bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation of the North American plate interior from a decade of continuous GPS measurements
Authors: Calais E. , Han J. Y. , DeMets C. , Nocquet J. M.
Published: June 2006

A combination of two independent geodetic solutions using data from close to 300 continuous GPS stations covering the central and eastern United States shows that surface deformation in the North American plate interior is best fit by a model that includes rigid rotation of North America with respect to ITRF2000 and a component of strain qualitatively consistent with that expected from glacial isostatic adjustment (GIA). After correcting for the North American plate motion, residual horizontal velocities show a north‐to‐south deformation gradient of ∼1 mm yr−1, mostly localized between 1000 and 2200 km from the GIA center, corresponding to strain rates of about 10−9 yr−1. At distances farther than 2100 km from the GIA center, horizontal residual velocities are random with no evidence for regions of elevated strain rates. In particular, we find no detectable residual motion at the 95% confidence level in the New Madrid Seismic Zone, where the average weighted misfit of 0.7 mm yr−1 is the same as the weighted misfit of our rigid plate model. Vertical velocities show (1) a maximum uplift rate of 10 mm yr−1 at the assumed GIA center, (2) a hinge line located 1500 km from that center, and (3) a subsidence rate up to 1.4 mm yr−1 in the forebulge, with a maximum located about 2000 km from the GIA center. Our results have the potential to better constrain glacial isostatic adjustment models and contribute to a better definition of stable North America for tectonic and geodetic applications.
Formation and circulation of the cold intermediate layer in the Gulf of Saint Lawrence
Authors: Smith G. C. , Saucier F. J. , Straub D.
Published: June 2006

The local heat content and formation rate of the cold intermediate layer (CIL) in the Gulf of Saint Lawrence are examined using a combination of new in situ wintertime observations and a three‐dimensional numerical model. The field observations consist of five moorings located throughout the gulf over the period of November 2002 to June 2003. The observations demonstrate a substantially deeper surface mixed layer in the central and northeast gulf than in regions downstream of the buoyant surface outflow from the Saint Lawrence Estuary. The mixed‐layer depth in the estuary remains shallow (<60 m) throughout winter, with the arrival of a layer of near‐freezing waters between 40 and 100 m depth in April. An eddy‐permitting ice‐ocean model with realistic forcing is used to hindcast the period of observation. The model simulates well the seasonal evolution of mixed‐layer depth and CIL heat content. Although the greatest heat losses occur in the northeast, the most significant change in CIL heat content over winter occurs in the Anticosti Trough. The observed renewal of CIL in the estuary in spring is captured by the model. The simulation highlights the role of the northwest gulf, and in particular, the separation of the Gaspé Current, in controlling the exchange of CIL between the estuary and the gulf. In order to isolate the effects of inflow through the Strait of Belle Isle on the CIL heat content, we examine a sensitivity experiment in which the strait is closed. This simulation shows that the inflow has a less important effect on the CIL than was suggested by previous studies.
Vertical migration of the toxic dinoflagellate Karenia brevis and the impact on ocean optical properties
Authors: Schofield Oscar , Kerfoot John , Mahoney Kevin , Moline Mark , Oliver Matthew , Lohrenz Steven , Kirkpatrick Gary
Published: June 2006

Vertical migration behavior is found in many harmful algal blooms; however, the corresponding impact on ocean optical properties has not been quantified. A near‐monospecific population of the dinoflagellate Karenia brevis was encountered off the west coast of Florida. The community was tracked for 24 hours by following a Lagrangian drifter deployed at the beginning of the experiment. A suite of inherent optical and cellular measurements was made. Over the 24 hour period, the K. brevis population increased during the day with concentrations peaking in the late afternoon (1600 local daylight time) in the upper 2 m of the water column. The increase in K. brevis in surface waters resulted in enhanced reflectance at the sea surface with distinct spectral changes. There was a 22% decrease in the relative amount of the green reflectance due to increased pigment absorption. There was enhanced red (35%) and infrared (75%) light reflectance due to the increased particle backscatter and chlorophyll a fluorescence; however, the relative impact of the fluorescence was relatively small despite high cell numbers due to the significant fluorescence quenching present in K. brevis. The relative change in the blue light reflectance was not as large as the change in green light reflectance, which is surprising given the pigment absorption in the blue wavelengths of light. The increased blue light pigment absorption was offset by a significant decrease in nonalgal particle absorption. The inverse relationship between K. brevis and nonalgal particles was robust. This relationship may reflect low grazing on K. brevis populations due to the neurotoxins associated with this dinoflagellate. The low‐grazing pressure may provide the mechanism by which this slow‐growing dinoflagellate can achieve high cell numbers in the ocean.
Analysis of a spectrally unique deposit in the dissected Noachian terrain of Mars
Authors: Noe Dobrea E. Z. , Bell J. F. , McConnochie T. H. , Malin M.
Published: June 2006

We have analyzed a spectrally anomalous dark intracrater deposit and an adjacent lighter‐toned fan‐shaped deposit in the dissected Noachian terrain of Mars using a combination of high spatial and spectral resolution remote sensing data sets. The spatial proximity of these two deposits and their dust‐free spectral character make these prime targets for (1) determining whether the dark‐toned deposit is derived from the fan‐shaped deposit and (2) constraining the nature and mineralogy of the fan‐shaped deposit. Stereo observations and derived digital elevation models of the of the fan‐shaped deposit show a set of three flows lobes. Calculations of the yield strength, based on morphometry of the lobes, indicate yield strengths consistent with those of other volcanic flows on Mars, although an aqueous origin cannot be discounted. The dark deposit consists of a mantle that forms dunes at its thickest portions and extends as a thinner veneer. We find no obvious morphologic association between the dark deposit and adjacent fan. Multispectral imaging from the THEMIS VIS and IR instruments show that the two deposits have different spectral characteristics, probably caused by differences in their mineralogy rather than their physical properties. Finally, modeling of MGS/TES spectra of the combined deposits indicates a feldspar‐rich composition that is possibly complemented by smaller quantities of alteration products such as carbonates, and possibly sulfates and clays. These results indicate that (1) there is no association between these deposits and (2) the combined deposits have a primarily igneous mineralogy, although some aqueous alteration may have occurred.
Volcanic deposits in shield fields and highland regions on Venus: Surface properties from radar polarimetry
Authors: Carter Lynn M. , Campbell Donald B. , Campbell Bruce A.
Published: June 2006

We compare Arecibo dual‐polarization radar image data for Venus to Magellan images and emissivity data to investigate the physical properties of volcanic deposits. Radar waves can easily penetrate smooth mantling layers such as ash, aeolian and crater‐derived deposits. If a circularly polarized radar wave refracts into a surface that is smooth at wavelength scales, the vertical component of the wave will be preferentially transmitted, resulting in a net linear‐polarized echo component. Arecibo polarimetry data were used to create maps of the degree of linear polarization in the radar echo. We find that some volcanic fields in plains regions on Venus are associated with enhanced linear polarization. These fields sometimes have nearby windstreaks which suggest fine‐grained surface material, and we infer that the radar wave is penetrating into mantling deposits that are a few centimeters to ∼1 m thick. Enhanced linear polarization values are also correlated with specific lava flows. These lava flows have emissivity values of 0.80 to 0.84, similar to many other flows on Venus. The enhanced linear polarization may be produced by penetration of the radar wave into very smooth lava flows with internal air gaps. High‐reflectivity, low‐emissivity areas near the summits of Theia and Tepev Montes also have a linearly polarized echo component consistent with surface penetration by the radar wave. The cause of the high linear polarization in summit regions remains uncertain, but perhaps the radar wave is able to penetrate into high dielectric material in limited cases of very smooth surface texture.
Radiation transport model for ablation hollows on snowfields
Authors: Tiedje T. , Mitchell Kevin A. , Lau Bayo , Ballestad A. , Nodwell E.
Published: June 2006

The ablation hollows or “suncups” that form on the surface of snowfields in summer are a wonderful example of pattern formation in nature. Suncups reduce the albedo of the snow and set a characteristic length for interaction of wind with the snowpack. They also contain information about the properties of the snow and its ablation rate, which could be extracted if we had a more quantitative understanding of how suncups form. A mathematical model is proposed that explains the shape, size, and dynamical behavior of suncups in terms of the interaction of solar radiation with the snowpack. Using a perturbation method, we derive a nonlinear partial differential equation for the time‐dependent shape of the snow surface from an approximate physical model for the interaction of solar radiation with snow. The resulting equation, which is similar to the Kuramoto‐Sivashinsky equation in fluid mechanics, has solutions with characteristic length and amplitude. We find expressions for the characteristic size of suncups in terms of the spectrally averaged diffusion length of solar radiation in snow. The model correctly describes the shape of suncups, with their spatially ordered patterns of parabolic valleys and V‐shaped ridges. It is also in remarkably good agreement with the observed length scales and growth rates. Depending on the relative values of the coefficients of the nonlinear terms in the differential equation, the suncup patterns can be either stationary in time or chaotic.
Global distribution and seasonality of active fires as observed with the Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) sensors
Authors: Giglio Louis , Csiszar Ivan , Justice Christopher O.
Published: June 2006

We describe a new global multiyear satellite fire product designed to meet the needs of the global modeling community. We use the new data set to analyze the global distribution of biomass burning using five different temporal metrics derived from 5 years of high‐quality satellite data acquired with the Moderate Resolution Imaging Spectroradiometer (MODIS), on board NASA's Terra satellite. The global distributions of fire pixel density, peak month, season length, and annual periodicity are described. As part of our analysis we show, for the first time, the global distribution of the fire radiative power (FRP), a relatively new remotely sensed quantity. We find that low FRP tends to be associated with areas of cropland burning. In the tropics and much of the subtropics, low FRP is also associated with more heavily forested areas, while higher FRP tends to occur in areas of grassland burning. In boreal forests this trend is reversed, with higher FRP occurring in areas of greater tree cover. We next combine 3 years of Terra and Aqua MODIS observations to show that a strong diurnal fire cycle is prevalent at tropical and subtropical latitudes. We also consider the consistency of the fire time series recorded by the two MODIS instruments, and find the month of peak burning and fire season length observed by each to be in good agreement in most areas. However, significant discrepancies with respect to seasonality do occur in some relatively small areas, and are most pronounced in tropical rain forest.
A general route diversity model for convergent terrestrial microwave links
Authors: Paulson Kevin S. , Usman Isa S. , Watson Robert J.
Published: June 2006

This research examines route diversity as a fade mitigation technique in the presence of rain for convergent, terrestrial, microwave links. A general model is derived which predicts the joint distribution of rain attenuation on arbitrary pairs of convergent microwave links, directly from the link parameters. It is assumed that pairs of links have joint rain attenuation distributions that are bilognormally distributed. Four of the five distribution parameters can be estimated from International Telecommunication Union recommendation models. A maximum likelihood estimation method was used in a previous paper to estimate the fifth parameter, that is, the covariance or correlation. In this paper an empirical model is reported, linking the correlation of log rain fade with the geometry and radio parameters of the pair of links. From these distributions, the advantage due to route diversity may be calculated for arbitrary fade margins. Furthermore, the predicted diversity statistics vary smoothly and yield plausible extrapolations into low‐probability scenarios. Diversity improvement is calculated for a set of example link scenarios.
Latitudinal dependence of noctilucent cloud growth
Authors: Karlsson B. , Rapp M.
Published: June 2006

The latitudinal variation of NLC particle sizes is studied using scattered solar radiation spectra from the OSIRIS instrument onboard the Odin satellite obtained during the austral summer period 1 January–17 February 2005. We show that the particles grow moderately larger when approaching the pole, with effective optical radii of 65 nm/76 nm at latitudes of 70°/90° S. Microphysical modeling suggests that particles grow larger as a consequence of a combined effect of the temperature decrease toward the pole, the available water vapor, and meridional transport times. Interestingly, at latitudes closest to the pole, NLC particle sizes show a bi‐modal structure. This structure is suggested to arise from repeated growth cycles due to extended residence times in supersaturated air.
Dust devils on Mars observed by the High Resolution Stereo Camera
Authors: Stanzel Christina , Pätzold Martin , Greeley Ronald , Hauber Ernst , Neukum Gerhard
Published: June 2006

Fourteen active dust devils were observed by the High Resolution Stereo Camera (HRSC) on Mars Express, which enable the first analysis of the forward speed of dust devils on Mars determined from orbit. Results show speeds on the order of 20 m/s, which compares favorably with values of the wind profiles estimated from the Martian Climate Database for higher altitudes. Smaller dust devils of 1 km height and very small diameters were found moving only at 1.5 to 6.0 m/s in agreement with surface wind speeds.
Rapid determination of earthquake magnitude using GPS for tsunami warning systems
Authors: Blewitt Geoffrey , Kreemer Corné , Hammond William C. , Plag Hans‐Peter , Stein Seth , Okal Emile
Published: June 2006

The 26 December 2004 Sumatra earthquake (Mw 9.2–9.3) generated the most deadly tsunami in history. Yet within the first hour, the true danger of a major oceanwide tsunami was not indicated by seismic magnitude estimates, which were far too low (Mw 8.0–8.5). This problem relates to the inherent saturation of early seismic‐wave methods. Here we show that the earthquake's true size and tsunami potential can be determined using Global Positioning System (GPS) data up to only 15 min after earthquake initiation, by tracking the mean displacement of the Earth's surface associated with the arrival of seismic waves. Within minutes, displacements of >10 mm are detectable as far away as India, consistent with results using weeks of data after the event. These displacements imply Mw 9.0 ± 0.1, indicating a high tsunami potential. This suggests existing GPS infrastructure could be developed into an effective component of tsunami warning systems.
Magnetic properties of Co-rich Co–Pt thin films electrodeposited on a Ru underlayer
Authors: Pattanaik Gyana , Weston James , Zangari Giovanni
Published: June 2006

Co-rich Co–Pt films were grown by electrodeposition from an amino-citrate based electrolyte on Si(011)∕Cu(111)∕Ru(0001) templates. The Ru(0001) surface provides an interface which induces the growth of an oriented hexagonal phase, thereby yielding hard magnetic properties and perpendicular anisotropy in films as thin as 10nm. Increase in film thickness only marginally compromises the hard magnetic properties probably due to the limited coarsening of the microstructure, oriented columnar growth, and magnetic grain isolation. The deposition current density plays an important role in optimizing microstructure and hard magnetic properties. Perpendicular squareness close to 1 and coercivities as high as 4.5kOe were obtained in thin as-deposited Co–Pt films.
Width dependence of annealing effects in (Ga,Mn)As nanowires
Authors: Sheu B. L. , Eid K. F. , Maksimov O. , Samarth N. , Schiffer P.
Published: June 2006

We study the time dependence of annealing on a series of GaAs-capped (Ga,Mn)As nanowires of varying widths. For different annealing times, our measurements indicate that decreasing the wire width monotonically increases the Curie temperature enhancement associated with annealing, as well as the drop in resistivity. These results are consistent with the lateral diffusion of interstitial Mn ions, which constitute an important source of defects in these materials. Furthermore, the thinner wires show a higher rate of change of conductivity with annealing time, suggesting a more efficient removal of Mn interstitials in thinner wires.
Temperature dependence of magnetic anisotropy in Mn-substituted cobalt ferrite
Authors: Melikhov Y. , Snyder J. E. , Jiles D. C. , Ring A. P. , Paulsen J. A. , Lo C. C. H. , Dennis K. W.
Published: June 2006

The temperature variation of magnetic anisotropy and coercive field of magnetoelastic manganese-substituted cobalt ferrites (CoMnxFe2−xO4 with 0⩽x⩽0.6) was investigated. Major magnetic hysteresis loops were measured for each sample at temperatures over the range 10–400 K, using a superconducting quantum interference device magnetometer. The high-field regimes of the hysteresis loops were modeled using the law of approach to saturation equation, based on the assumption that at sufficiently high field only rotational processes remain, with an additional forced magnetization term that was linear with applied field. The cubic anisotropy constant K1 was calculated from the fitting of the data to the theoretical equation. It was found that anisotropy increases substantially with decreasing temperature from 400 to 150 K, and decreases with increasing Mn content. Below 150 K, it appears that even under a maximum applied field of 5 T, the anisotropy of CoFe2O4 and CoMn0.2Fe1.8O4 is so high as to prevent complete approach to saturation, thereby making the use of the law of approach questionable in these cases.
Nucleation site density study of the L1 phase transformation in FePt nanoparticles
Authors: Ding Y. , Majetich S. A.
Published: June 2006

The fcc to L10 phase transformation in FePt nanoparticles prepared by standard high-temperature methods was investigated by measuring the magnetic switching field distribution from remanent hysteresis loops. With an immiscible overcoat to prevent sintering, the transformation rate is extremely slow. New results confirm previous findings that sintering increases the transformation rate, and show quantitatively that the nucleation site density controls this rate. The calculated nucleation density for 13 and 8 nm particles was about 1×1023 and 4×1023m−3, respectively.
Metalorganic chemical vapor deposition of magnetoresistive manganite films exhibiting electric-pulse-induced resistance change effect
Authors: Nakamura Toshihiro , Tai Ryusuke , Tachibana Kunihide
Published: June 2006

The behavior of the film precursors, Pr(DPM)3,Ca(DPM)2, and Mn(DPM)3, in the gas phase was investigated under actual chemical vapor deposition conditions of Pr1−xCaxMnO3. According to in situ infrared absorption spectroscopy, Pr(DPM)3 is much more stable against thermal decomposition than Ca(DPM)2. The atomic composition of the deposited film, such as the Ca∕(Pr+Ca) ratio, can be controlled using the precursor densities obtained by the in situ spectroscopic measurements. The praseodymium manganite films with the appropriate amount of the doped calcium can be deposited without any incorporation of carbon. The composition control on the basis of the in situ monitoring technique is expected to improve the reproducibility of the electrical and magnetic properties of the deposited film.
Infrared absorption from charge-density waves in La0.67−xPrxCa0.33MnO3 (x=0, 0.18, 0.36)
Authors: Lu Z. M. , Sun J. R. , Zhao Y. , Li S. T. , Liu H. Y. , Li Y. X.
Published: June 2006

The polycrystalline compounds with formula of La0.67−xPrxCa0.33MnO3 (x=0, 0.18, 0.36) were prepared by the standard solid-state reaction method. Infrared-absorption spectra of the three samples have been measured by a WQF-410 Fourier transform spectrophotometer with the wave numbers between 400 and 4400cm−1 in the temperature interval from 20 to 300 K. The stretching mode of the oscillation of the MnO6 octahedron in the samples was observed clearly. From the integration of the optical density Od(ω), we obtained that the carrier numbers decrease with increasing temperature, which can be attributed to the delocalization of charge carriers. The charge-density waveslike band gap has been extracted from the infrared-absorption spectra and its behavior is consistent with the change of the effective carrier numbers.
Ferromagnetic resonance study of polycrystalline cobalt ultrathin films
Authors: Beaujour J.-M. L. , Chen W. , Kent A. D. , Sun J. Z.
Published: June 2006

We present room-temperature ferromagnetic resonance (FMR) studies of polycrystalline ∥Pt∕10nmCu∕tCo∕10nmCu∕Pt∥ films as a function of Co layer thickness (1⩽t⩽10nm) grown by evaporation and magnetron sputtering. FMR was studied with a high-frequency broadband coplanar waveguide (up to 25 GHz) using a flip-chip method. The resonance field and the linewidth were measured as functions of the ferromagnetic layer thickness. The evaporated films exhibit a lower magnetization density (Ms=1131emu∕cm3) compared to the sputtered films (Ms=1333emu∕cm3), with practically equal perpendicular surface anisotropy (Ks≃−0.5erg∕cm2). For both series of films, a strong increase of the linewidth was observed for Co layer thickness below 3 nm. For films with a ferromagnetic layer thinner than 4 nm, the damping of the sputtered films is larger than that of the evaporated films. The dependence of the linewidth can be understood in terms of the spin-pumping effect, from which the interface spin-mixing conductance is deduced.
Real space observation of dipolar interaction in arrays of Fe microelements
Authors: Bolte Markus , Eiselt René , Meier Guido , Kim Dong-Hyun , Fischer Peter
Published: June 2006

Square lattice arrays of thin microelements of Fe are investigated by magnetic transmission x-ray microscopy. The influence of dipole interaction is analyzed by varying the interelement distance. For comparison isolated elements are prepared on the same sample. The magnetostatic field caused by interelement interaction leads to a substantial stabilization of the elements in the center of the array comparable to the magnetization process previously found by numerical solution of the Landau-Lifshitz equation for magnetic dot arrays. Micromagnetic simulations show that for high field strengths the dipolar interaction is collinear with the external field while in the low-field regime the strayfields have significant perpendicular components leading to a complex reversal mechanism.
Specific heat and thermal conductivity of HoN and ErN at cryogenic temperatures
Authors: Nishio Shohei , Nakagawa Takashi , Arakawa Takayuki , Tomioka Naoto , Yamamoto Takao A. , Kusunose Takafumi , Niihara Koichi , Numazawa Takenori , Kamiya Koji
Published: June 2006

The rare earth nitrides, HoN and ErN, were synthesized by the hot isostatic pressing method. Their specific heat CH(T) and the thermal conductivity κ were measured at cryogenic temperatures. In zero field, the peak values of the C0(T) of HoN and ErN are larger than those of the magnetic regenerators such as Er3Ni. The peak values of the adiabatic temperature change ΔT(T) of HoN and ErN showed similar or larger values compared with those of the candidate materials for the magnetic refrigerants such as ErAl2. The thermal conductivity of HoN and ErN are comparable to those of the magnetic regenerators such as Er3Ni. The present results indicate that HoN and ErN are promising materials as the magnetic refrigerant and regenerator for the cryogenic refrigeration system.
Low power consumption focusing actuator for a mini video camera
Authors: Yu Hsing-Cheng , Lee Tzung-Yuan , Lin Shir-Kuan , Kuo Li-Te , Wang Shyh-Jier , Ju Jau-Jiu , Huang Der-Ray
Published: June 2006

A novel low power consumption autofocusing actuator in a mini video camera is constructed in accordance with the result of a systematic design procedure of voice coil motors (VCM). This paper emphasizes the position control of such a VCM. The position feedback signals are provided by a magnetoresistive (MR) encoder. The position estimation algorithm (PEA) is developed to precisely decode the MR signals for the position of the moving part of the VCM. Different postures change the loading of the moving part of the VCM, so that an adaptive model-following control system based on the PEA is proposed to compensate for the loading variation. The experiments verify the fast dynamic performance and high power efficiency of the VCM.
Spin-flip scattering at Al surfaces
Authors: Poli N. , Urech M. , Korenivski V. , Haviland D. B.
Published: June 2006

Nonlocal measurements are performed on a multiterminal device to in situ determine the spin-diffusion length and in combination with resistivity measurements also the spin-relaxation time in Al films. By varying the thickness of Al we determine the contribution to spin relaxation from surface scattering. From the temperature dependence of the spin-diffusion length it is established that the spin relaxation is impurity dominated at low temperature. A comparison of the spin- and momentum-relaxation lengths for different thicknesses reveals that the spin-flip scattering at the surfaces is weak compared to that within the bulk of the Al films.
Structure and magnetocaloric properties of the Fe-doped HoTiGe alloy
Authors: Provenzano V. , Baumgold B. , Shull R. D. , Shapiro A. J. , Koyama K. , Watanabe K. , Singh N. K. , Suresh K. G. , Nigam A. K. , Malik S. K.
Published: June 2006

The structure and magnetocaloric properties of the Fe-doped HoTiGe compound were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy, x-ray diffraction, magnetometry, and calorimetry. As with the early studies on the undoped compound, the Fe-containing alloy exhibited an antiferromagnetic-to-paramagnetic transition and a magnetocaloric effect peak at 90K. The magnetization (M) versus temperature (T) data showed peaks at 10 and 90K, while M versus field (H) curves showed the presence of a field-induced transition for all T<120K; additionally, for all T<60K, open hysteresis loops at the magnetic transitions were observed. XRD measurements between 10 and 60K under various magnetic fields up to 3184kA∕m (40kOe) showed that the hysteresis was not accompanied by any change in crystallography. The magnetization derived entropy change −ΔSm vs T plot also showed the presence of two peaks, at 20 and 90K; but below 15K, −ΔSm increased steeply with decreasing temperature. It is believed that the minor phases in the Fe-doped alloy give rise to the magnetization-derived −ΔSm peak at 20K. The heat-capacity-derived −ΔSm vs T plot for the Fe-doped alloy also showed the presence of two peaks at 20 and 90K. However, the heat-capacity-derived −ΔSm did not show a rapid rise with decreasing temperature below 15K.
Anomalous positive exchange bias in Ni80Fe20∕NixFe1−xO thin-film bilayers induced by ion-beam deposition effects
Authors: van Lierop J. , Lin K.-W. , Ouyang H. , Tzeng Y.-M. , Guo Z.-Y.
Published: June 2006

We present results on a Ni80Fe20∕NixFe1−xO thin-film bilayer that shows a positive exchange bias loop shift of ∼90Oe at 10 K under zero-field-cooled conditions. Zero-field-cooled and field-cooled hysteresis loops were double shifted at temperatures below 200 K. This behavior is due to the presence of a range of antiferromagnetic crystallite sizes in addition to multiple magnetic phases (e.g., FeO, Fe2O3, and NiO). Furthermore, the positive exchange bias loop shift decreases linearly with increasing temperature, with a compensation temperature Tcomp∼220K, after which negative exchange bias is measured. This temperature dependence of the exchange bias reflects the competition between the Ni80Fe20 ferromagnet and antiferromagnetic Fe oxide and NiO phases as well as a range of local blocking temperatures. We attribute the appearance of a positive exchange bias loop shift at low temperatures to temperature-dependent changes in the interfacial pinning and exchange coupling due to a complex NixFe1−xO structure from energetic ion-beam bombardment effects during the film deposition.
Domain-wall pinning by steplike thickness change in magnetic thin film
Authors: Takezawa M. , Ejiri K. , Yamasaki J. , Asada H. , Koyanagi T.
Published: June 2006

A thin-film element with a steplike thickness change has been fabricated to investigate experimentally a pinning effect of domain walls by a shape control of thin-film devices. Using a Kerr microscope, domain observation has been done to measure pinning characteristics of the element. It has been shown that 40% steplike thickness change of the film thickness can realize a wall pinning, and a pinning field of 2.53 Oe is obtained. The pinning field increases with increasing steplike thickness change ratio.
Relaxation of the magnetization in magnetic molecules
Authors: Carretta S. , Bianchi A. , Liviotti E. , Santini P. , Amoretti G.
Published: June 2006

Several mechanisms characterize the relaxation dynamics in magnetic molecules. We investigate two of them, spin-lattice coupling and incoherent quantum tunneling. The effect of the phonon heat bath is studied by analyzing the exponential time decay of the autocorrelation of the magnetization. We show that in ferromagnetic (Cu6) and antiferromagnetic (Fe6) molecular rings this decay is characterized by a single characteristic time. At very low temperature, relaxation through incoherent quantum tunneling may occur in nanomagnets such as Fe8 or Ni4. The mixing between levels with different values of the total spin (S mixing) greatly influences this mechanism. In particular, we demonstrate that a fourth-order anisotropy term O44, required to interpret experimental electron paramagnetic resonance and relaxation data in Ni4, naturally arises when S mixing is considered in calculations.
Magnetization of electrodeposited nickel: Role of interstitial carbon
Authors: O’Reilly C. , Sanvito S. , Rhen F. M. F. , Stamenov P. , Coey J. M. D.
Published: June 2006

The magnetization of nickel foils electrodeposited under different conditions was not usually found to differ significantly from that of the bulk (55.4Am2kg−1). However, some galvanostatically deposited films from a citrate-based electrolyte showed a lower magnetization, which was rose to the bulk value after annealing at 575K, with no change in lattice parameter. Analysis of the influence of various lattice defects (nickel vacancies or interstitials, hydrogen or carbon impurities) using density functional theory indicates that nickel vacancies may be present in all of the films and that a nonequilibrium concentration of carbon interstitials is the likely explanation of the reduced magnetization in the citrate as-deposited nickel.
Structural, magnetic, and magnetostriction behaviors during the nanocrystallization of the amorphous Ni5Fe68.5Si13.5B9Nb3Cu1 alloy
Authors: Iturriza N. , García C. , Fernández L. , del Val J. J. , González J. , Blanco J. M. , Vara G. , Pierna A. R.
Published: June 2006

The changes in the magnetic properties (coercive field and saturation magnetostriction) of Ni5Fe68.5Cu1Nb3Si13.5B9 amorphous alloy after thermal treatment are reported. In order to develop a nanocrystalline structure, the thermal annealing was carried out by Joule heating currents of 1.7 and 1.8 A during different annealing times. Additionally, a microstructural characterization of the treated samples was performed by x-ray diffraction, determining the partial volume of the two, crystalline grains and residual amorphous matrix, existing phases. They seem to be correlated to the softening of the nanocrystallized samples in comparison to the as-cast one.
Size-dependent transition from shape to exchange dominated magnetic nanostructure
Authors: Uhlig W. Casey , Unguris John
Published: June 2006

In order to quantitatively investigate the interplay between shape anisotropy (magnetostatics) and exchange, patterned zigzag structures were prepared with sizes varying over two orders of magnitude. The magnetic state is a balance between shape anisotropy, which causes the magnetization to follow the serrated edge of the structure, and exchange, which prefers uniform magnetization. In intermediate-sized structures, we find that the magnetization along the center of the zigzag oscillates between approximately ±32° and is relatively independent of the device size. As the dimensions are reduced to less than a critical length λcr, the oscillation magnitude drops rapidly. On the other hand, the largest structures develop extended film properties such as multiple vortices and ripple.
Ti
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x
Co
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O
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∕
AlO
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Fe
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Co
0.9
magnetic tunnel junctions with varied AlOx thickness
Authors: Toyosaki H. , Fukumura T. , Ueno K. , Nakano M. , Kawasaki M.
Published: June 2006

Magnetic tunnel junctions are fabricated by laser molecular-beam epitaxy employing a room temperature ferromagnetic semiconductor Ti1−xCoxO2−δ and a ferromagnetic metal Fe0.1Co0.9 as electrodes and an AlOx tunnel barrier. The thickness of the AlOx barrier is systematically varied on a substrate during the growth by stencil mask. The junction resistance increases with the barrier thickness exponentially. The differential conductance and the tunneling magnetoresistance are significantly asymmetric with respect to bias voltage at low temperature, possibly due to the asymmetric junction structure and/or the degraded interface of AlOx∕Fe0.1Co0.9.
Magnetic and microwave properties of CoFe∕PtMn∕CoFe multilayer films
Authors: Pettiford C. I. , Zeltser A. , Yoon S. D. , Harri V. G. , Vittoria C. , Sun N. X.
Published: June 2006

CoFe ∕ PtMn ∕ CoFe films were deposited on seed layers of Ru or NiFeCr with CoFe film compositions being either Co-10at.%Fe or Co-16at.%Fe. Eight periods of the CoFe∕PtMn∕CoFe trilayers were also prepared. The magnetic properties and ferromagnetic resonance (FMR) of these films were characterized with vibrating-sample magnetometer, and field-sweep FMR system at X band (∼9.5GHz). The Ru-seeded CoFe∕PtMn∕CoFe sandwich films show excellent magnetic softness with a low hard axis coercivity of 2–4Oe, an easy axis Mr∕Ms of >98%, and a significantly enhanced in-plane anisotropy of 57–123Oe when CoFe layer thickness is above 200Å. Contrary to what was observed in the ferromagnetic/antiferromagnetic bilayer systems that have reduced FMR linewidth with the increase of film thickness, the CoFe∕PtMn∕CoFe trilayers with Ru seed layer show a minimum FMR linewidth of 45Oe at an intermediate CoFe layer thickness of 300Å at ∼9.5GHz.
A non-contact energy transferring system for an electric vehicle-charging system based on recycled products
Authors: Matsuda Y. , Sakamoto H. , Shibuya H. , Murata S.
Published: June 2006

A non-contact automatic charging system for electric vehicle application is presented. The principle is the same as that of the transformer where the primary and the secondary circuits are separable but coupled with each other without using the hand coupler. In this paper, we present a possibility of removing the core of the secondary coil on the body for reducing the weight of the car. In our experiments, the primary core, which is placed on the earth floor, is made of Mn–Zn ferrite with square shape as 1m×1m×10mm for a large cross-sectional area. The steel floor of the car assists to pass the magnetic flux. An efficiency rate over 90% with the test device of 2kW is obtained without the conventional secondary core. The leakage inductance is well compensated by a resonance capacitor inserted in the secondary coil. In this experiment, the distance between the primary and the secondary coil is 100mm and the switching frequency is 100kHz. In addition, we developed a pavement method for the system. The method utilizes plates made from the waste of expanded polystyrene and rubber mats made from used tire. The plates are set up on the rubber mats and these mats are arranged over the non-contact charging system. The pavements can be replaced easily when the system is exchanged. Therefore, this pavement method is not only practical for the non-contact charging system but is also useful for recycling of resources and reduction of waste matters.
Noncubic symmetry in Ca1−xEuxB6 (0.15≲x⩽1.00): An electron-spin-resonance study
Authors: Urbano R. R. , Pagliuso P. G. , Rettori C. , Schlottmann P. , Fisk Z. , Oseroff S. B.
Published: June 2006

The Eu2+ (4f7, S=7∕2) g value in Ca1−xEuxB6 (0.15≲x⩽1.00) was measured by means of electron spin resonance at two frequencies (fields), 9.4 (≈3.4kOe) and 34.4GHz (≈12.1kOe). The g value was found to be anisotropic and magnetic-field dependent. The amplitude of the anisotropy increases at low temperatures. The observed angular and temperature dependences of the g value suggest tetragonal symmetry caused, presumably, by a distortion along a direction perpendicular to the largest crystal face, the [001] direction. Due to the platelet shape of the samples, part of the anisotropy of the g value can also be attributed to demagnetization effects. The g values decrease at higher fields, which is interpreted in terms of a two-band model involving an exchange interaction between the localized Eu2+ 4f7 electrons with conduction Eu2+ 5d-like electrons and B 2p-like holes.
Planar coil system consisting of three coil pairs for producing a uniform magnetic field
Authors: Sasada I. , Nakashima Y.
Published: June 2006

A planar coil system that produces a uniform field and consists of three coil pairs has been designed and constructed. The design process involves the numerical solution of an equation based on the filamentary coil current and the truncation of the ratio of coil currents. This process makes it possible to realize the ratio by the coils’ number of turns and then modifying the geometrical parameters to make allowances for the practical cross sections of coil conductors. Although design parameters obtained using this process may not be optimum, the uniformity of the calculated magnetic field is satisfactory for most practical situations. The uniformity of the magnetic field was confirmed by constructing a coil system with an outer diameter equal to 1 m. The predicted area of uniformity (less than 0.01% error), for the proposed design, was six times larger than that obtained using a conventional Helmholtz coil of the same diameter.
Electronic and magnetic properties of double-impurities-doped TiO2 (rutile): First-principles calculations
Authors: Murugan P. , Belosludov R. V. , Mizuseki H. , Nishimatsu T. , Fukumura T. , Kawasaki M. , Kawazoe Y.
Published: June 2006

The electronic and magnetic properties of double-impurities-doped TiO2 (rutile) are explored using first-principles calculations within the generalized gradient approximation to examine their potential use as spintronic system. Calculations are performed on all possible sets of double impurities (M1 and M2) from M1=Cr, Mn, Fe, Co, and Ni, and M2=Mo, W, and Re. The results show the overlapping of the highest occupied impurity states with the bottom of the conduction band of the host system and the half-metallic nature in Fe- and W-doped TiO2, making them suitable as spintronic systems. These impurities preferentially substitute adjacent Ti sites and form a stable magnetic complex with oxygen atoms.
Bias voltage dependence of magnetic tunnel junctions comprising double barriers and amorphous NiFeSiB layers
Authors: Chun Byong Sun , Ko Seung Pil , Kim Young Keun , Hwang Jae Youn , Rhee Jang Roh , Kim Taewan , Ju Jae-Seon
Published: June 2006

A double-barrier magnetic tunnel junction (DMTJ) comprising an amorphous ferromagnetic NiFeSiB was investigated to reduce bias voltage dependence of tunneling magnetoresistance (TMR) ratio. The typical DMTJ structures were Ta45∕Ru9.5∕IrMn10∕CoFe7∕AlOx∕free layer7∕AlOx∕CoFe7∕IrMn10∕Ru60 (in nanometers). Various free layers such as CoFe 7, NiFeSiB 7, CoFe3.5∕NiFeSiB3.5, and NiFeSiB3.5∕CoFe3.5 were prepared and compared. The NiFeSiB-used DMTJ shows a low root-mean-square surface roughness of 0.17 nm, a resistance of about 860Ω, a Vh (voltage where the TMR ratio becomes half of its nonbiased value) of 1.1 V, and a high junction breakdown voltage of 2.0 V. The DMTJ with an amorphous NiFeSiB free layer offers smooth surface roughness resulting in reduced interlayer coupling field and bias voltage dependence.
Synchrotron-radiation spectroscopy of electron- and hole-doped collossal magneto-resistance double perovskites: BxA2−xFeMoO6 (A=Ba,Sr;B=La,K)
Authors: Kim G. , Lee S. S. , Wi S. C. , Kang J.-S. , Han S. W. , Kim J. Y. , Lee B. W. , Kim J. Y. , Shin H. J. , Parr B. G. , Park J.-H. , Min B. I.
Published: June 2006

The electronic structures of BxA2−xFeMoO6 (A=Ba,Sr;B=La,K) double perovskites have been investigated by using photoemission spectroscopy and soft-x-ray absorption spectroscopy (XAS) near the Fe 2p and O 1s absorption edges. The Fe 2p XAS spectra of undoped A2FeMoO6 (A=Ba,Sr) provide evidence for the mixed-valent Fe2+–Fe3+ states. The substitution of La3+ and K+ ions for A2+ ions causes the increasing Fe3+ component and increasing Fe2+ component, respectively. The states close to the Fermi level have mainly the Mo–Fe t2g(↓) character, consistent with the Fe2+–Fe3+ mixed-valent states. As the amount of the K+ substitution increases in KxSr2−xFeMoO6, the photoemission intensity near the Fermi level decreases, reflecting the decreasing carriers and the decreasing bandwidth of the itinerant t2g(↓) states.
Magnetic resonance studies of Co2+ ions in nanoparticles of SnO2 processed at different temperatures
Authors: Misra Sushil K. , Andronenko Serguei I. , Reddy K. M. , Hays J. , Punnoose A.
Published: June 2006

Cobalt doping (⩽1%) produces ferromagnetism at room temperature in semiconducting SnO2, presumably due to oxygen vacancies and/or changes in carrier concentration. Electron paramagnetic resonance (EPR) is a sensitive technique to investigate the Co ionic states and their local environments and/or interactions. This paper reports EPR studies of Co2+ ions doped in chemically synthesized nanoparticles of SnO2 carried out at 5K. EPR spectra were recorded from 600°C prepared SnO2 with Co concentrations of 0.5%, 1%, 3%, 5%, 8%, and 12% and from 1% Co-doped SnO2 prepared at temperatures of 150, 250, 350, 450, 600, and 830°C. Each EPR spectrum in samples with cobalt doping can be simulated as an overlap of spectra due to two broad ferromagnetic resonance lines and those due to interstitially and substitutionally incorporated Co2+ ions with effective spin S=1∕2 characterized by their particular g and A tensors. It is concluded that the Co2+ ions occupy substitutional as well as interstitial sites of SnO2 and that a fraction, albeit small, of the doped Co2+ spins contribute to the ordered ferromagnetic state. The relative concentrations of these different components depend on the annealing temperature and Co concentration of the samples.
Phenomenological theory of permeability in films having no in-plane magnetic anisotropy: Application to spin-sprayed ferrite films
Authors: Abe M. , Tada M. , Matsushita N. , Shimada Y.
Published: June 2006

In terms of the first-order magnetocrystalline anisotropy energy constant K1, we determined magnetic anisotropy in single-crystalline cubic films having their normal lines parallel to (hkl) axes. We found that the films have biaxial magnetic anisotropy, with which we derived permeability μ(ω)=μ′(ω)−jμ″(ω) (ω: angular frequency) and natural resonance angular frequency ω0, due to magnetization rotation in single-crystalline and polycrystalline films. For films that have preferential orientation of major crystal axes (such as [100] and [110]) perpendicular to the film plane but have random orientation in the film plane (i.e., exhibiting no in-plane anisotropy), the low-frequency permeability μ(ω⪡ω0) and ω0 follow the product rule μ(ω⪡ω0)ω02=γ2Ms2∕2μ02 (Ms: spontaneous magnetization, γ: gyromagnetic ratio, and μ0: permeability of free space). This is similar to that which applies for films having an in-plane uniaxial magnetic anisotropy field. Our phenomenological theory gave a plausible explanation for the permeability of spin-sprayed ferrite films that have no in-plane magnetic anisotropy and yet have high μ′(ω) of a few tens up to the gigahertz region.
Magnetic domain-free hard-magnet-biased soft magnetic underlayers for perpendicular media
Authors: Jung H. S. , Velu E. M. T. , Avenell M. , Malhotra S. S. , Bertero G.
Published: June 2006

We have successfully demonstrated single-domain hard-magnet-biased (HB) soft magnetic underlayers (SULs) by means of a synthetic antiferromagnetically (SAF)-coupled structure. Magnetically in-plane isotropic CoCrTa-based alloys as a hard-magnet pinning layer were used. Amorphous soft CoTaZr was chosen as a pinned layer to minimize coercivity (Hc) at a thickness of 50–200nm. Minor loops of CoCrTa∕Ru∕CoTaZr clearly showed single remanent magnetization and radial anisotropy orientation, and a single-domain structure was confirmed by Kerr images. Interfacial exchange energy (JAF) was in the range of 0.05–0.36erg∕cm2, which strongly depends on the kind of pinning layer used. HB SAF SUL exhibited a higher switching field (Hsw−) of 200–600Oe than Hc in a single CoCrTa layer. The difference between Hsw− and Hc depends on the composition of CoCrTa and the relative thickness ratio of CoCrTa and CoTaZr. A radial anisotropy of the pinning layer in any directions is induced by applying an external field greater than Hsw− at room temperature. HB SAF SUL with Hsw−=936Oe exhibited outstanding robustness to stray fields of up to 500Oe.
Influences of rapid annealing and substrate temperature on the magnetic properties of Co-Fe-V films
Authors: Ha Nguyen Duy , Phan Manh-Huong , Kim Chong-Oh
Published: June 2006

In this paper we report the results of a systematic investigation of influences of the deposition conditions on the microstructure and magnetic properties of Co-Fe-V thin films. The magnetic softness was optimized when the thin films were deposited at a sputtering pressure of 2mTorr and a sputtering power density of 3.82W∕cm2. A strong modification in the coercivity and its shape with respect to film thickness and substrate temperature was observed. Nanocrystalline Co49.12Fe48.65V2.23 thin films exhibited the superior soft magnetic properties (Bs=25.7kG, Hc=1.2Oe, Hk=24.5Oe) and the high electrical resistivity of 300μΩcm, which are beneficial for high-frequency and temperature applications. It was also found that rapid annealing caused considerable changes in the microstructure and hence the magnetic properties of the Co-Fe-V thin films.