bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of mechanical processing on giant magnetoresistance in melt-spun Co–Cu ribbons
Authors: Jiang J. S. , Pearson J. , Hinks D. , Bader S. D.
Published: July 2002

We have investigated the effect of uniaxial deformation on the giant magnetoresistance (GMR) effect in melt-spun Co–Cu ribbons. Postprecipitation deformation does not affect the Co particles, but the mechanical processing increases the structural disorder and the resistivity; thus the GMR effect is degraded. Deforming the metastable alloy prior to precipitation of the Co particles possibly affects the particle nucleation process. As a result, the low-field sensitivity of the GMR effect increases slightly.
Annealing effect on magnetic and electrical properties of epitaxial La0.8MnO3−δ thin films grown by chemical vapor deposition
Authors: Pignard S. , Vincent H. , Sénateur J. P. , Pierre J. , Abrutis A.
Published: July 2002

A new liquid source metalorganic chemical vapor deposition process has been developed in order to control precisely the amount of precursors vapors that is produced. Films of self-doped La0.8MnO3−δ have been deposited on LaAlO3 (012) substrates. X-ray diffraction measurements reveal an epitaxial growth. The as-deposited films exhibit both a ferromagnetic (Tc=200 K) and a metal–insulator (Tρ=130 K) transition. Postannealing experiments have been carried out and the results indicate the resistivity is considerably reduced, the temperature of transitions is raised to 320 K, and a magnetoresistance Δρ/ρ0=20% per tesla is obtained at 300 K in the 0–2 T range.
Mixed displacement-pressure formulation for acoustic anisotropic open porous media
Authors: Gorog S. , Panneton R. , Atalla N.
Published: July 2002

This article presents a general mixed displacement-pressure formulation to analyze the dynamic behavior of anisotropic open porous materials. This formulation is obtained in the time domain without neglecting the acceleration terms related to the fluid phase of the porous medium. The derivation of the presented formulation uses Coussy’s description of porous materials. For isotropic media and harmonic motions, the developed general mixed formulation reduces to the common set of equations of motion used in acoustics which results directly from Biot’s equations.
Thermal runaway in microwave heated isothermal slabs, cylinders, and spheres
Authors: Vriezinga C. A.
Published: July 2002

The absorption of electromagnetic energy within a microwave heated isothermal slab, cylinder, and sphere is analyzed and compared to each other. It is shown that the absorbed heat oscillates as a function of temperature, regardless of the geometry of the irradiated object. It is possible to formulate this behavior in a simple mathematical equation, which proves that the oscillation is basically caused by resonance of the electromagnetic waves within the object. This oscillation, combined with the heat loss, is found to be responsible for thermal runaway phenomenon in isothermal objects. Based on such an observation, a general rule to prevent thermal runaway has been developed.
Infrared transmission studies via lamellar gratings on Si wafer
Authors: Hava S. , Ivri J. , Auslender M. , Lacquet B. M.
Published: July 2002

Zero angle of incidence transmission studies through lamellar gratings on silicon wafers were performed. Gratings with feature sizes of the order of magnitude of the radiation wavelength were fabricated on silicon wafers using micromachining technology. We found that the normal unpolarized light transmission spectra of such grating wafers have an oscillatory behavior, with minima and maxima having transmission values of the order of 0.03 and 0.5, respectively. The two absorption notches at wavelengths 9.06 and 16.39 microns, which appear as dips in the smooth spectra, are diminished in some grating structures. The oscillatory behavior of the spectra proves the existence of coupled electromagnetic modes inside the grating cavities. Theoretical simulation of the spectra based on the S-matrix propagation algorithm are in agreement with the experimental results. The results indicate the possibility of obtaining, with a proper grating design, efficient narrow band filters and mirrors.
Modeling the power flow in normal conductor-insulator-superconductor junctions
Authors: Jochum J. , Mears C. , Golwala S. , Sadoulet B. , Castle J. P. , Cunningham M. F. , Drury O. B. , Frank M. , Labov S. E. , Lipschultz F. P. , Netel H. , Neuhauser B.
Published: July 2002

Normal conductor-insulator-superconductor (NIS) junctions promise to be interesting for x-ray and phonon sensing applications, in particular due to the expected self-cooling of the N electrode by the tunneling current. Such cooling would enable the operation of the active element of the sensor below the cryostat temperature and at a correspondingly higher sensitivity. It would also allow the use of NIS junctions as microcoolers. At present, this cooling has not been realized in large area junctions (suitable for a number of detector applications). In this article, we discuss a detailed modeling of the heat flow in such junctions; we show how the heat flow into the normal electrode by quasiparticle back-tunneling and phonon absorption from quasiparticle pair recombination can overcompensate the cooling power. This provides a microscopic explanation of the self-heating effects we observe in our large area NIS junctions. The model suggests a number of possible solutions.
Temperature dependence of exciton peak energies in multiple quantum wells
Authors: Pässler R.
Published: July 2002

The temperature dependence of the exciton peak energies as observed in short-period superlattice CdTe/ZnTe multiple quantum well (MQW) structures by Yoshimura et al. [Jpn. J. Appl. Phys., Part 1 34, 1459 (1995)] is fitted by an analytical four-parameter model developed recently by the author. Due to the dominance of short-wavelength phonons, the degree of concavity (superlinearity) of the MQW-specific electron-phonon spectral function is much more pronounced than in bulk samples of the constituent binary materials CdTe and ZnTe. We give an expression for the temperature dependence of exciton peak energies which is well suited particularly for analytical descriptions of the effective gap shrinkage phenomenon in narrow-well and short-period superlattice MQW structures.
Investigation of interface morphology and composition mixing in CdTe/CdS heterojunction photovoltaic materials using synchrotron radiation
Authors: Soo Y. L. , Huang S. , Kao Y. H. , Compaan A. D.
Published: July 2002

The interface microstructure in thin film photovoltaic materials is an important problem which can severely affect the light-conversion efficiency and stability of heterojunction solar cells. This is a long-standing fundamental problem, but has not been studied in the past by effective probing methods. In the present experiment, the interfacial roughness, correlation lengths of interface height fluctuations, effects of heat treatment, and diffusion of Te atoms across the heterojunction interface have been investigated by means of grazing incidence x-ray scattering and angular dependence of x-ray fluorescence using synchrotron radiation. We thus demonstrate that these x-ray techniques can provide a powerful tool for nondestructive characterization of the interfacial roughness and intermixing of selected atomic species in heterojunction photovoltaic materials.
Structural characterization of thin film ferromagnetic tunnel junctions
Authors: Smith David J. , McCartney M. R. , Platt C. L. , Berkowitz A. E.
Published: July 2002

Tunnel junctions comprised of two magnetic metal layers separated by a thin insulating oxide layer have been prepared by reactive sputtering onto thermally oxidized (100) silicon wafers at room temperature. The magnetic layers (thicknesses ∼30–50 nm) consisted of thin films of Co, Fe, and/or CoFe and the oxide barriers (thicknesses in the range 2–10 nm) included CoO, MgO, HfO2, and SiO2. The barriers were prepared by dc reactive sputtering from pure metal sources in mixed oxygen–argon atmospheres or by rf sputtering from oxide targets. Transmission electron microscopy in the cross-sectional geometry was used in this study to characterize the tunnel junction microstructure. Barriers of CoO and MgO were invariably polycrystalline with many crystallites extending across the entire barrier thickness, whereas barriers of SiO2 and HfO2 appeared to be amorphous. Although grain boundary diffusion has been proposed as a possible mechanism for providing shorts or “pinholes” between the magnetic electrodes, it was significant that both HfO2 (amorphous) and MgO (polycrystalline) showed high magnetoresistive response at low temperature.
Magnetic and structural properties of epitaxially grown FeTaN thin films
Authors: Varga L. , Jiang H. , Klemmer T. J. , Doyle W. D. , Payzant E. A.
Published: July 2002

Epitaxial FeTaN films (∼1500 Å) were grown as a function of nitrogen flow rate on epitaxial Cu(001) buffer layers (∼2000 Å) on Si(001) single crystal substrates to investigate the effect of Ta and nitrogen on the magnetocrystalline anisotropy and magnetostriction. Detailed structural investigation by transmission electron microscopy and x-ray diffraction showed that the FeTaN films were epitaxial with the Pitsch orientation relationship of FeTaN(110)∥Cu(001) and FeTaN〈111〉∥Cu〈110〉, which allows four different in-plane variants to coexist in the film. It was found that the saturation magnetization did not change with nitrogen addition (∼1600 emu/cc) up to 2% lattice dilation. The values of K1 and λ100 of Fe decreased slightly (20% and 10%, respectively), while λ111 increased with increasing nitrogen content and eventually changed sign at ∼2% normalized lattice dilation. These results qualitatively agree with our earlier findings on (001) oriented FeTaN epitaxial films on MgO single crystal substrates. Also, our calculated saturation magnetostriction for nanocrystalline samples agrees very well with published data on the same FeTaN composition. Based on Hoffmann’s ripple theory the ripple constant is calculated for nanocrystalline films using the Doyle–Finnegan model for the local average anisotropy and our measured single crystal constants. It was found that the effect of nitrogen on reducing the average anisotropy through the fundamental constants is not significant, and therefore the major factor in achieving a low ripple constant (i.e., soft magnetic properties) is the grain size, the number of grains across the thickness and the thin film stress.
Photoelectrochemical characterization of 6H–SiC
Authors: van de Lagemaat J. , Vanmaekelbergh D. , Kelly J. J.
Published: July 2002

Photoelectrochemical methods were used to characterize n-type 6H–SiC. The double layer capacitance obeyed the Mott–Schottky relationship over a large potential range (>6 V band bending). The flat-band potential was found to depend on pH with a displacement of about 40 mV per unit pH. The minority carrier diffusion length determined from the potential dependence of the photocurrent was 30 nm. From the dependence of the photocurrent on the photon energy, the absorption coefficient α(hν) was determined using the Gärtner model. The results are in excellent agreement with spectra reported in literature. Sub-band-gap photocurrent with photons of energy down to 1.96 eV (≈1 eV below the band gap) was also observed.
Mechanical strength of the solid-HDDR treated Nd–Fe–B-type materials
Authors: Kwon H. W. , Kang S. J.
Published: July 2002

The hydrogenation, disproportionation, desorption, recombination (HDDR) is known as a unique process through which a noncoercive cast Nd–Fe–B-type material can be easily converted into a coercive one. Although the conventional HDDR process generally leads to a powderlike material, a solid-HDDR material can be realized if the HDDR process is properly modified (solid-HDDR). In the present study, the change of mechanical strength (compressive strength) of the Nd–Fe–B-type material during the solid-HDDR has been investigated using a sintered magnet with composition Nd13.8Dy0.7Fe78.25Si0.15Mn0.6B6.5. It has been found that the low strength of the hydrided material was improved by the subsequent disproportionation. The restoration of the strength was explained by the eutectoidlike disproportionation structure containing fine neodymium hydride rod embedded in tough iron matrix. The high strength of disproportionated material was reduced radically in an earlier stage of recombination, and this was explained by the reduction of the disproportionated phase. The reduced strength was, however, recovered by further recombination, and this was explained by the fact that as the recombination continues the recombined grains become continuous and adhere together. The optimally HDDR processed material has a comparable or even higher strength with respect to the initial sintered material prior to the solid-HDDR. The present study suggested that the mechanical strength of Nd–Fe–B-type material could be retained even after the solid-HDDR.
Long-range antiferromagnetic couplings in [ZnTe|MnTe] superlattices
Authors: Lin J. , Rhyne J. J. , Furdyna J. K. , Giebutowicz T. M.
Published: July 2002

Magnetic semiconductor superlattices consisting of x monolayers of ZnTe alternated with y monolayers of MnTe [(ZnTe)x|(MnTe)y] have been grown in the zinc-blende structure by molecular beam epitaxy. For relative thin ZnTe nonmagnetic interlayers (3⩽x⩽6), neutron diffraction data show long range order within the MnTe layers and also an interlayer magnetic coupling across the semiconducting ZnTe interlayer extending over multiple bilayers. For the x=5, y=10; and x=4, 5, y=20 superlattices at low temperature (10 K), the spins in adjacent MnTe layers couple in an inphase antiferromagnetic structure with identical spin orientations in all MnTe layers. As the temperature is raised, this ordering slowly transforms into an antiphase coupling in which alternate MnTe layers have spin directions reversed. For increasing ZnTe layer thickness, a systematic reduction in the magnetic correlation range is observed, with the correlation range reducing to approximately one MnTe layer for x=6 and 7.
Microstructure and giant magnetoresistance of Co–Cu granular films fabricated under the extremely clean sputtering process
Authors: Tsunoda Masakiyo , Okuyama Kentaro , Ooba Makoto , Takahashi Migaku
Published: July 2002

In order to clarify the influence of the impurities in the sputtering atmosphere on the microstructure and the giant magnetoresistance (GMR) properties of nanogranular thin films, Co–Cu alloy films were prepared on quartz substrates at room temperature under the different purity of the sputtering atmosphere by changing the base pressure, 10−11 Torr extremely clean process (XC) and 10−7 Torr lower grade process (LG). The correlation between the microstructure and the GMR of films after an annealing procedure is discussed. As results, we found that; (1) A Co-rich phase combined with oxygen was formed at grain boundary in the films as deposited under the LG process; (2) the gradual progress of the grain growth of precipitates with increasing annealing temperature was observed in the XC-processed films, while the coarse grain growth of the matrix phase, resulting in the abrupt change of magnetoresistance occurred in the LG-processed films. We conclude that regulated impurity concentration in the films is an essential parameter to control the precipitation process from the supersaturated solid solution and to realize the desirable microstructure of the nanogranular GMR thin films.
Magnetic and structural properties of (Co1−xFex)Pt thin films
Authors: Jang P. W. , Kim D. W. , Park C. H. , Na J. G. , Lee S. R.
Published: July 2002

( Co 1−x Fe x ) Pt films were grown on a glass substrate by a rf sputtering and then annealed at 650–700 °C in a high vacuum. All the as-sputtered (Co1−xFex)Pt films deposited below 400 °C had a disordered structure and showed very low coercivities. With increasing the deposition temperature and Fe contents, the (111) texture was weakened in as-deposited (Co1−xFex)Pt ternary films. Vibrating sample magnetometer and x-ray diffraction data show that Co atoms in the L10 CoPt phase were substituted with Fe atoms. In-plane coercivities of these films decreased almost linearly with increasing Fe content which seemed to be due to the decrease of a crystalline anisotropy energy.
Piezomagnetic properties, saturation magnetostriction, and ΔE effect in DyZn at 77 K
Authors: Restorff J. B. , Wun-Fogle M. , Clark A. E.
Published: July 2002

Young’s modulus, magnetization, and magnetostriction measurements were made as a function of applied magnetic field (0<H<160 kA/m) and compressive stress (8.5 MPa<|T|<57.3 MPa) in [100] single crystal DyZn at 77 K. Piezomagnetic d constants greater than 300 nm/A and changes in Young’s modulus greater than 40 GPa were found. Pronounced features are abrupt changes in the elastic moduli, magnetostriction, and coupling factors arising from “jumps” in the magnetization occurring as the moment changes from one easy [100] axis to another. The characteristic magnetic fields at which this change occurs depend strongly upon the stress induced magnetic anisotropy. Magnetomechanical coupling factors reach 0.91.
Reversible processes and magnetic viscosity of nanocrystalline permanent magnets
Authors: Cornejo D. R. , Villas-Boas V. , Missell F. P.
Published: July 2002

The accurate determination of the magnetic viscosity parameter Sv requires the calculation of a new parameter η=(∂Mrev/∂Mirr)Hi which describes the dependence of reversible magnetization on irreversible magnetization. Measurements of the magnetic viscosity were performed at 300 K on the major demagnetization curves of two different nanocrystalline permanent magnetic materials: (i) melt-spun and flash-annealed Pr4Fe78B18 and (ii) mechanically alloyed and heat-treated Sm18Fe33Co49. We show that η is proportional to the intrinsic reversible susceptibility χrevi, in good agreement with predictions of the moving Preisach model. Measurements of the reversible susceptibility were made in order to determine η. Experimental values of η are positive on the major demagnetization curve in both materials, resulting in substantial corrections to Sv near Hc.
Optical and magneto-optical properties of Co/Pt/AlN multilayers
Authors: Atkinson R. , Dodd P. M. , Salter I. W. , Grundy P. J. , Tatnall C. J.
Published: July 2002

The optical and polar Kerr magneto-optical properties of a series of Co/Pt/AlN multilayers have been determined in the photon energy range 1.4–4 eV. Observations of the spectral variation of reflectivity are discussed in terms of the optical properties of the constituent materials using multilayer theory. Magneto-optic polar Kerr spectra over the same energy range are also discussed taking into account the modified magnetic properties resulting from undesirable structural changes in the films.
Basic mechanisms of an atomic force microscope tip-induced nano-oxidation process of GaAs
Authors: Okada Yoshitaka , Amano Shinji , Kawabe Mitsuo , Harris James S.
Published: July 2002

An atomic force microscope (AFM) tip-induced direct nano-oxidation process of GaAs(100) substrates has been investigated, and is viewed as a promising method for the fabrication of nanometer-scale electronic devices such as single electron tunneling transistors. The effects of the AFM drawing parameters such as tip bias voltage and writing speed as well as the ambient humidity on the oxide line height and width were explored. The rate of reaction and its dependence on electric field strength and oxide thickness were examined to understand the basic mechanisms involved in the tip-induced oxidation of GaAs. The rate of oxidation/anodization was found to decrease rapidly with oxide film growth, which was explained at the simplest level in terms of a self-limiting influence of decreasing electric field strength.
Study on the shear viscosity of several inorganic glasses
Authors: Takahashi H. , Hiki Y. , Kobayashi H.
Published: July 2002

The viscosities of metaphosphate, pyrophosphate, molybdate, and fluorophosphate glasses were measured under the shear deformation mode using a sandwich method from room temperature up to the glass transition temperature Tg. An optical method was used to measure the deformation under constant load as a function of time, and the results were analyzed using a mechanical model of anelasticity plus viscosity. In glasses containing long molecular chains, two relaxations appeared at lower and higher temperatures, while only one relaxation existed at higher temperatures in glasses without the chain. Both these relaxations were of the thermal activation type. A correlation between the frequency factor and the activation energy was found for the high temperature relaxation, and the values of the frequency factor were very large. Another apparatus, a rotation disk viscometer, was also used to measure the shear viscosity above Tg. The data obtained by the two experimental methods related to each other well, and the viscosity value at Tg was of the order of 108 Pa s. The viscosity was in the hydrodynamic regime at temperatures sufficiently above Tg, and in the hopping regime below a temperature near Tg.
Interdiffusion in InGaAs/GaAs: The effect of growth conditions
Authors: Khreis O. M. , Homewood K. P. , Gillin W. P.
Published: July 2002

The effect of growth temperature and group-V to group-III flux ratio on the intermixing process in molecular beam epitaxial grown InxGa1−xAs/GaAs multiquantum wells were studied by means of photoluminescence coupled with repetitive thermal anneal experiments. We have shown that, for a wide range of growth conditions (growth temperatures from 565 to 636 °C and flux ratios from 5:1 to 25:1) the interdiffusion is controlled solely by a constant background concentration of vacancies which are probably introduced into the substrate during its manufacture. We have shown that, only growth at very low temperatures (470 °C) will result in appreciable excess vacancies.
Effects of copper deficiency on the structure and microwave properties of YBa2Cu3O7−δ films deposited by laser ablation
Authors: Yoshitake T. , Hattori W. , Tahara S.
Published: July 2002

The work reported here evaluated the correlation between the copper composition and the structural and microwave properties of YBa2Cu3O7−δ (YBCO) films deposited on MgO substrates. Detailed x-ray diffraction measurements revealed that the superconducting YBCO phase in the films has a solubility range on the copper-poor composition side. The structure of the YBCO phase depends on copper composition: a lower copper composition is associated with a larger c-axis lattice constant and a decreased degree of orthorhombicity. These structural changes correlated well with increases in normal resistivity, decreases of transition temperature Tc, and increases in microwave surface resistance Rs. The films with less copper composition also show a more gradual decrease in Rs below Tc than do copper-rich films. These results suggest that changes in these properties are closely connected with copper deficiency that can occur more easily when the copper composition is low. The copper composition is, therefore, a crucial factor in developing YBCO films with low microwave loss.
Effect of processing conditions on the growth of strained Si1−XGeX layers on Si
Authors: Suh K. Y. , Lee Hong H.
Published: July 2002

We investigate several factors that determine the surface morphology in heteroepitaxial growth of Si1−XGeX films on Si, which include composition, temperature, and pressure. Phase boundary lines are derived that define the regions for planar and island growth in terms of composition–temperature and composition–pressure. Also derived is the roughening characteristic length as a function of temperature, pressure, and characteristic time. Our results can explain the literature data satisfactorily.
Two signals in electrically detected magnetic resonance of platinum-doped silicon p–n junctions
Authors: Kamigaki Yoshiaki , Miyazaki Takao , Yoshihiro Naotsugu , Watanabe Kikuo , Yokogawa Ken’etsu
Published: July 2002

We have found two electrically detected magnetic resonance (EDMR) signals at room temperature in forward-biased platinum (Pt)-doped (111) silicon p–n junction diodes with a linearly graded junction. The g values of the two EDMR signals are 1.991 (signal 1) and 1.978 (signal 2), respectively, when the surface of the diode is parallel to the magnetic field. The two signals increase after applying a large reverse-bias voltage to the junction. They decay with time; the decay rate after more than 1 h is smaller for signal 1 than for signal 2. The recombination current also changes in a similar manner as the EDMR signals. The intensity of the two EDMR signals each shows a known bell-shape dependence on a forward bias voltage; signal 1 is observed at slightly lower voltages than signal 2. The deep level transient spectroscopy (DLTS) spectrum from the diodes shows two peaks at 0.23 and 0.32 eV. For diodes with different Pt-diffusion temperatures, 865 and 885 °C, the ratio of the intensity of the EDMR signals corresponds to that of the platinum solubility in silicon, as does the ratio of the intensity of the DLTS peaks. Thus, we conclude that the two EDMR signals are related to the two Pt trap levels.
Structural and magnetic properties of the Ti/Fe multilayers
Authors: Fnidiki A. , Juraszek J. , Teillet J. , Duc N. H. , Danh T. M. , Kaabouchi M. , Sella C.
Published: July 2002

The structure and magnetic properties of the rf-sputtered Fe/Ti multilayers with the fixed Ti-layer thicknesses (series 1: tTi=1 nm and series 2: tTi=2 nm) and the variable Fe-layer thicknesses (1 nm⩽tFe⩽6 nm) have been studied by the high-angle x-ray diffraction, transmission electron microscopy, conversion electron Mössbauer spectrometry and vibrating sample magnetometer. The results show that Fe layers with thicknesses less than 1 nm are alloyed forming an amorphous TiFe2 phase. As the Fe-layer thickness increases, the iron-rich crystalline Fe–Ti alloy is formed at the interface and, finally, the pure crystalline α-Fe and Ti layers appear in the center of the individual subsystems. The spin orientation in Fe layers is then strongly aligned in the film plane. However, in the interfacial region, perpendicular spin orientation is evidenced. This perpendicular magnetic anisotropy is associated to the Fe-rich alloy at the interface and is discussed in terms of reduced symmetry effects on the band structure of the 3d(Fe)-itinerant electrons.
Size distribution of coherently strained InAs quantum dots
Authors: Schmidt K. H. , Medeiros-Ribeiro G. , Kunze U. , Abstreiter G. , Hagn M. , Petroff P. M.
Published: July 2002

The influence of the InAs coverage on the size and density of coherently strained InAs islands was investigated. At moderate InAs coverages the photoluminescence signal reflects the Gaussian size distribution of small coherently strained islands. However, before the coherently strained islands transform into dislocated ones the Gaussian line shape of their photoluminescence signal changes and a narrow peak appears on the low-energy tail. We attribute this change to an accumulation of coherently strained islands at a maximum size before dislocated island transformation occurs. Effects of luminescence from dislocated islands, size-dependent relaxation processes, capture efficiencies, and dot-dot coupling are also discussed. However, our calculations and the magnetophotoluminescence, as well as the photovoltage experiments, confirm our interpretation of a size accumulation process of coherently strained islands.
Influence of detection conditions on near-field optical imaging
Authors: Hecht B. , Bielefeldt H. , Pohl D. W. , Novotny L. , Heinzelmann H.
Published: July 2002

The process of image formation in transmission mode scanning near-field optical microscopy is analyzed both theoretically and experimentally. Changes in the dielectric and topographic properties of the sample influence not only the total transmitted intensity, but also its angular distribution in the far field. This opens up an additional source of optical information about the sample. Some of this additional information is retrieved by separate but simultaneous detection of the radiation emitted at angles smaller (allowed light) and larger (forbidden light) than the critical angle of total internal reflection, respectively. Different experimental setups and their respective advantages are discussed. High resolution, constant height mode optical images of test structures are compared with theoretical predictions. Forbidden-light optical images frequently provide enhanced resolution and/or contrast as compared to allowed light images. For small phase objects, in contrast to amplitude objects, a contrast reversal between forbidden and allowed light images is observed.
Phase diagram for a frustrated disordered Blume–Emery–Griffiths model
Authors: Puha I. , Diep H. T. , Campbell I.
Published: July 2002

The critical behavior of the three-dimensional Blume–Emery–Griffiths model with weak quenched disorder is studied using standard and histogram Monte Carlo calculations. It was argued in previous studies that, with the introduction of bond randomness, first-order behavior cedes to some degree to second-order behavior for d⩽2. We show, in d=3 spatial dimensions, first-order phase transitions that have taken place in the investigated model disappear only at a finite amount of randomness.
Determination of effects of deposition and anneal properties for tetranitratotitanium deposited TiO2 dielectrics
Authors: Kim Hyeon-Seag , Campbell S. A. , Gilmer D. C. , Kaushik V. , Conner J. , Prabhu L. , Anderson A.
Published: July 2002

Carbon and hydrogen free tetranitratotitanium was synthesized, which is believed to thermally decomposed primarily as: Ti(NO3)4→TiO2+4NO2+O2. The by-products of the thermal decomposition of tetranitratotitanium, which include NO2 and O2, may possibly provide a robust ultrathin tunnel interfacial layer. Due to the hydrogen free nature of thermolysis, N2O may form an oxynitride layer which has been shown to produce thermal oxynitrides with higher quality than NH3-based nitride oxides. Unlike titanium tetrakis isopropoxide (TTIP) deposited films, the interface state density more closely follows the “U” shape characteristic of conventional thermal SiO2/Si interfaces. The integrated interface state density is considerably less for the film annealed at higher temperature, which should produce considerably higher inversion layer mobilities. This improvement of the interface, compared to TTIP deposited films, is believed to be due to the elimination of water vapor from the deposition ambient.
DX centers in InxAl1−xAs
Authors: Sari Hüseyin , Wieder H. H.
Published: July 2002

The composition dependence of the energy levels of the DX centers in InxAl1−xAs/InyGa1−yAs heterostructures have been determined by means of Hall effect and persistent photoconductivity measurements made on gated Hall bar test structures, primarily in the indirect portion of the fundamental band gap of InxAl1−xAs. The energy of the DX center relative to the average of the main conduction band minima of the Brillouin zone, in the composition range, 0.1⩽x⩽0.34, is E(DX)∼0.3 eV; for x>0.4 the DX center is resonant with the conduction band.
Towards stimulated generation of coherent plasmons in nanostructures
Authors: Kempa K. , Bakshi P. , Du C. G. , Feng G. , Scorupsky A. , Strasser G. , Rauch C. , Unterrainer K. , Gornik E.
Published: July 2002

A possible generation scheme for growing coherent plasma oscillations (plasma instability) is presented. Specific quantum well structures, where a sufficient population inversion can be maintained in the carrier distribution by appropriate injection–extraction configurations, form the basis of this scheme. Self-consistent random phase approximation calculations show that a population inversion, leading to a plasma instability, can occur in such structures. A comparison between the calculated and the observed differential conductance curves suggests that such quantum well structures could be designed as active regions for the generation of terahertz frequency radiation sources.
Up-converted emission observed from a hybrid inorganic:organic composite thin film
Authors: Joshi Mukesh P. , DeLeon R. L. , Prasad P. N. , Garvey J. F.
Published: July 2002

Hybrid inorganic:organic composites of TiO2:APSS were fabricated by mixing the constituents in the gas phase using the technique of laser-assisted molecular beam deposition. Ultraviolet-visible and infrared spectra of the composite thin films indicate that the organic monomeric chromophore is physically embedded within the titanium dioxide matrix without any thermal degradation. Two-photon pumped up-converted fluorescence emission is observed in the films, such that irradiation of the film at 800 nm results in a highly visible green emission.
Fully in plane aligned SmCo based films prepared by pulsed laser deposition
Authors: Cadieu F. J. , Rani R. , Theodoropoulos T. , Chen Li
Published: July 2002

SmCo based films, ≈1–3 μm thick, have been directly crystallized onto moderately heated polycrystalline susbstrates, 375 °C, by high pulse energy pulsed laser deposition. Films have been deposited to compare shadow and direct deposition. Only for shadow deposition conditions has it been possible to deposit CaCu5-type structure films that exhibit hysteresis loops characteristic of single phase materials with high coercivities. The shadow deposited films are mirror-like, very fined grained (less that 0.2 μm), and with the crystallite c axes completely aligned onto the substrate plane. For optimally deposited films, room temperature hysteresis loops measured perpendicular to the film plane were closed with approximately zero coercivity. For such films, hysteresis loops measured in plane with fields to ±90 kOe at room temperature exhibited intrinsic coercivities of at least 22.5 kOe. Measurement fields of ±19 kOe yielded only minor loops that did not enclose the origin in some cases. The fully textured SmCo based films in the present study were deposited using λ=248 nm and a pulse energy of 1200 mJ. The magnetic properties are a function of the laser pulse rate and this has been studied from 5 to 50 Hz repetition rates.
Magneto-optical effects of Rh3+ and Rh4+ doped yttrium iron garnet
Authors: Kučera M. , Kuneš J. , Gerber R.
Published: July 2002

The Faraday rotation and magnetic circular dichroism (MCD) were studied in yttrium iron garnet epitaxial films Y3Fe5O12 doped with trivalent and tetravalent rhodium ions. The magneto-optical effects were measured in the spectral region from 0.5 to 2.5 eV (500–2400 nm) at temperatures between 80 and 300 K. The change in valency of Rh transpired to have a huge effect on the observed magneto-optical phenomena. The contribution from the trivalent Rh ions was very small compared with its tetravalent counterpart. Given the assumption that both the trivalent and tetravalent rhodium ions are in the low-spin state, then the Rh3+(4d6) ions have a negligible magnetic moment and therefore provide only a minor magneto-optical effect. In contrast, strong peaks in the Faraday rotation and MCD spectra are induced in the near infrared and visible regions due to an uncompensated spin moment in the Rh4+(4d5). At photon energies higher than 2.5 eV, the allowed charge transfer transitions to the iron 3d states played a more dominant role with no apparent contribution from the rhodium 4d states.
Spin wave resonance of amorphous Co1−xZrx thin films
Authors: Kim Yark Yeon , Baek Jong Sung , Rhie Kung Won , Lim Woo Young , Yu Seong Cho , Lee Soo Hyung
Published: July 2002

Ferromagnetic resonance experiments have been executed to investigate the annealing and the Zr concentration dependence of magnetic surface properties in amorphous Co1−xZrx (13.5<x<23) thin films. Spin wave resonance spectra for all annealing conditions consist of several volume modes and one or two surface modes. Both surfaces of the film have a hard axis perpendicular to the film plane (negative surface anisotropy) for all Zr concentration. The surface anisotropy Ks2 at substrate-film interface is varied from −0.12 to −0.4 erg/cm2 and the surface anisotropy Ks1 at film-air interface is steadily varied from −0.01 to −0.45 erg/cm2 with increasing annealing times. Also, we have quantitatively investigated the thickness of Zr oxidation in each annealing time by analyzing the surface and the volume modes with the uniaxial surface anisotropy model.
Remanent magnetization structures in single-layer perpendicular thin film media
Authors: Honda Y. , Hirayama Y. , Ito K. , Futamoto M.
Published: July 2002

An analytical magnetic force microscopy has been applied to investigate the relationship between the remanent magnetization and the film microstructure for various types of CoCr-alloy single-layer perpendicular media. The minimum size of irregular magnetic domain in CoCr and CoCrTa media is found to be an unit crystal grain, while that of CoCrPt media includes at least four magnetic crystal grains.
Ultrathin magnetic particles
Authors: Marty F. , Vaterlaus A. , Weich V. , Stamm C. , Maier U. , Pescia D.
Published: July 2002

We have fabricated ultrathin Co particles with various shapes, variable thicknesses δ (2 ML<δ<22 ML), and lateral size L ranging from 100 μm to ≈100 nm. We find that all particles are magnetized in-plane at room temperature and are in a single domain state, independently of shape and size—with some remarkable exceptions. We also find that the magnetic state of a particle can be manipulated without influencing the state of the neighbors.
Underlayer effect on magnetoresistance of top- and bottom-type spin valves
Authors: Fujikata Junichi , Hayashi Kazuhiko , Nakada Masafumi
Published: July 2002

The effect of underlayers on top- and bottom-type spin valves with PtMn and NiO is investigated. For the top-type spin valves with PtMn, magnetoresistance (MR) ratios are enhanced by using Zr underlayers compared to those for Ta underlayers. The bottom-type spin valves with PtMn showed larger MR ratios than the top-type spin valves as the free layer thickness decreased. The improved giant magnetoresistance results mainly from the increased Δρ due to the smoother interface for the spin valves. Spin valves with NiO underlayers showed smaller resistivity and an almost constant Δρ for a wide range of free layer thicknesses.
Observation of self poling in BaTiO3 thin films
Authors: Lubomirsky Igor , Chang David T. , Stafsudd Oscar M.
Published: July 2002

The dependence of ferroelectric properties of sol-gel derived BaTiO3 thin (0.35 μm) films on various Si substrates was investigated. It was found that only films deposited on p+ Si (1020 cm−3 B, 2% Ge) are (110) oriented and possess a few percent of the spontaneous polarization of single-crystal BaTiO3. The direction of polarization self restored after being reversed by external bias or heated above the Curie temperature. It was found that the pyroelectric coefficient was not zero above the Curie point, which indicated that the films are permanently subjected to an electric field, which originates from the contact potential between the film and the substrate. This conclusion was confirmed by surface photovoltage spectroscopy. Orientation of the films was attributed to the presence of Ge in the substrate, which decreased lattice mismatch between the (100) vector of the Si substrate and (110) vector of BaTiO3. The possibility of a paraelectric to ferroelectric transition driven by an electric field due to the contact potential difference must be taken into account for dynamic random access memory applications.
Infrared-reflection characterization of sintered SiC thermoelectric semiconductors with the use of a four-component effective medium model
Authors: Okamoto Y. , Ordin S. V. , Kawahara T. , Fedorov M. I. , Miida Y. , Miyakawa T.
Published: July 2002

Infrared (IR) reflection spectra of sintered SiC thermoelectric semiconductors are studied as a function of doping concentration as well as of sintering temperature. Attention is focused on the changes in the reststrahlen band. The peak and dip frequencies remain constant, implying we are probing stable optical phonon mode in the crystalline grains through the interaction with IR photons. In contrast, variation of spectral shape, including the peak and background reflectance seems to give valuable information regarding the quality of the sintered samples and dopant distribution within the crystal grains and grain boundaries. Measured spectra are analyzed by the use of a four-component effective medium model. In this model we assume the presence of: (1) pores, (2) intergranular materials, (3) crystalline grains, and (4) metallic inclusions (at higher doping levels of metallic impurities), with volume fractions fi(i=1–4), respectively. For frequency dependent complex dielectric functions we employed: (a) a single oscillator model appropriate to the single crystal for the crystalline grains, (b) a Drude model for the metallic inclusions, and assumed (c) another single oscillator model for the intergranular material. The parameters of the latter are determined to give a best fit to the spectrum of a low doping level sample. This model gives excellent overall fit to measured spectra with the ratio f2/f3 and the damping coefficients for the oscillators as adjustable parameters when the experimental estimates for the fraction of pores f1 and metallic inclusions f4 are used. This is remarkable in view of the situation that similar data could not, so far, be explained in terms of the simple Maxwell–Garnet model. The results suggest that careful analyses of spectral shape of IR reflection in the optical phonon resonance region can be used to get information on the intergranular to grain ratio or on the damping coefficients, which are related to the quality of sintered samples or to the distribution of doped impurities among grains and grain boundaries. The background reflectance also give information on the presence of metallic inclusions although the effects of scattering may affect the interpretation. These results combined with the possibility of local probing seems to imply that IR reflectance can offer a versatile means to check the quality of the sintered samples.
Role of boundary conditions and dimensions on the micromagnetics of a cobalt point contact
Authors: van Gorkom R. P. , Theeuwen S. J. C. H. , Wellock K. P. , Gribov N. N. , Caro J. , Radelaar S.
Published: July 2002

We have calculated the micromagnetic structure of a Co point contact, for applied magnetic fields parallel (H∥) and perpendicular (H⊥) to the device’s electrodes. Different boundary conditions and dimensions have been examined. In most situations a Néel wall is formed in the constriction. When the size of the device is reduced (or the exchange stiffness is increased), then the energy barrier between the state with and without the Néel wall is increased. The domain wall magnetoresistance (DWMR) and anisotropic MR (AMR) have been estimated, and they show a maximum in the DWMR for both field directions of the applied magnetic field and a maximum and minimum in the AMR for H∥ and H⊥, respectively.
Changes in the Fermi surface at the magnetization reorientation transition in Fe/Cu(100)
Authors: Madjoe Reginaldt H. , Koveshnikov Alexey N. , Harwell Christopher , Hall Randall , Stockbauer Roger L. , Kurtz Richard L.
Published: July 2002

We present a study of the evolution of the valence band structure of Fe/Cu(100) as a function of Fe coverage in the 0–12 monolayer range. Angle-resolved photoelectron spectroscopy was used to probe the valence electronic structure and to extract Fermi surface contours as a function of increasing Fe coverage. The first few monolayers show Fe-induced densities of states that are significantly different from those in thicker films. At 5 ML, distinct changes occur in the Fermi surface, where a magnetization reorientation transition has been observed previously.
Ab initio study of anisotropic magnetism in uranium compounds
Authors: Collins Eric M. , Kioussis Nicholas , Lim Say Peng , Cooper Bernard R.
Published: July 2002

We have applied two methods to investigate the origin in the electronic structure of the unusual magnetic behavior of the uranium monochalcogenides and monopnictides. First, we have carried out spin-polarized electronic structure calculations based on the full-potential linearized muffin-tin orbital (FPLMTO) method with only spin-polarization (orbital polarization only via spin-orbit coupling) and also with orbital polarization correction. Second, we have carried out first-principles calculations synthesizing (1) a phenomenological theory of orbitally driven magnetism using a model Hamiltonian which incorporates explicitly the hybridization-induced and Coulomb exchange interactions on an equal footing, and (2) FPLMTO electronic structure calculations allowing a first-principles evaluation of the parameters entering the model Hamiltonian. Within the purely band calculation greater success is obtained for the zero-temperature ordered moments for the more itinerant compounds (US and UP), while the synthesis of phenomenology and electronic structure method gives better agreement with experiment for the more localized pnictides (UBi, USb). Results for the ordered moments and ordering temperatures are presented, and the validity and limitations of the two methods are discussed.
Static and dynamic magnetic response of CeFe2
Authors: Caciuffo R. , Griveau J.-C. , Kolberg D. , Wastin F. , Rinaldi D. , Panchula A. , Canfield P.
Published: July 2002

The magnetic response of CeFe2 single crystals was studied by direct-current magnetization and linear and nonlinear alternating-current susceptibility measurements. Several anomalies have been observed below the Curie temperature (TC=228 K). A kink near 30 K in the real component of the linear susceptibility, χ1′(T), is accompanied by a frequency dependent peak in both the linear imaginary part, χ1″(T), and the third-harmonic nonlinear susceptibility, |(3/4)χ3H02|. It is suggested that these features are related to the development of antiferromagnetic spin fluctuations of growing spatial extension, indicating an electronic instability below 80 K.
Enhanced in-plane anisotropy of Tb–Fe thin films by Sm addition
Authors: Lim S. H. , Han S. H. , Kim H. J. , Choi Y. S. , Shima T. , Fujimori H.
Published: July 2002

Effects of Sm on the magnetic and magnetostrictive properties of Tb–Fe thin films are investigated. Four alloy systems, RxFe100−x (R=Tb+Sm) with x=39.8, 41.9, 43.7, and 45.8, are examined with Sm content varied from 0 (Sm free) to 2.2 at. %. In-plane anisotropy is found to be enhanced by the addition of Sm and the strongest in-plane anisotropy occurs in the Sm content range of 1 to 2 at. % depending on R content. At low magnetic fields of 1000 Oe and below, magnetostriction increases significantly with increasing Sm content, and reaches a maximum at an intermediate Sm content where well-developed in-plane anisotropy is observed. At higher magnetic fields of 3000–5000 Oe, however, no substantial improvement of magnetostriction occurs with the addition of Sm. The Sm content dependences of magnetization and coercive force are also examined.
Magnetization and magnetostriction of Tb1−xDyxZn single crystals
Authors: Cullen J. R. , Wun-Fogle M. , Teter J. P. , Restorff J. B. , Clark A. E.
Published: July 2002

Magnetization, magnetostriction, and elastic modulus measurements were made on single crystal specimens of Tb1−xDyxZn. Easy axis magnetization rotation as much as 26° were observed in the (001) plane of Tb0.75Dy0.25Zn below 33 K. From these measurements, values of the K4/K8 anisotropy ratios were calculated. No easy axis magnetization rotation was observed in the x=0.6 and x=0.8 single crystals. Magnetostriction and modulus measurements at 77 K in Tb0.4Dy0.6Zn showed a saturation magnetostriction of ∼5×10−3 and a maximum magnetomechanical coupling factor of 0.96.