bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnitude and origin of polychlorinated biphenyl (PCB) and dichlorodiphenyltrichloroethane (DDT) compounds resuspended in southern Lake Michigan
Authors: Hornbuckle Keri C. , Smith Gretchen L. , Miller Sondra M. , Eadie Brian J. , Lansing Margaret B.
Published: May 2004

Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) compounds are introduced into the water as a result of large‐scale storms and sediment resuspension in the southern basin of Lake Michigan. Settling and suspended sediments, as well as air and water samples, were collected in southern Lake Michigan over a 12 month period. Analysis of contaminant fluxes on settling particles shows that approximately 370 kg of PCBs and 110 kg of DDT compounds are resuspended in southern Lake Michigan during a single basin‐wide event (January 1999). Examination of contaminant signals indicates strong regional and temporal source‐receptor relationships between settling, suspended, and surficial sediments. The settling, suspended, and bottom surficial sediments in the shallow waters of the southern coastal region are enriched in lower molecular weight PCBs. The sediments in the water column and on the lake bottom in the deeper regions are enriched in higher molecular weight PCBs. Furthermore, falling sediments collected in the deeper regions of the lake are enriched in 4,4′‐DDT. The unique contaminant signal in deep water regions is surprising and suggests a source/receptor relationship among the bottom sediments and the sediments suspended and settling above them.
Mixed layer transformation for the North Atlantic for 1990–2000
Authors: Tandon A. , Zhao L.
Published: May 2004

The buoyancy balance between two outcropping isopycnals leads to diagnostics for quantifying water mass formation rates between them due to air‐sea buoyancy fluxes [Walin, 1982]. The surface air‐sea transformation gets modified by mixed layer processes so that the net formation rate below the winter mixed layer depth is different from that given by surface air‐sea fluxes alone. Here we estimate the role of time dependence and mixed layer deepening to quantify the water mass transformation due to mixed layer entrainment fluxes. We focus on the mixed layer transformation in the North Atlantic for 1990–2000 during the World Ocean Circulation Experiment period, using both entrainment parameters and isopycnal geometry. The water mass transformation due to mixed layer entrainment is calculated using a large number of gridded one‐dimensional mixed layer models forced by National Centers for Environmental Prediction (NCEP) reanalysis air‐sea fluxes (daily/6 hourly) to calculate the local entrainment parameters; Reynolds sea surface temperature and Levitus monthly salinity data determine the isopycnal geometry. To get a closed annual cycle in the mixed layer depth, any net annual heat flux is ascribed to advective processes. These are included in the annual mean, leaving any synoptic forcing in the NCEP forcing unperturbed. In general, the mixed layer transformation opposes air‐sea interaction, with amplitudes of (1.3 Sv) in the equatorial region (without equatorial upwelling contribution) and (0.5 Sv) in the overflow region. Mean cross‐isopycnal volume fluxes are O(1 Sv), with considerable interannual variability. These estimates of water mass formation due to mixed layer processes are sensitive to synoptic frequencies, but not to climatological mean air‐sea fluxes, and are within the imposed noise levels for inverse box models of the North Atlantic.
Radiation analysis in the space domain of laterally shielded planar transmission lines: 2. Applications
Authors: Tornero J. L. Gómez , Melcón A. Álvarez
Published: May 2004

The second part of this two‐piece paper applies the method developed in part 1 to show some interesting features for the practical analysis and design of leaky‐wave antennas. Novel analytical formulas based on the propagation and radiation discrete Parallel‐Plate Waveguide (PPW) spectrum coefficients described in the first part are presented, in order to calculate some interesting propagation and radiation aspects of leaky‐wave modes. These formulas will be used in the design of a slot‐line millimeter‐wave band leaky‐wave antenna, measuring parameters such as reflection and radiation losses, polarization purity, and coupling with undesired channel‐guide leaky modes. Comparisons with previous works for slot‐line leaky‐wave modes are presented, together with novel and interesting results, showing the usefulness of the proposed approach for the design of practical leaky‐wave laterally shielded planar printed antennas.
Modeling field‐scale dense nonaqueous phase liquid dissolution kinetics in heterogeneous aquifers
Authors: Parker J. C. , Park E.
Published: May 2004

This study investigates field‐scale DNAPL dissolution kinetics using high‐resolution numerical simulations of DNAPL releases and dissolved phase transport. A percolation model is employed to simulate the distribution of TCE within 10 × 10 × 10 m source zones with spatially heterogeneous aquifer properties following a release event. Distributed aquifer properties and DNAPL saturations are utilized to simulate coupled groundwater flow and long‐term dissolved phase transport. Grid‐scale dissolution rates are computed based on published bench‐scale relationships. Effective field‐scale mass transfer coefficients are computed from simulated TCE fluxes at the downstream source zone boundary. Heterogeneity in groundwater velocity and DNAPL distributions leads to field‐scale mass transfer coefficients that are much lower than laboratory‐scale values. Field‐scale mass transfer coefficients are observed to vary in direct proportion to the mean groundwater velocity, in contrast to laboratory studies that indicate proportionality with velocity to a power of ∼0.7. Computed field‐scale mass transfer coefficients vary approximately in proportion to relative DNAPL mass raised to an empirical depletion exponent, which is <1 for laterally extensive DNAPL lenses and >1 for more randomly oriented residual DNAPL regions. The former DNAPL geometries exhibit slow reductions in source concentration and contaminant flux with time as mass depletion proceeds. The latter DNAPL geometries exhibit significant and steady declines in source concentration and contaminant flux with time as depletion occurs.
Earthquake source parameters determined by the SAFOD Pilot Hole seismic array
Authors: Imanishi Kazutoshi , Ellsworth William L. , Prejean Stephanie G.
Published: May 2004

We estimate the source parameters of #3 microearthquakes by jointly analyzing seismograms recorded by the 32‐level, 3‐component seismic array installed in the SAFOD Pilot Hole. We applied an inversion procedure to estimate spectral parameters for the omega‐square model (spectral level and corner frequency) and Q to displacement amplitude spectra. Because we expect spectral parameters and Q to vary slowly with depth in the well, we impose a smoothness constraint on those parameters as a function of depth using a linear first‐difference operator. This method correctly resolves corner frequency and Q, which leads to a more accurate estimation of source parameters than can be obtained from single sensors. The stress drop of one example of the SAFOD target repeating earthquake falls in the range of typical tectonic earthquakes.
Antarctic oscillation and the dust weather frequency in North China
Authors: Fan Ke , Wang Huijun
Published: May 2004

The linkage between the Antarctic Oscillation (AAO) to the dust weather frequency (DWF) in North China is addressed. Here DWF denotes the number of days of dust weather events including dust haze, blowing dust and dust storm in one year. It is found that the interannual variation of AAO plays a significant role in the dust‐related atmospheric circulation during boreal spring. AAO and DWF correlate well, with positive AAO tending to decrease DWF in North China. Two possible mechanisms for the AAO‐DWF coupling are identified, one is related to a meridional teleconnection pattern; the other is related to a regional circulation pattern over the Pacific Ocean.
Stability and crystal structure of MgSiO3 perovskite to the core‐mantle boundary
Authors: Shim S.‐H. , Duffy T. S. , Jeanloz R. , Shen G.
Published: May 2004

We report in situ angle‐dispersive X‐ray diffraction measurements for MgSiO3 at 90–118 and 135–144 GPa and 300–2900 K. At 90–144 GPa, we observed a new diffraction peak at 2.57–2.62 Å as reported in Shim et al. [2001]. The pressure‐induced position shift of the new peak is consistent with those of MgSiO3 perovskite (Mg‐Pv), supporting that the new peak is associated with a modification in crystal structure of Mg‐Pv at 88 GPa. During laser heating above 2500 K at 144 ± 10 GPa, in addition to peaks of Mg‐Pv, we observed new peaks as well as peak splittings and intensity changes of some peaks. The major features in the diffraction patterns can be explained by the modified Mg‐Pv proposed by Shim et al. [2001] together with the post‐perovskite phase proposed by Murakami et al. [2004]. This supports the existence of a major phase transition in MgSiO3 under conditions close to those at the base of Earth's mantle.
Tectonic stress and seismogenic faulting in the area of the 1908 Messina earthquake, south Italy
Authors: Neri G. , Barberi G. , Oliva G. , Orecchio B.
Published: May 2004

Stress inversion of the twenty best‐quality earthquake fault‐plane solutions available in the area of the 1908 Messina earthquake showed a nearly uniform extensional regime with σmin constrained between N284°E and N312°E, coinciding with the direction of extension derived from geostructural data. The misfits of earthquake nodal planes and related slip vectors to the stress tensor allowed us to identify the fault planes of thirteen of the earthquakes used for inversion. In particular, the fault plane of 1908 earthquake was found in the north‐trending east‐dipping nodal plane of the focal mechanism. These findings and strain tensor estimates performed with the same dataset lead us to propose that in spite of stress uniformity detected over the study area the seismic strain orientations change significantly in the crustal volume under investigation due to different fault orientations in the different sectors. However, when comparing strong earthquakes with background seismicity in a given sector the strain orientations are found to be similar.
Sliding of a rough surface under oblique loading
Authors: Walsh Joseph B. , Zhu Wenlu
Published: May 2004

Sliding of a rough surface having a range of asperity heights is a gradual process, starting at contacts under relatively low normal shear load and spreading until the surface slides as a unit. We analyze this process theoretically for asperities with spherical tips, with heights having a probability density distribution given by a negative exponential. The case where applied normal traction increases concurrently with applied shear is treated in detail, resulting in analytical expressions for the normal and shear displacements. These results are used to show limitations on constitutive behavior for more complex normal stress‐shear stress histories.
A new topographic index to quantify downslope controls on local drainage
Authors: Hjerdt K. N. , McDonnell J. J. , Seibert J. , Rodhe A.
Published: May 2004

Topography is an important control on hydrological processes. One approach to quantify this control is the topographic ln(a/tanβ) index. This index has become widely used in hydrology, but it utilizes a relatively small portion of the information contained in a digital elevation model (DEM). One potentially important feature not considered in the implementation of the ln(a/tanβ) index is the enhancement or impedance of local drainage by downslope topography. This effect could be important in some terrain for controlling hydraulic gradients. We propose a new way of estimating the hydraulic gradient by calculating how far downhill (Ld, [m]) a parcel of water must move in order to lose a certain amount of potential energy (d, [m]). Expressed as a gradient, tanαd = d/Ld, values tend to be lower on concave slope profiles and higher on convex slope profiles compared with the local gradient, tanβ. We argue that the parameter d controls the deviation of hydraulic gradient from surface slope. While we determine this subjectively, landscape relief, DEM resolution, and soil transmissivity should be considered at the selection of d. We found the downslope index values to be less affected by changes in DEM resolution than local slope. Three applications are presented where the new index is shown to be useful for hydrological, geomorphological, and biogeochemical applications.
Simulation study of angle-resolved photoemission spectra and intramolecular energy-band dispersion of a poly(tetrafluoroethylene) oligomer film
Authors: Yoshimura Daisuke , Ishii Hisao , Ouchi Yukio , Miyamae Takayuki , Hasegawa Shinji , Okudaira Koji Kamiya , Ueno Nobuo , Seki Kazuhiko
Published: May 2004

Theoretical simulations of the angle-resolved ultraviolet photoemission spectra (ARUPS) for the oligomer of poly(tetrafluoroethylene) [(CF2)n; PTFE] were performed using the independent-atomic-center approximation combined with ab initio molecular orbital calculations. Previously observed normal-emission spectra for the end-on oriented sample (with long-chain axis perpendicular to the surface) showed the incident photon-energy (hν) dependence due to the intramolecular energy-band dispersion along the one-dimensional chain, and the present simulations successfully reproduced this hν dependence of the observed spectra. We employed the experimentally observed helical structure for PTFE oligomers for the simulations. We also calculated the density of states (DOS) for the planar zigzag structure, and examined the changes in the electronic structure due to the difference in the molecular structure by comparing the DOS for the helical and planar zigzag structures. Only a small change in the DOS was found between these structures, showing little change of the electronic structure between these conformations. We also evaluated the inner potential V0, which is the parameter defining the energy origin of the free-electron-like final state, and checked the validity of the value of −10 eV estimated in our previous study using the experimentally observed hν dependence of the peak intensity. The estimation of V0 was performed by pursuing the best agreement between the energy-band dispersion [E=E(k)] relation along the chain direction obtained from the simulated spectra and the experimentally deduced one. An excellent agreement in the topmost band was achieved when the assumed inner potential V0 was set at about zero. This value of V0 is much different from the value of V0=−10 eV in the previous study, suggesting the invalidity of the previous assumption at the estimation of V0 from the peak intensity variation with hν. Using the presently obtained V0, we could derive more reliable E=E(k) dispersion relation from the observed ARUPS spectra. The comparison of this newly derived relation gave good agreement with theoretically calculated E=E(k) relations, in contrast to the poor agreement for the previous results with V0=−10 eV.
Unusual magnetic and transport properties of layered compound ErMn6Sn6
Authors: Yao Jin-lei , Zhang Shao-ying , Liu Bao-dan , Shen Bao-gen , Wang Ru-wu , Zhang Li-gang , Yang De-ren , Yan Mi
Published: May 2004

The magnetic and magnetotransport properties of the polycrystalline ErMn6Sn6 compound have been investigated in the temperature interval of 5–380 K. The compound shows paramagetism, antiferromagnetism, and ferrimagnetism with decreasing temperature. In the antiferromagnetic state (67–362 K), the transition from antiferromagnetism to ferrimagnetism can be induced by an applied field, and the metamagnetic transition field increases from 0.2 kOe at 80 K to 15 kOe around 200 K and then decreases monotonously to 5 kOe at 330 K. The large magnetoresistance {MR=[R(H)−R(0)]×100%/R(0)} effect is observed with the metamagnetic behavior, such as −9.8% at 135 K under a field of 50 kOe. It is worth noting that ErMn6Sn6 displays the positive MR in the ferrimagnetic state and the negative one in the antiferromagnetic state, respectively, and the origin of the MR anomalies has been discussed.
Silicon inversion layer with a ferromagnetic gate: A novel spin source (invited)
Authors: McGuire J. P. , Ciuti C. , Sham L. J.
Published: May 2004

Novel spin transport behavior is theoretically shown to result from replacing the usual metal (or polysilicon) gate in a silicon field-effect transistor with a ferromagnet, separated from the semiconductor by an ultrathin oxide. The spin-dependent interplay between the drift current (due to a source-drain bias) and the diffusion current (due to carrier leakage into the ferromagnetic gate) results in a rich variety of spin dependence in the current that flows through such a device. We examine two cases of particular interest: (1) creating a 100% spin-polarized electrical current and (2) creating a pure spin current without a net electrical current. A spin valve consisting of two sequential ferromagnetic gates is shown to exhibit magnetoresistance dependent upon the relative orientations of the magnetization of the two ferromagnets. The magnetoresistance ratio grows to arbitrarily large values in the regime of low source-drain bias, and is limited only by the spin-flip time in the channel.
Step-induced slanted perpendicular magnetic anisotropy in 4°-miscut Si(111)/Cu/Au/Co/Au system
Authors: You Chun-Yeol , Lee Sukmock , Park Sungkyun , Falco Charles M.
Published: May 2004

We performed magneto-optic Kerr effect and Brillouin light-scattering measurements on a 4°-miscut Si(111)/Cu/Au(2ML)/Co(5ML)/Au system to understand the correlation we observed between slanted angle and magnetic anisotropy of the ultrathin Co layer. We find that the easy axis orientation is neither perpendicular nor in-plane with respect to the sample surface. We also find that the direction of incline is strongly correlated with the step direction, and that there is no such slanted magnetic anisotropy axis in films grown on a nonmiscut Si substrate. Therefore, we conclude that the slanted magnetic anisotropy axis is caused by the steps in the 4°-miscut Si(111) substrate.
Growth and properties of Co-doped TiO2 thin films grown on buffered Si substrate
Authors: Yang Hyuck Soo , Singh Rajiv K.
Published: May 2004

Epitaxial growth of a Co-doped anatase TiO2 thin film on silicon has been achieved by using SrTiO3/TiN bilayers as a buffer. All layers were sequentially formed by pulsed laser deposition. X-ray φ scan and selective area electron diffraction patterns revealed that SrTiO3/TiN buffer layers were grown with a cube-on-cube orientation relationship with silicon. Ferromagnetism was observed at room temperature with a coercivity of around 607 Oe. However, the ferromagnetism is attributed to the highly cobalt enriched TiO2 clusters which nucleate after a certain growth of film, as observed by atomic/magnetic force microscopy as well as cross-sectional transmission electron microscopy.
Magnetic properties of half-metallic Fe3O4 films
Authors: Jain S. , Adeyeye A. O. , Dai D. Y.
Published: May 2004

We have investigated in a systematic way the magnetic properties of Fe3O4 films grown directly on a Si(001) substrate and on a copper (Cu) buffer layer using the electron beam deposition technique. The effect of the Cu buffer layer thickness on the microstructure and magnetic properties of Fe3O4 has been studied. The effect of annealing on the magnetic properties of Fe3O4 films with various Cu buffer layer thicknesses was also studied. For Fe3O4 films deposited directly on Si(001), we observed two distinct switching fields due to the presence of two magnetic phases which are weakly coupled at the substrate interface.
Electronic delocalization and persistent currents in nonsymmetric-dimer mesoscopic rings threaded by magnetic flux
Authors: Hu X. F. , Peng Z. H. , Peng R. W. , Liu Y. M. , Qiu F. , Huang X. Q. , Hu A. , Jiang S. S.
Published: May 2004

We investigate electronic delocalization and magnetic-flux-induced persistent current in the mesoscopic ring, which is constructed according to the nonsymmetric-dimer (NSD) model. The flux-dependent energy spectra, electronic wavefunctions, and persistent currents are theoretically obtained. It is demonstrated that due to the localization-delocalization transition of electrons, the electronic state in the NSD ring can be localized, extended, and the intermediate case between extended states and localized ones. The persistent current (PC) approaches the behavior of free electrons if the Fermi level is around the near-resonant energy. Otherwise, the PC is depressed dramatically. This conclusion could be generalized to other correlated-disordered systems.
Asymmetrical magneto-impedance effect in Fe-rich amorphous wires
Authors: Garcia C. , Gonzalez J. , Chizhik A. , Zhukov A. , Blanco J. M.
Published: May 2004

Magnetoimpedance and magnetic properties of Fe-rich ferromagnetic amorphous wires of 0.050 mm diameter, prepared by an in-rotating-water technique following by a cold-drawing process to reduce the initial diameter of 0.125 mm, have been studied. A high value of magnetoimpedance phenomenon (about 60% real component and about 300% imaginary component) was measured in these microwires submitted to stress annealing by using the current annealing technique (annealing parameters: 150 mA during 90 min and 200 MPa). The application of a dc bias current affects strongly the field dependence of the magnetoimpedance ratio, inducing asymmetrical shape to the magnetoimpedance ratio. Such asymmetrical character is associated with the intrinsic helical anisotropy. The dc circular magnetic field produced by the dc electric current can modify in different ways the surface domain structure.
Intrinsic nonlinear ferromagnetic relaxation (invited)
Authors: Dobin A. Yu. , Victora R. H.
Published: May 2004

The intrinsic damping mechanism arising from the magnon–magnon scattering is theoretically studied in three dimensional and two dimensional ferromagnets. We develop an analytic theory, which identifies the three-magnon (in bulk) and four-magnon (in thin films) scattering processes, responsible for rapid relaxation. Micromagnetic simulations are used to confirm the analytic theory predictions, and to investigate the damping in different realistic technologically important systems. For the large angle rotation of magnetization, this intrinsic mechanism can dominate competing linear mechanisms even for rapidly relaxing metals.
Magnetoresistance in tunnel junctions using Co2(Cr,Fe)Al full Heusler alloys
Authors: Inomata K. , Tezuka N. , Okamura S. , Kurebayashi H. , Hirohata A.
Published: May 2004

We grew Co2(Cr1−xFex)Al Heusler alloy films using a magnetron sputtering system on thermally oxidized Si substrates at room temperature without any buffer layers. The x-ray diffraction patterns did not show the L21 structure as expected for the bulk but revealed the B2 and A2 structures, depending on the Fe concentration x, in which the structure tends to become the A2 with increasing x. The magnetic moment and the Curie temperature monotonically increased with increasing x. Spin-valve-type tunneling junctions consisting of Co2Cr1−xFexAl (100 nm)/AlOx (1.4 nm)/CoFe (3 nm)/NiFe (5 nm)/IrMn (15 nm)/Ta (10 nm) were fabricated on thermally oxidized Si substrates without any buffer layers using metal masks. The maximum tunneling magnetoresistance at room temperature was obtained as 19% for x=0.4.
Spin wave excitations in the antiferromagnetic state of Pr0.5Sr0.5MnO3
Authors: Krishnamurthy V. V. , Robertson J. L. , Mankey G. J. , Cavadini N. , Niedermayer Ch. , Mitchell J. F.
Published: May 2004

The layered A-type antiferromagnet Pr0.5Sr0.5MnO3 has been investigated by neutron scattering. Antiferromagnetic ordering is observed with a TN of 152.3 K and an exponent β of 0.148±0.01 that suggests 2d Ising behavior. The spin-wave excitations, measured for the neutron momentum transfer q perpendicular to the ferromagnetic planes at 2 K, show a gap of 2.3±0.2 meV at the zone center [0.5 0 0.5]. The dispersion near zone center yielded the spin-wave stiffness coefficient DSW of ∼100±10 meV Å2 which is twice the value found in the isostructural A-type antiferromagnet LaMnO3. The double-exchange interaction, introduced by hole doping, enhances DSW in Pr0.5Sr0.5MnO3. The spin wave dispersion at low q fits the dispersion of the Heisenberg model with nearest neighbor exchange interaction and single ion anisotropy.
Size effect of nanosized thin-film iron dot on growth of multiwall carbon nanotubes
Authors: Wong M. S. , Cheng K.-W. , Shee C.-H. , Ma Y.-R. , Wu J. C. , Liou Y. , Yao Y.-D.
Published: May 2004

Hot-filament chemical vapor deposition, using a mixture of methane and hydrogen, is used to grow multiwall carbon nanotubes (MWNTs) on 54-nm-thick iron dots with diameters of 970, 770, 340, and 140 nm. The size effect of the nanosized thin-film iron dot is presented on the MWNT growth. More MWNTs grow on larger iron dots. However, the diameters of the MWNTs that grow on iron dots with average diameters of ∼120 nm are independent of the sizes of the iron dots. An approach to growing MWNTs on the nanosized thin-film iron dots is described.
Crystallography ordering studies of the L1 phase transformation of FePt thin film with Ag top layer
Authors: Zhao Z. L. , Inaba K. , Ito Y. , Chen J. S. , Liu B. H. , Ding J. , Wang J. P.
Published: May 2004

Ag has been intensively studied to improve the phase transformation of the L10 FePt. The magnetic properties of the FePt thin films with ultrathin Ag top layers prepared by magnetron sputtering have been studied. The crystallopgraphic ordering of the L10 FePt is significantly promoted with Ag top layers deposited on the top of the FePt films. High resolution transmission electron microscope observations suggest that the phase transformation is liable to occur at the interface of Ag and FePt.
Dynamic magnetic susceptibility of Gd5Si2Ge2 and Gd4YSi1.9Ge2.1
Authors: Vecchini C. , Moze O. , Pecharsky A. O. , Pecharsky V. K. , Gschneidner K. A. , Brück E. , Bewley R. , Kolesnikov A.
Published: May 2004

The effects of diluting Gd with Y on the magnetic properties of the giant magnetocaloric effect material Gd5Si2Ge2 have been investigated by high incident energy inelastic neutron scattering, magnetization, and x-ray powder diffraction measurements. The dynamic response for Gd5Si2Ge2 at 15 and 150 K consists of two magnetic excitations extending up to 40 meV. From the x-ray powder diffraction data, Gd4YSi1.9Ge2.1 is monoclinic at room temperature, space group P1121/a with the 4e site at x=−0.0092(3), y=0.1005(2), z=0.1808(4) almost exclusively occupied by Gd (97%), while the remaining four Gd/Y sites are randomly occupied by Gd and Y. The magnetization measurements show that the ordering temperature of Gd4YSi1.9Ge2.1 is about half that of Gd5Si2Ge2, as the former orders ferromagnetically at 149 K with an effective paramagnetic moment of 7.87μB. The observed magnetic dynamic response for the Gd4YSi1.9Ge2.1 at 7 K is also different from the nondiluted compound, whereby the positions and intensities of the magnetic excitations have decreased markedly with respect to Gd5Si2Ge2.
Artificial domain wall nanotraps in Ni81Fe19 wires
Authors: Faulkner Colm C. , Cooke Michael D. , Allwood Dan A. , Petit Dorothée , Atkinson Del , Cowburn Russell P.
Published: May 2004

We report on the controlled pinning and depinning of head-to-head domain walls with individual artificial nanotraps in rounded L-shaped Ni81Fe19 wires. Domain walls were nucleated and injected into one arm of an L-shaped planar wire structure with a wire width of 200 nm and a thickness of 5 nm. The domain walls were propagated through a rounded corner into an orthogonal output wire by a 27 Hz anticlockwise rotating field. A highly sensitive magneto-optical Kerr magnetometer system was used to detect magnetization reversals around single wedge shaped nanotraps in the output wire of different samples. Domain wall propagation occurred at a mean measured x-field value of 6.8 Oe in the output wire arm when not interacting with a trap. Domain wall nanotraps with dimensions as small as depth Dt=35 nm and width Wt=55 nm were found to effectively pin domain walls. In general, the depinning field of a domain wall from a trap increased with trap size. Hysteresis loops and plots of domain walls depinning fields as a function of trap depth are presented.
Micromagnetoluminescence on ferromagnet–semiconductor hybrid nanostructures
Authors: Schömig H. , Halm S. , Bacher G. , Forchel A. , Kipferl W. , Back C. H. , Puls J. , Henneberger F.
Published: May 2004

We present a magneto-optical approach for probing the optical response of a diluted magnetic semiconductor to the fringe field of nanostructured ferromagnets with sub-μm spatial resolution. Scanning across a CdZnMnSe/ZnSe quantum well covered by a single 700 nm wide dysprosium (Dy) wire a redshift of the magnetoluminescence signal is found beneath the ferromagnetic stripe. This on one hand demonstrates the strength of our experimental technique and on the other hand gives an indication of a local band gap modulation due to the giant Zeeman effect caused by the fringe field of ferromagnetic nanostructures.
Nanocrystalline hard magnetic FePt powders
Authors: Lyubina J. , Gutfleisch O. , Müller K.-H. , Schultz L. , Dempsey N. M.
Published: May 2004

Fe 50+x Pt 50−x  (x=0,5,10.5) powders obtained by mechanical ball milling at liquid nitrogen temperature are investigated. The phase composition, chemical order, and magnetic properties are studied as a function of composition and annealing conditions. The annealed powders contain a mixture of the highly ordered L10 FePt, disordered FePt, as well as Fe3Pt and FePt3 phases. The highest coercivity of 0.7 T was achieved in the Fe50Pt50 powder annealed at 450 °C for 48 h. The annealed FePt powders have a lamellar microstructure with grains of about 40 nm. Coercivity increases with increasing L10 volume fraction and degree of chemical order.
Study of in-plane magnetic anisotropy of ultrathin epitaxial Fe films grown on vicinal Mo(110) surface
Authors: Usov V. , Murphy S. , Shvets I. V.
Published: May 2004

In situ surface magneto-optical Kerr effect was used in conjunction with scanning tunneling microscopy and low-energy electron diffraction to study the in-plane magnetic anisotropy of ultrathin Fe films on a vicinal Mo(110) substrate. A uniaxial anisotropy with the easy axis of magnetization along the [001] direction was found for this system down to nearly 2 monolayers coverage, contradicting the results of recent theoretical calculations. The easy axis of a step-induced anisotropy coincides with the surface step edges.
FePt and Fe nanocomposite by annealing self-assembled FePt nanoparticles
Authors: Lu M. H. , Song T. , Zhou T. J. , Wang J. P. , Piramanayagam S. N. , Ma W. W. , Gong H.
Published: May 2004

We present a simple fabrication of FePt and Fe nanocomposite by annealing self-assembled FePt nanoparticles. 5 nm FePt nanoparticles were prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in the presence of oleic acid and oleylamine as stabilizers. The as-synthesized FePt nanoparticles can self-organize well on a clean SiO/Si substrate and, then, were annealed in a vacuum using a rapid thermal process at different temperatures for 0.5 h. It is found that the annealing temperature plays a key role in determining the final products. The samples annealed at 550 °C and 700 °C consist of a FePt-face-centered-tetragonal (fct) phase with a coercivity of around 1000 and 8800 Oe, respectively, whereas, the samples annealed at 580 °C are composed of two phases: one is the FePt-fct phase and the other is a Fe-body-centered-cubic phase. The hysteresis loop of the sample annealed at 580 °C is also two-phase like with a kink at low field and its coercivity is around 8000 Oe. That indicates that Fe can be segregated from FePt by proper annealing, forming FePt and Fe nanocomposites.
An electron spin resonance study of magnetic excitations in the quantum antiferromagnet Ni(C5H14N2)2N3(PF6)
Authors: Honda Z. , Hagiwara M. , Katsumata K. , Yamada K.
Published: May 2004

We report the results of electron spin resonance (ESR) measurements on single crystals of the spin 1 quasi-one-dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6) in the high-field phase. We observed ESR transitions from the ground state with a q=π component above the critical field Hc. The experimental results are analyzed using the energy level scheme that is widely accepted for the spin 1 one-dimensional Heisenberg antiferromagnet below Hc.
Spin filtering in an electromagnetic structure
Authors: Seo K. C. , Ihm G. , Ahn K.-H. , Lee S. J.
Published: May 2004

We investigate possible spin-dependent resonant tunneling through double-barrier electromagnetic structure. We point out that previous related studies contain serious errors in the calculation and the correct ones show much reduced spin polarization in the tunneling. In this study, we show that the significant amount of spin polarization with nice resonant structures can be achieved by applying a proper electric field subject to the given magnetic barriers. The electric potential U, which is crucial in our model, is chosen to exactly cancel the A2 term originated from the applied magnetic field. In this way, we can remove unwanted obstacles and expedite the tunneling of electrons.
Picosecond optical control of the magnetization in exchange biased NiFe/FeMn bilayers
Authors: Weber M. C. , Nembach H. , Fassbender J.
Published: May 2004

A 9 ps short laser excitation is used to optically control the magnetization of a NiFe/FeMn exchange bias system on the picosecond timescale. Due to the laser excitation, the exchange coupling across the interface between the ferromagnetic and the antiferromagnetic layer is reduced. Within the first 20 ps, a fast reduction of the exchange bias field to about 50% of its initial value is observed. The fast optical unpinning is followed by a slower recovery of the bias field. This relaxation time is on the order of 170 ps.
Magnetic properties of uniaxial synthetic antiferromagnetic films
Authors: Zhao Zhiya , Mani Prakash , Lee W.-T. , Mankey Gary J.
Published: May 2004

A study of the properties of uniaxial synthetic antiferromagnetic films with the structure Si(100)/Ta(5 nm)/Co(a)/NM(b)/Co(c)/Ta(10 nm) prepared by oblique sputtering is reported. Easy axis and hard axis hysteresis loops show a strong uniaxial anisotropy. The structural origin of the anisotropy is revealed by atomic force microscopy. The magnetization switching process was measured by polarized neutron reflectometry. The system exhibits biquadratic coupling, since the experimental remanence differs from that calculated by a model considering only bilinear coupling. The dependence of the critical fields on top ferromagnetic layer thickness is measured. A fit including both bilinear and biquadratic coupling qualitatively agrees with the results.
Transport characteristics of magnetite thin films grown onto GaAs substrates
Authors: Watts S. M. , Nakajima K. , van Dijken S. , Coey J. M. D.
Published: May 2004

Magnetite thin films with a preferred (111) orientation have been deposited by reactive dc magnetron sputtering from a pure Fe target onto (100) GaAs substrates at 400 °C. The films show a clear Verwey transition in both the magnetization and sheet resistance as functions of temperature. For films deposited onto semiconducting n-type GaAs substrates, we have obtained asymmetric current–voltage (I–V) characteristics with a Schottky diodelike behavior in forward bias. Activation energy plots of the I–V data as a function of temperature indicate a barrier height of 0.3–0.4 eV. This does not take into account the contribution from tunneling across the narrow depletion layer in these junctions, so should be considered a lower bound to the actual Schottky barrier height. Our work points to the potential integration of half-metallic magnetite with GaAs-based heterostructures for spin-electronic devices.
Gyrotropic mode frequency of vortex-state permalloy disks
Authors: Ivanov B. A. , Zaspel C. E.
Published: May 2004

Submicron permalloy magnetic dots have a vortex ground state because of competition between the exchange and magnetostatic interactions, and the application of an in-plane magnetic pulse will result in precession of the vortex about the dot axis at a frequency in the sub-GHz range. The precession frequency of this mode is calculated using a perturbation technique based on vortex–magnon scattering including the magnetostatic interaction. These calculations show that the frequencies vary between 0.2 and 0.8 GHz for 60 nm disks or radii between 250 nm and 1000 nm, which agrees with recent experimental data.
Phase stability criteria for cubic and orthorhombic Fe3Pt and Fe3Pd
Authors: Duplessis R. R. , Stern R. A. , MacLaren J. M.
Published: May 2004

Using first-principles methods, we have calculated structural and magnetic properties of face-centered (L12) and orthorhombic (Pmm2, DO19) phases of Fe3Pt and Fe3Pd. For both alloys, the L12 cubic phase was determined to be the ground state. Unlike the related Co3Pt alloy, the Pmm2 phase cannot be artificially stabilized by controlling, that is, slightly increasing or decreasing, the basal lattice constant (by growing the samples on an appropriate substrate).
Interface magnetic properties of MnSe digitally doped in ZnSe-based quantum wells
Authors: Murayama A. , Nakayama E. , Tomita T. , Souma I. , Oka Y.
Published: May 2004

MnSe layers are digitally doped in Zn0.85Cd0.15Se quantum wells by atomic layer epitaxy. Suppression of the giant Zeeman shift of excitons is observed in a low magnetic field region, which can be attributed to antiferromagnetic properties of the MnSe. The critical field at which the Mn spins start to rotate toward the external field direction is determined from a fitted calculation using a modified Brillouin function. The giant magneto-optical properties are interpreted by the spatial overlap of the exciton wavefunction with the Mn spins at interfaces between the MnSe and Zn0.85Cd0.15Se layers.
Detailed modeling of temperature rise in giant magnetoresistive sensor during an electrostatic discharge event
Authors: Yang Y. , Shojaeizadeh S. , Bain J. A. , Zhu J. G. , Asheghi M.
Published: May 2004

With further miniaturization of the giant magnetoresistive (GMR) heads, the electrostatic discharge (ESD) failure has become the primary reliability issue in manufacturing of these sensors. In this article, the thermal response of the GMR read head to excessive current/voltage during an ESD event is investigated numerically, using a three-dimensional (3D) finite element analysis. Unlike the previous studies, the thermal properties of the GMR, Al2O3 gap, and shield layers used in the simulation are the experimentally measured values, which are different from the bulk values. The simulation results show that temperature in the GMR element sharply increases as the GMR dimensions are reduced, indicating the future GMR heads will be more susceptible to the ESD damages. In addition, thermal properties of the GMR elements and the gap materials play key roles in the accurate prediction of the temperature field in a GMR head during ESD events. The simulations are performed for both the current-in-plane (CIP) and perpendicular-to-plane configurations, indicating that latter can sustain much higher ESD voltage (∼160 V) than the CIP-GMR head (∼48 V) for 100 Gbits/in.2 recording density.
Thickness dependence of magneto-transport in Cu-Co granular thin films
Authors: Wang Jian-Qing , Dao NgocNga , Kim Nam H. , Whittenburg Scott L.
Published: May 2004

This work explores the thickness dependence of magneto-transport properties in Cu80Co20 granular thin films with different thickness. These results are compared with silver-based film series studied earlier. It was observed that the thickness dependence of the GMR effect was sensitive to the surface chemistry of the films. The extraordinary Hall effect (EHE) in these films was measured and found to be different from the Ag-based system. In the Cu-based system, the EHE is a weak function of film thickness over the range studied. When the variation of the spontaneous magnetization is taken into account the effective EHE has a universal thickness dependence.
Universal features of charge and spin order in a half-doped layered perovskite
Authors: Zaliznyak I. A. , Tranquada J. M. , Gu G. , Erwin R. W. , Moritomo Y.
Published: May 2004

We have investigated the peculiar structure of charge and spin ordering in the half-doped layered perovskite oxide La1.5Sr0.5CoO4 by elastic neutron scattering. Two samples with different preparation histories were studied. We find that the generic features of the ordered states, such as their short-range, glassy nature and the spin incommensurability, are sample-independent. At the same time, some subtle features of the ordered phases, such as the correlation lengths, differ.
Neutron scattering study of TbPtIn intermetallic compound
Authors: Garlea O. , Morosan E. , Bud’ko S. L. , Zarestky J. L. , Canfield P. C. , Stassis C.
Published: May 2004

Neutron diffraction techniques have been used to study the magnetic properties of a TbPtIn single-crystal as a function of temperature and magnetic field. In the absence of an externally applied magnetic field, the compound orders, below approximately 47 K, in an antiferromagnetic structure with propagation vector k=(12,0,12); the magnetic moments were found to be parallel to the [12̄0] direction. Measurements at 4.2 K, with a magnetic field applied along the [12̄0] direction, revealed metamagnetic transitions at approximately 20 kG and 40 kG.
Structure and magnetic properties of La(Fe0.88Al0.12)13Cx interstitial compounds
Authors: Liu X. B. , Altounian Z. , Beath A. D.
Published: May 2004

Structure and magnetic properties of La(Fe0.88Al0.12)13Cx interstitial compounds with x=0–0.8, were studied by x-ray diffraction and magnetic measurements. The interstitial compounds retain the NaZn13-type structure and the lattice constant increases with carbon content. The Wigner–Seitz cell volume and void calculations show there are seven different voids in the NaZn13 structure with the void at the 24d site (0, 0.25, 0.25) having the largest volume and the largest number of La neighbors. It is highly likely that the carbon atoms enter the 24d site. The small carbon doping collapses the antiferromagnetic state in La(Fe0.88Al0.12)13 and forms a ferromagnetic state. The magnetic transition temperature increases from 198 K to 280 K and the spontaneous magnetization (5 K) decreases from 22.9 μB to 21.3 μB per formula unit with increasing carbon content from x=0 to 0.8. The change in magnetic properties on carbon addition is attributed to cell volume expansion and Fe–Fe distance variations.
Semiconductivity, spin delocalization, and excited states of the single molecule magnets Fe8Br8 and Mn12–acetate (invited)
Authors: Zipse D. , North J. M. , Achey R. M. , Dalal N. S. , Hill S. , Edwards R. S. , Choi E. S. , Brooks J. S.
Published: May 2004

Some newly found properties of the single-molecule magnets Mn12–acetate and Fe8Br8 are summarized: they are semiconductors and their 20 unpaired (S=10) electrons are delocalized not only on the metal ions, but also quite significantly (several percent) on the organic linkers (ligands). Fe8Br8 has an S=9 excited state located at about 24 K (17 cm−1) above the S=10 ground state. The zero-field (D and E) parameters of the S=9 state differ from those of the S=10 state by 7%–8%. The band gap for Mn12–acetate was found to be 0.37 eV, while that for Fe8Br8 was 0.73 eV. Details of the experimental techniques used (EPR, NMR, isotope-labeling, four-point conductivity) are provided, together with the discussions of the results in the context of other experimental techniques, and theoretical calculations.
Influence of barrier overoxidation and annealing on the inelastic spin-dependent tunneling in AlOx-based junctions
Authors: Dimopoulos T. , Henry Y. , Da Costa V. , Tiusan C. , Ounadjela K.
Published: May 2004

The present work reports on the inelastic, spin-dependent tunneling in magnetic junctions with AlOx barrier and Co50Fe50 ferromagnetic (FM) electrodes. The identification of the transport inelastic channels is possible through their distinctive temperature dependencies. For the observed temperature behavior of the magnetotransport properties of the junctions, two spin-dependent, inelastic mechanisms are proposed: assisted tunneling due to interfacial (a) magnons and (b) metallic phonons. Their relative contributions are closely linked to the microstructural properties of the FM metal/oxide interfaces, related to the plasma oxidation of the tunnel barrier and to thermal annealing.
Growth, microstructures, and superconductivity of Bi2−xPbxSr2Ca1−yGdyCu2O8+z single crystals
Authors: Wang X. L. , Takayama-Muromachi E. , Li A. H. , Cheng Z. X. , Keshavarzi S. , Qin M. J. , Dou S. X.
Published: May 2004

Bi 2−x Pb x Sr 2 Ca 1−y Gd y Cu 2 O 8+δ  (x=0.34 and y=0.18, 0.34) crystals were grown by the self-flux method. The crystals have a cleavage thickness of only half unit cell up to two unit cells with Tc only dropping 20 K as y is increased from 0.18 to 0.34 for as-grown crystals. However, Tc increased to almost the same value of about 80 K after annealing in air regardless of the Gd doping levels. The co-doping produced enhanced flux pinning compared to the sole Gd doping. A secondary peak effect presented in crystals with x=0.34 and y=0.34 was explained by phase segregations containing Gd-rich clusters.
Tunneling hot spots and heating in magnetic tunnel junctions
Authors: Sousa R. C. , Prejbeanu I. L. , Stanescu D. , Rodmacq B. , Redon O. , Dieny B. , Wang Jianguo , Freitas P. P.
Published: May 2004

In this work the thermal heating of tunnel junctions is investigated doing one-dimensional numerical simulations by solving the heat equation. The temperature increase is proportional to the power density jV, which is confirmed by transport measurements on patterned μm size junctions. The observed temperature increase was 2.3 K/(mW μm−2) compared to a simulation result of 0.9 K/(mW μm−2). Tunneling AFM measurements on 4, 5.4, and 6.7 Å barrier half-junctions, show hot spots with current densities up to 13 times the average density value. The current concentration could explain the higher heating observed experimentally compared to the simulated value. The hot spot density is 600–900/μm2 occupying roughly 5% of the barrier surface.
First principles calculations of magnetoresistance as a function of external field in layered Co–Re hexagonal-close-packed superlattices
Authors: Stern R. A. , MacLaren J. M. , Charlton T. , Lederman D.
Published: May 2004

The magnetoresistance was calculated for a layered Co/Re hcp(101̄0) superlattice as a function of external magnetic field. Similar to recent experiments which showed a maximum magnetoresistance of 4.5%, the system modeled here had its growth axis along the (101̄0) axis and the magnetic easy axis in the plane of the film. Orientations of the magnetic moments in each Co layer as a function of external field were calculated using a self-consistent mean-field method, and were used as input parameters in the calculation of the conductivity tensor. The conductivity tensor was calculated via the Kubo–Greenwood linear response formalism within the layered-Korringa–Kohn–Rostoker approach to density functional theory. The total magnetoresistance is explained as a sum of anisotropic magnetoresistance and giant magnetoresistance. A calculated spin–flop transition at low fields has obvious consequences on the calculated magnetoresistance.