bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of clean stacking faults and oxide microdefects in Czochralski silicon
Authors: Futagami Motonobu
Published: February 2003

The effect of intrinsic gettering action by microdefects in Czochralski silicon containing substantial amounts of oxygen on the properties of stacking faults (SF’s) has been studied. It has been found that high-temperature oxidation of swirl-free wafers results in the generation of SF’s decorated with probably heavy metallic impurity precipitates around the Frank partial dislocations, while high-temperature oxidation of swirled wafers results in the generation of clean SF’s. The occurrence of clean SF’s is correlated with the presence of microdefects in the bulk of wafers. Transmission electron microscopy (TEM) observations revealed that the microdefects were the precipitates (believed to be some form of silicon oxide) with generator dislocations or punched-out dislocations and that these dislocations captured impurity precipitates. These observations suggest that the microdefect dislocations are more attractive to metallic impurities in silicon than the Frank partial dislocations of the SF’s.
Optical properties of diffusion-formed Au2Al
Authors: Inagaki T. , Arakawa E. T. , Callcott T. A.
Published: February 2003

Ellipsometric measurements have been made on the intermetallic compound Au2Al to determine the optical constants for photon energies between 0.6 and 3.7 eV. Polycrystalline samples were prepared by the interdiffusion between evaporated thin fils of Au and Al. The optical properties are characteristic of a metallic conductor with an interbrand threshold of about 0.8 eV. The results are compared with optical data for Au, Al and AuAl2, and with x-ray photoeletron and soft x-ray emission spectra for Au2Al. As compared with pure gold, it is concluded that interband adsorption is greatly enhance relative to the free-carrier absorption and that d-band electrons do not contribute significantly to the absorption observed below 3.7 eV.
Sharp profiles with high and low doping levels in silicon grown by molecular beam epitaxy
Authors: Iyer S. S. , Metzger R. A. , Allen F. G.
Published: February 2003

We find that heavy adsorbed dopant layers, up to several tens of equivalent monolayers, can be made to produce heavily doped n (Sb) and p (Ga) layers in molecular beam epitaxy grown silicon. By preadjusting the adlayer concentration to the required value while temporarily arresting silicon growth, arbitrarily sharp profiles of any sequence of dopant type with very high or low levels can be grown. Examples are given of p+ i p+ and n++p+ pp+ structures grown with transition thickness L?300 Å, and with controlled layer thicknesses of ∼1000 Å. Such structures, difficult to achieve otherwise, should be ideal for fabrication of high-frequency millimeter wave devices.
Particle statistics and transport in compensated semiconductors with localized charge carriers
Authors: Van Zandt L. L. , Honig J. M.
Published: February 2003

A comprehensive theory has been set up to deal with carrier excitation and thermoelectric effects in small-polaron materials characterized by diffusive motion of independent charge carriers. The model involves transport states populated by charge carriers which originate from a set of defect levels that are partially compensated by deep-lying trap states. Allowance is made for spin splitting of all these states arising from the parallel and antiparallel arrangement of electron spins relative to those prevailing on the cationic sites. It is shown that under normal circumstances the fraction f of occupied transport sites and the reduced Seebeck coefficient S are related by S≊log f. Hence, independent of any approximations, thermoelectric and conductivity measurements can be used to estimate the charge carrier densities and mobilities, respectively. In various limiting cases these results reduce to three well-known approximations. It is emphasized that these standard limiting results ought to be used with considerable caution; in particular, it is difficult to realize the experimental situation corresponding to the intrinsic regime.
Noise sources of hot carriers in space-charge regimes
Authors: Nougier J. P. , Vaissiere J. C. , Gasquet D. , Motadid A.
Published: February 2003

The noise term involved in the impedence field method, for modelling the noise of devices, which may work under both space-charge and hot carrier conditions, is shown to be proportional to the local noise temperature and to the local ac conductivity. This allows one to determine the noise source term experimentally, which is performed, as an example, for n-type silicon at 77 K. Also are established the mathematical conditions, under which the impedance field method reduces to the salami method.
The electrical characteristics of InP Schottky diodes
Authors: Hattori K. , Izumi Y.
Published: February 2003

Au-n+-type InP Schottky diodes have been fabricated using anodic oxidation and etching with aqueous HCl. The electrical characteristics are measured and discussed based upon the effects of surface states between the gate metal and semiconductor. Typical values of the barrier height, ideality factor and surface state density are evaluated as 0.55 eV, 1.34 and 4.2×1012 cm−2 eV−1, respectively. The mean electron affinity at the semiconductor surface is found to be about 0.5-eV-smaller than the bulk electron affinity. Further, the stability of the diode characteristics has been examined.
Fowler-Nordheim electron tunneling in thin Si-SiO2-Al structures
Authors: Krieger G. , Swanson R. M.
Published: February 2003

The Fowler-Nordheim tunneling of electrons from <100≳-oriented Si into thermally grown SiO2 has been studied. The effects of the Si band structure and the accumulation layer have been carefully considered. Classical image barrier lowering has also been analyzed. The agreement between the theory and the experimental results is excellent over a large range of tunneling current. The study enables a consistent treatment of various tunneling problems where a more simplified analysis is not adequate.
Pulse response properties of Josephson transmission lines and their application to logic circuits
Authors: Matsuda Azusa , Yoshikiyo Haruo
Published: February 2003

Pulse response properties for Josephson transmission lines have been investigated by computer simulation. Under certain conditions, these transmission lines with loss and bias current are found to have characteristic features similar to those for neural axons. A simple logic circuit is proposed that employs these pulse response properties and its operation is investigated through simulation.
Numerical analysis of vortex motion in two-dimensional array of Josephson junctions
Authors: Nakajima K. , Sawada Y.
Published: February 2003

We show that the equation which describes two- and three-dimensional arrays of small-area Josephson junctions is reduced to the following form, −∇×(∇×φ)−∂2φ/∂t2−Γ∂φ/∂t = sin φ, where φ is the two- or three-dimensional phase-difference vector, and sin φ is the vector whose components are sine functions of the components of φ, respectively. Based on the above equation we analyze numerically a two-dimensional square network of Josephson junctions, and discuss the vortex motion on the network.
Characterization of type-II superconductor via synthesis of observed induced-voltage waveforms
Authors: Griffths David J. , Kroeger Donald M.
Published: February 2003

Induced-voltage waveforms exhibited by type-II superconductors in response to a time varying magnetic field superimposed on a steady dc magnetic field have been compared to those calculated using a modification of a computer program developed by Rouze and Clem. This program allows a choice for the magnetic field dependence of critical current density, equilibrium magnetization, flux entry, and exit barriers as well as the specific from of the time-dependent magnetic field. Once agreement between predicted and observed waveforms has been achieved the separation of ac losses into pinning and annihilation contributions, their dependence on both dc bias field and time varying field amplitude as well as their spatial variation within the superconductor can be determined. We find reasonable agreement between a specific critical-state model collections of Jc(B),Heq(B), Hen(B), Hex(B), and experimental results in the case of Nb:38% Hf.
Optimization of the effects of power dependent refractive indices in optical waveguides
Authors: Sarid Dror , Stegeman George I.
Published: February 2003

The propagation of guided waves in planar optical waveguides characterized by an intensity dependent refractive index is analyzed. Closed form expressions for Δβk, the change in the propagation constant of the symmetric waveguide, were obtained using perturbation theory and were evaluated to predict optimum thickness for maximizing Δβ. It is found that the maximum value of Δβ is inversely proportional to the optimized thickness of the waveguide.
Nonhysteretic Josephson tunnel junctions for microwave detection
Authors: Hartfuss H. J. , Gundlach K. H. , Schmidt V. V.
Published: February 2003

We report on direct and heterodyne detection of 70-GHz radiation, using nonhysteretic superconductor-insulator-superconductor Josephson junctions with μm dimensions. The best value of noise equivalent power in the direct detection experiments was about 10−14 W at 1-Hz postdetection bandwidth and the best single sideband conversion efficiency in the heterodyne mode L−1c = −10 dB. In an experiment with L−1c = −11 dB a mixer noise temperature, including noise of the impatt local oscillator, of 2300 K is estimated.
Optically pumped laser lines of Na2 pumped by Kr+ (6471 Å) and HeNe (6328 Å) lasers: Identification of old lines and prediction of possible new lines
Authors: Verma K. K. , Stwalley W. C. , Zemke W. T.
Published: February 2003

We have examined the fluorescence spectra of Na2 excited by Kr+ (6471 Å) and HeNe (6328 Å) lasers in an effort to identify the optically pumped laser lines of this molecule [H. Welling and B. Wellegehausen, Laser Spectroscopy III (Springer-Verlag, New York, 1977), p. 365, and H. Itoh, H. Uchiki, and M. Matsuoka, Opt. Commun. 18, 271 (1976)]. For the 6471-Å pump, the line positions in our fluorescence spectrum show significant systematic disagreement with the optically pumped laser lines reported by Welling and Wellegehausen; however, our transition probability calculations have been used to make proper assignments. For the 6328-Å pump, in addition to the optically pumped laser lines reported by Itoh, Uchiki, and Matsuoka, we have observed some very interesting transitions which appear to be ideal wavelengths for a HeNe laser pumped Na2 laser. For both cases, we have listed a number of additional wavelengths which should lase under slightly improved conditions.
Efficient operation of an atomic thallium photodissociation laser at 535.0 nm
Authors: Scott D. A. , Piper J. A.
Published: February 2003

Results of experiments investigating the influence of resonance radiation trapping on the power and efficiency of the atomic thallium photodissociation laser are reported. Transverse pumping of a thallium iodide cell with added free metallic thallium has enabled conversion efficiencies from the ArF laser pump beam of greater than 7% to be achieved on a single Tl laser transition at λ 535.0 nm. Collisional deexcitation of the 72S1/2 upper laser level imposes a limit on the TlI densities which can be employed.
Multiple scattering of acoustic waves by random distributions of discrete scatterers with the use of quasicrystalline-coherent potential approximation
Authors: Tsang L. , Kong J. A.
Published: February 2003

Multiple scattering of acoustic waves by random distribution of discrete scatterers is treated within the framework of quantum mechanical potential scattering with the use of an acoustic potential operator. The effective field approximation (EFA) and quasicrystalline approximation (QCA) are imposed on the multiple scattering equations. The use of the operator technique facilitates the introduction of coherent potential (CP). Solutions are obtained for the complex effective propagation constant in the low frequency limit for spherical scatterers. Results from the three approximations, EFA, QCA, and QCA-CP (quasicrystalline approximation with coherent potential) are compared. Numerical results of the effective propagation velocities and the attenuation rates, as a function of the fractional volume occupied by the scatterers, are illustrated.
Suppression of shock excitation and nonlinear process of acoustic domains in CdS caused by a two-step pulse application
Authors: Kaneiwa Toshiyuki , Hata Tomonobu , Tokunaga Yoshiaki , Hada Toshio
Published: February 2003

The acoustic domains in CdS caused by the two-step pulse are studied with Ef an ultrasonic injection method and Brillouin scattering measurement. When the first-step field Ef is smaller than the synchronous field Ea i.e., Ef?Ea , the factor m of fm ( f; frequency) of the lattice attenuation (αl) increases with increasing Ef and we finally obtained m = 2 at Ef = Ea. This means that the deviation from f2.0 is caused not only by the nonlinear process but also by the shock excitation. On the other hand, when Ef≳Ea, the amplitude of the current waveform decreased drastically and the maximum intensity of the frequency spectra becomes weak and it’s frequency becomes higher. This means that the nonlinear process is suppressed.
Response of the electric field in a positive column in helium to a current perturbation
Authors: Ault S. , Raether M. , Sobhanian S.
Published: February 2003

The response of the electric field in a positive column of a hot cathode discharge in helium to a current perturbation has been measured over a wide pressure range. The relaxation of the electric field, electron density, and drift velocity proceed via a two time-constant process which can be interpreted as being due to direct electron impact ionization of helium atoms in the ground state and the production and subsequent ionization of metastable helium atoms in the 23S state.
A study of the strain in the damaged surface layer of V3Si after 2.0-MeV He-ion implantation
Authors: Schutz R. J. , Testardi L. R. , Weissmann S.
Published: February 2003

Strain induced by He-ion bombardment in 3–4-μm- thick surface layers of V3Si single crystals was studied using the x-ray back-reflection divergent-beam method. The strain matrix of the surface layer was determined. Analysis of the x-ray line broadening as a function of increasing dose showed that the strain varied with the depth distance from the surface. The depth strain gradient was confirmed by x-ray measurements carried out at different depth levels and by the application of a dual-element x-ray target. Calculations showed that the observed line broadening induced by a low dose of bombardment was closely related to the nuclear stopping power in the samples. For a high dose this simple relationship apparently did not hold. An annealing study showed that the strained surface layer relaxed in a two-step process. Strain reduction was time-independent (from 15 min to 2h) up to 600 °C. At 700 °C strain relaxation continued discontinuously, indicating that another mechanism became active at this temperature. An attempt was made to relate the present data to previous work on the degradation of superconducting properties of A-15 structures due to radiation damage.
Large-area quasihomeotropic orientation of liquid crystal and its application to guest-host positive display
Authors: Koshida Nobuyoshi
Published: February 2003

A simple method is described that enlarges the available area of the liquid-crystal orientation with a small tilt angle from homeotrpic alignment. Oblique deposition using a modified evaporation source extends the film topography over a much larger area and consequently continuing homeotropic surface treatment produces a large-area ’’quasihomeotropic’’ structure with a highly uniform tilt angle. A large-area, guest-host liquid-crystal cell perpared by this method shows a uniform electro-optical behavior in a positive color display mode.
Structural model of sputtered fluorinated amorphous silicon
Authors: Matsumura Hideki , Sakai Kunihiro , Kawakyu Yoshito , Furukawa Seijiro
Published: February 2003

Structure of a fluorinated amorphous-silicon alloy (a-Si:F), which is produced by the sputtering of Si in mixtures of Ar and SiF4 gases, is studied by transmission electron microscope (TEM). As a special technique to study the localization of both atomic species and particular types of Si-F configuration, the change of TEM micrograph due to anisotropic chemical etching of samples is observed, and it is compared with the similar changes in infrared absorption spectra and the Rutherford backscattering spectra. The evolved gases from heated a-Si:F are also analyzed to determine the role of Ar atoms in the microstructure. It is found that a-Si:F film consists of many small grains of a-Si network, and that both Si-F4 bonds and Ar atoms are localized at the grain boundary. Based on these results, the most possible structural model for a-Si:F, which suggests key factors to improve the properties, is presented.
Melting point relations for posttransition elements
Authors: Van Uitert L. G.
Published: February 2003

Posttransition elements with limited coupling between s and p or d subshells tend to exhibit metallic bonding. As this coupling increases, so do semicovalent and covalent bonding effects that weaken overall cohesion by tending to molecularize the crystal. In the extreme, essentially free-electron transfer is supplanted by spin-pair bonding. Metallic bonding and crystal cohesion may also be reduced by weakening, rather than strengthening, coupling, if inert (s2) pairs can stabilize. In addition, the contribution of each free valence electron to metal bonding is limited by the occupancy of completed d10 subshells, as well as the partial occupancy of s and p states of these elements.
Amorphous magnetic alloys of cobalt-titanium
Authors: Aboaf J. A. , Klokholm E.
Published: February 2003

Amorphous cobalt-titanium films were deposited by r.f. sputtering for titanium content in excess of 14 atom percent. The properties of amorphous CoTi films are similar to those of transition metal-metalloid glasses: they have soft magnetic properties and their resistivity is in the 100–200μΩcm range. Contrary to most metal-metalloid glasses, these films have very small magnetostriction, are most thermally stable, and more corrosion resistant.
Behavior of glassy Fe77B23 upon anneal in the absence of externally applied fields
Authors: Ramanan V. R. V. , Marti J. , Macur J.
Published: February 2003

Glassy Fe77B23 when annealed at 623 K, in vacuum and in the absence of external magnetic fields, shows a deterioration of its soft magnetic properties. The coercive field Hc is found to increase sharply with time of anneal. (Hc = 220 A/m after 60 minutes of anneal, compared to the ’as cast’ value of 9 A/m). X-ray diffraction (Mo-Kα) is unable to detect crystallinity in samples annealed for up to 60 min. However, TEM studies show the emergence of small crystallites occupying less than 1% of the total volume. The size and number of these crystallites increase with time till 90 min. X-rays then show the presence only of Fe3B. The TEM results indicate that the increase in Hc is the result of eutectic crystalliztion. At this same temperature, Fe76B24 also shows a similar effect with anneal time, but to a lesser extent.
The effect of heat treatment on amorphous Fe74Zr19Ta7 and Fe90Y10 alloys
Authors: Prater J. T. , Merz M. D.
Published: February 2003

Magnetic measurements are reported for two iron-based amorphous alloys: Fe90Y10 and Fe74Zr19Ta7. Each is prepared by sputter deposition. X-tay diffraction is used to established the amorphous structure and X-ray fluorescence analysis to confirm the composition. Fe74Zr19Ta7 has a Curie temperature of 195 K and a crystallization temperature of 733 K (460 °C). Annealing studies on Fe74Zr19Ta7 indicate that this alloy does not show the dramatic increases in Curie temperature that are commonly observed in amorphous alloys that contain metalloid elements. Rather, this alloy exhibits small irreversible decreases in the Curie temperature following heat treatments up to 733 K (460 °C), the crystallization temperature. The amorphous Fe90Y10 alloy shows only short range order and has a large anisotropy field that prevents the saturation of the magnetic moment in a 10 kOe field at 78 K. The anisotropy decreases upon crystallization to a bcc iron structure, but ferromagnetism is observed only after annealing the alloy at elevated temperatures.
Radiation effects in amorphous FexNi80−xP14B6
Authors: Franz W. T. , Steck G. , Kramer J. J. , Murray R. B. , Onn D. G.
Published: February 2003

Change in the Curie temperature and magnetic saturation of the amorphous ferromagnetic series FexNi80−xP14B6 for 20?x?34 induced by proton bombardment have been studied, and correlated with small angle x-ray scattering measurements performed for x = 20 at Oak Ridge National Laboratory. Both the Curie temperature and the low temperature saturation magnetization increase with proton fluence up to 1016 cm−2 but are constant for higher fluences. Protons of energy 2.25 MeV (range much greater than the sample thickness) are more effective at producing changes than protons of energy 0.25 MeV (range much less than sample thicness). Thus, hydrogen implantation is eliminated as the principal source of the observed changes. In addition, careful attention to sample temperature during irradiation excludes thermal annealing as the origin of the effect. Proton bombardment at the same fluences produces scattering centers that are observed by small angle x-ray scattering. The concentration of scattering centers increases with proton fluence up to 1016 cm−2, but remains constant thereafter. The size of the centers remains constant at about 16–30 Å. Possible structural changes to account for these observations are incipient recrystallization, void formation, and phosphorous segregation.
Anomalous eddy current loss and amorphous magnetic materials with low core loss (invited)
Authors: Fujimori H. , Yoshimoto H. , Masumoto T. , Mitera T.
Published: February 2003

Heat-treatment methods for obtaining low core loss in Fe rich amorphous alloys with high magnetic induction and the physical mechanism concerned will be discussed. Field annealing is necessary to avoid inducing local magnetic anisotropies or magnetic domain wall fixing, and then to make stress relieving effective. Consequently, field annealing can reduce hysteresis energy loss. However, core loss at high frequencies involves a fairly large anomalous eddy current loss. This is due to a large size of 180° magnetic domains resulting from field annealing. Oblique field annealing is, on the other hand, effective to reduce anomalous eddy current loss, because of increase in the number of 180° domain walls. The experimental relation between core loss and domain structure obtained on Fe(72)Co(8)Si(5)B(15) has satisfactorily been explained by the simple model on the basis of bar-like 180° wall motion. Magnetic properties of Fe(81)-(B, C, Si) (19) amorphous alloys suitable for transformer materials will also be reported. In Fe(81)B(13)C(2)Si(4), for example, core loss at 50 Hz is 1.3 mw⋅sec/kg at 15 KG and 25°C (2.2 mw⋅sec/kg at 15 KG and 80°C).
Effects of surface treatment and thinning on magnetic properties of rapidly quenched amorphous alloy ribbons
Authors: Becker J. J.
Published: February 2003

The magnetization curves and hysteresis loops of rapidly quenched transition-metal–glass-former amorphous ribbons of various compositions were measured as they were chemically thinned, down to about 10% of their original thickness. The specific saturation moment did not change showing that the ribbons are chemically homogeneous through their thickness. In general, the approach to saturation of as-cast ribbons remained remarkably constant. Although annealing experiments indicate that the approach to saturation is controlled by stresses, they are not distributed in such a way that they are affected by thinning of the sample. The coercive force initially changed rapidly, either up or down, with decreasing thickness, then increased linearly with reciprocal thickness. The results can be simply interpreted in terms of surface and volume pinning.
Coercivity effects of iron microcrystals in amorphous Fe81B13.5Si3.5 C2
Authors: Swartz J. C. , Haugh J. J. , Krause R. F. , Kossowsky R.
Published: February 2003

Primary crystallization of the titled alloy (Metglas 2605SC) occurs as dendritic microcrystals of αFe, which have cause a large increase in coercivity. This paper reports transmission electron microscopy measurements of the average length and number density of iron crystals as a function of annealing. The dendrites initially lengthen isothermally at a constant rate governed by an activation energy of (230±20) kJ/mole. The coercivity increases linearly with mean crystallite dimension between 0.1 and 0.6 μm, and stronger than linearly above 0.6 μm.
Zero-magnetostriction and low field magnetic properties of Co-TM-Zr amorphous alloys (TM = V, Cr, Mo or W)
Authors: Nose M. , Kanehira J. , Ohnuma S. , Shirakawa K. , Masumoto T.
Published: February 2003

The formation range and zero-magnetostrictive compositions for Co-TM-Zr (TM = V, Cr, Mo or W) amorphous alloys have been examined. And their low field magnetic properties also have been measured. The addition of TM elements extends the zirconium content forming amorphous single phase for Co-Zr system to the range of 5–18 at%. The zero-magnetostriction lines for all systems except for Co-W-Zr are located in the range of 7–15 at% TM. The crystallization temperature, Tx, for the alloys with Co less than 83 at% exceeds 500 °C, which is significantly higher than that for Co-Fe-Metalloids alloys. Increment of Co content in this type zero-magnetostrictive alloys raises Curie temperature, Tc, and increases saturation magnetization monotonically, but decreases Tx slightly. The present alloys containing Co less than 82 at% exhibit excellent low field magnetic properties such as coercivity, Hc = 7 mOe in static field and effective permeability, μe(1 kHz, 10 mOe) = 34,800 for annealed Co77Cr11.7Zr11.3 amorphous alloy.
Effect of tension on coercive force in amorphous (Fe1−xCox)77Si10B13 ribbons
Authors: Goto M. , Tange H. , Hamatake T.
Published: February 2003

Coercive force Hc was measured from observation of hysteresis loop as a function of tension σo and x in amorphous (Fe1−xCox)77Si10B13 ribbons. Tensions up to 4×109 dyne/cm2 and ac field, 380 Hz and 2.5 Oe max., were applied along the axis of straight ribbon. In the positive λs alloys (x?0.9), hysteresis loop easily became square type with increasing σo: After square type was attained, Hc increased almost linearly with further increase of σo. The rate of this increase, ΔHc/Δσo, was found to vary with x and to be nearly proportional to λs(x)/Ms(x). This result was qualitatively well explained from the viewpoint of wall coercive force with assumption of simple domain configuration.
Behavior of the amorphous ferromagnetic ribbons in the very low fields
Authors: Zhao-Hua Lin , Dao-Sheng Dai
Published: February 2003

The D.C. and A.C. magnetic properties and loss factors of five Co-based amorphous ribbons with different compositions in the low magnetic fields were measured. The results show that there is a distinct turning field Hp for B(H), μ(Hm) and 2πtan δ/μ−Bm. The existence of Hp can be explained by means of the domain wall pinning effect in the low fields. The measured Hp corresponds to the minimum pinning field (∼10 mOe) in samples. It is suggested that the large gradient of intrinsic stresses in the ribbons is main cause of the low field pinning effect on domain walls; then we obtained a formula for Hp which was estimated to be 2–20 milli-Oersteds.
Tetracriticality of RbMnF3
Authors: Shapira Y.
Published: February 2003

The boundary between the intermediate and spin-flop phases of RbMnF3 was determined from magnetostriction and differential susceptibility measurements. The results are in qualitative agreement with the theory of Bruce and Aharony.
Fluctuation induced first order transitions and symmetry breaking fields
Authors: Kerszberg Michel , Mukamel David
Published: February 2003

Model Hamiltonians which possess no stable fixed point or which lie outside the domain of attraction of their stable fixed point, are known to yield first order transitions within the renormalization group approach. By applying a symmetry breaking field, g, a continuous transition may be restored. The crossover from first order to continuous transition induced by symmetry breaking fields is analyzed. Two Landau-Ginzburg-Wilson models are considered: (a) the n = 6-component model associated with type-I fcc antiferromagnets (such as UO2), and (b) the n = 4-component model associated with type-II fcc antiferromagnets (such as TbP, TbAs, CeTe and TbSe). The symmetry breaking field corresponds to a magnetic field or a uniaxial stress. The phase diagrams are studied using large g expansions, means field calculations, and renormalization group techniques in d = 4−ε dimensions. It is found that the (g,T) phase diagrams are rather complex exhibiting fourth order critical points, tricritical points and critical end points.
Dilatational symmetry breaking in magnetic cooperative systems
Authors: Erber T. , Latal H. G. , Olenick R. P.
Published: February 2003

The breaking of the dilatational symmetry of dipole interactions by octupole admixtures (and mixtures of multi-polarities) has been demonstrated using a square Ewing array which can be symmetrically dilated. Experiments indicate that even few body systems (2×2, 3×3, 4×4 arrays) exhibit a multiplicity of metastable states for which discontinuous structural transitions occur. A combination of analogue and digital methods allows for computations of the energy surface and the assignment of a sharply defined range to the octupole forces. The cooperative nature of the system is manifest by the extreme rapidity in the increase of the range of the forces as the complexity of the system is augmented.
Solitons in one-dimensional magnets (invited)
Authors: Mikeska H. J.
Published: February 2003

We review recent theoretical results on nonlinear excitations in one-dimensional magnets. We deal with classical magnetic chains in a continuum description and discuss solutions to the full nonlinear equations of motion for ferromagnetic as well as antiferromagnetic exchange and additional single ion anisotropies and external magnetic fields. Easy-plane ferro- and antiferromagnetic chains in an external field breaking the easy-plane symmetry can be mapped approximately to the Sine-Gordon chain. We introduce this mapping and discuss the approximation involved. The kink modes of the Sine-Gordon chain are topologically stable excitations in these magnetic chains whereas in 1d magnets with different symmetries also pulse modes with continuously varying amplitudes are found to exist. We investigate the influence of nonlinear excitations on dynamic correlation functions in Sine-Gordon-like magnetic chains at finite temperatures. Kinks lead to a characteristic broadening of Bragg peaks in antiferromagnets and to a central peak in the dynamic response function of the xy ferromagnet. The latter is shown to be modified considerably by the lowest order corrections to the noninteracting kink/magnon approach.
Experimental evidence for magnetic solitons in the antiferromagnetic chains of (CD3)4NMnCl3 (invited)
Authors: Boucher J. P. , Regnault L. P. , Rossat-Mignod J. , Renard J. P. , Bouillot J. , Stirling W. G.
Published: February 2003

Different experimental results—neutron experiments, spin-lattice relaxation time measurements, and an analysis of the phase diagram TN(H)—obtained on the one-dimensional compound TMMC are reviewed and compared to the soliton model proposed for planar antiferromagnetic chains.
A comparison of static and dynamic properties of one-dimensional magnets and corresponding sG system
Authors: Loveluck J. M. , Schneider T. , Stoll E. , Jauslin H. R.
Published: February 2003

Using numerical transfer-integral and molecular-dynamic calculations, we demonstrate that the mapping of an easy-plane ferromagnet in a field to the sine-Gordon system fails at surprisingly low temperatures. The crucial implication for CsNiF3 is that the central peak observed by Kjems and Steiner at T = 10 K is more likely to be due to multimagnon difference processes, or pulse-soliton features of the nearly isotropic model rather than due to kink or breather solitons.
Computer simulation of the approach to equilibrium in the classical Heisenberg chain
Authors: Rudin S. , Heller P.
Published: February 2003

Computer studies of the approach to equilibrium in the classical 3-component Heisenberg chain, starting from a configuration with a large staggered magnetization (i. e., far from equilibrium) are reported. The equal time transverse and reduced longitudinal correlations g⊥(ℓ, t) and g∥(ℓ, t), respectively, were monitored for times long enough to show the approach to equilibrium. Results for g⊥ confirm predictions by Nelson and Fisher of wave-like behavior with a propagation speed equal to twice the zero-temperature spin wave velocity. The equilibration of g∥ was found to be slower and diffusive in nature. The fitted diffusivity appears to be comparable to the value of the spin diffusivity for the corresponding equilibrium problem.
Low temperature thermal expansion of CsNiCl3 and RbNiCl3
Authors: Rayne J. A. , Collins J. G. , White G. K.
Published: February 2003

The thermal expansion of the linear-chain antiferromagnets CsNiCl3 and RbNiCl3 has been measured from 1.5K to 90K. Anomalies in the linear expansion coefficients of CsNiCl3 near the spin-rearrangement and Néel temperatures show large differences due to the anisotropic spin-phonon interaction. The magnetic Grüneisen parameter for the associated volume coefficient is similar to that observed in other systems. For the one-dimensional ordering the corresponding Grüneisen parameter is inconsistent with that predicted from ultrasonic data. The thermal expansion behavior of RbNiCl3 near its Néel temperature differs markedly from that of CsNiCl3. Possible reasons for the difference are discussed.
A survey of analytic results for the 1-D Heisenberg magnets (invited)
Authors: Johnson J. D.
Published: February 2003

The linear, nearest-neighbor, magnetic systems described by the anisotropic, finite-field, spin-1/2, Heisenberg Hamiltonian H = Σi(SxiSxi+1+SyiSyi+1+ΔSziSzi+1 ) −HoΣiSzi, −∞<Δ<∞ and 0?H0, are increasingly attracting attention, both experimentally and theoretically. These systems are now known to be intimately related to models in quantum field theory, for quantum solitons, and for other many-body problems. In its own right, the Hamiltonian describes many physically realized systems; thus the theoretical prediction of some unexpected and interesting properties indicates experimental possibilities. We outline what has been learned, from the method of Bethe’s Ansatz, of the ground state, elementary excitations, and low-temperature thermodynamics as functions of Δ and Ho. We discuss the changes in behavior of the low-temperature thermodynamics as Δ and Ho are varied and give the relationship of these changes to the ground state and excitation spectrum characteristics. In small magnetic fields, unexpected structure in the low-temperature thermodynamics of the ferromagnetic Heisenberg magnet has been predicted.
Low-dimensional antiferromagnets of tetrahedral cobalt (II) (invited)
Authors: Carlin Richard L.
Published: February 2003

Several of the factors affecting magnetic ordering in cobalt (II) compounds are discussed. These include stereochemistry, crystal lattice dimensionality and crystal field effects. A summary of results on three low-dimensional compounds is presented, the compounds being Cs2CoCl4 and [Co(Pφ3)2X2], X = Cl, Br.
Neutron scattering evidence on Lifshitz behavior in MnP
Authors: Moon R. M. , Cable J. W. , Shapira Y.
Published: February 2003

We have measured the variation of q↘ in the fan phase of MnP in order to test whether the para-ferro-fan triple point is a Lifshitz point. Along the para-fan phase boundary, q↘ continuously decreases as the triple point is approached, extrapolating to zero at a temperature in good agreement with other measurements of the triple point. The temperature dependence of q↘ along this phase boundary is in approximate agreement with theoretical expectations for Lifshitz point behavior. These data support the conclusion that the triple point is a Lifshitz point.
Exactly soluble Ising models exhibiting multiphase points
Authors: Huse David A. , Yeomans Julia M. , Fisher Michael E.
Published: February 2003

A class of decorated spin 1/2 Ising models is introduced: all bonds of a hypercubic lattice parallel to one axis are decorated by n spins. Within each decorated bond, nearest neighbor ferromagnetic interactions compete with next-nearest neighbor antiferromagnetic interactions. An exact dedecoration transformation reduces the model to an anisotropic Ising model which is exactly soluble in two dimensions (d = 2) and for which accurate series expansion estimates are available for d = 3. Phase diagrams are presented for d = 2 and 3 : all exhibit a multiphase point at which many distinct, spatially modulated commensurate phases coexist. The variation of the characteristic wavevector and other properties are compared and contrasted with those of the axial next-nearest neighbor Ising (ANNNI) models.
Nonlinear microwave resonance behavior of itinerant holes in an organic conductor
Authors: Walsh W. M. , Rupp L. W. , Wudl F. , Nalewajek D. , Lee P. A. , DiSalvo F. J.
Published: February 2003

The spin resonance of holes in the single-stack organic conductor (TMTSF)2PF6 is readily observed from room temperature down to ∼l2 K with monotonically decreasing linewidth. Below that temperature no signal is observed at low microwave power but if the sample is exposed to microwave electric fields parallel to the needle axis the resonance reappears suddenly at higher microwave power. The threshold power for spin ’’resurrection’’ rises on cooling below 12 K and, in samples of improved purity, a second threshold marked by a distinct change in line shape appears below ∼9 K. These nonlinear magnetic effects are also accompanied by sharp but weak changes in the sample’s loading of the microwave cavity and may be qualitatively correlated with a decrease in DC conductivity accompanied by nonlinear electric-field response, as well as anomalous variations of the magnetic susceptibility. These results suggest a spin-density-wave ground state which is very easily disturbed by experimental probes.
Hyperfine magnetic field at cadmium impurity in Heusler alloys Ni2MnGa, Ni2MnIn, Cu2MnIn, and Au2MnIn
Authors: Elfazani M. , DeMarco M. , Jha S. , Julian Glenn M. , Blue James W.
Published: February 2003

The Time Differential Perturbed Angular Correlation (TDPAC) technique has been used to measuare the hyperfine magnetic field at cadmium impurity located at the Ga site in Ni2MnGa (Tc = 379 K) and at the In site in Ni2MnIn (Tc = 323 K), Cu2MnIn (Tc = 500 K), and Au2MnIn (Tc = 140 K). Measurements utilized the 84-nsec, 247-keV state in Cd-111. The temperature dependence of the hyperfine field, up to approximately .9Tc, was measured for Ni2MnGa, Ni2MnIn, and Cu2MnIn; in each case it approximately follows te Brillouin curve for J = 5/2. The sign of the hyperfine field at Cd has been measured to be negative at room temperature in Ni2MnGa, Ni2MnIn, and Cu2MnIn.
Pressure effect on the Curie point of the Heusler alloys Ni2MnSn and Ni2MnSb
Authors: Kaneko T. , Yoshida H. , Abe S. , Kamigaki K.
Published: February 2003

The pressure effect on the Curie point of the Heusler alloys Ni2MnSn and Ni2MnSb was measured. The pressure coefficients of the Curie point were determined to be (1/Tc) (dTc/dp) = 1.6×10−3 1/kbar for Ni2MnSn and 9×10−3 1/kbar for Ni2MnSb, respectively. The volume exchange striction of Ni2MnSn was also studied. The pressure coefficient of the Curie point estimated from the result of exchange striction was found to be 1.4×10−3 1/kbar, which is in good agreement with that by the direct measurement. The results are discussed on the basis of the molecular field theory taking account of the strain dependence of the exchange interaction and the Castellitz’s interaction curve.
Magnetoelastic properties of Sm1−xRxFe2 compounds
Authors: Bauminger E. R. , Savage H. T.
Published: February 2003

We have investigated the Mössbauer effect in SmFe2, Sm.9Dy.1Fe2 and Sm.7Ho.3Fe2. The easy axes of magnetization (EAM) as a function of temperature was determined. We find the Debye temperatures shift to lower values as the easy axis rotates toward 〈111〉. The Debye temperatures obtained here by observing the recoil-free fraction (RFF) at the iron sites are higher than values obtained from the RFF at the rare-earth sites or from ultrasonic data.
A study of the rhombohedral distortion of the magnetostrictive samarium-iron compounds with addition of molybdenum or vanadium
Authors: Liu Zen-Bao , Tai Li-Chi
Published: February 2003

The mechanical hardness and magnetostriction of annealed pseudo-binary compounds, based on the binary Laves phase, SmFe2 compound with additions of small percentage of Cu, Ni, V or Mo, have been studied. It is found that the compounds containing Mo have optimum hardness and values of magnetostriction. The pseudo-binary compounds SmFe2−xMox and SmFe2−xVx (x = 0.05, 0.1 and 0.2) have been studied by using X-ray counter diffractometer. Owing to the broadening and the splitting of line profiles at higher Bragg angles, a precision determination of lattice parameters becomes difficult. From the data the angles of rhombohedral cells and the relative change in lattice spacings of cubic (400) reflections in these compounds have been calculated.
Quadrupolar interactions in TmCu
Authors: Morin P. , Schmitt D.
Published: February 2003

The existence of quadrupolar interactions (exchange and magnetoelastic couplings) has been unambiguously proved in cubic rare earth intermetallic compounds. Separating the quadrupolar exchange and the magnetoelastic coupling, to study the disordered range, seems to be the most suitable : it is possible to develop perturbation theory applications and achieve all the symmetry lowering modes. The reliability of specific experiments such as ultrasonic velocity, parastriction and third order magnetic susceptibility measurements, is shown about TmCu. As in other isomorphous Tm compounds, quadrupolar interactions appear to be strong enough to compete with the bilinear ones and to be involved in the stability of the two commensurate and modulated antiferromagnetic structures.
Interaction effects in a random anisotropy crystalline alloy
Authors: Hadjipanayis G. , Gaunt P.
Published: February 2003

Crystalline alloys of Pt0.7Ni0.3Fe have been aged to produce regions of ordered tetragonal material whose size increases with aging time. The c axes are magnetic easy directions. The c axes of neighboring regions are at approximately 90° to each other. The magnetization curve of an alloy aged for 60 min at 695°C can be exactly superposed on the curve for 2900 min aging if it is shifted along the field axis by an exchange field λM, where λ is an interaction constant and M is the magnetization. Magnetization curves at 294 and 4.2 K, although very different, give similar values for λ. The value of λ found (26.4 cm3Oe2 erg−1) is consistent with the expression λ∼4(√AK)/(tMS2) where A is an exchange constant, K is the magnetic anisotropy energy density, t is the thickness of the lamellar tetragonal regions and MS is the spontaneous magnetization.
Determination of gas temperature and density by measuring ultraviolet gas absorption at two wavelengths
Authors: Wampler F. B. , Gentry R. A.
Published: February 2003

A technique is described which demonstrates how deployment of two different uv wavelengths may be utilized in absorption measurements to simultaneously derive both the temperature and number density of a gas. A mathematical formulation is presented which defines how one can estimate the sensitivity of the technique.
Magnetic ordering in amorphous and crystallized Fex-Ge1-x films
Authors: Randhawa H.S. , Malhotra L. K. , Chopra K. L.
Published: February 2003

Magnetic ordering in amorphous a-Fex-Ge1-x thin films, in the composition range 0.10⩽×⩽0.60, deposited at room temperature (300 K), has been studied using Ms̈sbauer spectroscopy, Curie termperature, and Lorentz electron microscopy observations. The absence of magnetic ordering was noted in a-Fex-Ge1-x films for x<0.40 down to 4.2 K. The onset of long-range magnetic ordering occurs at x≃0.5 even at room temperature. However, Fex-Ge1-x films for x⩾0.50 were found to be polycrystalline in nature. The absence of ferromagnetic ordering for x⩽0.40 is consistent with the rather small magnetic moment of Fe in the amorphous phase. The Fex-Ge1-x films for x⩾0.50 were found to contain the various intermetallics of Fe-Ge binary. In these intermetallics, Fe is known to possess a large magnetic moment and thereby the long-range magnetic ordering is being observed in these films.
Measurement of the proximity effect in ferromagnetic-normal metal thin film sandwiches
Authors: Meservey R. , Tedrow P. M. , Kalvey V. R.
Published: February 2003

A spin polarized tunneling measurement shows that ferromagnetism is suppressed in films of Ni thinner than three atomic layers when in contact with Al. In contrast, ferromagnetism was found in Fe, Co, Gd, and Tm films only one atomic layer thick when backed with Al. The present results agree with measurements of Ni, Fe, and Co using the anomalous Hall effect, but do not agree with photoemission results on Ni.
Electronic structure and magnetism of CuNi coherent modulated structures
Authors: Jarlborg T. , Freeman A. J.
Published: February 2003

The electronic structure and magnetism of coherent modulated structures of CuNi for varying numbers of Cu and Ni layers modulated along [111] and [100] directions has been determined theoretically by means of self-consistent spin polarized LMTO energy band studies and compared with experiment and with theoretical results separately obtained for bulk fcc and tetragonally distorted Ni metal. The magnetic moments in the Ni layers in CuNi are found to be reduced relative to that of fcc Ni indicating that the enhanced magnetism deduced from earlier ferromagnetic resonance observations must arise from other sources. These predictions have been confirmed recently by direct magnetization and neutron magnetic scattering studies.
Induced magnetization density in the 5f system UAl2
Authors: Rakhecha V. C. , Lander G. H. , Arko A. J. , Moon R. M.
Published: February 2003

Using a polarized-neutron diffractometer we have studied the induced magnetization density in the unit cell of the 5f system UAl2. Measurements have been made on single crystals at 4.2 K with an applied magnetic field of 42.5 kOe (induced magnetic moment 0.0344 μB per mole). Neutron wavelengths of 1.067 and 0.785 Å and different crystal thicknesses have been used to correct for and eliminate any effects from extinction. The major part of the magnetization density appears as a contribution localized at the U site, exhibiting a form factor similar to that of the f3 free ion, and extrapolating in the forward direction to the value given by the bulk susceptibility. However, there are two interesting aspects of the density. First, the form factor points differs significantly from a smooth curve. This indicates asphericity in the 5f electron distribution arising from the crystalline environment of the U atoms. Second, and more unusual, finite magnetic scattering amplitudes have been observed for a series of reflections to which the centrosymmetric density at the U site cannot contribute. We consider this as strong evidence of noncentrosymmetric bonding involving the 5f–6d electrons.