bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the x-ray diffraction patterns of epitaxial V/δ-Mn, Cr/δ-Mn, and Fe/δ-Mn superlattices on Ge(001)
Authors: Pohl J. , Christensen M. J. , Huljic D. , Köhler J. , Malang E. U. , Albrecht M. , Bucher E.
Published: July 2002

We have grown stoichiometrically identical superlattices comprising a bcc transition metal (V, Cr, Fe) together with the metastable high temperature bcc δ-Mn modification on Ge(001) substrates. Despite identical molecular beam epitaxial growth conditions and identical bulk crystal structures of V, Cr, and Fe with nearly identical lattice parameters, the superlattices show a very different crystallographic behavior. The lattice parameters of δ-Mn are found to be strongly dependent on the thickness of the Mn layers as well as the lattice parameters of the adjacent metals. Therefore, different distortions of the cubic bcc δ-Mn structure can be obtained, ranging from almost cubic structures in V/δ-Mn superlattices to large tetragonal distortions (c/a≈8%) in Cr/δ-Mn superlattices. Nevertheless, we found that the unit cell volume of the δ-Mn modification remains almost constant for thin Mn layers, and that the deduced cubic lattice parameter for δ-Mn (a=2.985 Å) significantly differs from previously predicted and published values. This result appears to be of great importance concerning the predicted magnetic properties of δ-Mn. All presented simulations were performed using the refinement program SUPREX written by Schuller, Fullerton, and Bruynseraede.
Frequency dependence of the phase transition in Pb(Mg1/3Nb2/3)O3−PbTiO3 relaxor ferroelectrics
Authors: Park Jae-Hwan , Hong Kug Sun , Park Soon Ja
Published: July 2002

To understand the frequency dependence of phase transitions and related physical properties of Pb(Mg1/3Nb2/3)O3-based relaxor materials, the dielectric constants, electric-field-induced polarization, and pyroelectric depolarization are studied under varying temperatures and measuring frequencies. A linear relationship between the transition temperature and the logarithm of frequency is experimentally observed.
Short-range-order state in the Sr2Nd1−xCaxCu2O5+yF1+δ (0⩽x⩽1) superconducting system
Authors: Li Jianqi , Isobe Masaaki , Takayama-Muromachi Eiji , Matsui Yoshio
Published: July 2002

The structural features of the Sr2Nd1−xCaxCu2O5+yF1+δ (0⩽x⩽1) oxyfluoride system have been investigated by electron diffraction and high resolution electron microscopy. The short-range-order (SRO) state has been observed in the Sr2Nd0.5Ca0.5Cu2O5+yF1+δ oxyfluoride (Tc≈70 K). This kind of SRO structure can be understood in terms of the ordering of insertion of fluorine and/or oxygen atoms located between the SrO(F) double layers. The most probable ordering scheme is proposed. The effects of Ca content on this kind of SRO state as well as other locally ordered states have also been investigated.
Diffusion modeling of zinc implanted into GaAs
Authors: Chase Michael P. , Deal Michael D. , Plummer James D.
Published: July 2002

The diffusion of implanted zinc in GaAs is studied and modeled for annealing temperatures of 625 through 850 °C. Secondary ion mass spectrometry data for the annealed profiles are presented. The substitutional interstitial diffusion (SID) mechanism is used to explain how the deviation of the local gallium interstitial concentration from its equilibrium value regulates the Zn diffusion. We are able to simulate both the box shaped profiles resulting from high temperature anneals and the kink-and-tail profiles resulting from lower temperature anneals. The simulation results have allowed us to determine Arrhenius relations for: the intrinsic diffusion coefficient for implanted Zn, DZnint=0.6075 exp(−3.21 eV/kBT) cm2 s−1; the equilibrium Ga interstitial concentration, CIGa*=7.98×1030 exp(−3.47 eV/kBT) cm−3; and the Ga interstitial diffusion coefficient, DIGa=0.4384 exp(−2.14 eV/kBT) cm2 s−1.
Epitaxial overgrowth of 13C diamond films on diamond substrates predamaged by ion implantation
Authors: Behr D. , Locher R. , Wagner J. , Koidl P. , Richter V. , Kalish R.
Published: July 2002

Homoepitaxial chemical vapor deposited (CVD) 13C diamond films were grown on 〈100〉 diamond substrates predamaged by implantation with 620 keV Xe ions. The structural quality of the overgrown films was analyzed by plain-view and cross-sectional micro-Raman spectroscopy. Implantation doses below 2×1014 cm−2, for which no damage detectable by Raman spectroscopy was observed in the substrate, had no effect on the quality of the overgrown films. For doses around 4×1014 cm−2, a pronounced predamage of the diamond substrate was found which had a strong degrading effect on the quality of the overgrown layer resulting in a drastic increase of the width of the optic zone-center phonon and in the appearance of Raman scattering from sp2-bonded carbon. Higher implantation doses up to 1×1015 cm−2 resulted in a complete etch removal of the predamaged graphitic surface layer during the initial phase of CVD growth, which thus had no effect on the quality of the film produced by the subsequent overgrowth.
Homeotropic reverse-mode polymer-liquid crystal device
Authors: Murai Hideya , Gotoh Tomohisa , Nakata Taisaku , Hasegawa Etsuo
Published: July 2002

We have proposed a new type of reverse-mode polymer-liquid crystal device: homeotropic reverse-mode polymer-liquid crystal (HRPLC). This device consists of a liquid crystal with a dielectric constant having negative anisotropy and a pair of glass plates covered with a homeotropic alignment layer. The HRPLC’s operation is the reverse of the usual; i.e., it is clear when no voltage is applied and opaque under applied voltage. We have confirmed that the HRPLC operates well in reverse mode and have studied the dependence of its properties on liquid crystal material, curing process, and cell thickness. Experimental results indicate the HRPLC has a 30:1 contrast ratio over an operating voltage range of 0–11 V. In special fabrication conditions, the transmittance–voltage curve of the HRPLC drops to a minimum at a certain voltage level and begins to increase at that point. We have proposed a model to explain this result.
The effect of temperature on the resonant tunneling and electric field domain formation in multiple quantum well superlattices
Authors: Xu Yuanjian , Shakouri Ali , Yariv Amnon
Published: July 2002

Analyzing the photocurrent spectra and the I–V characteristics of weakly coupled GaAs/AlGaAs multiquantum well structures, different transport regimes are distinguished. At low temperatures (below ∼50 K), due to the electron coherence over a few periods of the superlattice, electron transport is dominated by sequential resonant tunneling. At higher temperatures, evidences for the increased contribution of nonresonant transport processes, and the subsequent modification in the electric field distribution in the device, are presented.
Characterization of mixed strain quantum well structures
Authors: Uppal Kushant , Tishinin Denis , Dapkus P. D.
Published: July 2002

Polarization resolved photoluminescence from a cleaved sample edge (edge photoluminescence) is shown to be a useful tool for characterization of complex multiple quantum well InP based structures with wells of different strains. The polarization resolved luminescence resulting from the heavy- and light-hole transitions of In0.51Ga0.49As0.78P0.22 tensile and In0.9Ga0.1As0.52P0.48 compressive wells are found to match closely with theoretical values, validating assignments applied to the peaks obtained from photoluminescence. Strain distribution is shown to be an important effect when quantum wells of opposite strain are mixed together in the growth structure. The overlap of the transverse-electric (TE) and transverse-magnetic (TM) emissions found from edge photoluminescence on a mixed strain quantum well structure is shown to have an excellent match with the overlap of the TE and TM modes of a laser which uses the same structure in its active region.
Extinguishing by “slow quenching’’ in a thick grid Cs–Ba tacitron
Authors: Wernsman Bernard , El-Genk Mohamed S.
Published: July 2002

Transient Langmuir probe measurements of the plasma density, electron temperature, and plasma potential during “slow quenching’’ of a Cs–Ba tacitron at two different discharge conditions were made. Following the application of a negative voltage pulse on the grid, the grid aperture sheaths initially grew then shrank temporarily, due to an increase in the ion flux from the grid-collector region, then grew again until the discharge eventually extinguished. Discharge extinguishing occurred when the effective ionization cross section became decoupled from the continually rising electron temperature; hence, the discharge could not be maintained owing to the decrease in the ionization rate. This inability to maintain the discharge is considered the mechanism for extinguishing by slow quenching.
Comparison of band-filling and gain models for multiple-quantum-well lasers
Authors: Heinämäki A. , Tulkki J.
Published: July 2002

The gain of a separate-confinement heterostructure laser has been studied theoretically by different band-structure and band-state filling models. It is shown that for a shallow quantum-well structure the optical gain is reduced significantly by the noncomplete overlap of the envelope wave functions. The gain is reduced further by occupation of the cladding and barrier states in the laser structure. Comparison with experimental results shows that the Luttinger–Kohn model tends to underestimate the gain. It is suggested that the observed discrepancy is related to enhancement of the confinement by carrier induced space charge, an effect not included in the present calculation.
Photoluminescence of undoped bulk InP grown by the liquid-encapsulated vertical Bridgman technique
Authors: Kang Junyong , Matsumoto Fumio , Fukuda Tsuguo
Published: July 2002

The 4.2 K photoluminescence (PL) spectra of undoped bulk 〈100〉 InP grown by the liquid-encapsulated vertical Bridgman (LE–VB) techniques are characterized by three kinds of recombination peaks. A peak exhibited near band-gap energy is attributed to the recombination of bound excitons (BEs). At the low energy side of BEs, a series of peaks with the same energy interval are due to the recombination of donor–acceptor (DA) pairs with their longitudinal–optical (LO) phonon replicas, which is associated with the Zn acceptor. Recombination of deep levels (DLs) is characterized by a broadband with fine structure at the higher energy side, which seems to be associated with the recombination of native defects and their phonon replicas. The lattice relaxation of DA recombination is smaller while the recombination intensity of DLs is stronger as compared the 4.2 K PL spectra of the LE–VB crystals with those of seed crystals grown by the liquid-encapsulated Czochralski (LEC) technique. At room temperature, only a broadened peak near band-gap energy is recognized in both the LEC seed and as-grown LE–VB crystals, which is assigned as the recombination of band to bands. The PL mapping results show that the recombination intensity of band to bands in the LE–VB crystal is stronger than that in the LEC crystal. By combining the etched pit density analysis, the stronger PL intensity of band to band recombination in the LE–VB crystal is considered to be due to the lower densities not only of native defects responsible for the recombination of DLs but also of dislocations responsible for the etched pit.
Thermal properties of the organic nonlinear optical crystal 4-nitro-4′-methylbenzylidene aniline
Authors: Kerkoc P. , Lochran S. , Bailey R. T. , Cruickshank F. R. , Pugh D. , Sherwood J. N. , Blake A. J.
Published: July 2002

The thermal properties of high-quality nonlinear optical single crystals of 4-nitro- 4′-methylbenzylidene aniline (NMBA) have been measured in various temperature ranges. The specific heat was measured in the range from 273 to 373 K by differential scanning calorimetry and was found to obey the relationship Cp=2.3×10−3 T+0.487 J g−1 K−1. The peak melting point was detected at a temperature of 402 K with a corresponding enthalpy of melting ΔHm of 113.63 J g−1. Principal thermal expansion and thermal conductivity coefficients were determined at different temperatures. For example, at room temperature (295 K) they were α1=1.274×10−4 K−1, α2=0.826×10−4 K−1, and α3=0.239×10−4 K−1. The principal thermal conductivity coefficients were k1=0.40 W m−1 K−1, k2=0.19 W m−1 K−1, and k3=0.21 W m−1 K−1 and these values were independent of temperature up to 370 K.
Role of the evanescent states in the electron transport in quantum waveguides
Authors: Sheng Wei-Dong , Xia Jian-Bai
Published: July 2002

Recognizing the computational difficulty due to the exponential behavior of the evanescent states in the calculations of the electron transmission in waveguide structures, the authors propose two transfer matrix methods and apply them to investigate the influence of the evanescent states on the electron wave propagation. The study shows that the effect of the evanescent states on the electron transport is obvious when the electron energy is close to the subband minima. The results show that the calculated transmissions are much enhanced if the evanescent states are omitted in the calculations. For the multiple-stub structures, it is found that the connecting channel length has a critical effect on the electron transmission depending on it larger or smaller than the attenuation lengths of evanescent states. Based on the study of the evanescent states, a new kind of waveguide structures which exhibit quantum modulated transistor action is proposed.
Diffusion of Li, Na, and K in fluorinated Ti dioxide films: Applicability of the Anderson–Stuart model
Authors: Mattsson M. Stro/mme , Niklasson G. A. , Granqvist C. G.
Published: July 2002

Fluorinated Ti dioxide films were made by reactive sputtering. The mobility of Li, Na, and K in this host was studied by electrochemical techniques. Chronopotentiometry suggested that the cations occupy one type of site for cation/Ti ratios below 0.5, and that other sites are populated at higher ratios. Li and Na intercalation appeared to progress without major structural changes, whereas the intercalation of the larger K ions caused structural rearrangement. Impedance spectra were interpreted within a Randles circuit with a finite length Warburg element from which chemical diffusion coefficients were obtained at different intercalation levels and temperatures. The ion diffusion could be understood in detail from the classical Anderson–Stuart model [O. L. Anderson and D. A. Stuart, J. Am. Ceram. Soc. 37, 573 (1954)] as long as the structure remained unchanged, i.e., for the Li and Na intercalation, whereas K intercalation, expectedly, could not be reconciled with this model.
Intercalation of Bi2Sr2CaCu2O8+δ single crystal with C60: Characterization and micro-Raman investigation
Authors: Sathaiah S. , Zargaro R. A. , Pacheco Marcos T. T. , Grigorian L. S. , Yakushi K.
Published: July 2002

Micro-Raman and corroborative photoluminescence (PL); infrared (IR) absorption; scanning tunneling microscopy/spectroscopy (STM/STS) and x-ray diffraction (XRD) studies on the intercalation of Bi2Sr2CaCu2O8+δ (Bi-2212, host) with C60 (guest) reveal that intercalation drastically changes vibrational, electronic, and structural characteristics of both the guest and the host species. The predominant changes in vibrational modes such as splitting (651, 668 cm−1) in the radial mode (at 709 cm−1); anomalous intensity distribution; and appearance of forbidden modes in the Raman spectra of the guest have been related to the symmetry reduction in the guest sublattice and to the induced resonance effects due to the intercalation process. Further, the changes in Raman spectra corresponding to the host, such as the appearance of a strong Raman mode at 310 cm−1 (in the νCu–O region), redshift in the νBi–O mode, and the appearance of a band at 1443 cm−1 in the tangential mode region of the guest reveal the formation of semiconducting islands in the host sublattice due to the guest–host electron transfer process. Raman results have been correlated with PL, IR, STM/STS, and XRD data.
Anomalously high collection probability in thin film polycrystalline silicon solar cells from numerical modeling
Authors: Edmiston S. A.
Published: July 2002

The impact of grain size on the average collection probability of fine grained (<10 μm) polycrystalline silicon has been investigated using a numerical device simulator. This model predicts that the collection probability can improve dramatically once the depletion regions around adjacent grain boundaries overlap. Thus, contrary to most analytical models, the collection probability is not monotonic with grain size. The collection probability has a local maximum at a grain size determined by the grain boundary trap state density. The magnitude of the improvement is dependent upon the grain boundary recombination velocity.
On the photoionization spectra of quantum wells
Authors: Załużny M. , Nalewajko C.
Published: July 2002

The influence of the depolarization and exciton-like effect on the photoionization spectra of n-type quantum wells is studied theoretically employing the local density approximation. A critical discussion of the results obtained by other authors is given. Numerical examples for GaAs/AlGaAs and Si/SiGe quantum wells are presented.
The third-order nonlinear optical properties of porphyrin oligomers
Authors: Terazima Masahide , Shimizu Hitoshi , Osuka Atsuhiro
Published: July 2002

Using a single beam z-scan technique with a 30 ps laser pulse at 640 and 1064 nm, the real and imaginary parts of the third-order nonlinear optical susceptibilities of porphyrin oligomers for different numbers of repetition units in solutions were measured. At a probe wavelength 640 nm, the real parts of χ(3) (Re χ(3)) of oligomers which consist of porphyrins bridged by 1,4-phenylene moiety were found to be negatively enhanced significantly compared with that of the monomer. While Re χ(3) of the oligomers increased with increasing the porphyrin unit, the value per monomer unit remains almost constant; that is, Re χ(3) is proportional to the number of monomer units. The oligomers in which the porphyrin rings are directly attached together at the meso position exhibited enhanced imaginary parts of χ(3) at 640 and 1064 nm. The enhanced real part was also detected at 1064 nm. These unique properties are discussed in terms of the two photon resonance process.
Characterization of thin films of YBa2Cu3O7−δ using an interdigital radio frequency proximity probe technique
Authors: Feller J. R. , McKenna M. J. , Hucho C. , Sarma B. K. , Levy M. , Gavaler J. R.
Published: July 2002

A capacitively coupled interdigital probe technique is described whereby the electrical characteristics of thin films at arbitrary frequencies in the range from about 100 kHz to beyond 1 GHz may be studied. Patterning of the film, deposition of electrodes, and bonding of electrical leads are unnecessary, so that all measurements are nondestructive and noninvasive. Preliminary measurements of the superconducting transition in thin films of the high-temperature superconductor YBa2Cu3O7−δ in magnetic fields up to 1.5 T are presented and discussed. They show a large field-dependent peak, attributable to tunneling effects, just below the onset temperature. Anomalies are also seen at higher temperatures, providing evidence of a structural phase transition.
Radiographic imaging with image plates: The influence of the readout intensity on the image quality
Authors: Thoms M. , von Seggern H.
Published: July 2002

The image quality of radiographic images from image plate detectors is limited by two factors: first, the quality of the image plate itself and, second, the scanning procedure of the individual scanning device. In this study the impact of the latter on the image quality is investigated. A method to calculate the spatial resolution in the form of the line-spread function and the photostimulated luminescence intensity for various scanning laser beam intensities is presented. Theoretical results are compared to experimental ones obtained from a commercially available image plate. It is shown experimentally that the spatial resolution is reduced with increasing laser intensity of the readout beam, that the detected information shifts spatially and that the response of the photostimulated luminescence does not vary linearly with the intensity of the laser light. The results are explained by light scattering in the phosphor layer of the image plate and information bleaching during the readout procedure.
Comparison between the optical limiting behavior of chloroaluminum phthalocyanine and a cyanine dye
Authors: Hughes S. , Spruce G. , Wherrett B. S. , Kobayashi T.
Published: July 2002

The picosecond optical limiting characteristics of the optical limiting dyes hexamethylindotricarbocyanine iodide (HITCI) and chloroaluminum phthalocyanine (CAP) are compared and contrasted at 532 nm. From single pulse transmittance experiments, HITCI is shown to possess a serious limitation in its optical limiting behavior, where the regime of induced absorption becomes one of induced transmission for high irradiances. CAP, on the other hand, although possessing a smaller ratio of the excited-state to ground-state absorption cross-section, continues to exhibit optical limiting over a much broader dynamic range. From cross-polarized time-resolved excitation-probe measurements, HITCI exhibits a sharp negative spike around zero delay which originates from orientational coherent grating effects, while CAP does not exhibit any spike. These nonlinearities are explained theoretically as a complex interplay between a series of excited manifolds for the dyes and the radiation properties of the interacting laser pulse.
Porous structure of thick fiber webs
Authors: Hellén E. K. O. , Alava M. J. , Niskanen K. J.
Published: July 2002

The bulk properties and stochastic pore geometry of finite-thickness fiber webs are studied using a realistic model for the sedimentation of flexible fibers [K. J. Niskanen and M. J. Alava, Phys. Rev. Lett. 73, 3475 (1994)]. The resulting web structure is controlled by a dimensionless number F=Tfwf/tf, where Tf is fiber flexibility, wf fiber width, and tf fiber thickness. The fiber length (≫wf,tf) is irrelevant. With increasing coverage c̄, a crossover occurs at c̄=c0≈1+2F from a vacancy-controlled two-dimensional (2D) structure to a pore-controlled 3D structure. The 3D structures are isomorphic in that the pore dimensions are exponentially distributed, with the decay rate dependent only on F.
Internal photoemission at the Si/SiO2 and Si/metal interface
Authors: Boedecker K. , Könenkamp R.
Published: July 2002

We present experimental results from infrared photocurrent measurements at the Si/metal and Si/SiO2/metal interface. We observe internal photoemission from the Si valence band into metal states or into empty interface states. For the p-Si/SiO2/metal interface the photocurrent threshold occurs at a photon energy of 0.138 eV, indicating that the Fermi level is pinned close to the valence band. We argue that this is the case only for discrete locations of the interface and suggest that the pinning is caused by a defect-related acceptor level.
Giant magnetoresistance effect in CoZr/Cu/Co spin-valve films (abstract)
Authors: Ben-Youssef J. , Koshkina O. , Le Gall H. , Harfaoui M. El , Bouziane K. , Yamani M. El , Desvignes J. M.
Published: July 2002

A high sensitivity of giant magnetoresistance (GMR) has been observed recently from soft magnetic layers such as NiFe, NiFeCo, and FeCoB.12 Amorphous CoZr alloys present ultrasoft properties compared to NiFe.3 GMR has been investigated for amorphous CoZr/Cu/Co thin films grown by rf diode sputtering using a target consisting of a Co disk partially covered with a Zr foil. The influence of the argon pressure on Cu layer deposition, Cu thickness, and Zr content on magnetic and transport properties was analyzed. The highest value of transverse GMR obtained along the easy axis is 3.6% and the MR curve was saturated in a magnetic field of 100 Oe at room temperature. GMR shows scaling behavior with the sample composition. Very high sensitivity, around 1–2%/Oe was observed in a CoZr (3 nm)/Cu (3 nm)/Co (2 nm) sandwich. This study shows a large dependence of GMR on Cu thickness and the maximum of magnetoresistance strongly depending on the Ar pressure which modifies the interface roughness. The Zr content also influences the magnetotransport properties (ΔR/R and ΔR/RΔH). The difference in coercivity between soft magnetic CoZr and hard magnetic Co layers induces antiferromagnetic alignment. Therefore a high MR ratio and field sensitivity are achieved by improving the magnetic properties of the CoZr layer.
Effect of Fe cap layers on the spin density waves in epitaxial Cr(001) films
Authors: Bödeker P. , Sonntag P. , Schreyer A. , Zabel H. , Borchers J. , Hamacher K. , Kaiser H.
Published: July 2002

We have investigated proximity effects of Fe layers on the spin density waves (SDW) and the concomitant charge density waves or strain waves in thin epitaxial Cr[001] films using synchrotron and neutron scattering. Unlike in bulk Cr we observe a strong anisotropic occupation of the three possible SDWs with their wave vectors Q pointing along the {001} directions. In a pure 3000 Å thick Cr[001] film, the SDW exhibits an almost complete out-of-plane orientation, whereas in a Cr film of the same thickness capped by a 20 Å Fe layer the SDW becomes completely reoriented with Q now propagating in the plane. This SDW is preserved over the entire temperature range from 10 K up to the Néel temperature of about 311 K.
Preparation and magnetical studies of Mn50Al50/Al bilayer films
Authors: Kuo P. C. , Yao Y. D. , Chen W. R. , Huang J. H.
Published: July 2002

Mn 50 Al 50 /Al bilayer films were fabricated on a glass substrate by rf magnetron sputtering. The films were subsequently heat-treated in order to transform nonmagnetic MnAl ε-phase to magnetic τ-phase. The addition of Al buffer layer could enhance the adhesion of the MnAl films, and for Mn50Al50/Al bilayer films with Al layer thickness between 5 and 15 nm, we can obtain high saturation magnetization (>390 emu/cm3), and high coercivity (>2200 Oe) Mn50Al50/Al films for practical usage. Bending beam method analysis shows that the larger the residual stress of the Mn50Al50/Al bilayer film is, the higher the coercivity is. The relations between the saturation magnetization, the coercivity and the phase transition, the microstructures of the films are discussed.
Studies of optical and electronic properties in Co/Ag multilayers
Authors: Wang Y. , Chen L. Y. , Zhou S. M. , Zheng Y. X. , Hu A. , Zhai H. R. , Naik R. , Dunifer G. L. , Auner G. W.
Published: July 2002

We have studied the electronic structure and optical properties, in the photon energy range of 3.0–4.5 eV, of sputtered Co/Ag multilayers with a scanning ellipsometer and Kerr spectrometer. It is found for the multilayer series Co(1.2 nm)/Ag and Co/Ag with dCo/dAg=2/3 that the screened plasma frequency ωp* of the multilayers and the interband transition frequency ω0 for L3→L2′ (d band to Fermi surface near the L point) in the Ag layers shift towards lower energy with increasing Ag layer thickness or modulation wavelength. For the second series of samples, the Kerr rotation peak also shifts towards lower energy with increasing modulation wavelength. For a third series of Co/Ag(1.3 nm) multilayers, only ω0 moves towards lower energy with an increasing Co layer thickness. The variation of ω0 is not easily explained in terms of internal strains and changes of the lattice constants in the Ag layers. Further theoretical analysis is needed.
In situ Kerr microscopy of ultrathin magnetic films (abstract)
Authors: Giergiel J. , Kirschner J.
Published: July 2002

We developed a Kerr microscope designed as a simple add-on device to an existing vacuum chamber with sufficient sensitivity to permit in situ domain imaging for magnetic films grown in an ultrahigh vacuum environment. The performance of this microscope will be demonstrated by domain images obtained on Fe films deposited on Cu(001) and W(011). For systems with perpendicular magnetization sufficient signal/noise ratio (5) and 10 μm resolution can be obtained with single exposures as short as 0.7 s. This permits simultaneous acquisition of spatially resolved magnetometry data. Image averaging is used when the magnetization is in-plane. Monolayer sensitivity can be obtained in both cases. Examples of domain nucleation and wall propagation in several layer thick Fe/Cu(001) films will be given together with the estimation of their Barkhausen length. Wedge configuration was used to image magnetic behavior in the vicinity of the spin–reorientation transition. Preliminary data for domain wall behavior in 4 monolayer Fe/W(001) film with strong uniaxial in-plane anisotropy will also be presented.
Magnetic spectromicroscopy and microspectroscopy with submicrometer resolution (abstract)
Authors: Schneider C. M. , Frömter R. , Swiech W. , Ziethen Ch. , Schmidt O. , Fecher G. H. , Schönhense G. , Kirschner J.
Published: July 2002

Conventional techniques of magnetic domain imaging are usually not selective with respect to the chemical species in a system under investigation. This limitation can be overcome by employing soft x-ray magnetic dichroism which combines both magnetic sensitivity and chemical selectivity. We present first results on magnetic domain imaging at surfaces obtained with a newly developed photoelectron emission microscope using magnetic circular dichroism (MCD). Topographic studies on a silicon surface showed the instrument to be capable of a lateral resolution of better than 50 nm. Two approaches of separating chemical and magnetic information are demonstrated for Permalloy micropatterns on silicon. First, the lateral distribution of the different chemical species or the magnetic domains is obtained by subtracting images taken at different photon energies (spectromicroscopy). Second, a “small spot” mode permits the acquisition of x-ray absorption spectra from surface areas of less than 2 μm diameter. The latter technique is called microspectroscopy. On a Fe(100) whisker surface we observed magnetic domains with domain boundaries ∼300 nm wide. This value corresponds to the intrinsic width of a 180° domain wall at the surface, as determined by scanning electron microscopy with spin polarization analysis.1 The studies in Ref. 1 have also shown that this kind of domain wall behaves Neél-like at the surface, i.e., the magnetization vector M rotates within the film plane over the domain boundary. Exploiting the directional characteristics of MCD we can map the component of M normal to the domain boundary and thus selectively image the wall itself.
Magnetic anisotropy oscillations (invited)
Authors: Back C. H. , Weber W. , Würsch Ch. , Bischof A. , Pescia D. , Allenspach R.
Published: July 2002

The magnetic anisotropy in Co films epitaxially grown on Cu(001) is investigated by measuring magneto-optical Kerr hysteresis loops during film growth. As a function of Co thickness the magnetic anisotropy oscillates with a period of 1 monolayer. These oscillations are attributed to the periodic variations of the film morphology alternating between filled and incompletely filled atomic layers. Upon coverage of the Co films with Cu overlayers the anisotropy of the magnetic film is found to oscillate with increasing Cu layer thickness. We relate these oscillations to quantum interferences due to the confinement of electrons in ultrathin films.
Site-bond-correlated models for the disordered magnets: Application to KNipMg1−pF3 (abstract)
Authors: de Albuquerque Douglas F. , Fittipaldi I. P.
Published: July 2002

Site-bond-correlated (SBC) dilution picture has been successfully proposed to account for the striking differences experimentally observed by NMR measurements between random diluted magnet KNipMg1−pF3 and the isostructural compound KMnpMg1−pF3 (see for instance Ref. 1, and references therein). In the SBC picture, the coupling between two nearest-neighbors (nn) magnetic atoms is assumed to be dependent upon the random occupancy of the other nn sites. In this article we study the D-vector model disordered in accordance with the SBC picture in a d-dimensional hypercubic lattice within the framework of the mean field renormalization group. The study is based on two different models (denoted by A and B) for the exchange interactions, in which the random occupancy of the other nn sites is measured by means of a phenomenological parameter α. The critical boundaries of the ferromagnetic and the spin-glass phases with the paramagnetic one, are obtained for various values of the parameter α. The study reveals the existence of an interesting universal relation between the initial slope in the limiting correlated (α=0) and uncorrelated (α=1) cases, at p=1. It is shown that the D-vector classical model in the SBC version with inclusion of the relevant next-nearest-neighbors exchange interaction parameter, exhibits excellent agreement with the experimental data available for the compound KNipMg1−pF3 with α=0.145
Magnetic response of FeF2 films on (100) MgO (abstract)
Authors: Adenwalla S. , Felcher G. P. , Nogués J. , Schuller I. K.
Published: July 2002

Pairs of FeF2/Fe films show large exchange bias. In bulk FeF2 is antiferromagnetically ordered below 78 K, and the magnetic moments of the corner and center atoms in the rutile structure are respectively parallel and antiparallel to the tetragonal axis. Are the moments compensated in a thin film as well, or does a net magnetization develop, for instance at the interface with iron? A polarized neutron reflection measurement was taken on a single film of FeF2, 920 Å thick, grown in the (110) orientation on a MgO (100) face. In polarized neutron reflection is measured the polarization dependence of the reflectivity as a function of kz, the component of the neutron momentum perpendicular to the surface. From this, in principle, the detailed net magnetization profile along the thickness of the film can be obtained. Reflectivity patterns taken with the sample in different physical conditions (temperatures: 4.2–120 K, magnetic fields: 100–5000 Oe) showed the interference pattern characteristic for a 920 Å thick film. However the polarization dependence of the reflectivity was in all cases very weak and only by repeated runs it was possible to observe a statistically significant difference between patterns obtained at 80 K in field of 5 kOe and at 4.2 K after field cooling in the same field. In the paramagnetic region no polarization was observed; in the antiferromagnetic region weak polarization peaks were found at the values of kz corresponding to minima of the interference oscillations. The precision of the measurements does not allow to give yet a detailed depth profile of the net magnetization. While the presence of a strong ferromagnetic component close to the surface seems to be ruled out, the results can be fitted by a magnetization of 0.025 μB/Fe uniform throughout the film as well as by the presence of 1μB/Fe on the three atomic planes most adjacent to MgO.
Lattice effects on the charge and spin dynamics in perovskite manganites (invited) (abstract)
Authors: Hwang H. Y.
Published: July 2002

A detailed study of doped LaMnO3 with a fixed carrier concentration has revealed a rich phase diagram as a function of the average ionic radius of the La site 〈rA〉. The transition temperature TC, from a high-temperature paramagnetic insulator to a low-temperature ferromagnetic metal, decreases rapidly with reduced 〈rA〉. Systematic trends in the magnetotransport properties and the spin dynamics are strongly correlated with the proximity of the zero-temperature insulator phase. The general structure of this phase diagram can be understood by considering the role of static and dynamic distortions of the MnO6 octahedra and their evolution as a function of 〈rA〉.
Wear and degradation mechanisms of magnetic thin-film rigid disks with different lubricants using mass spectrometry
Authors: Bhushan Bharat , Cheng Yuping
Published: July 2002

Wear and degradation mechanisms of perfluoropolyether (PFPE) lubricants are studied using mass spectrometry and friction measurements during sliding in a high vacuum environment. Three kinds of lubricants with nonpolar and polar ends and with and without thermal treatment are applied over a thin-film disk with diamondlike film (DLC) overcoat. The results show that fluorocarbon fragments are generated from lubricants during a period of sliding with a low and stable coefficient of friction, followed by a sharp rise in frictional force and generation of gaseous products of DLC overcoat material. Increase in the friction is associated with lubricant depletion leading to intimate contact of the slider with the DLC overcoat. It is concluded that decomposition of PFPEs begins from the onset of sliding, and the DLC overcoat starts to wear simultaneously from the beginning of the sliding for untreated lubricants, but was well protected in the case of chemically bonded lubricants. Fully bonded lubricants better protect the DLC followed by partially bonded lubricants. Two bonded lubricants tested, exhibited similar performance.
Flying characteristics of a novel negative pressure slider “Papillon”
Authors: Kojima Naoto , Okada Kanzo , Yotsuya Michio , Ouchi Hironobu , Kawazoe Kazushige
Published: July 2002

This paper proposes a novel design of a 50% shaped rail negative pressure air bearing slider, the Papillon slider. This design attains constant fly height and near-zero roll characteristics across the disk, simultaneously. The head roll due to seek acceleration is suppressed by controlling static roll angle and improving roll stiffness of the air bearing. It is shown that the side rail shape can be configured so as to improve the roll stiffness. Experiments also show that the Papillon slider has good takeoff and contact start/stop performance.
Protective carbon films deposited by dc-bias facing targets sputtering with microscopic ultraflatness and strong sp3 coordination
Authors: Noda Kohki , Kawanabe Takashi , Naoe Masahiko
Published: July 2002

Carbon thin films were deposited on hard disks as protective layers by facing targets sputtering (FTS), and their characteristics were evaluated to determine whether they would be suitable protective layers for thin-film magnetic recording media. The performance and lifetime of a hard disk drive (HDD) are intimately related to the head-disk interface. Increase in performance due to reduction of the flying height and magnetic spacing, and longer product lifetime are related to the properties of protective layers covering the surfaces of hard disks. Currently, such layers are generally sputtered amorphous carbon films, whose characteristics are strongly dependent on various sputtering conditions such as the argon gas pressure, substrate temperature, and dc and rf bias voltages. In this study, the dependence of the characteristics of carbon films on the dc bias voltage of the FTS was investigated, and the characteristics were also compared with those obtained without a dc bias voltage supply. The carbon films were deposited at an argon gas pressure of 0.2 mTorr and a substrate temperature of 25 °C as room temperature, with several dc bias voltages and also without any bias voltage. There have been no reports to date of the successful use of such low gas pressures to realize excellent protective layers. The properties of the films were characterized by Raman spectroscopy, and the results were compared with previously reported ones obtained in different sputtering conditions at high argon pressures. Carbon films deposited, without plasma damage, by FTS, with dc bias voltage at argon gas pressures as low as 0.2 mTorr, showed a large population of sp3 coordination, columnless morphology, and a microscopically flat surface. These are better properties than those obtained with no dc bias voltage, and may lead to an intrinsically excellent protective layer for hard disks.
Landing zone skew angle, long term stiction, and contamination build up on slider surfaces of disk drives
Authors: Liu B. , Lim S. T. , Sheng G.
Published: July 2002

This work presents results of experimental investigation on the relationship between landing zone skew angle, long term stiction, and contamination build up on slider surface caused by slider-disk interaction in the landing zone. Results indicate that larger skew angle in the landing zone will lead to higher long-term stiction force and increases the likelihood of linelike contamination build up on slider surface.
Linearized muffin-tin orbital calculations of the magneto-optical properties of FePt multilayers
Authors: Lim S. P.
Published: July 2002

There exists experimental evidence that the magneto-optical spectra of FePt alloy films in the L10 structure show a strong enhancement near 2 eV with the onset of chemical ordering. This is in contrast to the disordered system and that of bulk Fe itself where no peak in the spectra is found at this energy. We present our calculated magneto-optical responses and the induced moments of Pt in FePt, as well as several other Fe/Pt multilayers based on the linearized muffin-tin orbital methodology. Our result for ordered FePt is in good agreement with experiment showing the peak near 2 eV. However, the Fe/Pt multilayers do not show any significant enhancement as observed in FePt and their magneto-optical response can be understood in terms of the magneto-optical response of bulk Fe (albeit with an expanded lattice constant reflective of the inter Fe spacing of the multilayers) and the relative number and ordering of the Fe and Pt layers.
Spatial homogeneity of thin films of colossal magnetoresistance materials by scanning ferromagnetic resonance (abstract)
Authors: Schurig David , Vier D. C. , Schultz S. , Oseroff S. , Ramesh R.
Published: July 2002

An effective method for preparing thin films of colossal magnetoresistance (CMR) materials is by pulsed laser deposition (PLD). We have studied such films by measuring the temperature and field dependence of dc resistance, magnetization, and specifically ferromagnetic resonance (FMR). With PLD it is possible to prepare samples with reasonable homogeneity as observed with x-ray diffraction and Rutherford backscattering. However, we have found that samples that appear to be reasonably, crystalographically homogeneous are not necessarily magnetically homogeneous. We believe that a powerful technique for examining magnetic homogeneity in this class of CMR samples is via FMR. In FMR, the resonance linewidth is an indicator of the average sample homogeneity, but this technique is much more informative when used in a scanning mode that we have developed. Scanning FMR data will be shown for several CMR samples prepared from La0.7R0.3MnO3 (R=Ca, Ba) targets using PLD. We find that some complex multiline spectra (observed when the sample is measured as a whole) are actually a superposition of simpler spectra with spatially localized resonance lines. Resonance lines are also found that are present throughout the sample. The spatial variation of FMR lines we observe is a direct measure of the spatial inhomogeneity of the magnetic environment. We will discuss the FMR spatial variations as a function of sample preparation, and subsequent oxygen and argon annealing conditions.
Anderson localization in doped manganates due to magnetic and structural disorder (abstract)
Authors: Byers Jeff M.
Published: July 2002

The nature of the metal–insulator transition in the doped manganates is not well understood. The difficulty in understanding the transition stems from the variety of physical phenomena that seem to be of importance. The manganates have both magnetic as well as structural transitions that correlate with the metal–insulator transition. In an effort to clarify the situation a model based on temperature (T) and field-dependent (H) mobility edges induced by quasistatic magnetic disorder is proposed. The dependence of the mobility edge on field and temperature is derived using the localization function technique. This technique essentially examines the quantum diffusion of a localized particle as a function of time. The mobility edges are shown to move through the Fermi level if the Fermi energy sits at the edge of a band as suggested by photoemission experiments. Additionally, the formation of polarons is enhanced in the vicinity of a mobility edge since the electronic wave functions are nearly fractal in character and further localized by lattice distortions. These lattice distortions can be considered as parasitic on the localization induced by the quasistatic spin disorder and have the same temperature dependence as the magnetic transition.
Coexisting ferro- and helimagnetism in Dy/Y superlattices
Authors: Theis-Bröhl Katharina , Ritley K. A. , Flynn C. P. , Hamacher K. , Kaiser H. , Rhyne J. J.
Published: July 2002

Neutron diffraction studies on Dy/Y superlattices grown with the c axis at an angle of approximately 35° to the film plane reveal a coexistence of helical antiferromagnetic order and ferromagnetic order. The coexistence of magnetic phases has been determined to arise from the development during growth of surface facets of the Y buffer layer, which was grown on bcc (211) Ta or Nb substrates. One of the superlattice facets produces an isotropic expansion of the Dy basal plane which favors the helical antiferromagnetic spin configuration, while the other facet causes an anisotropic contraction of the Dy basal plane that favors ferromagnetism. The net result of the growth anomaly is the apparent coexistence of the two magnetic states as observed by neutron scans made with the scattering vector oriented parallel to the nominal c crystal axis of the superlattice.
Granular thin film deposition by simultaneous spark erosion and sputtering
Authors: Shevchenko N. B. , Christodoulides J. A. , Meng-Burany X. , Hadjipanayis G. C.
Published: July 2002

We have investigated a new method of preparing granular thin films, which are composed of fine metallic particles embedded in a uniform matrix material. By our method, fine metallic particles are created by spark erosion in an inert gas environment and directly deposited onto a cooled substrate. Magnetron sputtering is employed concurrently thereby building up the matrix. Using such a deposition method, granular thin films are created without the need of any heat treatments and can be made with virtually any material and composition. Furthermore it is even possible to create granular thin films from miscible phases. The size of the particles can be controlled by varying the pressure under which the spark erosion is conducted up to a few Torr of Ar. We have applied our method to the case of magnetic particles in a nonmagnetic matrix. Preliminary transmission electron microscope measurements on Fe particles in a Cu matrix showed 10-nm-diam. Fe particles. Selected area diffraction patterns show that the film is composed of only the Fe and Cu phases. Similarly for the Gd–Ag system, 10 nm Gd particles were observed in an Ag matrix. Gd–Ag compounds that would be expected to form were not observed. Magnetic measurements for these systems agreed with the nanometer scale microstructure that was observed.
Influence of magnetic field on the response of FeSiB wire delay lines
Authors: Chiriac H. , Hristoforou E. , Neagu Maria , Darie I. , Barariu Firuţa
Published: July 2002

The effects of the exciting magnetic field as well as of the bias magnetic field applied at the exciting or receiving points for Fe77.5Si7.5B15 amorphous magnetostrictive wire, used as delay lines, have been investigated. Amorphous wires have been tested in the as-cast state and after the stress-relief process. The increase in the value of the exciting magnetic field leads to an increase in the value of the pulsed voltage output. The maximum values for the pulsed voltage output are obtained for about 5 μs pulse width and 15 A amplitude of the pulsed exciting current. The dependence of pulsed voltage output on the bias magnetic field at the exciting or receiving points is not monotonic for all tested samples. The maximum response is obtained for about 100–200 A/m and 100–300 A/m bias magnetic field applied in exciting and receiving points, respectively.