bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observation of inverse magnetoresistance in perovskite oxide tunnel junctions
Authors: Noh J. S. , Eom C. B. , Lagally M. G. , Sun J. Z. , Kim H. C. 
Published: May 2004

AbstractWe have observed a distinct inverse magnetoresistance in a hybrid tunnel junction. Two types of perovskite oxides, La0.67Sr0.33MnO3 and SrRuO3, were used as ferromagnetic electrodes with an SrTiO3 barrier in between them. Micron‐scale junctions were fabricated from 90° off‐axis sputtered trilayers, using standard optical lithography. Homo‐junctions that incorporate either La0.67Sr0.33MnO3 or SrRuO3 as both electrodes showed only normal positive magnetoresistances. In contrast, a clear inverse magnetic switching was found at 10 K for the hybrid junction. The spin polarization of SrRuO3 is about –9% as calculated based upon Julliere model, which is in quantitative agreement with the value (–10%) determined by the earlier tunneling experiment on SrRuO3/SrTiO3/Al structures. This is not only the manifestation of the existence of a negatively polarized material at the Fermi level, but also demonstrates that the widely‐cited Julliere model is applicable even to a negative polarization case. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Valence changes in La1−xCaxMnO3 thin films by NEXAFS
Authors: Lee Y. S. , Shin H. J. , Lee Y. P. 
Published: May 2004

AbstractLa1−xCaxMnO3 (LCMO) thin films were prepared on LaAlO3 (100) substrate by rf magnetron sputtering with various deposition conditions, i.e., temperature, thickness, composition, etc. The Mn valence states associated with the ferromagnetic transition of LCMO films have been investigated by using the O K‐edge X‐ray absorption spectra. The Mn4+/Mn3+ ratio in LCMO films changed by deposition conditions. It was found that the deposition condition in film fabrication leads to a change not only in Mn valence states, but in ferromagnetic transition. Finally, the valence states in LCMO films can be controlled by depositon conditions such as temperature, thickness, and composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A first‐principles study on the magnetism of an Fe chain along the [110] direction on Cu(001)
Authors: Jin Ying Jiu , Kim In Gee , Lee Jae Il 
Published: May 2004

AbstractThe electronic structures and magnetism of an Fe chain along the [110] direction on Cu(001) (Fe[110] chain) were investigated by using the all‐electron full‐potential linearized augmented plane‐wave method within the generalized gradient approximation. The calculated results showed that the Fe magnetic moment of the Fe[110] chain is 2.99 μB/atom. This value is much larger than that (2.22 μB/atom) of the bcc bulk iron, but the value is smaller than that (3.20 μB/atom) of the free standing Fe chain and that (3.11 μB/atom) of the Fe chain along the [010] direction on Cu(001). Large enhancement of the Fe magnetic moment of the Fe[110] chain is explained by the localization of the Fe d‐band due to the reduced coordination number which is confirmed from the calculated spin‐polarized layer‐projected density of states. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
EPR study of Pr0.7Sr0.3−xBaxMnO3 lanthanum manganites
Authors: Quang P. H. , Chung Y. S. , Ulyanov A. N. , Pismenova N. E. , Yu S. C. 
Published: May 2004

AbstractAmong the wide variety of colossal magnetoresistance materials the Pr‐compositions occupy some special places. Namely, in zero magnetic field the Pr1−yCayMnO3 samples are insulators for any level of Ca doping and show low field hysteresis. Pr0.7Ba0.3MnO3 composition is also insulating at low as well as at high temperatures. The combined Pr‐ and (Sr, Ba)‐doped perovskite‐like manganites should show interesting properties due to the large difference between the Pr and Sr, Ba ionic size. In this work we present an electron paramagnetic resonance (EPR) study of Pr0.7Sr0.3−xBaxMnO3 perovskite (x = 0.00, 0.15 and 0.30). We observed that the intensity of the EPR line decreases exponentially with temperature. The activation energy values derived from the temperature dependencies of EPR line intensity equals 0.16 eV, 0.09 eV and 0.08 eV for the x = 0.00, 0.15 and 0.30 compositions, respectively. The temperature dependence of the EPR linewidth showed a minimum near the TC. The temperature and concentration dependencies of EPR linewidth and line intensity will be discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First principles calculations on electronic structure and magnetism of (CrAs)1(GaAs)x (x = 1, 3, and 5) superlattices
Authors: Cha Gi‐Beom , Cho Sunglae , Hong Soon C. 
Published: May 2004

AbstractRecently CrAs, which has a NiAs structure in nature, was grown epitaxially in a zinc‐blende structure on a GaAs substrate and was proved to be a ferromagnetic half‐metal with Curie temperature over 400 K. In this study, we investigated zinc‐blende bulk CrAs and (CrAs)1(GaAs)x (x = 1, 3, and 5) superlattices, using the full‐potential linearized augmented plane‐wave method based on local spin density approximation. Their ferromagnetic states were found to be energetically more stable, compared to their antiferromagnetic states. The magnetism and electronic structure of CrAs in the superlattices were not modified significantly from those of the bulk zinc‐blende CrAs. The calculated total magnetic moments per Cr are 3.0 μB for all the systems, and As atoms are coupled antiferromagnetically to the Cr atoms. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large magnetocaloric effect in La0.845Sr0.155Mn1−xMxO3 (M = Mn, Cu, Co) perovskites
Authors: Phan Manh‐Huong , Phan The‐Long , Yu Seong‐Cho , Tho Nguyen Duc , Chau Nguyen 
Published: May 2004

AbstractWe present the results of an investigation on the magnetocaloric effect in the perovskites of La0.845Sr0.155Mn1−xMxO3 (M = Mn, Cu, Co). It is found that there was a large magnetic entropy change, i.e. a large magneto‐caloric effect, in all these samples. Among them, the magnetic entropy change reaches a maximum value of 2.67 J/kg K at the applied field of 13.5 kOe for the Cu‐doped sample, suggesting that this material would be a suitable candidate for the advanced magnetic refrigeration technology. The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the strong coupling between spin and lattice that occurs in the vicinity of the ferromagnetic‐paramagnetic transition temperature (TC) – which is experimentally verified by electron paramagnetic resonance study. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic and transport properties of La0.5Sr0.5(FexCo1−x)O3 (0 ≤ x ≤ 0.2) perovskites
Authors: Phan T. L. , Huynh T. N. , Phan M. H. , Khiem N. V. , Phuc N. X. , Chung Y. S. , Rhee J. R. , Yu S. C. 
Published: May 2004

AbstractThe magnetic and transport properties of La0.5Sr0.5(FexCo1−x)O3 (0 ≤ x ≤ 0.2) compounds were investigated. TC decreased slightly and the resistivity increased, even with a very small extent of Fe substitution. The Fe substitution induced additional antiferromagnetic Fe–O–Fe interactions that suppress strongly the ferromagnetism and conductivity, thus causing a separation between two phases at around 124 K for both x = 0.1 and 0.2 compositions. Spin‐glass behavior was observed for the Fe‐doped samples. The resistivity, can be described by the Mott's variable range hopping model in the low temperature region.
New materials search for spintronics applications: Synthesis of BiMn1−xFexO3 films via combinatorial chemistry
Authors: Yang C.‐H. , Song J. H. , Lee H. J. , Yoon S. , Koo T. Y. , Jeong Y. H. 
Published: May 2004

AbstractThe combinatorial chemistry method that employs multiple metal‐masks and shutters in the pulsed laser deposition of thin films was used to synthesize a series of BiMn1−xFexO3 (x = 0–0.4) films on single SrTiO3(001) substrates. The films showed a systematic variation of c‐axis x‐ray diffraction peaks with a discontinuity at x ∼ 0.15. They also possessed narrow full‐width‐at‐half‐maximum in the rocking curves. From the temperature dependence of magnetization, we were able to conclude that as substitution of Fe for Mn is increased, antiferromagnetic interaction becomes enhanced with consequent suppression of the ferromagnetic ordering and eventually antiferromagnetic states prevail below 45 K for x > 0.15. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoemission study of Zn1−xCoxO as a possible DMS
Authors: Wi S. C. , Kang J.‐S. , Kim J. H. , Lee S. S. , Cho S.‐B. , Kim B. J. , Yoon S. , Suh B. J. , Han S. W. , Kim K. H. , Kim K. J. , Kim B. S. , Song H. J. , Song H. J. , Shin H. J. , Shim J. H. , Min B. I. 
Published: May 2004

AbstractWe report a photoemission spectroscopy (PES) and X‐ray absorption spectroscopy (XAS) study for bulk Zn1−xCoxO samples (x = 0 and 0.1). Both the Co 2p XAS and the Co 2p core‐level PES spectra show that the doped Co ions in Zn1−xCoxO are in the divalent Co2+ (d7) states under the tetrahedral symmetry. A Co 2p → 3d resonant photoemission spectroscopy measurement shows that the Co 3d states lie near the top of the O 2p valence band. This work suggests that the doped Co ions in Zn1−xCoxO substitute properly for the Zn sites with Co2+ valence states. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structures and magnetic properties of Fen (n = 1–4) nanowires
Authors: Jo Chulsu , Lee J. I. 
Published: May 2004

AbstractSpin polarized total energy and electronic structure calculations are performed for thin Fe nanowires using the ab initio pseudopotential plane wave method within generalized gradient approximation. Binding energy, density of states, and magnetic moment are calculated for planar and staggered thin Fe wires, which are composed of four atoms or less. The most stable configuration is attained in zigzag geometry of which the bond length is stretched relatively to the planar nanowire. The Fe‐zigzag wire has the largest magnetic moment among isomers. Upon stretching the Fe2‐zigzag wire to a linear one, the magnetic moment increased to be proportional to the nearest‐neighbor distance. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of spinel‐type magnetic semiconductor ZnCo2O4 by reactive magnetron sputtering
Authors: Kim Hyun Jung , Song In Chang , Sim Jae Ho , Kim Hyojin , Kim Dojin , Ihm Young Eon , Choo Woong Kil 
Published: May 2004

AbstractWe report the synthesis of spinel oxide ZnCo2O4 thin films and the effects of the oxygen partial pressure in the sputtering gas mixture on their electrical and magnetic properties. The conduction type and carrier concentration were found to be dependent on the oxygen partial pressure ratio: n‐type and p‐type for the oxygen partial pressure ratio below ∼70% and above ∼85%, respectively. A ferromagnetic coupling was observable in p‐type ZnCo2O4, whereas an antiferromagnetic interaction was found for insulating and n‐type ZnCo2O4 film, revealing hole‐mediated ferromagnetic transition in ZnCo2O4. Arrott plot analysis of magnetization data at 5 K also indicated non‐zero spontaneous magnetization for p‐type ZnCo2O4. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication and characteristics of magnetic tunnel transistors using amorphous n‐type Si films
Authors: Lee S. S. , Lee J. Y. , Kim M. S. , Choi J. G. , Hwang D. G. , Rhie K. , Rhee J. R. 
Published: May 2004

AbstractA magnetic tunnel transistor (MTT) device using an amorphous n‐type Si semiconductor film for the base and collector consisting of [CoFe/NiFe] (free layer) and Si (top layer) multilayers is used to study the spin‐dependent hot electron magnetocurrent (MC) and the tunneling magnetoresistance at room temperature. A large MC of more than 40.2% is observed at the emitter–base bias voltage VBE of 0.62 V. The increasing emitter hot current and transfer ratio with the increase of the emitter–base voltage are due mainly to a rapid creation of a number of conduction‐band states in the Si collector. However, above a VBE of 0.62 V, a rapid decrease of the MC is observed in an amorphous Si‐based MTT. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular quantum theory: Separable electronuclear wave functions and vibronic states—A generalized diabatic approach
Authors: Tapia O. 
Published: May 2004

AbstractThe linear superposition principle is used to represent chemical and physical processes. A quantum state representation is obtained for model molecular systems. An exact Hamiltonian is first introduced and thereafter approximated by a sum of Coulomb Hamiltonian, electron–phonon (e–ph), relativistic effects, and coupling to external fields. A sharp separability ansatz is used to study the Coulomb Hamiltonian first; the electronic part is fully represented in Hilbert space (q space); a background of positive charge replaces nuclei in real space (ξ space). This QC model leads to diabatic electronic functions and diabatic potential energy (DPE) surfaces in real space. Next, the nuclear masses are introduced via a kinetic energy operator and added to the DPEs. The attractor property of the diabatic electronic functions is used to study mass fluctuation regimes. Fluctuations, if quantized, lead to the Q2C model; mass dynamics takes place in real space. The set of product functions {ϕj(q)ζjl(ξ)} provides a base to represent arbitrary electronic states. In this context, the linear superposition principle is naturally introduced. The formulation of chemical reactions, pump–probe experiments and a detailed study of H are topics examined from the present perspective. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
DFT study of HCN and NCCN reactions with hydrogen species
Authors: Basiuk Vladimir A. , Kobayashi Kensei 
Published: May 2004

AbstractEnergetic feasibility of the formation of aminoacetonitrile (or glycine nitrile) through a sequence of reactions of cyanogen (NCCN) with hydrogen species was evaluated, using density functional theory (DFT) calculations at the B3LYP/ 6‐31++G(d,p) theoretical level. A critical step in the cyanogen hydrogenation is the addition of first H atom. As a result of a positive activation barrier of ∼3–6 kcal mol−1 (depending on the attachment site), this process is hardly feasible under cold gas‐phase interstellar conditions, but might possibly be facilitated in the solid phase by proton tunneling effects. The addition of a third hydrogen atom requires much lower activation energy, especially if H adds on the NH group (0.2–0.8 kcal mol−1). The second and fourth steps (combination of C2HN2 and C2H3N2 radical species with hydrogen atoms) are highly exothermic; the need to get rid of excess energy makes them possible through grain‐surface processes only. As a whole, most of the hydrogenation reactions under study can be expected to take place in the solid phase (icy and silicate grains), and not in the gas phase under cold interstellar conditions. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
A (1 + ϵ)‐approximation algorithm for partitioning hypergraphs using a new algorithmic version of the Lovász Local Lemma*
Authors: Salavatipour Mohammad R. 
Published: May 2004

AbstractIn his seminal result, Beck gave the first algorithmic version of the Lovász Local Lemma by giving polynomial time algorithms for 2‐coloring and partitioning uniform hypergraphs. His work was later generalized by Alon, and Molloy and Reed. Recently, Czumaj and Scheideler gave an efficient algorithm for 2‐coloring nonuniform hypergraphs. But the partitioning algorithm obtained based on their second paper only applies to a more limited range of hypergraphs, so much so that their work doesn't imply the result of Beck for the uniform case. Here we give an algorithmic version of the general form of the Local Lemma which captures (almost) all applications of the results of Beck and Czumaj and Scheideler, with an overall simpler proof. In particular, if H is a nonuniform hypergraph in which every edge ei intersects at most |ei|2αk other edges of size at most k, for some small constant α, then we can find a partitioning of H in expected linear time. This result implies the result of Beck for uniform hypergraphs along with a speedup in his running time. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004
Some bounds on the coupon collector problem
Authors: Martinez Servet 
Published: May 2004

AbstractThis work addresses on the coupon collector problem and its generalization introduced by Flajolet, Gardy, and Thimonier. In our main results, we show a ratio limit theorem for the random time of the generalized coupon collector problem, and, further, we give the leading term and the geometric rate for the distribution of this random time, when the number of throws is large. For the classical coupon collector problem, we give a bound on the conditional second moment for the number of visits to the coupons, relying strongly on a result of Holst on extremal distributions. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004
Teaching students “ideas‐about‐science”: Five dimensions of effective practice
Authors: Bartholomew Hannah , Osborne Jonathan , Ratcliffe Mary 
Published: May 2004

AbstractIn this paper, we report work undertaken with a group of 11 UK teachers over a period of a year to teach aspects of the nature of science, its process, and its practices. The teachers, who taught science in a mix of elementary, junior high, and high schools, were asked to teach a set of “ideas‐about‐scienc” for which consensual support had been established using a Delphi study in the first phase of the project. Data were collected through field notes, videos of the teachers' lessons, teachers' reflective diaries, and instruments that measured their understanding of the nature of science and their views on the role and value of discussion in the classroom. In this paper, drawing on a sample of the data we explore the factors that afforded or inhibited the teachers' pedagogic performance in this domain. Using these data, we argue that there are five critical dimensions that distinguish and determine a teacher's ability to teach effectively about science. Whilst these dimensions are neither mutually independent nor equally important, they serve as a valuable analytical tool for evaluating and explaining the success, or otherwise, that individual teachers of science have when confronted with teaching aspects about science. In addition, we argue that they are an important means of identifying salient aspects of pedagogy for initial and in‐service training of science teachers for curricula that incorporate elements of “ideas‐about‐science” © 2004 Wiley Periodicals, Inc. Sci Ed, 88:655–682, 2004
Neurochemical interaction between dopaminergic and noradrenergic neurons in the medial prefrontal cortex
Authors: Pan Wynn H.T. , Yang Sze‐Yuan , Lin Shi‐Kwang 
Published: May 2004

AbstractGrowing evidence indicates that there is an interaction between the transmission of dopamine (DA) and norepinephrine (NE) in the noradrenergic and dopaminergic projections that converge in the medial prefrontal cortex (mPFC). The effects of the noradrenergic α1 and α2 receptors and the NE transporters on the DA outflow and those of the dopaminergic D1 and D2 receptors on NE release in the mPFC were investigated. Local infusions of NE (90, 150, and 300 nM) into the mPFC increased the extracellular release of DA in anesthetized rats. The α1 receptor antagonist (10 μM prazosin), but not the α2 receptor antagonist (100 μM piperoxan), blocked the NE‐induced increase of DA in the mPFC. In addition, local infusion of α1 receptor agonist (10 μM phenylephrine) enhanced DA release in the mPFC. Local application of DA in different concentrations into the mPFC increased extracellular NE levels. Intra‐mPFC infusion of a D1 receptor antagonist (10 nM SCH23390), inhibited the DA‐induced increase of NE; this did not happen with a D2 receptor antagonist (1 nM eticlopride). Local administration of a selective NE uptake inhibitor (1 μM desmethylimipramine) into the mPFC increased the outflows of both DA and NE in the mPFC. However, co‐infusion of DMI and prazosin blunted, but did not totally abolish, the DMI‐increase in the extracellular levels of DA and NE. These results suggest that in the mPFC, 1) extracellular NE could enhance DA release by activating the α1 receptors; and 2) extracellular DA increased the extracellular levels of NE by activating the D1 receptors. Synapse 53:44–52, 2004. © 2004 Wiley‐Liss, Inc.
Development of vigabatrin‐induced lesions in the rat brain studied by magnetic resonance imaging, histology, and immunocytochemistry
Authors: Preece N.E. , Houseman J. , King M.D. , Weller R.O. , Williams S.R. 
Published: May 2004

AbstractVigabatrin, the γ‐aminobutyric acid transaminase (GABA‐T)‐inhibiting anticonvulsant drug, was given orally at a dose of 275 mg/kg/day to rats (n = 6) in their feed for a period of 12 weeks, during which T2‐weighted magnetic resonance images (MRIs) and diffusion‐weighted MRIs (DWIs) were collected at weeks 1, 3, 6, 9, and 12. Half the rats (n = 3; and half their age‐matched littermate controls; n = 3) were then killed for histopathological confirmation of the observed VGB‐induced cerebellar and cortical white‐matter lesions. VGB was removed from the diet and additional MRIs of the remaining rats taken at weeks 14, 17, 20, and 24, at which time they (n = 3), along with remaining controls (n = 3), were also killed for histopathology. The T2‐weighted MRIs acquired were used to compute T2 relaxation time maps. Statistically significant VGB‐induced T2 increases were observed in the frontal and occipital cortices and in the cerebellar white matter (CWM). The cerebellar lesions were more clearly discerned by eye in the DWIs than by T2‐contrast alone. During the recovery period the VGB‐treatment group CWM‐T2 and CWM‐DWI hyperintensity greatly decreased as the reversible lesion disappeared. As expected, histological and immunocytochemical examinations demonstrated the presence of intra‐myelinic edema, microvacuolation, and reactive astrocytosis in the CWM and cortex after 12 weeks VGB‐treatment. In the remaining animals microvacuolation of the white matter had not completely resolved during the 12‐week recovery phase. The data show that quantitative MRI T2‐relaxometry can be used to detect VGB‐induced CNS pathology, and also suggest that DWI is particularly sensitive to the cerebellar lesion. The reversible neurotoxicity of global GABA‐elevation in experimental animals is discussed. Synapse 53:36–43, 2004. © 2004 Wiley‐Liss, Inc.
Unintended consequences of the Global Positioning System
Authors: Lever John A. 
Published: May 2004

AbstractThis article describes a framework for characterizing unintended consequences, especially in terms of the vernacular “Law of Unintended Consequences” as applied to the known and potential consequences of the Global Positioning System (GPS). It is shown that a subset of the unintended consequences related to the GPS belongs to the larger class of general locator devices. The risk of vulnerability of GPS is characterized in terms of impact of unavailability. The general usage or misuse effects are considered in the category of human factors. Privacy is treated in a legal context, and the potential losses of privacy from general locator devices are discussed. Also, legal devices to limit loss of privacy are described, as well as the use of locator devices by law enforcement agencies. The general framework of the article is to describe GPS as a particular case of the larger need to consider secondary consequences in the development and socialization of technology. © 2004 Wiley Periodicals, Inc. Syst Eng 7: 217–228, 2004