bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of the Interaction of Vacancies with Stress Fields in Metals. I. Derivation of Basic Equations
Authors: Girifalco L. A. , Kuhlmann-Wilsdorf D. 
Published: April 2005

A theory for the effect of stresses on vacancy concentration in simple metals is presented in which the variation of mechanical energy, electronic energy, and vibration frequencies with stress is taken into account. The vacancy is treated as a point of dilatation and a local soft spot in the crystal with the result that the mechanical energy consists of a term representing the work done by the volume of relaxation against the internal pressure, plus an additional term which is quadratic in the stresses. The electronic energy term is computed from the quasifree electron model based on phase-shift analysis, giving a term proportional to the dilatation. The variation of atomic frequencies with strain is treated by a generalized Gruneisen model which shows that the entropy of vacancy formation is proportional to the dilatation.
The internal work and electronic terms in the energy of interaction of a vacancy with a stress field decreases the vacancy concentration in dilated regions and increases it in compressed regions relative to the concentration in unstrained metal. The quadratic part of the mechanical energy, which comes from the softening of the crystal by the vacancy, always acts to increase the vacancy concentration in regions of high stress, regardless of the sign of the stress field. The entropic contribution, arising from the vibration frequencies, opposes the internal work and electronic terms, decreasing the vacancy concentration in compressed regions and increasing it in dilated regions. The final result is that the interaction energy of a vacancy with a stress field is a function whose magnitude decreases linearly with temperature.
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.
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.
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&lt;q1 that dominates the low-temperature conductivities.
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.
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.
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&gt;2, but here it is shown how the difficulty can be overcome by the use of thick films (&gt;2000 Å) of high anisotropy (anisotropy field Hk&gt;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.
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.
Sendust Sheet-Processing Techniques and Magnetic Properties
Authors: Helms H. H. , Adams Edmond 
Published: April 2005

A procedure has been developed whereby the brittle magnetic alloy of silicon, aluminum, and iron (Sendust) can be produced in sheet from through metal powder rolling techniques. Ring laminations stamped from this sheet at 0.014 in. thickness have the following dc properties: μ20=16 130; μmax=36 625; Hc=0.062 Oe; Br=3450 G; Bm=8960 G. High frequency (&lt;1 Mc/sec) loss values were lower than in laminated molybdenum Permalloy cores of the same thickness. The nominal Sendust composition is 9.5% silicon, 5.7% aluminum, and balance iron.
This new process should make possible more extensive use of Sendust in applications that can take advantage of its remarkable intrinsic characteristics such as high initial permeability, high resistivity, low magnetostriction, and low magnetocrystalline anisotropy.
Self-Consistent Correlation Method (S.C.C.M.) Applied to Ideal Ising and Heisenberg Magnetic Systems
Authors: Clapp P. C. 
Published: April 2005

The theory to be described here may be classified as a cluster theory of ferromagnetism. It is presently restricted to lattices with nearest-neighbor interactions, but is unrestricted in spin magnitude. Its point of departure from previous cluster theories is that it represents the effect of the other spins of the lattice on the cluster as a temperature-dependent exchange coupling, rather than as a molecular field. A second significant departure is to impose a consistency condition on the spin-spin correlation functions of the cluster rather than on the spin averages as in previous theories. This new cluster theory can be motivated from quite fundamental considerations, and achieves a significant improvement over previous cluster theories, especially in the region just above the Curie temperature.
Given a particular lattice, the cluster chosen for application of the theory consists of a central spin pair plus the additional spins and bonds necessary to form all the next most direct linked paths between the central spin pair. In the cluster Hamiltonian the central coupling has the constant value J while all the other couplings are taken to have a temperature-dependent value J′ (T) which will be evaluated self-consistently. J′ (T) can be understood physically as the direct coupling J plus an additional coupling caused by the correlative effect of spins outside the cluster acting on the cluster spins. The S.C.C.M. Hamiltonian can be derived more rigourously by writing the density matrix for the entire spin system and formally summing over all spin variables except those of the cluster. From this reduced density matrix it is possible to infer the form of the corresponding Hamiltonian. Apart from small terms which vanish at high temperatures, this is the S.C.C.M. Hamiltonian.
The method of determining J (T) for any particular case brings out the second feature of the theory. By demanding that the correlation between the central pair be equal to that of any other nearest neighbor pair, J (T) can be uniquely determined for any temperature. Since the average energy, the free energy, and the specific heat of the lattice are related to the nearest-neighbor correlation function, these properties are immediately obtainable from the cluster calculation. If the correlation function is calculated with an external magnetic field added, then the dc magnetic susceptibility and average magnetization can also be determined.
A complete presentation of the theory and results for the Heisenberg and Ising square and simple cubic lattices of spin one-half are contained in a paper by this author to be published elsewhere.
Magnetic Structure Investigations at the Nuclear Center
Authors: Bertaut E. F. , Roult G. , Delapalme A. , Bassi G. , Mercier M. , Murasik A. , Van Qui Vu , Aleonard A. , Pauthenet R. , Chevreton M. , Jansen R. 
Published: April 2005

The following structures are briefly described MnYO3, β-FeNaO2, GeNi2O4, and Cr3X4 (X=S, Se, Te) MnYO3. In this remarkable hexagonal layer structure there are fivefold coordinated Mn atoms. Their spins order below 46°K forming angles of 120° in the layer. Two different models may be inferred from powder data. The ambiguity is lifted by the fact that a weak ferromagnetism is observed. The ferromagnetic and the ``120° model'' must belong to the same representation which is here the identity representation.
β-FeNaO2. Each iron spin has 4 antiparallel neighbors. The antiferromagnetic axis is 0z. From group theory it is concluded that the weak ferromagnetism must be along 0y.
GeNi 2 O 4. Ni is on octahedral sites (B sites). Spin-ordering sets in below 15°K with doubling of the unit cell. The propagation vector of the antiferromagnetic arrangement is k0=[½½½]. The spin-value is S=1.1. The true symmetry is rhombohedral.
Cr 3 X 4. Cr3S4 has a huge magnetic unit cell. The structure is antiferromagnetic. In Cr3Se4 the same large magnetic cell is observed, but at low temperatures a second antiferromagnetic mode is superimposed. In Cr3Te4 a ferromagnetic structure is observed at room temperature, but below 80°K an antiferromagnetic configuration is superimposed which explains that the magnetization at saturation is inferior to the sum of the moments of the individual atoms.
Critical Alternating Currents in Superconductors
Authors: Young F. J. , Schenk H. L. 
Published: April 2005

Critical alternating currents are studied experimentally in 0.96-cm (⅜-in.) lengths and coils of superconducting wire. Critical current density vs frequency are measured for three short Nb-25% Zr wires having the same amount of cold work. For the 5-, 10-, and 20-mil (125-, 250-, and 500-μ) specimens, the critical ac density varies from 290 to 170 kA/cm2, 200 to 110 kA/cm2, and 107 to 54 kA/cm2, respectively, as the frequency is varied from 0.02 to 4.5 kc/sec. A short length of Nb–Ti wire 9 mils in diameter has a critical ac density that varies from 260 to 130 kA/cm2 as the frequency ranges from 0.01 to 4.5 kc/sec. In a 15-mil Nb3Sn specimen, the critical ac density is constant at 90 kA/cm2 from 0.01 to 4 kc/sec.
In a tightly wound Nb-25% Zr coil, the critical ac density is found to vary inversely with the one-fourth power of frequency. In a very loosely wound coil of the same material, the critical ac density varies inversely with the cube root of frequency. In all cases investigated, except for pure niobium, the exponent on the frequency varies from −0.25 to −0.36. In a Nb coil, no variation of critical ac density is observed below 200 cps. Above 200 cps, it behaves in the same way as the other coils tested. The data indicate that the critical ac density occurs such that the coil or short wire always becomes normal at the same level of power dissipation.