bluuebunny/crossref_metadata_2025 huggingface dataset:
The computational complexity of graph contractions I: Polynomially solvable and NP‐complete cases
Authors: Levin Asaf , Paulusma Daniel , Woeginger Gerhard J.
Published: December 2007

For a fixed pattern graph H, let H‐CONTRACTIBILITY denote the problem of deciding whether a given input graph is contractible to H. This paper is part I of our study on the computational complexity of the H‐CONTRACTIBILITY problem. We continue a line of research that was started in 1987 by Brouwer and Veldman, and we determine the computational complexity of the H‐CONTRACTIBILITY problem for certain classes of pattern graphs. In particular, we pinpoint the complexity for all graphs H with five vertices except for two graphs, whose polynomial time algorithms are presented in part II. Interestingly, in all connected cases that are known to be polynomially solvable, the pattern graph H has a dominating vertex, whereas in all cases that are known to be NP‐complete, the pattern graph H does not have a dominating vertex. © 2007 Wiley Periodicals, Inc. NETWORKS, 2008
Immunologische Grundlagen des Impfens. Hightech‐Training für das Immunsystem
Authors: Zündorf Ilse , Vollmar Angelika M. , Dingermann Theo
Published: December 2007

Impfungen simulieren eine Infektion mit einem bestimmten Pathogen und induzieren das Immunsystem. Wird das eingebrachte Antigen effizient über MHC‐Moleküle auf antigenpräsentierenden Zellen den T‐Zellen präsentiert, wird die adaptive Komponente des Immunsystems stimuliert. Der Vorteil daraus ist, dass nun die Immunantwort sehr spezifisch für das Antigen ist und dass ein immunologisches Gedächtnis gebildet wird, das beim Kontakt mit dem echten Pathogen sehr rasch reagieren kann. Verschiedene Impfstoffe und ‐strategien werden inzwischen angewendet, um der breiten Bevölkerung und auch den Spezialfällen der Neugeborenen und Älteren einen umfassenden Schutz vor zahlreichen Infektionskrankheiten zu bieten.
Adjuvantien für Humanvakzinen. Alte und neue Hilfsstoffe
Authors: Bröker Michael , Beyer Christine
Published: December 2007

Bei vielen Vakzinen, die inaktivierte Keime (Viren oder Bakterien) oder definierte Antigene enthalten, gibt die Packungsbeilage den Hinweis, dass das Medikament außer dem Wirkstoff “weitere Bestandteile” oder “Hilfsstoffe” besitzt. Darunter fallen auch Adjuvantien. Adjuvantien modulieren die Immunantwort und tragen wesentlich zur Wirksamkeit, aber auch zur Verträglichkeit der Vakzinen bei.
Reiseimpfungen. Wichtige Tipps für den Urlaub
Authors: Weinke Thomas , Güthoff Wolfgang , Liebold Ines
Published: December 2007

Impfungen gehören zu den wirksamsten Schutzmaßnahmen in der Medizin. Gerade Auslandsreisende setzen sich gegenüber der epidemiologischen Situation in Deutschland zusätzlichen Infektionsrisiken aus. Daher gehören zu den Vorbereitungen für eine Auslandsreise Reiseimpfungen essentiell zum Beratungsstandard.
Nobelpreis für die Etablierung von Knock‐out‐Mäusen
Authors: Winckler Thomas
Published: December 2007

Genetisch gezielt veränderte Mäuse werden in vielen Bereichen der biomedizinischen Grundlagenforschung als Modelle für humane Krankheiten eingesetzt und haben die Aufklärung von Pathogenitäts‐Mechanismen und die Entwicklung neuer Therapiestrategien revolutioniert.
Preparation and release behavior of temperature‐ and pH‐responsive chitosan material
Authors: Guo Bao‐Lin , Yuan Jin‐Fang , Gao Qing‐Yu
Published: December 2007

BACKGROUND: Chitosan is a polymer with good biocompatibility which makes it promising for potential applications in the field of drug delivery. A novel kind of copolymer, P(CS‐Ma‐graft‐NIPAm), was synthesized with chitosan (CS), maleic anhydride (Ma) and N‐isopropylacrylamide (NIPAm) by grafting and copolymerization.

RESULTS: The copolymers were characterized using Fourier transform infrared, 1H NMR and ultraviolet spectroscopies, and the molecular weight and polydispersity were determined using gel permeation chromatography. The aqueous solution properties of the copolymer and the controlled delivery of coenzyme A from it were also studied. The results showed that the copolymer had temperature and pH sensitivities, and that the release of coenzyme A from the copolymer was dependent on the release medium, namely the concentration of the copolymer, pH and temperature. Higher concentrations of the copolymer absorbed more coenzyme A than lower ones. Increasing temperature accelerated coenzyme A release from the copolymer. Also, the pH of the solution had a significant impact on the release of coenzyme A.

CONCLUSION: These results suggest that the novel copolymer could be used in drug delivery systems. Copyright © 2007 Society of Chemical Industry
Characterization of nanocellulose‐ reinforced shape memory polyurethanes
Authors: Auad María L , Contos Vasili S , Nutt Steve , Aranguren Mirta I , Marcovich Norma E
Published: December 2007

BACKGROUND: Shape memory polymers are capable of fixing a transient shape and of recovering their original dimensions by the application of an external stimulus. Their major drawback is their low stiffness compared to smart materials based on metals and ceramics. To overcome this disadvantage, nanocellulose was utilized as reinforcement.

RESULTS: Composites were prepared by casting stable nanocellulose/segmented polyurethane suspensions. The heat of melting of the polyurethane soft segment phase increased on cellulose addition. Composites showed higher tensile modulus and strength than unfilled films (53% modulus increase at 1 wt% nanocellulose), with higher elongation at break. Creep deformation decreased as cellulose concentration increased (36% decrease in 60‐minute creep by addition of 1 wt% nanocellulose). The nanocomposites displayed shape memory properties equivalent to those of the neat polyurethane, with recoveries of the order of 95% (referred to second and further cycles).

CONCLUSIONS: It is possible to markedly improve the rigidity of shape memory polymers by adding small amounts of well‐dispersed nanocellulose. However, this improvement did not have substantial effects on the material shape fixity or recovery. Shape memory behavior seems to continue to be controlled by the polymer properties. Copyright © 2007 Society of Chemical Industry
pH‐/temperature‐sensitive supramolecular micelles based on cyclodextrin polyrotaxane
Authors: Huang Jin , Ren Lixia , Chen Yongming
Published: December 2007

BACKGROUND: Based on the assembly strategy induced by host‐guest recognition in weak selective solvent, a kind of supramolecular nano‐micelles has been self‐organized from a water‐soluble diblock copolymer, poly(ethylene oxide)‐block‐poly(acrylic acid) (PEO‐b‐PAA), selectively included by ‐cyclodextrins (‐CDs).

RESULTS: The spontaneous aggregation of rod‐like ‐CD/PEO‐based pseudo‐polyrotaxanes (pseudo‐PRs) drove the formation of square‐piece in aqueous media and thereafter evolved to spherical assemblies with or without hollow structure as time prolonged, which were stabilized by uncovered hydrophilic PAA segments. Such morphological evolvement attributed to hydrogen bonding between ··CCOOH in PAA and ··COH in ‐CD. However, when alkaline media was used to inhibit hydrogen bonding by ionizing ··CCOOH, the assemblies were only uniform spheres of ca. 100 nm. Meanwhile, the order stacking of PR rods became the basic building units all the time. Herein, the supramolecular PRs contributed to temperature‐response character, namely the formation of assemblies is reversible stimulated with temperature changes. Additionally, the inhibition of deceasing pH to the ionization of free PAA segments made assemblies fuse as microspheres.

CONCLUSION: Such pH‐ and temperature‐sensitivity as well as the biocompatibility of components and water as media make a great potential of such nano‐particles as the biomedical materials with controlled‐release function. Copyright © 2007 Society of Chemical Industry
Effect of compatibilizer on the dispersion of untreated silica in a polypropylene matrix
Authors: Zoukrami Fouzia , Haddaoui Nacereddine , Vanzeveren Celine , Sclavons Michel , Devaux Jacques
Published: December 2007

BACKGROUND: A new processing method for polypropylene–untreated precipitated silica (PP/SiO2) composites based on the incorporation of a second polymer phase of polyamide 6 (PA6) is presented and compared with a more classic one making use of compatibilizers: glycerol monostearate (GMS), ethylene acrylic acid ionomer (IAAZE) and maleic anhydride grafted polypropylene (MA‐graft‐PP). The effects of processing methods and conditions on the microstructure and properties of PP/SiO2 composites prepared by melt compounding are investigated with a view to reduce the size of aggregates of silica from the micrometre to the nanometre scale and to improve the link between filler and matrix.

RESULTS: On the one hand, the presence of GMS and IAAZE compatibilizers significantly improves the dispersion of the silica particles. On the other hand, when using a PA6 second phase, the SiO2 particles are dispersed in PA6 nodules. Within these nodules, SiO2 appears dispersed at the nanoscale but with larger particles (‘aggregates’) of about 200 nm. Significant improvements in tensile strength and modulus are obtained using MA‐graft‐PP compatibilizer. An increase in impact strength is observed in the case of GMS compatibilizer. Thermal parameters indicate also that silica plays the role of nucleation agent for PP matrix. All improvements (tensile strength, modulus and impact strength) increase with the addition of compatibilized PA6 second phase.

CONCLUSION: By the incorporation of masterbatch of silica in PA6 as a second polymer polar phase, a successful new production method for PP/SiO2 nanocomposites has been developed. Interestingly, this method does not require any (expensive) pre‐treatment of the silica. Copyright © 2007 Society of Chemical Industry
Effect of the regioregularity of poly(3‐hexylthiophene) on the performances of organic photovoltaic devices
Authors: Urien Mathieu , Bailly Loïc , Vignau Laurence , Cloutet Eric , de Cuendias Anne , Wantz Guillaume , Cramail Henri , Hirsch Lionel , Parneix Jean‐Paul
Published: December 2007

BACKGROUND: The highest efficiencies of bulk‐heterojunction solar cells from poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) reported so far are close to 6%. Phenomena occurring during the photovoltaic process, such as the creation, diffusion and separation of excitons, as well as charge carrier transport, are governed by the active layer morphology. The latter phenomenon, which depends on the self‐organization of P3HT, can be influenced by its degree of regioregularity. The aim of this work is to clarify the relationship between the regioregularity of P3HT, the composition of P3HT/PCBM blends and the performances of photovoltaic devices.

RESULTS: Two types of P3HTs with different degrees of regioregularity have been synthesized and used as active layers with PCBM in photovoltaic cells. The higher performances in photovoltaic devices are obtained for high‐regioregular P3HT and can be explained considering the self‐organizing properties of high‐regioregular P3HT, leading to higher sunlight absorption and higher hole mobilities. In addition, this report demonstrates the importance of the ratio of P3HT versus PCBM in correlation with the regioregularity of P3HT on the optical properties, charge transport and characteristics of photovoltaic cells.

CONCLUSION: We have investigated the dependence of the photovoltaic properties of P3HT/PCBM blend‐based photovoltaic devices on the degree of regioregularity of P3HT. We find that the best performance is exhibited by devices based on highly regioregular P3HT. Also, the best performances are not obtained for the same P3HT:PCBM weight ratios for high‐regioregular P3HT (1:0.8) and low‐regioregular P3HT (1:3). Copyright © 2007 Society of Chemical Industry
Resistance to glyphosate from altered herbicide translocation patterns
Authors: Preston Christopher , Wakelin Angela M
Published: December 2007

Glyphosate‐resistant weeds have evolved as a result of the intensive use of glyphosate for weed control. An alteration in the way glyphosate is translocated within the plant has been identified as a mechanism of glyphosate resistance in populations of Lolium rigidum Gaud., L. multiflorum Lam. and Conyza canadensis (L.) Cronq. In these resistant plants, glyphosate becomes concentrated in the leaves rather than being translocating throughout the plant. This type of resistance is inherited as a single dominant or semi‐dominant allele. Resistance due to reduced translocation appears to be a common mechanism of resistance in L. rigidum and C. canadensis, probably because it provides a greater level of resistance than other mechanisms. This type of glyphosate resistance also appears to reduce the fitness of plants that carry it. This may influence how glyphosate resistance can be managed. Copyright © 2007 Society of Chemical Industry
Recoil hysteresis and temperature dependence of coercivity of Nd4Fe73.5Co3Hf0.5Ga0.5B18.5
Authors: Manjura Hoque S. , Hakim M. A. , Khan F. A. , Nghi N. H.
Published: December 2007

Recoil hysteresis and temperature dependence of coercivity have been measured for the sample of composition Nd4Fe73.5Co3Hf0.5Ga0.5B18.5 prepared by rapid quenching method with a wheel speed of 25 m/s and after subsequent annealing in an evacuated quartz tube under a pressure of 10–5 mbar at different temperatures and times. In the optimum and over‐annealed condition, recoil hysteresis loops have been measured by the application of progressively increasing negative field and successive withdrawal to the remanence and found to have steep recoil loop and small recoil area, which is characteristic to exchange‐biased system. Temperature dependence of coercivity in the range of 5 K to 380 K has been measured for the sample of composition Nd4Fe73.5Co3Hf0.5Ga0.5B18.5. Variation in the shape of the hysteresis loop has been observed in this temperature range. In the low temperature region i.e. below 150 K hysteresis loops are constricted due to spin reorientation of Nd2Fe14B at 135 K while above this temperature the hysteresis loops are characterized by convex M (H) curve similar to single‐phase permanent magnet. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microwave transmission loss in multi‐walled nanotubes
Authors: Jun S. C. , Cha S. N. , Lee S. , Jang J. E. , Jin Y. W. , Kim H. J. , Hone J. , Kim J. M.
Published: December 2007

Experimental results for microwave transmission losses of individual multi‐walled carbon nanotubes (MWNTs) are presented. Samples with MWNTs, as well as samples with‐out MWNTs, were fabricated with two types of electrode materials (Nb vs. Cr/Au) and configurations to compare AC transmissions loss as passive devices at room temperature. In the MWNT‐Nb samples, the transmitted current is higher and attenuation is lower than the MWNT‐Cr/Au samples. However, the transmission loss increases much faster in the Nb samples than Cr/Au samples with increasing frequency. Overall, their S ‐parameter measurements from 0.5 GHz to 110 GHz support frequency‐dependent microwave dissipation of the MWNTs and the metal‐electrode contact. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Retraction: Relaxor or classical ferroelectric behavior in A site substituted perovskite type Ba1–x(Sm0.5Na0.5)x TiO3
Authors: Abdelmoula N. , Chaabane H. , Khemakhem H. , Von der Mühll R. , Simon A.
Published: December 2007

The authors wish to retract their article in phys. stat. sol. (a) 203, 987 (2006). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI 10.1002/pssa.200521465
Size effect on NiFe/Cu/NiFe/IrMn spin‐valve structure for an array of PHR sensor element
Authors: Oh S. J. , Le Tuan Tu , Kim G. W. , Kim CheolGi
Published: December 2007

Conventional NiFe/Cu/NiFe/IrMn multilayer spin‐valve structure is used for patterning planar Hall effect (PHE) sensor fabrication. The three different junctions, 50×50 μm2, 20×20 μm2 and 5×5 μm2, were prepared by lithography technique for obtaining the PHE profiles. The PHE measurements were carried out for all three junctions using four probe methods. Increased sensitivities are obtained for smaller patterned junctions, while recording a value of 13.45 μV/Oe being the maximum sensitivity for 5×5 μm2 junction. The magnetic properties of the spin valves are characterized by vibrating sample magnetometer (VSM) to know the influence of exchange bias field on PHE signal. Structural and compositional aspects were examined by transmission electron microscopy (TEM) and energy dispersive spectrometer (EDX), which revealed that the diffusion of Cu layer into the magnetic layers indirectly helps PHE signal by bringing modifications to the anisotropy and coercivity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Order‐disorder transition and magnetic properties of Fe‐6.5Si alloy powder cores
Authors: Jang Pyungwoo , Lee Bonghan , Choi Gwangbo
Published: December 2007

Magnetic properties of Fe‐6.5%Si powder compact cores were analyzed when cores were annealed at 400 – 800 °C for up to 960 min. Hysteresis losses were larger than eddy current lossed in all cores. With increasing annealing temperature core loss decreased while eddy current loss showed minimum when annealed at 500 °C. Variation of DC and AC magnetic properties with annealing temperature and time could be successfully explained by order‐disorder transition, magnetostriction, resistivity, lubricant burn‐off, and surface oxidation of particles. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrochemical preparation of Co3Pt nanowires
Authors: Min Ji Hyun , Wu Jun Hua , Cho Ji Ung , Lee Ju Hun , Ko Young‐Dong , Liu Hong‐Ling , Chung Jin‐Seok , Kim Young Keun
Published: December 2007

Fabrication of Co‐Pt nanowire arrays with fcc‐Co3Pt phase was accomplished by DC electrodeposition in anodic aluminum oxide (AAO) nanotemplates. The microstructural and magnetic properties of the nanowires were investigated as a function of the deposition current density (Co concentration). The nanowires possess fcc‐Co3Pt phases and are ferromagnetic. Their crystallinity and magnetic performance was enhanced after annealing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrochemical synthesis of compositionally modulated NiFe nanowires
Authors: Rheem Youngwoo , Yoo Bongyoung , Koo Bon Keup , Myung Nosang V.
Published: December 2007

The compositionally modulated NiFe nanowires (200 nm in diameter) were electrodeposited from acidic chloride baths using anodized aluminas as scaffolds. Thin films were initially electrodeposited on copper substrates to investigate the effect of various electrodeposition parameters on film composition and microstructure. Film composition was strongly influenced by temperature and current density. At 40 °C, the composition was singificantly altered by current density. For example, body centered cubic Ni20Fe80 and faced centered cubic Ni80Fe20 thin films were electrodeposited at 5 and 20 mA cm–2, respectively. Based on thin film studies, the compositional modulated Ni80Fe20/Ni20Fe80 nanowires were synthesized by applying current pulses between 5 and 20 mA cm–2. The layer thickness was controlled down to tens of nm by adjusting the deposition time. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin accumulation and magnetotransport in Co–Al–Co single‐electron transistors
Authors: Shyu J. H. , Chen J. W. , Yao Y. D. , Wu J. K.
Published: December 2007

The bias‐voltage dependent oscillations of the magnetoresistance in Co‐Al‐Co single‐electron transistors have been investigated. Above the critical voltage comprising of superconducting gap and the charging energy, the conductance‐voltage characteristics show an oscillatory behavior with increasing bias‐voltage, resulting from the Coulomb staircase. We demonstrate that magnetoresistance could vary periodically from positive to negative values with bias‐voltage. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Planar Hall resistance sensor for biochip application
Authors: Thanh N. T. , Parvatheeswara Rao B. , Duc N. H. , Kim CheolGi
Published: December 2007

In this work, we introduce a new type of sensor by using planar Hall effect in spin valve structure for biochip application due to advantage of increasing sensor sensitivity. A single Dynabeads® M‐280 Streptavidin detection has been accomplished with the sensor pattern size of 3 × 3 µm2 that was fabricated from NiFe(6.0 nm)/Cu(3.5 nm)/NiFe(3.0 nm)/IrMn(10.0 nm) spin valve structure. Furthermore, it is also developed to integrated arrays by including 24 sensor patterns. In comparison with the other groups, our sensor performance is highlighted with the advantages of increased stability and high signal to noise; as such, the planar Hall effect sensor's behavior has proved a possibility for detection of the biomolecule. It is also feasible to provide a vehicle for studying other molecule interactions, particular single DNA molecule and for the detection of binding of the streptavidin functionalized magnetic beads to sensor bound biotin. Due to the simple fabrication scheme, this kind of Planar Hall effect based sensor can be easily integrated into other systems for applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of external magnetic field on magnetic properties and surface morphology of electrodeposited CoFeNi alloys
Authors: Kim Hyun Kyung , Chun Dong Won , Han Jun Hyun , Kim Kwang Bum , Jeung Won Young
Published: December 2007

The magnetic properties and surface morphology of CoFeNi alloy films electrodeposited under external magnetic field were investigated. It was observed that crystallographic anisotropy in CoFeNi films was induced due to the preferential orientation of applied magnetic field. In addition, the CoFeNi alloy films showed excellent magnetic property (low Hc), which is considered that not only the smaller grain size of the films, but also more uniform surface of the films than that deposited in absence of applied magnetic field. These observed phenomena could be explained with magneto‐hydrodynamic (MHD) convection of charged ions at the interface of electrode and electrolyte induced by Lorentz force. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bulk anisotropy Nd‐Fe‐B/α‐Fe nanocomposite permanent magnets prepared by sonochemistry and spark plasma sintering
Authors: Niu Peili , Yue Ming , Li Yongli , Huang Wei , Zhang Jiuxing
Published: December 2007

NdFeB/α‐Fe nanocomposite magnetic powders were prepared by sonochemical process. The powders were then submitted to a hot press and subsequent hot deformation process by spark plasma sintering (SPS) technique. Effect of α‐Fe content on structure and magnetic properties of both isotropic and anisotropic magnets was investigated. For hot pressed magnets, the remanence increases with the content of α‐Fe, while the coercive force drops simultaneously. After hot deformation, the magnets with no more than 2 vol% α‐Fe exhibit obvious anisotropic characteristic. For the magnets with more α‐Fe, however, the magnetic anisotropy disappears due to the absence of (00l) crystal texture after deformation. It is, therefore, expected that α‐Fe content plays an important role in the formation of C‐axis crystal texture during hot deformation process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhancing radioactive magnetic properties in monodispersed MFe2O4 nanoparticles
Authors: Park S. I. , Lim J. H. , Hwang Y. H. , Kim J. H. , Kim C. G. , Kim C. O.
Published: December 2007

The monodispersed hydrophilic magnetic fluids with nanometric M‐ferrite (M=Cu, Co, Ca, Ni) particles were prepared by sonochemical method. The substituted amounts of M elements were analyzed with different x values by ICP‐AES quantitatively for MxFe3‐xO4 particles. The biological tests were performed to observe the proper dosage and the toxicity by using S.D. rat with different core sources. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inverse giant magnetoresistance due to spin‐dependent bulk scattering in Fe1–xCrx/Cu/Co
Authors: Thi Ngoc Anh Nguyen , Thi Hoang Yen Nguyen , Yi Hyunjung , Joo Sung‐Jung , Shin Kyung‐Ho
Published: December 2007

Inverse giant magnetoresistance (IGMR) can be observed in multilayers with alternating two ferromagnetic layers F1 and F2 possessing opposite spin scattering asymmetries. We report here the observation of inverse current‐in‐plane giant magnetoresistance (CIP‐IGMR) in Fe1–xCrx/Cu/Co spin‐valve systems with varying Cr concentration and FeCr‐layer thickness. The highest magnitude of IGMR, –0.45%, has been achieved in the sample doped with 35 at.% Cr. It is shown that the proper substitution of Cr for Fe can alter spin‐dependent scattering in the Fe layer, causing the inversion of the bulk spin scattering asymmetry coefficient therefore resulting in CIP‐IGMR. The GMR has a dominant contribution to the observed inverse MR, rather than the anisotropic magnetoresistance (AMR) component. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromagnetic simulation of critical fields of rectangular and elliptical cells for the toggle‐mode magnetic random access memory
Authors: Kim K. S. , Lim S. H.
Published: December 2007

A micromagnetic simulation is carried out to examine the effects of the shape of exchange‐coupled trilayer cells on the magnetization switching behavior, in an effort to reduce the switching field in the toggle‐mode magnetic random access memory. Two different shapes of rectangular and elliptical cells are considered. The switching behavior of the elliptical cells shows a qualitative agreement with the single domain model for 3D ellipsoids. However, the magnetization‐flop field differs significantly, except for the small aspect ratio and the thickness asymmetry of the two magnetic layers. For the rectangular cells, the switching behavior differs significantly, particularly at a small aspect ratio, due to very strong demagnetizing fields, causing to form end domains. As the aspect ratio increases, the magnetization‐flop field increases while the saturation field decreases. This opposite dependence of the two critical fields on the aspect ratio results in the decrease in the write window margin with increasing aspect ratio. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Giant magnetoimpedence effects in micro‐patterned Co52Fe32B11Si5 amorphous ribbons
Authors: Park Sun Hee , Chun Dong Won , Han Jun Hyun , Kim Young‐Ho , Jeung Won Young
Published: December 2007

We report the giant magnetoimpedence (GMI) effect in Co52Fe32B11Si5 amorphous ribbon micro‐patterned using photolithography and wet etching process. The effects of AC frequency and amplitude on GMI characteristics are investigated in our micro‐patterned GMI devices. Furthermore, it is shown that thickness of patterned ribbon plays a significant role on the GMI behaviour and response condition of AC frequency and amplitude. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nondestructive testing for metallic flaws using inductive coil sensor with circular typed single loop excitation coil
Authors: Kim Ki Hyeon , Lee Jun Sik , Kim Nanyong , Jang Doguen , Kim Young Ho , Kim Jongryoul
Published: December 2007

AC magnetic field was used for the detection of flaws on surface of the conductive specimens. The nondestructive sensor probe was composed of the magnetic yoke coil as a sensing component and exciting single line coil. The excitation coil generated the AC magnetic fields with the frequency of around 27 kHz which were applied to the specimen with artificial flaws. The specimens were prepared with the various shape (slit and hole), size (minimum depth and width; 0.5 mm) of artificial flaws on each of material (Al, Cu; nonmagnetic metal, Fe, FeC; magnetic metal), respectively. The signal for the positions and shapes of surface flaws on metallic specimens were detected with high sensitivity with signal to noise ratio of over 15 by the magnetic yoke typed search coil. The images of flaws were obtained by measured output signal, which results were good coincidence with real flaws. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exchange coupling in FePt‐FePt3 nanocomposite films
Authors: Lin K.‐W. , Guo J.‐Y. , Liu C.‐Y. , Ouyang H. , van Lierop J. , Phuoc N. N. , Suzuki T.
Published: December 2007

In this study, the structural and magnetic properties of exchange coupled nanocomposite FePt‐FePt3 films were investigated. X‐ray diffraction and transmission electron microscopy results showed that after rapid thermal annealing (600 °C for 6 minutes), a phase transformation from [Pt+Fe] into composite FePt‐FePt3 phases was obtained. Annealing created an ordered FePt phase that resulted in a large room temperature coercivity (Hc ∼ 3200 Oe) compared to the as‐deposited film (Hc ∼ 20 Oe). While no exchange bias field (Hex ∼ 0 Oe) was measured at room temperature, the annealed sample showed significant Hex ∼ ‐500 Oe at lower temperatures (150 K ≤ T ≤ 250 K), indicative of exchange coupling between FePt and FePt3. The high blocking temperature (∼250 K) indicates FePt3 exhibits an enhanced Néel temperature. Further increasing the annealing temperature to 700 °C resulted in a reduction of Hex which is attributed to the transformation of FePt3 into the FePt phase at this higher annealing temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of transient annealing on patterned CoFeB‐based magnetic tunnel junctions
Authors: Wu Kuo‐Ming , Huang Chao‐Hsien , Lin Shiao‐Chi , Kao Ming‐Jer , Tsai Ming‐Jinn , Wu Jong‐Ching , Horng Lance
Published: December 2007

In this study, the transient annealing effect on the switching behavior of microstructured Co60Fe20B20‐based magnetic tunnel junctions has been studied through magnetoresistacne measurements (R‐H loop). Elliptical shape of devices with long/short axis of 4/2 micrometers was patterned out of sheet film stack of: Ta (20)/ PtMn (15)/ CoFeB (3)/ Al (0.7)‐oxide/ CoFeB (2)/ Ru (8)/ Ta (40) (thickness unit in nanometers) after a conventional long time field cooling annealing. The transient annealing was then executed by sample loading into a furnace with pre‐set temperatures ranging from 100 to 400 °C for only 5 minutes in the absence of any external magnetic field. The vortex‐like reverse of free layer in as‐etched MTJ evidently changes to single‐domain‐like reverser after 200∼250 °C transient annealing. The magnetoresistance was found to increase with increasing annealing temperatures up to 265 °C and then slowly decrease at higher annealing temperatures. The transient thermal annealing creates obvious efforts to repair magnetic properties of MTJ cell befor 265 °C annealing and results in less damage at temperature of 350 °C and 400 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coating of magnetic particle with polystyrene and its magnetorheological characterization
Authors: Kim Yoon Hee , Park Bong Jun , Choi Hyoung Jin , Seo Yongsok
Published: December 2007

Magnetic composite particles were prepared via dispersion polymerization of styrene in the presence of γ‐Fe2O3 nanoparticles. The fabricated magnetic composite nanoparticles were dispersed into non‐magnetic suspending media to be adopted for magnetorheological (MR) fluid, whose rheological properties can be drastically changed in the external magnetic field. The MR efficiency of γ‐Fe2O3/polystyrene composite based fluid was examined by a rotational rheometer equipped with a magnetic field supplier. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polymeric nanobead coated carbonyl iron particles and their magnetic property
Authors: Fang Fei Fei , Choi Hyoung Jin
Published: December 2007

Magnetic carbonyl iron (CI) particles have attracted great attention due to their high saturation magnetization and appropriate particle size for magnetorheological (MR) materials. However, hydrodynamic instability of the CI particle suspension which was attributed to the large density mismatch between the dispersed CI particles and the medium has affected its predominant role for MR applications. A novel magnetic CI/polystyrene (PS) composite with nano‐scaled PS spheres sprinkled on the surface of the CI particles was fabricated via a normal dispersion polymerization in this work. Physical properties, MR behaviors as well as the improvement in sedimentation problem were investigated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromagnetic study of magnetization reversal in patterned DyFeCo thin films
Authors: Lee Ching‐Ming , Ye L. X. , Lee J. M. , Wu Te‐Ho
Published: December 2007

Magnetization reversal in patterned perpendicular anisotropic DyFeCo films was investigated using micromagnetic simulations. The model consists of a square film of dimension 1 μm × 1 μm × 50 nm and a circular hole of diameter 500 nm on the top surface, with depth varying from 0‐30 nm. The results show that for shallower holes the coercivity decreases rapidly with the hole depth, but for the deeper holes, the coercivity in the hole region is much larger than in the land region. Further analysis indicates the variation in coercivity is due to the narrow transition region formed near the hole boundary where the magnetization has a tilted distribution determined mainly by the competition between anisotropy and exchange interactions. The simulation results are qualitatively consistent with our previous experimental outcome. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐frequency noise absorbing properties of nickel nanowire arrays prepared by DC electrodeposition
Authors: Jeong Jong‐Hyun , Kim Sun‐Hong , Min Ji Hyun , Kim Young Keun , Kim Sung‐Soo
Published: December 2007

Nickel nanowire arrays are fabricated by electrochemical deposition in highly ordered nanosized pores in AAO (anodized aluminum oxide) templates, and their static and high‐frequency noise absorbing properties have been investigated. Using the channelled AAO templates, a nickel nanowires array was fabricated by DC electrodeposition. Magnetic hysteresis was observed with a coercivity of 250∼300 Oe depending on the field orientation with respect to wire axis. Noise absorbing properties of the nickel nanowires array was measured using the microstrip line. S11 parameter increases with frequency and reaches a saturated value of about ‐10 dB. The reflected power (about 10%) is much less than that of nickel thin film (about ‐3 dB), which is due to higher in‐plane electrical resistance of the nanowire array structure. S21 decreases with frequency and has a value of ‐3 dB at 2 GHz. The attenuation of conduction noise through microstrip line is due to the magnetic loss of individual nickel nanowires. Power absorption of the Ni nanowire array was estimated to be 50% in the frequency range above 2 GHz. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructure study of the Co‐added FePt thin films with high energy density
Authors: Yuan F. T. , Hsiao H. N. , Chen S. K. , Chang H. W. , You K. L. , Yao Y. D.
Published: December 2007

Microstructure, crystal structure, and magnetic properties of the Fe49–xCoxPt51 (x = 0, 0.7, 1.3, 2.2) thin films deposited on glass substrates were investigated. The addition of Co was found to enhance the magnetization of the FePt L l0 phase, thus increases the energy product, (BH)max. A maximum value of (BH)max of 18.4 MGOe was obtained in the sample with x = 1.3 annealing at 500 °C. The microstructure results indicated that significant grain refining was found in the x = 2.2 sample, which reduced from averagely 60 nm for the x = 0.0∼1.3 sample to 30 nm. The concentration of Co was uniform in the Fe‐Pt‐Co film except x = 1.3 film, in which small grains with 10∼20 nm in diameter showed higher percentage of Co. Corresponding to the compositional inhomogeneity, X‐ray structural analysis revealed that the x = 1.3 film contained about 20 vol.% disordered fcc phase, which was much higher than the other composition samples (<7 vol.%). The exchanging coupling between the ordered and disordered phase can explain the enhanced magnetic properties. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic pinning‐effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 bilayer
Authors: Hsu Daniel , Lin J. G. , Wu W. F.
Published: December 2007

The vortex lines of superconductor can be driven by electrical currents, which are often coupled with a reliable control of flux quanta movement by defects or magnetic domains. In this work, the magnetic pinning‐effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers is investigated. It is found that by increasing the field from 0 to 5 Tesla, the critical current Ic of pure YBCO film at 50 K is suppressed by three orders of magnitude. However, in the NCMO/YBCO bilayer Ic is less sensitive to the field and maintains at the level of 100 mA at high field. This result indicates that the magnetic pining effect of NCMO is much more efficient than the conventional routes, which maybe related to the fine domain structure of NCMO film. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Compensation of native defects in PbTe and Pb1–xSnxTe
Authors: Babentsov V. N. , Sizov F. F.
Published: December 2007

Semi‐insulation of the narrow‐gap IV–VI semiconductor compounds PbTe and Pb1–xSnxTe used for infrared optoelectronic applications was investigated technologically and theoretically. Practically important cases in which the concentration of native defects greatly exceeds the intrinsic concentra‐ tion of free carriers due to the growth conditions are discussed. In particular, doping conditions for the semi‐insulation are determined for Cd, In and Ga compensating impurities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optically and electrically induced dissipation in quantum Hall systems
Authors: Nachtwei G. , Stellmach C. , Vasile G. , Hein G.
Published: December 2007

We have studied the onset of dissipation in quantum Hall systems (QHSs), patterned in various geometries (Hall bars, meanders and Corbino rings) from wafers with heterojunctions (GaAs/GaAlAs) and HgTe quantum wells with adjacent HgCdTe barriers. The QH samples were excited by electrical pulses with pulse durations tP of 0.5 ns ≤ tP ≤ 180 ns or by illumination with electromagnetic waves of 1.7 THz ≤ f ≤ 2.5 THz. These waves were either emitted coherently by a pulsed p‐Ge laser system or by a thermal source. In the case of excitation by electric pulses, it is necessary to exceed a certain critical pulse length $ t ^{\rm c}_{\rm P} $ which is a function of various extrinsic parameters and sample properties. For $ t _{\rm P} < t ^{\rm c}_{\rm P} $ no dissipation occurs inside the QHSs. Also, using THz illumination, the QHSs can be driven to dissipation. We found different mechanisms to be responsible for the photoresponse (PR) of the QHSs: non‐resonant (bolometric) and resonant (cyclotron resonance) contributions to the PR of the QHSs. First attempts to develop a quantitative model for the observed data are made. We are able to describe a part of the observations by either a drift model or a two‐level model. The quantitative agreement of these calculations with the measured data is, however, limited. This is due to the simplicity of the models applied so far and to the complex behaviour of QHSs when nonlinearly excited. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of electronic transport in the integer quantum Hall regime
Authors: Hohls Frank , Sukhodub Gennadiy , Haug Rolf J.
Published: December 2007

We examine different aspects of the dynamics of electronic transport in the integer quantum Hall effect. In the first part the quantum Hall plateau transition is studied. We present experimental results which confirm a universal scaling behaviour near the critical point of this quantum phase transition between adjacent quantum Hall phases. The second part focuses on the transport properties of quantum Hall edge channels. We use selective detection of individual channels to proof the existence of an inter‐edge magneto plasmon mode. Furthermore we study the equilibration between spin polarised edge channels at very high magnetic fields. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Penetration depth anisotropy in cuprates with pseudogap
Authors: Ghosh Angsula
Published: December 2007

We study the penetration depths along the a (λa), b (λb) and c (λc)‐axes in the presence of the pseudogap and d superconducting phases (DSC) in a simple model for cuprates. The pseudogap phase is addressed within the framework of the ordered d ‐density wave (DDW). The above scenario is considered using a mean‐field calculation of the tight binding model which incorporates two layers – a CuO2 plane and a CuO chain per unit cell. The CuO chains become superconducting due to the proximity to the planes below the critical temperature. Moreover our model includes a momentum dependent chain‐plane coupling. We observe distinct behaviors for the penetration depth results along the three directions which is consistent with the anisotropy observed in the experimental results. The temperature dependence of λc is ex‐ actly the same as that of the recent experimental results as demonstrated for Tc = 18 K in the underdoped region. We observe a qualititave difference in the temperature dependence of λa and λb when compared to our previous studies. However the phase diagram due to the inclusion of the momentum dependence of the coupling suffers no significant variation. The main result of our work then is that a simple proximity DDW model in which the pairing interaction is localized to the planes and the planes are coupled to the chains through a momentum dependent term can account for many observed experimental properties. The inclusion of the pseudogap and also the value of the chain‐plane coupling modifies the general trend of our results when compared to the simple DSC model without the coupling. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Half‐metallic ferromagnetism in wurtzite SrC
Authors: Zhang Chang‐wen , Yan Shi‐shen , Li Hua
Published: December 2007

The first‐principles full potential linearized augmented plane‐wave method within density‐functional theory is used to investigate electronic structure and magnetism of wurtzite (WZ) crystal structure SrC. It is shown that the WZ SrC is a true half‐metallic ferromagnet with a magnetic moment of 2μB per formula unit. The large HM gaps (0.72 eV) and robustness of half‐metallicity with respect to the lattice change make it possible candidate grown epitaxially on appropriate substrates in the form of films thick enough, and therefore should be useful in spintronics and other related applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and electronic properties of few‐layer graphenes from first‐principles
Authors: Huang J.‐R. , Lin J.‐Y. , Chen B.‐H. , Tsai M.‐H.
Published: December 2007

The first‐principles calculation method has been used to obtain structural and electronic properties of few‐layer graphenes (FLG's) with and without a cross‐film external electric potential, Vext. It is found that the AB stacking is more favorable than the AA stacking and the calculated layer spacing for the two‐layer AB stacked FLG is only 2.725 Å, which is substantially reduced from that of the bulk graphite of 3.257 Å. The two‐layer AB stacked FLG is found to exhibit a semi‐metal–semiconductor transition under Vext qualitatively in agreement with previous studies. However, the energy gap, Eg, is not limited at 0.3 eV as obtained in previous first‐principles calculation due to the reduced interlayer spacing. The threshold of the semi‐metal–semiconductor transition is 0.04 Volts. Vext also induces Eg's in 3‐ and 4‐layer AB stacked FLG's. However, in these FLG's the induced Eg's are small within 0.1 eV. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural, electronic and optical properties of II–IV–N2 compounds (II = Be, Zn; IV = Si, Ge)
Authors: Shaposhnikov V. L. , Krivosheeva A. V. , Arnaud D'Avitaya F. , Lazzari J.‐L. , Borisenko V. E.
Published: December 2007

A detailed study of structural, electronic and optical properties of II–IV–N2 ternary compounds (II = Be, Zn; IV = Si, Ge) has been performed by means of ab initio density functional theory calculations. The germanium containing compounds were found to be direct‐gap semiconductors with gaps of 3.37 eV and 1.67 eV for BeGeN2 and ZnGeN2, respectively, with oscillator strength of direct transition comparable to GaN. Two other silicon containing compounds are characterized by indirect gaps of 5.19 (3.32) eV for BeSiN2 (ZnSiN2). Crystal structure being orthorhombic and lattice parameters for BeSiN2 and ZnSiN2 are in good agreement with the available experimental data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Why are spin wave excitations all important in nanoscale magnetism?
Authors: Baberschke Klaus
Published: December 2007

For a proper interpretation of magnetic phenomena in low dimensional magnets, higher order spin wave excitations are more important than in bulk magnetism. Three different types of experiments will be discussed: (i) In a so‐called trilayer, two ferromagnetic films are coupled via a nonmagnetic spacer: FM1/ NM/FM2. The individual Curie temperatures can be shif‐ ted by 50 K or 100 K, just by tuning the NM thickness. This is impossible in 3D. (ii) Spin‐wave excitations are the major route to understanding the T‐dependence of the interlayer exchange coupling (IEC). (iii) The standard Gilbert damping is insufficient to describe the spin dynamics in nanomagnets. Magnon–magnon scattering, a reversible process in the magnetic subsystem, must first be disentangled in the spin dynamics, before determining the dissipative relaxation into the thermal bath. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Grain size reduction of CoCrPt–SiO2 media by oxidation of RuCr intermediate layer grain boundary
Authors: Park Sang Hwan , Kim Seon Ok , Oh Hoon Sang , Choa Sung Hoon , Lee Taek Dong
Published: December 2007

The grain size reduction mechanism of CoCrPt‐SiO2 perpendicular magnetic recording media by oxygen reactive sputtering of RuCr intermediate layer has been investigated as a function of oxygen content in the Ar sputtering gas. The media stack was Ta/Ru/RuCr/CoCrPt‐SiO2. It was found that, by the oxygen addition, Cr and Ru oxides were formed at grain boundaries of the RuCr layer and this was the reason of the intermediate layer grain size reduction, which induced the reduction of the recording layer grain size. C‐axis alignment of RuCr (0002) plane, however, was degraded as the oxygen gas ratio increased. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydrogenation‐assisted crystallisation of amorphous Nd‐Fe‐B material
Authors: Kwon H. W. , Jeong I. C.
Published: December 2007

Crystallisation of the Nd‐Fe‐B amorphous material assisted by a hydrogenation was investigated. The Nd‐Fe‐B amorphous material was prepared by mechanical milling of the Nd15Fe77B88 alloy ingot. The amorphous material was reacted with hydrogen gas to cause crystallisation. The hydrogenation facilitated the crystallisation of the amorphous Nd15Fe77B8 alloy, and the crystallisation was completed at the temperatures much lower than the ordinary thermal crystallisation temperature. The huge heat evolved from the hydrogenation assisted the crystallisation of the amorphous. The Nd15Fe77B8 material crystallised from the amorphous by the hydrogenation consisted of a mixture of NdHx, Fe and Nd1+xFe4B4 phases. The desorption of hydrogen from the mixture under vacuum at an elevated temperature led to a combination of Nd, Fe and Nd1+xFe4B4 phases into the Nd2Fe14B phase. The hydrogenation‐assisting crystallised material showed much higher coercivity after the desorption and combination with respect to the material thermally annealed without hydrogenation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)