bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Nuclear Indirect Exchange and Pseudodipolar Interactions in Alloys by Spin Echoes
Authors: Alloul H. , Froidevaux C. 
Published: February 2004

In alloys the spatial variations of the electronic density induce a distribution of the Knight shifts as well as a spread of the quadrupolar couplings.1 These effects create an inhomogeneous broadening of the NMR spectrum and have a strong influence on the shape of the spin-echo envelope of a given nuclear species.2 A general calculation involving 90°–180° pulse sequences has been performed assuming a broadening much larger than the contribution of the spin-spin interactions. It shows that the spin-echo envelope is a product of two factors, the first involving the quadrupolar effects and the second the spin-spin couplings. Each of these factors may have an oscillatory behavior the frequency of which is characterized either by the strength of the electric-field gradients or by the indirect spin-spin interactions.3
Experimental data illustrate this theoretical model in the case of a spin I=½. It yields values of the Ruderman-Kittel and the pseudodipolar coupling constants in Pb and Pt. For Sn and Cd only an order of magnitude of the exchange coupling constant has been deduced actually. The difficulty in the interpretation of the data in these last cases is due to the complicated crystal structure of these metals. These experimental data are summarized in the following table: bJMetal(kc/sec)(kc/sec)Pt0.39±0.084.0±0.2Pb2.2±0.34.8±0.5Sn≲5Cd≲0.25
Mössbauer Studies of Iron-Rare Earth Intermetallics
Authors: Bowden G. J. , Bunbury D. St. P. , Guimaraes A. P. 
Published: February 2004

The Mössbauer effect has been used to study the hyperfine field at the Fe sites of DyFe2, HoFe2, ErFe2, TbFe2, and SmFe2. The last three of these each show two superimposed hyperfine spectra with an intensity ratio of about 3:1. A similar result was found for ZrFe2 and TmFe2 by Wertheim et al.,1 who showed that it was consistent with the magnetization lying along a (111) direction. In DyFe2 and HoFe2 however we find only one Fe hyperfine spectrum at room temperature; it is shown that this would be expected if the magnetization is along a (100) direction. An explanation of these results is given on the basis of a simple ferromagnetic (antiferromagnetic) model for the light (heavy) rare earth intermetallics in which the direction of magnetization is determined by the easy direction for the rare earth ion.
The hyperfine fields at the Fe and Dy sites in DyFe2 have also been measured as a function of temperature. This parallels the work of Cohen2 on TmFe2 and allows a comparison of the rare earth-iron exchange in these intermetallics.
Temperature Dependence of the Anisotropy Constants of Gd, Tb, and Dy
Authors: Brooks M. S. S. , Goodings D. A. 
Published: February 2004

The sources of magnetocrystalline anisotropy have been studied for the ferromagnetic rare earth metals Gd, Tb, and Dy. In the weak anisotropy case of Gd the contributions to the anisotropy constants from the crystal field have been calculated by spin-wave theory treating the crystal-field terms as a perturbation. Estimates have also been made of the contributions to K1(T) from real and pseudo-dipole-dipole interactions and from the magnetoelastic coupling making use of magnetostriction data. The resulting agreement with the measurements of Graham and others of K2(T), K3(T) and K4(T) is good, but the situation is less satisfactory for K1(T). From the available experimental data the various crystal-field parameters have been estimated.
In Tb and Dy, in which there is a strong axial crystal field, the anisotropy constants are no longer well defined, except for small-angle deviations from the easy direction. The data of Rhyne and Clark for the effective anisotropy coefficients K20(T) and K66(T) have been analyzed in this light taking account of the torque balance conditions. The measured value of K20(0) for Tb leads to a value of the effective crystal-field parameter about 100 times larger than the corresponding value for Gd.
Resonance Properties of Ni1+xGexFe2−2xO4 Single Crystals
Authors: Krishnan R. 
Published: February 2004

Single crystals of the Ni1+xGexFe2−2xO4 system with 0≤x≤0.41 have been investigated in order to throw some light on the ionic distribution and properties of Ni2+ ions. The properties studied were K1, K2, g factor, and ΔH by means of ferrimagnetic resonance techniques in the temperature range of 4.2° to 393°K.
An increase in x results not only in a general decrease in K1 but also in a modification in its temperature dependence. For x≥0.36, K1/M and K1 actually begin decreasing below 80°K. From single-ion model of anisotropy a linear decrease of K1 with increase in x is predicted, whereas experimentally K1 falls off more rapidly for x≥0.36. To interpret this result an ionic distribution having Ni2+ in A sites is necessary, since from crystal-field considerations A site Ni2+ ions could contribute a positive K1. Since this contribution is larger at lower temperatures it counteracts the usual increase in -K1, thus diminishing the value at 4.2°K. The K1 found for x=0.32 could also be attributed to such A site Ni2+.
The above hypothesis is supported by the fact that for a sample with x=0.08 quenched from 1000°C which is known to increase A site Ni2+ concentration, K1 was found to vanish at 170°K.
The anomalous variation of g and the sharp increase of ΔH at 4.2°K with x are characteristic of A site Ni2+.
Our results indicate the presence of Ni2+ ions in A site for crystals of x≥0.3.
Dynamical Spin Correlations in Many-Spin Systems
Authors: Tahir-Kheli Raza A. 
Published: February 2004

Time-dependent correlations in many spin systems with anisotropic Heisenberg exchange interactions of arbitrary range are analyzed, using quantum-statistical Green's functions. The discussion is restricted to the ferromagnetic case and to two sublattice antiferromagnetic and ferrimagnetic orderings.
A scheme of higher-order random phase approximations, i.e., RPA II and modified RPA, is developed, thus extending the usual treatments involving the unembellished RPA.
The RPA II leads to a set of coupled nonlinear integral equations which cannot be solved at general temperatures. However, due to the simplicity of the ferromagnetic ground state, at low temperatures a rapidly convergent iterative procedure leads to a satisfactory solution which reproduces the spin-wave results.
The intra- and inter-sublattice longitudinal correlation functions are calculated in the modified RPA scheme, which consists in approximating the RPA II by the substitution of the usual RPA solutions for the transverse Green's functions, and the results are found to be satisfactory over the entire range of temperatures.
Magnetic Properties of Some Compounds with Pyrite Structure
Authors: Adachi K. , Sato K. , Takeda M. 
Published: February 2004

The magnetic properties of the dichalcogenide compounds with pyrite structure, CoS2, CoSe2, NiS2, NiSe2, and Co(SxSe1−x)2 were studied by means of magnetic measurements, neutron diffraction, NMR, and electrical resistivity in order to discuss their physical properties. Results obtained are as follows: CoS2 is a ferromagnetic with TC=124°K, θp=220°K, peff=2.13 μB, n=0.84 μB (at 0°K), and the exchange interaction J was estimated to be 24 cm−1 from the analysis of the low-temperature thermomagnetic curve. The internal magnetic field was observed to be 52 kOe at 80°K by NMR measurement. CoSe2 is an antiferromagnetic with TN=93°K, θp=−160°K, peff=2.20 μB; MnSe2 type antiferromagnetic spin ordering was determined by neutron diffraction at 53°K. NiS2 has an antiferromagnetic susceptibility with θp≃ −740°K and peff≃3.0 μB, but no magnetic ordering was observed by neutron diffraction at 53°K. NiSe2 exhibits weak constant paramagnetism, χM≈2×10−4 emu/mole. Co(SxSe1−x)2 forms a complete solid solution (0≤x≤1) with cubic pyrite structure and without ordering of S and Se. The magnetic phase diagram was determined, and the ferromagnetic region was found to exist up to 12% of Se at 0°K. The magnetic parameters of this system were determined and they show the so-called ``low spin state'' of cobaltous ion with one Bohr magneton. Electrical resistivities for the above compounds were semiconductive except for NiSe2 (metallic).
The theoretical and the experimental values of kTC/J for CoS2 (fcc, S=½) were compared. The experimental value was found to be 3.6. According to the result of the series-expansion method for the Heisenberg model, kTC/J was found to be 4.170 (kTC/J=6.00 for the Weiss approximation). It is concluded that the main origin of the discrepancy between theory and experiment is the influence of the more distant neighbor antiferromagnetic exchange interactions. The narrow ferromagnetic region in the Co(SxSe1−x)2 is explained by a statistical theory.
Alternating Antiferromagnetic Heisenberg Linear Chains
Authors: Duffy W. , Barr K. 
Published: February 2004

Calculations are reported of the eigenvalue spectrum and thermodynamic properties of the spin Hamiltonian H=2 | J | ∑ i=1N/2(S2i·S2i−1+aS2i·S2i+1)+gβH ∑ i=1NSiz,where SN=SN+1, for the case of spin ½. Exact eigenvalues were obtained corresponding to N=4, 6, 8, and 10 and alternation parameter a=0.2, 0.4, 0.6, and 0.8. Ground-state energies, energy gaps, and absolute-zero magnetizations are discussed as a function of N and a. Infinite chain behavior as a function of a is inferred, and compared with various approximate calculations including perturbation theory results for small a and the Hartree-Fock calculation of Bulaevskiǐ.1
The zero-field internal energy, entropy, specific heat, magnetic susceptibility, and short-range order at absolute zero are calculated and compared with the well-known results for uncoupled pairs (a=0) and the regular chain (a=1) calculations of Griffiths2 and Bonner and Fisher.3
Experimental data on solid organic free radicals are compared with these theoretical results.
An expanded version of this paper will be published elsewhere.
Low-Lying Energy Levels and Magnetic Susceptibility of Thulium in the Garnets
Authors: Pearson J. J. , Herrmann G. F. , Buchanan R. A. 
Published: February 2004

Susceptibility measurements on TmGaG, when analyzed in terms of a cubic crystal-field model, predict that there should be no excited energy levels lower than 104 cm−1 above the ground state.
Measurement and analysis of the spectrum of thulium in three different hosts, however, reveal the presence of levels lying well below 104 cm−1 and very sensitive to the detailed surroundings of the ion. A calculation of the energy levels of Tm3+ in the known crystal field for Yb3+ in the gallium garnet shows that a low-lying Λ5 triplet is split by the noncubic field to an extent which drastically affects the susceptibility. One is led to conclude that cubic models are insufficient for prediction of macroscopic magnetic properties in ions having degenerate cubic levels very near the ground state.
Fast Neutron Irradiation Effects in Superconducting Niobium
Authors: Sekula S. T. , Kernohan R. H. 
Published: February 2004

The superconducting magnetization behavior and transition temperatures of single crystals of Nb were investigated prior to and after a series of fast neutron irradiations (E&gt;1 MeV) in the Oak Ridge Research Reactor at a temperature of 40°C.1 In addition to increases in the upper critical field Hc2 and small changes in the transition temperature after irradiation, it has been found that defects have been created with the ability to pin magnetic flux as evidenced by an increase in the nonequilibrium behavior of the magnetization.
A greater degree of flux pinning in single-crystal Nb can be attained by fast-neutron irradiation than has heretofore been reported for pinning introduced by mechanical deformation, and for fast-neutron doses of approximately 2×1019 neutrons/cm2 the magnetization approaches that of a completely irreversible type II superconductor. The initial magnetization cycle and subsequent hysteresis loop for an irradiated sample are shown in Fig. 1 as well as the magnetization cycle prior to irradiation. Successive reductions in cross-sectional area of the highly irradiated sample and subsequent magnetization measurements reveal only a small size dependence of the hysteresis, indicating that rather steep flux gradients can be established even at applied fields close to the upper critical field. From size-dependent studies of the remanent moment it is concluded that a flux gradient has been established in a macroscopic surface sheath approximately 0.1 mm thick with the corresponding shielding current density calculated to be approximately 2×105 A/cm2.
Electrical Resistance of Thin Triode-Sputtered Gold Films
Authors: Toombs P. A. B. , Bennett P. 
Published: February 2004

Freshly prepared triode-sputtered gold films thicker than 200 Å on glass substrates exhibited a constant resistivity, about four times that of bulk gold, up to 4000 Å, the thickest films made. Annealing at 300°C for 4 h reduced their resistivity to twice that of bulk gold. Resistivity vs temperature curves were linear and parallel to the bulk gold curve.
Nucleation of the films were extremely rapid: Films deposited onto substrates at 70°C had resistivity only twice the final value at &lt;70 Å thickness. The gold also appeared to renucleate on grown parts of the film, since 2000 Å thick films exhibited no preferred orientation and had small crystals, 100 to 200 Å in the plane of the film, probably ∼60 Å thick. Film resistivity attained its final value as soon as a film became continuous, at about 100 Å with substrate at 70°C and about 250 Å at 250°C. This cannot be explained by invoking lamellar crystals, where the thickness of a single crystal is to be considered and not that of the whole film, since this would call for much higher film resistivity than observed. The alternative is that the film surfaces reflect conduction electrons specularly. This behavior is in marked contrast to that observed for solid films prepared by other techniques. The differences in behavior are fully discussed and reasons for the discrepancies are suggested.
A Powder Technique for the Evaluation of Nonlinear Optical Materials
Authors: Kurtz S. K. , Perry T. T. 
Published: February 2004

An experimental technique using powders is described which permits the rapid classification of materials according to
(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and
(b) existence or absence of phase matching direction(s) for second-harmonic generation.
Results are presented for a large number of inorganic and organic substances including single-crystal data on phase-matched second-harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.
Experimental System for Studying Itinerant d-Electron Ferromagnetism
Authors: Cloud W. H. , Jarrett H. S. , Bouchard R. J. , Butler S. R. , Frederick C. G. , Gillson J. L. 
Published: February 2004

Typical theoretical models of an itinerate electron ferromagnet consist of a single narrow band, but experimental data have been obtained primarily from the ferrous metals whose behavior is more complex because of overlapping broad s bands and narrow d bands. Transition metal sulfides of the cubic pyrite structure appear to have a doubly degenerate conduction band arising from atomic d orbitals of eg symmetry without overlapping s bands.1 The full band would contain four electrons per metal atom. Metallic conductivity is observed, except for the empty FeS2, exactly half-filled NiS2, and filled ZnS2 bands. The electron concentration, n, can be varied from zero to one electron per metal ion in the Fe1−xCoxS2 systems (n=x) and can be extended to higher values by use of the Ni1−yCoyS2 system (n=2−y).2 In these systems the effective moment obtained from paramagnetic susceptibility measurements is that of the isolated cobalt and nickel ions. It appears, therefore, that a model based on strong electron-electron correlation at the metal-ion sites would be applicable to these pyrite compounds. Such a model for a nondegenerate band has been given extensive theoretical treatment by Hubbard.3,4 Solutions for the degenerate case have also been indicated,5 and calculations of the Hubbard model for the two-fold degenerate band are currently being carried out.6 Significant features of the pyrite system which should be qualitatively explained by a theoretical model are:
(1) Ferromagnetism exists down to very low electron concentrations. A plot of Curie temperature vs n goes to zero at n≈0.05. For n&lt;0.05 the electrical resistivity vs temperature curves exhibit shallow minima at 20°K indicative of localized states. The loss of ferromagnetism below n≈0.05 may thus be due to loss of itinerancy and not to a critical electron concentration.
(2) The ferromagnetic moment, μs, is equal to one Bohr magneton per electron over a wide range of electron concentration 0.15 ≤n≤0.95. Ferromagnetic behavior is observed for 0.05&lt;n&lt;0.15, but the curve of magnetization vs applied field does not saturate, and μs appears to be less than n.
(3) In Ni1−yCoyS2 (n&gt;1) the saturation magnetization, Curie temperature, and Weiss constant decrease rapidly with Ni concentration, indicating strong antiferromagnetic Ni–Co interactions. Ferromagnetism disappears for n&gt;1.1. This would be expected if strong correlations at the Ni sites dominate.
(4) In Fe1−xCoxS2, μs decreases from 0.95 to 0.89 as n is increased from 0.95 to 1.0, but the effective moment in the paramagnetic state continues to increase linearly with cobalt concentration. Neutron-diffraction studies indicate a collinear spin state.7 A localized moment model which seems to explain much of the magnetic behavior cannot account for this decrease in μs with increasing Co concentration.
Temperature of the Restrike Channels of Exploding Wires
Authors: Lundquist Stig , Vlastós Antonios E. 
Published: February 2004

The temporal behavior of the temperature, the electron density and the thermal conductivity of the restrike channel of a thin exploding wire were studied, using the electrical conductivity of the restrike channel, which was determined by simultaneous measurements of the current through the channel, the voltage drop cross the channel and the channel radius assuming that the current distribution within the channel was homogeneous. In this study, in which the channel plasma was assumed to be fully and singly ionized, the Spitzer equations for the electrical and thermal conductivity of a fully ionized plasma and a modified pinch relation for the restrike channel were used. The results show:
(a) that the electrical conductivity reaches its maximum before the current maximum on the ledge observed on the voltage oscillograms;
(b) that the temperature and thermal conductivity reach their maxima at the conductivity maximum;
(c) that the electron density reaches its maximum after the conductivity maximum and near the current maximum;
(d) that the maximum values of the electrical conductivity, the temperature, the electron density and the thermal conductivity increase when the energy-input rate to the channel increases;
(e) that the validity of the assumptions made is in general confirmed.
For restrikes initiated at the exterior of the 13-cm-long 0.005-cm-diam constantan wires, the maximum values of the temperature and the electron density were found at 5 kV to the about 2×104 °K and 1023 electrons/m3 respectively, and at 23 kV to be about 4×104 °K and 1025 electrons/m3, respectively.
Depth Profiles of the Lattice Disorder Resulting from Ion Bombardment of Silicon Single Crystals
Authors: Feldman L. C. , Rodgers J. W. 
Published: February 2004

The depth profile of the lattice disorder resulting from the ion bombardment of single crystals is of interest in many applications. It has been shown that the channeling effect is sensitive to such lattice damage and has been used in extracting the total damage caused by short-range ion bombardment. This paper describes an extension of the channeling technique which yields not only the amount of damage but certain parameters of the depth distribution of the damage. This method is applied to the case of 200–500 keV light ion bombardment in silicon. The results of the measurements and analysis indicate
(1) Annealing at room temperature is an important process in determining the extent and characteristics of the damage.
(2) The peak of the damage distribution is 10%–20% shallower than the expected range of the ion.
(3) The widths of the damage distribution are significantly broader than the expected width of the ion distribution.
The Effect of Inflation on Government Revenue and Expenditure: The Case of the Islamic Republic of Iran
Authors: Alavirad Abbas 
Published: February 2004

AbstractThis paper provides an empirical analysis of the government budget deficit, money supply growth and inflation in the Islamic Republic of Iran. We use a simultaneous equation system to examine the effect of inflation on government revenue and expenditure, using quarterly data. Our major finding has been that the government budget deficit will increase in the inflationary condition. In addition, the deficit will increase money supply and this tends to increase inflation in Iran.
Comparative expression of vascular endothelial growth factor family members, VEGF‐B, ‐C and ‐D, by normal human keratinocytes and fibroblasts
Authors: Trompezinski S. , Berthier‐Vergnes O. , Denis A. , Schmitt D. , Viac J. 
Published: February 2004

Abstract:  The vascular endothelial growth factor (VEGF) family includes the related polypeptides VEGF‐B, ‐C and ‐D, which contribute to endothelial and lymphatic vessel development. The parental VEGF molecule, VEGF‐A, has been widely described in the skin, but the other members of the VEGF family have not yet been reported.The aim of our study was to determine whether the two main skin cells, keratinocytes and fibroblasts, expressed VEGF‐B, ‐C and ‐D in basal condition and after stimulation by either growth factors or the pro‐inflammatory cytokine tumour necrosis factor‐α (TNF‐α). Reverse‐transcription polymerase chain reaction (RT‐PCR) analysis on cultured normal human keratinocytes (NHKs) and normal human fibroblasts (NHFs) allowed the detection of different levels of VEGF‐B, ‐C and ‐D mRNA, in both cell types with similar RT‐PCR products in the skin cells. A semi‐quantitative evaluation of the VEGF family proteins by dot blot, using the different human recombinant VEGFs, showed different levels of VEGF‐B, ‐C and ‐D, in NHKs and NHFs. After cell stimulation by growth factors (epidermal growth factor (EGF) and transforming growth factor‐β1 (TGF‐β1) for NHKs and NHFs, respectively), a significant up‐regulation of the VEGF family member proteins was observed in NHFs but not in NHKs. Conversely, TNF‐α did not exert a significant effect. However, we could not detect any transcriptional modification in stimulated cells, whatever the stimulation duration. The addition of cycloheximide to the cell cultures strongly inhibited the increase of VEGF proteins in TGF‐β1‐stimulated NHFs. Taken together, the results underline the major role played by NHFs in the elaboration of the VEGF family proteins known to regulate wound healing, chronic inflammation and tumour angiogenesis and lymphangiogenesis.