bluuebunny/crossref_metadata_2025 huggingface dataset:
Petrogenesis of Hawaiian postshield lavas: Evidence from Nintoku Seamount, Emperor Seamount Chain
Authors: Shafer John T. , Neal Clive R. , Regelous Marcel
Published: May 2005

We report major and trace element and Sr and Nd isotope data for a 283 m thick sequence of postshield lavas drilled during Ocean Drilling Project Leg 197 from Site 1205, Nintoku Seamount, an approximately 56 m.y. old volcano from the Emperor Seamount Chain. At least 25 subaerially erupted lava flow units were sampled, of which all but one are alkali basalts. Clasts of hawaiite and mugearite are present in a conglomerate overlying the basement sequence. Similar rock types characterize the postshield stage of many young Hawaiian volcanoes. Major and trace element, and age‐corrected Sr and Nd isotope compositions of the Nintoku lavas are similar to those of young postshield lavas from the Hawaiian Islands. Concentrations of highly incompatible elements tend to increase, La/Yb and Nb/Zr ratios increase, and 87Sr/86Sr decreases with decreasing depth in the drill core. The more evolved rock types can be related to the underlying alkali basalts by fractional crystallization of olivine, clinopyroxene, plagioclase, and Fe‐Ti oxides, all of which occur as phenocryst or significant groundmass phases in these lavas. However, variations in the trace element and isotopic compositions of the Nintoku lavas indicate derivation from a heterogeneous mantle source. The isotopic and trace element compositions of the lavas can be modeled using a modified version of the Chen and Frey (1985) mixing model for Hawaiian lavas, in which small‐degree melts of the ∼60 m.y. old oceanic lithosphere beneath Nintoku, previously fertilized by small‐degree melts soon after its formation at a ridge axis, are mixed with melts from the Hawaiian plume. The contribution from the oceanic lithosphere became more important with time as Nintoku Seamount moved away from the Hawaiian plume axis. Together with other data from Leg 197, our results show that the 87Sr/86Sr ratios of not only shield but also postshield lavas from the Emperor Seamounts increased with decreasing age between ∼80 and 50 m.y. ago. For alkalic postshield lavas, this could result from either increased melting of the oceanic lithosphere beneath volcanoes situated on younger oceanic crust or lower degrees of incompatible trace element enrichment in the lowermost portions of younger oceanic lithosphere.
Discrete element simulations of gravitational volcanic deformation: 1. Deformation structures and geometries
Authors: Morgan Julia K. , McGovern Patrick J.
Published: May 2005

We have carried out two‐dimensional particle dynamics simulations of granular piles subject to frictional Coulomb failure criteria to gain a first‐order understanding of different modes of gravitational deformation within volcanoes. Under uniform basal and internal strength conditions, granular piles grow self‐similarly, developing distinctive stratigraphies, morphologies, and structures. Piles constructed upon cohesive substrates exhibit particle avalanching, forming outward dipping strata and angle of repose slopes. Systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal décollement; landslide forms grade from shallow slumps to deep‐seated landslide and, finally, to axial subsidence and outward flank displacements, or volcanic spreading. Surface slopes decrease and develop concave up morphologies with decreasing décollement strength; depositional layers tilt progressively inward. Spatial variations in basal strength cause lateral transitions in pile structure, stratigraphy, and morphology. This approximation of volcanoes as Coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings. The gentle slopes of Hawaiian volcanoes and Olympus Mons on Mars suggest weak basal décollements that enable volcanic spreading. High‐angle normal faults, favored above weak décollements, are interpreted in both settings and may explain catastrophic sector collapse in Hawaii and broad aureole deposits surrounding Olympus Mons. In contrast, steeper slopes and shallow detachment faults predominate in the Canary Islands, thought to lack a weak décollement, favoring smaller, more frequent slope failures than predicted for Hawaii. The numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes.
Regional variations in the diffusion of triggered seismicity
Authors: McKernon Conor , Main Ian G.
Published: May 2005

We determine the spatiotemporal characteristics of interearthquake triggering in the International Seismological Centre catalogue on regional and global scales. We pose a null hypothesis of spatially clustered, temporally random seismicity, and determine a residual pair correlation function for triggered events against this background. We compare results from the eastern Mediterranean, 25 Flinn‐Engdahl seismic regions, and the global data set. The null hypothesis cannot be rejected for distances greater than ∼150 km, providing an upper limit to triggering distances that can be distinguished from temporally uncorrelated seismicity in the stacked data at present. Correlation lengths L and mean distances between triggered events 〈r〉 are on the order of 10–50 km, but can be as high as 100 km in subduction zones. These values are not strongly affected by magnitude threshold, but are comparable to seismogenic thicknesses, implying a strong thermal control on correlation lengths. The temporal evolution of L and 〈r〉 is well fitted by a power law, with an exponent H ∼ 0.1 ± 0.05. This is much lower than the value H = 0.5 expected for Gaussian diffusion in a homogenous medium. We observe clear regional variations in L, 〈r〉 and H that appear to depend on tectonic setting. A detectable transition to a more rapid diffusion regime occurs in some cases at times greater than 100–200 days, possibly due to viscoelastic processes in the ductile lower crust.
Iodine 129/CFC 11 transit times for Denmark Strait Overflow Water in the Labrador and Irminger Seas
Authors: Smith J. N. , Jones E. P. , Moran S. B. , Smethie W. M. , Kieser W. E.
Published: May 2005

Iodine 129 discharged from nuclear fuel reprocessing plants in France and the United Kingdom is transported into the Nordic Seas on timescales of 3–5 years. Tracer 129I is subsequently injected into intermediate waters that overflow the sills between Greenland, Iceland, and Scotland and ventilate the North Atlantic Deep Waters (NADW). During the early 1990s, discharges of 129I increased by 600%, resulting in a large, well‐resolved tracer “front” whose passage through the Nordic Seas is presently being observed by a time series of 129I measurements on the WOCE (AR7W) section in the Labrador Sea. The highest 129I levels were measured below depths of 3000 m in Denmark Strait Overflow Water (DSOW). These levels increased by about 300% between 1997 and 2001 to values >40 × 107 atoms/L, indicating that the leading edge of the tracer “front” from the early 1990s was being observed entering the NADW. Using a simple mixing/advection model, 129I and CFC 11 results were used to calculate transit times of 0.4–2.6 years for the flow of DSOW from formation regions in the Nordic Seas to the Labrador Sea. Measurements on samples collected in the Irminger Sea in 2001 gave transit times of 0.3 years for core DSOW immediately south of Denmark Strait and about 2 years for locations off the southern tip of Greenland. An increase in DSOW transit times observed in the Labrador Sea between 1999 and 2001 probably reflects a more general weakening in the subpolar gyre of the North Atlantic during the 1990s.
Solute transport and storage mechanisms in wetlands of the Everglades, south Florida
Authors: Harvey Judson W. , Saiers James E. , Newlin Jessica T.
Published: May 2005

Solute transport and storage processes in wetlands play an important role in biogeochemical cycling and in wetland water quality functions. In the wetlands of the Everglades, there are few data or guidelines to characterize transport through the heterogeneous flow environment. Our goal was to conduct a tracer study to help quantify solute exchange between the relatively fast flowing water in the open part of the water column and much more slowly moving water in thick floating vegetation and in the pore water of the underlying peat. We performed a tracer experiment that consisted of a constant‐rate injection of a sodium bromide (NaBr) solution for 22 hours into a 3 m wide, open‐ended flume channel in Everglades National Park. Arrival of the bromide tracer was monitored at an array of surface water and subsurface samplers for 48 hours at a distance of 6.8 m downstream of the injection. A one‐dimensional transport model was used in combination with an optimization code to identify the values of transport parameters that best explained the tracer observations. Parameters included dimensions and mass transfer coefficients describing exchange with both short (hours) and longer (tens of hours) storage zones as well as the average rates of advection and longitudinal dispersion in the open part of the water column (referred to as the “main flow zone”). Comparison with a more detailed set of tracer measurements tested how well the model's storage zones approximated the average characteristics of tracer movement into and out of the layer of thick floating vegetation and the pore water in the underlying peat. The rate at which the relatively fast moving water in the open water column was exchanged with slowly moving water in the layer of floating vegetation and in sediment pore water amounted to 50 and 3% h−1, respectively. Storage processes decreased the depth‐averaged velocity of surface water by 50% relative to the water velocity in the open part of the water column. As a result, flow measurements made with other methods that only work in the open part of the water column (e.g., acoustic Doppler) would have overestimated the true depth‐averaged velocity by a factor of 2. We hypothesize that solute exchange and storage in zones of floating vegetation and peat pore water increase contact time of solutes with biogeochemically active surfaces in this heterogeneous wetland environment.
Applicability of statistical learning algorithms in groundwater quality modeling
Authors: Khalil Abedalrazq , Almasri Mohammad N. , McKee Mac , Kaluarachchi Jagath J.
Published: May 2005

Four algorithms are outlined, each of which has interesting features for predicting contaminant levels in groundwater. Artificial neural networks (ANN), support vector machines (SVM), locally weighted projection regression (LWPR), and relevance vector machines (RVM) are utilized as surrogates for a relatively complex and time‐consuming mathematical model to simulate nitrate concentration in groundwater at specified receptors. Nitrates in the application reported in this paper are due to on‐ground nitrogen loadings from fertilizers and manures. The practicability of the four learning machines in this work is demonstrated for an agriculture‐dominated watershed where nitrate contamination of groundwater resources exceeds the maximum allowable contaminant level at many locations. Cross‐validation and bootstrapping techniques are used for both training and performance evaluation. Prediction results of the four learning machines are rigorously assessed using different efficiency measures to ensure their generalization ability. Prediction results show the ability of learning machines to build accurate models with strong predictive capabilities and hence constitute a valuable means for saving effort in groundwater contamination modeling and improving model performance.
Etna 2004–2005: An archetype for geodynamically‐controlled effusive eruptions
Authors: Burton Michael R. , Neri Marco , Andronico Daniele , Branca Stefano , Caltabiano Tommaso , Calvari Sonia , Corsaro Rosa Anna , Del Carlo Paola , Lanzafame Gianni , Lodato Luigi , Miraglia Lucia , Salerno Giuseppe , Spampinato Letizia
Published: May 2005

The 2004–05 eruption of Etna was characterised by outpouring of degassed lava from two vents within Valle del Bove. After three months of eruption lava volumes were estimated to be between 18.5 and 32 × 106 m3, with eruption rate between 2.3 and 4.1 m3/s. Petrological analyses show that magma is resident in the shallow plumbing system, emplaced during the last South‐East Crater activity. SO2 flux data show no increase at the onset of the eruption and SO2/HCl ratios in gas emitted from the eruptive fissure are consistent with a degassed magma. No seismic activity was recorded prior to eruption, unlike eruptions observed since the 1980's. The purely effusive nature of this eruption, fed by a degassed, resident magma and the fracture dynamics suggest that magmatic overpressure played a limited role in this eruption. Rather, lateral spreading of Etna's eastern flank combined with general inflation of the edifice triggered a geodynamically‐controlled eruption.
Seismological evidence on characteristic time of crack healing in the shallow crust
Authors: Hiramatsu Yoshihiro , Honma Hiroshi , Saiga Atsushi , Furumoto Muneyoshi , Ooida Tooru
Published: May 2005

A continuous observation of shear wave splitting for 17 years reveals a unique temporal variation in seismic anisotropy in the shallow crust induced by a larger earthquake (MW5.7) beneath the Tokai region, Japan. The delay time between the fast and slow wavelets coseismically increased and then decreased back to the pre‐event value. The duration of the decreasing stage is about two years. The decrease may indicate crack healing in the upper 10 km of the crust. We approximate the temporal variation in the delay time as a function of logarithm of time, which is concordant with healing phenomena of cracks reported by laboratory experiments. The observation indicates that healing of cracks in crustal rocks is complete in approximately two years.
Schizophrenia and quality of life
Authors: Katschnig Heinz
Published: May 2005

Objective: The purpose of this paper is to examine critically results of quality‐of‐life research in schizophrenic patients living in the community.

Method: Based on the relevant literature results of specific studies are discussed in the light of the methodological problems of assessing quality of life in these people.

Results: Subjectively assessed quality of life was found to be higher in the less educated and in female patients, and when a sense of control is experienced. If negative or extrapyramidal symptoms are experienced and stigmatization is perceived, subjective quality of life is reported as being poorer. These results are discussed in view of the additional needs and fewer resources of this population, their stigma‐dilemma and their occasional difficulties in adequately assessing quality of life.

Conclusion: It is argued that subjective and quantitative measures of quality of life in schizophrenic patients should be supplemented by external assessment and qualitative methods.
Onset and early course as determinants of the further course of schizophrenia
Authors: Häfner H.
Published: May 2005

Objective: First treatment contact is preceded by a lengthy prodromal and psychotic prephase. We analysed the occurrence of symptoms and disabilities prior to first contact and their consequences for medium‐term illness course.

Method: A population‐based sample of 232 first episodes of schizophrenia was studied retrospectively using the IRAOS and compared with matched peers from the population of origin. Further illness course was studied prospectively at six cross‐sections over 5 years from first admission onwards.

Results: Three quarters showed a prodromal phase of 5 years (mean) and a 1‐year accumulation of psychotic symptoms. First to appear were depressive and negative symptoms and early signs of cognitive and social impairment. Social disability emerged 4 to 2 years before first contact. Further illness course was determined by stage of social development at psychosis onset with the consequence of a significantly poorer course for men than women because of men's earlier illness onset. Symptomatology, type of onset, age and gender influenced social course via stage of social development and, additionally, via young men's socially adverse illness behaviour.

Conclusion: Social course is determined by individual stage of social development at illness onset and by early illness course. Therefore, early detection and intervention are needed.
Long‐term course in schizophrenia: concepts, methods and research strategies
Authors: Gaebel W. , Frommann N.
Published: May 2005

Objective: This paper summarizes current knowledge about course and outcome in schizophrenia by selecting particular information and by drawing conclusions in the light of theoretical and methodological considerations, in order to illustrate future research strategies, as well as to consider novel targets of treatment.

Method: Based on examples from the literature the concepts of course and outcome as well as intervening factors of course and outcome are discussed by considering study results within their methodological and theoretical framework restrictions.

Results: The heterogeneity of the disorder, manifest in its variable phenomenology, illness course, treatment response and outcome, complicates research but at the same time offers clues to elucidate the heterogeneity of aetiology and pathogenesis. The search for intervening factors and predictors is of particular interest in order to explore the illness mechanisms.

Conclusion: Future research should focus on the biopsychosocial determinants of course and outcome in methodologically improved long‐term studies.
The interactive developmental model revisited
Authors: Strauss John
Published: May 2005

Objective: To provide a more adequate method for integrating our understanding of biological, psychological and social factors in schizophrenia, new concepts and a broader view of scientific method are required. This report aims to describe steps towards these concepts and methods.

Method: Using experiences from a range of research, clinical, and general life encounters, the author reviews assumption about objectivity and science in the mental health field where human experience is a crucial source of data and concepts.

Results: These experiences indicate that the more complex concepts of intentionality, emotional experience and expression, and the concept of experience have been largely ignored in much schizophrenia research and theory.

Conclusion: Some approaches to overcoming this lack are suggested.
A Novel Method to Derive Separate Gray and White Matter Cerebral Blood Flow Measures from MR Imaging of Acute Ischemic Stroke Patients
Authors: Simon Jessica E , Bristow Michael S , Lu Hong , Lauzon M Louis , Brown Robert A , Manjón José V , Eliasziw Michael , Frayne Richard , Buchan Alastair M , Demchuk Andrew M , Mitchell J Ross
Published: May 2005

Perfusion-weighted imaging (PWI) measures can predict tissue outcome in acute ischemic stroke. Accuracy might be improved if differential tissue susceptibility to ischemia is considered. We present a novel voxel-by-voxel analysis to characterize cerebral blood flow (CBF) separately in gray (GM) and white matter (WM). Ten patients were scanned with inversion-recovery spin-echo EPI (IRSEPI), diffusion-weighted imaging (DWI), PWI<6 h from onset and fluid attenuated inversion-recovery (FLAIR) at 30 days. Image processing included coregistration to PWI, automatic segmentation of IRSEPI into GM, WM and CSF and semiautomatic segmentation of DWI/FLAIR to derive the acute and 30-day lesions. Five tissue compartments were defined: (1) ‘Core’ (abnormal acutely and at 30 days), (2) ‘Growth’ (or ‘infarcted penumbra', abnormal only at 30 days), (3) ‘Reversed’ (abnormal acutely but normal at 30 days), (4) ‘MTT-Delayed ‘ (tissue with delayed mean transit time but not part of the acute or 30-day lesion), and (5) ‘Normal’ brain. Cerebral blood flow in GM and WM of each compartment was obtained from quantitative maps. Gray matter and WM mean CBF in the growth region differed by 5.5 mL/100 g min ( P = 0.015). Mean CBF also differed significantly within normal and MTT-Delayed compartments. The difference in the reversed region approached statistical significance. In core, GM and WM CBF did not differ. The results suggest separate ischemic thresholds for GM and WM in stroke penumbra.
MR Perfusion and Diffusion in Acute Ischemic Stroke: Human Gray and White Matter have Different Thresholds for Infarction
Authors: Bristow Michael S , Simon Jessica E , Brown Robert A , Eliasziw Michael , Hill Michael D , Coutts Shelagh B , Frayne Richard , Demchuk Andrew M , Mitchell J Ross
Published: May 2005

It is thought that gray and white matter (GM and WM) have different perfusion and diffusion thresholds for cerebral infarction in humans. We sought to determine these thresholds with voxel-by-voxel, tissue-specific analysis of coregistered acute and follow-up magnetic resonance (MR) perfusion- and diffusion-weighted imaging. Quantitative cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and apparent diffusion coefficient (ADC) maps were analyzed from nine acute stroke patients (imaging acquired within 6 h of onset). The average values of each measure were calculated for GM and WM in normally perfused tissue, the region of recovered tissue and in the final infarct. Perfusion and diffusion thresholds for infarction were determined on a patient-by-patient basis in GM and WM separately by selecting thresholds with equal sensitivities and specificities. Gray matter has higher thresholds for infarction than WM ( P<0.009) for CBF (20.0 mL/100 g min in GM and 12.3 mL/100 g min in WM), CBV (2.4 mL/100 g in GM and 1.7 mL/100 g in WM), and ADC (786 × 10−6 mm2/s in GM and 708 × 10−6 mm2/s in WM). The MTT threshold for infarction in GM is lower ( P = 0.014) than for WM (6.8 secs in GM and 7.1 secs in WM). A single common threshold applied to both tissues overestimates tissue at risk in WM and underestimates tissue at risk in GM. This study suggests that tissue-specific analysis of perfusion and diffusion imaging is required to accurately predict tissue at risk of infarction in acute ischemic stroke.
Reducing the threshold current density of AlInGaAs∕GaAs double quantum well lasers with n-type delta doping
Authors: Fekete D.
Published: May 2005

It is demonstrated that by positioning n-type Te-δ doping in the vicinity of two coupled quantum wells (QWs), a threshold current density of 67A∕cm2 per QW is obtained for a strained double QW AlInGaAs∕GaAs laser designed to emit light at 0.8μm. This low value stems in part from the higher initial electron population in the QWs but is mainly due to the enhanced coupling between the two QWs resulting from the overlap of the confined fundamental electronic levels in the two QWs under the injected current density at threshold.
Stress annealing of Fe–Ga transduction alloys for operation under tension and compression
Authors: Wun-Fogle M. , Restorff J. B. , Clark A. E. , Dreyer Erin , Summers Eric
Published: May 2005

The addition of Ga to bcc α-Fe increases the magnetostriction of Fe in the [100] direction (a factor of 12 for Fe81Ga19). The effect of annealing highly textured polycrystalline Fe81.6Ga18.4 rods under compressive stresses of −100 and −150MPa for 10–100min at temperatures between 625°C and 635°C was examined. After annealing, all samples showed nearly full performance at near-zero stresses. Samples annealed with −100MPa stress maintained a high magnetostriction up to ∼20MPa tensile stress; the sample annealed with −150MPa stress maintained its magnetostriction up to ∼30MPa.
Crystal structure and magnetic properties of MnBi–Bi nanocomposite
Authors: Kang K. , Lewis L. H. , Moodenbaugh A. R.
Published: May 2005

Isolated NiAs-type MnBi nanoparticles of 10 nm diameter, embedded in a Bi matrix, were fabricated by melt-spinning and then annealing at 528 K for 1 h. A large coercivity, over 16 kOe at 300 K, with a positive temperature coefficient is observed. In agreement with bulk results, ac susceptibility measurements show a spin reorientation around 90 K coincident with an abrupt decrease in the coercivity with decreasing temperature. The high coercivity at 300 K is attributed to a mixture of nucleation and pinning mechanisms for magnetic reversal.
The structural and magnetic properties of Ni2Mn1−xMxGa (M=Co, Cu)
Authors: Khan Mahmud , Dubenko Igor , Stadler Shane , Ali Naushad
Published: May 2005

In Ni2MnGa (cubic structure of L21 type) a first order martensitic structural transition, from the parent cubic (austenitic) phase to a low temperature complex tetragonal structure, takes place at TM=202K, and ferromagnetic order in the austenitic phase sets at TC=376K. In this work, the Mn sites in Ni2MnGa have been partially substituted with magnetic Co and nonmagnetic Cu, and the influence of these substitutions on the structural and magnetic properties of Ni2Mn1−xMxGa (M=Co and Cu) have been studied by XRD and magnetization measurements. X-ray diffraction patterns indicate that the Co doped system possess a highly ordered Heusler alloy L21 type structure for 0.05<x<0.12, and the Cu doped compounds possess L21 structure for 0.05<x<0.10. The ferromagnetic ordering temperature increases with increasing Co concentration for this system, and rapidly decreases with increasing Cu concentration. Both systems show the increase in TM with increasing Co and Cu concentration. (T-x) phase diagrams have been plotted. The results are discussed in terms of 3d-electron concentration variation.
Domain propagation in He-ion-bombarded magnetic wires with opposite exchange bias
Authors: McCord Jeffrey , Schäfer Rudolf , Theis-Bröhl Katharina , Zabel Hartmut , Schmalhorst Jan , Höink Volker , Brückl Hubert , Weis Tanja , Engel Dieter , Ehresmann Arno
Published: May 2005

Exchange-biased IrMn/CoFe full films are magnetically structured with He-ion bombardment into stripes with antiparallel-aligned loop shift. The patterning results in a two-step magnetization loop corresponding to two regions of oppositely aligned exchange bias. The longitudinal magnetization reversal through head-on domain-wall motion and partial penetration of magnetization from neighboring strips is highly asymmetric involving ripplelike domain structures and incoherent rotation of magnetization. In addition, Néel-wall-like structures with a preferred sense of rotation are formed at the edges of the strips. Along the transverse direction the reversal is dominated by the switching of the magnetic border structures between the strips. Complicated domain patterns are generated under other external field angles.
Exchange bias and magnetic structure in modulation-doped manganite superlattices
Authors: Campillo G. , Hoffmann A. , Gomez M. E. , Prieto P.
Published: May 2005

Superlattices of antiferromagnetic (AF) La1∕3Ca2∕3MnO3 and ferromagnetic (F) La2∕3Ca1∕3MnO3 were grown using sputtering technique. The AF layer thickness ranged between 3.9nm⩽tAF⩽15.6nm while the F layer thickness was kept constant (7.8 nm). Hysteresis measurements after field cooling, show an exchange bias up to a temperature of ∼100K. Surprisingly, the saturation magnetization increases with antiferromagnetic layer thickness and can exceed the expected bulk value for the La2∕3Ca1∕3MnO3 composition, whereas the interface coupling energy between the AF and F layers derived from the exchange bias is constant. This suggests that magnetization depth profile extends beyond the chemical doping interface.
The effects of the thickness of magnetically hard- and soft-phase layers on magnetic properties and exchange coupling in multilayer magnets
Authors: Liu W. , Sui Y. C. , Zhou J. , Sun X. K. , Chen C. L. , Zhang Z. D. , Sellmyer D. J.
Published: May 2005

The structure and magnetic properties of multilayer magnets containing a hard phase [HP≡(Nd0.95Dy0.05)(Fe,Co,Nb,B)5.5] and a soft phase (SP≡Fe and Fe65Co35) have been investigated. For the nanocomposite multilayer of Si(substrate)/Ti(30nm)∕[HP(xnm)∕SP(ynm)]n∕Ti(30nm), the remanence enhancement has been observed at different thickness and volume fractions of hard- and soft-phase layers. The remanence increases and the coercivity decreases with the addition of soft phase, in comparison with the results of the single-layer film. For the multilayer of Si(substrate)∕Ti(30nm)∕[HP(15nm)∕Fe(5nm)]n∕Ti(30nm) annealed at 575 °C for 30 min, the coercivity of the multilayer reaches a maximum at n=20. Effects of the layer thickness and volume fraction of hard- and soft-phase layers on magnetic properties and exchange coupling in the multilayer films have been observed.
Large magnetocaloric effect in melt-spun LaFe13−xSix
Authors: Gutfleisch O. , Yan A. , Müller K.-H.
Published: May 2005

A very large value of magnetic entropy change ∣ΔS∣=31J∕kgK was obtained at 201K under 5T in LaFe11.8Si1.2 melt-spun ribbons subjected to a very short-time annealing (2h∕1050°C). This value is much higher than that of a bulk LaFe11.44Si1.56 in this temperature range. The large ∣ΔS∣ is attributed to the first-order thermally induced transition at the Curie temperature TC, and is enhanced even further due to a more homogenous element distribution. With increasing Si concentration, TC is increased and ∣ΔS∣ is decreased due to a weakening or an even disappearance of the first-order magnetic phase transition.
Large magnetocaloric effect in single crystal Pr0.63Sr0.37MnO3
Authors: Phan Manh-Huong , Peng Hua-Xin , Yu Seong-Cho
Published: May 2005

This article reports the magnetocaloric effect in a single crystal Pr0.63Sr0.37MnO3, which undergoes a very sharp ferromagnetic-to-paramagnetic phase transition at ∼300K. A large magnetic entropy change of 8.52J∕kgK and a large adiabatic temperature change of 5.65K for an applied field change of 50kOe were observed around 300K; this allows water to be used as a heat transfer fluid in the room-temperature magnetic refrigeration regime. The distribution of entropy change (ΔSM) was found to be very uniform and which is desirable for an Ericson-cycle magnetic refrigerator. The large magnetic entropy change induced by a relatively low magnetic field change is beneficial for household application.
Classical magnetoresistance in a curved wire
Authors: Hershfield Selman , Chen Zhihong
Published: May 2005

The semiclassical magnetoresistance due to the Lorentz force is computed for current flowing in a curved wire in the form of a two-dimensional annulus. The surface scattering is taken to be diffuse, and the bulk scattering is s wave and elastic. Near zero magnetic field the resistance has a minimum instead of the maximum in a straight wire. The resistance continues to decrease until it reaches a local minimum at a field corrseponding to a cyclotron radius in between the inner radius and the outer radius of the annulus. Thus, in a curved wire the optimum magnetic field for reducing surface scattering is not zero field as for a straight wire, but a field which allows electrons to go part way around the curves. This result explains the negative magnetoresistance near zero field seen in systems contained curved wire segments and shows how geometry can be used to tune the semiclassical magnetoresistance in the regime where surface scattering dominates.
Thickness dependence of exchange anisotropy of polycrystalline Mn3Ir/Co-Fe bilayers
Authors: Imakita Ken-ichi , Tsunoda Masakiyo , Takahashi Migaku
Published: May 2005

The dependence of exchange anisotropy of polycrystalline Mn3Ir∕Co70Fe30 bilayers on the antiferromagnetic layer thickness (dAF) was investigated. The degree of order of a Mn–Ir layer in the examined bilayers was almost constant of 0.45, regardless of dAF. The findings are stated as follows. A maximum unidirectional anisotropy constant (JK) of 1.3erg∕cm2 is obtained at dAF=10nm. The critical thickness of dAF, where JK becomes half of its maximum value, is less than 5 nm and comparable to that of the bilayer with disordered Mn–Ir. The blocking temperature (TB) is enhanced in several-ten degrees with ordering of the Mn–Ir layer.
High coercivity and exchange coupling of Ni∕NiO nanocomposite film
Authors: Yi J. B. , Ding J. , Zhao Z. L. , Liu B. H.
Published: May 2005

A coercivity of 2.4kOe was achieved at room temperature after magnetic annealing a pure Ni film at 650K for 20min under O2 partial pressure of 0.001torr. The interface structure of Ni∕NiO during the formation of NiO under magnetic field and the small grains may be responsible for the large coercivity. Additionally, the surface NiO, dipolar interaction of Ni particles, and the composition of NiO inside the film may affect the coercivity as well.
Ion-beam-induced chemical-vapor deposition of FePt and CoPt particles
Authors: Xu Q. Y. , Kageyama Y. , Suzuki T.
Published: May 2005

FePt and CoPt particles have been directly deposited on Si3N4 substrate by ion-beam-induced chemical-vapor deposition (IBICVD) with a focused ion-beam system. The as-deposited FePt particles are amorphous and crystallize into fcc structure after annealing at 600°C. The as-deposited CoPt particles and the CoPt particles annealed at 600°C are both in fcc structure, but annealing improves the crystallization of the CoPt particles. After applying a 20-kOe magnetic field perpendicular to the Si3N4 substrate, the magnetic force microscopy images of annealed FePt and CoPt particles both show concentric domain patterns, implying the alternately up- and downward perpendicular components of magnetizations. The successful fabrication of FePt and CoPt particles may lead to the potential application of IBICVD for nanoparticles and clusters which have not been synthesized yet.
Magnetization reversal in a YFe2-dominant DyFe2∕YFe2 exchange-coupled superlattice: An x-ray magnetic circular dichroism and polarized neutron reflectometry study
Authors: Dumesnil K. , Dufour C. , Mangin Ph. , Fitzsimmons M. R. , Park S. , Rhyne J. J. , Rogalev A. , Borchers J. A.
Published: May 2005

Combined chemical-selective XMCD and depth-resolved PNR experiments have been performed to unravel magnetic configurations in a [(30Å)DyFe2∕(120Å)YFe2]22 superlattice, in which the magnetization of the soft YFe2 layer dominates. The magnetization of the YFe2 component is nearly always saturated, flipping directly from positive to negative saturation, while the net magnetization of the hard DyFe2 component significantly varies in high fields and is probably nonuniform.
Lateral correlation length of magnetization reversal in thin magnetic films
Authors: Berger A. , Margulies D. , Do H. , Ktena A. , Dahmen K.
Published: May 2005

We determine the lateral correlation length L of the magnetization reversal process in thin magnetic films. For this purpose, we have devised an experimental system, which allows tuning of the effective disorder level by means of the local bias field distribution acting upon the magnetic film. This disorder is hereby counteracting the intergranular exchange coupling within the film, which tends to synchronize the reversal process. We observe a sharpening of the switching field distribution upon narrowing the exchange bias field distribution. Quantitative comparisons between these two quantities allow the determination of L without the need for adjustable parameters.
Blocking temperature in exchange coupled MnPt∕CoFe bilayers and synthetic antiferromagnets
Authors: Rickart M. , Guedes A. , Ventura J. , Sousa J. B. , Freitas P. P.
Published: May 2005

Exchange coupled Mn51.5Pt48.5∕Co90Fe10 bottom-pinned bilayers and synthetic antiferromagnets (SAFs) were prepared by magnetron sputtering. Exchange bias, coercivity, and blocking temperature were determined as a function of the MnPt thickness. Interfacial exchange energy was found to be Jex=0.4erg∕cm2 for a Mn51.5Pt48.5(t⩾20nm)∕Co90Fe10 (5nm) bilayer. Thermal stability of the bilayers was analyzed by separation of the blocking temperature distribution in (a) width ΔTB and (b) center temperature TB,center of the distribution. For thick MnPt films ΔTB is constant but steadily increases for thin films. SAF structures show higher exchange coupling and higher blocking temperatures at thin layer thickness (tMnPt=8.5nm).
Clamping effect on the magnetic behavior of europium epitaxial thin films
Authors: Soriano S. , Dumesnil K. , Dufour C. , Hennion M. , Borchers J. A. , Mangin Ph.
Published: May 2005

Epitaxial thin films of europium experience significant strains when deposited on a sapphire substrate with a niobium buffer. We demonstrate that the relative population of the magnetic domains is affected, in particular, in the presence of a slight tilt of the film growth axis relative to the substrate. The application of a magnetic field further modifies the population of the domains giving rise to unusual irreversible effects. These results could help to elucidate the magnetoelastic properties of bulk europium, which are still unknown.
A new approach for improving exchange-spring magnets
Authors: Jiang J. S. , Pearson J. E. , Liu Z. Y. , Kabius B. , Trasobares S. , Miller D. J. , Bader S. D. , Lee D. R. , Haskel D. , Srajer G. , Liu J. P.
Published: May 2005

It is demonstrated here that an already ideal exchange–spring magnet can be further improved by intermixing the interface. This is counter-intuitive to the general expectation that optimal exchange–spring magnet behavior requires an ideal, atomically coherent soft–hard interface. Epitaxial Sm–Co/Fe thin-film exchange–spring bilayers are thermally processed, by annealing or high-temperature deposition, to induce interdiffusion. With increasing processing temperature, the hysteresis loop becomes more single-phase-like, yet the magnetization remains fully reversible. The interface is characterized via synchrotron x-ray scattering and electron microscopy elemental mapping. The magnetization behavior is modeled by assuming a graded interface where the material parameters vary continuously. The simulations produce demagnetization curves similar to experimental observations.
Magnetization reversal in single-layer and exchange-biased elliptical-ring arrays
Authors: Jung Wonjoon , Castaño F. J. , Morecroft D. , Ross C. A. , Menon Rajesh , Smith Henry I.
Published: May 2005

Arrays of elliptical rings with long axis of 3μm, short axis of 1.8μm, and widths of 400nm and above were fabricated by zone-plate-array lithography and lift-off processing. Hysteresis loops of NiFe elliptical rings with different widths indicate the “vortex” state is more stable for narrower rings. Micromagnetic simulations reveal that the magnetization configurations of wider rings are more complicated than that of narrower ones. Elliptical-ring arrays fabricated from exchange-biased thin film structures display shifted hysteresis loops and the same width dependence of the stability of the vortex state.
The addition effects of alkaline earth ions in the chemical synthesis of ε-Fe2O3 nanocrystals that exhibit a huge coercive field
Authors: Ohkoshi Shin-ichi , Sakurai Shunsuke , Jin Jian , Hashimoto Kazuhito
Published: May 2005

An iron oxide/silica composite material, which was prepared by combining reverse-micelle and sol-gel techniques, exhibited a huge coercive field Hc of 20kOe (1.6×105Am−1) in our previous work. The key of this synthetic procedure was the added Ba2+ ions that created a single phase of ε-Fe2O3. In the present work, the addition effect of Ca2+ ions to this procedure was investigated. Consequently, rod-shape ε-Fe2O3 nanocrystals (40–120nm×15–20nm) were obtained and a Hc value of 20kOe was observed. Thermodynamical analysis that considered the surface energy of nanoparticle suggested that a single ε-Fe2O3 phase was generated by retarding the crystal growth of Fe2O3 particles under the presence of alkaline earth ions.
IrMn as exchange-biasing material in systems with perpendicular magnetic anisotropy
Authors: van Dijken Sebastiaan , Besnier Magali , Moritz Jerome , Coey J. M. D.
Published: May 2005

Contact between a Co∕Pt multilayer and an IrMn film leads to perpendicular exchange bias. The exchange bias field does not depend on the degree of (111) film texture and for Co∕Pt multilayers with IrMn at the bottom it can be enhanced by magnetic field annealing. The perpendicular exchange bias of the Co∕Pt–IrMn system is limited by a misalignment between the Co spins and the film normal, which is due to a negative magnetic anisotropy contribution from the Co∕IrMn interface (KSCo∕IrMn=−0.09mJ∕m2). The insertion of a 3Å thick Pt layer at the Co∕IrMn interface maximizes the perpendicular exchange-bias field.
Direct measurement of spatially localized ferromagnetic-resonance modes in an antidot lattice (invited)
Authors: Pechan Michael J. , Yu Chengtao , Compton R. L. , Park J. P. , Crowell P. A.
Published: May 2005

Recent ferromagnetic-resonance (FMR) measurements and related simulations on antidot structures suggested the existence of spatially localized modes. In this report we confirm the existence of these modes using time-resolved Kerr microscopy (TRKM) as a local probe of the magnetodynamics. FMR measurements on an antidot array (a 40-nm-thick permalloy film with a hole size of 1.5μm and a hole lattice spacing of 3μm×5μm) at frequencies between 10 and 35GHz reveal two main resonances, whose relative amplitudes and orthogonal uniaxial in-plane anisotropies suggest the existence of modes localized between holes along each of the principal axes. TRKM measurements in applied fields ranging from 100to600Oe show explicitly the existence of these two modes—one at low frequency between the holes along the short axis and one at higher frequency between the holes along the long axis. TRKM also reveals additional mode structure, most notably a low-frequency mode localized along the edges of the antidots, similar to the edge modes observed in magnetic wires.
Magnetization reversal in patterned ferromagnetic and exchange-biased nanostructures studied by neutron reflectivity (invited)
Authors: Temst K. , Popova E. , Van Bael M. J. , Loosvelt H. , Swerts J. , Buntinx D. , Bruynseraede Y. , Van Haesendonck C. , Fritzsche H. , Gierlings M. , Leunissen L. H. A. , Jonckheere R.
Published: May 2005

We have measured the off-specular polarized neutron reflectivity of periodic arrays of micron-sized rectangular polycrystalline ferromagnetic Co bars and exchange-biased Co∕CoO bars, which were prepared by a combination of electron-beam lithography and evaporation techniques. The intensity of the first-order off-specular neutron satellite reflection was monitored as function of the magnetic field parallel to the long edge of the bars, allowing analysis of the magnetization reversal process using the four spin-polarized scattering cross sections. The neutron data are compared with calculations based on a micromagnetic simulation. The influence of shape anisotropy on the reversal mechanism is demonstrated.
Investigation of magnetoimpedance effect in amorphous thin-film microstructures
Authors: Giouroudi I. , Hauser H. , Musiejovsky L. , Steurer J. , Didosyan Y. S.
Published: May 2005

The objective of this research is to correlate the magnetic properties of CoFeB trilayer thin films with the impedance responses and to investigate the potential use of this material for magnetoimpedance (MI) sensor applications. Two layers of 50-nm-thin amorphous CoFeB layers with a central 100-nm copper layer were sputtered onto a thermally oxidized Si wafer. Strips and meanders of 4–20-μm width were structured by plasma etching. The MI effect of the 50∕100∕50-nm trilayer was improved after field annealing, exhibiting a maximum of up to 9% in a 20-μm-wide meander.
Grain-size effects in exchange-biased FeMn∕NiFe bilayers
Authors: Manzoor Sadia , Vopsaroiu M. , Vallejo-Fernandez G. , O’Grady K.
Published: May 2005

Fe Mn ∕ Ni Fe exchange-biased films have been deposited on Si substrates and the average grain size in the antiferromagnet systematically varied from 54to70Å. Vibrating-sample magnetometer measurements at room temperature show that the exchange field increases by a factor of about 3 with increasing grain size. Changes in the coercivity were much smaller. We believe the grain-size effects are due to thermal activation phenomena. Training effects give rise to a greater reduction in the exchange field for the system with the smallest grains. The absence of a significant change in the coercivity implies that it is primarily controlled by interfacial effects.
Ballistic hole magnetic microscopy
Authors: Haq E. , Banerjee T. , Siekman M. H. , Lodder J. C. , Jansen R.
Published: May 2005

A technique to study nanoscale spin transport of holes is presented: ballistic hole magnetic microscopy. The tip of a scanning tunneling microscope is used to inject hot electrons into a ferromagnetic heterostructure, where inelastic decay creates a distribution of electron-hole pairs. Spin-dependent transmission of the excited hot holes into an underlying p-type semiconductor collector induces a hole current in the valence band of the semiconductor, with magnetocurrent values up to 180%. The spin-filtering of holes is used to obtain local hysteresis loops and magnetic imaging with spatial resolution better than 30nm.
Effects of epitaxial lift-off on interface recombination and laser cooling in GaInP∕GaAs heterostructures
Authors: Imangholi Babak , Hasselbeck Michael P. , Sheik-Bahae Mansoor , Epstein Richard I. , Kurtz Sarah
Published: May 2005

Photoluminescence of GaAs passivated with GaInP is studied over the temperature range 7–450K. Different photocarrier recombination mechanisms are identified as the temperature changes. An interface recombination velocity of less than 0.6cm∕s is measured at 300K. Lift-off processing inhibits but does not preclude laser cooling of GaAs.
Quantum well intermixing enhancement using Ge-doped sol-gel derived SiO2 encapsulant layer in InGaAs∕InP laser structure
Authors: Djie H. S. , Ho C. K. F. , Mei T. , Ooi B. S.
Published: May 2005

The intermixing enhancement in InGaAs∕InGaAsP quantum well laser structure has been investigated using the Ge-doped sol-gel derived SiO2 encapsulant layer. A band-gap shift of ∼64nm has been observed from 16% Ge-doped SiO2 capped sample at the annealing temperature of 630°C with effective intermixing suppression using the e-beam-evaporated SiO2 layer. Ge incorporation in the sol-gel cap reduces the mismatch of thermal expansion coefficients efficiently retaining preferential vacancies, and therefore enhancing the interdiffusion rate. The intermixed material retains a good surface morphology and preserves the optical quality as evidenced by the absence of any appreciable photoluminescence linewidth broadening.
Room-temperature boron displacement in crystalline silicon induced by proton irradiation
Authors: Piro A. M. , Romano L. , Mirabella S. , Grimaldi M. G.
Published: May 2005

The effect induced by proton irradiation on B-doped crystalline Si at room temperature is investigated in detail. The displacement of B atoms out of substitutional lattice sites is shown to be induced at room temperature by proton irradiation at energies ranging between 300 and 1300 keV. This phenomenon was studied by means of channeling and nuclear reaction analysis techniques using the B11(p,α)Be8 nuclear reaction at 650 keV proton energy. For all the irradiation energies used, the fraction of displaced B atoms increases exponentially with proton irradiation fluence until saturation occurs. The B displacement rate strongly increases by decreasing the irradiation energy. We show that B off-lattice displacement is not due to a direct interaction of the proton beam with B atoms, but to the Si self-interstitials (ISi) generated in the lattice by the irradiating beam. The displacement results from the formation of a mobile B-ISi pair when a ISi is trapped by a substitutional B. The measured damage rate has been interpreted in terms of the ISi-B substitutional trapping probability and the resulting cross section at room temperature is (1.00±0.05)×10−16cm2.