bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetostrictive torque sensor and its output characteristics
Authors: Shimada Munekatsu
Published: July 2002

A magnetostrictive torque sensor which can be installed in an automobile transmission to measure torque has been developed. The sensor shaft consists of two grooved sections. An ac bridge circuit formed by two coils surrounding the grooved sections and two fixed resistors is used to detect torque. The shaft material is a newly developed Cr–Mo steel. The sensitivity of the sensor is stable over a wide temperature range. However, the zero point of the sensor output drifted as much as 10% of the full scale of the sensor when the temperature was uniformly raised by 50 °C. To solve the temperature drift problem, the output characteristics of the bridge circuit were examined. It was found that the output signal (sinusoidal wave) from an initially balanced bridge consisted of torque and temperature components. Each component showed a constant phase angle. The torque phase angle was a fixed value whereas that of the temperature was controllable. A method was devised for separating the temperature phase angle from the torque one by about 90° and then eliminating the temperature component from the output signal. The resulting temperature drift of the sensor was less than 1% of the full measurement scale per 50 °C. This paper describes the shaft material, magnetostrictive properties of the shaft, torque and temperature dependence of coil impedances and output characteristics of the bridge circuit.
Resonant magnetic scattering from 5f magnetic materials (invited)
Authors: Stirling W. G. , Lander G. H.
Published: July 2002

Over the last five years, the large resonant enhancements of the magnetic x-ray scattering amplitudes at the MIV and MV absorption edges of actinide materials (U, Np) have been exploited in a series of magnetic diffraction investigations at the National Synchrotron Light Source. This work is reviewed with a discussion of measurements on a series of antiferromagnetic materials with contrasting magnetic properties, UAs, USb, U0.85Th0.15Sb, UO2, URu2Si2, and NpAs.
Angular dependence of auto-oscillations in YIG
Authors: Shields P. J. , Paget K. M. , Wigen P. E.
Published: July 2002

High-power, perpendicular, ferromagnetic resonance (FMR) in thin yttrium-iron-garnet (YIG) disks produces fingerlike regions of auto-oscillation as a function of static field and excitation power. These fingers are associated with the magnetostatic modes found in the low-power FMR spectra and are characterized by their onset frequency (1–10 MHz) and excitation power (2–15 dBm). Using a 9.22 GHz excitation source, the characteristics of the first finger have been examined as the static field is rotated away from the perpendicular orientation. This has been done at room temperature for four samples of varying characteristics. Very little sensitivity exists in the onset frequency within 4° of perpendicular, while in the same range a slight variation in onset power has been observed. In general, the onset frequency has been found to decrease as the static field rotates away from perpendicular. Results for the onset attenuation are inconclusive. Numerical results based upon a microscopic Hamiltonian derived for the perpendicular orientation have been examined for two of the samples to provide a first approximation of the observed spin-wave dynamics. The experimentally observed trend in onset frequency has been reproduced. A region in which the nature of the observed auto-oscillations changes dramatically has been found in three of the samples at roughly 15° off perpendicular. This region may be the result of the increased coupling of the magnetostatic modes to an increasing number of short-wavelength spin waves as the static field is rotated and the system rises above the bottom of the spin-wave band.
Co alloy media made on amorphous carbon substrate
Authors: Kuwabara Masago , Sato Motoharu , Onishi Yoshihiko , Visokay Mark R. , Hayashi Hidetaka , Inoue Hidetoshi , Muramatsu Kazuo
Published: July 2002

Co-based alloy media were made on recently developed ultra densified amorphous carbon (UDAC) substrates which have several advantages over NiP/Al, glass, and ceramics substrates. It was found that the coercivity (Hc) of media made on UDAC substrates was higher than that on NiP/Al substrates, as was the adhesion performance. The latter is a result of the formation of Cr–C compound at the interface.
Preparation and characterization of thin films of M-type barium ferrite on microcrystalline carbon substrates with diffusion barrier sublayers
Authors: Sin Kyusik , Sivertsen John M. , Judy Jack H. , Hoshi Youichi , Speliotis Dennis E.
Published: July 2002

Hexagonal barium ferrite films have been grown on microcrystalline carbon substrates for the first time and thermally oxidized SiO2/Si wafers using dc facing targets sputtering. Si3N4 and SiO2/Cr underlayers were effective in preventing carbon diffusion into the barium ferrite films during deposition at high temperatures (550–600 °C). X-ray diffraction spectra showed that the c axis of the crystals are perpendicular to the film surface. The dispersion of the c axis (Δθ50) was 2.5°. The perpendicular coercivity varied from 860 to 1200 Oe and the saturation magnetization (Ms) was about 300 emu/cm3. The delta M curves were negative in the in-plane direction and positive in perpendicular directions.
Theoretical studies of the magneto-crystalline anisotropy: Monolayer Co
Authors: Wang Ding-Sheng , Wu Ruqian , Freeman A. J.
Published: July 2002

Using our newly developed state tracking method and eliminating the coupling between quasidegenerate pairs of states at the Fermi surface in advance, highly stable and precise results for the magneto-crystalline anisotropy energy are obtained for a Co monolayer film in a first principles calculation with a small number of k points (421 in the full Brillouin zone). The easy direction of magnetization is found to lie in the layer plane in contrast to the Fe monolayer when both match their lattice constant to the same Cu(001) substrate. This result is explained in terms of their electron occupation and differences in the spin-orbit coupling between their occupied and empty states.
Magnetic x-ray dichroism in 2p absorption spectra of Fe/Cu(001)
Authors: Waddill G. D. , Tobin J. G. , Pappas D. P.
Published: July 2002

Large magnetic circular dichroism using circularly polarized synchrotron radiation has been observed at the L2,3 absorption edges of thin (1–12 monolayers) fcc Fe films grown on Cu(001). Dramatic changes in the 2p branching ratio are observed when the orientation of photon helicity and sample magnetization are varied from parallel to antiparallel. The temperature and film thickness dependence of the perpendicular anisotropy in these films could be monitored by variations in the 2p branching ratio. Finally, our results are described in a simple theoretical framework that allows a determination between the predicted low- and high-spin phases for fcc Fe. Our data suggest a high-spin phase with a moment of 2.0–2.5 μB/atom. Interestingly, thicker films with remanant magnetic moments in the film plane present smaller branching ratio variations consistent with either a reduced moment or with domain closure for these films. The surface sensitivity and elemental specificity of this technique make it particularly attractive for the study of surface and thin film magnetism.
Secondary recrystallization behavior and magnetic properties of grain oriented 2.2% Si-1.5% Mn steel
Authors: Yashiki H. , Kaneko T.
Published: July 2002

The secondary recrystallization behavior and magnetic properties in ultralow carbon 2.2% Si-1.5% Mn steel containing 0.008% sol.Al was investigated. It was found that the atmosphere of final annealing plays an important role on the secondary recrystallization in this steel. In the case of annealing in N2 containing gas, good magnetic properties equivalent to those of conventional grain-oriented electrical steel were obtained. However, annealing in 100% H2 gas resulted in poor magnetic properties. Annealing in N2 containing gas can be considered as causing a sharp {110}<001≳ texture due to the strengthened inhibition resulting from an increase in fine nitrides. These results suggest the possibility of a new simple processing of grain-oriented electrical steel.
Specific heat of dense Kondo compounds CexLa1−xNi
Authors: Sato Kiyoo , Umehara Izuru , Isikawa Yosikazu , Mori Katsunori , Takeda Hideki
Published: July 2002

The electrical resistivity and the specific heat of CexLa1−xNi systems were measured in the temperature range from 1.3 to 300 K. The magnetic specific heats for various concentrations of Ce were represented by Schottky type anomalies. The Kondo temperatures TK and the crystalline electric field parameters were estimated for various concentrations.
Upper critical field studies on Sc5−xDyxIr4Si10 system
Authors: Ghosh K. , Ramakrishnan S. , Nigam A. K. , Chandra Girish
Published: July 2002

In this paper we report the upper critical field studies of Sc5−xDyxIr4Si10 (for x=0, 1, 1.5, and 1.75). Analysis of upper critical magnetic fields yields Hc2(0) of 10 and 8.2 kOe for the superconducting samples Sc5Ir4Si10 and Sc4Dy1Ir4Si10, respectively. We obtain the lower values of Hc2(0) of 1.0 and 0.8 kOe for Sc3.5Dy1.5Ir4Si10 and Sc3.25Dy1.75Ir4Si10, respectively, where the coexistence of antiferromagnetism and superconductivity are observed from the measurements of ac susceptibility and resistivity in the presence of dc magnetic field.
Reptation effects in particulate systems. II. Experimental studies
Authors: Lewis V. G. , Mayo P. I. , O’Grady K.
Published: July 2002

In this paper we report the results of experimental reptation measurements on a chromium dioxide videotape sample. The reptation-induced changes in magnetization are found to be due entirely to thermally activated reversals which are strongly influenced by the sweep rate of the cycling applied field. This experimental evidence is found to be in exact agreement with the theoretical predictions of sweep-rate-dependent time-dependence and reptation effects published in the preceding article [El-Hilo et al. (these proceedings)].
Magnetism of antiferromagnetic α-Mn
Authors: Itoga H. , Isozaki M. , Nagai Y. , Nakao H. , Ukai T. , Mori N.
Published: July 2002

The approximate d bands of antiferromagnetic α-Mn are formulated, using Deegan’s prescription and the formulas of Slater and Koster, in consideration of the crystal and magnetic structures. The magnetic moments of 29 atoms are calculated by adopting reasonable coefficients of the effective exchange interaction. The obtained result is much the same as the experimental result.
The dependence of the local magnetic moments in disordered alloys on nearest environment (abstract)
Authors: Arzhnikov A. K. , Dobysheva L. V.
Published: July 2002

The paper is devoted to the formation of the magnetic moments in the disordered transition metal-metalloid alloys. They are simple binary alloys Fe-Al, Fe-P, Fe-Si. The successful interpretation of the results by the modified Jaccarino-Walker models implicating the local magnetic moment conception corroborates the justification of the use of these models. Again, the description of the magnetism of transition metals by band calculations supports the need to use the collectivized electron model, based on the opposite concept to the local moment models. Certainly the consequent self-consistent first principle calculations within the framework of collectivized electron models are not possible today because of the technical difficulties of these tasks. Thus, we believe it is necessary to use simpler models that take into account the main details of the above-mentioned alloys. An s-d model of disordered binary alloy with the Hubbard electron interaction like that of Ref. 1 is considered in the paper. The dependence of the local magnetic moment on the number of nonmagnetic atoms in the nearest neighborhood is received in solving the self-consistent equation for the local magnetic moment. The model proposed allows us to qualitatively describe the experiments on the changes of the hyperfine field, isomer shift, and magnetization with concentration, and accounts for the appearance of the states with local and antiferromagnetic ordering. In spite of the band character of the model, the obtained dependencies of the local magnetic moment on the number of the neighboring nonmagnetic atoms weakly depend on the concentration, which gives the grounds for the conventional usage of the modified Jaccarino-Walker models in interpreting the experiment.
Magnetic behavior of Fe-Nb and Fe-Zr alloys nanocrystallized by means of flash annealing
Authors: Gorria P. , Orue I. , Plazaola F. , Barandiaran J. M.
Published: July 2002

Recently nanocrystalline alloys obtained from Fe-rich amorphous metallic glasses have shown excellent soft magnetic properties for technical applications. They include 4d elements like Nb or Zr for obtaining nanometer-size crystals after heat treatments of about 1 h at temperatures around 500 °C. Flash annealing, using an electrical current flowing along the sample, is a useful method for performing heat treatments in short periods of time without need of controlled atmosphere. Grain sizes in the range 8–20 nm were determined from x-ray diffraction in crystallized alloys prepared by flash annealing technique. These are grain sizes even smaller than the ones obtained in furnace treated samples. Magnetic softening of the alloys is observed after the heating. Magnetization work, permeability, coercitive force, etc., are very similar after applying both types of treatments.
Radiation frequencies for magnetically nonsaturated ferrite patch antennas (abstract)
Authors: How H. , Rainville P. , Harackiewicz F. , Vittoria C.
Published: July 2002

Recently there has been great interest in making use of ferrite materials in patch antenna designs in order to incorporate phase shifting, impedance matching, frequency tuning, and nonreciprocal effects in the operation of patch antennas. It has been reported in Ref. 1 that the radiation frequency of a microstrip antenna can be tuned by varying the biasing magnetic field. However, no quantitative analysis or prediction exists for the tuning mechanism of ferrite patch antennas. A ferrite patch antenna identical to that reported in Ref. 1 was fabricated and tested at Rome Laboratory. Radiation frequencies and the reflection coefficient of the patch antenna were measured as a function of magnetic bias field strength and direction. Radiation patterns were also measured. As previously reported in Ref. 1, radiation patterns were found to be similar to those occurring in an isotropic dielectric patch antenna. However, in this paper experimental data on the patch radiation frequencies are reported and analyzed. Two different radiation modes were actually measured whose frequencies behaved differently under the application of a biasing magnetic field. We have identified these two modes of radiation with a transverse mode whose radiation frequency increased with increasing magnetic field and a longitudinal mode whose radiation frequency decreased with the applied magnetic field. We have formulated a theoretical model for radiation of these two modes based upon a multi-domain configuration of the ferrite substrate. The theory, which contains no adjustable parameters, compares reasonably well with the experiments.
The free-powder magnetization of ferrimagnetic rare-earth transition-metal compounds
Authors: Zhao Z. G. , de Châtel P. F. , de Boer F. R. , Buschow K. H. J.
Published: July 2002

Magnetization curves have been calculated for single crystals of ferrimagnetic rare-earth transition-metal compounds that are free to rotate in the applied magnetic field. The calculations have been performed taking into account the magnetic-anisotropy constants of the rare-earth and transition-metal sublattices up to the fourth order. Seven different types of rotation processes can be distinguished.
Equilibrium analysis of magnetization reversal in cobalt and permalloy platelets (abstract)
Authors: Wongsam M. A. , Chantrell R. W.
Published: July 2002

The local equations of stable equilibrium for the magnetization distribution in a ferromagnetic system in the micromagnetic approximation are derived from the Gibbs free energy, by application of the principle of minimum total potential. The resulting boundary value problem consists of a system of second order integrodifferential equations and boundary conditions for the magnetization distribution. These are solved iteratively using a finite-difference method and applied to the study of thin regularly shaped cobalt particles of sub and supra micron sizes with various aspect ratios and exchange coupling strengths. Permalloy platelets are also studied for size and aspect ratio dependence. Magnetization curves and distributions are calculated and the effect of aspect ratio and exchange coupling on the distributions are deduced. Comparison with previous calculations using finite element techniques1,2 are made. Variational methods using Hamilton’s principle suggest that a dynamic extension can be developed3,4 to model the transient processes associated with the irreversible phases of the magnetization reversal. Such a model based on equations of motion in the Hamiltonian form is currently being developed.
MicroMAG-2D system for domain wall dynamics simulation (abstract)
Authors: Osipov Sergey G. , Korchagin Mechislav L. , Achkasov Vadim V.
Published: July 2002

MicroMAG-2D (version 2.0) system has been developed for investigations of statics and dynamics of two-dimensional 180° domain walls in the thin ferromagnetic films with arbitrary uniaxial anisotropy. This system is intended for developers of magnetic memory devices, physicists (experimentators and theoreticians), and may be used for illustration at high school (university) educational process. Static structure is a result of solving of nonlinear variational micromagnetic problem with magnetostatic interaction. Domain wall dynamics is computed by direct integration of Landau–Lifshits–Gilbert equation. Computational method used fast algorithm for demagnetization field and unconditionally stable scheme for temporal integration. Domain wall is keeping in the center of computational region by shadowing method.1 MicroMAG-2D system consists of (a) initial data generation module; (b) computational module; (c) Editor/Viewer module; (d) Animator module. System requirements: IBM PC AT compatible (Intel 80386/387 or 80486 processor).
The influence of potential barriers on magnetoresistance of magnetic multilayers (abstract)
Authors: Levy Peter M. , Zhang Shufeng , Camblong Horacio E.
Published: July 2002

There is an emerging interest in the CPP (current perpendicular to the plane of layers) geometry for transport measurements1 and we report on new developments on the CPP-MR (magnetoresistance). Specifically we show that the effect of spin-dependent potentials in magnetic multilayers is far more pronounced for CPP-MR than for CIP-MR (current in the plane of layers). This adds to the difference between CIP-MR and CPP-MR that is due to the spin-dependent scattering in the multilayers.2 The potentials seen by the spin up and the spin down conduction electrons are different, and they depend on the orientation of the magnetic layers relative to one another, i.e., they are different for ferro and antiferromagnetically aligned layers. We have determined the Bloch functions appropriate to these spin-dependent potentials,3 and have used the Kubo formalism to calculate the resistivity and magnetoresistance for both CIP and CPP geometries. In general these potentials do affect the CIP-MR; however, for uniform scattering, we find no effect of the potentials on the CIP-MR. On the contrary, these potentials affect the CPP-MR in all circumstances, even for uniform scattering of the conduction electrons. Due to spatial and spin inhomogeneities in magnetic multilayers, the current varies from one layer to another for a uniform electric field parallel to the layers, CIP. However, for current perpendicular to the plane of the layers, CPP, it is the electric field that varies from one layer to another. We describe the distributions in both cases, and we compare our results on the CPP-MR with recent data on Co/Ag and Co/Cu.4
Temperature and doping dependence of the magnetic susceptibility in the cuprates
Authors: Glenister Rodney L. , Singh Rajiv R. P.
Published: July 2002

We compare the uniform magnetic susceptibility χ for the cuprates as a function of doping δ and temperature T, with those calculated for the t−J model in a high-temperature expansion. Experiments show that, in all the cuprate families at low doping, χ increases with doping and has a maximum as a function of temperature at some finite T. This peak shifts to lower temperatures with doping. In the higher doping regime the susceptibility saturates at low temperatures and does not show any appreciable downturn in the normal state. In the low doping regime, our calculations correctly capture this increase in the susceptibility and the shift in its temperature dependent peak to lower temperatures with doping. At high doping, (≥25%), we find that χ decreases with increasing hole concentration and the susceptibility saturates at low temperatures. The magnitude of the susceptibility is found to increase with increasing t/J. For a doping of 15% it increases from ∼0.1/J to 0.2/J as one increases t/J from 1 to 4.
Ferromagnetic resonance in Ag coupled Ni films
Authors: Rezende S. M. , Moura J. A. S. , de Aguiar F. M. , dos Santos C. A. , Schreiner W. R. , Teixeira S. R.
Published: July 2002

We present an X-band ferromagnetic resonance (FMR) study of polycrystalline single Ni films and of two Ni layers separated by an Ag layer at room temperature. Films were deposited by sputtering on glass using Ag over- and underlays. The single Ni films have a FMR mode with a dependence of the resonance field on the angle α between the magnetic field and the plane in good agreement with theory. In samples with two Ni films coupled through an intervenient Ag layer, only one FMR mode is observed if the two Ni have identical thicknesses. When the films have different thicknesses a second weak resonance appears. The field difference between the two modes is a measure of the coupling between the Ni films. Results were obtained for a series of samples with the Ag thickness varying in the range 10≤t≤30 Å. Surprisingly, the two modes have opposite behavior with the variation of α, for all values of t. The results suggest that the coupling is antiferromagnetic when the field is parallel to the film plane and ferromagnetic when perpendicular, regardless of t.
Magnetic properties of Co/MgO multilayered films
Authors: Nishikawa Masakazu , Kita Eiji , Erata Tomoki , Tasaki Akira
Published: July 2002

Multilayered thin films composed of Co and MgO layers were fabricated with an ultrahigh vacuum deposition technique. Magnetization measurements suggest that antiferromagnetic Co oxides do not form at the interface with the MgO layers. An enhancement of the magnetization is observed in a film with the Co layer thickness thinner than 30 Å. The maximum enhancement is about 10% of the bulk magnetization of hcp Co metal in a Co/MgO(22/30 Å) multilayered thin film whose magnetization is 180 emu per gram of Co.
Signature of linear (Bulaevskii–Ginzburg) domain walls near T
c of Ba-hexaferrite
Authors: Kötzler J. , Hartl M. , Jahn L.
Published: July 2002

The domain wall dynamics of a BaFe12O19 single crystal has been studied by measurements of the linear ac susceptibility parallel to the easy axis between 10 and 106 Hz. In the temperature interval 0.98 Tc≤T≤Tc=742.5 K, both dispersion and absorption reveal pure relaxational behavior, the damping rate ΓW of which exhibits a distinct minimum about T*=0.992 Tc. Based on previous results on low-temperature ferromagnets (Tc≤3 K) and recent theoretical work, the speeding up of ΓW∼(Tc−T)−0.7 toward Tc is related to the relaxation of linear domain walls proposed by Bulaevskii and Ginzburg. For the first time, additional support for this wall type is gained from the magnitude of the wall-reconstructuring temperature T*. The steep rise of ΓW below T* can be related to Bloch-wall damping, however, the shape of the crossover of ΓW about T* remains to be explained.
The magnetic relaxation enhancement effects of Mössbauer line shapes in Ni–Zn–Co ferrite system
Authors: Ling Qi-Fen , Li Guo-Dong , Li De-Xin , Guo Shu-jiao
Published: July 2002

The results of ferromagnetic resonance and Mössbauer studies on a series of spinel ferrites Ni0.6−xZn0.40CoxFe2O4 with composition x=0, 0.01, 0.02, 0.03 are reported in this paper. The linewidths of both spectra have a maximum value at temperatures near and below the Curie temperature, respectively. Both these phenomena might be explained by using the effect of the magnetic longitudinal relaxation for magnetically ordered systems.
Site preference for Zn2+ and Ge4+ in mixed ferrite ZnxGe1−xFe2O4
Authors: Kim Chul Sung , Ko Heung Moon , Lee Woon Hwa , Lee Choong Sub
Published: July 2002

Small amounts of Zn2+ and Ge4+ substituting for GeFe2O4 and ZnFe2O4, can efficiently increase the Neél temperature, thereby can be applied to magnetic device. The site preference of Fe2+ and Fe3+ in mixed ferrite ZnxGe1−xFe2O4 (X=0.6) with Mössbauer absorption and x-ray diffraction was studied. Analysis of x-ray diffraction indicates that the lattice constant is not in accord with Vegard’s law, suggesting Fe2+ and Fe3+ are located not only at B sites but at A sites. It is found that Debye temperatures of GeFe2O4 and ZnFe2O4 are 380±5 K and 361±5 K from Mössbauer measurements. Zn2+ and Ge4+ randomly occupy A site or B site. Mössbauer spectra of Zn0.6Ge0.4Fe2O4 reveal line broadening with increasing temperature and the relaxation effect at low temperature.
Magnetism in the insulating parents of the high-T
c superconductors: Well or ill understood?
Authors: Mahanti S. D. , Kaplan T. A. , Chang Hyunju , Harrison J. F.
Published: July 2002

We discuss appreciable differences between the results for the covalent reduction of the ordered moment in antiferromagnetic CuO2 planes obtained by various groups, including the present authors. We explain the differences as due to differences in definition, the definition that we used being closely based on experiment (magnetic neutron Bragg scattering), in contrast to the others. We also discuss the large difference between the zero-point spin fluctuations as calculated by one of the groups and the well-known result of spin wave theory.
Kerr rotation measurements on amorphous U-As-Co thin films
Authors: Fumagalli P. , Plaskett T. S. , McGuire T. R.
Published: July 2002

Thin films of (U-As)100−xCox alloys are prepared by magnetron sputtering over the entire composition range x and the polar Kerr rotation and magnetization are measured. The absolute value of the maximum Kerr rotation decreases rapidly from −0.48° for Co (x=100) to −0.09° for x=66 at 300 K. A similar decrease is observed at 10 K but at a slightly slower rate. The Kerr rotation as well as the magnetization are negligible at x≂50, indicating a suppression of the magnetic moments in Co and U, simultaneously. This result is explained in terms of filling in the Co 3d conduction band. At x≤30, U develops a magnetic moment at 10 K but Co does not seem to contribute to the magnetization for these compositions.
Magnetic properties and microstructures of dense branching morphology observed in Bi/Al/Mn/SiO multilayers
Authors: Shang C. H. , Huang D. , Luo H. L. , Wang Y. J. , Kong L. C.
Published: July 2002

A new type of domain structure observed in the annealed Bi/Al/Mn/SiO films is described. The domain is embedded into a round colony called dense branching morphology. Increasing ramified branches and conspicuous circular envelopes are two distinguished features of the colony. Magnetic measurement indicated that the branches of different contrasts were relevant to the different magnetization orientations in the films. It was also revealed that the Kerr rotation topography in high spatial resolution could exactly match the branch geometry on the morphology. Composition analyses showed that intensive diffusion and segregation of Bi atoms during the thermal annealing contributed a lot to the formation of the domain structure.
Hybrid waves in magnetostrictive ferromagnetics
Authors: Lanotte L. , Luponio C.
Published: July 2002

Interaction between acoustic field and electromagnetic field, in a magnetostrictive ferromagnetic material produces both transversal quasiacoustic waves (QACW) and quasielectromagnetic waves (QEMW) named hybrid waves. Properties of hybrid waves have been studied and their dependence on conductivity has been emphasized in the piezomagnetic case. To this end, the system of Maxwell’s equations, Newton’s law of force, and piezomagnetic state equations were solved for an infinite continuous medium. It is shown that for a particular conductivity value σc, the hybrid modes coincides in a mixed propagation mode we called MHWM. The dispersion relation, in the case of separate hybrid waves, as well as in the mixed mode MHWM, is discussed. The MHWM has a velocity Vc, which is independent of wave number k. Moreover we point out that (a) for very high σ, the QEMW velocity reaches a k-independent value while the QACW velocity falls to zero, (b) the behavior of σc(k), at constant Vc, is linear, (c) for σ≠σc, at constant σ, the QEMW velocity and QACW velocity behaviors versus k are nonmonotonics.
Fundamental mode operation of high-power InGaAs/GaAs/AlGaAs laser arrays
Authors: Tsang J. S. , Liou D. C. , Tsai K. L. , Chen H. R. , Tsai C. M. , Lee C. P. , Juang F. Y.
Published: July 2002

A new ridge waveguide laser array with stable fundamental mode operation has been fabricated. By introducing absorption regions in all the laser stripes except for the central one, the electric field distribution of the laser arrays and the modal gains of the array supermodes are changed, resulting in fundamental mode operation. The threshold current of an array with five elements is typically 40 mA and the maximum output power is higher than 150 mW. The single-lobed far-field pattern centered at 0° with full width at half maximum of 2° is obtained at 1.5 times of the threshold current (Ith).
BCl3/HN3 gas breakdown behavior: Observation of BCl(A-X) emission
Authors: Wright M. W. , Schlie L. A. , Black G.
Published: July 2002

BCl(A-X) band emission peaked at 272 nm plus N2(C-B) spectra from dc breakdown initiated detonations in HN3/BCl3 gas mixtures are reported. Negligible NH(A-X) emission at 336.0/337.1 nm is observed in contrast to its strong intensity in pure HN3 breakdown-induced decomposition. The presence of the HN3 detonation appears to enhance the production of BCl(A-X) emission indicating the liberation of chemical energy from the HN3 decomposition to excited BCl but at low effective yields of 8×10−4%.
Surface impedance measurements of superconducting (NbTi)N films by a ring microstrip resonator technique
Authors: Andreone A. , DiChiara A. , Peluso G. , Santoro M. , Attanasio C. , Maritato L. , Vaglio R.
Published: July 2002

In the framework of the search for new materials for sputter coated superconducting rf cavities for particle accelerators, an innovative method to measure the rf properties of superconducting films, based on an inverted microstrip ring resonator technique, is presented. Test measurements on well characterized Nb sputtered films show excellent agreement with the Bardeen, Cooper and Schrieffer theory and prove the good resolution of the method. New results obtained by this technique on the surface impedance of (NbTi)N reactively sputtered films, including the temperature dependence and the rf field amplitude dependence of the surface resistance and the temperature dependence of the magnetic field penetration depth, are then presented and discussed.
Microwave heating characteristics of rutile
Authors: Kudra T. , Raghavan G. S. V. , van de Voort F. R.
Published: July 2002

Thermophysical properties of rutile ore were determined experimentally and used to quantify the heating effect due to microwave absorption. Temporal variation of the temperature/heating rate was established and related to the intensity of volumetric heat generation, mass of sample, and water load volume. The receptivity of natural rutile to microwave energy as well as the anisotropic effect were confirmed.
Photoluminescence of n-type CdTe:I grown by molecular beam epitaxy
Authors: Giles N. C. , Lee Jaesun , Rajavel D. , Summers C. J.
Published: July 2002

Liquid helium temperature and temperature-dependent photoluminescence (PL) spectroscopy have been performed on highly n-type-doped CdTe:I films grown by molecular beam epitaxy. The samples were grown on 2° off (001) oriented bulk CdTe substrates at substrate temperatures from 170 to 250 °C, and exhibit room-temperature electron concentrations of 1×1017 cm−3. The brightest PL edge emission at liquid helium and room temperatures was observed from a sample grown at 210 °C. At T=5 K, the iodine donor radiative recombination was observed at 1.593 eV, corresponding to a donor ionization energy of 14 meV for the ITe substitutional donor, in agreement with the predicted hydrogenic donor ionization energy for CdTe. The thermal quenching behavior of the edge emission peak is a two-step process involving both 10 and 14 meV activation energies. These activation energies are related to the thermalization of the ITe donor from the ground state to the first excited state (1s→2s, 10 meV), and complete thermalization from the donor ground state to the conduction band (14 meV).
Diamond grown on single-crystal beryllium oxide
Authors: Argoitia Alberto , Angus John C. , Wang Long , Ning Xiajie I. , Pirouz Pirouz
Published: July 2002

Diamond has been grown on single-crystal beryllium oxide by hot-filament chemical-vapor deposition. The diamond particles were characterized by Raman spectroscopy, and the morphology and microstructure investigated by scanning electron microscopy and plan-view and cross-sectional transmission electron microscopy. Diamond grew epitaxially on the basal plane of BeO with the epitaxial relationship {111}diamond∥{0001}BeO and 〈11̄0〉diamond rotated by less than 6° with respect to 〈112̄0〉BeO. Diamond was also grown on the (112̄0) prism plane of BeO. A selected-area-diffraction pattern obtained from a plan-view of these specimens indicated the presence of a set of spots that corresponded to the {101̄0} planes of hexagonal diamond or to the 1/3(422) forbidden spots of cubic diamond. During diamond deposition on (112̄0)BeO surfaces, small particles of beryllium carbide (Be2C) were also observed.
Ellipsometric study of ambient-produced overlayer growth rate on YBa2Cu3O7−x films
Authors: Sieg Robert M. , Alterovitz Samuel A. , Warner Joseph D.
Published: July 2002

An ellipsometric study of ambient-reaction-produced BaCO3 overlayer growth on laser-ablated YBa2Cu3O7−x is presented as a function of time. The effects of the anisotropy of YBa2Cu3O7−x on the ellipsometric data inversion process are discussed, and it is concluded that with certain restrictions on the data acquisition method, the anisotropic substrate can be adequately modeled by its isotropic pseudodielectric function for the purpose of overlayer thickness estimation. It is found that after an initial period of rapid growth attributed to the chemical reaction of the exposed surface bonds, the BaCO3 overlayer growth is linear at 1–2 Å per day. This slow growth rate is attributed to the complexity of the BaCO3 forming reaction, together with the need for ambient reactants to diffuse through the overlayer.
Pulse photoconductivity in vacuum-deposited thin films of α-metal-free phthalocyanine with inhomogeneous trap concentration
Authors: Valerián H. , Nešpůrek S.
Published: July 2002

By using pulsed photoconductivity techniques, transient action spectra on vacuum-sublimed α-metal-free phthalocyanine thin films have been obtained in the wavelength range 350–700 nm. The transient photocurrents have been determined at field strengths lower than 107 V m−1 by the range-limited carrier transport with spatially distributed traps, the μτ product of photogenerated holes in the sample varying from about 4×10−15 to 2×10−13 m2 V−1 and the electron μτ product being ∼6×10−16 m2 V−1. The inhomogeneity of the trap concentration in the sample bulk was suggested to explain different shapes of the photoresponse spectra for different directions of the sample irradiation. The result indicates that spatial distribution of local states can be approximated by the exponential function; local states are predominantly distributed in the vicinity of the substrate. A new method for determination of the spatial trap distribution parameter with resolution better than 0.1 μm is presented.
Monte Carlo simulation of electron behavior in an electron cyclotron resonance discharge
Authors: Kuo S. C. , Kunhardt E. E. , Kuo S. P.
Published: July 2002

Electron behavior in an electron cyclotron resonance microwave discharge maintained by the TM01 mode fields of a cylindrical waveguide has been investigated via a Monte Carlo simulation. Since this discharge has high degree of ionization (≥1%), a self-consistent simulation of the plasma dynamics is achieved through the use of the ponderomotive and grad B (−μ∇∥B) forces. Accumulation of negative charges on the boundary surface sets up a sheath whose influence is also taken into account. The time averaged, spatially dependent electron energy distribution (EED) is computed self-consistently by integrating electron trajectories subjected to the microwave fields, the divergent background magnetic field, the space charge field, and the sheath field, and taking into account electron–electron collisions and collisions with the neutral hydrogen atoms. The EED is characterized by two electron temperatures with the population of the tail increasing for decreasing pressure. At low pressures (∼0.5 mTorr), the sheath potential is on the order of 100 V and decreases with increasing pressure. This observation suggests a pressure range for operation of reactors for diamondlike carbon film deposition.
Reduction of plasma electron density in a gas ionized by an electron beam: Use of a gaseous dielectric
Authors: Reid Max B.
Published: July 2002

Propagation of an electron beam through a gas creates a secondary electron/ion plasma which can have subsequent deleterious effects on the propagation of the beam. In the case of pulsed electron beams with short micropulse durations, these effects can be greatly reduced through the use of a small doping fraction of an electron attachment gas. We present a model which allows the calculation of the reduction in unbound plasma electron density attainable with a gaseous dielectric dopant. Potential problems with a dopant, including increased ionization, increased scattering, altered refractive index, and dopant saturation and fragmentation, are discussed.
Lamb wave propagation in magnetostrictive polycrystalline ferrite plates
Authors: Ermolov V. , Luukkala M.
Published: July 2002

The launching and propagation of Lamb waves in magnetostrictive polycrystalline ferrite plates was studied. The influence of a magnetic overlay situated parallel to the surface of the plate in the vicinity of the meander-type transducer on the efficiency of the transducer was investigated. The results obtained show that Lamb wave velocities are more sensitive to magnetic fields than Rayleigh wave velocity, and that the use of a magnetic overlay essentially improves the efficiency of the meander type transducer.
Surface tension measurements of refractory liquid metals by the pendant drop method under ultrahigh vacuum conditions: Extension and comments on Tate’s law
Authors: Vinet B. , Garandet J. P. , Cortella L.
Published: July 2002

The pendant drop method, used in an ultrahigh vacuum drop tube, allowed new determinations of the liquid surface tension of the refractory metals. After a description of the melting apparatus, the amazing reproducibility in terms of droplets masses (≂0.6%) observed is discussed herein. Evidence is given of the harmful action of hydrogen bubbles contained in the commercial rods. Working with very thin wires (down to 0.3 mm), a variation curve for the Harkin’s correction factor of Tate’s law in its untabulated range is proposed. The validity of the representation of this factor is discussed via a dimensional analysis. Finally, new values of σLV for pure Re (2.510 J m−2), W (2.310 J m−2), Ta (2.010 J m−2), Nb (1.840 J m−2), Ir (2.140 J m−2), and Zr (1.435 J m−2) are proposed.
Analysis of the linearized energy and momentum balance equations of the single electron gas transport model
Authors: Loechelt Gary H. , Blakey Peter A. , Joardar Kuntal
Published: July 2002

The linearized energy and momentum balance equations of the single electron gas transport model are considered. A general analytic solution is obtained for transient velocity responses to arbitrary time dependent field perturbations. A criterion for the occurrence of velocity overshoot following a field step is determined. Various characteristics of such overshoot are established, and a new ‘‘differential overshoot mobility’’ is defined. Compact analytic expressions are obtained for Thornber’s augmented drift-diffusion overshoot coefficient B, and the small-signal complex mobility. Calculated results are presented for electron transport in silicon at 77, 300, and 450 K, for material that is undoped and for material that is doped n type at a level of 1018 cm−3.
The effects of 1 MeV electron irradiation on the current-voltage characteristics of Au/p-InP structures
Authors: Thomas H. , Luo J. K.
Published: July 2002

Current-voltage (I-V) measurements have been carried out on p-type InP Schottky diodes following 1 MeV electron radiation. Having received an electron fluence of 1016 cm−2, the I-V-T properties of the diodes show that the conduction mechanism is dominated by thermionic-field emission at low temperature under forward or reverse bias, while that of samples having received an electron fluence of <1015 cm−2, conduction is dominated solely by the thermionic emission of carriers. The characteristic value E0 of thermionic-field emission showed a corresponding defect density of 5×1017–1018 cm−3. The radiation defects introduced in the InP cells were found to appear as deep traps, which caused a significant increase in the series resistance of the diodes. The dominant defects showed an activation energy of 0.3 eV obtained from the temperature dependence of the series resistance of the diodes, and were almost entirely removed following a 10 min anneal at 100 °C. These characteristics show that the dominant defects found did not correspond to the defects H3, H4, and E2 usually observed by deep level transient spectroscopy.
Nonimaging characterization of imperfect single crystals by means of a three-crystal diffractometer for high energy synchrotron radiation
Authors: Bouchard R. , Kouptsidis S. , Neumann H. B. , Schmidt T. , Schneider J. R.
Published: July 2002

A three-crystal diffractometer for synchrotron radiation with energies of 100 keV and higher has been used in a nondispersive setting to map out the distribution of Bragg scattered intensity in the scattering plane with very high resolution. By using perfect silicon crystals in symmetrical Laue geometry for reflection 220 as monochromator and analyzer, respectively, a resolution of ≊2×10−4 Å−1 in the direction parallel to the reciprocal lattice vector G220 and of ≊10−5 Å−1 in the direction perpendicular to G220 has been achieved at high counting rates. As a first example the mosaic structure of a plastically deformed silicon crystal has been characterized with respect to its mosaic distribution and lattice parameter fluctuations. Second, the study of a silicon-germanium gradient crystal, produced by means of the chemical vapor deposition technique, demonstrated that the substrate peak could be well separated from the intensity distribution of the gradient crystal. A two-dimensional contour plot of the intensity distribution in the vicinity of 220 shows the variation of the lattice parameters in the gradient crystal, as well as the lattice plane tilts of the substrate and the silicon-germanium layers.
Variational calculations of ground and higher states of metal-oxide-semiconductor inversion layer in a nonuniform electric field
Authors: Rao M. , Rothwarf A.
Published: July 2002

We present variational calculations of the ground and higher-energy states for (100)Si metal-oxide-semiconductor inversion layers in the electric field induced by the gate voltage as represented by a recently proposed logarithmic potential. The ground-state energies are calculated in the electric quantum limit using the well-known Fang–Howard trial wave function. The higher-energy states are obtained using a Gram–Schmidt orthogonalization approach, beginning with trial wave functions that resemble the Laguerre functions. We compare our results with the standard triangular potential approximation involving the Ai(z) Airy function and its roots.
The structural and superconducting properties of the YBa2Cu3O7−δ-HfO2 system
Authors: Koshy J. , Thomas J. K. , Kurian J. , Yadava Y. P. , Damodaran A. D.
Published: July 2002

Superconductivity in YBa2Cu3O7−δ with HfO2 addition has been studied by x-ray diffraction, temperature-resistivity measurements, and scanning electron microscopy. The studies revealed that HfO2 addition up to 5 wt % does not have any detrimental effect on the superconducting properties of YBa2Cu3O7−δ. It is also found that the widely accepted procedure of slow cooling or prolonged heating at 600 °C for oxygenation of the samples is not essential to obtain superconductivity in an HfO2-added YBa2Cu3O7−δ system. A superconducting transition (92 K) was obtained by directly quenching the HfO2-added samples in air from a sintering temperature of 950 °C. A tetragonal to orthorhombic transformation has taken place within seconds, indicating that the rate of oxygen absorption has increased tremendously by HfO2 addition. The implications are discussed.
A new model for the absorption coefficient of narrow-gap (Hg,Cd)Te that simultaneously considers band tails and band filling
Authors: Herrmann K. H. , Happ M. , Kissel H. , Möllmann K.-P. , Tomm J. W. , Becker C. R. , Kraus M. M. , Yuan S. , Landwehr G.
Published: July 2002

A semiempirical model is presented that correlates the broadening of the absorption edge with both transitions below the energy gap and with transitions by the Kane band model. This model correctly fits both the absorption and luminescence spectra of narrow-gap (Hg,Cd)Te samples that have been grown by the traveling heater method as well as by molecular-beam epitaxy. The accuracy of the band-gap determination is enhanced by this model.
Time-of-flight analysis of a plasma jet from a spark plug in vacuum
Authors: Buraczyk D. E. , Edelmon G. G. , Zieher K. W.
Published: July 2002

The composition of a plasma jet and the velocity distribution of the different ions from an arc plasma source are investigated by a double time-of-flight method. The plasma source consists of a marine spark plug in coaxial configuration driven from a capacitor bank. The analysis of the plasma jet is performed by pulsed acceleration of plasma ions and measurement of their time of flight to a distant electron multiplier tube. Mainly oxygen and aluminum ions from the insulator are detected. The velocity of the highly ionized ions extends to 14 cm/μs. The lower ionized particles have lower initial velocities. The hydrogen ion content increases with increased time between shots.
A model of laser ablation in nonmetallic inorganic solids
Authors: Okano Akiko , Matsuura Anne Y. , Hattori Ken , Itoh Noriaki , Singh Jai
Published: July 2002

A model is presented of laser ablation, primarily applicable to nonmetallic solids. The model does not include any critical phenomena, but assumes evolution of vacancy clusters due to the emission of atoms bonded weakly around vacancies and vacancy clusters on surfaces. The result of calculation shows a high power dependence of the yield on the laser fluence, agreeing with the experimental results.