bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong magnetic field-induced segregation and alignment of nonmagnetic particles
Authors: Sun Zhi , Guo Muxing , Vleugels Jef , Van der Biest Omer , Blanpain Bart
Published: March 2011

A strong magnetic field, e.g., >10 T, is considered an important tool in the process of small nonmetallic inclusions removal and related anisotropic materials preparation. In the present paper, a model system of aluminum containing alumina particles is used to investigate the strong magnetic field effects. Considerable segregation is induced by the applied gradient magnetic field, whereas no segregation is observed in a gravity field because of the convection. A high gradient magnetic field, together with the particle size and treatment time, is an important factor in generating the segregation. At the same time, magnetic alignment is detected after the strong magnetic field treatment. The (00l) crystal planes of alumina are found to be aligned to the strong magnetic field direction. Experimental results agree with the theoretical calculations based on the theory of magnetic energy. Additionally, the rotation time for the alignment is estimated and the time for alumina particles of 15 μm is found to be <1 s. However, the alignment is easily disturbed by the convection during the quenching outside of the strong magnet, especially for small particles where the rotation time is much shorter. The present results offer a better understanding of the strong magnetic field effects on the behavior of nonmagnetic particles in a conductive fluid.
Synthetic characterization and surface modification of FePt nanoparticles
Authors: Wei D. H. , Yao Y. D.
Published: March 2011

Monodispersive FePt magnetic nanoparticles (NPs) with hydrophobic ligand were chemically synthesized and with controllable surface-functional properties. In order to compare and obtain the high saturation magnetization of FePt NPs, the synthesized solvents were changed from octyl to phenyl ether leading to effectively increase magnetization due to the increased particle size and isolated distance of each NPs. The surface modification of FePt NPs by using mercaptoacetic acid (thiol) and 11-mercaptoundecanoic acid (MUA) as a phase transfer reagent through ligand-exchange turned the NPs hydrophilic, and the FePt NPs were water-dispersible. Transmission electron microscopy images indicate that the NPs are slightly agglomerate after ligand-exchange. Fourier transform infrared spectroscopy (FTIR) spectra suggest that thiol and MUA functional group bond to the FePt atoms of the surface. The water-dispersible FePt NPs used as heating agents could reach the demand of biocompatibility and provide heat response for magnetically induced hyperthermia in biological fields.
High B
s Fe84−xSi4B8P4Cux (x = 0 – 1.5) nanocrystalline alloys with excellent magnetic softness
Authors: Kong Fanli , Wang Anding , Fan Xingdu , Men He , Shen Baolong , Xie Guoqiang , Makino Akihiro , Inoue Akihisa
Published: March 2011

The magnetic properties of annealed Fe84−xSi4B8P4Cux (x = 0, 0.5, 0.75, 1.0, 1.25, 1.5) soft-magnetic alloys prepared by melt–spinning were investigated. In this alloy system, the appropriate addition of the Cu element promotes the precipitation of α-Fe(Si), as well as inhibits the precipitation of other phases. The saturation magnetic flux density Bs increases and the coercivity Hc markedly decreases simultaneously with increasing Cu content until x = 1.25. The Fe82.75Si4B8P4Cu1.25 alloy annealed at 873 K for 1.8 ks shows a high Bs of 1.83 T and excellent soft-magnetic properties such as a low Hc of 2.1 A/m and a high effect permeability of 31 600. It is found that a 1%–1.25% addition of Cu is effective for the improvement of soft-magnetic properties for the present alloy system.
A study of spin–flipping in sputtered IrMn using Py-based exchange-biased spin-valves
Authors: Acharyya R. , Nguyen H. Y. T. , Pratt W. P. , Bass J.
Published: March 2011

To study spin–flipping within the antiferromagnet IrMn, we extended prior current-perpendicular-to-plane giant magnetoresistance studies of Permalloy (Py)-based exchange-biased-spin-valves containing IrMn inserts to thicker IrMn layers—5 nm ≤ tIrMn ≤ 30 nm. Unexpectedly, AΔR = A(RAP − RP)—the difference in specific resistance between the antiparallel (AP) and parallel (P) magnetic states of the two Py layers—did not decrease with increasing tIrMn, for tIrMn ≥ 5 nm, but rather became constant to within our measuring uncertainty. This constant looks to be due mostly to a new, small magnetoresistance in thin Py layers. The constant complicates isolating the spin-diffusion length, lsfIrMn, in bulk IrMn, but lsfIrMn is probably short, ≤1 nm. Similar results were found with FeMn.
Precessional switching by ultrashort pulse laser: Beyond room temperature ferromagnetic resonance limit
Authors: Tsukamoto Arata , Sato Tetsuya , Toriumi Shingo , Itoh Akiyoshi
Published: March 2011

Conventional pure magnetic recording schemes have a serious and unavoidable problem known as the ferromagnetic resonance (FMR) limit. Here we demonstrate a fast precessional switching via interplay of ultrafast heating by ultrashort pulse laser and large temperature dependency of magnetic resonance. In ferrimagnetic GdFeCo, when the temperature approaches the angular momentum compensation point TA, both frequency of FMR mode and the Gilbert damping parameter increase significantly. High-speed and strongly damped precessional switching was triggered with ultrafast heating of a Gd24.5Fe66.1Co9.4 across its magnetization compensation point TM up to TA, under a static applied magnetic field. To initiate and investigate the magnetization reversal, we have used an all-optical pump-probe technique employing an amplified Ti:sapphire laser system with 90 fs pulses. In particular, following the laser excitation with low pump fluence (0.9 mJ/cm2) the magnetic system relaxes back toward initial state while the rather high pump fluence (3.3 mJ/cm2) excitation induces a metastable opposite magnetic state. After the sudden heating which causes just 30% reduction of magnetization at first breakdown, consequently magnetization was started to rotate across Mz = 0 within 6 ps during first precession and finished the high damped precessional motion within few cycles into opposite direction.
Sintering dense NiZn ferrite by two-step sintering process
Authors: Su Hua , Tang Xiaoli , Zhang Huaiwu , Zhong Zhiyong , Shen Jian
Published: March 2011

A two-step sintering process has been adopted to produce NiZn ferrite with composition of (NiO)0.35(ZnO)0.57(CuO)0.08(Fe2O3). The densification, microstructure, and magnetic properties of the ferrite have been investigated and compared with those of ferrites produced by the traditional final-stage sintering process. It was found that the sample produced by a two-step sintering process with a high temperature of 1200 °C and a lower temperature of 1100 °C attained more than 96% of the theoretical density and had a uniform microstructure with a small average grain size. It also exhibited good performances in terms of permeability and Q-factor. Hence, this would seem to be an effective method for producing dense ferrites with a microstructure composed of small and even grains, which is a very effective strategy for improving the magnetic properties of ferrites.
Conduction electron spin–flipping at sputtered Co90Fe10/Cu interfaces
Authors: Nguyen H. Y. T. , Acharyya R. , Pratt W. P. , Bass J.
Published: March 2011

From measurements of the current-perpendicular-to-plane magnetoresistance of ferromagnetically coupled [Co90Fe10/Cu]n multilayers, within sputtered Permalloy-based double exchange biased spin-valves, we determine the parameter δCo(90)Fe(10)/Cu = 0.19 ± 0.04 that sets the probability P of spin–flipping at a Co90Fe10/Cu interface via the equation P = 1 – exp(−δ).
Room temperature ferromagnetism in N-doped rutile TiO2 films
Authors: Bao N. N. , Fan H. M. , Ding J. , Yi J. B.
Published: March 2011

Room temperature ferromagnetism has been experimentally observed in TiO2:N films prepared by pulse laser deposition under N2O atmosphere. The ferromagnetism appears when the N2O partial pressure is higher than 10−5 Torr. XPS study has revealed that N substitutes O at the partial pressure of 10−5 Torr, whereas additional N atoms occupy interstitial sites besides substituting N at higher N2O partial pressures. Our study indicates that the origin of the ferromagnetism is the O substitution with N. Each substituted N has a magnetic moment of approximately 0.9 μB. The substitution of O also resulted in p-type behavior, accompanied with magnetoresistance and anomalous Hall effect.
Comparative study of the magnetic properties of positive and nearly zero magnetostrictive submicron amorphous wires
Authors: Chiriac Horia , Lostun Mihaela , Ababei Gabriel , Óvári Tibor-Adrian
Published: March 2011

Rapidly solidified submicron amorphous wires with positive and nearly zero magnetostriction are studied in order to understand the effect that a significant reduction in the diameter of the metallic nucleus has on their magnetic behavior and anisotropy distribution. Submicron wires with metallic nucleus diameters between 350 and 800 nm were investigated with hysteresis loop measurements, the magneto-optical Kerr effect, and ferromagnetic resonance studies. The analysis of the results shows the dominant role of shape anisotropy in nearly zero magnetostrictive submicron wires, as well as in positive magnetostrictive ones with nucleus diameters smaller than 350 nm. Magnetoelastic anisotropy is still important in positive magnetostrictive submicron wires with metallic nucleus diameters larger than 500 nm.
Anisotropic magnetoresistance in low-doped La0.78Ca0.22MnO3 crystals
Authors: Markovich V. , Jung G. , Yuzhelevski Ya. , Gorodetsky G. , Mukovskii Ya. M.
Published: March 2011

Unusual behavior of anisotropic magnetoresistance (AMR) has been encountered in low-doped La0.78Ca0.22MnO3 single crystals. In contrast with previous studies of AMR in manganites, as the maximal effect was observed around TC, the AMR of La0.78Ca0.22MnO3 single crystals (TC ≈ 189 K) increases monotonously with decreasing temperature, reaches a maximum around 140 K, and then decreases with further temperature decrease. Moreover, around the maximum, AMR increases almost linearly with magnetic fields and only at fields exceeding H ∼ 7 kOe does it start to saturate. The observed unusual enhancement of AMR may be ascribed to the changes in magnetic domain structure at temperatures below 150 K as observed previously by us using a magneto-optical imaging technique.
The feasibility of bit-patterned recording at 4 Tb/in.2 without heat-assist
Authors: John Greaves Simon , Muraoka Hiroaki , Kanai Yasushi
Published: March 2011

Magnetic recording on bit patterned media with dot densities of 4 Tbit/in.2 was simulated. Head field distributions of shielded, single pole write heads with various main pole widths were used for recording. Write windows, showing the range of head positions which resulted in error-free recording and no adjacent track erasure, were calculated. The bit aspect ratio (BAR) and magnetic spacing between the write head and the medium were varied and the system with the lowest write error rate was found to be a 1:1 BAR, shingled recording system. For single-track recording a 2:1 BAR and a magnetic spacing of 3.5 nm gave the lowest write-error rate.
Evidence for a possible quantum critical point in a Cr-Si alloy doped with Mo
Authors: Sheppard C. J. , Prinsloo A. R. E. , Alberts H. L. , Strydom A. M.
Published: March 2011

The magnetic behavior and possibility of quantum criticality in a (Cr0.98Si0.02)1−yMoy alloy system (0 ≤ y ≤ 0.09) is investigated through electrical resistivity, specific heat, and thermoelectric power measurements in a temperature range 2–350 K. Alloys with 0 ≤ y ≤ 0.011 depict first-order Néel transitions that give way to continuous Néel transitions for 0.011 < y ≤ 0.038. The Néel temperature, TN(y), seems to be suppressed down to 0 K at a critical concentration yc ≈ 0.04. The Sommerfeld coefficient of specific heat γ(y) peaks at y ≈ yc, showing a sharp decreasing trend on decreasing y to below yc. This behavior is reminiscent of that observed for γ of the prototypical Cr1−xVx quantum critical system, and indeed also portrays the physics of a quantum critical point in the present (Cr0.98Si0.02)1−yMoy system.
Magnetization process and domain structure in the near-surface region of conventional amorphous wires
Authors: Chiriac Horia , Lostun Mihaela , Óvári Tibor-Adrian
Published: March 2011

Results on the study of the surface magnetization process and domain structure by magneto-optical Kerr effect in conventional rapidly quenched amorphous magnetic wires are reported. Domain imaging confirms the presence of a bamboo-type structure in the near-surface region of these materials. Surface Kerr loops show that the overall magnetization in the near-surface region has a large axial component, besides the circular one. A bistable magnetic behavior on the axial direction has been emphasized. A circularly applied field leads to the disappearance of axial magnetic bistability. Kerr loops are changed by the presence of 180° interdomain walls in the near-surface region.
Magnetic behavior of CoPt–AlN granular structure laminated with AlN layers
Authors: Yu Youxing , Shi Ji , Nakamura Yoshio
Published: March 2011

The magnetic behavior of CoPt–AlN granular structure laminated with AlN layers has been studied. Ultrathin multilayer structure, [CoPt0.5 nm/AlN0.5nm]4, is used as the precursor of the magnetic layers, which are separated by 5-nm-thick AlN layers. Upon thermal annealing, the ultrathin multilayer transforms into CoPt–AlN granular structure, and the thick AlN layers remain to be spacers. When the film was annealed at 400 °C, the out-of-plane direction becomes the easy axis of magnetization, although the coercivity remains small. TEM observation has proved that CoPt shows disklike shape at such an annealing temperature. When increasing the annealing temperature to 600 °C and above, the films show “isotropic” magnetic behavior due to the formation of equiaxial CoPt particles in the magnetic layers.
A compact model of domain wall propagation for logic and memory design
Authors: Zhao W. S. , Duval J. , Ravelosona D. , Klein J.-O. , Kim J. V. , Chappert C.
Published: March 2011

Current-driven domain wall motion is very promising for low-power, high-density, and high-speed circuits. By combining this shifting scheme with magnetic tunnel junction (MTJ) for reading and writing processes, it opens new routes for nonvolatile logic and memory applications that are crucial for the future of spintronics. This paper reports on a compact model for domain wall-MTJ-based circuit design, simulation, and evaluation. It integrates spin transfer torque mechanism for magnetization reversal and domain wall nucleation, current-driven domain wall pinning/motion behaviors, and tunnel resistance theory of MTJ nanopillar, in which the free layer is one storage element of magnetic stripe. This model is programmed with a very flexible structure to achieve the best simulation precision and efficiency, and provide easy parameter configuration interface. It is compatible with classical computer-aided design environment and can be cosimulated directly with CMOS design kits. By using the compact model, we have successfully simulated a domain wall propagation shift register.
Softening of magnons in ferromagnetic manganites
Authors: Schlottmann P.
Published: March 2011

The magnon modes of narrow-band manganites display softening and broadening for large k vectors. We critically review the several models proposed to explain the anomalous dispersions. A mechanism for the softening and shortened lifetime based on the motion of the eg electrons that reduces the Hund’s rule exchange between the eg and t2g electron spins is presented.
Phase diagram of two-dimensional spin crossover systems using the atom-phonon coupling model
Authors: Espejo M. Paez , Gîndulescu A. , Linares J. , Nasser J. , Dimian M.
Published: March 2011

Spin crossover compounds have attracted considerable research interest over the last few years due to their great potential for technological use in memory, sensors, switching, and display devices. They manifest a diverse phase transition behavior upon application of various physical stimuli, such as, heat, light, and pressure. The theoretical framework of this study is the so-called atom-phonon coupling model, which presumes elastic interactions between nearest-neighbor molecules with elastic constants depending on the electronic state of each molecule. The atom-phonon coupling model has been successful in approximating characteristics of the spin crossover compounds behavior, but has only been applied to a chain of molecules. In this paper we present results obtained for compounds with a 2D structure and we study the role of the elastic constants ratio on the phase diagram.
Half-metallic Fe2CrSi and non-magnetic Cu2CrAl Heusler alloys for current-perpendicular-to-plane giant magneto-resistance: First principle and experimental study
Authors: Ko V. , Qiu J. , Luo P. , Han G. C. , Feng Y. P.
Published: March 2011

We present results of our first principle and experimental study on new Heusler alloys candidates for half-metallic electrode and nonmagnetic spacer in current-perpendicular-to-plane giant magneto-resistance devices. The electronic structures of Fe2CrSi and Cu2CrAl are characterized by high density of states at the Fermi level in the majority spin band with a good match in their majority band structures near the Fermi level. The calculated interfacial spin polarization in Fe2CrSi/Cu2CrAl (100) superlattice is ∼80%. We have also epitaxially grown ferromagnetic A2 Fe-Cr-Si and nonmagnetic L21 Cu-Cr-Al (100) films on Cr-buffered MgO(100) substrates.
Giant spin Hall effect of Au films with Pt impurities: Surface-assisted skew scattering
Authors: Gu Bo , Ziman Timothy , Guo Guang-Yu , Nagaosa Naoto , Maekawa Sadamichi
Published: March 2011

We show theoretically a novel route to obtain giant room temperature spin Hall effect (SHE) using surface-assisted skew scattering. By a combined approach of density functional theory and the quantum Monte Carlo (QMC) method, we have studied the SHE due to a Pt impurity in different Au hosts. We show that the spin Hall angle could become larger than 0.1 on the Au (111) surface, and decreases by about a half on the Au (001) surface, while it is small in bulk Au. The QMC results show that the spin-orbit interaction (SOI) of the Pt impurity on the Au (001) and Au (111) surfaces is enhanced, because the Pt 5d levels are lifted to the Fermi level due to the valence fluctuations. In addition, there are two SOI channels on the Au (111) surface, while only one for Pt either on the Au (001) surface or in bulk Au.
Influence of Mn doping on domain wall motion in Pb(Zr0.52Ti0.48)O3 films
Authors: Zhu Wanlin , Fujii Ichiro , Ren Wei , Trolier-McKinstry Susan
Published: March 2011

Mn-doped PbZr0.52Ti0.48O3 (PZT) films were utilized to study the effect of acceptor dopant concentration on the mobility of ferroelectric domain walls. For chemical solution deposited PZT films between ∼0.5–2μm in thickness doped with 1–2mol.% Mn, the low field relative permittivity remained between 900 and 1000. With increasing Mn concentration, a threshold field developed in the ac field dependence of the relative permittivity. Furthermore, both the reversible and irreversible Rayleigh constants decreased. These observations are consistent with the possibility that MnTi’–VO•• (or MnTi’’–VO••) defect dipoles act as strong pinning centers.
Departures from local thermodynamic equilibrium in cutting arc plasmas derived from electron and gas density measurements using a two-wavelength quantitative Schlieren technique
Authors: Prevosto L. , Artana G. , Kelly H. , Mancinelli B.
Published: March 2011

A two-wavelength quantitative Schlieren technique that allows inferring the electron and gas densities of axisymmetric arc plasmas without imposing any assumption regarding statistical equilibrium models is reported. This technique was applied to the study of local thermodynamic equilibrium (LTE) departures within the core of a 30 A high-energy density cutting arc. In order to derive the electron and heavy particle temperatures from the inferred density profiles, a generalized two-temperature Saha equation together with the plasma equation of state and the quasineutrality condition were employed. Factors such as arc fluctuations that influence the accuracy of the measurements and the validity of the assumptions used to derive the plasma species temperature were considered. Significant deviations from chemical equilibrium as well as kinetic equilibrium were found at elevated electron temperatures and gas densities toward the arc core edge. An electron temperature profile nearly constant through the arc core with a value of about 14000–15000 K, well decoupled from the heavy particle temperature of about 1500 K at the arc core edge, was inferred.
Monte Carlo study of phonon dynamics in III-V compounds
Authors: Hamzeh Hani , Aniel Frédéric
Published: March 2011

The Monte Carlo (MC) stochastic method is used to solve the phonon Boltzmann transport equation. A solution scheme taking into account all the different individual types of Normal and Umklapp processes which respect energy and momentum conservation rules is presented. The use of the common relaxation time approximation in the MC solver is thus avoided. A generalized Ridley theoretical scheme is used instead to calculate three-phonon scattering rates, with the Grüneisen constant as the only adjustable parameter. A method for deriving adequate adjustable parameters is presented. Polarization branches with real nonlinear dispersion relations for transverse or longitudinal optical and acoustic phonons are considered. Zone-center longitudinal optical (LO) phonon lifetimes are extracted from the MC simulations for GaAs, InP, InAs, and GaSb. Decay channels contributions to zone-center LO phonon lifetimes are investigated using the calculated scattering rates. Vallée-Bogani’s channel is found to have a negligible contribution in all studied materials, notably GaAs. A comparison of phonons behavior between the different materials indicates that the previously reported LO phonon lifetimes in InAs and GaSb were quite underestimated.
Transient operation of the relativistic S-band magnetron with radial output
Authors: Sayapin A. , Shlapakovski A.
Published: March 2011

The influence of the time-varying accelerating voltage and electromagnetic waves reflected from the output window of the antenna on the operation of a relativistic S-band magnetron with radial output is analyzed. It is shown that within the range of radiation frequencies generated by the magnetron, the antenna with the dielectric window and feed waveguide can be considered as a resonant load. Depending on the phase relations between the reflected electromagnetic waves and those traveling in the magnetron, minimal coupling between the magnetron cavities adjacent to the place of microwave extraction can be realized. In this regime, the magnetron represents an open-end chain of coupled cavities and maintains the effective interaction of the electron flow and generated electromagnetic wave at a decreasing voltage. As the drift velocity of electrons decreases and its difference from the electromagnetic wave phase velocity increases, the microwave frequency changes. The changed frequencies do not necessarily belong to and are not limited by the discrete spectrum of closed resonant ring waveguide structures.
Next generation of prototype direct current superconducting cable for railway system
Authors: Tomita M. , Suzuki K. , Fukumoto Y. , Ishihara A. , Muralidhar M.
Published: March 2011

The authors design and develop a prototype DC superconducting cable for railways. For the preliminary evaluation 2 m Bi-2223 DC cable is used. The maximum current flowing in the cable cooled by liquid nitrogen was 1720 A in the inner sheet wire and 2430 A in the outer sheet. The experimental results and simulations led to the conclusion important for practical applications that the leakage of magnetic field was negligible. This result is of crucial importance, in particular for use in railway systems.
Visible-light-driven photocatalysts: (La/Bi + N)-codoped NaNbO3 by first principles
Authors: Liu Guodong , Ji Shulin , Yin Liangliang , Xu Guoping , Fei Guangtao , Ye Changhui
Published: March 2011

To improve the photocatalytic activity of NaNbO3 for water splitting, the bandgap and the band edges of NaNbO3 should be tailored to match the visible part of the solar spectrum and hydrogen and oxygen redox potentials. By analyzing the band structures of La/Bi-doped and (La/Bi + N)-codoped NaNbO3, we found that the pseudointermediate band (PIB) was formed in the bandgap in all the doped systems because of the orbital splitting of the Nb 4d induced by the dramatically enlarged O-Nb-O angles. The PIB could make the wide bandgap semiconductors absorb visible-light photons as long as it was degenerate or partially degenerate. Considering that the appropriate band edges and absorption properties, we believe that (La/Bi + N)-codoped NaNbO3 materials are promising photocatalysts for hydrogen production through water splitting under visible-light irradiation without other modifications.
Deposition temperature induced magnetic anisotropy variation in FePt-C soft/hard multilayer films
Authors: Huang L. S. , Hu J. F. , Chow G. M. , Chen J. S.
Published: March 2011

Multilayer exchange spring media were fabricated by subsequently reducing the deposition temperature of the FePt-C film from the bottom layer to the top layer. Magnetic anisotropy and coercivity of FePt-C film increased with the increasing of deposition temperature because the chemical ordering of L10 FePt improved with deposition temperature. A two-layer microstructure was observed in the multilayer samples with a closely-packed granular hard layer and an isolated granular overlayer consisting of the soft magnetic layers deposited at lower temperatures. The coercivity of the tri-layer media was reduced to 5.4 kOe, half of that of the hard single layer FePt-C (10.8 kOe). The thermal stability of the multilayer structure was maintained although some soft magnetic layers involved.
Principles of nanowire alignment in an electric field
Authors: Ruda H. E. , Shik A.
Published: March 2011

Alignment of semiconductor and metal nanowires in the electric field created by a periodic system of planar electrodes was studied theoretically. The alignment depends dramatically on the relationship between the nanowire length L, separation between electrodes a, and electrode width b as well as on the nanowire dielectric constant ɛ compared to that of the environment ɛ0. For ɛ>ɛ0 nanowires tend to align orthogonal to the electrode edges, following the average direction of electric field. Their particular position relative to the electrodes depends on L and was calculated for different values of L/a and b/a. For ɛ<ɛ0 long nanowires, with L > a, align parallel to the electrode edges (perpendicular to the field) while those with L < a.
Design of and data reduction from compact Thomson parabola spectrometers
Authors: Morrison J. T. , Willis C. , Freeman R. R. , Van Woerkom L.
Published: March 2011

Thomson parabola spectrometers are used to characterize MeV ion beams produced in high intensity laser interactions. These spectrometers disperse multiple ion species according to their charge to mass ratio through the use of parallel electric and magnetic fields. Analytical solutions for ion deflection in electric and magnetic fields have been used to extract ion spectra with the assumption that fringing effects are negligible. Experimental space restrictions and dynamic range requirements necessitate designs that stress the analytical assumptions. Depending on design parameters, the error in the analytical assumption can be comparable to the energy resolution. Estimates are provided to approximate the error on the total ion deflection. A method for modeling ion trajectories including fringing effects is presented using software freely available or in common use. The magnetostatic fields are modeled in 3D, including material properties of nearby magnetic materials using RADIA. Electrostatic fields are modeled in 2D for a spectrometer implementing angled plates using the partial differential equation toolbox in MATLAB®. Using these models to calculate the ion trajectory allows for analysis of a Thomson parabola spectrometer with an arbitrary field configuration.
Anisotropic magnetoresistance in low-doped La0.79Ca0.21MnO3 crystals
Authors: Yuzhelevski Ya. , Markovich V. , Jung G. , Gorodetsky G.
Published: March 2011

Anisotropic magnetoresistance (AMR) in La0.79Ca0.21MnO3 single crystals has been investigated. In contrast with previous studies, in our experiments AMR increases with decreasing temperature, reaches the maximum below TC and decreases with further temperature decrease. Variations of MR while rotating the sample around the [110] crystalline direction may be associated with uniaxial magnetocrystalline anisotropy. The unusual enhancement of AMR below TC is ascribed to changes in the magnetic domain structure revealed by magneto-optical techniques.
Case study for active solar space heating and domestic hot water preparation in a passive house
Authors: Badescu Viorel
Published: March 2011

Models for five components of an active solar heating system are described. The integrated model was implemented to Pirmasens Passive House (Rhineland Palatinate, Germany). Two series schemes of interconnection for the domestic hot preparation system and the space heating system, respectively, are analyzed. Rather similar results were obtained in both cases. The active solar system starts operation when the incoming solar irradiance exceeds a threshold value depending on the ambient temperature and the amount of thermal energy stored in the water tank. The combined effect of passive and active solar systems is not able to cover the space heating demand for the entire days of January. Most part of the collected solar energy is used for domestic hot water preparation. The results show that the series interconnection is unfavorable for the space heating system.
Voltage control of the magnetic coercive field: Multiferroic coupling or artifact?
Authors: Vopsaroiu M. , Cain M. G. , Woolliams P. D. , Weaver P. M , Stewart M. , Wright C. D. , Tran Y.
Published: March 2011

The ability to dynamically tune the coercive field of magnetic thin films is a powerful tool for applications, including in magnetic recording disk technologies. Recently, a number of papers have reported the electrical voltage control of the coercive field of various magnetic thin films in multiferroic composites. Theoretically, this is possible in magneto-electric (ME) multiferroics due to the piezoferroelectric component that can be electrically activated to dynamically modify the properties of the magnetic component of the composite via a direct or strain mediated ME coupling. In this paper we fabricated and examined such structures and we determined that the magnetic coercive field reduction is most likely due to a heating effect. We concluded that this effect is probably an artifact that cannot be attributed to a multiferroic coupling.
Plasmonic core-shell gold nanoparticle enhanced optical absorption in photovoltaic devices
Authors: Qu Di , Liu Fang , Yu Jiafan , Xie Wanlu , Xu Qi , Li Xiangdong , Huang Yidong
Published: March 2011

The enhancement effect of optical absorption with core-shell gold nanoparticles on the surface of wafer-based silicon photovoltaic devices has been studied. The obvious enhanced photocurrent is observed, especially when the wavelength is above 800 nm, and the highest enhancement value is about 14% around the wavelength of 1100 nm. The simulation results indicate that the presence of dielectric coating shell could improve the surface plasmon based scattering effect at longer wavelength range, which provides a good understanding of the experiment results.
Pyroelectric coefficient difference under open and short circuit conditions and their enhancements in laminate composites
Authors: Hockley M. J. , Chang H. H. S. , Huang Z.
Published: March 2011

The pyroelectric coefficient is normally measured under the short circuit condition, while many pyroelectric applications are under the open circuit condition. We present experimental results demonstrating a difference in the pyroelectric coefficient under open and short circuit conditions. We also present results on pyroelectric coefficient enhancement using laminate composites, and show that this technique can enhance the pyroelectric coefficient at open circuit condition, as well as at short circuit condition.
A generalized 3ω method for extraction of thermal conductivity in thin films
Authors: Zong Zhao-Xiang , Qiu Zhi-Jun , Zhang Shi-Li , Streiter Reinhard , Liu Ran
Published: March 2011

It has been found that in the low-frequency regime, the experimentally determined thermal conductivity of thin dielectric films deviates significantly from the theoretical expectation based on Cahill’s 3ω thermal model. It is shown in the present work that this deviation is mainly caused by the heat transport in the heater strip, which is neglected in Cahill’s one-dimensional model. By taking this mechanism into account, an analytical model is developed to simultaneously consider the heat transport in the heater strip and the heat flow into the underlying substrate. The validity of this two-dimensional model is confirmed by experiments using specially designed test structures as well as by numerical simulation. The results show that the heat transport along the heater strip, originated from a nonuniform temperature, becomes comparable to that in the substrate at low frequencies. This effect of a nonuniform temperature distribution can also be exploited for extraction of the thermal conductivity of the metallic strip itself.
Effects of hyperbolic rotation in Minkowski space on the modeling of plasma accelerators in a Lorentz boosted frame
Authors: Vay J.-L. , Geddes C. G. R. , Cormier-Michel E. , Grote D. P.
Published: March 2011

The effects of hyperbolic rotation in Minkowski space resulting from the use of Lorentz boosted frames of calculation on laser propagation in plasmas are analyzed. Selection of a boost frame at the laser group velocity is shown to alter the laser spectrum, allowing the use of higher boost velocities. The technique is applied to simulations of laser driven plasma wakefield accelerators, which promise much smaller machines and whose development requires detailed simulations that challenge or exceed current capabilities. Speedups approaching the theoretical optima are demonstrated, producing the first direct simulations of stages up to 1 TeV. This is made possible by a million times speedup thanks to a frame boost with a relativistic factor γb as high as 1300, taking advantage of the rotation to mitigate an instability that limited previous work.
Differential flexibility of the secondary structures of lysozyme and the structure and ordering of surrounding water molecules
Authors: Sinha Sudipta Kumar , Bandyopadhyay Sanjoy
Published: March 2011

We have performed an atomistic molecular dynamics simulation of an aqueous solution of hen egg-white lysozyme at room temperature with explicit water molecules. Several analyses have been carried out to explore the differential flexibility of the secondary structural segments of the protein and the structure and ordering of water around them. It is found that the overall flexibility of the protein molecule is primarily controlled by few large-amplitude bistable motions exhibited by two coils; one connecting two α-helical segments in domain-1 and the other connecting a 310 helix and a β-sheet in domain-2 of the protein. The heterogeneous structuring of water around the segments of the protein has been found to depend on the degree of exposure of the segments to water. The ordering of water molecules around the protein segments and their tagged potential energies have been found to be anticorrelated with each other. Some of these findings can be verified by suitable experimental studies.
Rotationally correlated reactivity in the CH (v = 0, J, Fi) + O2 → OH (A) + CO reaction
Authors: Ohoyama H. , Yamakawa K. , Oda R. , Nagamachi Y. , Kasai T.
Published: March 2011

The rotational-state-selected CH (v = 0, J, Fi) beam has been prepared by using an electric hexapole and applied to the crossed beam reaction of CH (v = 0, J, Fi) + O2 → OH (A) + CO at different O2 beam conditions. The rotational state selected reactive cross sections of CH (RSSRCS-CH) turn out to depend remarkably on the rotational state distribution of O2 molecules at a collision energy of ∼ 0.19 eV. The reactivity of CH molecules in the N = 1 rotational states (namely |J = 1/2, F2〉 and |J = 3/2, F1〉 states, N designates the angular momentum excluding spin) becomes strongly enhanced upon a lowering of the rotational temperature of the O2 beam. The RSSRCS-CH in these two rotational states correlate linearly with the population of O2 molecule in the specific ${\rm K}_{{\rm O}_{\rm 2} }$KO2 frame rotation number states: $ {\rm CH} (| {{\rm J} = 1/2,{\rm F}_{\rm 2} }\rangle)\; \hbox{with}\; {\rm O}_2 (| {{\rm K}_{{\rm O}_{\rm 2} } = {\rm 1}}\rangle); {\rm CH} (| {{\rm J} = 3/2,{\rm F}_{\rm 1} }\rangle)\; \hbox{with}\; {\rm O}_2 (| {{\rm K}_{{\rm O}_{\rm 2} } = {\rm 3}}\rangle).$ CH (|J=1/2,F2⟩)withO2(|KO2=1⟩); CH (|J=3/2,F1⟩)withO2(|KO2=3⟩).These linear correlations mean that the rotational-state-selected CH molecules are selectively reactive upon the incoming O2 molecules in a specific rotational state; here, we use the term “rotationally correlated reactivity” to such specific reactivity depending on the combination of the rotational states between two molecular reactants. In addition, the steric asymmetry in the oriented CH (|J = 1/2, F2, M = 1/2〉) + O2 ($| {{\rm K}_{{\rm O}_{\rm 2} } = 1}\rangle$|KO2=1⟩) reaction turns out to be negligible (< ±1%). This observation supports the reaction mechanism as theoretically predicted by Huang et al. [J. Phys. Chem. A 106, 5490 (2002)] that the first step is an intermediate formation with no energy barrier in which C-atom of CH molecule attacks on one O-atom of O2 molecule at a sideways configuration.
Time-resolved study of excited states of N2 near its first ionization threshold
Authors: Moise Angelica , Prince Kevin C. , Richter Robert
Published: March 2011

Two-photon, two-color double-resonance ionization spectroscopy combining synchrotron vacuum ultraviolet radiation with a tunable near-infrared (NIR) laser has been used to investigate gerade symmetry states of the nitrogen molecule. The rotationally resolved spectrum of an autoionizing 1Σg− state has been excited via the intermediate c4 (v = 0) 1Πu Rydberg state. We present the analysis of the band located at Tv = 10 800.7 ± 2 cm−1 with respect to the intermediate state, 126 366 ± 11 cm−1 with respect to the ground state, approximately 700 cm−1 above the first ionization threshold. From the analysis a rotational constant of Bv = 1.700 ± 0.005 cm−1 has been determined for this band. Making use of the pulsed structure of the two radiation beams, lifetimes of several rotational levels of the intermediate state have been measured. We also report rotationally-averaged fluorescence lifetimes (300 K) of several excited electronic states accessible from the ground state by absorption of one photon in the range of 13.85–14.9 eV. The averaged lifetimes of the c4 (0) and c5 (0) states are 5.6 and 4.4 ns, respectively, while the b′ (12), c′4 (4, 5, 6), and c′5 (0) states all have lifetimes in the range of hundreds of picoseconds.
Derivation of the generalized Langevin equation in nonstationary environments
Authors: Kawai Shinnosuke , Komatsuzaki Tamiki
Published: March 2011

The generalized Langevin equation (GLE) is extended to the case of nonstationary bath. The derivation starts with the Hamiltonian equation of motion of the total system including the bath, without any assumption on the form of Hamiltonian or the distribution of the initial condition. Then the projection operator formulation is utilized to obtain a low-dimensional description of the system dynamics surrounded by the nonstationary bath modes. In contrast to the ordinary GLE, the mean force becomes a time-dependent function of the position and the velocity of the system. The friction kernel is found to depend on both the past and the current times, in contrast to the stationary case where it only depends on their difference. The fluctuation–dissipation theorem, which relates the statistical property of the random force to the friction kernel, is also derived for general nonstationary cases. The resulting equation of motion is as simple as the ordinary GLE, and is expected to give a powerful framework to analyze the dynamics of the system surrounded by a nonstationary bath.
Shock wave structure for generalized Burnett equations
Authors: Bobylev A. V. , Bisi M. , Cassinari M. P. , Spiga G.
Published: March 2011

Stationary shock wave solutions for the generalized Burnett equations (GBE) [A. V. Bobylev, “Generalized Burnett hydrodynamics,” J. Stat. Phys. 132, 569 (2008)] are studied. Based on the results of Bisi et al. [“Qualitative analysis of the generalized Burnett equations and applications to half-space problems,” Kinet. Relat. Models 1, 295 (2008)], we choose a unique (optimal) form of GBE and solve numerically the shock wave problem for various Mach numbers. The results are compared with the numerical solutions of Navier–Stokes equations and with the Mott–Smith approximation for the Boltzmann equation (all calculations are done for Maxwell molecules) since it is believed that the Mott–Smith approximation yields better results for strong shocks. The comparison shows that GBE yield certain improvement of the Navier–Stokes results for moderate Mach numbers.
First-principles study of the electronic structure and optical properties of Ce-doped ZnO
Authors: Zhang Yun Geng , Zhang Guang Biao , Xu Wang Yuan
Published: March 2011

Density functional theory calculations by using both generalized gradient approximation (GGA) method and the GGA with considering strong correlation effect (GGA+U) were performed to elucidate the effect of Ce-4f orbit on the electronic structure of ZnO. It is found that after the cerium incorporation, a new localized band appears between the valence and conduction bands, which corresponds to the majority spin of Ce-4f states. It is this localized band that constructs a bridge between the valence and conduction states, which will improve the optical performance of ZnO. ZnO:Ce is a degenerate semiconductor. The strong correlation effect is very important for the 4f orbit of the Ce atom in ZnO:Ce. The mismatch of the majority and minority spin for the Ce-4f, Ce-5d states and the spin-polarized holes in O-2p states induced by Ce doping leads to the presence of the magnetic order for ZnO:Ce. We also studied the band structure and optical properties of ZnO:Ce with lacking one electron and two electrons, respectively. With the deficiency of the electrons, the Fermi level moves downward. The magnetism disappears when the system lacks two electrons. The analysis of optical properties shows that ZnO:Ce is a promising dielectric material and has potential applications in optoelectric devices.
Huge Seebeck coefficients in nonaqueous electrolytes
Authors: Bonetti M. , Nakamae S. , Roger M. , Guenoun P.
Published: March 2011

The Seebeck coefficients of the nonaqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide, and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol, and ethylene-glycol are measured in a temperature range from T = 30 °C to T = 45 °C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1 M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or “structure making” effects of tetraalkylammonium ions on the structure of alcohols.
Interaction between water and defective silica surfaces
Authors: Chen Yun-Wen , Cheng Hai-Ping
Published: March 2011

We use the density functional theory method to study dry (1 × 1) α-quartz (0001) surfaces that have Frenkel-like defects such as oxygen vacancy and oxygen displacement. These defects have distinctively different effects on the water–silica interface depending on whether the adsorbent is a single water molecule, a cluster, or a thin film. The adsorption energies, bonding energies, and charge transfer or redistributions are analyzed, from which we find that the existence of a defect enhances the water molecule and cluster surface interaction by a large amount, but has little or even negative effect on water thin film–silica surface interaction. The origin of the weakening in film–surface systems is the collective hydrogen bonding that compromises the water–surface interaction in the process of optimizing the total energy. For clusters on surfaces, the lowest total energy states lower both the bonding energy and the adsorption energy.
Indications of field-directing and self-templating effects on the formation of organic lines on silicon
Authors: Zikovsky Janik , Dogel Stanislav A. , Salomons Mark H. , Pitters Jason L. , DiLabio Gino A. , Wolkow Robert A.
Published: March 2011

It has previously been shown that multimolecular organic nanostructures form on H-Si(100)-2×1 via a radical mediated growth process. In this mechanism, growth begins through the addition of a molecule to a silicon surface dangling bond, followed by the abstraction of a neighboring H atom and generation of a new dangling bond on the neighboring site. Nanostructures formed by this mechanism grow along one edge of a dimer row. Here, we explored the possibility of using lithographically prepared, biased metal contacts on the silicon surface to generate an electric field that orients molecules during the growth process to achieve growth in the perpendicular-to-row direction. The formation of some nanostructures in a direction that was nearly perpendicular to the dimer rows was achieved, whereas such features were not formed in the absence of the field. Analysis of the scanning tunneling microscopy images suggests that the formation of these nanostructures may involve self-templating effects in addition to dangling bond diffusion rather than a straightforward addition/abstraction mechanism. These initial results offer some indication that a molecular pattern writer can be achieved.
Strong intermolecular coupling between the HF stretching and H2O bending vibrations in HF:H2O binary amorphous solids: Breakdown of the electrostatic description of the hydrogen bond
Authors: Marcotte Guillaume , Ayotte Patrick
Published: March 2011

The coupling mechanism between the HF stretching and H2O bending vibrations observed in the infrared spectra of HF:H2O binary amorphous solids is analyzed using a simple cluster model. The intermolecular vibrational coupling derived from electrostatic potentials is one order of magnitude smaller, and of the opposite sign, than that obtained from electronic structure-based potentials. This highlights the distinctively covalent character of strong H-bonds and unveils fundamental weaknesses of electrostatic descriptions of vibrational energy transfer in liquid water and aqueous solutions.
Ga14Sb86 film for ultralong data retention phase-change memory
Authors: Lu Yegang , Song Sannian , Song Zhitang , Liu Bo
Published: March 2011

Ga14Sb86 film has been studied to explore its suitability as a novel active material for phase change memory application. With a crystallization temperature about 220 °C, Ga14Sb86 film has the activation energy of crystallization larger than 4.6 eV obtained both by nonisothermal and isothermal methods. This leads to an ultralong data retention, which is characterized by the temperature for ten years data retention at 162 °C. The reversible phase change can be realized by a pulse as short as 20 ns. Ga14Sb86-based cell shows a good endurance up to 3.2x105 SET-RESET cycles during endurance test.