bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitation spectra of generalized antiferromagnetic Heisenberg spin chains (abstract)
Authors: Parkinson J. B. , Bonner J. C.
Published: July 2002

We compare the excitation spectra in the presence of a magnetic field of a number of integrable (exactly solvable) and nonintegrable quantum spin chains of various spin value s. The archetypal Bethe-ansatz integrable model is the s= 1/2 Heisenberg antiferromagnet (HB AFM). The excitation spectra are characterized by a soft mode which tracks across the Brillouin zone as the field increases to its saturation value. A class of Bethe-ansatz integrable models with SU(2) symmetry and the general spin s display excitation spectra qualitatively similar to the spin- 1/2 model above, for all s. A second class of Bethe-ansatz integrable models has SU(n) symmetry, where n=2s+1. Like the SU(2) integrable chains, these models have gapless excitation spectra, but the basic Brillouin zone changes from k=±2π/(2s+1)a. Studies show that periodicity of the SU(3) member of the class changes (increases) as the field increases to saturation. For both classes of integrable models, there is a single type of excitation pattern which is generically similar for all s. In the case of the other models, on the other hand, numerical studies show that the excitations divide into at least two distinct classes. In the case of the s=1 HB AFM, at high fields (corresponding to SzT=N,N−1, . . .,N/2) the excitations map approximately onto the complete set of excitations for s= 1/2 , whereas at low fields (SzT=N/2,N/2−1,. . .,0) the excitations have notable classical character. In the case of the s=1 model with pure biquadratic exchange, one set of excitations, corresponding to SzT even (SzT=N,N−2,. . .,2,0), again shows an approximate mapping to the complete excitation set for s= 1/2 . The second class of excitations, corresponding to SzT odd, are very different. They are symmetric about k=±π/2a for all SzT, i.e., correspond to a basic Brillouin zone of ±π/2a.
Theoretical studies of high T
c superconductors (invited) (abstract)
Authors: Scalapino D. J.
Published: July 2002

The current theoretical ideas concerning the mechanism responsible for the high transition temperature of the superconducting oxides will be reviewed.
Measured fields and performance of recording heads
Authors: Brug J. A. , Gill H. S. , Murdock E. , Naberhuis S. , Tarnopolsky G. , Simmons R.
Published: July 2002

A method is presented for obtaining the longitudinal magnetic field produced by recording heads. The method entails the use of a microloop to directly measure the perpendicular field Hy across the gap region of the head and the calculation of the longitudinal field Hx using a transform of Hy(x). This method has been applied to the study of narrow-track, thin-film heads. The ability to predict the shape of the readback waveform from a measurement of the head field is demonstrated.
Substitutional site preference in a quasicrystal
Authors: Eibschütz M. , Lines M. E. , Chen H. S. , Waszczak J. V. , Papaefthymiou G. , Frankel R. B.
Published: July 2002

Iron has been successfully incorporated in the quasicrystal i-Al74Si6Mn20−xFex up to a concentration x=7. A combination of magnetic susceptibility and Mössbauer study establishes the fact that there are at least two ‘‘classes’’ in Mn sites and that Fe substitutes for only one of them. High-field Mössbauer measurements at 4.2 K show that the substituted iron carries no local moment, while low-temperature susceptibility data indicate that its presence does not perturb the Curie–Weiss amplitude of the sample. The inference is that both magnetic and nonmagnetic Mn sites must be present in the quasicrystal and that iron can substitute only from among the latter. The simplest interpretation would be in terms of two ‘‘classes’’ on Mn sites (one supporting a local moment, one not), although the possibility of there being more than one class of nonmagnetic site cannot yet be excluded.
Epitaxial film growth and metastable phases of single crystal Dy by molecular beam epitaxy
Authors: Yang Kai-Yueh , Homma Hitoshi , Schuller Ivan K.
Published: July 2002

We have grown two novel epitaxial phases of dysprosium (Dy) on vanadium (V) by the molecular beam epitaxy technique. Surface structures are studied by in situ reflection high-energy electron diffraction, and bulk structures are studied by x-ray diffraction after removal from the growth chamber. The new hcp phases are ∼4% expanded uniformly in the (0001) plane and ∼9% and ∼4% expanded out of plane, along the c axes, for noninterrupted and interrupted deposition cases, respectively. We also observed (2×2), (3×3), and (4×4) Dy surface reconstruction patterns and a series of structural changes as the Dy film thickness increases.
Local structure of Al75(Mn,Cr,Ru,Re,Si)25 icosahedral alloys studied by pulsed neutron scattering (abstract)
Authors: Dmowski W. , Egami T. , Bancel P. A. , Heiney P. A. , Volin K.
Published: July 2002

The discovery of an icosahedral phase in a rapidly quenched Al-Mn1 alloy has stimulated intensive research on the structure of these materials. We studied several single-phase icosahedral alloys to address a problem of isomorphous substitution and quasicrystallinity in these solids. The use of neutrons is attractive because the neutron scattering length of Mn is negative and this provides additional diffraction contrast. Since icosahedral solid lacks translational symmetry we used approach based on the pair distribution function (PDF) which gives an averaged distribution of interatomic distances. We observed significant differences in the diffraction pattern (DP) depending on kind of element that substituted Mn. For instance partial substitution by Cr resulted in strong (110000) peak while (100000) remained very weak. After total substitution DP was still different from the x-ray DP for Mn. For Ru the (100000) peak was the strongest whereas for Re (110000). Substitution of Al by 3% of Si caused an increase of (100000) and (110000). The peak positions in PDFs correspond well to distances calculated for the three-dimensional Penrose tiling, suggesting the presence of a quasicrystalline substructure. The observed changes in diffraction patterns and PDFs indicate nonrandom substitution in these alloys, for instance, Ru is found only on vertices. The vertex-vertex distances are predominantly observed in Al-Mn positional correlations. The effect of compositional order on local structure and magnetic properties will be discussed.
High T
c thin-film superconductivity: Science and technology (invited)
Authors: Geballe T. H.
Published: July 2002

Thin films of high Tc superconducting oxide structures have been synthesized by a number of different methods by Stanford researchers. High-quality films are believed to be yielding intrinsic electrical and optical properties which have scientific and technological implications.
Spatially dependent correlation functions in the Anderson model (abstract)
Authors: Chen Kan , Jayaprakash C. , Krishnamurthy H. R.
Published: July 2002

We report results from a first principles calculation of spatially dependent correlation functions around a magnetic impurity in metals described by the nondegenerate Anderson model. Our computations are based on a combination of perturbative scaling theory and numerical renormalization group methods. Results for the conduction election charge density around the impurity and correlation functions involving the conduction electron and impurity charge and spin densities will be presented. The behavior in various regimes including the mixed valent regime will be explored.
Improved calculations of magnetoelastic properties in collinear metamagnets
Authors: Tuszyński J. A.
Published: July 2002

Metamagnets such as Mn3GaC, Fe-Rh, Mn2−xCrxSb, and Mn1−xCrxSb exhibit strong magnetoelastic couplings via strain dependence of exchange integrals. The purpose of this paper is to improve the calculations of the relevant elastic and magnetic ensemble averages for model Hamiltonians using some novel non-Gaussian approximations. The results derived are applicable to a wide range of magnetically ordered spin systems placed on anharmonic crystal lattices in the presence of an exchange-striction mechanism. It is found that the commonly invoked polynomial series expansions for the temperature dependence of the displacement and magnetization are valid only at sufficiently low temperatures. At significantly higher temperatures exponential series expansions are found to be more appropriate. Intermediate temperature ranges involve special functions of the parabolic cylinder type.
Compositional dependence of recording noise in amorphous rare-earth–transition-metal magneto-optical disks
Authors: Nagato K. , Kawamoto A. , Sato T. , Yorozu T.
Published: July 2002

The compositional dependence of recording-power sensitivity and recording-noise characteristics of TbFeCo and TbDyFeCo films have been studied systematically. The sensitivity depends on the compositional ratio of rare earth (RE) and transition metal (TM) rather than on Co content. This is explained by the fact that the temperature at which the coercive force (Hc ) coincides with the bias magnetic field of 500 Oe, hereafter denoted as T′, varies drastically by altering the RE-to-TM ratio. High recording noise is observed for compositions having Tcomp close to TC. When TC−Tcomp≳70 °C, optimal carrier-to-noise ratios are obtained. These results are explained qualitatively by the behavior of domain-wall motion in the vicinity of the magnetically reversed domain.
Sublattice magnetization and spin reorientation in Nd2Fe14B (abstract)
Authors: Muraleedharan K. , Kaindl G. , Wortmann G. , Perscheid B. , Koon N. C.
Published: July 2002

Considerable efforts have recently been made in understanding the magnetic behavior of the rare-earth transition-metal compound Nd2Fe14B, which orders ferromagnetically at Tc=600 K and exhibits a spin-reorientation transition at TSR=135 K. In an effort to obtain direct information on the spin configuration and magnetic ordering in this technologically important compound, we have performed a Nd-145 Mössbauer study on a single crystal of Nd2Fe14B using the 72.5-keV nuclear gamma resonance of Nd-145. The results clearly show that the temperature dependence of the Nd-sublattice magnetization is totally different from that of the macroscopic magnetization, i.e., dropping off far below Tc. The results suggest that the spin-reorientation transition in Nd2Fe14B is driven by an ordering of the Nd sublattice below TSR.
Collective density fluctuations in heavy-fermion systems (invited)
Authors: Fulde P. , Becker K. W.
Published: July 2002

Density fluctuations in heavy-fermion systems are discussed. Particular attention is paid to the hydrodynamic modes and it is pointed out how they differ from those of ordinary metals. A large Landau–Placzek ratio should help to make the quasiparticle diffusion mode observable. The role of the Coulomb interaction is discussed and it is shown that a low-lying optical plasmon should exist. The latter can be overdamped. It compliments the acoustic plasmon (or zero sound) mode into which the quasiparticle diffusion mode goes over for q values outside the hydrodynamic regime. In a recent experiment quasielastic light scattering due to density fluctuations has been observed in UPt3. Furthermore, it is shown that the attenuation mechanism of longitudinal ultrasound in heavy-fermion systems is very different from that of ordinary metals.
Photoemission and BIS spectra of narrow-band uranium systems (abstract)
Authors: Riseborough P. S.
Published: July 2002

The joint photoemission and inverse photoemission spectra should yield the density of states for removing or adding an electron to the system. In the heavy fermion systems there is a large discrepancy between the experimentally measured density of states and the density of states obtained from local density functional band structure calculations. This discrepancy is clearly indicative of manybody effects. Arko and collaborators1 have recently discovered that similar manybody anomalies can be found in the narrow-band uranium systems. In a systematic series of studies on uranium compounds and alloys, it was observed that for the systems in which the f  bands are expected to be more localized, the one-electron spectra were found to be broader. We have performed calculations using an N-fold degenerate Hubbard model, utilizing an expansion in the Coulomb interaction. The infinite set of diagrams containing independent single loops have been evaluated. This approximation should be exact in the limit N→∞. We obtain a qualitative agreement with the experimental findings.
Magnetic ac susceptibilities of CsMnF4⋅2H2O and NH4MnF4⋅2H2O weak ferromagnets (abstract)
Authors: Andrés Mercedes , Palacio Fernando , Lahoz Fernando
Published: July 2002

The influence of a strong Jahn–Teller effect, present in high spin Mn (III) compounds, favors a tendency to form chains or layers of corner sharing octahedra. Therefore, fluoromanganate (III) derivatives so far investigated have exhibited lower dimensionality magnetic properties.1,2 In this communication we present what appears to be the first two examples of three-dimensional magnetic behavior in fluoromaganate (III) systems. Magnetic ac susceptibilities of the titled compounds have been measured on single crystals in the temperature range of 1.1 to 4.2 K and on powdered samples between 4.2 and 100 K. Measurements show a smooth increment in the susceptibility down to about 4 K where an abrupt increase and very sharp peaks of about 0.4 K half width appear at 1.75 and 1.55 K for the NH4 and Cs derivatives, respectively. The fit from high-temperature series expensions for a Heisenberg S=2 simple cubic lattice gives ‖J‖/k=0.08 K with g=2.00 for the NH4MnF4⋅2H2O and ‖J‖/k=0.06 with g=2.00 for the CsMnF4⋅2H2O.
Magnetic properties of some FeCl−4 salts (abstract)
Authors: Lowe Carol , Zora J. A. , Seddon K. R. , Carlin Richard L.
Published: July 2002

The compound of stoichiometry [(4-chloropyridinium) FeCl4]2⋅4-chloropyridinium chloride is found to belong to the space group P21/n. The unit cell consists of eight FeCl4 anions, twelve [4-ClpyH]+ cations and four chloride ions. The ac susceptibility at zero-applied field, which was measured on a polycrystalline sample, exhibits a sharp peak with a maximum at Tc=2.725 K. This is behavior characteristic usually of either a ferromagnet or a canted antiferromagnet. The analogous pyridinium salt has the same constitution and orders at 2 K; the existence of canting in this compound is less evident. The ethylammonium compound orders at 2 K as well. These materials belong to a large series of tetrahaloferrates which exhibit unusual magnetic behavior and which are under extensive investigation.
On the anisotropy energies for YCo5, RCo5, Y2Co17, and R2Co17
Authors: Takahashi H. , Hikosaka K. , Ohtsuka S. , Seo A. , Ukai T. , Mori N.
Published: July 2002

The approximate d bands for YCo5, RCo5, Y2Co17, and R2Co17 (Th2Zn17 and Th2Ni17 type) are formulated by Deegan’s prescription and the formulas of Slater and Koster. The experimental results of YCo5 and Y2Co17 are discussed by using these approximate d bands. For RCo5 and R2Co17 the discussions are made by adopting the localized model and the band model for 4f electrons.
Magnetic properties, hyperfine interactions, and spin dynamics in the layer compounds CsVF4 and RbVF4
Authors: Ziolo J. , Corti M. , Borsa F. , Rigamonti A. , Paleari A. , Spinolo G.
Published: July 2002

The magnetic properties of the layer compounds CsVF4 and RbVF4 have been investigated by means of magnetic susceptibility measurements and by NMR and relaxation measurements of 19F, 133Cs, and 87Rb nuclei. The crystals are found to undergo an antiferromagnetic transition at about 50 K with weak ferromagnetic behavior and pronounced two-dimensional correlations. The paramagnetic shift and the relaxation rates are analyzed in terms of the hyperfine fields generated by the magnetic vanadium ions.
Electron-hole interaction in TmSe1−xTex under pressure
Authors: Neuenschwander J. , Wachter P. , Bührer W. , Fischer P.
Published: July 2002

Semiconducting TmSe1−xTex (x=0.55, 0.68) reveals at low temperatures an anomalous peak structure in the resistivity pressure relation followed by a first-order transition into a metallic state. It is believed that the electron-hole interaction plays an important role and speculated that these data show the transition from a normal semiconductor to an excitonic insulator followed by a transition into an electron-hole liquid. Neutron scattering indicates ferromagnetism in pressure-driven metallic TmSe0.45Te0.55 below ∼5 K.
A three-octave-band bandwidth Y circulator (abstract)
Authors: Duh Young Mouh
Published: July 2002

So far the limit bandwidth of Y circulators has been an octave. Now a three-octave-band bandwidth Y circulator whose isolated port loss is above 17 dB in the frequency range from 2.5 to 9 GHz can be obtained owing to two arts being adopted. The continuous tracking circuit is used [that is, a series impedance X is connected to the electrical center of junction X=j(ωL−1/ωC), there being ωCL=1/ωCC at circulating angular frequency ωC ], the reactance slope parameter of imaginary part of circulating imput impedance1 being adjusted to zero or nearly so. Values K/μ or P(=M/ω) are kept unchanged by modulating the internal bias field H0 with the frequency of the input signal so as to make the value of unsaturated magnetization intensity M change with the change in frequency ω at same rate.
Automatic field problem formulation for CAE stations
Authors: Hoole S. Ratnajeevan H. , Vidyasagar Samuel , Weeber Konrad
Published: July 2002

A requirement for the successful spread of computer-aided engineering techniques in the analysis of electromagnetic devices is that the program should be usable by the uninitiated. Many advances have been made in devising interactive, easy to use programs that can be used in the classroom and in design. However, the use of these programs presupposes the ability of the user to formulate the correct boundary-value problem. While it is straightforward to impose a far-away Dirichlet boundary, lines of symmetry must be used to reduce the problem to a smaller one with the proper Dirichlet and Neumann boundaries, and no program does this. In this paper a program that automatically formulates the problem is introduced. The rules for searching for lines of symmetry and region reduction are formalized for axisymmetric and translationally symmetric problems.
Miniaturization limit of a cloth inductor
Authors: Matsuki H. , Miyazawa H. , Murakami K. , Yamamoto T.
Published: July 2002

A cloth-structured magnetic device was designed, and the optimized relation between amorphous fiber and conductive fiber size was shown. The inductance, equivalent resistance, and quality factor of cloth-structured magnetic devices were calculated. Furthermore, the stray capacitance of the device was estimated from the analysis of an equivalent circuit. A cloth inductor of only 0.7 mm thickness could be made, which could have an inductance of 100 μH, a rating current of 100 mA, and a quality factor over 60. Regarding the further miniaturization of the device, the magnetic flux distribution established inside the cloth inductor was measured. The miniaturization limit was estimated, which was influenced by the magnetic permeability and the aspect ratio of the fibers.
Microstructure of oblique incidence CoNi thin films (abstract)
Authors: Ho H.-M. , Thomas G. , Gau J.-S.
Published: July 2002

Because of its application as recording media for high-density recording, oblique incidence thin films have been studied by many investigators. It is well known that oblique incidence thin films have a columnar structure, however, localized microstructural information, i.e., obtained directly from individual columns, has not yet been reported. In this study, the microstructure of CoNi oblique incidence thin films have been examined by transmission electron microscopy and microdiffraction technique. Results of thin films prepared with various incident angles indicate that the columns in oblique incidence thin films are single crystals and the c axis of the columns does not necessarily coincide with the column axis. These results and results of the effect of incident angle on column alignment and on the c-axis texture will be presented in this paper.
Fe-based semimagnetic semiconductors (invited)
Authors: Mycielski Andrzej
Published: July 2002

Recently, the family of semimagnetic semiconductors (SMSC) or diluted magnetic semiconductors (DMS) typically involving manganese ions, i.e., Cd1−xMnxTe, Cd1−xMnxSe, Zn1−xMnxTe, Hg1−xMnxTe, was extended to include iron ions in selenium and tellurium II-VI compounds. Contrary to Mn-based DMS where d states of Mn are energetically superimposed on the valence-band continuum, for Cd1−xFexSe and Zn1−xFexSe the Fe2+(3d6) is a donor whose energy level lies deeply in the energy gap. On the other hand, for Hg1−v−xCdvFexSe with x≤0.15 and v≲0.40, the Fe2+ level is a resonant donor located in the conduction band. Also in the case of this material, the mobility of free electrons is surprisingly high, while the Dingle temperature is low. Because of the Coulomb interaction between the ionized donors Fe3+(3d5) at low T, there will appear a correlation of the positions of charges in this system. This leads to a kind of ‘‘condensation’’ of the charges in the system of donors and to their ‘‘crystallization’’ at even lower T (i.e., formation of a ‘‘charge superlattice’’ or a localized Wigner crystal of ionized donors). The space ordering of ionized donors dramatically influences the free-carrier scattering and consequently leads to high mobilities and low Dingle temperatures. Another implication of intersite repulsion is the existence of the Coulomb gap in the one-electron d-band density of states. We discuss some of the effects related to its formation. We shall also present some magnetic properties of these new DMS: the specific heat, magnetic susceptibility, and the magnetization.
The structural model of the interglobular voids in chains of magnetic metal powders (abstract)
Authors: Mehandiev D. R. , Dragieva I. D. , Slavcheva M. S. , Buchkov D. T.
Published: July 2002

The theoretical structural models of the chains from single-domain globules as types I and M are presented. The chain of a model type M possessing a hexagonal cross section and with prevailing octahedral voids are typically for powders, obtained by chemical reduction process. The chain of a model type I possessing a pentagonal cross section and tetrahedral voids are established for powders prepared by the same process with application of dc magnetic field. Some experimental results and an interpretation of the physical properties of these powders confirming the differences between structural models: types I and M of chains of single-domain globules are discussed.
Overview of magneto-optic isolator materials and devices (invited) (abstract)
Authors: Tsushima K.
Published: July 2002

Recent research and developments on magneto-optic materials and devices using nonreciprocal properties are described. Investigations on the growth of Bi-substituted iron garnet bulk crystals and LPE-grown thin films are extensively carried out, and high quality and compact isolators for near-infrared wavelengths are realized. Temperature coefficient of the angle of Faraday rotation is decreased enough by using a combination of Bi and rare-earth ions substituted in these host garnets. These materials are also used as magneto-optic switches and magnetic field (current) sensors. Basic research on waveguide-type of magneto-optic devices is another subject. It is shown that growth-induced birefringence found in LPE-grown Bi–rare-earth iron garnet films is effective to achieve phase matching between TE and TM modes in a planar waveguide. The author would like to summarize some other subjects on magneto-optic recording materials being done at many research laboratories.
Faraday rotator materials for lasers (invited) (abstract)
Authors: Weber M. J.
Published: July 2002

Materials exhibiting strong Faraday rotation are of interest for components in laser systems. These include optical isolators, circulars, modulators, and switches in sizes ranging from microdevices for integrated optics to 30-cm-diam rotators for Nd:glass lasers used in inertial confinement fusion research. Properties of diamagnetic, paramagnetic, ferromagnetic, dilute magnetic semiconductors and free carrier rotators have been evaluated for various laser applications and for operation in the spectral range from the infrared to the ultraviolet and at various temperatures. Both crystalline and amorphous materials are considered; forms include bulk materials, fibers, and thin films. The characteristics of selected materials, including bismuth-substituted rare-earth iron garnets, Cd1−xMnxTe, and rare-earth doped glasses and crystals, are discussed. Relative figures of merit based on specific rotation, losses, cost, and special properties such as the nonlinear refractive index are also given.
Direct investigations of Bloch line memory functions by wall resonance spectroscopy
Authors: Heidmann J. , Krause H. , Engemann J.
Published: July 2002

Pairs of vertical Bloch lines (VBL) stabilized by a periodic in-plane field potential are the storage elements in the Bloch line memory concept. Wall resonance spectroscopy (WRS) is used for the verification of VBL’s in a wall section equivalent to one memory cell of a locally stabilized stripe domain. This corresponds to an area of about 5×5 μm in a 5-μm bubble garnet film. The sequential VBL propagation induced by z-field pulsing was demonstrated directly by means of a simple test chip with current VBL confinement, and a current loop for the drive pulses as main features. VBL detection is simply carried out by exciting the domain wall, which resonance signal vanishes when a VBL is present. The stripe is stabilized inside a 10% groove. Moreover, the local wall mass as well as the restoring constant could be inferred from the resonance line shape. The first WRS experiment with very high local resolution (2 μm) applied to localized stripe domains clearly demonstrates its potential usefulness for device testing, error mode detection, and optimization.
Generation of vertical Bloch lines in ion-implanted (111) garnet films
Authors: Fernandez-de-Castro J. J. , Friedlaender F. J.
Published: July 2002

In the rotating gradient experiment (RGE), a magnetic bubble moves continuously in a circular trajectory, and vertical Bloch lines (VBL) are generated from Bloch curves (BC) when field gradients are increased. Three samples, from the same wafer, are studied by means of the RGE. Two of the three samples have been ion implanted at 200 keV with Ne+ at 1 and 2×1014 atoms/cm2. The dynamic transitions and the bubble states, winding number (S), and the dimensionless momentum (p) are investigated for the implanted and unimplanted samples. Changes in S and p are observed in the unimplanted sample, but only p can be modified in the implanted films. The experimental data gives evidence that the value of p always increases by two after each of the dynamic transitions in the implanted samples. Also, changes (Δp) in the value of p, in the intermediate region between transitions, are a result of an increase in the size of the BCs. The increase in resistance to growth and punch-through of BCs, and to translation of VBLs is found to cause the velocity and Δp of implanted films to increasse further in the region between transitions. The bubble trajectories in the unimplanted and lightly implanted samples form circles for all bubble states observed. However, the heavily implanted sample exhibits an elliptical trajectory because the bubble translational velocity changes with position as a result of an in-plane anisotropy. The ratio of the major to the minor axes is sometimes larger than 2.
On the ferro-cone-fan magnetic transitions in MnP
Authors: Becerra C. C. , Oliveira N. F. , Migliano A. C.
Published: July 2002

By measurements of ac susceptibility we have studied the phase boundaries on MnP in the vicinity of the point where the ferromagnetic, the cone, and the fan phases meet. The present data are consistent with the assignment of second order to the cone-fan transition line. This line, then, ends at a critical end point on the ferromagnetic boundary.
Crossover of the spectral weight function: A new interpretation of some large q neutron scattering data (abstract)
Authors: Chow Lee , Fisher David
Published: July 2002

Dynamic scaling theory proposed by Halperin and Hohenberg has been successfully applied to small q neutron scattering data in the past. However, some large q constant E scan neutron scattering data on Fe1 and Ni2 cannot be explained by the dynamic scaling theory with a Lorentzian spectral weight function. Here we proposed that the spectral weight function crosses over to a Gaussian function at large q. With this crossover hypothesis, we were able to explain the qw vs q0 behavior in the constant E scan data, and the discrepancy in the material-dependent constant A, obtained from large and small q data. The physical origin of this crossover phenomena can be explained as follows. At large q, each neutron probes a small region in the sample, and the overall effect will be an inhomogeneously broadened line shape, namely a Gaussian spectral weight function. Recently Folk and Iro3 proposed an asymptoic RG theory approach to explain the discrepancies between large q neutron data and the dynamic scaling theory. Our proposed Gaussian line-shape function is in excellent agreement with the line-shape function obtained by Folk and Iro at large q.
Magnetic tricritical behavior of ethylammonium tetrachlorocuprate
Authors: Long Jerome R. , Haines Donald N. , Drumheller John E.
Published: July 2002

In order to investigate the prediction by Tuthill that a tricritical point may exist in the phase diagram of spin-flop antiferromagnets with intermediate anisotropy, an experimental reexamination of the phase diagram of the quasi-two-dimensional system (C2H5NH3)2CuCl4 was performed. Measurements were made of the differential magnetic susceptibility, dM/dH, vs dc field and temperature in the (10 K, 100 Oe) region of the proposed tricritical point. A low amplitude, low frequency, ac biphase SQUID susceptometer was used. The sample was a single crystal with field along the antiferromagnetic easy (orthorhombic a-axis) direction. The data show some evidence of the existence of at least one tricritical point, but the results are not definitive.
Precision measurements of the magnetization and its temperature derivative of Ni and dilute Ni alloys at 290 K
Authors: Hunter D. , Arrott A. S. , Grynszpan R. I. , Dassonvalle P. , Langlois P.
Published: July 2002

Precision measuring techniques (±5 ppm) are applied to correct μSR (muon spin rotation) data for the effect of the Lorentz field. The samples are high-purity Ni and Ni alloys in the form of short cylinders. Some of the samples contain voids. While not a problem for μSR, it is for the measurement of magnetization. Data are presented for the magnetization and its temperature derivative of dilute alloys of Ti, V, and Cr in Ni at 290.5 K.
The contribution of Cu2+-Cu2+ pairs to EPR (abstract)
Authors: Shen Guo-Yin , Xu Chang-qing , Bai Gui-Ru
Published: July 2002

A theoretical description is given of the exchange interaction between two Cu2+ ions in φ4AsCuCl3 crystals. The crystal field theory is used to investigate the single Cu2+ ion in the crystal, which is the basis of the further consideration of Cu2+-Cu2+ pairs exchange interaction Js1s2. The theoretical expressions of the transition energy levels, magnetic susceptibility, g factors, and zero-field splitting have been obtained. The calculation results agree with the experiment. The agreement between the calculation result of D(−0.116 cm−1), E(0.041 cm−1), and that of experiment D(−0.11 cm−1) E(0.009 cm−1) in φ4AsCuCl3 implies that the zero-field splitting is mainly due to the exchange interaction, the crystal field, and the spin-orbit coupling. Since the J value here is not large, the Cu2+-Cu2+ pairwise coupling contributes little to the electronic splitting and g factors, which is just the experimental results. In the calculation of pairs contribution, no adjustable parameters are introduced. So it is possible to obtain the EPR parameters as long as we know the crystal structure.
High-resolution magnetic imaging by force microscopy (invited) (abstract)
Authors: Wickramasinghe H. K. , Martin Y.
Published: July 2002

The scanning tunneling microscope is a unique tool which is capable of imaging conducting and semiconducting surfaces with atomic resolution. More recently, the atomic force microscope has been able to extend the class of objects that can be imaged with atomic resolution to include insulators. The work in this paper is concerned with a modified version of an atomic force microscope—the laser heterodyne force probe— which is capable of measuring force gradients (magnetic and other) down to 10−6 N/m and forces down to 10−12 N with high spatial resolution. Magnetic images are obtained by measuring the forces on a magnetized iron tip as the tip is rastered across the sample to be imaged and displaying the result on a computer display. The forces and force gradients are measured through a change in oscillation amplitude of the ‘‘vibrating reed’’ tip when the tip is driven at or near its fundamental resonance. Images of both dynamic fields from a thin film magnetic recording head and static fields from written domains have been obtained with 1000-Å resolution. With further work we believe it should be possible to improve this resolution to around 100 Å.
Magnetoresistive measurement of the exchange constant in varied thickness Permalloy films (abstract)
Authors: Smith N. , Markham D. , Doyle W. , LaTourette D.
Published: July 2002

A recently developed method1 for the magnetoresistive measurement of the exchange constant in Permalloy films is applied to multiple films of varied thickness. Passing a dc current along the easy axis of a thin-film single-domain Permalloy stripe generates an inhomogeneous internal magnetic field. This field opposes exchange forces and causes the film magnetization to fan in opposite directions through the film thickness, forming a variable angle Bloch wall parallel to, and extending throughout, the film plane. The magnetization fanning is readily observable via dc magnetoresistive detection. Values for the exchange constant A are obtained by comparing experimental measurements with a micromagnetic model1 that employs A as the single free parameter. Present measurements on several films of thickness between 2000 and 4000 Å confirm the predicted strong film thickness dependence of magnetization fanning amplitude, and are all shown to be consistent with a single value for the Permalloy exchange constant of A=1.1±0.1×10−6 ergs/cm. This value is equal to the previous1 independently obtained value. The present technique for measurement of A is demonstrated to yield consistent values for the exchange constant in different films of varied thickness, and does not require additional postulates (as do spin-wave resonance techniques) concerning surface anisotropy or saturation magnetization inhomogeneities.
Influence of oxygen on recording characteristics in vacuum-evaporated Co-Cr thin films
Authors: Kugiya F. , Suzuki M. , Kanno F. , Yoshida Y. , Kitakami O. , Fujiwara H. , Speliotis D. E.
Published: July 2002

The influence of oxygen contamination of Co-Cr thin films during evaporation was investigated by measuring their magnetic properties and recording characteristics. By increasing the amount of added oxygen, perpendicular anisotropy of Co-Cr thin films was degraded, causing an increase of the coercive force Hc and squareness ratio Mr/Ms in the longitudinal direction. In recorded signal characteristics, the addition of oxygen results in a decrease of the dipulse ratio and a degradation of the recording density response through the enhancement of recording demagnetization. In noise characteristics, it results in reverse dc erase noise response with a peak at some reverse current which is characteristic of longitudinal thin-film recording media, while the noise in the presence of signal does not show an increase with increasing recording density, which is quite different from the longitudinal thin films. Another distinctive result was that even a sample with a small amount of oxygen, where magnetic properties and recording density response were roughly the same as the samples without intentional addition of oxygen, showed a very huge dc erase noise.
Optical properties of chemically reduced photochromic glasses
Authors: Borrelli N. F. , Wedding Brent
Published: July 2002

Photochromic glasses subjected to reducing treatments at elevated temperatures develop a colored layer through the reduction of the silver halide phase. The nature of this process is investigated with respect to the temperature and time of the reduction treatment. An explanation of the color development is offered based on the comparison to an alternate way of producing the reduced silver absorption. In addition, the optical bleaching that is observed is discussed and a mechanism is proposed.
Transparent CdZnSO thin films with tailored d spacings
Authors: Qiu S. N. , Qiu C. X. , Shih I.
Published: July 2002

Work has been done to investigate properties of polycrystalline CdZnSO thin films prepared by sputtering. It was found that the magnitude of the diffraction peaks decreased progressively as the ZnO content was increased from 0% to 70% and increased as the ZnO content was further increased from 70% to 100%. The value of the d spacing of the CdZnSO films was also found to be affected by the ZnO content. The absorption edge was examined by transmission measurements and a rapid increase from 2.6 to about 3.2 eV was found in the range from 60% to 80% ZnO.
Spatial and temporal distributions in exploding-wire plasmas
Authors: Vijayan T. , Rohatgi V. K.
Published: July 2002

The effect of small energy pulses (τ∼0.1–10 ns) in exploding-wire plasmas has been analytically investigated in this study. It is shown that the deposited energy distribution is an increasing function of the radial distance in wire. The energy distribution is more pronounced with smaller τ and becomes uniform for τ>10 ns for given wire radius ∼12.5 μm. The resulting fragments exhibit a distribution in sizes and are smaller towards the wire surface due to a higher energy density (E) than around the axis. For E∼Ee (the energy density needed for total evaporation), the fragment sizes range from μm to nm from axis towards surface, respectively. Subsequent to explosion, for E≥Ee, there are distributions in plasma temperature (Tp) and plasma density (Np) as well. Typically for E∼10 kJ/g in copper, Tp is more than a few percent higher at the leading end than in the trailing end. As compared to this, E≫Ee gives a uniform plasma with uniform Tp irrespective of τ. Consequently, uniform plasma can be obtained either with very large E, or in case of small E with large τ.
Evidence of space-charge conduction in a HgI2 crystal
Authors: Ahmad-Bitar Riyad N. , Abdallah M. Al-Haj , Mahmud Y. A. , Wishah K. A. , Abdul-Gader M. M. , Hassan M. A.
Published: July 2002

The ac impedance method was used to deduce the bulk resistance from the complex impedance plane plots for 20-μm-thick HgI2 crystal. The bulk resistance was obtained as a function of temperature from 290 K down to 11 K. Two activation energies, ≂0.24(2) and 0.12(2) eV, were deduced above 170 K. Below this temperature, the bulk resistance decreased with decreasing temperature, indicating a space-charge-limited current conduction mechanism. The assumption of a uniform trap distribution and space-charge conduction gave 1013 cm−3 for trap density. The room-temperature charge carrier density was found to be 6×106 cm−3, much larger than the intrinsic free-electron density.
Accurate experimental and theoretical comparisons between superconductor-insulator-superconductor mixers showing weak and strong quantum effects
Authors: McGrath W. R. , Richards P. L. , Face D. W. , Prober D. E. , Lloyd F. L.
Published: July 2002

We have made a systematic study of the gain and noise in superconductor-insulator-superconductor mixers employing Ta based, Nb based, and Pb-alloy based tunnel junctions. These junctions displayed both weak and strong quantum effects at a signal frequency of 33 GHz. The effects of energy gap sharpness and subgap current were investigated and are quantitatively related to mixer performance. Detailed comparisons are made of the mixing results with the predictions of a three-port model approximation to the Tucker theory. We have measured mixer performance with a novel test apparatus which is accurate enough to allow for the first quantitative tests of theoretical noise predictions. We find that the three-port model of the Tucker theory underestimates the mixer noise temperature by a factor of about 2 for all of our mixers. In addition, predicted values of available mixer gain are in reasonable agreement with experiment when quantum effects are weak. However, as quantum effects become strong, the predicted available gain diverges to infinity, which is in sharp contrast to the experimental results. Predictions of coupled gain do not always show such divergences.
Annealing behavior of refractory metal multilayers on Si: The Mo/Ti and W/Ti systems
Authors: Puppin E. , Krishnamurthy V. , Helms C. R.
Published: July 2002

Structures consisting of alternate layers of Mo/Ti and W/Ti have been sputter deposited on Si(100) substrates and their annealing behavior has been studied using Auger sputter profiling. The anneals were performed under typical processing conditions. Two major driving forces control the observed reactions: the silicidation of the metals and the oxidation of Ti. The prevalence of one of them depends both on the structure of the as-deposited film and on the annealing temperature. In the case where silicidation prevails a multisilicide layer is formed, with no alteration with respect to the initial disposition order of the metal films. Intermixing between the reacted layers starts to be observed at 900 °C. The behavior of common contaminants such as oxygen and carbon has been studied.
Magneto-mechanical damping at low temperatures in purified iron
Authors: Govaer D. , Beshers D. N.
Published: July 2002

The damping behavior of zone-refined iron was investigated at low temperatures as a function of strain amplitude of oscillation, magnetic field, frequency, and temperature. Observations of increased damping at relatively low temperatures are correlated with reports of other investigators. These features appear to be associated with the hysteretic breakaway of domain walls from pinning points. As temperature increases the hysteretic process becomes thermally assisted and diminishes. The parameters for this process are an attempt at frequency of the order of 106 Hz, or somewhat more, and an activation energy of the order of 0.02 eV or more. It appears that the interaction of moving dislocations with domain walls can also assist depinning from the unspecified pins.
Crystallographic properties and optical energy gap values for (CuIn)x(AgIn)yCd2zTe2 alloys
Authors: Guerrero Eunice , Quintero Miguel , Woolley J. C.
Published: July 2002

Polycrystalline samples of (CuIn)x(AgIn)yCd2zTe2 were prepared by a melt and anneal technique. Guinier x-ray powder photographs were used to determine equilibrium conditions and lattice parameter values. Two single-phase fields, with zinc-blende and chalcopyrite structures, are found to exist in the diagram. Comparison of the experimental results with the expressions proposed by Jaffe and Zunger has been made. It was found that these equations, used with Phillips radii, give good agreement for parameter a for Cu-rich samples but poorer agreement elsewhere and also for c and c/a. Optical absorption measurements were carried out on most of the samples to determine values of the optical energy gap E0 at room temperature. These values of E0 are found to show a nonlinear variation with z. This variation is discussed in terms of the effects of p-d hybridization on the valence band and the change in crystal structure.
Titanium silicides formed by rapid thermal vacuum processing
Authors: Dexin C. X. , Harrison H. B. , Reeves G. K.
Published: July 2002

Rapid thermal vacuum processing (RTVP) has been employed to form silicides of titanium on both single and polycrystalline silicon. Resistivity values as low as 13 μΩ cm were obtained for reaction temperatures in the range 600–900 °C for various times (≤30 s). For the lower temperature (600 °C) the conversion to TiSi2 was observed through both physical (Rutherford backscattering) and electrical (four-point-probe) techniques. The native oxide of silicon was also seen to be broken up by the thermal treatment and the oxide moving to the surface to form a stable thin TiO2 surface layer. Unlike previous reports of the formation of titanium silicides in gas we have observed a clean sharp silicon-silicide interface.
Experimental verification of beta-decay-driven sublimation in deuterium-tritium ice held in spherical fusion targets
Authors: Mruzek M. T. , Musinski D. L. , Ankney J. S.
Published: July 2002

A nonuniform layer of deuterium-tritium (DT) ice inside a spherical inertial confinement fusion (ICF) target held in an isothermal cryogenic environment should be driven toward uniformity by the beta-decay heat of the tritium. Experiments have been performed at KMS fusion to verify this hypothesis. Two major conclusions may be drawn from the initial results: (1) the beta decay of the tritium does deposit energy in the target, as evidenced by melting of DT ice when the target is well insulated from its surroundings, and (2) solid layers of DT ice sublime because of beta-decay heat. Both conclusions are reinforced by companion studies with nonradioactive hydrogen-deuterium (HD) ice in similar targets held under similar experimental conditions.
Spin-glass behavior in mixed metal oxides with a rutile-type structure
Authors: Labarta A. , Obradors X. , Tejada J. , Berry F. J. , Sarson M.
Published: July 2002

We report here on the magnetic properties of compounds of composition Fe1−xCrxSbO4 and Fe1−xGaxSbO4. The introduction of paramagnetic Cr3+ and diamagnetic Ga3+ into the rutile-related iron antimonate lattice does not destroy the antisite atomic ordering which exists in iron antimonate of composition FeSbO4. The initial slope of the Curie temperature dependence on x is similar in both series, indicating that Fe3+-Cr3+ interactions are very small. The magnetic susceptibility measurements recorded from the compounds of composition Fe1−xCrxSbO4, x<0.4, and Fe0.9Ga0.1SbO4 show them to behave as spin glasses at low temperatures. The inhibition of compounds of the type Fe1−xCrxSbO4, x>0.4, and Fe1−xGaxSbO4, x>0.1 to undergo a spin-glass transition above 4.2 K is associated with a dilution effect.
Resist heating in excimer laser lithography
Authors: Abe Takayuki , Arikado Tsunetoshi , Takigawa Tadahiro
Published: July 2002

Intensity dependence of the photochemical reaction rate, and thus the exposure reciprocity, for excimer laser beam irradiation to resist has been investigated. The reciprocity law did not hold for KrCl excimer laser beam irradiation concerning the sensitivity of the poly(methyl methacrylate) (PMMA) resist. It is also shown that this failure of the reciprocity law originates from a resist sensitivity change caused by the resist temperature rise due to irradiation (resist heating). For PMMA, the laser beam with a pulse energy of 15 mJ/cm2 and a wavelength of 222 nm raised the resist temperature by about 30 °C, resulting in a thermally assisted photochemical reaction.