bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shock-Wave Compression of Barium Titanate and 95/5 Lead Zirconate Titanate
Authors: Doran Donald G. 
Published: February 2004

The shock compression of the ceramics BaTiO3(5%CaTiO3) and Pb(Zr0.95Ti0.05)O3(1 wt%Nb2O5) was measured in the ranges 5–200 kbar and 2–140 kbar, respectively. Barium titanate exhibits a two-wave structure above 30 kbar; the first wave has a velocity of 6.27 mm/μsec. The cusp in the Hugoniot at 30 kbar is interpreted as a dynamic elastic limit. Comparison of the first wave velocity with the measured longitudinal sound speeds of the tetragonal (ferroelectric) and cubic (paraelectric) phases (5.4 and ∼6.2 mm/μsec, respectively) suggests, as does other evidence, that the material begins to transform to the cubic phase in the neighborhood of 7 kbar. Below 7 kbar, subsonic velocities are observed and it is speculated that this phenomenon is associated with domain reorientation.
The particular lead zirconate composition studied has a two-wave structure above about 40 kbar; the position of the cusp in the Hugoniot depends sensitively on initial density. This cusp is presumably the Hugoniot elastic limit. A weak cusp is also observed at about 2 kbar. The wave velocity is essentially sonic below 2 kbar and subsonic above 2 kbar, increasing to about sonic in the neighborhood of 40 kbar.
Preparation of a Stabilized Nb3Sn-Based Superconducting Tape by a Diffusion Process
Authors: Gavaler J. R. , Patterson A. , Autler S. H. 
Published: February 2004

A diffusion process has been developed for the preparation of Nb3Sn ribbon which can subsequently be stabilized to any desired level. The preparation process is described in detail with emphasis on the effect of reaction time, reaction temperature, and contamination on the critical current of the Nb3Sn. Under optimum conditions, short samples of the ribbon showed a current density of approx 105 A/cm2 in a field of 100 000 G.
The superconducting ribbon, after the diffusion reaction, is partially stabilized by a thin layer of tin which remains on the surface. To further stabilize the ribbon to any desired level, another metal can be bonded to the Nb3Sn through this layer of tin.
A small copper-stabilized test magnet was constructed to determine the degree of degradation occurring when the ribbon is wound into magnet. This magnet was found to have approximately the same current-carrying capacity as short samples of the ribbon.
Proton Magnetic Resonance in Partially Deuterated Antiferromagnetic CuCl2·2H2O
Authors: Benoit H. , Drocourt J-M. , Legrand J-P. , Renard J-P. 
Published: February 2004

We have studied the magnetic resonance of protons in antiferromagnetic CuCl2·2H2O when hydrogen is replaced by deuterium in a proportion c.
We show that the deuteration involves a diminution of the magnetization in the ground state and a diminution of the Néel temperature, both proportional to the deuterium concentration c.
We explain these effects by a diminution of the ferromagnetic exchange integral between next-nearest neighbors due to the difference between zero-point energies of hydrogen and deuterium.
Conduction-Electron Polarization in Rare Earth-Platinum Alloys
Authors: Vijayaraghavan R. , Rao V. Udaya Shankar , Malik S. K. , Marathe V. R. 
Published: February 2004

Nuclear magnetic resonance studies of 195Pt in the rare-earth-platinum intermetallic compounds of the composition RPt2 and RPt5 (R≡La, Ce, Pr, and Nd) have been made in the temperature range 80° to 300°K. They have the cubic (MgCu2 type) and the hexagonal (CaCu5 type) Laves structures, respectively. In RPt5 componuds, there are two inequivalent platinum sites and correspondingly, two 195Pt resonances are observed in each compound. The platinum Knight shifts which are positive, are strongly temperature dependent in all but the lanthanum compounds. The magnetic susceptibilities have been measured in the same temperature range. The Knight shift (K) versus susceptibility curves are straight lines, intersecting the K axis at K0, corresponding to the lanthanum compounds.
The EPR of Gd3+ in GdPt2 has been observed and a g value of 1.8735 has been obtained. The paramagnetic Curie temperatures are positive for RPt2 compounds and negative for the others. The results have been discussed in terms of the RKKY theory and the Anderson-Clogston mixing. Values of J(0) have been obtained for the two sets of intermetallic compounds.
Magnetic Behavior of Cobalt and of Nickel in Compounds with Rare Earth Metals
Authors: Lemaire R. , Paccard D. , Pauthenet R. , Schweizer J. 
Published: February 2004

We discuss the value of the intrinsic magnetic moment of cobalt in intermetallic compounds of the formula RxCov, where R is a rare earth element or yttrium. The experimental values of this moment are determined from the results of neutron-diffraction studies and those of measurements of the absolute saturation magnetization on certain compounds: R2Co17, RCo5, R2Co7, RCo3, and RCo2. The electronic configuration of cobalt is greatly modified, both by the addition of the conduction electrons of the rare earth atoms or yttrium and by the magnetic interactions resulting from these atoms. This behavior of cobalt permits the explanation of certain apparent anomalies in the properties of the alloys, viz., the differences between the Curie temperatures of the compounds of the same series are too large to be attributable to the interactions between the rare earths along; the magnetizations and Curie temperatures of the alloys with cerium are smaller than those of the corresponding compounds with yttrium; and certain compounds RCo2 present a ferrimagnetic-paramagnetic first-order transition.
The variation of the Curie temperatures of the compounds RxNiv, as a function of rare earth percentage, can be explained by the behavior of the moment of nickel analogous to that of cobalt.
Magnetic Properties of the Intermetallic Compounds DyxY1−xFe2
Authors: Piercy A. R. , Taylor K. N. R. 
Published: February 2004

Measurements of the bulk magnetization have been made between 4.2°K and the Curie points for eleven compounds in the series DyxY1−xFe2. The Curie temperatures increase continuously through the series. The compounds near to x=0.3–0.4 exhibit temperature compensation points, and the saturation moments show that the equilibrium concentration occurs at x≃0.28. In addition, the coercivity increases rapidly in this region and has a value in excess of 10 kOe at x=0.35, T=4.2°K.
If both the Fe and Dy moments remain constant or vary linearly through the series, the equilibrium concentration would occur at x≃0.35. Consideration of the results of these and other similar compounds indicates that the Fe moment varies nonlinearly with x. It is suggested that the Fe moment is approximately 1.4 μB for x&lt;⅓ and increases gradually for larger x to about 2 μB. It is further proposed that this behavior may be explained by the presence of a shallow minimum in the density-of-states curve, sufficient to stabilize the moment for x&lt;⅓, but such that the increased coupling allows the moment to increase for higher Dy concentrations.
The Fe moments in other RE Fe2 compounds are correlated with this model, taking the Curie temperatures as a measure of the exchange energies.
Magnetic Study of the Manganous Sulfates MnSO4 and MnSO4·H2O
Authors: Allain Y. , Krebs J. P. , de Gunzbourg J. 
Published: February 2004

The magnetization measurements up to 420 kOe made on antiferromagnetic powder specimens of MnSO4 and MnSO4·H2O between 1.6° and 70°K have revealed saturation fields of 250 and 320 kOe, respectively. The saturation value of the magnetization is in good agreement with the theoretical value for Mn2+(5 μB). The moment before saturation does not vary linearly with the applied field. This fact could be explained by spin-wave theory or by a biquadratic term in the exchange energy. The anisotropy and the exchange fields have also been estimated from our experiments. The susceptibility versus T plot has given the Néel temperature TN and the effective moment which corresponds to the S state of Mn2+.
Specific heat measurements have also been accomplished on MnSO4. They confirm our value for TN (11.5°K) and show three other peaks below the Néel temperature, two of which could correspond to the transitions theoretically forseen for this magnetic structure (cycloidal cone spiral) by Solyom.
OH Groups and Fe Valence in Hydrothermal and Flux-Grown YIG
Authors: Wood D. L. , Kolb E. D. , Remeika J. P. 
Published: February 2004

In the transparent region of Yttrium Iron Garnet (YIG) in the infrared, it has been shown that Fe2+ and Fe4+ both give broad optical absorption accompanied by electrical conductivity. The conductivity is n-type for Fe2+ ions and p-type for Fe4+ ions, both involving a hopping mechanism. Heat treatment of YIG in a reducing atmosphere produces Fe2+ at rather low temperatures, and in hydrogen gas the equilibrium is controlled by temperature rather than the diffusion rate. At the same time the Fe2+ is formed, OH groups appear in the structure, and their optical absorption near 3 μ affords another way of monitoring the reversible changes in iron valence for this treatment.
Hydrothermal YIG is formed with OH groups already present, but with all Fe ions trivalent. The amount of OH present in crystals grown from KOH is much less than for crystals grown from NaOH, and the primary mechanism for admitting the proton into the structure involves substitution of an alkali or a vacancy for the Fe3+ ion. Removal of the OH by heat treatment in oxygen produces Fe4+ ion, and p-type conductivity. Fourteen distinct lines in the 3 μ region are seen in the infrared spectra of crystals containing protons introduced in various ways, including a small amount even in flux-grown crystals. These lines arise from OH groups in different environments in the lattice.
Quantitative Study of the Magnetization Ripple in Ferromagnetic Ni–Fe Alloy Films
Authors: Suzuki T. , Wilts C. H. 
Published: February 2004

Magnetization ripple in Ni–Fe thin films has been investigated by several workers, but no systematic study of the ripple structure over a significant range of alloy composition, substrate deposition temperature, and measurement temperature has been published. The present report describes the results of such a study. Room-temperature measurements of the ripple amplitude θ0 and wavelength λ have been measured as a function of alloy composition from 50% Ni to 90% Ni for films deposited at room temperature. In addition, θ0 and λ have been measured from 25° to 450°C for 76% Ni films evaporated at temperatures from −180° to 400°C. For all data, θ0 and λ are in order of magnitude agreement with Hoffmann's calculations (10−2 rad and 1 μ, respectively). As a function of alloy composition, the ripple amplitude exhibits a minimum in the vicinity of 73% Ni. The wavelength is independent of alloy composition. For 76% Ni films deposited at −180°C, the ripple wavelength is independent of measuring temperature. The amplitude θ0 decreases to zero at about 330°C and does not reappear at higher temperatures, contrary to the reappearance reported by others. For higher deposition temperatures, the scatter in the data is much higher than for −180°C and ripple could be observed as high as 450°C.
The ripple amplitude increases with substrate deposition temperature, as expected from the increase in grain size. Two points concerning the present data should be emphasized. (1) The results are in reasonable agreement with Hoffmann's theory. (2) The data constitute a systematic description of magnetization ripple in Ni–Fe films.
Mössbauer Measurements in ZnY (Ba2Zn2Fe12O22) and Mn0.625–ZnY Ferrites
Authors: Albanese G. , Asti G. , Lamborizio C. 
Published: February 2004

By means of the Mössbauer technique, the hyperfine magnetic fields and the electric quadrupole interactions in ZnY (Ba2Zn2Fe12O22) and Mn0.625–ZnY planar ferrites have been investigated.
From the obtained spectra it is deduced that the Zn ions are randomly distributed over the tetrahedral sites of both S and T blocks and that Mn is substituting for Fe3+.
The magnetic transition temperature for Mn0.625–ZnY turns out to be TC = (143±5)°C, not much different from that of ZnY, where TC = 135°±5°C.
In these compounds the angle between the magnetic moment and the electric-field gradient differs from 90° showing the presence of angles between the magnetic moments of iron ions.
Magnetic Study of the Manganate Phases: CaMnO3, Ca4Mn3O10, Ca3Mn2O7, Ca2MnO4
Authors: MacChesney J. B. , Williams H. J. , Sherwood R. C. , Potter J. F. 
Published: February 2004

Two series of manganate phases have been prepared and their magnetic properties measured. The first series consists, in addition to CaMnO3, of three phases having layered structures. In these, tetravalent manganese ions are contained in single or multiple perovskite layers, which are separated from each other by nonmagnetic calcium-oxygen layers. Magnetic exchange of the type Mn4+–O–Mn4+ is disrupted between layers and decreased Néel temperatures would be expected to result. In a second series of phases, the size of the CaMnO3 unit cell was increased by partial substitution of strontium for calcium. Increased separation of manganese ions produced by this means was expected to reduce Néel temperatures. However, contrary to these expectations, Néel temperatures remained approximately constant for the first series of phases and increased for the second.
This apparent enigma can be viewed in terms of the effect of chemical substitution and lattice geometry upon the strength of exchange interactions. As pointed out by Goodenough,1 the overlap integral is increased as the result of partial substitution of larger A-site cations for calcium. On the other hand, geometrical influences are important to understanding the insensitivity of Néel temperatures to decrease in the number of near-neighbor magnetic ions that occurs as nonmagnetic layers are inserted in the perovskite structure.
Strain-Sensitive Thin Magnetic Films
Authors: Onyshkevych L. S. 
Published: February 2004

For the sonic film memory highly strain-sensitive ferromagnetic thin films are required with magnetic properties comparable to those of good Permalloy memory films. Research has shown that films prepared by evaporation from 60% Ni, 25% Fe, 15% Co melts meet the requirements.
These films have Hc and Hk values below 15 Oe and are usually inverted. They are well oriented with good squareness in the easy axis. X-ray diffraction measurements show them to have a single phase (fcc).
The strain-sensitivity is about an order of magnitude higher than that of the most sensitive Ni–Fe alloys with comparable values of Hc and Hk. Typically, a strain of about 5×10−5 causes: (1) a rotation of the easy axis by ∼25°, (2) a significant change in the values of Hc, Hk, and (3) a decrease in the switching threshold by at least a factor of two. The change in Hk and the rotation of the easy axis agree in general with theoretically predicted behavior.
Dynamic strain measurements show these films to be suitable for memory use with coincidence writing (strain pulse—magnetic field pulse) and nondestructive read.
A Coupled Magnetic Film Device for Associative Memories
Authors: Wang C. P. 
Published: February 2004

It is well known that a pair of magnetostatically coupled films with easy axes at 90° to each other exhibit biaxial anisotropy. However, when an external bias magnetic field is applied along the easy direction of one of the films, only two states of the coupled system have minimum energy. It can be shown that these two stable states are not collinear in magnetization orientations and the resulting switching characteristic is quite different from that of a uniaxial coupled film device.
A new associative memory device based on the above-mentioned switching characteristics is presented in this paper. Nondestructive content interrogation is feasible on this device by applying a current on the strip line intervening between two magnetic layers. When the polarity of the interrogation current mismatches the state of the device, a signal is induced in a detection strip line orthogonal to the interrogation line and located on top of both magnetic films. On the other hand, when the current polarity matches the device state, none or very little flux change is experienced by the detection line. The mismatch signal is always of one polarity independent of the device state.
A device sample with electroplated magnetic and conductive layers and photoetched strip lines has been fabricated. The scheme of two storage cells per bit is adopted to cancel capacitive noise. Two 2-bit (4 cells) words have been successfully operated in a parallel by bit content search mode. The measured mismatch to match ratio for a single bit is better than eight.
Critical Magnetic Scattering of Neutrons in Chromium
Authors: Hamaguchi Y. , Tsunoda Y. , Kunitomi N. 
Published: February 2004

The magnetic properties of the metallic chromium can be interpreted in terms of itinerant electron model. The angular distribution of the neutron diffuse scattering around its (1δ0) satellite reflection has been measured with the temperature of TN−20°C≤T≤TN+33°C. Improvement of the instrumental resolution has made it possible to observe the correlation range more accurately and to determine its anisotropic property.
Correlation range of the spin system above the Néel temperature, which was analyzed from the experimental data on the basis of the Ornstein-Zernike-type correlation function and the static approximation, has been obtained as κ12(Q∥) ∝ (T − TN)0.70±0.2 and κ12(Q⊥) ∝ (T − TN)0.54±0.2. The temperature dependence is remarkably smaller than those obtained in various substances and the theoretical conclusions of Ising or Heisenberg model.
Temperature Dependence of Isomer Shift and Hyperfine Field near the Curie Point in Iron
Authors: Preston Richard S. 
Published: February 2004

Current theories of critical-point phenomena predict that in the region below the Curie temperature TC, the spontaneous magnetization M of a ferromagnet varies with temperature T according to M/M0 = h(1 − T/TC)β for T→TC. Values of h and β have been calculated for theoretical models, and β is of special interest because of the possibility that it is a simple number such as ⅓ or ½. Measured values of β for various ferromagnets seem to cluster about these two values.
Pure iron is a favorable case for determining h and β by the Mössbauer effect since the hyperfine field should be closely proportional to M. However, previous results for iron1 showed a rather sharp discontinuity in the isomer shift at TC, and this is difficult to reconcile with the accepted opinion that the magnetic transition in iron is of higher than first order. If this were a first-order transition, then β would not be a meaningful parameter.
A more careful study of the Mössbauer effect in the vicinity of this transition is now being made. The temperature control has been further improved since the most recent results of this work were published2 and the uncertainty in temperature during any run is now of the order of 0.03°C. It now appears that the jump in the isomer shift, although sharper than it seemed to be originally, is not really a discontinuity, but is in fact spread out over a temperature range of about 0.3°C. When the values h, TC, and β are simultaneously adjusted for least-squares fits of the theoretical relation to the new data taken in two temperature ranges, the results are: β=0.342±0.004, h=1.49±0.03 for 0.99TC≤T≤0.999TC, and β=0.37±0.02, h=1.7±0.2 for 0.999TC≤T≤0.9999TC.
Internal Fields at the Two Sites of the Spinel System Ni1+xGexFe2−2xO4 by Mössbauer Effect
Authors: Fatseas G. A. , Krishnan R. 
Published: February 2004

In the study of ferrites, some authors have found two Mössbauer resonances of Fe3+ in tetrahedral (A) and octahedral (B) sites. The lower value of the internal field at the nucleus of Fe3+ in A sites has been attributed to the dipolar field, resulting from deviations from cubic symmetry, and to the more covalent nature of iron-oxygen bonds.
When the A site behaves as a perfect tetrahedron, the quadrupole interaction being absent, the dipolar field is excluded and the decrease in the field HA can be attributed to the effect of covalence alone. Those requirements are fulfilled in the spinel system Ni1+xGexFe2−2xO4. No quadrupole interaction is evident in any of these spectra.
The lower value of HA in all cases is attributed to the covalent effects in Fe3+–O2− bonds in A sites. The variation of HA and HB with x at 300°K is shown to be the effect of Curie temperature. At 80°K HB is independent of x, whereas HA decreases with an increase in x. This diminution in HA is attributed to the modification brought about by the presence of Ge4+ in A sites making the Fe3+–O2− bonds more covalent. This hypothesis is supported by the lower isomer shift of A sites.
Influence of Crystallite Size on the Magnetic Properties of Acicular γ-Fe2O3 Particles
Authors: Berkowitz A. E. , Schuele W. J. , Flanders P. J. 
Published: February 2004

Magnetic properties have been measured for a number of samples of acicular γ-Fe2O3 particles of the type used in magnetic recording tapes. The average particle size and shape were approximately the same for all samples. However, the average crystallite sizes of the samples, as determined from x-ray line broadening, ranged from 50 to 700 Å. All magnetic properties measured showed a strong dependence on average crystallite size. Saturation magnetization at room temperature, σ, decreased sharply with decreasing crystallite size. An excellent fit to the σ vs crystallite size data was made by assuming that the crystallites were separated by a nonmagnetic grain boundary on the order of 6 Å wide. Room-temperature coercive force decreased with decreasing crystallite size, and the ratio Hc(83°K)/Hc(293°K) increased sharply with decreasing crystallite size.
The data support a particle model in which the constituent crystallites interact magnetostatically across nonmagnetic grain boundaries. A critical crystallite diameter of order 400 Å may be inferred. Below this crystallite size, superparamagnetic behavior is observed; above this size, noncoherent magnetization reversals in the crystallites are suggested. This model is quite consistent with the ``fanning'' mode of reversal based on a ``chain-of-spheres'' model which has been considered by several authors to be most compatible with their data on γ-Fe2O3 particle assemblies.
Magnetic Impurities in Metals
Authors: Blandin A. 
Published: February 2004

This paper discusses some features of the electronic structure of magnetic impurities in metals.
For impurities in normal metals, applications of the model of resonant scattering states are made in the following directions: (1) discussion of the orbital degeneracy within the Hartree-Fock approximation and applications, particularly to cerium; (2) discussion of the magnetic solutions: effective values of J, occurrence of magnetism, and the Kondo effect; (3) influence of correlation.
The properties of impurities in transition metals are also discussed: magnetic moments, specific heat, resistivity. Evidence for two-current conduction in ferromagnetic metals is given. The paper ends with a discussion of dynamical properties of impurities.