bluuebunny/crossref_metadata_2025 huggingface dataset:
Glassy alloy identification marker
Authors: Hasegawa Ryusuke
Published: July 2002

For a small magnetic excitation H below magnetic saturation, a nonlinearity term proportional to H3 is added to the conventional B-H behavior for glassy Perminvar alloys. The additional nonlinearity term results in generation of even harmonics with similar amplitudes as the conventional odd harmonics. This effect can be utilized in systems identifying multiple objects carrying precoded markers made of small strips of these materials.
Magnetically modulated microwave absorption measurement of the penetration depth in a polycrystalline YBa2Cu3O7−x thin film
Authors: Karim R. , Vittoria C. , Widom A. , Chrisey D. B. , Horwitz J. B.
Published: July 2002

In previous work, a magnetically modulated microwave absorption (MMMA) technique to measure the Ginzburg–Landau parameter κ=(Λ/ξ) in high-Tc superconductors (bulk samples of YBCO) was described. In this work, how this technique can be applied to the measurement of the London penetration depth Λ is described. Data are reported for the temperature variation of Λ in a well-characterized c-axis-oriented polycrystalline thin film of YBa2Cu3O7−x, prepared by a pulsed laser deposition technique. For low temperatures, Λ(0)≂3640 Å with the microwave electric field oriented parallel to the c axis. The temperature dependence of Λ(0)/Λ(T) can be well described by the two-fluid model. The data are also reasonably fit by a BCS model, however the MMMA technique (in the work here reported) does not have the resolution at low temperatures to obtain strong quantitative evidence for an energy gap Δ (even if it exists).
Inverse magnetostriction effect on magnetoresistive response for evaporated NiFe and NiFeCo films
Authors: Tatsumi T. , Tsukamoto Y. , Yamada K. , Motomura Y. , Aoyama M.
Published: July 2002

The relations between inverse magnetostriction energy ε and magnetoresistive (MR) response have been investigated for Ni82Fe18 films and Ni82Fe12Co6 films that have about twice the uniaxial anisotropy energy as the NiFe films. To obtain films with various ε values (50–800 J/m3), internal stress σ for the films is changed by the deposition conditions and film thickness control. The σ is measured by the bending method. The σ changes for both films are related to microstructure differences. Hysteresis or Barkhausen jump is observed for the NiFe films with absolute ε value ‖ε‖ more than 120–130 J/m3, and for the NiFeCo films with ‖ε‖ more than 300–330 J/m3. The threshold ‖ε‖ values are on the same order of magnitude as the calculated uniaxial anisotropy for each film. To obtain smooth MR response, it is very important to reduce the ‖ε‖ to less than the uniaxial anisotropy energy value, by deposition conditions and film thickness control.
Theoretical and experimental study of the electronic structure of PtMnSb
Authors: Ebert H. , Schütz G.
Published: July 2002

The electronic structure of PtMnSb has been studied by means of the linear muffin-tin-orbital method of band-structure calculation. In agreement with earlier investigations a so-called half-metallic behavior has been found. Until now, this exotic feature of the band structure of PtMnSb, which is made responsible by some authors for its high Kerr rotation, could not clearly be confirmed by experiment. Using the Korringa–Kohn–Rostoker band-structure technique it could be shown that lattice imperfections, which can never be completely suppressed in this system, have a dramatic impact on the spin polarization in the vicinity of the Fermi level. This explains why photoemission experiments could find only a degree of photoelectron polarization at the threshold noticeable below the ideal value of 100%. To get further insight into these problems, x-ray-absorption measurements using circularly polarized radiation have been performed at the L2,3 edges of Pt, the K edge of Mn, and the L1 edge of Sb. The results of these experiments, which give in a component-resolved way a rather direct access to the spin polarization for the unoccupied part of the conduction band, are found in reasonable agreement with theoretical data.
Transition metal implants in In0.53Ga0.47As
Authors: Gulwadi Sadanand M. , Rao Mulpuri V. , Berry Alok K. , Simons David S. , Chi Peter H. , Dietrich Harry B.
Published: July 2002

Single- and multiple-energy Fe, Cr, and V ions were implanted into InGaAs. Annealing of the implanted InGaAs samples caused a redistribution of the implanted atoms, as determined by secondary ion mass spectrometry. Coimplantation of Fe with P did not prevent this redistribution. A transport equation calculation of Fe-implantation-induced stoichiometric disturbances in InGaAs was done. The lattice quality of implanted InGaAs was investigated by photoreflectance measurements. Fe-implanted InGaAs has a resistivity close to the intrinsic limit, whereas Cr- and V-implanted InGaAs have a lower resistivity than the unimplanted material.
Interaction of Bloch-wall pairs in thin ferromagnetic films
Authors: Jakubovics J. P.
Published: July 2002

Micromagnetic structures are computed for pairs of 180° domain walls in thin films, driven together by applied magnetic fields. It is shown that the field required to annihilate the walls depends strongly on their relative symmetry. There are six possible symmetries for pairs of walls, two of which show no resistance to annihilation. For the other four symmetries, the applied field needed to annihilate the walls varies by large amounts according to the symmetry. The resistance to annihilation decreases with increasing film thickness. Experimental studies of interactions of domain-wall pairs, in which examples of both low and fairly high resistance to annihilation have been observed, provide qualitative support for these results. It is concluded that wall interactions can contribute significantly to the coercivity of soft magnetic films.
Comparison of the effects of post-oxidation anneals on the initial properties and the radiation response of rapid thermally processed oxides
Authors: Schubert W. K.
Published: July 2002

The effects of post-oxidation processing on the initial performance (as measured here by pre-irradiation fixed-charge and interface-state densities) and radiation response of rapid thermally processed, metal-oxide-semiconductor (MOS) capacitors are investigated. The processing dependencies for the major groups of processing- and radiation-induced defects are discussed with respect to recent gains in understanding of the Si-SiO2 interfacial structure. Processing conditions for ideal initial properties are found to be quite different than those required for optimum radiation response. Guidelines for optimal post-oxidation thermal processing are given, taking into consideration both the initial performance and radiation response of the MOS device. The results indicate that even when using rapid thermal processing, post-gate oxide anneals above 900 °C degrade the radiation tolerance.
Enhanced mechanical and magnetic properties of granular metal thin films
Authors: Schlesinger T. E. , Cammarata R. C. , Gavrin A. , Xiao John Q. , Chien C. L. , Ferber M. K. , Hayzelden C.
Published: July 2002

The mechanical properties of Ag-Al2O3 and Ni-Al2O3 granular metal films, as well as the magnetic behavior of the nickel-based films, is presented. Enhancements in the mechanical properties of these materials, as measured by low load indentation techniques, were observed for a metal volume fraction p of about 0.55. This volume fraction corresponded to the percolation threshold pc as determined from the magnetic measurements. A peak in the compliance as a function of p was observed, similar to elastic anomalies reported for small bilayer period superlattices. A discontinuity in the rate of change of hardness as a function of p was also observed, and believed to result from a change in deformation mechanism at pc.
Microstructure of buried CoSi2 layers formed by high-dose Co implantation into (100) and (111) Si substrates
Authors: Bulle-Lieuwma C. W. T. , Van Ommen A. H. , Vandenhoudt D. E. W. , Ottenheim J. J. M. , de Jong A. F.
Published: July 2002

Heteroepitaxial Si/CoSi2/Si structures have been synthesized by implanting 170-keV Co+ with doses in the range 1–3×1017 Co+ions/cm2 into (100) and (111) Si substrates and subsequent annealing. The microstructure of both the as-implanted and annealed structures is investigated in great detail by transmission electron microscopy, high-resolution electron microscopy, and x-ray diffraction. In the as-implanted samples, the Co is present as CoSi2 precipitates, occurring both in aligned (A-type) and twinned (B-type) orientation. For the highest dose, a continuous layer of stoichiometric CoSi2 is already formed during implantation. It is found that the formation of a connected layer, already during implantation, is crucial for the formation of a buried CoSi2 layer upon subsequent annealing. Particular attention is given to the coordination of the interfacial Co atoms at the Si/CoSi2 (111) interfaces of both types of precipitates. We find that the interfacial Co atoms at the A-type interfaces are fully sevenfold coordinated, whereas at the B-type interfaces they appear to be eightfold coordinated.

It is shown that these interface configurations introduce defects in the three-dimensional CoSi2 precipitates and Si matrix. As a result, the nuclei are subjected to compressive strain. It is argued that the combination of interface energy and strain results in a larger stability of small B-type nuclei as compared to A type. When the precipitates grow beyond a critical size of some 20–30 nm, A-type precipitates become more stable, finally resulting in a buried layer of aligned orientation if the layer thickness is larger than about 30 nm. If smaller, it is argued that upon prolonged annealing the layer will have a twinned orientation (B type). Annealed layers of aligned orientation in (100) Si are found to contain interfacial dislocations of edge type with Burgers vectors b=a/4〈111〉 and b=a/2〈100〉. These dislocations are associated with boundaries separating domains having different interface structures. For (111) Si, there exist edge-type dislocations with Burgers vector b=a/2〈110〉. The final state of strain can be attributed to the difference in thermal expansion between CoSi2 and Si. The strain at room temperature corresponds to a fully relaxed layer at about 700 °C. Below this temperature, dislocations become immobile.
Effects of oxidation conditions on the formation of paramagnetic centers at and near the Si/SiO2 interface
Authors: Awazu Koichi , Kawazoe Hiroshi , Ando Toshio , Watanabe Kikuo
Published: July 2002

To discern the most important parameter determining the concentration of paramagnetic centers, the effects of chemical treatments before and/or after oxidation, the type of furnaces, the cooling rate after oxidation, and oxidation temperature were examined. The effects of chemical treatments for cleaning on Pb and E′ centers before and/or after oxidation were negligible. Two types of furnaces were prepared: One where contamination by the outer air could be prevented and one where it could not be prevented, called an air-removed furnace and a conventional furnace, respectively. The concentration of Pb and E′ centers at the Si/SiO2 interface fabricated in a conventional furnace was, however, drastically smaller than that fabricated in an air-removed furnace. The cooling rate after oxidation did not determine the concentration of E′ centers but affected Pb centers. The oxidation temperature also determined the concentration of both Pb and E′ centers. It was found that the parameter most effective in determining the concentration of paramagnetic centers was the type of furnace, whether there was contamination from air or not. The paramagnetic centers (such as Pb and E′ centers) react with some element(s) in the air. It is expected that such elements are not N2 gas but hydrogen-related impurities in the air, perhaps H2O.
Thermally stable ohmic contacts to p-type GaAs. IX. NiInW and NiIn(Mn)W contact metals
Authors: Hallali P.-E. , Murakami Masanori , Price W. H. , Norcott M. H.
Published: July 2002

Thermally stable, low-resistance p-type ohmic contacts have been developed by depositing NiInW metals on GaAs substrates in which Be and F were coimplanted. The contacts provided resistances of about 1.4 Ω mm after annealing at temperatures in the range of 300–800 °C for short times. The electrical properties did not deteriorate after annealing at 400 °C for more than 100 h, which far exceeds the requirements for current GaAs device fabrication. The present study demonstrated for the first time that thermally stable, low-resistance ohmic contacts to both n- and p-type GaAs can be fabricated using the same metallurgy. In addition, NiInW ohmic contacts were prepared by simultaneous (one-step) annealing for ion-implant activation and contact formation, which simplifies significantly the device fabrication process. A factor-of-2 reduction of the contact resistances was achieved by slight etching of the GaAs surface prior to the contact metal deposition so that the metal/GaAs interface contacted the peak position of the Be concentration in the GaAs substrate. Another method used to reduce the contact resistance was to add a small amount of Mn to the NiInW metals: the resistance decreased with increasing amounts of Mn. The contacts had smooth morphology and shallow depth, less than 70 nm, which is desirable for very-large-scale integration device application.
Development of silver-sheathed bismuth superconducting wires and their application (invited)
Authors: Sato Ken-ichi , Shibuta Nobuhiro , Mukai Hidehito , Hikata Takeshi , Ueyama Munetsugu , Kato Takeshi
Published: July 2002

The development results for silver-sheathed bismuth (2223 phase) superconducting wires in the past two years have suggested that three different fields of application will be feasible in the very near future. The first field is large current conductor application in liquid nitrogen operation. The second is magnet application (relatively low magnetic field below 1 Tesla, such as for semiconductor crystal pulling and magnetic separation) in liquid nitrogen operation. The third is super-high field application above 20 Tesla in liquid helium operation. In this paper, we will describe the state of the art of high-Tc superconducting wires using a combination of bismuth high-Tc phase and powder-in-tube technique. Maximum Jc at 77.3 K reached to 53 700 A/cm2 in a zero magnetic field, 42 300 A/cm2 at 0.1 Tesla and 12 000 A/cm2 at 1 Tesla. Prototypes, such as a 1000 A carrying conductor at 77.3 K, a 1000 Gauss coil at 77.3 K and a super-high field coil at 4.2 K were made and tested successfully.
Effect of additives on hot deformation behavior of melt-spun Nd-Fe-Co-B magnets
Authors: Yoshida Y. , Yoshikawa N. , Nishio T. , Kasai Y. , Panchanathan V. , Croat J. J.
Published: July 2002

The effect of various additives on hot workability was investigated for alloy systems of (Nd13.6−xRx)(Fe77.6−yTyCo2.8)B6.0: R=Ce, Dy; x=0, 1, 2; T=Al, Si, V, Cu, Ga, Zr, Nb, Mo, Sn; y=0, 0.5, 1.0. A semiquantitative comparison of the effect of various additives was made by measuring the crack opening displacement (CODmax) in test specimens deformed in an open (unconstrained) configuration. Among the additives, cerium and silicon improved the hot workability while niobium and tin severely deteriorated the workability. The remanence anisotropy ratio was inversely related to CODmax. Detailed microstructural investigations were carried out with alloys which had only cerium or tin to study the reason for their hot workability behavior in comparison to the base alloy. The improved hot workability of cerium added alloy is related to the lower melting temperature of the intergranular phase and faster grain growth compared to the base alloy. Tin addition prevented grain growth with no endothermic peak in a differential thermal analysis curve, indicating the absence of boundary phase melting, and leading to poor hot workability.
A neutron diffraction and Mössbauer effect study of the magnetic structure of Y2(Fe1−xMnx)14B
Authors: Marasinghe G. K. , Pringle O. A. , Long Gary J. , James W. J. , Yelon W. B. , Grandjean F.
Published: July 2002

The magnetic structures of a series of Y2(Fe1−xMnx)14B samples, with x equal to 0.03, 0.10, 0.25, and 0.37, have been studied by powder neutron diffraction and Mössbauer spectroscopy. Y2(Fe0.97Mn0.03)14B and Y2(Fe0.9Mn0.1)14B are ferromagnetic at both 295 and 85 K, Y2(Fe0.63Mn0.37)14B is paramagnetic at both 295 and 85 K, whereas Y2(Fe0.75Mn0.25)14B is paramagnetic at 295 K and is partially ordered at 78 K. The magnetic structure of Y2(Fe0.75Mn0.25)14B is explained in terms of the preferential Mn occupancy of the transition metal 8j2 site in the Y2Fe14B structure. Small amounts of Mn located in this site are very effective in disrupting the long-range ferromagnetic coupling.
Photoemission characterization of the H2 plasma etched surface of InP
Authors: Nelson Art J. , Frigo Sean , Mancini Derrick , Rosenberg Richard
Published: July 2002

Synchrotron radiation soft x-ray photoemission spectroscopy was used to characterize the surface chemistry of InP before and after exposure to a H2 plasma. The low-power H2 plasma was generated with a commercial electron cyclotron resonance plasma source using a mixture of H2 and Ar with the plasma exposure being performed at ambient temperature. Plasma species were identified with quadrupole based mass spectrometry and optical emission spectroscopy. Photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence-band electronic structure as well as changes in the In 4d and P 2p core lines. The results were correlated in order to relate the plasma species and characteristics to changes in surface chemistry.
Growth and magnetoresistance of Fe/Cr superlattices on Ge(100)
Authors: Folkerts W. , Hoving W. , Coene W.
Published: July 2002

We have studied the growth, structural properties, and magnetoresistance of Fe/Cr superlattices on Ge(100) substrates. The Fe/Cr superlattices were found to grow bcc(100) and epitaxially aligned. From Rutherford backscattering (RBS) and reflection high energy electron diffraction it is found that some intermixing occurs at the Ge–Fe interface. Using low energy electron diffraction, transmission electron microscopy, x-ray diffraction and RBS it is shown that Fe/Cr superlattices grow epitaxially matched on Ge(100) and have flat and sharp interfaces. We investigated for Fe/Cr on Ge(100) the magnetoresistance as a function of Cr interlayer thickness tCr=8–14 Å. The maximum value is found for tCr=12 Å (ΔR/RS=15% at room temperature, ΔR/RS=95% at 4 K). A comparison is made with multilayers of the same composition, deposited on glass substrates.
Specific heat and thermal diffusivity of strontium barium niobate (Sr1−xBaxNb2O6) single crystals
Authors: Choy C. L. , Leung W. P. , Xi T. G. , Fei Y. , Shao C. F.
Published: July 2002

The specific heat and thermal diffusivity of Sr1−xBaxNb2O6 (x=0.33 and 0.48) single crystals have been measured between 130 and 500 K, and the sound velocity has been measured at 295 K. At x=0.33 the specific heat shows a broad peak at 335 K, indicating the onset of a ferroelectric phase transition. The peak sharpens and shifts to about 383 K at x=0.48. A jump in the thermal diffusivity D is observed at the transition. Away from the transition, however, D is roughly independent of temperature. There is very little anisotropy in D, with the value along the a axis marginally higher than that along the c axis. Outside the transition region the phonon mean free path l is approximately constant, and has values of 5.1 and 5.6 Å, respectively, below and above the transition. The low values of D and l are due to the disorder arising from the random distribution of five Sr/Ba ions over six possible sites in a unit cell.
Ultrasound attenuation in quasi-two-dimensional semiconductor quantum-well structures
Authors: Rodrigues C. , Nunes O. A. C.
Published: July 2002

Ultrasound attenuation by electrons is considered for a quasi-two-dimensional semiconductor quantum-well structure. The attenuation coefficient, α, is calculated quantum mechanically and found to vary with the width of the quantum well. It is found that the attenuation can be enhanced over its value in a bulk semiconductor as the thickness of the quantum well decreases.
Control of microstructure in a-SiC:H
Authors: Lu Hsueh Yi , Petrich Mark A.
Published: July 2002

We demonstrate a means of controlling the microstructure and carbon content in amorphous hydrogenated silicon carbide (a-SiC:H) thin films prepared in a plasma-enhanced chemical vapor deposition system. The capacitively coupled, parallel-plate deposition apparatus includes provision for adjusting the potential of the powered electrode by application of an additional, independent dc voltage. This voltage affects the deposition chemistry. Films prepared when various positive and negative dc voltages are applied are studied with infrared absorption, nuclear magnetic resonance, and electron spin resonance. Their optical band gaps, electrical conductivities, and dark conductivity activation energies are also measured. The films have carbon contents ranging from 1 to 4 at. %. We find that we can alter the microstructure of a-SiC:H by adjusting the powered-electrode potential during deposition, and that these microstructural changes are reflected in the film properties. A small increase in the self-biased voltage of the powered electrode leads to a film with the least amount of infrared-observable microstructure and the highest photoconductivity. Applying an external dc voltage leads to an increase in deposition rate regardless of voltage polarity. The films prepared with externally applied voltage all have lower hydrogen contents than the film prepared with self-biased voltage, which may explain the observed property changes. The addition of an external dc voltage can have beneficial effects on the deposition rate, structure, and properties of a-SiC:H films.
Very low-emittance solar selective surfaces using new film structures
Authors: Zhang Qi-Chu , Mills David R.
Published: July 2002

New cermet film structures suitable for selective solar absorbers, composed of two cermet sublayers with identical metal volume fractions in each sublayer, on metal reflectors with an antireflection dielectric layer coating are described. The absorbing cermet sublayers have thickness and volume fractions such that solar radiation is absorbed internally and by phase cancellation interference. They are substantially transparent in the thermal infrared region. Modeling of the new cermet layer structures has revealed a number of different selective surfaces, involving a variety of practical cermet materials, with better performance than recent published results. For example, the best predicted ratio of absorptance to normal emittance α/ε at room temperature is 46 for a Cu-SiO2 cermet, 49 for a Cu-Al2O3 cermet and a Au-Al2O3 cermet. The best laboratory results of α/ε at room temperature thus far are 46 for a Cu-SiO2 cermet, and 45 for a Au-Al2O3 cermet. From computer modeling, using published experimental dielectric functions of a Co-Al2O3 cermet, absorptance of 0.93 and normal emittance of 0.026 at 50 °C (α/ε=36) could be obtained for a two-cermet-sublayer film on a Mo reflector with an Al2O3 antireflection layer.
Magnetic viscosity, thermal relaxation, and thermal equilibrium noise in Co-based amorphous alloys at milliKelvin temperatures
Authors: Vitale S. , Tommasini R. , Cerdonio M. , Bonaldi M. , Cavalleri A. , Durin G.
Published: July 2002

We report measurements of the magnetic reversible complex permeability and of the related thermal noise for a few Co-based soft ferromagnetic amorphous alloys. The measurements were performed in the 16 mK–4.2 K temperature range and in the 0.1 Hz–1 kHz frequency range with a superconducting quantum interference device magnetometer. The data show the existence of a temperature independent magnetic viscosity together with a thermal relaxation of the spin subsystem to the heat bath. This last feature shows up as a partial rolloff of the real permeability from an isothermal low-frequency value to an adiabatic high-frequency one. The noise due to the sample is found in good agreement with the standard fluctuation-dissipation prediction for the thermal noise.
The bonded unipolar silicon-silicon junction
Authors: Bengtsson Stefan , Andersson Gert I. , Andersson Mats O. , Engström Olof
Published: July 2002

The electrical and optical properties of wafer bonded unipolar silicon-silicon junctions were investigated. The interfaces, both n-n type and p-p type, were prepared using wafers with hydrophilic surfaces. The current versus voltage characteristics, the current transients following stepwise changes in the applied bias, and the capacitance versus voltage characteristics as well as the temperature dependence of the current and capacitance were experimentally obtained and theoretically modeled. The proposed model assumes two distributions of interface states, one of acceptors and one of donors, causing a potential barrier at the bonded interface. It is argued that the origins of the interface states are impurities and crystallographic defects in the interfacial region. The capacitance of the bonded structures includes contributions from the depletion regions as well as from minority carriers. When bonded n-n type samples were illuminated with light of photon energies larger than the silicon band gap the current across the junction increased. This is caused by the photogenerated increase in the minority carrier concentration in the interfacial region, which results in a lowering of the potential barrier. Illumination of n-n type structures with light of photon energies lower than the band gap caused a considerable photocurrent at low temperatures. In this case the observed behavior cannot be explained by interaction with the interface states. Instead, the mechanism is the change in the occupancy of deep electron traps caused by the illumination. These traps are located in the silicon in a small volume around the bonded interface with energies close to the center of the band gap and with a peak concentration of about 1013 cm−3. Impurities present on the silicon surfaces before bonding and impurities gettered to the bonded interface are possible reasons for the increased concentration of deep electron traps in the vicinity of the bonded interface.
Afterglow decay kinetics of nonuniform plasmas with cylindrical symmetry: Application to the measurement of electron decay in large, photoionized plasmas in atmospheric-pressure helium
Authors: Stalder K. R. , Eckstrom D. J.
Published: July 2002

Experiments and analytical methods for determining electron-ion recombination and attachment coefficients in highly collisional, cylindrically symmetric plasmas are presented. Photoionization by sparkboard light sources of tetrakisdimethylaminoethylene (TMAE) seeded in atmospheric-pressure helium is used to produce the plasma. The electron density is probed by microwave transmission techniques. The effective recombination coefficient for electrons recombining with TMAE ions in atmospheric pressure helium is found to be (9.0±1.1)×10−6 cm3 s−1 for Te=300 K.
Vibrations of circular disk dielectric resonators
Authors: Lee P. C. Y. , Yang J. S.
Published: July 2002

Two-dimensional equations for guided electromagnetic waves propagating in a dielectric plate surrounded by free space were recently derived from the three-dimensional Maxwell’s equations. These equations are employed for the study of vibrations of circular disk dielectric resonators embedded in free space. Closed form solutions are obtained for which the continuity conditions of the tangential E and H fields at the end faces and the lateral cylindrical surface are accommodated. It is found that the solutions represent two types of modes: (1) the modes in which the electric field is transverse to the axis of the disk [transverse electric (TE) modes] and (2) the modes in which the magnetic field is transverse to the axis of the resonator [transverse magnetic (TM) modes]. Frequency equations are solved and resonance frequencies are computed as functions of the diameter-to-thickness ratio a/b for TE and TM modes. It is found that the computational results presented as Ω̂ [≡ω/(π/2b)c] vs a/b curves are independent of the refractive index n̂. Hence, these curves can be conveniently applied to the dielectric disks of any n̂. Predicted results are compared with the experimental data by Cohn [IEEE Trans. Microwave Theory Tech. MTT-16, 218 (1968)], Chow [IEEE Trans. Microwave Theory Tech. MTT-14, 439 (1966)], and Yee [IEEE Trans. Microwave Theory Tech. MTT-13, 256 (1965)], and with the computational results by Chow [IEEE Trans. Microwave Theory Tech. MTT-14, 439 (1966)] and Yee [IEEE Trans. Microwave Theory Tech. MTT-13, 256 (1965)]. It may be seen that present predictions agree overall with different sets of experimental data and for modes of various types and order.
Type-I and type-II noncritical phase matching of LiB3O5 crystal
Authors: Wu Baichang , Xie Fali , Chen Chuangtian
Published: July 2002

Noncritical phase-matching properties for LiB3O5 crystal are reported. Second-harmonic generation (SHG) with temperature-tuned phase matching was measured at a fundamental wavelength ranging from 1340 to 900 nm with corresponding temperature tuning from −10 to 280 °C. Based on the experimental results a new type of SHG device has been made from the crystal, and the advantage of such a device is also demonstrated.
NMR study of the short range order in Fe–B amorphous powders prepared by borohydride reduction
Authors: Mao M. X. , Li F. S. , Cheng Z. H. , Xue D. S. , Liu X. M. , Zhang C. L. , Zhang Y. D.
Published: July 2002

The Fe–B amorphous alloys powders with high boron concentration can be prepared by borohydride reduction (BHR). By adjusting technological factors, the Fe100−xBx amorphous powders with compositions ranging from x=17 to 40 can be easily obtained, but it is difficult to make the amorphous ribbons with such a high B concentration by using rapidly quenched technique, which can usually obtain the amorphous ribbons with the compositions ranging from x=12 to 25. Up to now, there are different points of view about if the short range order (SRO) in the Fe–B amorphous powders prepared by the BHR around room temperature is the same with that in the amorphous ribbons made by rapidly quenched and vapor depositing techniques. In this paper, the SRO in Fe100−xBx amorphous powders with various boron concentration prepared by the BHR have been studied by the zero field spin echo nuclear magnetic resonance (NMR) technique. It was shown that the types of SRO in these samples vary with the B concentration. There exist Fe3B- and Fe2B-like SRO and a small amount of α-Fe in the samples with lower B concentration, while there are Fe3B- and FeB-like SRO in the alloys with higher B concentration. Fe3B-like SRO, however, only exists in the amorphous ribbons obtained by rapidly quenched method. It can be concluded that there are different types of SRO in the amorphous alloys prepared by different methods. This conclusion can explain the reason why the average hyperfine field at Fe sites deceases with the B concentration increasing.
Soft x-ray magnetic circular dichroism (invited) (abstract)
Authors: Chen C. T.
Published: July 2002

Recent developments in synchrotron radiation instrumentation have made possible the production of high quality circularly polarized light in the soft x-ray region (150–1500 eV).1,2 Magnetic circular dichroism (MCD), the difference in the absorption intensity of magnetic systems using left- and right-circularly polarized light, has been exploited in the visible, VUV, and hard x-ray spectral regions to provide valuable information on the electronic and magnetic properties of magnetically oriented systems. Soft x-ray magnetic circular dichroism (SXMCD) has several advantages over the VUV and hard x-ray spectral regions: the major electronic states that are responsible for magnetism, i.e., the 3d states of transition metals and the 4f states of rare-earth elements, can be reached via strong dipole transitions from their respective well-separated 2p3/2, 2p1/2, and 3d5/2, 3d3/2 sharp core levels. Compared to MCD in the visible region, known as the magneto-optical Kerr effect, SXMCD offers element and site specificity with relatively easier data interpretation. A brief review of the principles of SXMCD2 and current instrumental developments will be given. SXMCD measurements conducted at the Dragon beamline on a wide variety of magnetic systems, including transition metals, surfaces, ultrathin films, alloys, ferrites, rare-earth compounds, and biological samples will be utilized to demonstrate the capability of SXMCD as a tool for basic and applied magnetism research.2,3
Electronic structure of Nd2Fe17N
Authors: Gu Zongquan , Lai Wuyan , Zhong Xue-Fu , Ching W. Y.
Published: July 2002

The electronic structures of ternary compound Nd2Fe17N with N atoms on 9e, 3b, and 18g sites are calculated and compared. The local moments on different Fe sites are in good agreement with experiments. The mechanism of increasing Curie temperature by N doping is checked by additional calculations with lattice expansion. The results show that the change in interatomic interaction is more important than the lattice expansion effect.
High-field magnetization process in Sm2Fe17N3.0: Importance of exchange-enhanced mixing of excited J multiplets
Authors: Kato Hiroaki , Yamada Motohiko , Kido Giyuu , Nakagawa Yasuaki , Iriyama Takahiko , Kobayashi Kurima
Published: July 2002

The high field magnetization process in Sm2Fe17N3.0 has been investigated by using dc magnetic fields of up to 260 kOe generated by a hybrid magnet. It was found that the hard-axis magnetization at 4.2 K is only 78% of the easy-axis value in the field of 260 kOe, while at 296 K, it almost saturates at the same field, the saturation value being about 3% smaller than that along the easy axis. Experimental results have been analyzed on the basis of a model calculation taking the excited J multiplets of the Sm ion into account. It has been found that, when the field is applied along the hard axis at 296 K, the Sm magnetic moment rotates away from the field direction and finally, at the saturation field, it becomes antiparallel to the field so that the Sm and Fe moments are arranged ferrimagnetically. The origin of such a magnetization process was clearly explained as a result of the mixing of the excited J multiplets caused by the Sm–Fe exchange interaction. Observed anisotropy of saturation magnetization at 296 K was thus attributed primarily to this field-induced ferrimagnetic structure in the hard direction.
Magnetic ordering in granular Ni–Al2O3
Authors: Gavrin A. , Chien C. L.
Published: July 2002

We have produced granular Ni–Al2O3 solids by magnetron sputtering, and the entire composition range has been studied. The percolation threshold (pc) has been identified to be near 55 percent Ni by volume, in agreement with other granular metal systems. Below pc, the samples display typical single domain magnetic behaviors, including superparamagnetism and enhanced coercivity. However, above percolation the samples display ferromagnetic transitions which differ substantially from the transition in pure Ni. We have performed a scaling analysis of the ferromagnetic transition in several such materials, and have obtained values of the Curie temperatures and the critical exponents. These are the first such analyses of the ferromagnetic-paramagnetic transition in granular magnetic solids. We have observed a depression of the Curie temperature as the Al2O3 content of the samples is increased, as well as a substantial variation of the critical exponents. The variation of Tc may be understood in terms of finite size scaling.
Pulse excitation method for measurement of high frequency magnetic properties of large cores (abstract)
Authors: Hikosaka Tomoyuki , Miyamoto Masahiro , Yamada Mamoru , Morita Tadashi
Published: July 2002

It is very important to obtain saturated magnetic properties from reverse saturation (full B-H curve) of ferromagnetic cores to design magnetic switches which are used in high power pulse generators. The magnetic switch is excited in the high frequency range (∼MHz). But, it is extremely difficult to measure full B-H curve of large toroidal cores of which diameter is some hundreds of mm, using the conventional ac excitation method at high frequency. The main reason is poor output ability of power source for core excitation. Therefore we have developed pulse excitation method to get high frequency magnetic properties. The measurement circuit has two sections. One is excitation part composed by charge transfer circuit. The others is reset part for adjustment initial point on direct B-H curve. The sample core is excited by sinusoidal voltage pulse expressed as 1−cos(2π ft). Excitation frequency f is decided by the constants of the elements of the charge transfer circuit. The change of magnetic flux density ΔB and magnetic field H are calculated, respectively, by measuring the induced voltage of search coil and magnetizing current. ΔB-H characteristics from reverse saturation of four different kinds of large cores were measured in frequency range from 50 kHz to 1 MHz. Core loss increases in proportion to Nth powers of the frequency, where the index N depends on each of cores. N is about 0.5 in case of winding ribbon cores, such as Fe-based amorphous, Co-based amorphous, and Finemet, but N is about 0.2 in case of the Ni-Zn ferrite.
X-ray magnetic scattering—New developments (invited) (abstract)
Authors: Gibbs Doon
Published: July 2002

Although the sensitivity of x-ray scattering to magnetization densities has been known for many years, it was not until the calculations of Platzman and Tzoar and the experiments of de Bergevin and Brunel in the nineteen seventies that the possibility of x-ray magnetic scattering studies of solids was clearly recognized. Complementary to neutron magnetic scattering, x-ray magnetic scattering experiments especially benefit from the high q resolution and polarization and energy characteristics available from synchrotron radiation. In this talk, we describe the results of x-ray magnetic scattering studies in a variety of materials, including rare earths, actinides, and transition elements. We highlight some recent experiments that use resonant techniques, and indicate new directions in x-ray magnetic scattering studies of bulk materials, at surfaces, and in multilayers using existing and next-generation insertion device beamlines.
Nonlinear response to picosecond pulse excitations in metal backed magnetic layers (abstract)
Authors: How H. , Vittoria C. , Trott K.
Published: July 2002

For years there has been great interest in the radar survivability communities concerning the response of materials to narrow picosecond pulse excitation. In this report, we have calculated the nonlinear response of magnetodielectric thin layers to picosecond excitation utilizing direct time-domain integration. This is in contrast to our previous frequency-domain calculations,1 where the nonlinear properties of the material were dealt with only in an approximate manner. Using time domain calculations, relaxations, hysteresis, and magnetization phenomena associated with the response are, therefore, investigated in depth. The purpose of this calculation was to provide an analytical method by which physical properties of materials can be identified under picosecond pulse excitation as well as to explore special cases of excitations in which picosecond pulses are efficiently absorbed. The calculations indicate that by examining the reflected wave form of the incident rectangular picosecond pulse the amount of magnetic hysteresis and saturation of the material may be estimated. It is shown that magnetic hysteresis will affect the shape of the trailing edge of the reflected signal, whereas the magnetic saturation effect can be identified from the slope of the reflected pulse step. Examples of designing effective picosecond pulse screening structures have also been illustrated. The difference in between the time domain and frequency domain calculations are, therefore, discussed and compared.
Magnetic properties and crystal structure of CoCrTaPt thin film for longitudinal recording media
Authors: Utsumi Kentaro , Inase Toshio , Kondo Akio
Published: July 2002

Magnetic properties and crystal structure of sputtered CoCrTaPt/Cr and CoCrTa/Cr thin films were studied as a function of Pt content and the substrate temperature. It was observed that the coercivity increased with Pt content or the substrate temperature, and that the coercivity was saturated with a small amount of Pt at high substrate temperature compared to at low substrate temperature. X-ray diffraction study showed that at high substrate temperature, Co(11.0) grew epitaxially on Cr(200). That indicates c axis of hexagonal-close-packed Co phase lies in the film plane. It was also shown that diffraction angles of Co planes shifted lower with the addition of Pt. These shifts are attributed to the diffusion of Pt into the Co lattice, and the shifts are promoted by the increase of the substrate temperature. The addition of Pt led to the increase of crystalline magnetic anisotropy constant (Ku), and the increase of Ku was also promoted by the increase of the substrate temperature. The increase of the coercivity by the addition of Pt is considered to be caused by the increment of in-plane crystalline magnetic anisotropy which is due to the diffusion of Pt into the Co lattice. The increase of the coercivity by the increase of the substrate temperature is attributed to the increment of the in-plane component of the c axis.
Metastable ferromagnetic phase formation in 35–50 at. % Mn—Ga thin films
Authors: Matsui T. , Suzuki M. , Morii K. , Nakayama Y.
Published: July 2002

Thin Mn—Ga films with the composition of 35–50 at. % Mn were fabricated by means of a conventional vacuum evaporation method on glass and NaCl substrates heated at 473 K. The metastable ferromagnetic phase was formed in the samples as well as the Mn2Ga5 phases. The analysis of the x-ray and microbeam electron diffraction patterns suggested that the crystal structure of this phase was correlated with a long-range ordered structure composed of a certain number of the Mn2Ga5 cell. It was demonstrated that the presence of the metastable phase affected the magnetic properties; the metastable single-phase films had a high coercivity up to about 320 kA/m and a fairly large saturation magnetization of about 550 mT, which were comparable to those for the MnGa-σ-phase and AlMn-τ-phase.
Crystal structure and magnetic properties of Pb substituted Ba-ferrite sputtered films for perpendicular magnetic recording media (abstract)
Authors: Morisako Akimitsu , Matsumoto Mitsunori , Naoe Masahiko
Published: July 2002

Ba-ferrite (BaM) sputtered films are suitable for a high density perpendicular recording medium.1 There were some problems to be solved in preparing BaM films. One of the most important problems is that a high substrate temperature Ts was necessary. Ts for preparing BaM films with c-axis dispersion angle Δθ50 as small as 2°–3° is about 620 °C and a high Ts limits the selection of substrate material. In this paper, Pb substituted BaM[(Ba⋅Pb)M] films were prepared by dc magnetron sputtering and their crystal structure and magnetic properties were studied. The substrate is a thermally oxidized silicon wafer. The target is a sintered ferrite disk (8 cm diameter) with stoichiometric composition of BaM and Pb content was controlled by the numbers of Pb chips on this disk. Argon and oxygen gas were introduced into a chamber and discharge gas pressure was set at 2 mTorr. Partial oxygen gas pressure was 0.01 mTorr and an applied power was 50 W. The thickness of (Ba⋅Pb)M films was about 1500 Å. The films prepared at Ts below 300 °C were amorphous and those prepared at Ts ranging from 300 to 400 °C consisted of spinel-like phase. Saturation magnetization Ms of these films was almost zero. The films prepared at Ts above 400 °C consisted of both hexagonal and spinel-like ferrites.2 Intensity of diffraction lines from hexagonal ferrite became strong as Ts was elevated and those for hexagonal ferrite were only from c-plane such as (004), (006), (008), (0010), (0012), and (0014). Usually, the lines from the (004), (0010), and (0012) planes cannot be observed in bulk BaM. This implies that the c axis is well oriented perpendicularly to the film plane. (Ba/Pb)M films prepared at Ts about 520 °C possess Δθ50 of about 1°, Hc⊥ of 1.0 kOe, and Ms of about 250 emu/cc.
Macroscopic quantum tunneling: An overview of the background (invited) (abstract)
Authors: Leggett A. J.
Published: July 2002

Macroscopic quantum tunneling is a phenomenon that has attracted much recent attention, both experimental and theoretical, in the contexts of superconducting devices, magnetic materials, and other systems. The reasons for this interest are threefold: its implications for the foundations of quantum mechanics, its significance as a test of approximate and phenomenological approaches to the quantum formalism under the most ‘‘extreme nonclassical’’ conditions, and its possible technological consequences, e.g., for magnetic storage. This talk is a brief review of the general background, which in particular compares and contrasts the current situation with regard to magnetic systems with that obtaining in the longer-established area of superconducting devices.
Antiferromagnetism and crystal-field effects in CeCuX3 (X=Al,Ga) compounds
Authors: Mentink S. A. M. , Bos N. M. , van Rossum B. J. , Nieuwenhuys G. J. , Mydosh J. A. , Buschow K. H. J.
Published: July 2002

We have studied two new tetragonal compounds, CeCuAl3 and CeCuGa3, which both display very large specific-heat, c(T), values at low temperature. CeCuAl3 orders antiferromagnetically below TN=3.0 K, while CeCuGa3 remains paramagnetic down to 0.4 K. The large values of c(T) in these and other cerium intermetallics are interpreted as resulting from an unusually small crystal-field splitting and the possible presence of atomic disorder.
Transport and magnetic properties of polycrystalline Nd1.85Ce0.15CuO4−y under applied magnetic fields
Authors: Barbeta V. B. , Westphal C. H. , Jardim R. F. , Maple M. B. , Obradors X.
Published: July 2002

Systematic studies of transport and magnetic properties on polycrystalline Nd1.85Ce0.15CuO4−y specimens under applied magnetic fields as high as 8 kOe have revealed strong evidence of granularity in this system. Electrical resistivity measurements show two superconducting transitions. One of the transitions occurs at higher temperature and is almost insensitive to applied magnetic field and current density, while the other one occurs at lower temperature and is strongly modified by the application of magnetic field and changes in the current density. In the low-field limit (H<100 Oe), a drastic broadening of the superconducting transition is observed. Magnetic susceptibility χac measurements show similar features. There are two well-defined contributions to the diamagnetic signal below 20 K which are particularly evident in the resistive component of χac where two peaks can be identified. The application of an applied magnetic field shifts both peaks towards low temperatures. All the results can be satisfactorily explained in terms of weakly linked Josephson junctions between superconducting islands. The islands have a superconducting transition at higher temperature, and the long-range order phase coherence is achieved through Josephson coupling at lower temperatures.
Magnetic properties of Fe(Co) metal particles prepared with exfoliated MoS2 monolayers
Authors: Templeton T. L. , Arrott A. S. , Curzon A. E. , Gee M. A. , Li X.-Z. , Yoshida Y. , Schurer P. J. , LaCombe J. L.
Published: July 2002

Monomolecular layers of exfoliated MoS2 are incorporated in the process of the formation of Co ferrite from aqueous solutions. The presence of MoS2 is found to limit the coalescence of particles during reduction to Fe(Co) metal. That MoS2 inhibits the full conversion to metal is confirmed by Mössbauer effect spectroscopy. Magnetization measurements are interpreted on the basis of noncollinear magnetization patterns resulting from competing surface anisotropies.