bluuebunny/crossref_metadata_2025 huggingface dataset:
Realizing steady-state tokamak operation for fusion energy
Authors: Luce T. C.
Published: March 2011

Continuous operation of a tokamak for fusion energy has clear engineering advantages but requires conditions beyond those sufficient for a burning plasma. The fusion reactions and external sources must support both the pressure and the current equilibrium without inductive current drive, leading to demands on stability, confinement, current drive, and plasma-wall interactions that exceed those for pulsed tokamaks. These conditions have been met individually, and significant progress has been made in the past decade to realize scenarios where the required conditions are obtained simultaneously. Tokamaks are operated routinely without disruptions near pressure limits, as needed for steady-state operation. Fully noninductive sustainment with more than half of the current from intrinsic currents has been obtained for a resistive time with normalized pressure and confinement approaching those needed for steady-state conditions. One remaining challenge is handling the heat and particle fluxes expected in a steady-state tokamak without compromising the core plasma performance.
Terahertz spectroscopic imaging of a rabbit VX2 hepatoma model
Authors: Park Jae Yeon , Choi Hyuck Jae , Cho Kyoung-Sik , Kim Kyu-Rae , Son Joo-Hiuk
Published: March 2011

Terahertz (THz) spectroscopic imaging technique was applied to classify the tumor region in the rabbit liver with VX2 hepatocellular carcinoma. Within the measurement range of 0.1–2 THz, the average reflectance values for all tumor samples were more than 4% higher than those for healthy cells, and the terahertz measurements correlated well with histological analysis results. This study on paraffin-embedded tissues showed the alteration of cell density and protein content in tumors, excluding the effect of water.
Enhanced reflection loss characteristics of substituted barium ferrite/functionalized multi-walled carbon nanotube nanocomposites
Authors: Ghasemi Ali , Shirsath Sagar E. , Liu Xiaoxi , Morisako Akimitsu
Published: March 2011

In this research work, magnetic multi-walled carbon nanotube (MWCNTs) nanocomposites have been created by the assembly of Mn-Co-Ti-substituted barium ferrite nanoparticles onto the surface of MWCNTs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to demonstrate the successful attachment of ferrite nanoparticles to MWCNTs. Vibrating sample magnetometry (VSM) confirmed the relatively strong dependence of saturation magnetization on the volume percentage of MWCNTs. Microwave absorption of the MWCNTs/doped barium ferrite (BaM) nanocomposites is evidently enhanced compared to that of pure MWCNTs and ferrite nanoparticles. The maximum reflection loss increased significantly with an increase in volume percentage of MWCNTs in nanocomposites.
Magnetic phase transitions and magnetocaloric properties of (Gd12-xTbx)Co7 alloys
Authors: Zheng Z. G. , Zhong X. C. , Yu H. Y. , Liu Z. W. , Zeng D. C.
Published: March 2011

The structure and magnetocaloric properties of polycrystalline (Gd12-xTbx)Co7 (x=0, 4, and 8) alloys with Ho12Co7-type monoclinic structure have been investigated. A spin reorientation transition occurs at about 123 K for the alloy with x=0. The peak values of magnetic entropy change −ΔSM under a magnetic field change ΔH of 5 T is 8.8 J·kg−1·K−1 at 160.8 K (Tc), 8.2 J·kg−1·K−1 at 140.8 K (Tc), and 7.1 J·kg−1·K−1 at 118.9 K (Tc) for the alloys with x=0, 4 and 8, respectively. The refrigerant capacities reach 478, 327, and 160 J·kg−1 for x=0, 4, and 8, respectively. The relatively large magnetic entropy change and reversible magnetization behavior make these alloys a good choice for magnetic refrigeration applications in the temperature range of 118–160 K.
Perpendicular ferrimagnetism in strained Mn2As film
Authors: Hwang Younghun , Choi Jeongyong , Duc Dung Dang , Shin Yooleemi , Cho Sunglae
Published: March 2011

Ferrimagnetic Mn2As thin films with perpendicular magnetic anisotropy were successfully grown on Si(100) by molecular-beam epitaxy. From the reflection high-energy electron diffraction and X-ray diffraction patterns, the orientation of the Mn2As film on Si was along the c-axis in the tetragonal crystal structure. Mn2As film exhibited ferrimagnetic ordering at temperatures greater than 300 K, which differs from antiferromagnetic or paramagnetic behaviors in the bulk form. The magnetic moment of Mn2As determined by saturated magnetization was 0.51 µB per unit cell.
Capacitance-voltage and deep-level-transient spectroscopy characterization of defects near SiO2/SiC interfaces
Authors: Basile A. F. , Rozen J. , Williams J. R. , Feldman L. C. , Mooney P. M.
Published: March 2011

Metal-oxide-semiconductor (MOS) interfaces on n-type 4H and 6H-SiC annealed in nitric oxide (NO) for various times were electrically characterized by high-frequency capacitance-voltage and deep-level-transient spectroscopy (DLTS) measurements. Different types of traps were distinguished by DLTS based on the energy-resolved DLTS spectra and comparing DLTS spectra from the two polytypes. Oxide traps, found at much higher densities in the larger bandgap 4H-SiC, are reduced by NO annealing, and their capture behavior is analytically modeled with a tunneling-dependent capture rate. An interface trap distribution is found in 6H-SiC MOS centered at 0.5 eV below the conduction band. Near interface traps in the SiC within 0.1 eV below the conduction band edge, detected at equal concentrations in both polytypes, are not passivated by NO annealing.
Quantum-confinement effect on holes in silicon nanowires: Relationship between wave function and band structure
Authors: Morioka Naoya , Yoshioka Hironori , Suda Jun , Kimoto Tsunenobu
Published: March 2011

The authors theoretically studied the valence band structure and hole effective mass of rectangular cross-sectional Si nanowires (NWs) with the crystal orientation of [110], [111], and [001]. The E–k dispersion and the wave function were calculated using an sp3d5s∗ tight-binding method and analyzed with the focus on the nature of p orbitals constituting the subbands. In [110] and [111] nanowires, longitudinal/transverse p orbitals are well separated and longitudinal component makes light (top) subbands and transverse component makes heavy subbands. The heavy subbands are located far below the top light band when NW has square cross-section, but they gain their energy with the increase in the NW width and come near the band edge. This energy shift of heavy bands in [110] NWs shows strong anisotropy to the direction of quantum confinement whereas that in [111] NWs does not have such anisotropy. This anisotropic behavior and the difference among orientations are understandable by the character of the wave function of heavy subbands. Regarding the [001] nanowires, the top valence state is formed by the mixture of longitudinal/transverse p orbitals, which results in heavy effective mass and large susceptibility to lateral-size variation. The correlation of the wave function of hole states between nanowires and bulk is also discussed briefly.
Study of loss in superconducting coplanar waveguide resonators
Authors: Sage Jeremy M. , Bolkhovsky Vladimir , Oliver William D. , Turek Benjamin , Welander Paul B.
Published: March 2011

Superconducting coplanar waveguide (SCPW) resonators have a wide range of applications due to the combination of their planar geometry and high quality factors relative to normal metals. However, their performance is sensitive to both the details of their geometry and the materials and processes that are used in their fabrication. In this paper, we study the dependence of SCPW resonator performance on materials and geometry as a function of temperature and excitation power. We measure quality factors greater than 2 × 106 at high excitation power and 6 × 105 at a power comparable to that generated by a single microwave photon circulating in the resonator. We examine the limits to the high excitation power performance of the resonators and find it to be consistent with a model of radiation loss. We further observe that while in all cases the quality factors are degraded as the temperature and power are reduced due to dielectric loss, the size of this effect is dependent on resonator materials and geometry. Finally, we demonstrate that the dielectric loss can be controlled in principle using a separate excitation near the resonance frequencies of the resonator.
Self heating in AlInN/AlN/GaN high power devices: Origin and impact on contact breakdown and IV characteristics
Authors: Gonschorek M. , Carlin J.-F. , Feltin E. , Py M. A. , Grandjean N.
Published: March 2011

It is observed experimentally that high electron mobility transistor devices with short channel length processed from nitride AlInN/AlN/GaN heterostructures containing 2D electron gases (2DEGs) with densities beyond 2 × 1013 cm−2 exhibit temperatures up to 1000 K if they are driven at high drain-source voltages. Corresponding current-voltage (IV) characteristics show a peaklike behavior with a maximum saturation current (IDS,max) up to 2 A/mm. The goal of this article is to describe device heating in the framework of LO phonon statistics and its dependence on channel length, carrier density, and applied voltage. The strong channel heating, on the other hand, affects the transport mobility and must be taken into account to correctly interpret IV characteristics and resolve the discrepancy with metal oxide semiconductor field effect transistor models. Furthermore, the breakdown of ohmic contacts can directly be related to the channel temperature, i.e., the channel reaches the melting point of the contact metallization. In addition, the model correctly predicts the behavior of IV curves versus 2DEG density and transistor initial ambient temperature. For 2DEGs confined in triangular potential wells formed at the heterointerface, a maximum IDS is found for 2DEG densities between 2 × 1013 and 3 × 1013 cm−2.
Understanding the distribution of iron in multicrystalline silicon after emitter formation: Theoretical model and experiments
Authors: Schön J. , Habenicht H. , Schubert M. C. , Warta W.
Published: March 2011

We studied the behavior of iron in multicrystalline silicon during phosphorus diffusion by spatially resolved measurements and physical modeling. We present improvements to the previously used models for internal gettering in multicrystalline silicon and phosphorus diffusion gettering. 2-dimensional simulations are used for optimization of the phosphorus diffusion processes for intentionally contaminated wafers regarding the iron distribution, without changing the emitter characteristics. Simulations and experimental results show a reduced interstitial iron concentration after an additional low temperature step at the end of the phosphorus diffusion. The concentration of iron precipitates was reduced by a short annealing at 900°C before the phosphorus diffusion, leading to a carrier lifetime three times higher than compared to the standard process.
Luminescence imaging of polymer solar cells: Visualization of progressing degradation
Authors: Seeland M. , Rösch R. , Hoppe H.
Published: March 2011

We apply luminescence imaging as tool for the nondestructive visualization of degradation processes within bulk heterojunction polymer solar cells. The imaging technique is based on luminescence detection with a highly sensitive silicon charge-coupled-device camera and is able to visualize with time advancing degradation patterns of polymer solar cells. The devices investigated have been aged under defined conditions and were characterized periodically with current-voltage (I-V) sweeps. This allows determining the time evolution of the photovoltaic parameters and—in combination with the luminescence images—understanding differences in the observed degradation behavior. The versatile usability of the method is demonstrated in a correlation between local reduction of lateral luminescence and a fast decrease of the short-circuit current (Isc) due to the loss of active area. Differences in the degradation of photovoltaic parameters under varied aging conditions are discussed.
Scanning microwave microscopy and scanning capacitance microscopy on colloidal nanocrystals
Authors: Humer I. , Bethge O. , Bodnarchuk M. , Kovalenko M. , Yarema M. , Heiss W. , Huber H. P. , Hochleitner M. , Hinterdorfer P. , Kienberger F. , Smoliner J.
Published: March 2011

In this paper, the dielectric constants of colloidal nanocrystals are investigated by scanning capacitance microscopy (SCM) and scanning microwave microscopy (SMM). Whereas SMM provides frequencies from 1 up to 18 GHz, conventional SCM is restricted to values below 20 kHz. With both techniques, C(V) and dC(V)/dV curves are acquired on various nanocrystalline films (Fe3O4, CoFe2O4, PbS) with monolayer thickness and on uncovered reference areas on the same samples. As we find, the dielectric constants of these nanocrystals are significantly larger as those of the bulk materials. A strong decrease of the permittivity with increasing frequency is also found.
Magnetic anisotropy in bulk nanocrystalline SmCo5 permanent magnet prepared by hot deformation
Authors: Yue M. , Zuo J. H. , Liu W. Q. , Lv W. C. , Zhang D. T. , Zhang J. X. , Guo Z. H. , Li W.
Published: March 2011

Bulk anisotropic nanocrystalline SmCo5 magnets have been prepared by hot deformation method. The height reduction of the magnets plays a key role in inducing the crystallographic alignment in the magnet. Increase of height reduction to 90% leads to the formation of platelet shape grains perpendicular to the press direction; correspondingly c-axis crystallographic texture and magnetic anisotropy were developed in the deformed magnets. The coercivity of the magnets increases first,and then decreases again with the increase of the height reduction. The magnet with 70% height reduction exhibits a high coercivity over 5 T.
Enhancement in magnetic torque of cylindrical micro rotor by usage of directly consolidated α-Fe/Pr2Fe14B-based nanocomposite thick-films
Authors: Yamashita F. , Nishimura S. , Kobayashi O. , Itoh M. , Nakano M. , Fukunaga H. , Ishiyama K.
Published: March 2011

An advanced preparation method was carried out to obtain a magnetized cylindrical micro rotorfabricated from directly consolidated isotropic α-Fe/Pr2Fe14B nanocomposite thick-films with self-bonding layer. A magnetic torque of the above film with the remanence value of 0.97 T, the coercivity value of 650 kA/m, and the (BH)max value of 142 kJ/m3 was investigated under different field strengths. Namely, magnetic torque of the above-mentioned rotor with a single pole pairincreased by 117%, compared with that of Fe3B/Nd2Fe14B films with the remanence value of 1.1 T, the coercivity value of 334 kA/m, and the (BH)max value of 95 kJ/m3. It was found that the use of α-Fe/Pr2Fe14B films is effective in obtaining a multipolarly magnetized micro rotor with highly dense torque as well as magnetic stability.
Magnetic switching and magnetic transitions in ErCo2 probed by radio-frequency transverse susceptibility
Authors: Figueroa A. I. , Chandra S. , Phan M. H. , Srikanth H. , Bonilla C. M. , García L. M. , Bartolomé F. , Bartolomé J. , Herrero-Albillos J.
Published: March 2011

ErCo2 represents a typical example of magnetism of itinerant electron systems and metamagnetic processes and has been the subject of extensive research. We present here the first study of radio-frequency transverse susceptibility (TS) of bulk ErCo2 using a self-resonant tunnel-diode oscillator technique. TS measurements reveal the collective magnetic switching of the Er moments at temperatures below the ferrimagnetic transition temperature, Tc∼32 K, and the existence of Co nanoclusters with short-range correlations at Tc<T<Tf (Tf denoted as the flipping temperature). The difference in the magnetic configuration between the ferrimagnetic, parimagnetic, and paramagnetic states, as well as the change from the paramagnetic to parimagnetic regime upon varying dc magnetic fields are also probed by TS experiments. These findings are discussed in the context of our previous investigations using other different techniques which provide further insights into the magnetism and the so-called parimagnetism phenomenon in ErCo2.
A study of radiation damage effects on the magnetic structure of bulk Iron
Authors: Wang Yang , Nicholson D. M. C. , Stocks G. M. , Rusanu Aurelian , Eisenbach Markus , Stoller R. E.
Published: March 2011

Defects, defect interactions, and defect dynamics in solids created by fast neutrons are known to have significant impact on the performance and lifetime of structural materials. A fundamental understanding of the radiation damage effects in solids is therefore of great importance in assisting the development of improved materials - materials with ultrahigh strength, toughness, and radiation resistance. In this presentation, we show our recent theoretical investigation on the magnetic structure evolution of bulk iron in the region of the radiation defects. We applied a linear scaling ab-initio method based on density functional theory with local spin density approximation, namely the locally self-consistent multiple scattering method (LSMS), to the study of magnetic moment distributions in a cascade at the damage peak and for a series of time steps as the interstitials and vacancies recombined. Atomic positions correspond to those in a low energy cascade in a 10|000 atom sample, in which the primary damage state and the evolution of all defects produced were simulated using molecular dynamics with empirical, embedded-atom inter-atomic potentials. We will discuss how a region of affected moments expands and then recedes in response to a cascade evolution.
Effect of spin polarized current on magnetic phase transition of ordered FeRh wires
Authors: Naito T. , Suzuki I. , Itoh M. , Taniyama T.
Published: March 2011

We report on spin polarized current injection from Co wires into a B2-ordered FeRh wire, which shows the magnetic phase transition from the antiferromagnetic (AF) state to the ferromagnetic state at 370 K. Current–voltage characteristics of a Co/FeRh wires junction sample show a marked feature in the AF state below 380 K, while the feature disappears above 380 K, indicating that the noticeable feature is associated with the antiferromanetic–ferromagnetic phase transition induced by the spin polarized current injection into the FeRh wire. We attribute the spin polarized current induced phase transition to a possible modulation of the s-d exchange interaction arising from the spin polarization of itinerant electrons and Rh atoms in the FeRh wire.
Magnetic properties and microstructure of Ag2Se/FePt particulate films
Authors: Tsai Jai-Lin , Tai Hsueh-Wei , Tzeng Hsin-Te
Published: March 2011

Multilayer Ag/[Ag2Se(t)/FePt(1nm)]10 (thickness t = 0.1–0.4 nm) were alternately deposited on a glass substrate and subsequently annealed by rapid thermal process (RTP) at 800 °C for 3 min. After RTP, the interface between FePt and Ag2Se was intermixed to form particulate films. The grains size of the L10 FePt decreased from 9.8 to 7.7 nm when the total thickness of Ag2Se intermediate layer increases to 1 nm. The Ag/(Ag2Se/FePt)10 particulate film showed perpendicular magnetization and a slight increase in out-of-plane coercivity over that of the original thickness of Ag2Se. The Ag2Se atoms were immiscible with FePt phase but the FePt grains were refined and separated well from the Ag2Se phase. Compared with Ag/FePt bilayer, the grains of the FePt were refined and uniformly separated in the Ag/[Ag2Se(t)/FePt]10 multilayer with t = 0.1 nm.
Plasmon resonance enhancement of Faraday rotation in thin garnet films
Authors: Tkachuk S. , Lang G. , Krafft C. , Rabin O. , Mayergoyz I.
Published: March 2011

Garnet films have been grown over (100)-oriented substituted gadolinium gallium garnet substrates partially populated with gold nanoparticles in order to study plasmon resonance enhancement of magneto-optic effects. The results of measurements of light transmission through these films as well as Faraday rotation are reported.
Preparation and magnetic properties of hard-magnetic (CoPt)/soft-magnetic (FeCo) composite nanocable array
Authors: Zhou D. , Zhu M. G. , Zhou M. G. , Guo Z. H. , Li W.
Published: March 2011

An array of hard-magnetic (CoPt)/soft-magnetic (FeCo) composite nanocable has been fabricated in the pores of porous anodic aluminum oxide templates: CoPt nanotubes were first prepared by high temperature chemical reduction method; FeCo alloy was then electrodeposited into the CoPt nanotubes. The morphology and structure of the nanocable array were characterized by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The magnetic measurements showed that two apparent kinks appear in the hysteresis loop after the FeCo alloy was deposited into the CoPt nanotubes, which may be attributed to the hard-magnetic phase being partly or even completely decoupled from the soft-magnetic phase.
Effect of the TiN content in the Pd–TiN seed layer on the microstructure and magnetic properties of Co/Pd multilayered media
Authors: Kim Sung Man , Chun Dong Won , Lee Jung Joong , Jeung Won Young
Published: March 2011

[Co(0.2 nm)/Pd(0.8 nm)]20 multilayered films on 15 nm Pd–TiN seed layers were fabricated by dc magnetron sputtering without heating the substrate. The effects of TiN content on microstructure and magnetic properties of the [Co/Pd] multilayered media were studied. By increasing the TiN content in the Pd–TiN seed layer to an optimum level, coercivity of the [Co/Pd] multilayered media increased to 6.7 kOe. However, further increase of TiN content beyond 22 vol % reduced coercivity (Hc), implying that there exists a critical TiN concentration to enhance the magnetic property of the [Co/Pd] multilayered media. Transmission electron microscopic observations revealed that well-isolated [Co/Pd] multilayered grains with apparent grain boundaries were achieved by controlling the TiN content in the Pd–TiN seed layer. The average grain diameter was 8 nm with a dispersion of 11.2%, grown on the Pd–TiN seed layer with TiN content of 22 vol %.
Analysis on electric power consumption characteristics of cylindrical linear oscillatory actuator with Halbach permanent magnet array mover under electromechanical resonance frequency
Authors: Ko Kyoung-Jin , Jang Seok-Myeong , Choi Ji-Hwan , Choi Jang-Young , Sung So-Young , Park Young-Tae
Published: March 2011

This paper deals with electric power consumption characteristics of cylindrical linear oscillatory actuator with Halbach permanent magnet array mover under electromechanical resonance frequency. The control parameters such as back-emf constant, torque constant, resistance, and inductance are obtained from characteristic equations and experimental results. Then, the voltage equation and mechanical motion equation after deriving control parameters are proposed by impedance modeling considering mechanical component, and theoretical resonance frequency is predicted by impedance modeling. Finally, dynamic simulation and experimental results are presented for drive characteristics such as current, power factor, and displacement according to the various values of frequency, and this paper find that the current and electric power consumed in linear actuator have the minimum value at the resonance frequency.
Magnetic properties of Mn and Co doped PbPdO2
Authors: Joon Lee Kyu , Choo Sung Min , Saiga Yuta , Takabatake Toshiro , Jung Myung-Hwa
Published: March 2011

We report the dramatic change of gapless semiconductor properties by different chemical doping elements of Co and Mn into PbPdO2. The metal-insulatorlike transition temperature TMI = 100 K for PbPdO2 shifts to a higher temperature of 150 K by the Co doping and to a lower temperature of 70 K by the Mn doping. Because of the anisotropic band structure with the majority of heavy holes and the minority of light electrons, the transport and magnetic properties are significantly changed by the chemical doping elements. At low temperatures, the Co doping enhances ferromagnetic interactions, whereas the Mn doping favors antiferromagnetic interactions. These results are of great interests because you can control the magnetic ordering as well as manipulate the carrier density by changing the doping elements. These materials could be a good candidate for spintronics applications.
Magneto absorption measurements of nano-size ɛ-AlxFe2-xO3 powder materials at millimeter wavelengths
Authors: Afsar Mohammed N. , Li Zijing , Korolev Konstantin A. , Namai Asuka , Ohkoshi Shin-ichi
Published: March 2011

Ferromagnetic absorption spectra of ɛ-AlxFe2-xO3 powders with various x parameters and densities were obtained using free space quasi-optical spectrometer. Two absorption peaks located at around 95 and 105 GHz have been found. The 95 GHz absorption corresponds to x parameter value of 0.66; while the 105 GHz absorption corresponds to x-parameter value of 0.49. The absorption peak shifts to the lower frequency with increasing value of x parameter. The change in densities resulted in change in absorption intensity. The absorption characteristics are repeatable for these specimens prepared even at eight months interval. These absorbers are composed of ɛ-AlxFe2-xO3 nanomagnets and prepared by sol-gel techniques. Free space quasi-optical spectrometer equipped with a set of tunable backward-wave oscillators as power sources is used in this work to study the transmittance and absorption property of this series of materials at millimeter wave frequencies. The transmittance and absorbance spectra of ɛ-AlxFe2-xO3 powders with different x values (x = 0.66 and 0.49) and densities are recorded using the free space spectrometer. Strong magnetic absorption centering at 95 GHz (corresponding to x = 0.66) and at 105 GHz (x = 0.49) are found for all densities.
First order transition in Dy5Si3Ge: Transport and thermal properties, and first principles calculations
Authors: Nirmala R. , Paudyal Durga , Pecharsky V. K. , Gschneidner K. A. , Nigam A. K.
Published: March 2011

Transport properties of the intermetallic compound Dy5Si3Ge have been studied across its structural and magnetic transitions. The compound has a monoclinic crystal structure at room temperature, and orders magnetically at 74 K (TN) and 62 K (TC). Upon cooling it undergoes a structural transition to an orthorhombic structure near TC. Below ∼50 K, Dy5Si3Ge exists in a structurally phase separated state and is ferromagnetically ordered. The electrical resistivity and heat capacity of Dy5Si3Ge show interesting hysteretic behavior in the vicinity of the structural transition in zero field. First principles calculations suggest that Ge and Si atoms preferentially occupy intraslab andinterslab sites in Dy5Si3Ge, respectively, which leads to dominant ferromagnetic interactions within both the orthorhombic and monoclinic structures.
Phase diagram and dynamics in Er1−xYxMnO3
Authors: Vajk O. P. , Gunasekera J. , Wang Y. , Heitmann T.
Published: March 2011

Strong coupling between the ferroelectric and magnetic order has been previously observed in hexagonal HoMnO3 at a spin reorientation transition between a P6′3cm′ and a P6′3c′m magnetic phases. Understanding the transition between these phases may help illuminate the mechanism of multiferroic coupling in hexagonal R MnO3. In order to study this transition, single-crystal samples of the hexagonal multiferroic Er1−xYxMnO3 were grown at different compositions. YMnO3 orders in a P6′3cm′ phase, whereas ErMnO3 orders in a P6′3c′m phase. Er1−xYxMnO3 transitions completely from the P6′3cm′ to the P6′3c′m phase over a very narrow composition range on the Y-rich side of the phase diagram, and the phase boundary exhibits reentrant behavior. Inelastic neutron scattering measurements were performed on these samples, quasielastic scattering similar to that found in YMnO3 was observed. In the P6′3cm′ phase, this quasielastic scattering is centered at Bragg positions which correspond to the P6′3c′m and vice versa. These results may provide important information about the competition between these two magnetic phases.
Electron and hole drift velocity in chemical vapor deposition diamond
Authors: Gabrysch Markus , Majdi Saman , Twitchen Daniel J. , Isberg Jan
Published: March 2011

The time-of-flight technique has been used to measure the drift velocities for electrons and holes in high-purity single-crystalline CVD diamond. Measurements were made in the temperature interval 83≤T≤460 K and for electric fields between 90 and 4×103 V/cm, applied in the 〈100〉 crystallographic direction. The study includes low-field drift mobilities and is performed in the low-injection regime to perturb the applied electric field only minimally.
Anomalous heat capacity and x-ray photoelectron spectroscopy of superconducting FeSe1/2Te1/2
Authors: Awana V. P. S. , Govind  , Pal Anand , Gahtori Bhasker , Kaushik S. D. , Vajpayee A. , Kumar Jagdish , Kishan H.
Published: March 2011

The bulk polycrystalline sample FeSe1/2Te1/2 is synthesized via the solid state reaction route in an evacuated, sealed quartz tube at 750°C. The presence of superconductivity is confirmed through magnetization/thermoelectric/resistivity studies. It is found that the superconducting transition temperature (Tc) is around 12 K. The heat capacity (Cp) of superconducting FeSe1−xTex exhibits a hump near Tc, instead of a well-defined lambda transition. X-ray photoelectron spectroscopy studies reveal well-defined positions for divalent Fe, Se, and Te, but with sufficient hybridization of the Fe (2p) and Se/Te (3d) core levels. In particular, divalent Fe is shifted to a higher binding energy, and Se and Te to a lower one. The situation is similar to that observed previously for the famous Cu-based high Tc superconductors, where the Cu (3d) orbital hybridizes with O (2p). We also found the satellite peak of Fe at 712.00 eV, which is attributed to the charge-carrier localization induced by Fe at the 2c site.
Dot arrays of L1-type FePt ordered alloy perpendicular films fabricated using low-temperature sputter film deposition
Authors: Shimatsu T. , Inaba Y. , Kataoka H. , Sayama J. , Aoi H. , Okamoto S. , Kitakami O.
Published: March 2011

Using ultrahigh vacuum sputter film deposition, we fabricated L10-type Fe50Pt50 ordered alloy perpendicular films on MgO(001) single-crystal substrates and 2.5 in. glass disks at low substrate temperatures of 200–350 °C. Then we examined the magnetic properties of the dot arrays made from these films. The uniaxial magnetic anisotropy Ku for L10-type FePt films (10 nm in thickness) deposited with a Pd underlayer on MgO(001) substrates reached about 2 × 107 erg/cm3 at the substrate temperature Ts of 200 °C, and 3 × 107 erg/cm3 at Ts = 250 °C. The order parameter S was about 0.46 at Ts = 300 °C. Moreover, Ku for L10-FePt films fabricated on glass disks using MgO/Cr underlayers shows 3.4 × 107 erg/cm3 at Ts = 300 °C, which was almost equal to that for FePt single-crystal films deposited on Pd/MgO(001). The switching field distribution σ/Hc for dot arrays made from L10-FePt film [5 nm in thickness, on Pd/MgO(001) at Ts = 250 °C] was small; σ/Hc = 0.11 for a dot diameter of 15 nm. This value was smaller than that of hcp-Co75Pt25 dot arrays (σ/Hc = 0.18). The difference was mainly attributable to the degree of the easy axis distribution. This result demonstrates the homogeneous formation of a L10-type ordered structure in the FePt layers.
Characterization of coercivity at a recording speed of granular media for thermally assisted recording
Authors: Inoue D. , Inaba Y. , Komiyama K. , Shimatsu T.
Published: March 2011

As a fundamental study of thermally assisted recording, remanence coercivity at recording speed and the energy barrier for magnetization switching for granular media were evaluated as a function of temperature T. We characterized those for CoPtCr-oxide granular media as a trial examination. Remanence coercivity was measured at measurement time t′ of 1 s (using an electromagnet) and 10−5 s (pulse field); they were defined, respectively, as Hr and HrP for T of 300–473 K. Assuming that the value of t′ at a recording speed is 1 ns and the value of remanence coercivity at the recording speed, Hr(1 ns), was evaluated by fitting Hr and HrP to Sharrock’s equation. Moreover, the values of the energy barrier for magnetization switching, ΔE, were estimated. The value of Hr(1 ns) at T = 573 K, which is a typical temperature for thermally assisted recording, as estimated by extrapolation was about 6.2 kOe for the single medium and 5.5 kOe for the stacked medium. These values were about 1 order of magnitude larger than those of Hr at T = 573 K. Moreover, the reduction ratio of ΔE on increasing T showed good agreement with that of perpendicular uniaxial magnetic anisotropy, Ku. These results indicate that a large Ku reduction on increasing T was necessary to enhance the reduction of recording coercivity at elevated recording temperatures.
Investigation of dissipation elements in a fully developed turbulent channel flow by tomographic particle-image velocimetry
Authors: Schäfer L. , Dierksheide U. , Klaas M. , Schröder W.
Published: March 2011

A new method to describe statistical information from passive scalar fields has been proposed by Wang and Peters [“The length-scale distribution function of the distance between extremal points in passive scalar turbulence,” J. Fluid Mech. 554, 457 (2006)]. They used direct numerical simulations (DNS) of homogeneous shear flow to introduce the innovative concept. This novel method determines the local minimum and maximum points of the fluctuating scalar field via gradient trajectories, starting from every grid point in the direction of the steepest ascending and descending scalar gradients. Relying on gradient trajectories, a dissipation element is defined as the region of all the grid points, the trajectories of which share the same pair of maximum and minimum points. The procedure has also been successfully applied to various DNS fields of homogeneous shear turbulence using the three velocity components and the kinetic energy as scalar fields [L. Wang and N. Peters, “Length-scale distribution functions and conditional means for various fields in turbulence,” J. Fluid Mech. 608, 113 (2008)]. In this spirit, dissipation elements are, for the first time, determined from experimental data of a fully developed turbulent channel flow. The dissipation elements are deduced from the gradients of the instantaneous fluctuation of the three velocity components u′, v′, and w′ and the instantaneous kinetic energy k′, respectively. The measurements are conducted at a Reynolds number of 1.7×104 based on the channel half-height δ and the bulk velocity U. The required three-dimensional velocity data are obtained investigating a 17.75×17.75×6 mm3 (0.355δ×0.355δ×0.12δ) test volume using tomographic particle-image velocimetry. Detection and analysis of dissipation elements from the experimental velocity data are discussed in detail. The statistical results are compared to the DNS data from Wang and Peters [“The length-scale distribution function of the distance between extremal points in passive scalar turbulence,” J. Fluid Mech. 554, 457 (2006); “Length-scale distribution functions and conditional means for various fields in turbulence,” J. Fluid Mech. 608, 113 (2008)]. Similar characteristics have been found especially for the pdf’s of the large dissipation element length regarding the exponential decay. In agreement with the DNS results, over 99% of the experimental dissipation elements possess a length that is smaller than three times the average element length.
Clear correspondence between magnetoresistance and magnetization of epitaxially grown ordered FeRh thin films
Authors: Suzuki Ippei , Naito Tomoyuki , Itoh Mitsuru , Sato Tetsuya , Taniyama Tomoyasu
Published: March 2011

Magnetoresistance and magnetization of the CsCl-type ordered FeRh epitaxial thin films grown on MgO(001) substrates are investigated as a function of temperature and film thickness. All the films show a clear first-order magnetic phase transition from the antiferromagnetic state to the ferromagnetic state at around 380 K. A large negative variation in the field-dependent magnetoresistance of the FeRh thin films, which is accompanied by the field-induced magnetic phase transition, is found to be well scaled with the magnetization squared M2. The results indicate that the magnetoresistance primarily arises from spin-dependent scattering through the s–d exchange interactions between conduction electrons and the localized magnetic moments.
Intrinsic magnetism in BaTiO3 with magnetic transition element dopants (Co, Cr, Fe) synthesized by sol-precipitation method
Authors: Liu Hongxue , Cao Baobao , O’Connor Charles
Published: March 2011

A study of BaTiO3 nanoparticles doped with different transition metals including Co, Fe, and Cr is presented. X-ray diffraction and electron microscopy studies indicated that all the samples are highly crystalline and that transition metal dopants are successfully incorporated into BaTiO3 without detectable secondary phases. Raman spectra featured three characteristic broad bands centered approximately 300, 520, and 715 cm−1 from the tetragonal BaTiO3 without any extra peak present that may be attributed to other impurity phases. Temperature- and field-dependent magnetometry measurements and analysis revealed that all the samples show paramagnetic-like behavior originating from the transition metal ions. These results not only allow the exclusion of potential secondary ferromagnetic or antiferromagnetic phases, but also suggest that transition metal ions (Co, Cr, and Fe) in BaTiO3 shown in this study are present as isolated paramagnetic centers.
Size effect on magnetic properties of hexagonal HoMnO3 nanoparticles
Authors: Han T. C. , Tsai M. R. , Wei C. Y.
Published: March 2011

We have synthesized a series of hexagonal HoMnO3 nanoparticles with different particle sizes (30 – 200 nm) by a modified Pechini method to study systematically the effect of particle size on their structural and magnetic properties. The magnetic characterization indicates that with increasing the particle size, the antiferromagnetic (AFM) transition temperature increases from 50 to 70 K. Further analysis suggests that the rising of AFM transition temperature with the increasing particle size should be from the structural origin, in which the strength of AFM interaction is dependent on the in-plane lattice parameters. Furthermore, with a decrease in particle size, the Mn-spin reorientation temperature (TSR) is enhanced from 39 to 43 K. These results show an important coupling between the Mn3+ and Ho3+ ion spins as well as a TSR that is driven by the cooperative MnO5 site rotation.
Magnetic properties of NiO and (Ni, Zn)O nanoclusters
Authors: Peck M. A. , Huh Y. , Skomski R. , Zhang R. , Kharel P. , Allison M. D. , Sellmyer D. J. , Langell M. A.
Published: March 2011

Rock-salt NiO and Ni0.7Zn0.3O nanoparticles were investigated by x-ray diffraction, atomic-force microscopy, and magnetic measurements. Nanoparticle diameters varied from 8 to 30 nm depending on reaction conditions. There are two main magnetization contributions, the field-induced spin canting of the antiferromagnetic sublattices and the magnetization rotation caused by uncompensated spins interacting with the magnetic field. The former is a bulk effect, modified by the presence of Zn, whereas the latter is a nanoscale effect that increases with decreasing particle size. The relative contributions of the two effects depend on particle size with a critical size of about 18 nm resulting in bulklike behavior.
Amplification of direct current magnetic responses of magnetic nanobeads due to induced self-assembly of magnetic microbeads
Authors: Morimoto Y. , Takamura T. , Ishikawa R. , Ko P. J. , Sandhu A.
Published: March 2011

Detection of small concentrations of sub-200-nm-sized SPBs (superparamagnetic beads with sizes similar to target molecules) used as ‘magnetic labels’ is critical for the development of rapid, highly sensitive, and portable point of care treatment (POCT) systems. Currently, magnetoresistive (MR) biosensors are used for the detection of large concentrations of SPBs but such an approach is not suitable for monitoring small numbers of sub-200-nm SPBs due to the intrinsic noise of these electronic devices. In order to overcome this limitation of conventional MR sensors, we have developed a simple procedure for detecting small concentrations of sub-200-nm-diameter SPBs for biosensing by exploiting magnetically induced self-assembly of micrometer-sized SPBs onto nanometer targets. Here, our approach enables the physical amplification of the signal from otherwise undetectable nano-SPB targets using Hall biosensors without using the application of ac, magnetic fields or lock-in detection, thereby enabling the production of a simple POCT protocol for a wide range of applications.
Collective focusing of intense ion beam pulses for high-energy density physics applications
Authors: Dorf Mikhail A. , Kaganovich Igor D. , Startsev Edward A. , Davidson Ronald C.
Published: March 2011

The collective focusing concept in which a weak magnetic lens provides strong focusing of an intense ion beam pulse carrying a neutralizing electron background is investigated by making use of advanced particle-in-cell simulations and reduced analytical models. The original analysis by Robertson [Phys. Rev. Lett. 48, 149 (1982)] is extended to the parameter regimes of particular importance for several high-energy density physics applications. The present paper investigates (1) the effects of non-neutral collective focusing in a moderately strong magnetic field; (2) the diamagnetic effects leading to suppression of the applied magnetic field due to the presence of the beam pulse; and (3) the influence of a finite-radius conducting wall surrounding the beam cross-section on beam neutralization. In addition, it is demonstrated that the use of the collective focusing lens can significantly simplify the technical realization of the final focusing of ion beam pulses in the Neutralized Drift Compression Experiment-I (NDCX-I), and the conceptual designs of possible experiments on NDCX-I are investigated by making use of advanced numerical simulations.
Transition representations of quantum evolution with application to scattering resonances
Authors: Strauss Y.
Published: March 2011

A Lyapunov operator is a self-adjoint quantum observable whose expectation value varies monotonically as time increases and may serve as a marker for the flow of time in a quantum system. In this paper it is shown that the existence of a certain type of Lyapunov operator leads to representations of the quantum dynamics, termed transition representations, in which an evolving quantum state ψ(t) is decomposed into a sum ψ(t) = ψb(t) + ψf(t) of a backward asymptotic component and a forward asymptotic component such that the evolution process is represented as a transition from ψb(t) to ψf(t). When applied to the evolution of scattering resonances, such transition representations separate the process of decay of a scattering resonance from the evolution of outgoing waves corresponding to the probability “released” by the resonance and carried away to spatial infinity. This separation property clearly exhibits the spatial probability distribution profile of a resonance. Moreover, it leads to the definition of exact resonance states as elements of the physical Hilbert space corresponding to the scattering problem. These resonance states evolve naturally according to a semigroup law of evolution.
Microfabricated atomic vapor cell arrays for magnetic field measurements
Authors: Woetzel S. , Schultze V. , IJsselsteijn R. , Schulz T. , Anders S. , Stolz R. , Meyer H.-G.
Published: March 2011

We describe a method for charging atomic vapor cells with cesium and buffer gas. By this, it is possible to adjust the buffer gas pressure in the cells with good accuracy. Furthermore, we present a new design of microfabricated vapor cell arrays, which combine silicon wafer based microfabrication and ultrasonic machining to achieve the arrays of thermally separated cells with 50 mm3 volume. With cells fabricated in the outlined way, intrinsic magnetic field sensitivities down to 300 fT/Hz1/2 are reached.
Blob-induced toroidal momentum transport in simple magnetized plasmas
Authors: Labit B. , Theiler C. , Fasoli A. , Furno I. , Ricci P.
Published: March 2011

The link between toroidal flows and density blobs is experimentally demonstrated in TORPEX simple magnetized plasmas: momentum is transferred from an ideal-interchange mode to density blobs. The phase shift between the toroidal flow and the density perturbations observed in the interchange mode where the blob is born is conserved along the blob radial trajectory. This leads to dipolar structures of the blob-induced flow or to monopolar perturbations, so large that the toroidal flow gets transiently reversed. The turbulent toroidal momentum flux is dominated either by the nonlinear flux or by the convective part but not by the Reynolds stress component.
Numerical simulation of laminar plasma dynamos in a cylindrical von Kármán flow
Authors: Khalzov I. V. , Brown B. P. , Ebrahimi F. , Schnack D. D. , Forest C. B.
Published: March 2011

The results of a numerical study of the magnetic dynamo effect in cylindrical von Kármán plasma flow are presented with parameters relevant to the Madison Plasma Couette Experiment. This experiment is designed to investigate a broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl number Pm can be of order unity (i.e., the fluid Reynolds number Re is comparable to the magnetic Reynolds number Rm). This is in contrast to liquid metal experiments, where Pm is small (so, Re⪢Rm) and the flows are always turbulent. We explore dynamo action through simulations using the extended magnetohydrodynamic NIMROD code for an isothermal and compressible plasma model. We also study two-fluid effects in simulations by including the Hall term in Ohm’s law. We find that the counter-rotating von Kármán flow results in sustained dynamo action and the self-generation of magnetic field when the magnetic Reynolds number exceeds a critical value. For the plasma parameters of the experiment, this field saturates at an amplitude corresponding to a new stable equilibrium (a laminar dynamo). We show that compressibility in the plasma results in an increase of the critical magnetic Reynolds number, while inclusion of the Hall term in Ohm’s law changes the amplitude of the saturated dynamo field but not the critical value for the onset of dynamo action.
Dielectric relaxation and magnetic behavior of bismuth-substituted yttrium iron garnet
Authors: Siao Yu-Jhan , Qi Xiaoding , Lin Chun-Rong , Huang Jung-Chun-Andrew
Published: March 2011

Y3−xBixFe5O12 (x = 0–1.0) was prepared by solid state reaction. X-ray diffraction showed a gradual increase of lattice parameter with the Bi concentration, indicating that Bi had been incorporated into the lattice. Dielectric responses of the samples at room temperature increased initially at low Bi (x < 0.4) and then decreased rapidly at high Bi (x ≥ 0.6). Temperature dependence of dielectric constant showed a huge steplike increase at the temperatures between 20 and 200 °C, increasing with Bi. X-ray photoelectron spectroscopy revealed the presence of Fe2+ and Bi2+ in the samples, which might be responsible for the dielectric behaviors. An increase of coercivity and Curie temperature with Bi was observed. This was accompanied by a reduction of the saturation magnetization, whose variation with T follows a modified Bloch law.
Field ionization model implemented in Particle In Cell code and applied to laser-accelerated carbon ions
Authors: Nuter R. , Gremillet L. , Lefebvre E. , Lévy A. , Ceccotti T. , Martin P.
Published: March 2011

A novel numerical modeling of field ionization in PIC (Particle In Cell) codes is presented. Based on the quasistatic approximation of the ADK (Ammosov Delone Krainov) theory and implemented through a Monte Carlo scheme, this model allows for multiple ionization processes. Two-dimensional PIC simulations are performed to analyze the cut-off energies of the laser-accelerated carbon ions measured on the UHI 10 Saclay facility. The influence of the target and the hydrocarbon pollutant composition on laser-accelerated carbon ion energies is demonstrated.