nickel-aluminum-gallium spinel system showed an improvement of approximately ten times in power handling capability over a ferrite in the magnesium manganese system. Samples of nickel-aluminum-gallium spinels that were hot pressed showed a hundred times improvement in the power handling capability compared to the magnesium manganese ferrite.

A description of the techniques and procedures required for flame spraying and hot pressing materials in this system is given.
Temperature Dependence of the Magneto-Optic Effect and Resonance Phenomena in Oriented MnBi Films
Authors: Chen D. , Gondō Y.
Published: April 2005

Oriented MnBi films exhibit extremely large magneto-optic Kerr rotation and crystalline anisotropy energy at room temperature. These physical properties are examined experimentally over a range of temperature from 300° to 84°K. The samples studied are polycrystalline thin MnBi films with the c axis of the crystallites oriented perpendicular to the plane of the film. The magneto-optic Kerr rotation is measured with a 6328-Å He–Ne laser source. As the temperature decreases from 300° to 84°K, the following experimental results are obtained: (1) the Kerr rotation decreases by a factor of 32 when the film is in the remanent state; (2) the Kerr rotation increases by a factor of 10 when the film is in the saturation state; (3) the resistivity decreases by a factor of 2; and (4) the reflected light intensity decreases by a factor of 6.

The ferromagnetic resonance absorption at 9.02 Gc/sec is observed in the temperature range between 170° and 84°K, with the direction of the external dc field both perpendicular and parallel to the c axis of the film. The anisotropy constant estimated from the FMR data decreases from 4.5×106 erg/cm3 at 162°K to zero at 84°K. This temperature dependence is in good agreement with Guillaud's result calculated from magnetization measurements. The spectroscopic splitting factor g is estimated to be 2.1 at liquid-nitrogen temperature, which is smaller than the previously reported value.
Internal Magnetoelastic Coupling Constant of Nickel Ferrite
Authors: Goldberg Norman , McCann William
Published: April 2005

The coupling of the spin system to ionic displacements in a ferromagnetic crystal can cause displacements of the ions which do not result in external strains. A search was made for such magnetostrictive displacements of the oxygen ions in nickel ferrite by looking for a change in the intensity of the 442 x-ray diffraction line. The sample was a disk-shaped single crystal of nickel ferrite cut so that the face of the sample was a (221) plane. The intensity of the line when the magnetization was perpendicular to the disk was compared with the intensity when the magnetization was essentially in the plane of the disk near a [111] (easy) direction; these intensities were found to be equal to within 0.5%. The equilibrium ionic displacements were expressed in terms of the internal magnetoelastic coupling constants, assuming plausible modes of displacement of the oxygen ions. Changes in the structure factor of the 442 line resulting from these displacements were calculated. From these results and our upper limit for the fractional difference in the x-ray intensity, we find that Bintγ≤1.6×108 and Bintε≤0.8×108, where Bintγ and Bintε are phenomenological magnetoelastic coupling constants appropriate to oxygen displacements belonging to the Γγ representation and Γε representation, respectively. Similar measurements on cobalt ferrite have been initiated, and changes in the intensity of the x-ray diffraction line have been observed as the magnetization direction was changed. Preliminary results yield values of Bint at least ten times as large as in nickel ferrite.
New Ferromagnetic 5:2 Compounds in the Rare-Earth—Palladium Systems
Authors: Berkowitz A. E. , Holtzberg F. , Methfessel S.
Published: April 2005

Gd5Pd2 is ferromagnetic below 335°K. The isostructural Tb5.10Pd1.90, Dy5.07Pd1.93, and Ho5.04Pd1.96 have paramagnetic metamagnetic transitions at 62°, 41°, and 27°K, respectively, and become ferromagnetic at lower temperatures with extremely high hysteresis. Energy products (B×H)max = 20 to 26×106 GOe at 4.2°K have been observed.
Magnetic Properties of Eu
Authors: Arnold G. P. , Olsen C. E. , Nereson N. G.
Published: April 2005

Additional data on the magnetic properties of the rare-earth metal Eu have been obtained from neutron diffraction data utilizing an improved powder sample consisting of metal filings. Previous diffraction data on Eu, obtained from a rolled metal foil sample, indicated that the metal became antiferromagnetic at a Néel temperature of 87°K. Information regarding the magnetic moment could not be obtained from the metal foil since the diffraction peak intensities indicated the sample had a preferred orientation; also, the magnetic structure determination was uncertain.

The present data verify the transition to an antiferromagnetic state below 91°K which consists of a helical spin structure with the magnetic moments lying parallel to a cube face and with the screw axis directed perpendicular to the moments or along the [100] direction. This structure is based upon the facts that the diffraction data show a single pair of magnetic satellite reflections equally spaced in reciprocal lattice space about each nuclear reflection and, in particular, the [000±] reflection from the magnetic cell is observed. Information regarding the period of the helical structure was obtained from the separation of the satellite reflections. The separation was observed to change very little with temperature and corresponds to a period of 3.5a at T/TN = 1 and increases to 3.6a at T/TN = 0.05, where a is the lattice spacing.

The intense [000±] magnetic reflection occurring at a scattering angle of 4.8° permits a calculation of the ordered magnetic moment in Eu. If one takes the magnetic form factor equal to 1 at the above small scattering angle, the experimental saturated ordered moment is 5.9±0.4 μB. Assuming that the magnetic constituent of metallic Eu is a Eu++ ion and is, therefore, characterized by an 8S7/2 state having spin only, the theoretical ordered moment should be gJ = gS = 7 μB. The smaller value of the measured ordered moment as compared to the maximum theoretical value is also characteristic of other rare earth metals.

Data on the product of magnetic moment times magnetic form factor (μf) can be obtained from the magnetic satellite diffraction peaks occurring at various scattering angles. These values from Eu are in reasonable agreement with similar values of μf obtained from the compound EuO in earlier work.

The intensity of the magnetic diffraction peaks as a function of temperature deviates from the usual Brillouin pattern. Instead, the magnetic intensity variation with temperature is proportional to (TN−T)½ over a considerable region below the Néel temperature; this same temperature dependence was also observed in the rolled foil sample. Data taken on the intensity of the nuclear peaks at four different sample temperatures above the Néel temperature over the range from 100° to 293°K indicate an apparent Debye temperature variation from about 70° to 122°K, respectively.

We expect to publish the above results giving more details in another journal in the near future.
Magnetic Properties of Fe3MnTm and Some Related Intermetallic Compounds
Authors: Williams H. J. , Sherwood R. C. , Wernick J. H. , Nesbitt E. A.
Published: April 2005

The magnetic properties of intermetallic compounds of stoichiometry Fe3MnR, where R is Y, Tm, Er, Dy, or Ho, have been measured in fields up to 14 kOe at temperatures ranging from 1.4° to 300°K and in fields up to 80 kOe at 4.2°K. The moments of the Mn and R atoms are in opposition to those of the Fe atoms so that a compensation point is observed for Fe3MnTm. When Fe3MnTm is cooled in a weak field from 300°K through its compensation point at 60° to 4.2°K the magnetization reverses and a field of 25 kOe is required to reduce it to zero.
Changes in Magnetization of Single-Crystal Dysprosium, Erbium, and Holmium in High Magnetic Fields
Authors: Flippen R. B.
Published: April 2005

Measurements are reported on the behavior of magnetization with field of single-crystal dysprosium, erbium, and holmium in pulsed magnetic fields up to 165 kOe. These elements go progressively on decreasing temperature from a paramagnetic to antiferromagnetic to ferromagnetic state. Sufficiently high external fields applied along spin axes in single-crystal samples can cause spin realignment by overcoming the internal exchange and anisotropy fields. The strengths of the internal fields can be determined in this manner. Measurements with an external field H applied in the basal plane of Dy and of Ho, and with H parallel to the c axis in Er, confirm previous static field measurements of Hc for the AF/F transition. No change in spin alignment is seen in Dy with H parallel to c up to 165 kOe. In Ho below 80°K fields near 100 kOe produce strong changes in magnetization with H parallel to the c axis. Below 20°K fields up to 17 kOe in the basal plane in Er produce a sharp change in magnetization indicative of spin realignment. The magnetization of Er with H parallel to a is measured at 4.2°K in static fields up to 56 kOe. The magnetization increases sharply between 15 and 20 kOe, reaching 50 emu/g at 20 kOe. Little change is found above 40 kOe where M is 120 emu/g. These results are discussed with regard to the internal fields in Dy, Ho, and Er.
Metamagnetism of Some Rare-Earth Copper Compounds with CeCu2 Structure
Authors: Sherwood R. C. , Williams H. J. , Wernick J. H.
Published: April 2005

Magnetic moments of the series of rare-earth copper (RCu2) intermetallic compounds have been measured at temperatures from 1.4° to 300°K. These compounds have an orthorhombic crystal structure and are isostructural with CeCu2. The susceptibility at high temperatures of most of the compounds followed the Curie—Weiss law giving effective moments close to those of the trivalent rare-earth ions. Eu and Yb appeared to be divalent. At low fields antiferromagnetic behavior was indicated in some of these compounds by peaks in the curves of moment vs temperature, and by a lack of remanence. Metamagnetic behavior was observed when measurements were made at 4.2°K and with fields up to 80 000 Oe. For example, the moment of TbCu2 increased abruptly at a critical field, and at 80 000 Oe, although not yet saturated, had a moment of 6.2 Bohr magnetons. The moments of EuCu2 and GdCu2 increased gradually, and at 80 000 Oe reached moments of 5.7 and 6.0 Bohr magnetons, respectively. These results indicate a relatively weak antiferromagnetic exchange interaction in these compounds.
A Neutron Diffraction Investigation of the Magnetic Structure of TbMn2
Authors: Corliss Lester M. , Hastings Julius M.
Published: April 2005

TbMn2 crystallizes with the cubic Laves-phase structure (C15-type) which may be regarded as the spinel structure without the anions. The ``A'' sites are occupied by Tb ions and the ``B'' sites by Mn ions. Neutron diffraction powder patterns run at 4.2°K exhibit a number of extra reflections characteristic of a modulated magnetic structure. These additional reflections can be indexed on the basis of a spiral modulation propagated along [110] with a wavelength of 8.0 Å. The spiral axis is along [001]. The ``B'' sites are ordered in a manner which is entirely analogous to the low-temperature ordering of Fe3O4; the two sublattice spirals being 180° out of phase. The A sublattice is in phase with a particular one of the two B sublattices. The combination of the internally compensated B sites and the ferromagnetically coupled A sites leads to a ferrimagnetic spiral.
Field Dependence of Anisotropy in Ytterbium-Doped Yttrium Iron Garnet
Authors: Pearson R. F. , Tweedale K.
Published: April 2005

Torque curves were measured on two single crystals of Yb-doped yttrium iron garnet (containing 5% or 10% Yb) at temperatures from 77° to 4.2°K in applied fields ranging from 2500 to 15 000 Oe. At 20°K the maximum peak height of the (110) torque curve for these crystals was reduced by 12% as the applied field increased from 5000 to 15 000 Oe; the change in peak height was proportional to H and is approximately given by the relation ΔL=−0.32 ΔH, where ΔL is measured in ergs/cm3 and H is in oersteds. This field dependence was more pronounced at 14°K but had disappeared at 4.2° and 77°K. We consider the anisotropy energy of the system using the one ion model, and represent the energy of the Yb ground-state doublet (assumed to be well separated from other states) by a spin Hamiltonian of the form H=He·G·S+Ha·g·S,where He·G is the exchange splitting, and Ha is the applied field and g is the usual paramagnetic tensor for this doublet level with S=½, as given by K. A. Wickersheim and R. L. White [Phys. Rev. Letters 8, 483 (1962)]. The temperature variation of the free energy of the system derived from this Hamiltonian was used to compute (110) torque curves as a function of temperature, applied field and concentration of ytterbium. These theoretical curves were then compared with the experimental results, and gave good agreement for the predicted value of ΔL/ΔH at the maximum torque peaks, though as had been previously noted [J. W. Henderson and R. L. White, Phys. Rev. 123, 1627 (1961)] the absolute values of the torque are lower than those found experimentally.
Variation with Temperature of the Magnetocrystalline Anisotropy of Several Nickel Iron Ferrites
Authors: Chapman F. W. , Michel R. E. , Poplawsky R.
Published: April 2005

An investigation of the magnetocrystalline anisotropy K1 by microwave resonance measurements is reported for a series of nickel iron ferrite crystals in the temperature range of 4.2° to 300°K. Values of K1/Ms, where Ms is the saturation magnetization, calculated from previous torque measurements of K1 on similar materials agree with the present measurements of K1/Ms over a temperature range from 300°K to some lower temperature that is dependent on the composition. At this temperature, which decreases with increasing Fe2+ content, the microwave values of K1/Ms decrease sharply, while those derived from torque measurements continue to increase with decreasing temperature. The linewidth ΔH is anisotropic and temperature dependent with ΔH in the [111] direction exhibiting a maximum as a function of temperature. The value of g-effective increases as the temperature is lowered. There is qualitative, although not quantitative agreement between our data and theoretical results due to Clogston. Large magnetic annealing effects occur for each sample below a certain temperature. This temperature also depends upon the Fe2+ content.
Piezomagnetism of Biased Ferrites
Authors: Greifer Aaron P.
Published: April 2005

New developments in the synthesis and processing of magnetostrictive materials that are highly piezomagnetic in the polarized state are briefly described and interpreted in terms of the relationship for reversible stress sensitivity derived by Bozorth and Williams. In the system MnO–CoO–Fe2O3, a coupling coefficient 0.39 has been obtained for Mn0.970Co0.068Fe1.962O4 and 0.33 for Mn0.932Co0.068Fe2O4. Solid solutions of the nickel cobalt and manganese cobalt ferrites are also piezomagnetic. These materials require atmosphere control during the firing process. When similar processing is applied to the commercially established nickel cobalt ferrites, a coupling coefficient 0.42 is obtained for Ni0.974Co0.026Fe2O4 without requiring quenching from high temperatures. It is suggested that the high piezomagnetic activity of the manganese cobalt ferrites can be understood if the appropriate strain term in the expression derived by Bozorth and Williams is better identified by the easy direction magnetostriction instead of the polycrystalline magnetostriction. This interpretation leads to the prediction that magnetite with the correct cobalt ferrite addition is highly piezomagnetic.
Electrical Conductivity in the Spinel System Co1—xLixV2O4
Authors: Rogers D. B. , Goodenough J. B. , Wold A.
Published: April 2005

The electrical conductivity in the system Co1—xLixV2O4 has been investigated to obtain more information about the physical properties manifested by d electrons in the region of transition from a localized to a collective state.

Experimental data for the spinel system Co1—xLix[V2]O4 are presented that indicate R(V) ≈ Rc(V), the V ion separation R is nearly a defined critical separation Rc. All members of the system are semiconductors above 70°K, but are characterized by rather low values for resistivity and activation energy. Substitution of V4+ on the spinel B-sites effects an initial increase in both these parameters at room temperature, an apparent contradiction to the ``Meyer—Neldel rule,'' which predicts a rapid decrease of activation energy with addition of ``mixed valencies.'' Plots of resistivities as functions of reciprocal temperature indicate that most of the members are characterized by two activation energies: q1 that is dominant at higher temperatures, and q2<q1 that dominates the low-temperature conductivities.
Some Considerations on the Magnetic Carriers in Ferromagnetic Transition Metals
Authors: Izuyama Takeo , Kubo Ryogo
Published: April 2005

Some properties of itinerant electron ferromagnets are examined theoretically on the basis of a simple model in which the electron Coulomb interaction is assumed to be effective only in an atomic cell. Results of our previous study on the neutron diffraction phenomena are briefly reviewed. An itinerant electron model seems to be capable of accounting for almost all features such as diffuse scattering, critical scattering, and paramagnetic scattering. It is emphasized that the spin-wave modes play very important roles. The study is extended to the low-temperature behavior of spin waves. Unlike the spin waves in a Heisenberg model, the spin-wave frequency in metallic ferromagnets has a T2 term in its temperature dependence. This is shown by a phenomenological consideration and also by explicit calculations on a s-d model and an itinerant electron model. Finally it is pointed out that the specific heat of the simple itinerant model has a singularity of (T-Tc)−½ around the Curie point.
Band Theory of Ferromagnetism, Antiferromagnetism, and Spin Waves
Authors: Mattis Daniel C.
Published: April 2005

Intra-atomic exchange (Hund's rule mechanism) and Heisenberg nearest-neighbor exchange are examined for their role in the ferromagnetism of metals with degenerate bands. The equations of motion of spin waves valid near T=0°K are derived, and a number of branches are found. When the equations are solved in the approximation that kF«size of the Brillouin zone, the spin waves all have positive energy, and have wave vectors not exceeding 0.9kF in magnitude. When the electrons approximately half-fill the Brillouin zone, it is possible for some spin waves to have negative energy, and for an antiferromagnetic state to become stable. This is not proved, but indicated on the basis of an earlier calculation that also showed that ferromagnetism is less stable against antiferromagnetism in face-centered cubic materials than in either the simple, or body-centered cubic structures.
Theory of Electrical Resistivity of Ferromagnetic Metals
Authors: Liu S. H.
Published: April 2005

This paper gives a brief account of a new calculation of the electrical resistivity of ferromagnetic metals on the s-d or s-f exchange model. It points out that the conventional treatment of the problem taking the s-d interaction as a small perturbation to a system of free electrons and ferromagnetically coupled spins is basically inconsistent with the indirect exchange theory. The consistent formulation of the problem is then given with the help of the Kubo method of electrical conductivity. The correlation functions involved in the Kubo formula are evaluated by the equation of motion method for many body problems. The hierarchy of equations of motion is terminated at a finite order by the decoupling approximation. The resulting equations are solved and the solutions are used to calculate the conductivity. A new result that comes out of this theory is that the low-temperature electrical resistivity is proportional to the density of spin waves and has a T32 dependence on the temperature T. This result is in quantitative agreement with the experimental findings of Kondorsky et al.
Electronic Specific Heat Associated with Localized States in Actinide Metals
Authors: Scott W. R. , Jaccarino V. , Wernick J. H. , Maita J. P.
Published: April 2005

Motivated by the observations that the substitution of U for Th in the intermetallic compound ThAl2 results in the formation of localized magnetic moments at the uranium sites, we have made measurements of the low-temperature specific heat of a range of compounds, Th1−xUxAl2, in the temperature range 1.7° to 20°K. We have observed that the value of γ, the electronic contribution, increases with the addition of U; which increases we associate with the formation of localized 5f-like states on the U atoms and close to the Fermi energy. We calculate from the observed values of γ that the change in density of states per U atom ranges from 140 states eV−1 per U atom on the addition of 0.5 at.% U to 80 states eV−1 per U atom on the addition of 18 at.% U. That these states contribute to the specific heat indicates that they form close to the Fermi energy, a condition, within the framework of current theories, favorable to their being magnetized.
Variation of the Internal Fields and Isomer Shifts at the Fe Sites in the FeAl Series
Authors: Stearns M. B.
Published: April 2005

The Mössbauer technique was used to measure the internal magnetic fields and isomer shifts of Fe57 atoms residing at the various sites in the FeAl series. Alloys of Al content varying from 0 to 50 at. % were studied. In the disordered region (<21 at. % Al) five different type sites were observed, corresponding to Fe atoms having 8 through 4 nearest-neighbor (nn) Fe atoms. The internal field decreased by about 0.07 HFe for each nn Al atom. In the ordered region sites having 8 through 2 nn Fe atoms were observed. For A type sites (4 nn Fe atoms and 4 nn Al atoms at 25 at. % Al) the internal field decreased by 0.11–0.12 HFe for each nn Al atom. In the region above about 30 at. % Al the alloys are not ferromagnetic but information on the type ordering could be obtained from the isomer shifts. Over the whole series the isomer shift indicated that there is progressively less electronic charge at the nucleus as the number of nn Al atoms increased.
Effect of Mode Degeneracy on Output of Gaseous Optical Masers
Authors: Harding G. O. , Li Tingye
Published: April 2005

The output power of a multimoding gaseous optical maser is maximum when the modal resonances are so densely packed in frequency that the Doppler-broadened atomic resonance line is fully saturated. However, certain critical geometrical configurations cause the modes to coincide at some frequencies and leave other bands of frequencies unoccupied. Such a degenerate condition leads to mode competition and reduced power output. We have observed this phenomenon using a 6328-Å He-Ne optical maser and have found good agreement with theory.
Clean Up of Inert Gases in a Penning Discharge Studied by a Tracer Technique
Authors: Kawasaki Koji , Sugita Toshio , Kohno Isao , Watanabe Jiro , Hayashi Nobuyuki
Published: April 2005

In order to obtain further information of the pumping action of a diode getter ion pump for inert gases, the clean up of inert gases, principally the ion sputtering patterns on the cathode and the location of ion on each electrode, has been observed for pumps with various cells by the use of radioactive tracer Xe131m. The radioactivity of each electrode was counted by a G-M counter. Inert gases are cleaned up principally at the cathode; about 20% as much is cleaned up at the anode.
Induced Electric Fields in Coaxial Geometry
Authors: Hart Philip J.
Published: April 2005

Although electromagnetic theory has been known for a century, and Biot's (also called Ampere's) formula in its simple form, dH = (1/4π)(Idl sinθ/r2), is often used, the corresponding relationship, dE = −(1/4π) (φdl sinθ/r2), for the electric field induced in space by a filament of time-varying magnetic flux, seems not to have been recognized or used to any great extent. The discussion here presented, using the example afforded by coaxial conductors, illustrates some aspects of how this latter relationship may be used to solve for induced electric fields, including those for coaxial systems of both finite and infinite length with hollow or solid center conductors. The magnetically induced electric field fringes outward near the shorted end of a coaxial system, and a method is shown for finding the radial positions of a given line of electric force when coaxial conductors of different dimensions are connected together.
Image Properties of a Superconducting Ground Plane
Authors: Sass A. R.
Published: April 2005

The Green's-function technique is utilized in the determination of the field distribution of an infinitely long current carrying conductor of arbitrary but constant cross section above a superconducting ground plane of finite thickness. It is assumed that the superconductor can be described by the phenomenological London equations. The integral expressions that are obtained are solved analytically for a few special cases of interest. Under conditions that are often encountered in a physical system, a modified image method can be utilized in order to calculate the field distribution to within 2% of the computer solution.
An Example of Hole Diameter in Thin Plates Due to Hypervelocity Impact
Authors: Rolsten R. F. , Wellnitz J. N. , Hunt H. H.
Published: April 2005

An equation was derived to calculate or predict the diameter of a hole which forms in a thin plate as a result of the normal impact from a high-velocity steel particle. The calculated diameter for aluminum and stainless steel plates in the thickness range 0.010 to 0.063-in. (0.25 to 1.6 mm) was observed to be larger than the experimental value since material properties were neglected in the derivation of the mathematical expression. Excellent agreement between the calculated and experimental values was obtained when a 10% relaxation effect was applied to the calculated hole diameter. Concordance was observed over the impact velocity range of approximately 9000 to 16 100 ft/sec (2743 to 4907 m/sec).

The holes observed in aluminum plates 0.090 to 0.187 in. (2.3 to 4.7 mm) in thickness were larger than those observed in plates 0.063 in. (1.6 mm) and thinner. Moreover, the mathematical expression was not applicable to these thicker plates. This nonconformity was attributed to a difference in impact mechanism.
Third-Order Elastic Moduli of Anisotropic Solids
Authors: Einspruch Norman G. , Manning Robert J.
Published: April 2005

Finite elasticity theory is applied to the evaluation of the third-order elastic constants of crystalline solids. Results are presented for cubic, hexagonal, tetragonal, and orthorhombic symmetry.
Structure of Oriented, Vapor-Deposited GaAs Films, Studied by Electron Diffraction
Authors: Müller Egon K.
Published: April 2005

Gallium arsenide films deposited on germanium surfaces of the types (111), (110), and (100) by flash evaporation in vacuum were investigated by electron diffraction. The substrate temperatures ranged from 300° to 670°C, the films varied from 0.4 to 4 μ in thickness, the deposit rates from 2 to 30 Å/sec. The evaporator was kept at 1450°C. For deposition temperatures above 300°C the films showed extensive orientation effects on the single crystal germanium. On the (111) and (100) surfaces, epitaxy free of twinning was obtained for substrate temperatures above 600°C. For lower temperatures the electron diffraction patterns reveal stacking faults along the (111) planes of the deposits, leading to twin spots and interference lines, and even to a change from the cubic zinc blende to the hexagonal wurtzite structure.
Effect of Crystal Orientation on Ge-GaAs Heterojunctions
Authors: Fang F. F. , Howard W. E.
Published: April 2005

The electrical characteristics of Ge-GaAs heterojunctions, in particular n-n junctions, have been studied experimentally. Barrier voltages, determined from the temperature dependence of reverse current and from capacitance vs voltage, depend upon the crystal orientation of the interface. This is seen to imply a corresponding variation of the conduction band discontinuities; namely ΔEc[111]Ga > ΔEc[111]As >ΔEc[110]. The voltage dependence of the reverse current is interpreted in terms of the shift of the Fermi level with respect to the conduction band edge in the accumulation layer. The transient behavior of n-n heterojunctions yields a switching time for 20 mA less than 10−9 sec, and no observed storage time.
Nonhomogeneous Straining and Fracture Mechanism in a Filled Elastomer
Authors: Ronay Maria
Published: April 2005

This paper presents an experimental study of the strain concentrations arising near the edges of elliptical cutouts in uniformly strained, flat strips of polyurethane rubber filled with a high volume percentage of an inorganic salt. The strain concentrations are studied under various conditions of uniform straining, for strains up to fracture initiation.

The fracture mechanism at the root of the cutout is studied micrographically and it is found that the local fracture process is similar to that in unfilled elastomers, with consecutive rupture of highly deformed strands of the elastomeric material.
Neutron Diffraction Effects with Moving Lattices
Authors: Shull C. G. , Gingrich N. S.
Published: April 2005

Observations are reported on the effect of specimen motion upon the neutron diffraction pattern of iron. Specimen speeds of 120 m/sec combined with a neutron speed of 3310 m/sec are found to produce easily measured angular shifts, integrated intensity changes, neutron wavelength alteration, and peak width changes all of which are dependent upon the direction of motion relative to the scattering vector. The effects can be conveniently interpreted with the reciprocal lattice construction and the calculated changes with motion agree satisfactorily with the observations.
Čzochralski Growth of Doped Single-Crystal Lanthanum Trifluoride (LaF3) for Lasers
Authors: Hiller M. A. , Stafsudd O. M.
Published: April 2005

A method of growing large, optically clear lanthanum trifluoride crystals has been developed. The method is quite simple and fast in that setup time per run is considerably shorter than that required by other growth methods.
Threshold Displacement Energies and Subthreshold Displacements in Copper and Gold Near 10°K
Authors: Bauer W. , Sosin A.
Published: April 2005

These experiments were undertaken to determine more precisely the minimum energy Td needed to displace an atom from its lattice position. The resistivity increase as a function of integrated flux was measured at various electron energies. The damage-production curve, thus obtained, was the sum of two components. The first contribution is due to direct displacement processes. From a projection of this component to zero, we estimate TdCu=16–19 eV and TdAu=33–36 eV. The second contribution, the subthreshold events, are due to various ``soft spots'' associated with unavoidable impurities in the nominally 99.999% pure copper and gold specimens. It has been shown that displacements near dislocations do not contribute in a significant manner. It has been further shown that the formation of light-atom interstitials can contribute to subthreshold processes. While this does not conclusively prove that subthreshold processes in nominally pure copper and gold are due to the presence of light-atom impurities, we believe this to be the most probable subthreshold mechanism.
Electrical Resistivity Measurements in Detonating Composition B and Pentolite
Authors: Jameson R. L. , Lukasik S. J. , Pernick B. J.
Published: April 2005

Measurements of electrical resistivity in the detonation zone of Pentolite and Composition B have been made. The first probe configuration consisted of rails of copper on opposite sides of the charge and parallel to the direction of propagation of the detonation. The second consisted of two parallel copper wires mounted in a ceramic insulator with the wire ends either placed against an explosive face or cast into the explosive. The third consisted of two copper plates oriented to resemble the letter T, one plate having its flat side against an explosive face, the other plate having its thin edge placed against an opposite face. The current under an applied external voltage was recorded; by means of suitable calibrations, the electrical resistivity was calculated. Resistivity in Pentolite and Composition B was the order of 1 Ω-cm from all probes. The zone of highest conductivity in 2.5-cm-diam Pentolite and Composition B charges was about 1 cm long on the axis of the charge, narrowing to less than 0.2 mm at the surface. The conduction front in Baratol was located within the von Neumann spike.
Effect of Lattice Defects on the Magnetization Curve of Ferromagnets
Authors: Seeger A. , Kronmüller H. , Rieger H. , Träuble H.
Published: April 2005

This paper presents a theoretical treatment of the action of internal stresses on domain walls and on uniformly magnetized Weiss domains. The theory is based on micromagnetics, dislocation theory, and probability theory. Experimental results on the domain structure, the temperature dependence of the reversible susceptibility, and the coercive field of plastically deformed nickel, cobalt, and silicon-iron single crystals and neutron-irradiated nickel single crystals are discussed on the basis of the theory. The experiments are interpreted in terms of the magneto-elastic interaction between dislocations and magnetization and agree satisfactorily with the theoretical predictions. The observed variations of the domain structure during the magnetization process can be accounted for in terms of the theory of phases (Néel, Lawton, and Stewart) and the mobility of the domain walls.
Optimization of Magnetic Parameters in Thin Films DRO Storage Elements
Authors: Petschauer R. J. , Rausch W. V. , Morawetz P. L.
Published: April 2005

The digit current margins of a DRO magnetic film memory are determined by the disturb and writing or restoring thresholds. In an actual memory these thresholds will vary with both the film parameters and the drive line configuration. The effect of the magnetic parameters of the storage elements on these thresholds is determined by measuring the digit current margins of storage element arrays of varied magnetic parameters in a test apparatus simulating the memory operations and drive line configuration. A figure of merit calculated from these margin measurements is introduced and is used to determine the optimum film parameter values. To illustrate the effectiveness of the technique, data obtained during the experimental determination of optimum array coercivity are presented and the resultant figure of merit is discussed. Results indicate that array coercivities of 2.5 to 2.6 Oe yield maximum digit current margins. Interpretation of results of restore current measurements in terms of skew and dispersion currents is also presented.
Control of Properties of Magnetic Thin Films for Shifting Registers
Authors: Tickle A. C.
Published: April 2005

The operation of a domain wall motion shifting register depends on the fact that the critical threshold field Hs, required to introduce a reverse domain into a saturated, uniaxial, anisotropic, magnetic thin film is greater than the critical threshold field H0, required to move walls of already exiting domains. Thus, an important parameter characterizing the performance of the register is the nucleation factor η defined as η=Hs/H0. This must be large to obtain wide tolerance in the shifting field, H, as H0≤H≤Hs. It must also be large in order to obtain high speed, as wall velocity varies as H − H0. Normally it is difficult to produce films with η>2, but here it is shown how the difficulty can be overcome by the use of thick films (>2000 Å) of high anisotropy (anisotropy field Hk>15 Oe. Experimental results are given for Ni-Fe-Co alloys showing that Hs and Hk both increase with the cobalt concentration, whereas H0 decreases with increasing film thickness. Hence the two fields Hs and H0 can be controlled independently, and in this way values of η of up to 12 have been obtained. The ratio of nickel to iron is adjusted for zero magnetostriction.

Measurements were made by observation by the Kerr effect of domains in an actual shifting register. There is a tendency for domains to nucleate at the edges of the film when shifting fields are applied, the nuclei growing to represent spurious information. It is shown how this is prevented by gradually reducing the thickness of the film at the edges. When domains are propagated along the film another difficulty is observed, that occasional remanent nuclei from the trailing edge walls remain unshifted, and grow during subsequent shifting cycles, to represent spurious information. It is shown that this can be prevented by applying a biassing field of about 1 Oe which tends to erase the remanent nuclei. Also, when the shifting fields are readjusted to operate with the bias field the effect is further enhanced. However, this field reinforces the demagnetizing field of the domains and so causes them to break up into narrow bars in order to reduce their total field energy. This break up reduces the magnetic flux which can be detected by the output sense conductor. When either a thicker film is used to increase the output signal, or the register is reduced in size to increase the operating speed, the effect of the demagnetizing field is accentuated and the domains become very narrow in the hard direction. This effect can be reduced by using a film with a higher value of H0.

Shift registers with a packing density of 40 bits/in., cycle time of 1 μsec, shifting fields of about 14 Oe, and biasing fields of about 1 Oe have been produced.
Radiation from a Ferrite Cylinder
Authors: Palais J. C.
Published: April 2005

A theoretical and experimental investigation has been made of a ferrite post in the aperture of a rectangular waveguide. This problem is representative of a general class of problems where an anisotropic obstacle is superimposed on an isotropic discontinuity. In the example treated by the diffraction approach, a simple solution has been obtained which predicts and explains the observed phenomena. A modified aperture is especially interesting because it offers good opportunity for directly measuring the effects of ferrite obstacles on rf fields. It also has the practical advantage of serving as a scanning antenna. The analysis of this radiating structure is also shown to apply to circulators that use cylindrical ferrites.

In general, the theory shows that the energy in the far fields is directed at some angle φ with respect to pure forward scatter. A corresponding asymmetry is also present in the field plots inside the ferrite. The field displacement within the material is shown to explain this far field beam shift.

Experimentally, continuous scanning from a waveguide was obtained over ±30° with a MgMn ferrite post 0.297 in. (0.754 cm) in diameter and with applied fields of less than 300 G. The frequencies were from 9.0–10.3 Gc/sec. The low reflection coefficients obtained make this a practical antenna. Beam patterns are presented, as are curves comparing the theoretical and experimental results.
A Review of the Problem of Fine-Particle Interactions with Special Reference to Magnetic Recording
Authors: Wohlfarth E. P.
Published: April 2005

The problem of interactions between the fine iron oxide particles used in the coatings of magnetic recording tapes is reviewed. Particular attention is paid to the factors influencing the initial susceptibility of the anhysteretic remanence curve which is related to the sensitivity of the tape under high-frequency biasing conditions. As a satisfactory discussion of particle interactions and the anhysteretic process is not possible, it is necessary to rely on a number of theoretical models which are considered critically. For pairs of particles interacting positively or negatively a complete discussion is, however, possible, and this introduces the concept of anhysteresis as a growth process. This concept is then extended as far as possible to assemblies, where it is seen to be necessary to modify the usual Preisach model in a number of essential ways. The characteristic properties of several different recording tapes, namely the reduced saturation remanance and the initial anhysteretic susceptibility, are tabulated and discussed. Results for some other hard magnetic materials are also considered.
Spin-Wave Resonance in Magnetic Films on the Basis of the Surface-Spin-Pinning Model and the Volume Inhomogeneity Model
Authors: Kooi C. F. , Wigen P. E. , Shanabarger M. R. , Kerrigan J. V.
Published: April 2005

Two models of spin-wave resonance in magnetic films are briefly reviewed. These are the surface-spin-pinning model and the volume inhomogeneity model. The intensities and frequencies of the resonance lines, the spin-wave-phonon interaction, the critical angle, and several other experiments are then discussed in relation to these two models. It is concluded that the evidence tends to favor the volume inhomogeneity model with surface spin pinning being very weak or absent. A consequence of this conclusion is that it is very difficult to determine exchange parameters by means of spin-wave resonance in films.
Low-Temperature Properties of a Heisenberg Antiferromagnet
Authors: Harris A. Brooks
Published: April 2005

It is shown how the propagator formalism can be used to obtain the low-temperature expansion of the free energy of an isotropic Heisenberg antiferromagnet. The lowest-order terms in such an expansion can be calculated using the proper self-energy evaluated at zero temperature. The analytic properties of this quantity are investigated by expressing it in terms of time ordered diagrams. The low-temperature expansion of the free energy is shown to be of the form AT4+BT4+CT8, where A, B, and C are given by Oguchi correctly to order 1/S. For spin ½ the term in 1/S2 gives a 2% reduction in A for a body-centered lattice.
Spin-Wave Excitation in Cubic Rare-Earth Compounds
Authors: Tsuya Noboru , Ebina Yoshio
Published: April 2005

Some of the cubic rare-earth compounds are ferromagnetic at low temperatures. However the observed magnetic moment is much smaller than it is for the free ion, because of the effect of the strong crystalline field on the trivalent rare-earth ions.

Solving the one-ion Hamiltonian numerically, we construct approximate ferromagnetic spin wave states of an unusual nature, in that they involve ionic states of orbital as well as spin angular momentum in both a crystalline and an exchange field. From the excitation spectrum of these states, we calculate the temperature dependencies of the specific heat, strong-field susceptibility, and g factor of a ferromagnetic array of trivalent rare-earth ions, and attempt to predict the behavior of HoN and TbN.
Experimental Studies of Standing Spin-Wave Modes in Ferromagnetic Films
Authors: Nisenoff M. , Terhune R. W.
Published: April 2005

Standing spin-wave mode measurements have been made on thin films of Permalloy, cobalt, and iron using microwave frequencies between 9.8 and 32 Gc/sec. Clear experimental evidence has been obtained for the existence of the theoretically predicted k2 dependence of the magnetic field spacings with the magnetic field both parallel and normal to the plane of the film. In most of these films, deviations from the k2 law were observed for low-order spin waves with the applied field normal to the plane of the film. In this region, the dependence ranged from near quadratic to linear and a distinctly different intensity variation for the lines was observed. With the applied field in the plane of the film, for thicknesses d less than 1200 Å, the intensity behavior of the higher-order modes increased very rapidly with microwave frequency. The pinning conditions for the standing spin waves deduced from these observations can be qualitatively explained by assuming that the rf magnetization at an air interface is completely unpinned and that the film has surface layers of lower magnetization than the bulk.
Deposition Temperature and Compositional Dependence of Negative Anisotropy in Nickel-Iron Films
Authors: Weiss G. P. , Smith D. O.
Published: April 2005

An investigation of the deposition temperature (200° to 350°C) and compositional (80% to 87% Ni) dependence of negative anisotropy (K−) in nickel-iron films has been made. The results indicate that the number of K− regions is zero below a critical temperature which depends on composition and increases with increasing temperature; the more negative the magnetostriction λ (λ<0 for % Ni>83), the lower the critical temperature. The following qualitative hypothesis is suggested for the origin of K− regions: It is known that deposited metal films have a real surface area much larger than the macroscopic area of the deposit. Thus the films are actually porous and mass diffusion between adjacent crystallites occurs in order to lower surface energy at the expense of strain energy. If the mass diffusion were anisotropic, for example, by depending on the direction of M, then anisotropic strain would be generated. The resulting anisotropic strain coupled to ± magnetostriction would then generate local K± (or K∓ since the sign of the strain has not been specified) regions.