bluuebunny/crossref_metadata_2025 huggingface dataset:
Groundwater‐induced flooding in macropore‐dominated hydrological system in the context of climate changes
Authors: Pinault J.‐L. , Amraoui N. , Golaz C.
Published: May 2005

The groundwater‐induced flooding that occurred in the Somme Basin during April 2001 damaged numerous dwellings and communication routes, and economic activity of the region was flood‐bound for more than 2 months. It was the first time that such a sudden event was recognized as resulting from groundwater discharge, despite the Somme valley not being prone to flooding. Because of a dual porosity of the chalk in the basin, nonlinear processes, involving a hydraulic continuity between the macropores of the unsaturated zone and the chalk groundwater, govern water migration through the unsaturated zone. Such a process is the result of switching behavior of groundwater recharge from matrix flow to macropore flow due to accumulated wetness over several years. There is much evidence to support that the flood probability model is climate‐dependent for the studied region because nonlinear processes amplify the effects of nonstationarities of climatic inputs. An estimation of the return period of catastrophic flooding depends on the long‐term precipitation fluctuations. This has implications for flood risk assessment requiring the need to distinguish between short‐ and long‐term flooding risks. Other basins that may not appear particularly prone to flooding could also be subjected to similar groundwater‐induced flooding should the long‐term precipitation fluctuations observed in the north of France since the beginning of the 1980s persist. Similar extraordinary situations can occur in Belgium and England, whereby significant flooding results in substantial contribution of groundwater flows.
Coastal watershed management across an international border in the Tijuana River watershed
Authors: Fernandez Linda
Published: May 2005

The paper develops and applies a game theoretic model of upstream and downstream countries to examine cooperative and noncooperative strategies of a common watershed. The application to the Tijuana River watershed shared by the United States and Mexico provides quantification of the strategies for internalizing water quality externalities to upstream and downstream originating from sedimentation. Results show that different transfer payments, such as the Chander/Tulkens cost sharing rule and the Shapley value, imply the size of the existing transfer from downstream to upstream could increase the amount currently allocated.
The role of topography on catchment‐scale water residence time
Authors: McGuire K. J. , McDonnell J. J. , Weiler M. , Kendall C. , McGlynn B. L. , Welker J. M. , Seibert J.
Published: May 2005

The age, or residence time, of water is a fundamental descriptor of catchment hydrology, revealing information about the storage, flow pathways, and source of water in a single integrated measure. While there has been tremendous recent interest in residence time estimation to characterize watersheds, there are relatively few studies that have quantified residence time at the watershed scale, and fewer still that have extended those results beyond single catchments to larger landscape scales. We examined topographic controls on residence time for seven catchments (0.085–62.4 km2) that represent diverse geologic and geomorphic conditions in the western Cascade Mountains of Oregon. Our primary objective was to determine the dominant physical controls on catchment‐scale water residence time and specifically test the hypothesis that residence time is related to the size of the basin. Residence times were estimated by simple convolution models that described the transfer of precipitation isotopic composition to the stream network. We found that base flow mean residence times for exponential distributions ranged from 0.8 to 3.3 years. Mean residence time showed no correlation to basin area (r2 < 0.01) but instead was correlated (r2 = 0.91) to catchment terrain indices representing the flow path distance and flow path gradient to the stream network. These results illustrate that landscape organization (i.e., topography) rather than basin area controls catchment‐scale transport. Results from this study may provide a framework for describing scale‐invariant transport across climatic and geologic conditions, whereby the internal form and structure of the basin defines the first‐order control on base flow residence time.
Mantle potential temperatures at Hawaii, Iceland, and the mid‐ocean ridge system, as inferred from olivine phenocrysts: Evidence for thermally driven mantle plumes
Authors: Putirka Keith D.
Published: May 2005

Temperature differences between lavas erupted at ocean islands and mid‐ocean ridges are crucial to documenting the existence of mantle plumes. Olivines are useful for T estimation because they provide a less homogenized account of the melting process compared to glass and whole rock samples. Olivine‐liquid equilibria, and olivine phenocrysts from Hawaii, Iceland, and several mid‐ocean ridge localities, indicate higher melting temperatures compared to mid‐ocean ridges (MORs) by at least ∼250 ± 52°C and 165 ± 62°C, respectively. When translated to differences in mantle potential temperature, ΔTp, Hawaii and Iceland potential temperatures are hotter than ambient MORs by 213–235 and 162–184°C, respectively, similar to estimates required by geodynamic models for mantle thermal upwellings. Absolute mantle potential temperatures are more uncertain as they depend on estimates of melt fraction and depth of equilibration, but olivine‐liquid equilibria support the following estimates: TpHawaii = 1688°C; TpIceland = 1637°C; TpMORs = 1453–1475°C. All of these estimates include the effects of H2O, Na2O + K2O, and SiO2 on olivine‐melt equilibria and are robust against other variations in source or liquid composition, such as FeO and CO2. These estimates show that at least at Iceland and Hawaii, volcanism is driven by large temperature anomalies whose magnitudes are consistent with the existence of thermally driven mantle plumes.
The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle
Authors: Shakhova Natalia , Semiletov Igor , Panteleev Gleb
Published: May 2005

The seepage of methane (CH4) through the seabed of the world's shelves is considered to be ubiquitous. Although numerous observations of methane seepages from shallow marine sources have been reported, there were only a very few observations made over the Arctic shelves and none for the East‐Siberian Sea (ESS) or Laptev Sea (LS). We present two years of data obtained during the late summer period (September 2003 and September 2004) for both the ESS and LS shelves. According to our data, the surface layer of shelf water was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water suggest that the bottom layer is somehow affected by near‐bottom sources. Considering the possible formation mechanisms of such plumes, we favor thermo‐abrasion and the effects of shallow gas or gas hydrates release.
Martian magnetic paleopoles: A geostatistical approach
Authors: Sprenke Kenneth F.
Published: May 2005

Various attempts have been made to locate magnetic paleopoles on Mars by modeling individual magnetic field anomalies. In this study, a quite different approach, based on geostatistics, is taken. Discreet magnetic sources form magnetic doublet anomalies in the magnetic field that tend to align with the horizontal direction of magnetization. A semivariogram of radial field polarities on Mars indicates that magnetic field anomalies of opposite polarity tend to be separated by 14°. This phenomenon is interpreted to be due to the presence of magnetic doublet anomalies in the field. Accordingly, the autocovariances of the field polarity along longitudinal lines relative to over 1000 trial paleopole locations were examined. Magnetic paleopoles within about 50° of (230°E, 17°N) and (50°E, 17°S) were found to best explain the geostatistical structure of the polarity of the martian magnetic field.
Glutamyl‐tRNA mediates a switch in RNA polymerase use during chloroplast biogenesis
Authors: Hanaoka Mitsumasa , Kanamaru Kengo , Fujiwara Makoto , Takahashi Hideo , Tanaka Kan
Published: May 2005

Chloroplast genes of higher plants are transcribed by two types of RNA polymerase that are encoded by nuclear (NEP (nuclear‐encoded plastid RNA polymerase)) or plastid (PEP (plastid‐encoded plastid RNA polymerase)) genomes. NEP is largely responsible for the transcription of housekeeping genes during early chloroplast development. Subsequent light‐dependent chloroplast maturation is accompanied by repression of NEP activity and activation of PEP. Here, we show that the plastid‐encoded transfer RNA for glutamate, the expression of which is dependent on PEP, directly binds to and inhibits the transcriptional activity of NEP in vitro. The plastid tRNAGlu thus seems to mediate the switch in RNA polymerase usage from NEP to PEP during chloroplast development.
Effect of cobalt substitution on magneto-transport properties of Nd0.7Sr0.3Mn1-xCoxO3 (0.0⩽x⩽1)
Authors: Asthana Saket , Nigam A. K. , Bahadur D.
Published: May 2005

Magnetic and transport studies of the compounds Nd0.7Sr0.3Mn1-xCoxO3 (0.0⩽x⩽1) have been carried out. The compositions crystallize in single-phase ortho-perovskite. The conduction mechanism could be explained using the small polaron correlated hopping model. The thermal irreversibility in zero-field and field-cooled magnetization data increases with Co content, which is due to the different spin states of the Co. Transition of Co3+ from high spin∕intermediate spin to low spin state is observed at low temperatures. The nonsaturating M-H behavior is observed in cobalt containing samples due to suppression of double-exchange interaction which favors long-range ferromagnetic order.
Are strain-induced effects truly strain induced? A comprehensive study of strained LCMO thin films
Authors: Dvorak Joseph , Idzerda Y. U. , Ogale S. B. , Shinde Sanjay , Wu Tao , Venkatesan T. , Godfrey R. , Ramesh R.
Published: May 2005

We report results on strained La2∕3Ca1∕3MnO3 (LCMO) films that are able to distinguish between true strain effects and effects due simply to the reduced film thickness. Biaxially strained LCMO films were grown on SrTiO3, NdGaO3, and LaAlO3. The films on SrTiO3 and LaAlO3 are elastically strained and those on NdGaO3 are only slightly strained. We observe that both the saturation moment (Msat) and the Curie temperature (TC) are suppressed as the films become thinner, regardless of the strain. Thus, the decrease in Msat and TC is due to the two-dimensional nature of the films and not the strain.
Improved selectivity in magnetic random access memory arrays using hysterons
Authors: Kessler B. S. , Arrott A. S.
Published: May 2005

One of the two overlapping circles in the hysteron contains a vortex that provides a handedness that breaks the symmetry of the response to magnetic fields. This is exploited to provide mode selection that keeps unselected bits locked from switching in a magnetic random access memory, MRAM. A permanent magnet bias field is used to assure that all bits return to the locked-state in the absence of signals from the current-carrying word and digital lines.
Element-specific magnetic properties of Co2MnSi thin films
Authors: Stadler S. , Minott D. H. , Harley D. , Craig J. P. , Khan M. , Dubenko I. I. , Ali N. , Story K. , Dvorak J. , Idzerda Y. U. , Arena D. A. , Harris V. G.
Published: May 2005

Co 2 MnSi thin films were grown on Al2O3 (a plane) and GaAs (001) substrates and on thin silicon nitride windows using pulsed laser deposition. Angle-dependent magneto-optic Kerr effect measurements reveal both a uniaxial and a fourfold magnetocrystalline anisotropy for films grown on GaAs (001). X-ray magnetic circular dichroism spectra were measured at the L2,3 edges of the thin films as a function of aluminum cap layer thickness, and transmission mode L2,3 x-ray absorption through a 1000-Å Co2MnSi film grown on a silicon nitride membrane were measured, indicating that deviations from metalliclike spectra are likely due oxidation or contamination. Element-specific moments for Co and Mn were calculated from the X-ray magnetic circular dichroism data of a nonoxidized film.
Magnetostriction and stress measurements in plasma-sprayed MnZn ferrite films
Authors: Yan Q. Y. , Gambino R. J. , Sampath S.
Published: May 2005

The coercivity of the plasma-sprayed MnZn ferrite films decreases significantly after annealing in air at the temperature range of 500–800 °C. Magnetostriction and surface stress changes incurred in these ferrite films after the annealing process has been measured. It is found that the effects of the external stress on the magnetic properties of the plasma-sprayed MnZn ferrite films are minor. The coercivity mechanism arising from the magnetoelastic effects due to the nonzero magnetostriction has been analyzed to be small and is not dominant in controlling the magnetization process in these ferrite films.
Frequency domain modeling of hysteresis with superimposed orthogonalized polynomial functions
Authors: Damnjanovic A. , Parsley G. M. J.
Published: May 2005

A frequency domain modeling approach of hysteresis is introduced in this study. The model is based on the representation of the hysteresis curve as an orthogonal, orthonormal polynomial sum of two sets. Fitting a polynomial of the nth and rth degree to represent the normalized excitation curve and hysteresis losses called a “consuming” functions solves the identification problem. Harmonics of the hysteresis and the excitation current are obtained with the harmonic balance method. This modeling approach also can be applied in the study of phase-shifted flux harmonics, magnetostriction, and their effects on magnetic material.
Current-perpendicular-to-the-plane spin-valve films with iron-added magnetite layers
Authors: Hoshiya Hiroyuki , Hoshino Katsumi
Published: May 2005

A current-perpendicular-to-the-plane (CPP)-spin-valve sensor with iron-added magnetite layers (IMLs) was investigated. We prepared bottom synthetic-pin spin-valve films with CoFe∕IML∕CoFe sandwiched layers as both free layers and pinned layers. The slope of resistance-change-area product (ΔRA) versus IML thickness is around 0.5–0.6Ωμm2∕nm, and this indicates that using IMLs results in large bulk scattering. Magnetite and iron grains were observed in transmission electron microscopy images even in a 2-nm-thick IML in a CPP giant magnetoresistance structure. As a result, ΔRA up to 2–2.5mΩμm2 and MR ratio of 2.0%–2.6% at RA of 0.08–0.1Ωμm2 were obtained by using IML in CPP-spin-valve films.
Unusual magnetic susceptibility and magnetoresistance in [Fe∕Cr(001)]10 multilayers at low temperatures
Authors: Aliev F. G. , Guerrero R. , Pryadun V. V. , Martinez J. L. , Villar R.
Published: May 2005

Transport and magnetic properties near a field-induced orientation phase transition (OPT) from the easy to the hard axis in the magnetization of antiferromagnetically coupled epitaxial [Fe∕Cr(100)]10 multilayers have been studied. It was found that in the vicinity of the OPT both the amplitude of the magnetic susceptibility anomaly and the relaxation rate of the magnetoresistance change dramatically below a few Kelvin. These observations, together with the previously observed strong reduction of zero-field magnetic losses at temperatures below 5–7 K, indicate a qualitative transformation of the magnetic dynamics in Fe∕Cr multilayers at very low temperatures.
Tunneling anisotropic magnetoresistance: Creating a spin-valve-like signal using a single ferromagnetic semiconductor layer
Authors: Rüster C. , Gould C. , Jungwirth T. , Girgis E. , Schott G. M. , Giraud R. , Brunner K. , Schmidt G. , Molenkamp L. W.
Published: May 2005

This article reports on a spintronics device based on the ferromagnetic semiconductor (Ga,Mn)As. Our transport measurements on a Au∕AlOx∕(Ga,Mn)As tunnel junction yield the surprising result that it is possible to get a spin-valve-like signal using only one magnetic layer. The strong spin-orbit coupling in (Ga,Mn)As creates significant anisotropies in the density of states with respect to the magnetization orientation. This, together with a two-step magnetization reversal creates a bistable magnetoresistive device with properties unattainable in current metal based spin-valves.
Magnetic properties of polydisperse and monodisperse NiZn ferrite nanoparticles interpreted in a surface structure model
Authors: Swaminathan R. , McHenry M. E. , Poddar P. , Srikanth H.
Published: May 2005

Static and dynamic magnetic properties of cuboctahedrally truncated polydisperse, rf plasma torch synthesized NiZn ferrite nanoparticles have been studied. The transmission electron microscopy (TEM) determined nanoparticle size distribution was log-normal (mean=11.7nm, σ=10.9nm). Magnetic properties are interpreted using a polyhedral surface structure model, for the observed (111) and (100) nanoparticle surfaces. To determine the magnetic anisotropy fields and isolate anisotropy contributions of the (100) and (111) surfaces, rf transverse susceptibility (TS) measurements were performed. The TS data showed broad peaks observed at characteristic anisotropy fields, consistent with the large particle size distribution. A surfactant-mediated size selection technique was used to obtain monodisperse nanoparticles with a log-normal size distribution (mean=6nm, σ=2.9nm). TS measurements on the monodisperse samples showed absence of anisotropy peaks, with the smaller particles being dominated by (111) surfaces with isotropic canted triangular spin structures.
Superparamagnetic state in single ferromagnetic layers and antiferromagnetic/ferromagnetic bilayers
Authors: Traistaru O. , Fujiwara H. , Misra A. , Jung H. S.
Published: May 2005

Analytical calculations have been made to determine the conditions for a minimum energy barrier between equilibrium states that can enable a superparamagnetic (SPM) behavior in exchange-coupled antiferromagnet (AF)/ferromagnet (FM) systems. It has been found that the promotion and suppression of SPM depend on the relative strength of FM/AF and FM/FM interactions, with the premise that the AF exchange stiffness is greater than the FM one and its anisotropy is large enough. The effect has also been investigated through simulations using the Heisenberg model and Monte Carlo method. The results show that FM/AF coupling facilitates the onset of SPM.
Direct correlation of reversal rate dynamics to domain configurations in micron-sized permalloy elements
Authors: Lau J. W. , Beleggia M. , Schofield M. A. , Neumark G. F. , Zhu Y.
Published: May 2005

The distribution of states upon the removal of applied magnetic field in an array of 7.5×7.5μm2 permalloy square elements, as observed by transmission electron microscopy in Lorentz mode, shows a predominance of two states: the vortex state and the seven-domain state. The distributional dependence of these two states on the rate of change of the reversal field is established. Micromagnetic simulations suggest that vortex nucleation and the subsequent domain-wall propagation are the two primary mechanisms for magnetization reversal. The kinetics of the two pathways is examined in a manner that conforms to the observed distribution of states.
New type of single chain magnet based on spin canting in an antiferromagnetically coupled Co(II) chain
Authors: Sun Zhong-Ming , Prosvirin Andrey V. , Zhao Han-Hua , Mao Jiang-Gao , Dunbar Kim R.
Published: May 2005

The new cobalt diphosphonate compound with a 1D zig–zag chain structure is the first example of its kind that has been recognized to exhibit single-molecule magnets behavior. The slow paramagnetic relaxation of the magnetization is explained on the basis of Ising anisotropy resulting from spin canting of antiferromagnetically coupled Co ions. The energy gap is in accord with the predictions of Glauber’s theory for a one-dimensional Ising system.
Ground state phase diagrams of an anisotropic spin-12 Δ-chain with ferro- and antiferromagnetic interactions
Authors: Kaburagi M. , Tonegawa T. , Kang M.
Published: May 2005

Using spin wave theory as well as numerical methods, we investigate the ground state phase diagram of an anisotropic spin-12 Δ-chain in which the nearest-neighbor exchange interactions between apical and basal spins are ferromagnetic and those between basal spins are antiferromagnetic. The calculated phase diagram interpolating between Heisenberg and Ising chains shows that there exists a region connecting the ferromagnetic and the so-called canted antiferromagnetic regions.
Thermally assisted-writing giant magnetoresistance with perpendicular magnetization
Authors: Lai Chih-Huang , Wu Zhi-Hao , Lin Chao-Cheng , Huang P. H.
Published: May 2005

Giant magnetoresistance (GMR) samples composed of TbCo∕Co∕Cu∕Co∕TbFeCo layers were fabricated with a GMR ratio of 4% and magnetization perpendicular to the film planes. A large coercivity (12 kOe) of the free layer (TbCo∕Co) guarantees the thermal stability at room temperature. A lower Curie temperature of the free layer than that of the pinned layer (Co∕TbFeCo) enables us to switch the magnetization of the free layer by thermally assisted writing while that of the pinned layer keeps unchanged at the temperatures between Curie temperatures of two layers. When the sample was heated up to 180 °C, the required switching field was only 10 Oe.
Magnetic properties of Mn–Al–C alloy powders produced by mechanical grinding
Authors: Saito Tetsuji
Published: May 2005

The saturation magnetization of the milled powders gradually decreased as the milling time increased due to the transformation of the magnetic τ phase into the amorphous phase. On the other hand, the coercivity of the milled powders increased to a peak value of 4.35kOe, then decreased with increasing milling time. When the amorphous powders were annealed at relatively high temperatures, the annealed powders consisted mostly of the magnetic τ phase. The optimally annealed Mn–Al–C–Ni powders exhibited a high remanence of 60emu∕g with a coercivity of 1.95kOe, which is comparable to those of the gas-atomized Mn–Al–C–Ni powders.
Complex permittivity and permeability of barium and strontium ferrite powders in X, KU, and K-band frequency ranges
Authors: Bahadoor Adil , Wang Yong , Afsar Mohammed N.
Published: May 2005

This paper presents accurate results for the complex permittivity, ε=ε′−jε″ and permeability, μ=μ′−jμ″ of barium ferrite powder (BaFe12O19) and strontium ferrite powder (SrFe12O19), in the frequency range from 8.0to26.5GHz. The complex permittivity and permeability are determined via the waveguide transmission/reflection (TR) technique and the waveguide cavity resonator (CR) technique at 25°C and relative humidity <75%. Measurements reveal that the real permittivities of BaFe12O19 and SrFe12O19 are, respectively, 2.497<εBa′<2.678, and 2.597<εSr′<2.712. BaFe12O19 has an average real permeability μBa′=1.078 and SrFe12O19 has an average real permeability μSr′=1.063. The imaginary permittivities are respectively εBa″<0.081 and εSr″<0.077. The imaginary permeabilites are respectively μBa″<0.095 and μSr″<0.106.
Magnetization reversal and nanostructure refinement in magnetically annealed Nd2Fe14B∕α-Fe-type nanocomposites
Authors: Cui B. Z. , Yu C. T. , Han K. , Liu J. P. , Garmestani H. , Pechan M. J. , Schneider-Muntau H. J.
Published: May 2005

Nanostructure refinement, magnetic anisotropy and hard magnetic property enhancement have been observed in melt-spun Nd2.4Pr5.6Dy1Fe84Mo1B6 nanocomposites annealed in an in-plane or out-of-plane field of 1.2T. The magnetic annealing results in an enhancement of an out-of-plane (110) crystal texture of α-Fe and an in-plane uniaxial magnetic anisotropy of the 2:14:1 phase. Magnetic annealing also introduces finer, less angular and more homogeneously distributed soft and hard nanograins. Field dependent torque measurement indicates a complex magnetization reversal mechanism in these nanocomposites. Compared with the sample annealed without a field, there is a noticeable improvement in the hard magnetic properties for the magnetically annealed samples. Especially, the energy product (BH)max was enhanced by 26.6% (from 94to119kJ∕m3). The improvement in the magnetic properties is a result of the enhanced crystallographic texture, nanostructure refinement, and in-plane uniaxial magnetic anisotropy enhancement.
Magnetic network model including loss separation and Preisach principles for the evaluation of core losses in devices
Authors: Dupré Luc , Sergeant Peter , Vandenbossche Lode
Published: May 2005

In this paper, a method is developed to calculate the core loss in a switched reluctance machine. The magnetic circuit of the motor is described as a magnetic network. The electromagnetic behavior of each magnetic network element takes into account the iron loss using the Preisach model and the principle of loss separation. Using the numerical routines, the local core loss in the different motor sections is calculated. The global core loss is compared with the experimentally determined core loss.
Magnetic and half-metallic properties of the full-Heusler alloys Co2TiX(X=Al,Ga;Si,Ge,Sn;Sb)
Authors: Lee S. C. , Lee T. D. , Blaha P. , Schwarz K.
Published: May 2005

The electronic structure and magnetic properties of the full-Heusler alloys Co2TiX (X element from groups III, IV and V) were studied by first principle calculations. Previous calculations found Co2TiAl and Co2TiSn not to be half metallic. In this paper, however, it will be shown that the alloys with X=Al,Si,Ge,Sn are half metallic and ferromagnetic. The effect of atomic disorder in the Ti–Al sublattices reduces the half metallicity of the Co2TiAl Heusler alloy.
Optimization of high Bsat FeCo films for write pole applications
Authors: Mao Ming , Schneider Thomas , Bubber Randhir , Kools Jacques , Liu Xubo , Altounian Zaven , Lee Chih-Ling , Devasahayam Adrian , Rook Katrina
Published: May 2005

FeCo films and their lamination with ultrathin NiFe layers down to 5Å were deposited using dc magnetron sputtering techniques. Soft magnetic FeCo films were obtained at an optimal target power of 500W and an optimal deposition pressure of 2mTorr with high saturation flux density, Bsat>2.4T, and low easy-axis coercivity, Hce⩽15Oe, and hard-axis coercivity, Hch⩽3Oe, at a film thickness of 2000Å. While the magnetostriction remains at ∼4×10−6 the stress was further optimized by applying substrate bias at a controlled level ⩽50V without sacrificing film magnetic softness.
Magnetic properties of L21-structured Co2(Cr,Fe)Al films grown on GaAs(001) substrates
Authors: Hirohata A. , Kurebayashi H. , Okamura S. , Masaki T. , Nozaki T. , Kikuchi M. , Tezuka N. , Inomata K. , Claydon J. S. , Xu Y. B.
Published: May 2005

Both polycrystalline Co2CrAl and epitaxial Co2FeAl full Heusler alloy thin films with the perfectly ordered L21 structure have been grown onto GaAs(001) substrates at 673 K. The Co2FeAl films, in particular, consist of an almost single phase with the crystalline relationship ofCo2FeAl(001)⟨110⟩‖GaAs(001)⟨110⟩. The element specific magnetic moment per Co atom is found to agree well with the theoretical calculation, while that per Fe atom is decreased. By substituting the Fe with Cr atoms, Co2(Cr,Fe)Al films can preserve these ideal properties and can show half metallicity at room temperature.
Magnetic small world nanomaterials: Physical small-world networks
Authors: Novotny M. A. , Zhang X. , Yancey J. , Dubreus T. , Cook M. L. , Gill S. G. , Norwood I. T. , Novotny A. M. , Korniss G.
Published: May 2005

The question addressed is whether magnetic materials based on physical small-world networks are possible. Physical constraints, such as uniform bond length and embedding in three dimensions, are the features added to make small-world networks physical. Results are presented to further determine if physical small-world networks can exist and the effect of the small-world connections on the critical phenomena of Ising models on such networks. Spectra of the Laplacian on randomly collapsed bead-chain networks are studied. The scaling function for the order parameter of an Ising model with physical small-world connections is presented.
Temperature, wavelength, and polarization dependent time resolved optical spectroscopy of half-metallic CrO2
Authors: Huang H. , Seu K. , Reilly A. , Kadmon Y. , Egelhoff W. F.
Published: May 2005

Cr O 2 is an important transition metal oxide due to its half-metallic behavior. We have performed ultrafast laser pump-probe differential transmission experiments on epitaxial CrO2(110). Polarizations parallel and perpendicular to the c axis were used, at wavelengths corresponding to important magnetic excitations: 1300 (1eV), 800 (1.5eV), and 650nm(2eV). Anisotropy is observed in the polarization-dependent measurements and is attributed to the electronic orbital anisotropy. A critical change of transient transmission is also observed at the Curie temperature of 386K. This behavior reveals the close relationship between the optical absorption and the spin dynamics of this material.
Analytical description of magnetization relaxation to equilibrium
Authors: Bertotti Giorgio , Magni Alessandro , Bonin Roberto , Mayergoyz Isaak D. , Serpico Claudio
Published: May 2005

Approximate analytical expressions are obtained for the magnetization relaxation to equilibrium in a thin film element with in-plane anisotropy subject to a constant external field applied along the easy axis. First, exact analytical solutions are obtained for the constant-energy motions taking place in the limit case where the damping constant is zero. Then a separate equation is derived and solved for the slow relaxation to equilibrium of the system energy. Final expressions for the magnetization relaxation are obtained by using the ensuing time-dependent energy in the solutions for the undamped dynamics.
Magnetism and vacancy ordering in PrBaCo2O5+δ (δ⩾0.50)
Authors: Frontera C. , García-Muñoz J. L. , Carrillo A. E. , Caneiro A. , Ritter C. , Martín y Marero D.
Published: May 2005

This work presents an investigation of the central role of oxygen on the physical properties of highly ordered layered cobaltites. It includes the study of the structural and magnetic properties of PrBaCo2O5+δ compounds with high oxygen content (0.5⩽δ⩽0.90), with special emphasis on PrBaCo2O5.75. For δ=0.75 the ordering of oxygen vacancies gives rise to a tetragonal (P4∕mmm) structure with a≈c≈2ap. On cooling, a ferromagnetic spin alignment precedes the apparition of antiferromagnetic order (canted G-type). The compounds are ferromagnetic for δ⩾0.80. Measurements on PrBaCo2O5.75 support that, above the magnetic ordering temperature, Co3+ ions in octahedral environment are in HS state.
On the reduced vector Preisach model of hysteresis
Authors: Cardelli Ermanno , Della Torre Edward , Pinzaglia Enrico
Published: May 2005

We discuss the use of a reduced vector Preisach model (RVPM) as a numerical tool for the analysis of vector rotating and alternating magnetic fields. In particular, we discuss the possibility of computing the vector fields using a fast procedure when the Preisach functions is factorable and the material is a single-quadrant medium along the principal axes. In addition, we discuss the behavior of the RVPM model for two different analytical Preisach distributions, whether they are factorable or not, and show that the model needs a correction factor, even for an isotropic media.
Spin injection in thermally assisted magnetic random access memory
Authors: Deak James G.
Published: May 2005

An integrated thermal, micromagnetic, spin-momentum-transfer (SMT) model was developed to study the effect of SMT on the programming current required for thermally assisted magnetic random access memory (MRAM). The thermal portion of the model is used to compute Joule heating by the spin-polarized current, and it is based on a Crank–Nicolson inhomogeneous heat equation solver. The magnetic portion of the model is based on a micromagnetic Langevin dynamic Landau–Lifshitz–Gilbert solver including SMT torque. Simulations of thermally assisted magnetization reversal of 0.09-μm MRAM elements, heated by passing current through the barrier separating the pinned and free layers, were performed. The free layer of the MRAM elements was switched using a magnetic field at fixed heating-SMT current bias. Results suggest that a spin-polarized heating current can be used to lower the programming current required to write thermally assisted MRAM if the direction of the heating current is properly synchronized with the reversal field.
Effects of buffer layer on the electronic properties of half-metallic Fe3O4
Authors: Jain S. , Adeyeye A. O. , Boothroyd C. B.
Published: May 2005

We have investigated in a systematic way the effect of buffer layer materials on the metal-insulator transition and also on the I–V characteristics of half-metallic Fe3O4 films. Using an electron-beam deposition technique, we have grown 150nm of Fe3O4 films directly on Si(001) substrate, on 20-nm Fe2O3 and 20-nm SiO2 buffer layers. We observed that for a fixed Fe3O4 film thickness, the metal-insulator transition is strongly dependent on the buffer layer materials. From the I–V characteristics, we observed an insulator-like gap structure in the density of states below the transition temperature which disappears gradually with increasing temperature.
Deformation induced magnetite nanostripes on GaAs
Authors: Lu Y. X. , Ahmad E. , Xu Y. B.
Published: May 2005

We demonstrate the synthesis of magnetite nanostripes on GaAs(100) through control of substrate processing and postgrowth annealing. The GaAs substrates were prepared by chemical and thermal treatments with a chevron-featured reflection high-energy electron diffraction (RHEED) pattern observed along the GaAs(100)[011] direction. This chevronlike pattern becomes less prominent after Fe growth but appears again after the oxidation of the Fe into magnetite. This is due to the formation of nanostripes on the GaAs(100). However, the magneto-optical Kerr effect (MOKE) measurements show the easy axis is along the [01¯1] direction. This may suggest that magnetoelastic coupling plays a more important role than that of shape anisotropy.
Relation between physical and phenomenological aspects in the framework of an energetic hysteresis model
Authors: Haumer P.
Published: May 2005

In this work, an interpretation of the underlying physical and phenomenological aspects is presented in a way that the magnetization process is considered as a process of order. For this purpose the energetic model of ferromagnetic hysteresis is modified so that the local magnetic energy terms, such as anisotropy or applied field energy, are condensed to the corresponding statistical domain classes via expectation values. Furthermore, the anhysteretic magnetization curve is interpreted as a consequence of internal entropy changes, relative to an a priori defined domain configuration at the demagnetized state. Finally, irreversible energy terms take dissipative losses into account.
Magnetic properties of a metal-organic chain system [Co(bpdc)(H2O)2]∙H2O (bpdc=biphenyldicarboxylate)
Authors: Yuen Tan , Lin C. L. , Zan J. A. , Pan Long , Li Jing
Published: May 2005

The magnetic properties of a recently discovered metal-organic magnetic chain compound, [Co(bpdc)(H2O)2]∙H2O, were investigated using measurements of magnetic susceptibility M(T)∕H, isothermal magnetization M(H), and heat capacity C(T). The room temperature crystal structure of [Co(bpdc)(H2O)2]∙H2O is monoclinic, space group C2∕c, with lattice parameters a=6.950Å, b=31.585Å, c=6.226Å, and β=95.84°. The M(T)∕H data above 40K were fit to Curie–Weiss law with an effective moment of 5.37μB and a Curie–Weiss temperature of +26K. A spontaneous antiferromagnetic ordering with a transition temperature of 5.5K was observed in the low field M(T)∕H data. In addition, a metamagnetic transition at 500G was found in M(H), measured at 2K. The sizable anomaly observed in C(T) confirms the magnetic phase transition and the transition temperature. The total magnetic entropy removal at 5.5K is 800mJ∕molK. The nature of the magnetic properties is discussed in terms of the ferromagnetic intrachain exchange interaction between the Co(II) ions through the bridging hydrogen atoms along the magnetic chain and the antiferromagnetic Co–Co interchain coupling.
Magnetism in La substituted Sr hexaferrite
Authors: Küpferling M. , Novák P. , Knížek K. , Pieper M. W. , Grössinger R. , Wiesinger G. , Reissner M.
Published: May 2005

The electronic structure of LaxSr1−xFe12O19 (x=0, 0.25, 0.5, 0.75, 1) hexaferrite is calculated using the density functional theory and generalized gradient approximation (GGA). The GGA+U method is used to improve the description of strongly correlated Fe 3d electrons. Fe-sublattice preferences for the magnetic moments introduced by La substitution were calculated. The results are compared with measurements of the magnetization performed in a vibrating sample magnetometer at 4.2 K, from which the magnetic moment per unit cell of La hexaferrite was derived. The calculations were started in order to find an explanation for the extraordinary behavior of the magnetocrystalline anisotropy of La containing M-type hexaferrites, which was confirmed by singular point detection measurements.
Applicability of the coherent potential approximation for transmission through disordered interfaces
Authors: Velev Julian , Butler William H.
Published: May 2005

We present a study of ballistic conductance through substitutionally disordered Fe–Cr(100) interfaces. The effects of interface disorder on the conductance are investigated using (a) a supercell approach (SA) where disorder is approximated by randomly generated configurations within large two-dimensional supercells and (b) the layer adapted coherent potential approximation (CPA). The SA gives simultaneously the specular and diffuse part of the transmission. The CPA, on the other hand, accounts only for specular transmission. We observe excellent agreement between the CPA result and the specular part of the transmission obtained via the SA. However, the CPA, in the absence of vertex corrections does not account for the diffuse transmission and therefore cannot be used to describe phenomena such as current perpendicular to the plane giant magnetoresistance (CPP GMR).
Study of the size dependence of exchange bias using in situ magnetoresistance measurements
Authors: Morecroft D. , Prieto J. L. , Blamire M. G.
Published: May 2005

Due to the general trend towards miniaturization of magnetic devices, it is important to understand the size dependence of exchange bias. An exchange bias spin valve structure of the form Ta∕NiFe∕Cu∕NiFe∕IrMn∕Ta was used with the IrMn exchange bias layer at the top, which enabled in situ magnetoresistance measurements to be carried out as the antiferromagnetic (AFM) layer was gradually milled away in an argon ion miller. The MR decreased when the thickness was reduced below 3 nm. Optical and focused ion beam (FIB) lithography were used to micro and nano pattern wire arrays in the IrMn layer.
Hybrid Fe3O4∕GaAs(100) structure for spintronics
Authors: Lu Y. X. , Claydon J. S. , Ahmad E. , Xu Y. B. , Ali M. , Hickey B. J. , Thompson S. M. , Matthew J. A. D. , Wilson K.
Published: May 2005

Fe 3 O 4 ∕ Ga As hybrid structures have been studied using reflection high-energy electron diffraction (RHEED), x-ray photoelectron spectroscopy (XPS), x-ray magnetic circular dichroism (XMCD), and low-temperature vibrating-sample magnetometry (VSM). The samples were prepared by oxidizing epitaxial Fe thin films in a partial pressure of 5×10−5mbar of oxygen at 500K for 180s. Clear RHEED patterns were observed, suggesting the epitaxial growth of Fe oxides with a cubic structure. The XPS spectra show that the oxides were Fe3O4 rather than γ-Fe2O3, as there were no shake-up satellites between the two Fe 2p peaks. This was further confirmed by the XMCD measurements, which show ferromagnetic coupling between the Fe cations, with no evidence of intermixing at the interface. The VSM measurements show that the films have a magnetic uniaxial anisotropy and a “quick” saturation property, with the easy axes along the [01¯1] direction. This detailed study offers further insight into the structure, interface, and magnetic properties of this hybrid Fe3O4∕GaAs(100) structure as a promising system for spintronic application.
Micromagnetic study of domain-wall pinning characteristics with grooves in thin films
Authors: Asada H. , Ii H. , Yamasaki J. , Takezawa M. , Koyanagi T.
Published: May 2005

The pinning characteristics of a 180° domain wall with grooves are investigated using the micromagnetic simulation. The depinning fields required to pull the wall out of the grooved region were strongly related to the pinning characteristics at each step edge. The depinning field difference between the wall movement directions was improved by the increase of the lower depinning field compared to that with the steplike thickness change. It was also found that the depinning fields for various groove widths were almost constant and the wall displacement was further suppressed by the narrower groove having the vertical edge.
Magnetic properties of (Fe, Co)–B–Si–Nb bulk glassy alloys with high glass-forming ability
Authors: Amiya Kenji , Urata Akiri , Nishiyama Nobuyuki , Inoue Akihisa
Published: May 2005

The glass-forming ability and magnetic properties of (Fe, Co)–B–Si–Nb glassy alloys have been investigated. The maximum diameter for the formation of a glassy alloy rod was 2.0mm for Fe72B20Si4Nb4 and 4.0mm for (Fe0.5Co0.5)72B20Si4Nb4. A number of local-ordered regions are recognized in Fe72B20Si4Nb4 bulk glassy alloy by high-resolution transmission electron microscopy. However, no local-ordered regions are observed in (Fe0.5Co0.5)72B20Si4Nb4 bulk glassy alloy. Saturation magnetization, coercive force, and maximum permeability were 1.14T, 1.5A∕m, and 32 000, respectively, for the (Fe0.6Co0.4)72B20Si4Nb4 bulk glassy alloy.
Spin-injection efficiency and magnetoresistance in a ferromagnet-semiconductor-ferromagnet trilayer
Authors: Agrawal S. , Jalil M. B. A. , Teo K. L. , Liew Y. F.
Published: May 2005

We present a drift-diffusion transport model to evaluate the spin-injection efficiency η and magnetoresistance (MR) ratio in a ferromagnetic (FM) metal-semiconductor (SC)-FM metal trilayer structure. This model takes into account the differential interfacial resistances (IR) for spin-up and spin-down electrons and spin relaxation within the SC layer. The electrochemical potential μ for both spin directions is analytically solved and expressions for η, spin polarization of current P, and the MR ratio are derived. The presence of IR at the FM-SC boundary is crucial for generating a large spin splitting of μ, and consequently a high injection efficiency η. The IR needs to fulfill the requirements of (i) of a large magnitude comparable to the resistance of the SC layer and (ii) high asymmetry with respect to the two spin directions. To increase η from 1% to 30%, we require a large IR of 10−5Ωcm2 and a spin asymmetry of 10:1. There are more stringent requirements for achieving a high MR ratio. An IR of 10−5Ωcm2 and FM contact polarization Pc of 80% will only yield an MR ratio of 10%. We require a much larger IR ⩾10−4Ωcm2 or virtually half-metallic contacts, i.e., Pc of ∼100% to achieve high MR ratio exceeding 50%.
Nucleation of ordered solid phases of proteins via a disordered high-density state: Phenomenological approach
Authors: Pan Weichun , Kolomeisky Anatoly B. , Vekilov Peter G.
Published: May 2005

Nucleation of ordered solid phases of proteins triggers numerous phenomena in laboratory, industry, and in healthy and sick organisms. Recent simulations and experiments with protein crystals suggest that the formation of an ordered crystalline nucleus is preceded by a disordered high-density cluster, akin to a droplet of high-density liquid that has been observed with some proteins; this mechanism allowed a qualitative explanation of recorded complex nucleation kinetics curves. Here, we present a simple phenomenological theory that takes into account intermediate high-density metastable states in the nucleation process. Nucleation rate data at varying temperature and protein concentration are reproduced with high fidelity using literature values of the thermodynamic and kinetic parameters of the system. Our calculations show that the growth rate of the near-critical and supercritical ordered clusters within the dense intermediate is a major factor for the overall nucleation rate. This highlights the role of viscosity within the dense intermediate for the formation of the ordered nucleus. The model provides an understanding of the action of additives that delay or accelerate nucleation and presents a framework within which the nucleation of other ordered protein solid phases, e.g., the sickle cell hemoglobin polymers, can be analyzed.
Hot plasma effects in gas discharge plasma
Authors: Godyak Valery
Published: May 2005

The subject of this paper is an abbreviated review of a recent study of rf discharges operating at low pressures where hot electron and nonlinear effects are essential. In this operational regime anomalous skin effect and collisionless electron heating may occur. From the direct measurement of electromagnetic fields and rf current density it was possible to infer the rf power absorption and to distinguish collisional and stochastic regimes of electromagnetic field interaction with bounded plasma. Some new features found in experiments with rf plasmas, associated with electron thermal motion and nonlinear effects induced by the rf Lorentz force, are discussed, together with corresponding theoretical results.
Dense orientationally ordered states of a single semiflexible macromolecule: An expanded ensemble Monte Carlo simulation
Authors: Martemyanova J. A. , Stukan M. R. , Ivanov V. A. , Müller M. , Paul W. , Binder K.
Published: May 2005

Using a coarse-grained model we perform a Monte Carlo simulation of the state behavior of an individual semiflexible macromolecule. Chains consisting of N=256 and 512 monomer units have been investigated. A recently proposed enhanced sampling Monte Carlo technique for the bond fluctuation model in an expanded ensemble in four-dimensional coordinate space was applied. The algorithm allows one to accelerate the sampling of statistically independent three-dimensional conformations in a dense globular state. We found that the temperature of the intraglobular liquid–solid transition decreases with increasing chain stiffness. We have investigated the possible intraglobular orientationally ordered (i.e., liquid-crystalline) structures and obtained a diagram of states for chains consisting of N=256 monomer units. This diagram contains regions of stability of coil, two spherical globules (liquid and solid), and rod-like globule conformations. Transitions between the globular states are rounded first-order ones since the states of liquid, solid, and cylinder-like globules do have different internal symmetry.