bluuebunny/crossref_metadata_2025 huggingface dataset:
Microfocusing and polarization effects in spherical neck ceramic microstructures during microwave processing
Authors: Birnboim A. , Calame J. P. , Carmel Y.
Published: July 2002

During microwave sintering of compacted ceramic powders, the electric field distribution within the ceramic body on a macroscale is determined by a combination of the operating frequency, the sample shape, and its permittivity. In contrast, our studies show that on a microscopic scale, the local electric fields are disproportionately intense close to grain boundaries and rough surfaces due to strong focusing. Also, the electric field in the interparticle contact zone exhibits preferred polarization directions despite illumination by a randomly polarized wave. This can lead to a highly nonuniform energy deposition and accelerated mass transfer rates via ponderomotive diffusion and plasma generation.
Analysis of specular and textured SnO2:F films by high speed four-parameter Stokes vector spectroscopy
Authors: Rovira P. I. , Collins R. W.
Published: July 2002

A rotating-compensator multichannel ellipsometer has been applied to measure the unnormalized Stokes vector that describes the polarization state of light reflected from specular and textured SnO2:F transparent conducting films on glass substrates. This four parameter spectroscopy yields the ellipsometric angles (ψ, Δ), the reflectance R, and the degree of polarization p, with a potential repetition time of 32 ms for all four 100 point spectra from 1.5 to 3.75 eV. The rotating-compensator design permits high accuracy evaluation of Δ over its full range (−180°<Δ⩽180°), even in the presence of random depolarization. This allows accurate analyses of the microscopic structure and optical properties of the SnO2:F films, based on fits to (ψ, Δ) using an ideal (specular) multilayer model. Differences between the reflectance spectrum predicted from the ideal model and that from experiment can be understood by including light scattering at the film surface due to texture (i.e., macroscopic roughness on the scale of the wavelength) in the model. The macroscopic roughness layer distribution can be extracted based on fits to R. The information obtained optically from {(ψ, Δ), R} is corroborated by direct structural measurements. Finally, we find that the spectra in p for both the specular and textured SnO2:F films exhibit oscillations that are attributed to sample nonuniformities over the beam area, with possible contributions from other sources. The similarity of p for both samples, along with the consistency of the (ψ, Δ) analysis results for the textured SnO2:F film, suggest that the scattering generated by the texture does not distort the information accessible through the polarized component of the reflected beam.
Longitudinal spin-density-wave ordering in thin epitaxial chromium layers
Authors: Rots M. , Demuynck S. , Cottenier S. , Dekoster J. , Meersschaut J.
Published: July 2002

Thin chromium films molecular beam epitaxy grown on partly relaxed MgO/Fe substrates held below T=150 °C are found either nonmagnetic below a chromium thickness around 5.0 nm or in a single-Q magnetic domain with the longitudinal (spins-out-of-plane) spin-density-wave (SDW) ordering stable up to 500 K. The longitudinal SDW-to-paramagnetic transition, the absence of the spin-flip transition and the actual character of the SDW depends on specific growth conditions. The present results reveal the spin-flip transition in chromium as an anisotropy effect rather than an intrinsic feature of the SDW ordering.
Anisotropic magnetism in Nd5Rh4Sn10 single crystal
Authors: Patil N. G. , Ramakrishnan S. , Becker B. , Nieuwenhuys G. J. , Menovsky A. A. , Mydosh J. A.
Published: July 2002

Our recent studies on polycrystalline samples of the R5Rh4Sn10 series have shown unusual multiple ordering with a first order magnetic transition in tetragonal Nd5Rh4Sn10 at low temperatures. In this study, we report resistivity, susceptibility, and heat capacity (in various fields up to 10 T) in a single crystal of Nd5Rh4Sn10. We observe antiferromagnetic ordering of Nd3+ spins along the c axis while they order ferromagnetically along the a axis. The first order transition was rapidly suppressed with fields above 4 T along the c axis while it was marginally affected up to 10 T for field along the a axis. We propose a tentative model to explain this feature.
Nonlinear microwave-magnetic resonator operated as a bistable device
Authors: Prabhakar A. , Stancil D. D.
Published: July 2002

The excitation of large amplitude spin waves causes a shift in the resonance frequency of a ferrite resonator towards higher frequency values. Using this shift, a resonator can be designed to operate in a bistable mode where the history of the input power determines the output power. A theoretical calculation for a resonator with a linewidth of 1.5 MHz, measured at 10 GHz, predicts a discontinuous jump in output power by a factor of about 3.5 as the input power is increased to about 0.7 mW. The phenomenological model that describes the bistability also provides an explanation for the foldover of ferromagnetic resonance curves at high input power levels. An appropriate choice for the operating frequency ensures that the estimated input power required to observe the bistable behavior is below the predicted threshold power for spin-wave auto-oscillations at the main resonance.
Magnetic properties of Ti/Fe double layers grown on MgO(100) by direct current magnetron sputtering
Authors: Fermin José R. , Azevedo Antonio , Li Biao , de Aguiar F. M. , Rezende Sergio M.
Published: July 2002

The purpose of this work is to investigate the magnetic properties of Ti(tTi)/Fe(104 Å) bilayers deposited by dc magnetron sputtering onto MgO(100) substrates. In-plane ferromagnetic resonance (FMR) has been used to measure the resonance field HR and linewidth ΔH as a function of the azimuthal angle and Ti layer thickness. The FMR spectra were obtained at room temperature and at a microwave frequency of 12.3 GHz. The dependence of ΔH with respect to the azimuthal angle is explained by taking into account the combined effects of intrinsic damping and angular dispersion of the cubic axes. The dependence of the magnetic relaxation on Ti thickness exhibits two different regimes. It decreases for the first Ti layers (tTi<30 Å) and increases up to a saturation value for Ti thickness around 90 Å. Other magnetic parameters such as effective magnetization, magnetocrystalline, and perpendicular anisotropies are also discussed.
Theory of dipole-exchange spin waves in ultrathin antiferromagnetic films
Authors: Pereira J. Milton , Cottam M. G.
Published: July 2002

A spin wave theory is developed for ultrathin antiferromagnetic films in the regime where the effects of the dipole–dipole and exchange interactions may be comparable. A microscopic model with a Hamiltonian representation of the above terms is employed, giving a description of linear spin waves in lowest order and the dominant spin wave interactions as higher-order effects. Applications are made to rutile-structure antiferromagnets (such as MnF2), perovskite-structure antiferromagnets (such as RbMnF3), and layered antiferromagnets (such as K2NiF4), which exhibit quite different behavior.
Effect of lattice distortion on magnetic and electronic state of α″-Fe16N2
Authors: Okamoto Satoshi , Kitakami Osamu , Shimada Yutaka
Published: July 2002

We have studied the correlation of the magnetic moment and electronic state of α″-Fe16N2 with the lattice distortion. The epitaxial (α″+α′)-Fe16N2 films were fabricated on Ag(001) underlayers by sputter beam method. With decreasing the film thickness, the unit cell volume of α″-Fe16N2 increased and distinct enhancement of the magnetic moment up to 2.8μB/Fe atom was found. The precisely determined x-ray diffraction intensity ratio Iα″(002)/Iα″(006) apparently reduced with increase of the unit cell volume. From our theoretical calculations, reduction of Iα″(002)/Iα″(006) means increase of the valency of N atoms in α″-Fe16N2. Therefore, it is considered that increase of the magnetic moment of α″-Fe16N2 is attributed to the charge transfer from N to Fe due to lattice expansion effect. This is the first observation showing close relationship between the electronic state and the magnetic moment of α″-Fe16N2.
Head parameter sensitivity study of the intrinsic field reversal time
Authors: George Peter K. , Jury Jason C. , Judy Jack
Published: July 2002

Studies to establish the key head sensitivity parameters affecting the intrinsic field reversal time are reported. The effect of supply voltage, eddy current damping, head moment, and turns are investigated using the nonlinear, eddy current damped, thin-film write head model proposed by Klaassen and Hirko [IEEE Trans. Magn. 32, 3524 (1996)]. The model is realized using PSPICE circuit simulation. Eddy current time constant dependencies derived by Wood, Williams, and Hong [IEEE Trans. Magn. 26, 2954 (1990)] are used to explore materials with magnetizations ranging from 4πMS=10–20 kG, resistivities of 25 and 125 μΩ-cm and heads with 10–15 turns. Confirmation of the above writer sensitivities has been investigated using a short yoke 37 turn, high moment, low eddy current CoTaZr inductive head. From the experimentally determined model parameters, rise time results are computed for an improved 10 turn writer design. The results are shown to approach or exceed the limiting dynamics of the spin system.
The relationship between high speed switching characteristics and the fluctuation field
Authors: Stinnett S. M. , Doyle W. D. , Koshkina O. , Zhang L.
Published: July 2002

Current thin film high performance media have very high viscosity and consequently a significant dependence of the remanent coercivity HCR on the measurement time. The fluctuation field Hf is a parameter commonly used to describe thermal effects and is defined in terms of the magnetic viscosity and the irreversible susceptibility χIRR. Previous work has shown that the viscosity is independent of time down to 10−8 s. Here we examine the time dependence of χIRR on a variety of particulate and high density thin film media at both long times (5–1000 s) and very short times (1–20 ns). It was found that χIRR was independent of time down to ∼10 ns. However, below 10 ns, χIRR decreased rapidly, signaling the probable onset of gyromagnetically controlled switching.
Large change of the giant magnetoresistance behavior after changing the spacer from Cu to CuMn alloy in Co/spacer/Co structures
Authors: Wang H. , Jin Q. Y. , Zhou S. M. , Shen Y. H. , Li F. M. , Chen L. Y. , Zhu X. R. , Shen H. L. , Pan M. H. , Lu M.
Published: July 2002

The giant magnetoresistance (GMR) effects in sandwiched Co/Cu/Co and Co/CuMn/Co structures have been investigated. The GMR oscillates with the spacer thickness for both cases, but is nearly antiphased. With diluted Mn atoms in the Cu spacer, the GMR curve as a function of the magnetic field changes a lot, and the saturation/switching field for GMR can be reduced greatly compared with that in Co/Cu/Co systems. This may indicate one way to obtain a highly sensitive GMR.
Remanent states in periodic antidot permalloy arrays
Authors: Torres L. , López-Dı́az L. , Alejos O. , Iñiguez J.
Published: July 2002

It has been recently suggested that periodic antidot arrays in magnetic media could be a suitable system for high density data storage because hard axis magnetic switching has remanence and hence, memory. In this work a numerical micromagnetic study of periodic antidot permalloy arrays is presented. Remanent states are obtained after saturation of the sample along the hard axis direction for different antidot sizes w (0.32 μm⩽w⩽2.16 μm) and different separation distances d between antidots (w/2⩽d⩽3w). Our micromagnetic model allows us to study these systems beyond the experimental results presently available so that we can explore the high density limit. The signal to noise ratio decreases significantly for separation distances d⩾w and increases steadily with the antidot size w in the range analyzed. The remanent configurations are similar to the experimental data obtained by scanning Kerr microscopy.
Improved magnetic properties and growth anisotropy of chemically modified Sr ferrites
Authors: Lee Jung W. , Cho Yong S. , Amarakoon Vasantha R. W.
Published: July 2002

Magnetic properties and microstructural characteristics of SrO⋅5.9Fe2O3 chemically modified with Si and Ca were investigated by changing experimental parameters such as additive composition, the ratio of Ca/Si, and sintering condition. A novel particulate coating method utilizing sol–gel reactions was used to uniformly incorporate the additives of Si and Ca. This method was very successful in obtaining homogeneous grain growth and fine grains. A sample containing the gel additives of 0.6 wt % SiO2 and 0.7 wt % CaO and sintered at 1200 °C for 4 h was found to significantly suppress abnormal grain growth, resulting in submicron-sized grains and high density. A distinct grain boundary phase containing Si and Ca was observed by increasing the sintering temperature to 1250 °C. The resultant microstructural characteristics favorably affected magnetic properties. For example, the chemically modified sample exhibited a higher coercivity of 3530 Oe compared to a value of 2050 Oe obtained for the sample without the additives. On the other hand, an increase in the ratio of Ca/Si or in sintering temperature tended to induce a large anisotropy during grain growth.
The Néel temperature of Mn100−xRhx alloys in ordered and disordered states
Authors: Yamauchi R. , Fukamichi K. , Yamauchi H. , Sakuma A. , Echigoya J.
Published: July 2002

The concentration dependence of the room-temperature lattice constant and the Néel temperature of Mn100−xRhx (15⩽x⩽30) disordered and ordered alloys was investigated in order to clarify the difference in the antiferromagnetic properties. The room-temperature lattice constant increases with increasing x and the difference between the disordered and ordered alloys was hardly observed. The Néel temperature increases with increasing x in both the disordered and ordered states. This behavior is not explained by the variation of the strength of the exchange interaction as a function of the Mn–Mn distance but by the number of 3d electrons in the Mn site. The Néel temperature in the ordered state is 130–160 K higher than that in the disordered state, indicating that the exchange interaction is enhanced by ordering.
Similarity between the effects of pressure and electron concentration on the magnetic behavior of a Cr+0.2 at. % Ir alloy
Authors: le Roux S. J. , Smit P. , Alberts H. L.
Published: July 2002

An experimental study of the magnetic phase transition temperatures of a Cr0.998Ir0.002 alloy doped with V and Mn to respectively decrease and increase the electron concentration per atom (eA), is reported. A correspondence between the electron concentration- and pressure-temperature magnetic phase diagrams of the Cr0.998Ir0.002 alloy system, doped with V, is observed through the application of a linear scaling of 6.1 GPa per 1% change in eA between the pressure and eA scales of the two diagrams.
Crystal structure and magnetism of SrV6O11 single crystals
Authors: Hata Y. , Kanke Y. , Kita Eiji , Suzuki H. , Kido G.
Published: July 2002

Magnetic property and specific heat of mixed valence vanadium oxide SrV6O11 were investigated. Single crystals and polycrystals were synthesized with a solid state reaction. Four-circle x-ray structural analysis discovered a structural transition at a temperature range between room temperature and 353 K. This transition corresponds to that of NaV6O11 at 245 K. Specific heat measurement of SrV6O11 was performed between 20 and 150 K and two anomalies were observed at 42 and 73 K. These anomalies are consistent with the two peaks in the temperature dependence of magnetization. Below 42 K, SrV6O11 shows metamagnetism and its critical field is about 4 T at 5 K. Its basic magnetic structure at 73 K is considered to be an antiferromagnetic state formed by the localized electron system.
Relative merits of Cl2 and CO/NH3 plasma chemistries for dry etching of magnetic random access memory device elements
Authors: Jung K. B. , Cho H. , Hahn Y. B. , Lambers E. S. , Onishi S. , Johnson D. , Hurst A. T. , Childress J. R. , Park Y. D. , Pearton S. J.
Published: July 2002

A typical magnetic random access memory stack consists of NiFe/Cu/NiFeCo multilayers, sandwiched by contact and antioxidation layers. For patterning of submicron features without redeposition on the sidewalls, it is desirable to develop plasma etch processes with a significant chlorinated etch component in addition to simple physical sputtering. Under conventional reactive ion etch conditions with Cl2-based plasmas, the magnetic layers do not etch because of the relatively involatile nature of the chlorinated reaction products. However, in high ion density plasmas, such as inductively coupled plasma, etch rates for NiFe and NiFeCo up to ∼700 Å min−1 are achievable. The main disadvantage of the process is residual chlorine on the feature sidewalls, which can lead to corrosion. We have explored several options for avoiding this problem, including use of in situ and ex situ cleaning processes after the Cl2-etching, or by use of a noncorrosive plasma chemistry, namely CO/NH3. In the former case, removal of the chlorine residues with in situ H2 plasma cleaning (to form volatile HCl that is pumped away), followed by ex situ solvent rinsing, appears effective in preventing corrosion. In the latter case, the CO/NH3 plasma chemistry produces metal carbonyl etch products, that are desorbed in the simultaneous presence of an ion flux. The etch rates with CO/NH3 are much lower than with Cl2 over a broad range of source powers (0–1500 W), radio frequency chuck powers (50–450 W), pressures (1–30 mTorr) and plasma compositions. We have tried substitution of CO2 for CO, and addition of Ar to produce faster etch rates, without success. Maximum rates of ∼300 Å min−1 for NiFe and NiFeCo were obtained with CO/NH3 under optimum conditions. The etched sidewalls tend to be sloped because of mask erosion during plasma exposure, in contrast to the case of Cl2-based chemistries where the sidewalls are vertical.
Effect of ion-irradiation-induced disorder on the low-field magnetoresistance of La0.67A0.33MnO3 (A=Sr, Ca)
Authors: Watts S. M. , Li M. , Wirth S. , Dahmen K.-H. , von Molnár S. , Xiong P. , Katz A. S. , Dynes R. C.
Published: July 2002

We report on a systematic study of the correlation between the disorder produced by ion irradiation and the magnetoresistance (MR) behavior of two doped manganite films: a highly textured La0.67Sr0.33MnO3 film on a (100) LaAlO3 substrate and a film of La0.67Ca0.33MnO3 on a YSZ substrate with a high degree of large-angle grain boundary disorder. The films were grown via metal organic chemical vapor deposition and exposed to irradiation of 200 keV Ne ions. The temperature and field dependence of the resistivity were measured on the same samples at different levels of damage. For the Sr-doped film, the bulk magnetic properties were observed to degrade faster with cumulative damage than transport. For both films at low temperature, a low-field hysteretic MR was either induced or enhanced by ion damage. These effects are discussed in terms of diffusive transport through “granular” magnetically disordered regions.
Resistivity and Hall effect at high temperatures in La0.67Ca0.33MnO3
Authors: Jakob G. , Westerburg W. , Martin F. , Adrian H. , van Bentum P. J. M. , Perenboom J. A. A. J.
Published: July 2002

The resistivity tensors of La0.67Ca0.33MnO3 films were investigated at temperatures from the Curie temperature up to 600 K in magnetic fields up to 20 T. The diagonal transport is described by hopping of a small spin polaron cluster of 4 ions to nearest-neighbor spins. A spin-dependent activation energy and a mean field approximation for the magnetization of clustered polaron spins and unclustered Mn ion spins allowed the description of ρ(B,T) with a minimum of free parameters. The electron-like low field Hall coefficient showed a thermally activated behavior with an activation energy higher than that extracted from diagonal data.
Anisotropy induced by the bowed-substrate sputtering technique in positive/negative magnetostriction FeB/CoSiB bilayers
Authors: Garcı́a D. , Muñoz J. L. , Castaño F. J. , Prados C. , Asenjo A. , Garcı́a J. M. , Vázquez M.
Published: July 2002

CoSiB and FeB single layers and CoSiB/FeB bilayers with thicknesses ranging from 250 to 1500 Å were grown on bowed glass substrates using rf sputtering. A magnetoelastic anisotropy was induced in the magnetic layers after removing the films from the sputtering chamber. The positive (FeB) and the negative (CoSiB) magnetostrictive single layers showed an easy magnetization axis transverse and parallel to the compression axis, respectively. The magnetic behavior of the CoSiB/FeB bilayers is shown to be extremely sensitive to the thickness of each layer, to their thickness ratios, and also to the deposition sequence of the layers on the substrate. These results are discussed in terms of the interactions between two magnetic phases with easy magnetization axes transverse to each other.
Influence of lateral propagating modes on laser output characteristics in selectively oxidized vertical cavity surface-emitting lasers with double oxide layers
Authors: Huang Yong-Zhen
Published: July 2002

The influence of lateral propagating modes on the threshold current and the spontaneous emission factor in selectively oxidized vertical cavity surface-emitting lasers (VCSELs) is investigated based on the mode behaviors of lateral propagating modes and the rate equation model. The numerical results show that the lateral propagating modes may be trapped in the aperture region for the selectively oxidized VCSEL with two oxide layers, one above and one below the active region. The output characteristics of VCSELs can be affected due to the reabsorption of the quasitrapped lateral propagating modes. A lower threshold current can be expected for a VCSEL with double oxide layers than that with a single oxide layer. The numerical results of rate equations also show that a larger spontaneous emission factor can be obtained by fitting the output–input curves for the VCSEL with double oxide layers.
Dissociation of benzene in a pulsed glow discharge
Authors: McCorkle Dennis L. , Ding Weixing , Ma Cheng-Yu , Pinnaduwage Lal A.
Published: July 2002

Destruction of benzene in a benzene/Ar mixture subjected to a pulsed glow discharge was studied. The destruction efficiency was much improved compared to a dc glow discharge, and the destruction efficiency increased with decreasing pulse width at a constant pulse frequency. Diagnostics experiments were conducted to elucidate the destruction mechanisms involved. The results show that excitation transfer from the metastable states of Ar to benzene in the afterglow of the discharge was primarily responsible for the destruction of benzene.
Observation of lossless radiative modes of a dielectric sphere
Authors: Yi Soung-Soo , Stafsudd Oscar M.
Published: July 2002

A theoretical investigation of plane-wave electromagnetic scattering in active dielectric sphere predicted the existence of anomalous resonances that occur at discrete wavelengths. These resonances may be understood from a leaky wave phase matching boundary conditions, in which the gain in the dielectric exactly makes up for the radiative loss of a mode. This results in a radiative mode that does not decay in time, therefore it is described as a lossless radiative mode. Experiments have been performed to verify the existence of these resonances. Optical pumping was used to provide the gain, and the threshold of each resonant mode was found to be a function of the dye concentration and the radius of the dielectric sphere.
Enhancement of Curie temperature of the 2:17 phase in nanocomposite Sm2(Fe,Co)15Cr2C2/(Fe,Co) magnets
Authors: Chen Zhongmin , Daniil Maria , Hadjipanayis George C. , Moukarika Aliki , Papaefthymiou V.
Published: July 2002

The proximity effect on the Curie temperature of exchange-coupled melt-spun nanocomposite Sm2(Fe,Co)15Cr2C2/(Fe,Co) magnets consisting of a fine mixture of hard and soft phases has been examined using thermomagnetic measurements, x-ray diffraction (XRD), Mössbauer and transmission electron microscopic studies. A significant enhancement in the Curie temperature of the 2:17 phase is observed in these magnets (27 °C in Sm2Fe15Cr2C2 and 102 °C in Sm2Fe11Co4Cr2C2) as compared to their patent cast alloys. XRD and Mössbauer analysis confirm that both the cast alloys and the nanocomposite magnets are comprised of the same phases [rhombohedral 2:17 and bcc Fe(Co)]. The unit cell volume of the 2:17 phase is slightly larger in ribbons and it is found to contribute to about 15% of the total Curie temperature enhancement. Microstructural studies revealed that the grain size is reduced from 10 to 20 μm in the cast alloy to 20–60 nm in the melt-spun magnets. The enhancement of the Curie temperature is believed to arise mainly from the exchange coupling effect between the 2:17 phase and the Fe(Co) phase which results in an extra exchange field at the 2:17 grains. Furthermore, the enhancement of the Curie temperature is found to increase with the volume fraction of the Fe(Co) phase in the magnets. It is also interesting to note that the Curie temperature of the Fe(Co) phase in the magnets remains unchanged as compared with their parent alloys, because the exchange coupling effect disappears completely at temperature above the Curie temperature of the 2:17 phase.
Interband optical properties of molecular-beam epitaxially grown GaAs1−xSbx on GaAs substrates
Authors: Ferrini R. , Geddo M. , Guizzetti G. , Patrini M. , Franchi S. , Bocchi C. , Germini F. , Baraldi A. , Magnanini R.
Published: July 2002

Spectroscopic ellipsometry (SE) from 0.8 to 5 eV and photoreflectance (PR) from 0.7 to 1.5 eV were used to study the interband optical response at room temperature of epitaxial GaAs1−xSbx layers with 0<x<0.5. The samples were grown by molecular-beam epitaxy at 520 °C on (001)-GaAs substrates and characterized by low-temperature photoluminescence and x-ray diffraction. The complex dielectric function ε̃(ω) of GaAs1−xSbx vs x was derived from the ellipsometric spectra after mathematically removing the oxide overlayer effects. The SE and PR spectra were analyzed with their energy derivatives in terms of standard analytical line shapes: in particular the E0, E1, E1+Δ1. E0′, and E2 critical point energies were derived as a function of x. On this basis the energy-shift model is appropriate to interpolate ε̃x(ω) for any x<0.5, thus allowing a nondestructive optical diagnostic of epitaxial heterostructures based on GaAs1−xSbx.
Strain relaxation of GaNxAs1−x on GaAs (001) grown by molecular-beam epitaxy
Authors: Pan Z. , Wang Y. T. , Li L. H. , Wang H. , Wei Z. , Zhou Z. Q. , Lin Y. W.
Published: July 2002

A series of samples consisting of a strained layer of GaNxAs1−x of different thickness, covered by a GaAs cap layer of 100 nm were grown by molecular-beam epitaxy. The samples have been characterized by high-resolution x-ray diffraction and simulations based on the dynamical theory in order to determine the strain relaxation in GaNxAs1−x layers. It is found that there is a huge difference between the critical thickness determined by x-ray diffraction and the theoretical calculations according to the Matthews and Blakeslee model. The critical thickness of GaNxAs1−x on GaAs is ten times smaller than the theoretical value. The strain relaxation is a crucial point that affects the quality of GaNAs. Photoluminescence measurements are in good agreement with the x-ray diffraction results. The optical properties degraded rapidly when the GaNxAs1−x thickness exceeded the critical thickness determined above.
Ag–Mn nanoparticles: Three-dimensional finite size effect of the spin glass state
Authors: Ederth J. , Hoel A. , Johansson C. I. , Kiss L. B. , Olsson E. , Granqvist C. G. , Nordblad P.
Published: July 2002

Ag–Mn nanoparticles were prepared by advanced gas evaporation. Their composition corresponded to Ag0.89Mn0.11, and the particle size distribution was log normal. The particles demonstrated an unambiguous spin glass behavior with the temperature dependent magnetic susceptibility displaying a plateau at ∼25 K. The magnetic domains were limited by the size of the particles.
Thermal stability and oxygen-loss characteristics of Pt(O) films prepared by reactive sputtering
Authors: Saenger K. L. , Cabral C. , Lavoie C. , Rossnagel S. M.
Published: July 2002

Pt(O) films having compositions ranging from pure Pt to amorphous platinum oxide a-PtOx (x∼1.4) were prepared by reactive sputtering and examined during and after heating to temperatures used for deposition and processing of high-epsilon (HE) and ferroelectric (FE) materials (400–650 °C). A two stage decomposition process was observed for a-PtOx (x∼1.4) films heated in N2, with the first stage of decomposition beginning at temperatures well below 400 °C. In an O2 ambient, decomposition was accompanied by formation of a crystalline Pt3O4 phase prior to complete decomposition to metallic Pt. However, the relatively slow rate of oxygen loss from a-PtOx suggests that significant amounts of oxygen should remain in Pt(O) electrodes after HE/FE layer deposition.
Elastic properties of nanoparticle chain aggregates of TiO2, Al2O3, and Fe2O3 generated by laser ablation
Authors: Ogawa K. , Vogt T. , Ullmann M. , Johnson S. , Friedlander S. K.
Published: July 2002

Previous studies have shown that nanoparticle chain aggregates (NCA) of titania are elastic [S. K. Friedlander, H. D. Jang and K. H. Ryu, Appl. Phys. Lett. 72, 1 (1998)]. The NCA were a few tenths of a micron long and composed of (approximately) 7 nm primary particles. They were produced by thermal decomposition of titanium tetraisopropoxide vapor in nitrogen. The goal of this study was to see whether the elastic behavior depends on (a) the material properties, (b) primary particle size, and (c) method of NCA formation. For this purpose, titania, alumina, and iron oxide NCA were generated by laser ablation. Rotating metal foil targets were mounted in a small cylindrical chamber and exposed to an excimer laser beam. The resulting aerosol was swept out by an oxygen stream. The generator was operated to produce NCA with similar mobility diameter and primary particle size. The NCA were deposited on the carbon or formvar films of an electron micrograph grid. Under the electron beam a hole develops in the carbon film in the neighborhood of the deposited NCA. The NCA then stretch and contract as described in our earlier study [S. K. Friedlander, H. D. Jang and K. H. Ryu, Appl. Phys. Lett. 72, 1 (1998)]. The titania, alumina, and iron oxide NCA generated by laser ablation all showed elastic behavior for primary particles smaller than about 10 nm. However, titania NCA composed of 36 nm primary particles did not exhibit elastic behavior indicating that very small primary nanoparticles are needed for this phenomenon to occur. The small scale stretching and contraction of chain segments were studied by measuring changes in the bond angles between adjoining particles and in the lengths of the segments studied. The elastic behavior is probably associated with local folding of chain segments due to van der Waals forces. Under tension, folded chains straighten but when the tension is relaxed, folds tend to reform but not reversibly. Rotation and sliding probably occur at the boundaries between particles during stretching. We hypothesize that elastic behavior is a general property of NCA composed of transition metal oxides with primary particles smaller than 10–15 nm; the phenomenon has now been observed for NCA produced in two ways, thermal decomposition and laser ablation. These phenomena may play a role in the action of nanoparticle additives such as fumed silica and carbon black used to improve the properties of rubber. NCA elasticity may also contribute to the ductile properties of nanoparticle compacts.
Electromigration-induced drift in damascene and plasma-etched Al(Cu). I. Kinetics of Cu depletion in polycrystalline interconnects
Authors: Proost Joris , Witvrouw Ann , Maex Karen , D’Haen Jan , Cosemans Patrick
Published: July 2002

In this work, a direct and quantitative comparison is presented on the rate of electromigration-induced Cu depletion for polycrystalline damascene and reactive ion etched (RIE) Al(Cu). Kinetic data are derived from the incubation time, obtained from drift characteristics of both unpassivated and passivated Blech-type test structures between 155 and 230 °C. Since the incubation time represents the time necessary for the electron wind to deplete the critical length free of Cu, both electromigration (EM)-threshold and the rate of Cu depletion was systematically investigated. For the latter specific microstructural features, related to Al2Cu precipitate morphology and distribution, are discussed. EM-threshold on the other hand is a more intrinsic characteristic of the interconnect, depending on geometrical and mechanical properties (like aspect ratio and encapsulation). For geometrically equivalent, unpassivated structures, it was found that the improvement in incubation time for the damascene implementation is predominantly controlled by a higher critical length caused by its encapsulation inside the dielectric. For passivated structures, the impact of encapsulation on enlarging the maximum elastic stress buildup becomes similar. As a result, the difference in threshold between passivated damascene and RIE was observed to decrease. The incubation time in passivated structures becomes more importantly controlled by the kinetics of Cu depletion. It is demonstrated that it is most effective to maximize the degree of intergranular θ precipitation to retard the Cu depletion rate in polycrystalline structures. Implications on the relative EM performance under operating conditions for damascene and RIE Al(Cu) are also discussed.
Energy-level engineering of self-assembled quantum dots by using AlGaAs alloy cladding layers
Authors: Kim Y. S. , Lee U. H. , Lee D. , Rhee S. J. , Leem Y. A. , Ko H. S. , Kim D. H. , Woo J. C.
Published: July 2002

The ground-state energy level of an InAs quantum dot (QD) system can be changed from 1070 to 700 nm by changing the aluminum composition in the AlxGa1−xAs matrix. For all the QDs, the lattice-mismatched strains are the same as that of InAs/GaAs QDs, so that QDs are easily formed. Photoluminescence signals from the structures were strong at low temperature and stayed relatively high at room temperature. The results suggest that these highly strained QDs in the alloy matrices could be an excellent choice for the energy-level engineering of QDs.
Annealing kinetics of {311} defects and dislocation loops in the end-of-range damage region of ion implanted silicon
Authors: Robertson L. S. , Jones K. S. , Rubin L. M. , Jackson J.
Published: July 2002

The evolution of both {311} defects and dislocation loops in the end-of-range (EOR) damage region in silicon amorphized by ion implantation was studied by ex situ transmission electron microscopy (TEM). The amorphization of a (100) n-type Czochralski wafer was achieved with a 20 keV 1×1015/cm2 Si+ ion implantation. The post-implantation anneals were performed in a furnace at 750 °C for times ranging from 10 to 370 min. After annealing the specimen for 10 min, the microstructure showed a collection of both {311} defects and small dislocation loops. The evolution of a specific group of defects was studied by repeated imaging of the same region after additional annealing. Quantitative TEM showed that {311} defects followed one of two possible evolutionary pathways as annealing times progressed; unfaulting to form dislocation loops or dissolving and releasing interstitials. Results indicate that in this temperature regime, {311} defects are the preferential site for dislocation loop nucleation.
Sensor properties of a robust giant magnetoresistance material system at elevated temperatures
Authors: Lenssen K.-M. H. , Kuiper A. E. T. , van den Broek J. J. , van der Rijt R. A. F. , van Loon A.
Published: July 2002

The temperature dependence of the giant magnetoresistance (GMR) ratio, resistance and exchange-biasing field for a spin valve comprising an Ir19Mn81-biased artificial antiferromagnet (AAF) has been studied up to 325 °C. Up to 200–250 °C the temperature effects are reversible, at higher temperatures gradual irreversible changes are observed, probably due to atomic diffusion. The magnetoresistance effect is even at 200 °C still higher than for anisotropic magnetoresistance sensors at room temperature. The resistance of the multilayer shows a maximum around 250 °C. We found that this is due to the peculiar behavior of Ir–Mn, which has a negative temperature coefficient of the resistance. This provides a possibility to tune the temperature coefficient for the complete multilayer by varying the thickness of the Ir–Mn layer. The relative decrease of the exchange-biasing field as a function of temperature is much smaller for spin valves with AAF than for conventional spin valves (without AAF). Furthermore, it was demonstrated that the GMR ratio can be increased to 12% at room temperature by using a dual spin valve with two AAFs.
Structural characterization of periodic arrays of magnetic dots
Authors: Temst K. , Van Bael M. J. , Moshchalkov V. V. , Bruynseraede Y.
Published: July 2002

We have investigated the structure and regularity of macroscopically large arrays of submicron magnetic Au/Co/Au dots, which were prepared by combining electron beam lithography, molecular beam epitaxy, and lift-off techniques. Atomic force microscopy was used to characterize the surface roughness of the dots and to show the reproducibility of dot size and periodicity over large areas; low-angle x-ray diffuse scattering experiments were employed to construct a mapping of the reciprocal space in the vicinity of the (000) reflection of the dots. The reciprocal space mapping thus provides information about the internal structure of the dots, as well as about the lateral periodicity of the dot array. This work underlines the important complementarity of scanning probe and x-ray diffraction techniques for the detailed characterization of patterned structures. We observed that the x-ray diffraction patterns are extremely sensitive to the orientation of the dot lattice with respect to the incoming x-ray beam, allowing a quantitative analysis of the lateral periodicity of the dot array and the size of the individual dots.
Effect of ion doping on CuO magnetism
Authors: Borzi R. A. , Stewart S. J. , Punte G. , Mercader R. C. , Curutchet G. A. , Zysler R. D. , Tovar M.
Published: July 2002

We have investigated the magnetism of 0.5 at. % Fe3+-doped CuO samples by Mössbauer spectroscopy and magnetization studies. The Curie–Weiss-type behavior observed for low-field-magnetization measurements at temperatures higher than 220 K is interpreted as an uncompensation of moments enhanced by the doping. The results are compared with 1.2 at. % Zn2+-doped CuO magnetization results and previous ones for samples doped with divalent ions. Trivalent ion doping produces an increase in the susceptibility with a peak at TN. The magnetic coupling of Fe2+ ions to the magnetic lattice is found to be about four times stronger than that of Fe3+.
Enhancing current-perpendicular magnetoresistance in Permalloy-based exchange-biased spin valves by increasing spin-memory loss
Authors: Gu J. Y. , Steenwyk S. D. , Reilly A. C. , Park W. , Loloee R. , Bass J. , Pratt W. P.
Published: July 2002

Inserting a thin (t*=0.5 or 1 nm) layer of the antiferromagnet FeMn into the “free” Permalloy (Py) layer of a sputtered, current-perpendicular exchange-biased spin valve, Nb/FeMn/Py (pinned)/Cu/Py (free)/Nb, is shown to enhance AΔR, the difference in specific resistance between the states where the magnetizations of the two Py layers are parallel and antiparallel to each other. Such an increase is taken as evidence that spin-memory loss (spin relaxation) due to the FeMn is strong, and that judicious insertion of a source of spin relaxation into a multilayer with high specific resistance contacts can enhance AΔR, the numerator of the magnetoresistance.
Behavior of excited argon atoms in inductively driven plasmas
Authors: Hebner G. A. , Miller P. A.
Published: July 2002

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s5 and 1s4, in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s5 level is metastable and the 1s4 level is radiatively coupled to the ground state but is radiation trapped. The argon data are compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the data suggest that both processes play a major role in determining the excited state density. At lower rf power and pressure, excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rf powers and pressures investigated, the spatial distributions tended to flatten in the center of the discharge while the density at the edge of the discharge was unaffected. The spatially resolved excited state density measurements were combined with previous line integrated measurements in the same discharge geometry to derive spatially resolved, absolute densities of the 1s5 and 1s4 argon excited states and gas temperature spatial distributions. Fluorescence lifetime was a strong function of the rf power, pressure, argon fraction and spatial location. Increasing the power or pressure resulted in a factor of 2 decrease in the fluorescence lifetime while adding Cl2 or BCl3 increased the fluorescence lifetime. Excited state quenching rates are derived from the data. When Cl2 or BCl3 was added to the plasma, the maximum argon metastable density depended on the gas and ratio. When chlorine was added to the argon plasma, the spatial density profiles were independent of chlorine fraction. While it is energetically possible for argon excited states to dissociate some of the molecular species present in this discharge, it does not appear to be a significant source of dissociation. The major source of interaction between the argon and the molecular species BCl3 and Cl2 appears to be through modification of the electron density.
Mode mixing in ferromagnetic resonance in magnetic microspheres
Authors: Voltairas P. A. , Fotiadis D. I. , Massalas C. V.
Published: July 2002

The problem of ferromagnetic resonance in magnetic microspheres is revisited due to related experiments in this size range. The eigenfrequency spectrum is examined more rationally compared to previous numerical computations, due to proper selection of the radial dependence of the solution. The cylindrically symmetric modes studied agree with experiments on Ni micrometer-size particles for an exchange constant A=2×10−7 erg/cm, while the error is less than 9% for the well-known value of A=3.4×10−7 erg/cm.
Magnetic properties of nanosized powders of magnetic oxides synthesized by pulsed laser ablation
Authors: Shinde S. R. , Kulkarni S. D. , Banpurkar A. G. , Nawathey-Dixit Rashmi , Date S. K. , Ogale S. B.
Published: July 2002

We present a detailed study of synthesis by pulsed laser ablation and the magnetic characterization of nanosized powders of iron oxides and strontium ferrite. In the case of iron oxide, it is found that the particle formation and their growth take place in the gas phase before reaching the cold finger (used as substrate for condensation). However, in the case of strontium ferrite, the as-condensed material is amorphous, and requires annealing at high temperature to induce nanoparticle growth. Very high values of intrinsic coercive field (∼6665±10 Oe) are realized for the strontium ferrite powder having an average particle size of about 35 nm. The temperature variation of coercive field and remanence of the nanosized powders is found to be substantially different from those of the corresponding bulk materials.
The temperature dependence of the dynamic interactions in (0.01 Gd, 0.99 Eu) (OH)3
Authors: Malhotra V. M. , Buckmaster H. A. , Kerr K. A.
Published: July 2002

The temperature dependence of the EPR fine structure linewidths of (0.01 Gd, 0.99 Eu) (OH)3 monocrystals has been measured to study the dynamic interactions in this lattice. It is inferred from the complex behavior that static strain is the dominant linewidth broadening mechanism if T<85 K and that dynamic magnetic interactions dominate if 85 K<T. An abrupt change in the linewidth ratios observed between 100 and 115 K cannot be explained by the above mechanisms. It is suggested that a structural change may occur near 115 K. X-ray diffraction structural data supports this proposal. However, the temperature accuracy of these latter measurements is insufficient to be definitive. It appears that the rate at which a-dimension of the unit cell contracts changes at about 115 K and represents a transition from an easy to a hard mode of contraction.
The capacitance for a single crystal face of an fcc metal/electrolyte interface
Authors: Henderson Douglas , Schmickler Wolfgang
Published: July 2002

Our earlier calculation of the ‘‘inner layer’’ interfacial capacitance of a jellium/hard sphere fluid model of the double layer is extended to metal single crystal faces by means of a pseudopotential. The agreement with experiment for Ag is qualitatively satisfactory with the capacitances of the crystal faces ordered correctly and with the relative differences δC/C given with good accuracy.
Static versus dynamic distortions in the triangular cluster compound [Cr3O(CH3COO)6]Cl⋅6H2O
Authors: Güdel Hans U.
Published: July 2002

Statically distorted triangular complexes determine the magnetic properties of [Cr3O (CH3COO)6Ch⋅6H2). This follows from a study of the low-temperature structural and spectroscopic properties. (AIP)
Curie and Pauli susceptibilities in AsF5 doped polyacetylenes and the kinetics of doping
Authors: Chien James C. W. , Warakomski J. M. , Karasz F. E.
Published: July 2002

Polyacetylene was doped with AsF5 by a cyclic procedure. All samples of trans-[CH(AsF5)y]x where y is the mole of AsF5 per CH unit contains only Curie spin susceptibility for 0<y<1.2×10−3. Dopant ion distribution is uniform and there is no indication of formation of metallic domains. On the other hand, the temperature dependent EPR results of cis-[CH(AsF5)y]x showed the samples to have both Curie and Pauli susceptibilities for 5.2×10−7<y<1.1×10−2 with the latter contribution increasing with increase in dopant concentration. These doping behaviors together with the earlier results of iodine doping and AsF5 doping by a more rapid method are attributed to the kinetics of the diffusion of different dopant and their rates of reaction (chage transfer) with the cis- and trans-[CH]x.
Energy sudden dissociative collisions: Structure and applications of factorization relations
Authors: Chan C. K. , Hoffman D. K. , Evans J. W.
Published: July 2002

In the energy sudden (ES) approximation for nonreactive molecular collisions, there exist factorization relations by which an arbitrary T-matrix element can be predicted as a spectroscopic linear combination of those out of some other, input state. These were first discovered for ground state input but this restriction was later removed. This general form of the spectroscopic factorization relations is straightforwardly extended here to ES dissociative collisions. One finds that in predicting dissociation amplitudes out of some state, it is necessary to use input data out of a higher (energy) bound state. Thus ground state factorization relations cannot be used. The structure of two natural forms of the factorization relation coefficients (equivalent by virtue of ES consistency conditions among T-matrix elements out of a single state) are analyzed in detail for a collinear atom-truncated square-well diatomic oscillator system. Relevance of these results to the prediction of (dissociative) state specific vibrational enhancement/inhibition is discussed.