bluuebunny/crossref_metadata_2025 huggingface dataset:
Effectiveness of the Picture Exchange Communication System (PECS) on Communication and Speech for Children With Autism Spectrum Disorders: A Meta-Analysis
Authors: Flippin Michelle , Reszka Stephanie , Watson Linda R.
Published: May 2010

Purpose

The Picture Exchange Communication System (PECS) is a popular communication-training program for young children with autism spectrum disorders (ASD). This meta-analysis reviews the current empirical evidence for PECS in affecting communication and speech outcomes for children with ASD.

Method

A systematic review of the literature on PECS written between 1994 and June 2009 was conducted. Quality of scientific rigor was assessed and used as an inclusion criterion in computation of effect sizes. Effect sizes were aggregated separately for single-subject and group studies for communication and speech outcomes.

Results

Eight single-subject experiments (18 participants) and 3 group studies (95 PECS participants, 65 in other intervention/control) were included. Results indicated that PECS is a promising but not yet established evidence-based intervention for facilitating communication in children with ASD ages 1–11 years. Small to moderate gains in communication were demonstrated following training. Gains in speech were small to negative.

Conclusions

This meta-analysis synthesizes gains in communication and relative lack of gains made in speech across the PECS literature for children with ASD. Concerns about maintenance and generalization are identified. Emerging evidence of potential preintervention child characteristics is discussed. Phase IV was identified as a possibly influential program characteristic for speech outcomes.
Transitions between corona, glow, and spark regimes of nanosecond repetitively pulsed discharges in air at atmospheric pressure
Authors: Pai David Z. , Lacoste Deanna A. , Laux Christophe O.
Published: May 2010

In atmospheric pressure air preheated from 300 to 1000 K, the nanosecond repetitively pulsed (NRP) method has been used to generate corona, glow, and spark discharges. Experiments have been performed to determine the parameter space (applied voltage, pulse repetition frequency, ambient gas temperature, and interelectrode gap distance) of each discharge regime. In particular, the experimental conditions necessary for the glow regime of NRP discharges have been determined, with the notable result that there exists a minimum and maximum gap distance for its existence at a given ambient gas temperature. The minimum gap distance increases with decreasing gas temperature, whereas the maximum does not vary appreciably. To explain the experimental results, an analytical model is developed to explain the corona-to-glow (C-G) and glow-to-spark (G-S) transitions. The C-G transition is analyzed in terms of the avalanche-to-streamer transition and the breakdown field during the conduction phase following the establishment of a conducting channel across the discharge gap. The G-S transition is determined by the thermal ionization instability, and we show analytically that this transition occurs at a certain reduced electric field for the NRP discharges studied here. This model shows that the electrode geometry plays an important role in the existence of the NRP glow regime at a given gas temperature. We derive a criterion for the existence of the NRP glow regime as a function of the ambient gas temperature, pulse repetition frequency, electrode radius of curvature, and interelectrode gap distance.
Spectroscopic ellipsometry investigation of the optical properties of nanostructured Si/SiNx films
Authors: Keita A.-S. , Naciri A. En , Delachat F. , Carrada M. , Ferblantier G. , Slaoui A.
Published: May 2010

In this paper we use spectroscopic ellipsometry to investigate the optical properties of silicon quantum dots (Si-QDs) embedded in silicon-rich silicon nitride (SRSN) films over the (1.5–5.9 eV) photon energy range. These films were elaborated by microwave plasma enhanced chemical vapor deposition for various gas flow ratio [R=(NH3)/(SiH4)]. We have analyzed the ellipsometric data using various modeling methods: Forouhi–Bloomer (FB) and Tauc–Lorentz (TL) dispersion formulas and wavelength-by-wavelength (λ-by-λ) numerical inversion. This comparative study allowed us to analyze in depth the influence of ammonia flow on the physical properties of SRSN films and Si-QDs. FB and TL models and λ-by-λ inversion have revealed that the imaginary dielectric function of the Si-QDs, is characterized by a single broad peak similar to that of amorphous silicon. The fitted band gap (Eg) and the other optical properties were found to depend on the ammonia flow. We also determined that Eg obtained by FB model seems to be less realistic than that obtained with TL dispersion formula. According to TL model, the obtained Eg values of Si-QDs varied between 1.58 and 2.07 eV with the change in R from 1.64 to 1.79. This band-gap extension is in good agreement with measurements observed by photoluminescence.
Crystal structure and magnetic properties of melt spun SmCo7−xMx (M=Ta, Cr, and Mo; x=–0.6) ribbons
Authors: Hsieh C. C. , Chang H. W. , Guo Z. H. , Chang C. W. , Zhao X. G. , Chang W. C.
Published: May 2010

The crystal structure and magnetic properties of melt spun SmCo7−xMx (M=Ta, Cr, and Mo; x=0–0.6) ribbons have been investigated. Based on x-ray diffraction analysis, it is found that a pure TbCu7-type structure is formed in the melt spun SmCo7−xTax (x=0–0.3) ribbons, while minor amount of additional 2:17 phase appears for the SmCo7−xMx (M=Cr and Mo; x=0.1–0.6) ribbons, implying that the elements in VIB group (Cr and Mo) are inferior to the element in VB group (Ta) in stabilizing metastable 1:7 phase. The result, analyzed by Rietveld refinement method, shows that Ta, Cr, and Mo may occupy the 2e site of 1:7 phase, which leads to the enhancement of the magnetic anisotropy field of 1:7 phase, just like Ti, Zr, Hf, Nb, or V did. From the magnetic performance point of view, with increasing the content of doping element x from 0 to 0.6, the maximum coercivity of SmCo7−xMx ribbons is enhanced from 1.9 kOe for binary SmCo7 to 11.3 kOe for M=Ta, 6.6 kOe for M=Cr, and 7.5 kOe for M=Mo, respectively, while the remanent magnetization is all reduced for the above ternary alloy ribbons.
Permanent magnetism of dense-packed nanostructures
Authors: Skomski R. , Liu Y. , Shield J. E. , Hadjipanayis G. C. , Sellmyer D. J.
Published: May 2010

The effect of nanostructuring on magnetostatic interactions in permanent magnets is investigated by model calculations. Emphasis is on the energy product as a function of packing fraction of the magnetic phase, of the magnet’s macroscopic shape, and of the nanoscale feature size. The main difference between nanostructured and macroscopic magnetic bodies, namely, the transition between coherent and incoherent reversal, has a far-reaching impact on demagnetizing field and energy product. For small magnet sizes, the energy product is substantially enlarged, up to μ0Ms2/4 for soft magnetic materials, but this effect is difficult to exploit in real devices. In bulk magnets, the energy product depends on the packing fraction f of the soft phase and exhibits a maximum μ0Ms2/12 for f=2/3. Nanoscale magnetization processes involve demagnetizing factors different from the macroscopic ones used to determine the optimum shape of permanent magnets. Confusion of these two types of demagnetizing fields yields unphysical mechanisms, such as hysteresis-loop overskewing and the addition of self-interaction fields to the external field.
Design of magnetic concentrators for high sensitivity anisotropic magnetoresistor devices
Authors: Mansour Malik , Coillot Christophe , Chanteur Gerard , Roux Alain , Nguyen Van Dau Frédéric
Published: May 2010

In this work, a very promising shape of magnetic concentrators taking advantage of the symmetrical flux leakage of Mn–Zn ferrite magnetic cores is presented. This configuration consists of two ferromagnetic rods separated by two air gaps allowing to place anisotropic magnetoresistance sensors in the core axis. Results from three-dimensional finite elements modeling are presented. We show that an appropriate shape optimization of core extremities enables to improve significantly the amplification factor without any increase in length.
Numerical simulation of wave propagation in Y- and Z-type hexaferrites for high frequency applications
Authors: Wang J. W. , Geiler A. L. , Harris V. G. , Vittoria C.
Published: May 2010

The dispersion characteristics of microstrip lines on magnetically anisotropic substrates are studied utilizing the Galerkin’s method in the spectral domain. Specifically, we calculate the differential phase shifts of devices consisting of Z-type (Zn2Z) and Y-type (Zn2Y) ferrites as a function of applied magnetic field. Our theoretical formulism is effective in modeling highly magnetically anisotropic materials, which are becoming increasingly important for the next generation of microwave devices. Such a theoretical treatment of anisotropic ferrite magnetic materials is presently unavailable in commercial numerical simulation tools.
Magnetic anisotropy in itinerant magnets
Authors: Skomski R. , Kashyap A. , Solanki A. , Enders A. , Sellmyer D. J.
Published: May 2010

The structural dependence of the magnetocrystalline anisotropy of itinerant permanent magnets (or nanostructures of iron-series 3d elements) is investigated by model and tight-binding calculations. Magnetic nanostructures yield strong oscillations of the anisotropy as a function of the number of d electrons per atom, which can be tuned by alloying. While interatomic hopping is usually more important in metals than crystal-field interactions, we find substantial crystal-field corrections for some configurations, especially for the atomic square. Finally, we compare our results with Néel model.
Colossal room-temperature coercivity in size-selected cobalt ferrite nanocrystals
Authors: Cedeño-Mattei Y. , Perales-Pérez O. , Uwakweh O. N. C. , Xin Y.
Published: May 2010

It has been well established that a fine tuning in cobalt ferrite nanocrystal size within the single domain region would lead to the achievement of extremely high coercivity values at room-temperature. If so, the high coercivity and chemical stability expected for this ferrite will increase its attractiveness for magneto-optical recording applications. The present work addresses the development of a size-sensitive phase separation method for cobalt ferrite nanocrystals that is based on selective dissolution of the superparamagnetic fraction and subsequent size-sensitive magnetic separation of single domain nanoparticles. Ferrite nanocrystals synthesized under size-controlled conditions were first contacted with acidic solutions under precise conditions of acid concentration and contact time, followed by a magnetically assisted phase separation in water. Produced nanocrystals were characterized by x-ray diffraction, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy techniques. The attained coercivity value of 9.4 kOe was mainly attributed to the enlargement of the average crystal size within the single domain region coupled with the removal of the superparamagnetic fraction in the ferrite powders.
IrMn and FeMn blocking temperature dependence on heating pulse width
Authors: Lombard L. , Gapihan E. , Sousa R. C. , Dahmane Y. , Conraux Y. , Portemont C. , Ducruet C. , Papusoi C. , Prejbeanu I. L. , Nozières J. P. , Dieny B. , Schuhl A.
Published: May 2010

We have determined the write power density dependence on heating pulse width and antiferromagnet (AF) thickness using magnetic tunnel junctions whose storage layer is exchange biased with IrMn or FeMn. An increase in write power density needed to write the storage layer has been observed for both AF as pulse width is decreased from 0.1 ms to 10 ns. Quasistatic blocking temperatures (Tb) were measured on both full sheet and patterned samples, showing a reduction in Tb for patterned samples which we link to process induced damages. Power-temperature relationship was established based on a correspondence between writing power for long pulse duration and quasistatic Tb measurement. Both write power density and associated temperature results show a dependence of the Tb on AF thickness at pulse width as short as 10 ns. Particularly for IrMn, the relationship between write power and pulse width becomes weakly dependent on the AF thickness above a certain AF thickness. The write power density is significantly lower for thinner AF layer. This suggests a critical thickness below which the AF writing process deviates from bulk behavior.
Texture and magnetic properties of exchange bias systems
Authors: Aley N. P. , Bowes M. , Kröger R. , O’Grady K.
Published: May 2010

We report on the magnetic and structural properties of IrMn/CoFe exchange bias systems deposited onto a dual seed layer of NiCr(X)/Ru(5 nm), with X=2, 6, and 20 nm. Samples with the structure NiCr (Xnm)/IrMn (7 nm)/CoFe (3 nm)/Ta (10 nm) with X=2, 6, and 20 nm were prepared by dc sputtering for magnetic characterization. A second set of samples with structure NiCr (Xnm)/IrMn (10 nm) with X=2, 6, and 20 nm were deposited onto TEM grids for structural characterization by TEM. A method of manipulating of the TEM grid to allow a qualitative analysis of the in-plane texture of the samples is described and used to analyze the microstructure of these samples. The microstructure and particularly the texture are correlated with the anisotropy constant (KAF) of the antiferromagnet (AF) layer, with an optimum NiCr seed layer of 6 nm to give a maximum value of KAF of 1.2×107 ergs/cc.
A high-resolution field-emission-gun, scanning electron microscope investigation of anisotropic hydrogen decrepitation in Nd–Fe–B-based sintered magnets
Authors: Soderznik Marko , McGuiness Paul , Zuzek-Rozman Kristina , Škulj Irena , Yan Gaolin , Kobe Spomenka
Published: May 2010

In this investigation commercial magnets based on (Nd,Dy)14(Fe,Co)79B7 were prepared by a conventional powder-metallurgy route with a degree of alignment equal to ∼90% and then exposed to hydrogen at a pressure of 1 bar. The magnets, in the form of cylinders, were observed to decrepitate exclusively from the ends. High-resolution electron microscopy was able to identify the presence of crack formation within the Nd2Fe14B grains, with the cracks running parallel to the c axis of these grains. Based on the concentration profile for hydrogen in a rare-earth transition-metal material, it is clear that the presence of hydrogen-induced cracks running perpendicular to the ends of the magnet provides for a much more rapidly progressing hydrogen front in this direction than from the sides of the magnet. This results in the magnet exhibiting a macroscopic tendency to decrepitate from the poles of the magnet toward the center. This combination of microstructural modification via particle alignment as part of the sintering process and direct observation via high-resolution electron microscopy has led to a satisfying explanation for the anisotropic hydrogen-decrepitation effect.
Refrigerant capacity and direct measurements of the magnetocaloric effect on LaFe11.2Co0.7Si1.1Cx materials
Authors: Balli M. , Fruchart D. , Sari O. , Huang J. H. , Rosca M.
Published: May 2010

In this paper, we report on the magnetic properties and magnetocaloric effect (MCE) in NaZn13-type LaFe11.2Co0.7Si1.1Cx (x=0.1 and 0.3) close to room temperature. The Landau theory as well as the temperature dependence of magnetization data revealed that LaFe11.2Co0.7Si1.1C0.1 and LaFe11.2Co0.7Si1.1C0.3 exhibit a second-order magnetic transition near their Curie temperature. We have calculated the magnetocaloric effect both in terms of isothermal entropy change and adiabatic temperature change using the magnetization and the direct measurements. Under an external field change from 0 to 5 T, −ΔS is 14.5 J/kg K (TC=290 K) and 8 J/kg K (TC=310 K) for x=0.1 and 0.3, respectively. The calculated refrigerant capacity for a field change in 0–5 T is about 305 and 286 J/kg K, for LaFe11.2Co0.7Si1.1C0.1 and LaFe11.2Co0.7Si1.1C0.3 respectively, which is larger than that of some magnetocaloric materials with a first-order phase transition (Gd5Ge2Si2). ΔTad decreases with increasing C content. It was found to be about 1.5 for x=0.1 and 1.2 for x=0.3 under 1.48 T.
Colossal magnetoresistance mechanism in doped manganites based on the canted ferromagnetic phase
Authors: Khutsishvili Koba O. , Fokina Nathalie P.
Published: May 2010

It is demonstrated that in the doped manganites the antiferromagnetic phase transforms into the ferromagnetic canted phase under the action of the mobile electron hopping. It is shown that the colossal magnetoresistance effect can be conditioned by the change in the magnetization canting angle at the application of a constant magnetic field. The evaluation of the magnetoresistance value in the ferromagnetic canted phase model is carried out and it is shown that it qualitatively and quantitatively agrees with the experiment.
Enabling suspension-based biochemical assays with digital magnetic microtags
Authors: Mitrelias T. , Cooper J. F. K. , Vyas K. N. , Palfreyman J. J. , Hong B. , Hayward T. J. , Barnes C. H. W.
Published: May 2010

Microarrays and suspension-based technologies have attracted significant interest over the past decade with applications in medical diagnostics and biochemical multiplexed assays. However, the throughput of microarrays will always be limited by the array density and the slow kinetics, while the suspension (or bead)-based technologies are currently limited by the number of distinct codes the beads can carry. A novel digital magnetic tagging technology based on magnetic tags that can be used as encoded microcarriers for biomolecular probes, is presented here. The highly disruptive platform technology can provide a very large number of unique codes, enabling a high degree of multiplexing. The design principles of a novel magnetic laboratory-on-a-chip device comprising microfluidic channels with embedded magnetic tunneling magnetoresistive sensors are also discussed.
Compact electromagnetically operated microfluidic system for detection of sub-200-nm magnetic labels for biosensing without external pumps
Authors: Morimoto Y. , Takamura T. , Sandhu A.
Published: May 2010

The combination of small sample analyte volumes, high sensitivity, ease of use, high speed, and portability is an important factor for the development of protocols for point of care biodiagnosis. Currently, handling small amounts of liquids is achieved using microfluidic systems but it is challenging to satisfy the remaining factors using conventional approaches based on biosensors employing detection of fluorescent labels. Thus to resolve the other requirements, biosensing systems based on the detection of functionalized superparamagnetic beads acting as “magnetic labels” are being studied as an alternative approach. Notably, for greater quantification, there are increasing demands for the use of sub-200-nm magnetic labels, which are comparable in size to actual biomolecules. However, detection of small numbers of sub-200-nm diameter magnetic beads by magnetoresistive device-based platforms is extremely challenging due to the intrinsic noise of the electronic devices. In order to overcome the limitation, we have developed a simple procedure for detecting sub-200-nm diameter magnetic labels for biosensing via magnetically induced self-assembly of superparamagnetic beads. Applying our approach to conventional microfluidic systems satisfies the most of prerequisites; however conventional microfluidic systems attached to the external pumps are yet suitable for point of care biodiagnosis. Here we propose the development of an alternative biosensing system based on our previous work that does not require external pumps to achieve miniaturization.
The enhanced elastic modulus of nanowires associated with multitwins
Authors: Yoo Jun Hwan , Oh Soo Ik , Jeong Myeong Sik
Published: May 2010

In this study, we performed molecular static simulations to investigate the enhanced elastic modulus of multiply twinned nanowires (MTNs) that had fivefold twin planes. MTNs have the same size-dependent elastic behavior as twin-free nanowires (TFNs), however, the simulation results reveal stiffer elastic behavior of MTNs when compared with that of TFNs of the same size. This is because atomic rearrangement occurs inside MTNs through the intrinsic elastic deformation as a result of their unique geometry. These results are supported by the elastic-modulus distribution on the cross-sectional area—the elastic modulus increases close to the central part of MTNs—and the intrinsically strained structure that has a highly compressed central portion in the radial direction.
Polyol-based synthesis of hydrophilic magnetite nanoparticles
Authors: Maity Dipak , Chandrasekharan Prashant , Si-Shen Feng , Xue Jun-Min , Ding Jun
Published: May 2010

In this paper, we report direct synthesis of hydrophilic magnetite (Fe3O4) nanoparticles by thermolysis of iron (III) acetylacetonate in four different liquid polyols, e.g., di(ethylene glycol) (DEG), tri(ethylene glycol) (TEG), tetra(ethylene glycol) (TTEG), and poly(ethylene glycol) (PEG) and characterization of the properties relevant to their surface structure and colloidal stability in an aqueous medium. Fe3O4 nanoparticles prepared in the medium DEG or TEG can be well suspended in aqueous solution, while Fe3O4 nanoparticles prepared in TTEG or PEG agglomerate when these nanoparticles are prepared at their refluxing temperature. However, the aqueous stability of the PEG coated particles prepared at 220 °C are good due to the increase in amount of surface-adsorbed polyol coating (27 wt %) and associated positive charges (+30 mV).
Platinum attachments on iron oxide nanoparticle surfaces
Authors: Palchoudhury Soubantika , Xu Yaolin , An Wei , Turner C. Heath , Bao Yuping
Published: May 2010

Platinum nanoparticles supported on metal oxide surfaces have shown great potential as heterogeneous catalysts to accelerate electrochemical processes, such as the oxygen reduction reaction in fuel cells. Recently, the use of magnetic supports has become a promising research topic for easy separation and recovery of catalysts using magnets, such as Pt nanoparticles supported on iron oxide nanoparticles. The attachment of Pt on iron oxide nanoparticles is limited by the wetting ability of the Pt (metal) on ceramic surfaces. A study of Pt nanoparticle attachment on iron oxide nanoparticle surfaces in an organic solvent is reported, which addresses the factors that promote or inhibit such attachment. It was discovered that the Pt attachment strongly depends on the capping molecules of the iron oxide seeds and the reaction temperature. For example, the attachment of Pt nanoparticles on oleic acid coated iron oxide nanoparticles was very challenging, because of the strong binding between the carboxylic groups and iron oxide surfaces. In contrast, when nanoparticles are coated with oleic acid/tri-n-octylphosphine oxide or oleic acid/oleylamine, a significant increase in Pt attachment was observed. Electronic structure calculations were then applied to estimate the binding energies between the capping molecules and iron ions, and the modeling results strongly support the experimental observations.
Change in magnetic properties of a cold rolled and thermally aged Fe–Cu alloy
Authors: Park D. G. , Ryu K. S. , Kobayashi S. , Takahashi S. , Cheong Y. M.
Published: May 2010

The variation in magnetic properties of a Fe–1%Cu model alloy due to a cold rolling and a thermal aging has been evaluated to simulate the radiation damage of reactor pressure vessel of nuclear power plant. The thermal aging was conducted at 500 °C with different aging times in series. The hysteresis loops, magnetic Barkhausen noise (BN) and Vickers microhardness were measured for prestrained, strained, and thermal aged samples. The coercivity increased by a plastic strain and decreased by thermal aging, The BN decreased in the prestrained and strained samples but large changes were observed in the strained sample. These results were interpreted in terms of the domain wall motion signified by a change in the mean free path associated with microinternal stress and copper rich precipitates.
Influential parameters on electromagnetic properties of nickel–zinc ferrites for antenna miniaturization
Authors: Souriou David , Mattei Jean-Luc , Chevalier Alexis , Queffelec Patrick
Published: May 2010

Electromagnetic properties of nickel–zinc ferrites based materials make them potential candidates for applications linked to telecommunications. In the present study, nanosized particles of spinel ferrite Ni0.5Zn0.3Co0.2Fe2O4 were prepared by coprecipitation method. An optimized material is obtained after adequate heat treatment and partial filling of the porosity by epoxy resin. This material lies between ceramic and composite medium (with porosity close to 40%), and shows almost constant complex permeability and permittivity in the frequency range from 0.1–0.7 GHz, and equal to ∼3.5-j0.15 (loss tangent∼0.04) and ∼4-j0.2 (loss tangent∼0.02), respectively. The refractive index n is close to 3.75. These electromagnetic properties, in particular the low levels of losses, show that this material could be useful to the design of miniaturized antennas in the VHF-uhf (300–700 MHz) range of frequency.
Accurate modeling of voltage and current waveforms with saturation and power losses in a ferrite core via two-dimensional finite elements and a circuit simulator
Authors: Salas R. A. , Pleite J.
Published: May 2010

This paper presents a new dynamic model of equivalent circuit to simulate in the time-domain the effects of saturation and power losses in a nonlinear magnetic component. The parameters of the model are a nonlinear inductance and a nonlinear loss resistance that are computed via two-dimensional finite elements. The effectiveness of the model is analyzed in the case of a soft ferrite inductor excited by a sinusoidal voltage source at frequencies of 500 Hz and 40 kHz. The resulting voltage and current waveforms of the inductor taken in the laboratory are then compared with those computed via the PSIM circuit simulator. PSIM is a simulation software designed for power electronics, motor control, and dynamic system simulation.
Structural and size dependent magnetic properties of single phase nanostructured gadolinium-iron-garnet under high magnetic field of 32 tesla
Authors: Chinnasamy C. N. , Greneche J. M. , Guillot M. , Latha B. , Sakai T. , Vittoria C. , Harris V. G.
Published: May 2010

Here we report the single phase nanostructured Gd3Fe5O12 garnets with different grain sizes (bulk, 75, 47, 35, and 22 nm) were prepared by ball milling for various milling times. Both the average grain size and the lattice parameter were estimated from the x-ray diffraction line broadening. The F57e Mössbauer spectra were recorded at 300 and 77 K for the samples with different grain sizes clearly evidenced the formation of Fe2+ ions induced by milling and the content of Fe2+ increases with milling time. At 4.2 K, a significant increase in saturation magnetization (+11%) has been observed for the 47 nm particles. The magnetization is strongly applied field dependent and no saturation effect is observed even at fields as high as of 320 kOe. The results presented here have been explained in terms of the key role played by the Fe2+ ions.
Effects of static magnetic fields on light scattering in red chromatophore of goldfish scale
Authors: Iwasaka M.
Published: May 2010

Light scattering in a guanine crystal plate of goldfish scales was observed with and without static magnetic field exposure. Under a microscopic image with dark-field-illumination, the structural color of the scale by guanine plates was observed, and isolated chromatophores showed a twinkling which was the intermittent light scattering of the light from the side. The light scattering was quenched by static magnetic fields of more than 0.26 tesla (T). The quenching was reversibly occurred when the applied external magnetic fields were changed between ambient fields and 5 T. The quenched light scattering did not improve when the magnetic field was decreased from 5 to 0.3 T. It recovered to the original twinkling state about one minute after reaching an ambient geomagnetic field level. The mechanism of the quenched light scattering was speculated to be concerned with the possible magnetic orientation of guanine crystal plates, which were sustained by protein fibers in the red chromatophore. The diamagnetic complex of guanine crystal plates and protein fibers are the candidates for the nanosized light scattering controller based on the magnetic orientation mechanism.
Electric detection of the spin-Seebeck effect in ferromagnetic metals (invited)
Authors: Uchida K. , Ota T. , Harii K. , Ando K. , Nakayama H. , Saitoh E.
Published: May 2010

The spin-Seebeck effect (SSE) converts a temperature gradient into spin voltage, driving force for nonequilibrium spin currents, in a ferromagnetic metal. In this study, the SSE in ferromagnetic Ni81Fe19, Ni, and Fe films has been investigated by means of the inverse spin-Hall effect (ISHE) in Pt films at room temperature. The ISHE allows us to detect the SSE signals as electric voltage separated from extrinsic thermoelectric effects. The experimental results show that the sign of the thermally induced spin voltage due to the SSE is reversed between the higher- and lower-temperature ends of the ferromagnets. We also measured the spatial distribution and the sample-width dependence of the ISHE voltage induced by the SSE.
Ferromagnetic resonance on metal nanocrystals in Fe and Ni implanted ZnO
Authors: Ankiewicz A. O. , Martins J. S. , Carmo M. C. , Grundmann M. , Zhou Shengqiang , Schmidt H. , Sobolev N. A.
Published: May 2010

We studied the angular dependence of the ferromagnetic resonance (FMR) spectra of (0001)ZnO single crystals implanted with Ni and Fe ions and compared the results to the data obtained by other experimental techniques, especially, x-ray diffraction (XRD) and superconducting quantum interference device magnetometry. The FMR revealed the formation of metal nanocrystals (NCs) embedded in the ZnO lattice in an oriented way. Whereas in the case of Ni, the conclusions drawn from the FMR studies corroborated the XRD and magnetometry results with respect to the alignment of the NCs in the host lattice, in the case of the Fe NCs, the FMR clearly shows that the hard magnetization axis (which is ⟨111⟩ in bcc Fe) is oriented perpendicular to the sample surface (parallel to the [0001]ZnO axis), at variance with the former XRD observations.
Suppression of blocking behavior in a macroscopic fcc crystal of nanoparticles
Authors: Desautels R. D. , Kasyutich O. , van Lierop J.
Published: May 2010

We have used a protein crystallization technique to fabricate three-dimensional (3D) ordered arrays of magnetoferritin nanoparticles up to a few hundreds of micrometers in size in the form of free standing perfectly faceted crystals. We compare the ac and dc susceptibilities of the nanoparticles in an uncrystallized system (amorphous assembly) and in a macroscopic 3D fcc crystal of nanoparticles. Completely different magnetism is measured due to the different interparticle interactions in the two systems. For example, at temperatures above 50 K the uncrystallized nanoparticle system is superparamagnetic while the 3D crystal displays no superparamagnetism up to 400 K.
Measuring the effects of low energy ion milling on the magnetization of Co/Pd multilayers using scanning electron microscopy with polarization analysis
Authors: McMorran B. J. , Cochran A. C. , Dumas R. K. , Liu Kai , Morrow P. , Pierce D. T. , Unguris J.
Published: May 2010

The dependence of the magnetization profile of Co/Pd multilayer films with very thin individual layers, Co(0.4 nm)/Pd(0.6 nm), on the energy of ion milling is investigated using scanning electron microscopy with polarization analysis (SEMPA). The effect of Ar ion milling on the Co/Pd magnetization angle distribution is compared for ion milling at 50 eV, 1 keV, and 2 keV. We find that 1 and 2 keV Ar ion milling causes a measurable change in the out-of-plane magnetization angle distribution as material is removed, but ion milling with 50 eV Ar ions does not significantly alter the magnetization. This enables quantitative imaging of all three vector components of the surface magnetization of the Co/Pd multilayer films with 20 nm lateral spatial resolution using SEMPA.
Effects of vortex chirality and shape anisotropy on magnetization reversal of Co nanorings (invited)
Authors: He Kai , Smith David J. , McCartney Martha R.
Published: May 2010

The effects of vortex chirality and shape anisotropy on the magnetization reversal of thin Co nanorings with and without slots have been investigated using off-axis electron holography and micromagnetic simulations. Stepped hysteresis loops were determined and typical well-defined states, including onion states, vortex states, flux-closure (FC) states, and omega (Ω) states were identified during reversal for different element shapes. The chirality of the vortex (vortices) formed after the onion states determined the switching mechanism. The Co nanorings and slotted rings with applied field parallel to the slots showed multistep switching via onion-FC-onion mode, also involving the formation and annihilation of vortex (vortices), whereas slotted rings with applied field perpendicular to the slots exhibited simple one-step switching by abrupt chirality reversal of the FC states. The influence of shape anisotropy on switching fields is also discussed in terms of demagnetization energy.
Fabrication of perpendicularly magnetized magnetic tunnel junctions with L1-CoPt/Co2MnSi hybrid electrode
Authors: Hiratsuka T. , Kim G. , Sakuraba Y. , Kubota T. , Kodama K. , Inami N. , Naganuma H. , Oogane M. , Nakamura T. , Takanashi K. , Ando Y.
Published: May 2010

Magnetic tunnel junctions (MTJs) of perpendicularly magnetized L10-CoPt/Co2MnSi/MgO/FePt structure were fabricated. In-plane x-ray diffraction measurements and element specific evaluation of magnetic properties using soft x-ray magnetic circular dichroism were carried out to examine quite thin Co2MnSi (CMS) inserted layer between CoPt and MgO interface. Ordered B2-CMS was successfully fabricated onto L10-CoPt as thin as 1 nm thick, and CMS layer shows perpendicular magnetic anisotropy below 3 nm thick via exchange coupling with CoPt layer. In the MTJ-stacking, epitaxial growth was confirmed except for partial misalignment in the upper FePt layer, and coercive field difference clearly appeared between the bottom and the top ferromagnetic electrodes.
Effect of annealing on the magnetic tunnel junction with Co/Pt perpendicular anisotropy ferromagnetic multilayers
Authors: Wang Yi. , Wang W. X. , Wei H. X. , Zhang B. S. , Zhan W. S. , Han X. F.
Published: May 2010

Perpendicular magnetic tunnel junctions (pMTJs) with tunneling magnetoresistance (TMR) as high as 14.7% at room temperature were fabricated. The continuous film and pMTJs with Co/Pt multilayer magnetic electrodes and AlOx tunnel barrier were annealed at different temperatures and the effect of annealing on their properties was investigated. The hysteresis loops and X-ray reflectivity measurement show that the interdiffusion of Co and Pt atoms is slight when annealed below 523 K. However, the patterned magnetic tunnel junction gets TMR ratio from 12.3% to the maximum value of 14.7% after annealing at 483 K for 1 h.
Modification of the Δ1 and Δ5 electron states induced by alloying effects in Fe-based alloys for magnetic tunnel junctions
Authors: Belhadji B. , Calmels L.
Published: May 2010

We have studied the modification of the electron states with Δ1 and Δ5 symmetries, induced by alloying effects in bcc Fe-based alloys. The corresponding density of states has been calculated for disordered alloys with the code SPR-KKR, which is based on the density-functional theory and uses the Korringa–Kohn–Rostoker method and the coherent potential approximation for the description of the chemical disorder. We have studied the modification of the Δ1 and Δ5 densities of states of Fe1−xMx alloys as a function of the nature of the alloy metal M (M=V, Cr, and Co) and as a function of its chemical content x.
Magnetic tunnel junctions with large tunneling magnetoresistance and small saturation fields
Authors: Egelhoff W. F. , Höink V. E. , Lau J. W. , Shen W. F. , Schrag B. D. , Xiao G.
Published: May 2010

There is a continuing need for greater sensitivity in magnetic tunnel junction (MTJ) sensors. We have found a new approach to achieving large tunneling magnetoresistance (TMR) with a very soft free layer. The high TMR is achieved by conventional means of annealing a bottom pinned MTJ that has Ta and Ru capping layers. The soft free layer is achieved by etching almost to the MgO tunnel barrier and depositing a thick soft magnetic film. The results are far superior to annealing the MTJ with the thick soft layer already deposited.
Equilibrium shapes of ferrofluid under different forces using continuum shape sensitivity analysis and level set method
Authors: Kim Young Sun , Park Il Han
Published: May 2010

In this paper, a method for numerical simulation of the shape of a ferrofluid under external magnetic fields and the gravitational field is presented. The final shape is determined by an equilibrium condition of energy in a coupled system of electromagnetic fields and ferrofluid in the presence of gravity. The shape of the ferrofluid is captured by using the level set technique. The velocity field is calculated using continuum shape sensitivity analysis based on the material derivative concept. The numerical algorithm is implemented with a standard finite element procedure and tested on a shaping problem of ferrofluid located under an electromagnet. The numerical results showed that the proposed algorithm and numerical techniques are feasible and effective means of calculating ferrofluid shape variation under magnetic fields and the gravitational force.
Silica coated magnetic nanoparticles for separation of nuclear acidic waste
Authors: Han H. , Johnson A. , Kaczor J. , Kaur M. , Paszczynski A. , Qiang Y.
Published: May 2010

Fe 2 O 3 magnetic nanoparticles (MNPs) have been coated with silica, followed by covalent attachment of the actinide specific chelators to separate nuclear waste in acidic conditions. A general model is developed to relate the surface coating to the particle’s magnetization change, providing an alternative way to characterize the size-distribution/aggregation of MNPs. The optimized silica coating protects the Fe2O3 MNPs from iron leaching under highly acidic conditions, facilitates the dispersion of MNPs, and dramatically increases the loading capacity of chelator onto the MNPs. Compared with the uncoated counterparts, the silica coated MNPs show enhanced actinide separation efficiency.
Visualization of magnetic microparticles in liquid and control of their motion using dynamic magnetic field
Authors: Tokura S. , Hara M. , Kawaguchi N. , Izawa J. , Amemiya N.
Published: May 2010

Visualization technique of micro- or nanoparticles with sufficient spatial and temporal resolutions is required for quantitative study of motion of magnetic particles and their control using a dynamic magnetic field. Based on the particle tracking velocimetry method, a visualization system of micron-size particles has been developed. A proof-of-concept experiment of controlling magnetic particles using a dynamic magnetic field was made, and motions of magnetic particles under a dynamic magnetic field were visualized successfully using the developed system: the motions of particles synchronizing with the applied dynamic magnetic field could be observed.
Microseparator for magnetic particle separations
Authors: Lee Chiun-Peng , Lai Mei-Feng
Published: May 2010

In this study, a magnetic particle microseparator using patterned magnetic films to switch on and off separation is proposed, and numerical simulation is performed to analyze the function of the microseparator. Two magnetic films with the same magnetic dipole moment and different magnetization switching fields are used to produce open and closed magnetic fluxes that can exert different forces on the magnetic particles. For the case of open magnetic flux where the separation is on, almost all magnetic particles are trapped by the magnetic force, and the separation rate is 87.5%. For the case of closed magnetic flux where the separation is off, most of the magnetic particles pass through the separation region without being trapped.
Ca
3
(
Ru
1
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x
Cr
x
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2
O
7
: A new paradigm for spin valves
Authors: Cao G. , Korneta O. , Chikara S. , DeLong L. E. , Schlottmann P.
Published: May 2010

A spin valve is a device structure whose electrical resistance can be manipulated by controlling the relative spin alignment of adjacent metallic, magnetic layers separated by nonmagnetic insulating layers. The spin valve effect is thought to be a delicate quantum phenomenon that depends upon the precision deposition and nanoscale patterning of artificial thin-film heterostructures whose quality and performance are difficult to control. We have observed a novel, strong spin valve effect in bulk single crystals of Ca3(Ru1−xCrx)2O7 having an anisotropic, bilayered crystal structure. This discovery opens new avenues for understanding the underlying physics of the spin valve effect, and for realizing their potential in practical devices.
Thickness dependence of magnetic and transport properties in organic-CoFe discontinuous multilayers
Authors: Wang W. X. , Wang Y. P. , Zhang X.-G. , Wang Y. , Zou Jin , Han X. F.
Published: May 2010

Spin-dependent transport measurement in 3-hexadecyl pyrrole (3HDP) with a CoFe layer and the current-in-plane geometry is reported. Transport properties indicate the CoFe layers are discontinuous when their thicknesses are smaller than 6 nm. The temperature dependence of the conductance suggests that the transport mechanism is likely small polaron hopping. The observed positive magnetoresistance ratio at low temperature gives evidence of spin-conserving transport.
Coupled oscillations of double-walled carbon nanotubes
Authors: Po Giacomo , Ghoniem N. M.
Published: May 2010

A study of the coupled axial and angular oscillations of double-walled carbon nanotubes (DWNTs) was performed using molecular dynamics simulations. In order to determine the oscillation frequencies inner and outer shells have been assumed to behave as rigid bodies, a 6–12 Lennard–Jones potential was used to model the van der Waals forces between them, and friction was neglected. Armchair (5, 5)/(10, 10) configurations, with tube lengths in the range of 25–1000 Å were investigated. The axial oscillation frequency was found to be a decreasing function of the DWNT length L (∼78 GHz for L=25 Å and ∼2 GHz for L=1000 Å). The angular oscillation frequency was found to be nearly constant at ∼58 GHz, independent of the DWNT length. In addition, sustained high-frequency angular motion can be maintained for sufficiently long DWNT (on the order of a few nanometers). For shorter DWNTs, the angular motion can be altered by interference with the axial motion, and becomes irregular.
Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10–30 nm grain size prepared by chemical vapor deposition
Authors: Michaelson Sh. , Stacey A. , Orwa J. , Cimmino A. , Prawer S. , Cowie B. C. C. , Williams O. A. , Gruen D. M. , Hoffman A.
Published: May 2010

The thermal stability of nanocrystalline diamond films with 10–30 nm grain size deposited by microwave enhanced chemical vapor deposition on silicon substrate was investigated as a function of annealing temperature up to 1200 °C. The thermal stability of the surface-upper atomic layers was studied with near edge x-ray absorption fine structure (NEXAFS) spectroscopy recorded in the partial electron yield mode. This technique indicated substantial thermally induced graphitization of the film within a close proximity to the surface. While in the bulk region of the film no graphitization was observed with either Raman spectroscopy or NEXAFS spectroscopy recorded in total electron yield mode, even after annealing to 1200 °C. Raman spectroscopy did detect the complete disappearance of transpolyacetylene (t-PA)-like ν1 and ν3 modes following annealing at 1000 °C. Secondary ion mass spectroscopy, applied to investigate this relative decrease in hydrogen atom concentration detected only a ∼30% decrease in the bulk content of hydrogen atoms. This enhanced stability of sp3 hybridized atoms within the bulk region with respect to graphitization is discussed in terms of carbon bond rearrangement due to the thermal decomposition of t-PA-like fragments.
Magnetoresistance and magnetocaloric effect in metamagnetic alloys Ni45Co5Mn36.5In13.5
Authors: Chen L. , Hu F. X. , Wang J. , Shen J. , Zhang J. , Sun J. R. , Shen B. G. , Yin J. H. , Pan L. Q.
Published: May 2010

Magnetoresistance (MR) and magnetocaloric effect around martensitic transformation were investigated in a Ni45Co5Mn36.5In13.5 alloy. The martensitic temperature (TM) locates at ∼260 K. An external magnetic field can drive TM to a lower temperature at a rate of ∼9.2 K/T. Associated with the field-induced metamagnetic behaviors, a large MR takes place. The maximal MR exceeds 80% under a field of 5 T around 235 K. More attractive is that the MR behavior is fully recoverable against magnetic field. We also studied the magnetocaloric effect associated with the martensitic transformation and found a large magnetic entropy change (ΔS) around 252 K.
Large magnetic entropy change in nanocrystalline Pr0.7Sr0.3MnO3
Authors: Mahato Rabindra Nath , Sethupathi K. , Sankaranarayanan V. , Nirmala R.
Published: May 2010

Nanocrystalline Pr0.7Sr0.3MnO3 sample has been prepared by sol-gel method. The room temperature powder x-ray diffraction data show single phase nature of the sample and confirm the cubic crystal structure with Fm3¯m space group. The average crystallite size is calculated using Scherrer formula, and it is found to be ∼25 nm. Transmission electron microscopy image shows that the particles are spherical in shape and the average particle size is ∼35 nm. The sample undergoes ferromagnetic ordering at 235 K (TC) and obeys the Curie–Weiss law in the paramagnetic region. The maximum value of the magnetic entropy change |ΔSM|max is ∼6.3 J kg−1 K−1, and the relative cooling power is ∼385 J kg−1 for a field change of 50 kOe. The Arrott plot confirms that the magnetic ordering is of second order nature. The experimentally observed magnetic entropy change of the sample obeys Landau theory of phase transition well.
Dielectric and magnetic properties of 0.4PZT+0.6NiCuZn-ferrite composites modified with P2O5–Co2O3
Authors: Jia Lijun , Zhang Huaiwu , Li Tao , Liu Yingli , Wen Qiye , Shen Jian
Published: May 2010

P 2 O 5 and Co2O3 have been introduced to 0.4PZT+0.6NiCuZn-ferrite composites in order to improve their electromagnetic properties, particularly for the suppression of electromagnetic interference. The nonlinear fitting of the results of permeability dispersion has revealed the relationships between domain wall resonance, spin rotation relaxation mechanisms, microstructure, and local induced anisotropy. The P2O5 additive can enhance the bulk density and static permeability due to its instantaneous liquid phase at low temperature. The existence of local induced anisotropy caused by ordering of Co ions results in a decrease in static permeability and an increase in the Q-factor. Meanwhile, the addition of Co2O3 can improve the dielectric constant and the loss tangent (tan δe) by increasing the oxygen vacancy concentration. The further decrease in tan δe of the samples codoped with P2O5 and Co2O3 is mainly attributed to P5+ in the grain boundary which can increase cation vacancies in the grain boundary region.