bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties behaviors in Fe88Zr7B4Cu1 nanocrystalline alloy prepared by different postanneal cooling rates
Authors: Kim K. Y. , Lee J. S. , Noh T. H. , Kang I. K. , Kang T.
Published: July 2002

Effects of cooling rate after annealing on the soft magnetic properties were investigated for an Fe88Zr7B4Cu1 alloy with nanoscale grain structure, which was prepared by melt quenching. As the cooling rate increased, the effective permeability improved and the remanence ratio, which indicates the orientation of magnetic anisotropy (degree of pair ordering), decreased. The increase of permeability and decrease of remanence ratio were considered to result from the suppression of the induced magnetic anisotropy. Furthermore, the variation of disaccommodation behaviors with cooling rate was investigated in the Fe88Zr7B4Cu1 nanocrystalline alloy. It was found that the value of D (intensity of disaccommodation) was a little higher for the samples obtained from the high cooling rate than that for the low cooling rate. This result can be explained by domain structure stabilization due to local induced magnetic anisotropy.
The rf permeability of dc planar magnetron sputtered FeNi multilayer films (abstract)
Authors: Grimes Craig A. , Ballantyne Catherine C.
Published: July 2002

Recording heads are commonly built in a multilayer stack to eliminate or reduce domain walls by allowing flux closure, or magnetostatic coupling, between the magnetic layers across nonmagnetic spacers. Use of an electrically insulating spacer material will reduce eddy current shielding increasing the high frequency performance of the head. As magnetic recording systems continue their trend to higher operating frequencies knowledge of the rf permeability of head-like multilayer materials becomes quite important. We examine the complex, rf permeability spectra of dc planar magnetron sputtered FeNi multilayer films as a function of spacer material, number of layers, and thickness of the spacer and magnetic layer. The permeability spectra are measured using a permeameter over the frequency range 3–300 MHz. The spacer materials examined include several metals and metal alloys, the corresponding oxides, silicon, and silicon nitride. The magnetic layer is, by weight, 81.8% Ni and 18.2% Fe. We have found that for a constant magnetic layer thickness, as the nonmagnetic spacer thickness decreases from 30 to 10 nm the permeability magnitude of the multilayer stack increases and the resonance frequency shifts to lower values. As the spacer thickness increases above 30 nm the permeability response remains constant with a negligible value of μ″. The permeability spectra are approximately the same for spacer layers made of metal or their corresponding oxides. Spacer layers made of Si3N4 result in permeability spectra with the highest permeability magnitudes. For example, the permeability magnitude of a multilayer stack composed of four 120 nm FeNi layers separated by 10 nm spacers is approximately 2000 for metal spacers, 2300 for Si spacers, and 4200 for Si3N4 spacers. For a fixed number of multilayer pairs and constant spacer layer thickness making the FeNi layer thicker tends to increase the permeability magnitude, reduce the resonance frequency, and lower the low frequency coercive force.
Write/erase cyclability of TbFeCo for mark edge recording
Authors: Awano Hiroyuki , Ojima Masahiro , Shimazaki Katsusuke , Ohnuki Satoru , Ohta Norio
Published: July 2002

Domain size changes due to thermal relaxation after high laser power irradiation on amorphous TbFeCo films were studied. In order to achieve mark edge recording for high-density magneto-optical memory, accurate domain size recording is required even after a million erase/write cycles. Highly accelerated erase/write test was performed on typical recording media, rare-earth (RE) -rich and transition-metal (TM) -rich disks. The elongation of the domain size written on the TM-rich film after erase/write cycles was clearly evident; however, the change in the domain size of RE-rich films was small. The small domain size change of the RE-rich disk can be explained in terms of the rapid increase in the coercive force with decreasing temperature and the smaller domain-wall driving force at recording temperature than those for the TM-rich disk, even though both have the same level of structural relaxation.
Spin-Peierls transition in CuGeO3: Electron paramagnetic resonance study
Authors: Oseroff S. , Cheong S-W. , Fondado A. , Aktas B. , Fisk Z.
Published: July 2002

Measurements of electron paramagnetic resonance (EPR) at 9 and 35 GHz between 2 and 300 K in single crystals and powder samples of CuGeO3 are presented. Below 14 K a large decrease in the intensity of the Cu2+ EPR signal is observed. The data can be interpreted as due to a spin-Peierls transition. However, an alternative interpretation in terms of a simple structural transition cannot be ruled out. An opening of an energy gap of ∼25 K is calculated from the analysis.
High magnetic field research: Overview of facilities and science and technology opportunities (invited) (abstract)
Authors: Crow J. E. , Schneider-Muntau H. J. , Parkin D. M. , Sullivan N.
Published: July 2002

A number of specialized facilities have been developed or are under development throughout the world to support research at high magnetic fields in a broad range of science and technology areas. These facilities provide continuous magnetic fields up to 32–35 T and pulsed fields up to 50–70 T for tens of ms periods with fields beyond 100 T for several μs. During the last several years, new laboratories have been planned and are being developed within the United States and Japan with major expansions of facilities occurring in France, The Netherlands, and other countries. The National High Magnetic Field Laboratory, presently under construction in the United States, will include superconducting magnets (B≤20 T), resistive magnets (B≤25–35 T depending on bore and power), hybrid magnet (B≤45–50 T), and pulsed fields (B≤60–70 T for 100 ms, B≤50–70 T for 10–20 ms and B≤250 T for about 10 μs). These new facilities within the United States and elsewhere will expand the research opportunities at the extremes of parameter space, i.e., magnetic field, ultralow temperatures, and high pressures, for researchers in the life and condensed matter science areas. An overview of the facilities throughout the world will be presented along with a brief discussion of the science opportunities and recent results at the extremes of high magnetic field.
The sign reversal of the acoustoelectric effect in anisotropic superconductors (abstract)
Authors: Goltsev A. V.
Published: July 2002

Experimental and theoretical investigations of high-temperature superconductors have revealed that the Fermi surface contains both electron- and hole-like parts, and the superconducting gap has large anisotropy in the a-b plane. In the present paper we show that these two findings are sufficient to produce the sign reversal of the acoustoelectric effect observed in films of YBa1Cu3O7−δ in transition from the normal to superconducting state. For the purpose of studying the effect we derive a diagram method and calculate the acoustoelectric current produced by an acoustic wave in the normal state of an anisotropic metal. Then, we find that superconducting fluctuations decrease the current. Finally, we investigate the acoustoelectric effect in the mixed superconducting state. In this state the normal acoustoelectric current arises due to the quasiparticle excitation drift produced by the acoustic wave. It is compensated by the superconducting current which forces vortices to move. It is the motion that produces the acoustoelectric voltage in the superconducting state. We conclude that if the superconducting gap takes different values on the electron- and hole-like parts of the Fermi surface, then the acoustoelectric voltage can sharply change the sign near the superconducting transition. This effect is caused by the change of relative concentrations of the electron- and hole-like excitations.
Antiferromagnetic spin correlation suppression and superconducting characteristics improvement in YBa2Cu3O6+δ films under light illumination (abstract)
Authors: Eremenko V. , Fomin V. , Kachur I. , Piryatinskaya V. , Prikhod’ko O.
Published: July 2002

Improvement of YBa2Cu3O6+δ film superconducting characteristics that are dependent on the charge carrier concentration is possible not only by means of oxygen doping, but also by light illumination. New results may be presented as follows: (i) The spectral distribution of the light absorption coefficient of Y-Ba-Cu-O films strongly depends on the index δ: there are relatively narrow bands in the spectrum at small δ and their intensity falls down as δ increases. The films with δ∼0.5–0.75 are metallized under light illumination: the resistivity at T<Tc decreases, the critical temperature Tc rises, the absorption band with an energy of E=2.2 eV vanishes gradually, and the two-magnon band in the Raman spectrum also vanishes, which indicates a decrease of the antiferromagnetic spin correlation. The above changes occur only if the photon energy is higher than that of the optical gap. The photoinduced changes are long lasting at T<180 K. (ii) The charge carrier density increase is not the only effect of light illumination. We have observed an increase in the critical current density Jc (measurements were carried out in the pulse regime) of YBa2Cu3O6.9 films after continuous red light illumination. Such photoinduced changes are also long lasting if T<Tc and a current pulse amplitude do not exceed Jc.
Scattering theory of perpendicular transport in metallic multilayers (invited)
Authors: Bauer Gerrit E. W. , Brataas Arne , Schep Kees M. , Kelly Paul J.
Published: July 2002

Electronic transport in metallic multilayers is discussed in the language of the Landauer–Büttiker scattering formalism. The semiclassical conductance through a disordered interface can be unambiguously separated into specular and diffuse scattering contributions. Analytical results are derived for the perpendicular conductance of multiple disordered interfaces. Predictions for the transport properties of interfaces with dilute but strongly scattering defects should be accessible to verification by experiments. First results of first-principles calculations of ballistic transport in magnetic multilayers are presented.
Effect of additives on thermal stability of Nd-Fe-B bonded magnets (abstract)
Authors: Nishio T. , Yagi H. , Furuya T. , Kasai Y.
Published: July 2002

Effects of Zr and Nb on magnetic properties and thermal stability were studied for Nd-Fe-B bonded magnets. Bonded magnets with a composition of Ndx(Fe94-x-y)B6Ty, where T=Zr and Nb; x=11.0, 11.5, and 12.0; y=0, 0.5, 1.0, 1.5, and 2.0; were prepared by using melt spun ribbons. The addition of Zr up to 0.5 at .% increased the (BH)max of the bonded magnets, and further addition of Zr decreased the (BH)max at each Nd content level. Hci increased monotonously with an increase in Zr. (BH)max and Hci of the Nb containing bonded magnets also showed similar behavior. Irreversible flux loss after exposure at 180 °C for 1000 h significantly reduced with an increase in the Zr content at each Nd content level. Both the structural flux loss and the thermal fluctuation flux loss were reduced with an increase in the Zr content. An irreversible flux loss of about 5% was obtained when the Nd and Zr content were 11.5 at .% and 2.0 at. %, respectively. A similar value of irreversible flux loss was also obtained in Nb containing bonded magnets with the same composition. It was found that the oxygen pickup by the bonded magnets during the heat resistant test was well correlated to the structural loss of the bonded magnets. A structural flux loss of less than 3% was obtained when the oxygen pickup was less than 0.4 wt. % for both additives. SEM studies revealed that the grain size of the 2-14-1 phase observed in the additive-containing specimens was finer than that of the base alloy.
Magnetic and ferromagnetic resonance studies in Co-Cu composite films
Authors: Krishnan R. , Lassri H. , Seddat M. , Tessier M. , Guruswamy Sivaraman , Sahay Satyam
Published: July 2002

Co1−xCux composite films with 0≤x≤83 have been sputter deposited on to water-cooled glass substrates. Transmission electron microscopy and scanning tunneling microscopy studies reveal clusters whose average size is 250 Å. Magnetization when corrected to the Co volume is independent of Cu concentration and is equal to that of bulk Co. The in-plane saturation field is about 200 Oe at x=0, starts increasing for x=40, and shows a peak value of 1.2 kOe for x=60. Coercivity shows a similar behavior. Out-of-plane perpendicular anisotropy develops with the increase in Cu concentration. The ferromagnetic resonance studies show that (i) the linewidth increases for x≳75 and (ii) perpendicular anisotropy, probably induced by stress, also increases with x. Annealing up to 300 °C does not produce any noticeable changes but when annealed at 400 °C the perpendicular anisotropy decreases indicating some stress relief.
Magnetic reversal in small structures
Authors: Paul D. I. , Cresswell A.
Published: July 2002

In this paper we establish a model explaining the experimentally observed anomalous enhanced coercivity of granular magnetic solids and thin films or multilayers that have pinned surface magnetic moments. We also predict a normalized critical length for the material, above which the magnetic reversal mechanism is coercive and below which it occurs by a switching mode which is non-energy dissipative. The model used assumes a dependence of the magnetization along the small dimension of the granule or the depth of the layer. The contribution of the exchange term is obtained using the Landau semi-classical formalism, and thus we do away with the mean field approximation. The coercivity is defined in such a manner as to retain its nonreversible nature. Results are presented in dimensionless units. When applied to cobalt and iron, they show coercivities larger than the theoretical maximum obtainable without pinning in accord with experimental data.
On the resistivity minimum in amorphous metallic spin-glasses (abstract)
Authors: Koetzler J. , Thummes G.
Published: July 2002

Though the occurrence of a low-temperature resistivity minimum is a rather general feature of magnetic metallic glasses, its origin—whether magnetic or structural—is still under debate. We have performed temperature and magnetic-field-dependent measurements of the resistivity ρ(T,B) and the magnetization M(T,B) on amorphous Ni80−xFexSi8B12 below and above the critical concentration for ferromagnetic order (xc=4). In the ferromagnetic and reentrant phases ρ(T→0) increases as (−T1/2), which can be related to a quantum effect from modified electron-electron interaction in the presence of structural disorder.1 In marked contrast, in the conventional spin glass (x=2.4) ρ(T→0,B=0) exhibits a linear increase below the freezing temperature Tf=6.2 K. A reanalysis of literature data reveals a linear upturn of ρ(T→0) to occur in other amorphous spin glasses, too, with a quasi-universal law: Δρ/ρ≊−4(2) 1E−3 T/Tf. This finding will be discussed in terms of elastic scattering from the spin-glass order parameter2 and, alternatively, in terms of quantum interference on closed diffusion paths in the presence of inelastic spin-flip scattering. Recently, for the latter case, a linear T-law has been predicted to evolve from a crossover from dynamic spin scattering to the static limit at zero temperature.3
Dependence of the anisotropic magnetoresistance on aspect ratio in cobalt films (abstract)
Authors: Tondra Mark , Miller B. H. , Dahlberg E. Dan
Published: July 2002

High quality measurements of the anisotropic magnetoresistance, defined as the difference in the resistivities when the saturated sample magnetization is parallel and perpendicular to the current, are performing using four terminal measurements. What is occasionally not considered in these measurements is the geometry of the sample and contacts. This work reports how the anisotropic magnetoresistance (AMR), measured with four in-line point contacts attached to thin film specimens, is affected by the geometry of the films. Cobalt samples were lithographically narrowed in 2 mm steps from 10 mm×10 mm to 2 mm×10 mm. For each of the five sizes, the AMR and resistivity were measured using the four-probe-in-line technique with 3 mm from one contact to the next. The results show that the measured AMR increases by a factor of 2 from the widest to narrowest size. This width dependence of the AMR arises from spreading of the current between the voltage contacts. In order to make an accurate assessment of the AMR, the current across the entire width of the sample must be parallel to the line joining the voltage contacts. Similar work has been performed by A. Iwaide et al., and published in J. Magn. Soc. Jpn. 16, 197 (1992). The results reported in this abstract are in agreement with those in the above-mentioned paper.
Magnetovolume effects in strong paramagnets
Authors: Moroni E. G. , Jarlborg T.
Published: July 2002

We present calculations of magnetovolume properties for different strong paramagnetic systems such as ZrV2, TiBe2, and ZrZn2 in the C15 structure. These materials show indications of anti-Invar behavior, i.e., enhanced magnetostriction, and thermal expansion.
Remanence and coercivity in exchange coupled amorphous R-TM/Fe bilayers and multilayers (abstract)
Authors: Wan Hong , Tsoukatos A. , Hadjipanayis G. C.
Published: July 2002

We have investigated the hysteresis behavior of rare-earth (R)-transition metal (TM) bilayers and multilayers consisting of a fine mixture of hard and soft phases. The films with bilayer thickness in the range of 5–100 Å were fabricated using a dc sputtering system. X-ray diffraction was used to check the crystal structure and multilayer structure. The magnetic properties were measured with a SQUID magnetometer in the temperature range of 10–300 K with fields up to 55 kOe. A strong exchange coupling between the hard magnetic phase (R-TM) and the soft phase (Fe) leads to a smooth hysteresis loop in samples with a certain thickness range. The remanent magnetization is enhanced significantly at the expense of a reduced coercivity. For example, in NdFe/Fe multilayer films, the reduced remanence increases from 0.63 to 0.92 at 10 K while the coercivity decreases from 9.3 to 1 kOe as the Fe layer thickness is varied from 0 to 10 nm. The effect of interface roughness on the exchange coupling has been investigated via different sputtering pressures and rates. The dependence of magnetic hysteresis on the layer thickness and temperature has been examined and the results will be reported.
Effects of exchange bond disorder on transport measurements
Authors: Stampe P. A. , Ma H. , Kunkel H. P. , Williams G.
Published: July 2002

Measurements of the low field resistive anisotropy (LFRA) in amorphous Fe91Zr9 with and without hydrogen loading are presented. The temperature dependence of these data is compared with model calculations of the quadrupolar term [〈〈S2Z〉T〉J−S(S+1)/3], from which it is concluded that the model calculations reproduce both the temperature and the exchange bond dependence of this transport coefficient.
Magnetic and magnetoresistive properties of inhomogeneous magnetic dual-layer films
Authors: Oti John O. , Russek Stephen E. , Sanders Steven C.
Published: July 2002

Magnetic and magnetoresistive properties of sputtered Co alloy dual-layer films are compared with micromagnetic simulations. The simulations elucidate the details of the switching behavior of the dual-layer films as a function of the interlayer exchange and magnetostatic interactions. The simulations have led to a conceptual understanding of the coercive field splitting caused by the interlayer interactions. A calculation of the anisotropic magnetoresistance (AMR) has been included in the simulations. The AMR provides a second independent macroscopic quantity (in addition to the average magnetization) which can be measured and compared with the micromagnetic simulations. The AMR is more sensitive to the micromagnetic structure perpendicular to the applied field and is a better test of the accuracy of the micromagnetic model. The simulations qualitatively describe the measured AMR data on CoNi–Cr–CoNi dual layers.
Magnetoresistance and exchange effects of NiCo/Cu sandwich films with oxide overlayer
Authors: McGuire T. R. , Plaskett T. S.
Published: July 2002

Giant magnetoresistance (GMR) of 8% at 4.2 K is found in sandwich films having the composition Ni0.7Co0.3(50 Å)/Cu(t)/NiCo(50 Å)/NiCoO(40 Å) where NiCoO is a mixed oxide overlayer that exchange couples with the NiCo alloy layer. These films show a MR temperature dependence quite similar to that previously reported for Co/Cu/Co/CoO where the MR becomes small above 200 K. When bilayers of CoO/NiO are placed on the NiCo layer, the temperature dependence of MR extends to 250 K. The magnitude of the MR at 4.2 K scales with the magnitude of the saturation magnetization in the NiCo and Co films.
Magnetothermopower in antiferromagnetically coupled Co-Re superlattices
Authors: Sousa J. B. , Pinto R. P. , Almeida B. , Braga M. E. , Freitas P. P. , Melo L. V. , Trindade I. G.
Published: July 2002

Results are reported on the magnetothermopower of antiferromagnetically coupled Co-Re superlattices, obtained in a film of 150 Å Re/(Co 22 Å Re 5 Å)×16/50 ÅRe, from 10 to 300 K and in magnetic fields 0<H<10 kOe. At low temperature the magnetothermopower, ΔS=S(H)−S(0), is positive reaching a maximum around 100 K (ΔS/S≂10% at saturation), and fading away when T≳250 K. At each temperature, the field dependence of ΔS is rather close to that observed in the magnetoresistance. The temperature dependence of ΔS is consistent with the model of Piraux et al. [J. Magn. Magn. Mater. 110, L247 (1992)] based on a two-spin-channel conduction with electron spin mixing due to magnon scattering (ρ↑↓). In this model the sign of ΔS depends on whether the parameter α=ρ0↓/ρ0↑ is greater (ΔS<0) or smaller than unity (ΔS≳0). The results for Co-Re superlattices, showing ΔS≳0, support this prediction, since α<1 for Re impurities in Co, from previous studies.
Structural and magnetotransport properties of Co/Re superlattices
Authors: Huai Y. , Cochrane R. W. , Bian X. , Sutton M.
Published: July 2002

Structural properties of sputtered Si/Re 50 Å/(Co 20 Å/Re x Å)40 superlattices have been investigated in detail by low- and high-angle x-ray-diffraction measurements. The low-angle x-ray reflectivity data have been analyzed using an optical model and the high-angle data have been treated on the basis of a trapezoidal model. The fitted results indicate that the films with small xRe=3, 5, and 7 Å are essentially composed of pure Co layers and Re rich alloy (∼80%) interfaces about 3–5 monolayers thick. The magnetoresistance (MR) data of the antiferromagnetically coupled films have been analyzed using a semiclassical MR model of interfacial spin-dependent scattering.
Short period oscillation of the interlayer exchange coupling in sputtered Co-Re superlattices
Authors: Leal J. L. , Freitas P. P.
Published: July 2002

A short period oscillation was observed in the interlayer exchange coupling of sputtered Co-Re superlattices, superimposed on a long period oscillation. This effect is observed on hcp-textured samples with the c axis perpendicular to the plane of the film. The variation of the exchange coupling strength with the spacer thickness can be described using the Bruno and Chappert theory with two oscillatory terms, with periods of 2.9±0.2 and 10.2±0.2 Å. Both magnetization and magnetoresistance measurements reflect the influence of this multiperiodic exchange.
The temperature dependence of the bilinear and biquadratic exchange coupling in Fe/Cu, Ag/Fe(001) structures (abstract)
Authors: Celinski Z. , Heinrich B. , Cochran J. F.
Published: July 2002

The exchange coupling through nonmagnetic metallic interlayers is described by bilinear and biquadratic exchange coupling terms. In simple metals such as Cu(001) and Ag(001), the bilinear exchange coupling exhibits strong short wavelength oscillations (∼2 ML). The exchange coupling through non ferromagnetic interlayers is strongly affected by the interface roughness. Realistic interfaces consist of finite atomic terraces that result in variations of the interlayer thickness. Slonczewski showed that in this case the biquadratic exchange term can be produced by frustration of local magnetic moments. Recent band structure calculations showed that the biquadratic exchange coupling can be intrinsic. In this case its strength is usually found to be significantly weaker than that of bilinear coupling. The temperature dependence of biquadratic exchange coupling is expected to be different for the Slonczewski and intrinsic mechanisms. The intrinsic biquadratic exchange coupling is expected to vary with temperature faster than that predicted by the Slonczewski mechanism. In the present studies using the FMR and MOKE techniques we have investigated extensively the temperature dependence of the bilinear and biquadratic exchange coupling in Fe/Cu/Fe and Fe/Ag/Fe(001) structures. The quantitative studies of the exchange coupling were carried out in the temperature range 77–400 K. By growing the first Fe layer at various substrate temperatures one can prepare samples possessing interfaces with a variable atomic terrace width at the Fe/Cu, Ag interface. That way one can control the strength of the biquadratic exchange coupling. Two limits were investigated: (a) The strength of the biquadratic term in the exchange coupling was much smaller (10%) compared to the bilinear term; (b) the strength of the biquadratic term was comparable to the bilinear exchange coupling. The results are discussed within the framework of existing theories.
151Eu Mössbauer study on Fe/Eu multilayers
Authors: Baggio-Saitovitch E. , Passamani E. C. , Mibu K. , Shinjo T.
Published: July 2002

Mössbauer spectroscopy with 151Eu nuclei was applied to study magnetic properties of Fe/Eu multilayers as a function of the Eu layer thickness. The Mössbauer spectra at 4.2 K for [Fe(40 Å)/Eu(x Å)] with x=70, 100, and 200 consist of two magnetic components: a major component with hyperfine parameters close to those of bulk Eu metal and an additional component with a smaller hyperfine field. The latter component is attributed to Eu at the interface region. The spectrum at 4.2 K for [Fe(40 Å)/Eu(30 Å)] has only a component with a reduced hyperfine field, indicating that the Eu layers lose the bulk magnetic properties.
Magnetic resonance in PdFe alloys near Tc
Authors: Medina A. N. , Oliveira V. S. , Gandra F. G. , Gomes A. A.
Published: July 2002

Magnetic resonance results in Pd1−xFex, with various Fe concentrations, are reported. The samples were prepared in the form of foils, 200 and 100 μm thick, and Fe concentrations of 0.2, 0.5, 1.0, and 1.5 at. %. The experiments were carried out at low temperature, close to the Tc of each alloy. For the more concentrated alloys and magnetic field perpendicular to the foil, more than one line is observed. The anomalies in the resonance spectrum are interpreted in terms of the existing giant moments in these alloys.
Ge composition and temperature dependence of the deposition of SiGe layers
Authors: Gu Shulin , Zheng Youdou , Zhang Rong , Wang Ronghua , Zhong Peixin
Published: July 2002

SiH4 and GeH4 deposition of Si1−xGex layers by a rapid thermal process very low pressure chemical vapor deposition method has been studied in this paper. The Ge incorporation rate increases to a maximum value and then decreases as temperature increases. The growth rate of the SiGe alloy reaches its maximum value and then decreases as Ge composition increases. Ge incorporation also enhances the Si deposition rate in the Si1−xGex alloy. These results have been explained by increasing the hydrogen desorption rate at low temperatures and low value of x (the germanium concentration) and decreasing the adsorption probability of reactive hydrides at high temperature and high value of x.
Effect of various obstacles on oscillatory magnetoconductance of quantum double-coupled channels
Authors: Fan Xu-dong , Gu Ben-yuan , Yang Guo-zhen , Lin Tsung-han
Published: July 2002

The characteristics of the magnetoconductance of a nonuniform electron waveguide containing various shaped obstacles are investigated by using a model of two-coupled tight-binding chains and the transfer-matrix approach. The variation of the magnetoconductance as a function of total magnetic flux Φ threading the obstacle region is presented. The effect of the interchain tunneling modulation on the magnetoconductance for double-mode and single-mode transport processes is different. When the energy of the incident electrons is just above the threshold energy for the opening of the second propagating mode at zero magnetic field, at some magnetic flux, the conductance abruptly decreases owing to the presence of mode quenching. The magnetoconductance for various multiply connected structures and one-dimensional superlattice (1DSL) type tunneling modulation structures is also evaluated. Owing to the presence of the miniband gaps to be formed by 1DSL structures, different patterns in the magnetoconductance are found.
Optimum design and preparation of a-Si/a-Si/a-SiGe triple-junction solar cells
Authors: Xu Zhongyang , Zou Xuecheng , Zhou Xuemei , Zhao Bofang , Wang Changan , Hamakawa Y.
Published: July 2002

A series of systematic studies have been made on both optimum design and preparation technology of high efficiency a-Si/a-Si/a-SiGe triple-junction solar cells. It has been found that current matching is one of the key factors affecting the fill factor of two-terminal tandem solar cells, and excess carrier recombination at the p-n interface acting as an internal electrode is dominated by the density of the minority carriers, interfacial states, and geometrical factor match of the materials at the p-n interface. In this work, μc-Si:H with wide band gap and high conductivity, which was prepared at low substrate temperature, was used as an n layer of a-Si:H solar cells. In order to improve the n-i interface property, a novel approach involving the insertion of an n−a-Si:H buffer layer at the n-i interface was developed. The experimental results show that the buffer layer of appropriate thickness could enhance the fill factor and open circuit voltage of a-Si:H based solar cells. In addition, highly photosensitive a-SiGe:H(F) films used for a bottom cell in a-Si/a-Si/a-SiGe triple junction solar cells have been obtained by glow discharge of a gas mixture (SiH4—GeF4—H2) under conditions of high hydrogen dilution ratio and low deposition pressure. At present, the conversion efficiency of the a-Si/a-Si/a-SiGe triple-junction solar cell of 11.5% with Voc=2.48 V, Jsc=6.58 mA/cm2, and FF=70.4% has been obtained under AM1(100 mW/cm2) illumination by optimization of the solar cell structure and preparation technology.
Group effective indices of different types of optical fibers measured around 1550 nm
Authors: Pozzi F. , De Bernardi C. , Morasca S.
Published: July 2002

The effective group indices of different single mode fiber types (standard, dispersion shifted or dispersion compensated, polarization maintaining, pure silica core, erbium doped) have been measured in the wavelength range 1.500–1.580 μm; their values range from 1.4635 to 1.4778 at 1.54 μm. These values have been determined by a resonant-cavity method, which provides an accuracy to the fourth decimal place.
Exchange coupling in [Dy‖Er] metallic superlattices
Authors: Lee W. T. , Kaiser H. , Rhyne J. J. , Dumesnil K. , Dufour C. , Mangin Ph. , Marchal G. , Erwin R. W. , Borchers J. A.
Published: July 2002

Magnetic exchange coupling in metallic superlattices of [Dy‖Er], grown by molecular-beam epitaxy, has been examined by neutron diffraction. In a superlattice of 65-Å layers of Dy and 55-Å layers of Er, distinct ordering temperatures were observed for the Dy and Er layers. Basal plane helical ordering of the Dy layers was initiated at temperatures close to TN for bulk Dy (178 K) with a long-range interaction, preserving both phase and chirality, mediated through the Er layers. At a temperature near 70 K, the helical coupling of the Dy spins is replaced by an antiferromagnetic coupling of adjacent ferromagnetically ordered Dy layers coexisting with a remanent helical order. At a temperature well below TN of bulk Er, c-axis ordering of the Er spins occurs in the superlattice, and in measurements at 10 K there is evidence of basal plane moment ordering in the Er.
Nonlinear absorption in (Cd,Zn)Se/ZnSe single quantum wells
Authors: Houser Glenn D. , Garmire Elsa
Published: July 2002

Room-temperature measurement of nonlinear transmission in (Cd,Zn)Se/ZnSe single quantum wells is reported. Changes in absorption near the band edge due to optically excited carriers were measured for two samples with different well widths as a function of wavelength and intensity. The change in absorption occurred at the n=1 and n=2 heavy-hole excitons, as well as in the continuum states above the band edge. The peak values for change in absorption are −7000 cm−1 at 10 kW/cm2 for the narrow well and −8000 cm−1 at 50 kW/cm2 for the wide well. Change in refractive index was calculated from the absorption results. Saturation intensities for the excitonic absorption were 13.3 kW/cm2 for the 7.5 nm well and 2.7 kW/cm2 for the 15 nm well. The data show spectra and carrier densities that are consistent with phase-space filling as the predominant mechanism for absorption change, in agreement with low-temperature results.
Plasma-anode electron gun
Authors: Santoru Joseph , Schumacher Robert W. , Gregoire Daniel J.
Published: July 2002

The plasma-anode electron gun (PAG) is an electron source in which the thermionic cathode is replaced with a cold, secondary-electron-emitting electrode. Electron emission is stimulated by bombarding the cathode with high-energy ions. Ions are injected into the high-voltage gap through a gridded structure from a plasma source (gas pressure ≤50 mTorr) that is embedded in the anode electrode. The gridded structure serves as both a cathode for the plasma discharge and as an anode for the PAG. The beam current is modulated at near ground potential by modulating the plasma source, eliminating the need for a high-voltage modulator system. During laboratory tests, the PAG has demonstrated square-wave, 17-μs-long beam pulses at 100 kV and 10 A, and it has operated stably at 70 kV and 2.5 A for 210 μs pulse lengths without gap closure.
Comparison of transport scattering and single-particle relaxation times in modulation-doped heterostructures
Authors: Mao J. M. , Huang Y. , Du Q. H. , Zhou J. M. , Cai L. H. , Li N. , Zhou W. Y. , Qian S. F. , Wang G. , Fu C. S. , Ding X. Z. , Xie S. S.
Published: July 2002

The transport scattering and single-particle relaxation times which characterize a two-dimensional electron system have been investigated by using thermal neutron irradiation. The ratios of transport scattering time to single-particle relaxation time are observed to vary from 1.7 to 7.8 depending on the electron density. A decrease in single-particle relaxation time is found while the transport scattering time increases as the electron concentrations increase. These phenomena are relevant to the Hall plateau broadening and enhancement of Shubnikov–de Haas oscillations in such an experiment.
Very intense pulsed electron beam
Authors: Sanford T. W. L. , Halbleib J. A. , Welch D. R. , Mock R. C.
Published: July 2002

An intense beam of pulsed electrons has been developed using the extended planar-anode diode to extract and focus the HERMES-III beam in a low-pressure gas cell without anode destruction. Measurements and a simulation model are compared and found in good agreement for focal lengths of ∼7–8 cm. They show that with this source a peak dose (peak dose rate) ∼200 J/g (8×1014 rad/s) in graphite can be generated with useful areas of 70 cm2. For the shorter focal length of ∼11 cm, the model predicts that a peak dose (peak dose rate) of 3800 J/g (1.5×1016 rad/s) can be generated over an area of 5 cm2.
Nitrogen-implantation induced enhanced adhesion of amorphous SiC films deposited on stainless steel and Cu
Authors: Laidani Nadhira , Miotello Antonio , Guzman Luis , Tuccio Stefano , Calliari Lucia
Published: July 2002

The effects of N+ implantation into SiC films deposited on stainless steel and Cu substrates were examined in connection with the adhesion properties of the SiC films. The films were deposited at 453 K by rf magnetron sputtering and N+ implantation of 1×1016–5×1017 ions/cm2 was done at room temperature at either 30 or 160 keV ion energy. Chemical characterization of the implanted bilayers, at the interface region, and compositional depth profiles were obtained by Auger electron spectroscopy. The adhesion of the films was examined using a scratch tester and scanning electron microscopy equipped with an energy dispersive spectroscopy microanalyzer. Microhardness measurements and indentation fracture toughness analysis were made on SiC films deposited on cemented tungsten carbide. In the SiC/Cu bilayers, an adhesion enhancement was found which is thought to be due to the higher fracture toughness of the ceramic film, induced by N implantation. In the SiC/steel bilayers, the mechanism for the increase in adhesion is attributed to the improved mechanical properties of the SiC film and to the enhanced interfacial bonding due to formation of Si-(N,C)-Cr complexes.
Magneto-Hall characterization of delta-doped pseudomorphic high electron mobility transistor structures
Authors: Look D. C. , Jogai B. , Stutz C. E. , Sherriff R. E. , DeSalvo G. C. , Rogers T. J. , Ballingall J. M.
Published: July 2002

Conventional Hall-effect determination of the two-dimensional electron gas (2DEG) concentration n2D in pseudomorphic high electron mobility transistor structures is invalid because of interference from the highly doped GaAs cap. Furthermore, the usual methods of dealing with this cap-interference problem, namely, (1) etching off the cap totally, (2) etching the cap until the mobility reaches a maximum, or (3) growing a separate structure with a thin, depleted cap, in general, give n2D values that are too low. However, we show here that magnetic-field-dependent Hall (M-Hall) measurements can separately determine the carrier concentrations and mobilities in the cap and 2DEG regions, as verified by comparison with a self-consistent, four-band, k⋅p calculation and also by electrochemical capacitance-voltage measurements in structures with different cap and spacer thicknesses.
Hydrogenation of boron in silicon during low temperature gas and liquid phase processing
Authors: Filangeri Edward M. , Nishida Toshikazu
Published: July 2002

Capacitance-voltage profiling of the spatial variation of the space-charge density near the silicon surface demonstrates the passivation of the boron acceptor at low temperature (90–100 °C) by chemical polishing, water, and forming gas conditions employed in the semiconductor process environment. The depth profile of the hydrogenated boron acceptor following low temperature forming gas anneals is consistent with trap-limited hydrogen transport proposed by Herrero. A hydrogen diffusion coefficient of 8.75×10−13 cm2/s is obtained on 1.2×1015 boron/cm3 p-type silicon at 100 °C.
Thermo-optic investigation of heating during electrical breakdown in avalanche photodiodes
Authors: Hunt J. H. , Holmes R. B.
Published: July 2002

We have experimentally determined the internal temperature rise caused by electrical breakdown in a silicon avalanche photodiode by observing changes in the diode’s optical properties. The spatial profile and temporal dependence of the temperature rise are both measured as a function of photodiode voltage. The results are consistent with a thermo-optic theoretical model, which assumes a scaling of the width of the breakdown filament that increases with the magnitude and duration of the steady-state breakdown current. The radius of the optical modulation was experimentally observed to range from about 1.5 to 3 μm. A single free parameter is used to obtain consistency between theory and experiment: the breakdown filament’s full width at half maximum is assumed to equal 1.28 μm for an overvoltage of 10 V and a delay of 96 ns, for the diode studied. Modulation of the read beam was observed at a level as low as 10±6 absorbed photons per write pulse, demonstrating near-photon-counting response.
Orientation of YBa2Cu3O7−x films on unbuffered and CeO2-buffered yttria-stabilized zirconia substrates
Authors: Skofronick G. L. , Carim A. H. , Foltyn S. R. , Muenchausen R. E.
Published: July 2002

YBa2Cu3O7−x (YBCO) films deposited by pulsed laser ablation on unbuffered and CeO2-buffered yttria-stabilized zirconia (YSZ) substrates were studied by x-ray diffraction and transmission electron microscopy to investigate film orientation. From φ scans it was determined that the unbuffered films possess two major in-plane orientation relationships with the substrate. Both have (001)YBCO∥(001)YSZ, with either [100]YBCO∥[100]YSZ or [110]YBCO∥[100]YSZ, a 0° or 45° orientation, respectively. As deposition temperature increases, satellite peaks that straddle the 0° or 45° orientations develop. The Σ boundary and near coincident site lattice descriptions are applied to the discussion of these misorientations. In general the CeO2-buffered YBCO films align with to the 45° orientation to the CeO2 buffer layer. Out-of-plane film orientation was investigated for both unbuffered and CeO2-buffered YBCO films and expressed as a ratio of the amount of c⊥ material to a⊥ material. Buffered films exhibited c⊥ material to a⊥ material ratios approximately twice those of unbuffered films. Transmission electron microscopy combined with the x-ray data was used to develop an explanation for the trends in the variation of the c⊥/a⊥ ratio with film deposition temperature.
Electron paramagnetic resonance of porous p-silicon
Authors: Gupta C. L.
Published: July 2002

p-type porous silicon is studied by electron paramagnetic resonance which shows an anisotropic hyperfine structure due to 11B and a weak isotropic signal at room temperature corresponding to an amorphous phase in porous silicon. The weaker isotropic signal is found overlapped with the strong anisotropic dangling bond signal when the porous silicon-containing wafer is scanned. It is argued that the large hyperfine splitting of 11B is predominantly due to the interaction of quantum-confined carriers with boron nuclei.
Violet laser emission in copper halides
Authors: Reimann K. , Rübenacke St.
Published: July 2002

With two-photon excitation into the longitudinal exciton or into the excitonic continuum copper halides show laser emission at wavelengths of 413.3 nm (CuI), 422.5 nm (CuBr), and 391.9 nm (CuCl). The linewidth of the emission is very narrow in CuI and CuBr (below 0.004 nm) and much broader in CuCl (0.4 nm). The laser transition occurs between the bottleneck of the exciton polariton and the longitudinal optical phonon.
Application of positron age-momentum correlation measurement to the study of defects in electron irradiated synthetic silica glass
Authors: Watauchi S. , Uedono A. , Ujihira Y. , Yoda O.
Published: July 2002

Age-momentum measurements and positron lifetime measurements were carried out in order to investigate vacancy-type defects produced in 3 MeV electron irradiated synthetic silica glasses, in which 1 ppm and 300 ppm of –OH bonds were contained. A high formation probability of positronium (Ps) was found for unirradiated specimens. These Ps atoms were considered to be formed in open-volume defects (∼7×10−2 nm3). The formation probability of Ps was drastically decreased by the electron irradiation, especially for the specimens which contained 1 ppm of –OH bonds, even though the size of the open-volume defects and the momentum distribution of electrons at the open-volume defects are independent on the –OH concentration and on the electron irradiation. Since the values of second lifetime components of positron lifetime spectra were ∼300 ps and very close to the estimated value of the lifetime of the positrons which are considered to be trapped in the mono- or divacancies, the decrease of formation probability of Ps can be attributed to an increase of positron annihilation in vacancy-type defects generated by the electron irradiation. Positrons were suspected to be trapped in such defects.
Initial stages of misfit dislocation formation in compressively strained Si-Ge short period superlattices
Authors: Dynna M. , Weatherly G. C.
Published: July 2002

The initial stages of strain relaxation in two (SimGen)p short period superlattices grown on Si have been studied by transmission electron microscopy. Relaxation occurs by the formation of 60° dislocations which terminate at heterogeneous sources close to the surface of the sample. The rate of strain relaxation in the short period superlattices has been compared to the rate in homogeneous Si1−xGex layers grown in the same chamber and having equivalent effective stresses to drive the dislocations. The rate of dislocation nucleation was observed to be much higher in the short period superlattices. This was attributed to the tendency for Ge island formation during the growth of the superlattices, leading to localized strain centers which act as easy dislocation sources on annealing.
GaAs asymmetrically doped n-i-p-i- superlattices for 10 μm infrared subband detector and modulator applications
Authors: Vaghjiani H. L. , Johnson E. A. , Kane M. J. , Grey R. , Phillips C. C.
Published: July 2002

A theoretical framework for the design of asymmetrically doped n-type n-i-p-i- superlattices for subband detector applications in the 10 μm spectral range is described. Excellent agreement is found with the subband absorption spectra measured in a series of GaAs n-type n-i-p-i- samples and oscillator strengths, transition energies, and dipole matrix elements comparable with conventional quantum-well heterostructure detectors are found. Pronounced IR-absorption modulation by optical pumping with band-gap radiation is seen, due to the enhanced interband recombination time resulting from the type-II n-i-p-i- potential. The prospective advantages of n-type n-i-p-i- devices for the detection and modulation of 10 μm radiation are discussed.
Surface recession and oxidation of silicon during bombardment by low energy oxygen ions
Authors: Svensson B. G. , Mohadjeri B. , Petravić M.
Published: July 2002

Vertical expansion of a silicon surface bombarded by 10 keV O+ ions is demonstrated using surface stylus profilometry. The surface expands gradually as the incorporated oxygen concentration increases, and a maximum is obtained when the bombardment dose reaches the critical one for formation of a continuous surface layer of SiO2. Through a combination of crater depth measurements and chemical etching the surface recession and the incorporation of oxygen are monitored as a function of bombardment dose. Comparison is made with calculations based on a model where simultaneous sputter erosion and surface swelling are taken into account. The surface swelling is assumed to be proportional to the retained oxygen dose. Experimentally determined sputtering yields are utilized in the calculations, and good agreement is shown with the measured data.
Kinetic studies of laser chemical vapor deposition of titanium nitride
Authors: Chen Xiangli , Mazumder Jyoti
Published: July 2002

TiN films have been deposited on Ti-6Al-4V substrates by a cw CO2 laser chemical vapor deposition process with TiCl4, H2, and N2. Pulsed dye laser induced fluorescence spectroscopy is used to obtain transient gas phase Ti atomic concentration above the substrate. Multi-wavelength pyrometry is applied to measure the surface temperature during deposition. Film growth rates and compositions are obtained by stylus profilometry and Auger electron spectroscopy. Relationships between the growth rate and TiCl4, H2, and N2 partial pressures are established, from which the rate-controlling reactions and activation energy are obtained.