bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic states controlled by energetic ion irradiation in FeRh thin films
Authors: Fujita Nao. , Kosugi S. , Saitoh Y. , Kaneta Y. , Kume K. , Batchuluun T. , Ishikawa N. , Matsui T. , Iwase A.
Published: April 2010

Changes in magnetic properties and lattice structure of FeRh films by 180 keV–10 MeV ion (H, He, and I) irradiation are studied. In spite of the irradiation with different ion species and wide range of energies, the changes in magnetization are dominated by solely a single parameter; the density of energy which is deposited through elastic collision between the ions and the samples. For the low deposition energy density, the magnetization increases with increasing the deposition energy density, while the lattice structure remains unchanged. When the deposition energy density becomes larger, however, the magnetization decreases after reaching the maximum value. The decrease in the magnetization accompanies the crystal structure change from B2 to A1. The present results imply that the magnetic state of FeRh films can be designedly controlled by the energetic ion irradiations.
Giant magnetic entropy change in colossal magnetoresistance in La0.7Ca0.3MnO3 material in low field
Authors: Debnath J. C. , Zeng R. , Kim J. H. , Dou S. X.
Published: April 2010

The structural, magnetic, and magnetocaloric properties of the manganite La0.7Ca0.3MnO3 have been studied. Change in the giant magnetic entropy was observed without any noticeable magnetic hysteresis but with small thermal hysteresis losses. We observed a first order magnetic phase transition around 251 K. The magnetic entropy change observed in this work is estimated to be 5.27 J/kg K for field changes from 0 to 1.5 T based on magnetization measurements. This value is about twice as large as those for other perovskite manganites and is even larger than for Gd-based magnetic materials at low fields. In addition, the entropy change was estimated by using the heat capacity method, which can be well explained by the Maxwell relation.
Magnetostrictive and elastic properties of Fe100−xMox (2<x<12) single crystals
Authors: Huang M. , Mandru A. O. , Petculescu G. , Clark A. E. , Wun-Fogle M. , Lograsso T. A.
Published: April 2010

In this paper we investigate the magnetostrictive [(3/2)λ100 and (3/2)λ111] and elastic (c′ and c44) behavior of single crystalline alloys Fe100−xMox for 2<x<12; the magnetoelastic coupling constants (−b1 and −b2) are computed from the measurements. Similar to other Fe–X (X=Al, Ga, and Ge) alloys, the tetragonal magnetostriction (3/2)λ100 increases monotonically from ∼70×10−6 at ∼2.5 at. % Mo to a maximum of either ∼100×10−6 at ∼8 at. % Mo for the slow cooled crystals or ∼125×10−6 at ∼11 at. % Mo for quenched crystals. A sharp decrease after the peak is observed for the slow cooled crystals due to the formation of a second phase. The rhombohedral magnetostriction (3/2)λ111 of the Fe–Mo alloys is found to be insensitive to the Mo content. This behavior is distinctly different from other Fe–X (X=Al, Ga, and Ge) alloys where a slight decrease in magnitude and a sign reversal upon chemical ordering was observed for (3/2)λ111. Both shear elastic constants (c′ and c44) for Fe–Mo are remarkably insensitive to the Mo content, which is also distinct from the other Fe-based alloys used in the comparison. The two magnetoelastic coupling constants −b1=3λ100c′ (with values from 7.15 to 9.77 MJ/m3) and −b2=3λ111c44 (with values from −4.96 to −5.81 MJ/m3) were calculated and compared with those of other Fe–X (X=Al, Ga, and Ge) alloys.
Correlation of magnetic ordering and electric polarization in multiferroic LuMn1−xFexO3 (≤x≤0.2)
Authors: Lin J. G. , Chen Y. S. , Han T. C.
Published: April 2010

We have synthesized a series of LuMn1−xFexO3 (0≤x≤0.2) samples and study the effect of Fe-doping on their magnetic and dielectric properties. The magnetic characterization indicates that with increasing Fe-content up to 0.2, the antiferromagnetic (AFM) transition temperature increases from 90 to 105 K. A corresponding shift in the peak-positions of specific heat and dielectric anomaly is observed, indicating a strong correlation between the magnetic ordering and the electric polarization. Further analysis suggests that the rising of AFM transition temperature with increasing Fe-content should be from the structural origin, in which the strength of AFM interaction as well as the electrical polarization is dependent on the in-plane lattice parameters.
Experimental and modeling studies of the magnetomechanical effect in substituted cobalt ferrites for magnetoelastic stress sensors
Authors: Lo C. C. H.
Published: April 2010

This paper reports on experimental and modeling studies of the magnetomechanical effect in Mn- and Cr-substituted cobalt ferrites (CoMnxFe2−xO4 and CoCryFe2−yO4 with 0≤x≤0.3 and 0≤y≤0.4), which show promise for magnetoelastic sensor applications due to their high levels of magnetostriction λ and strain derivative dλ/dH. The difference in differential permeabilities measured along and perpendicular to uniaxial applied stresses was found to vary reversibly with applied stresses, indicating the feasibility of using the substituted cobalt ferrites for stress sensor applications. Stress-induced permeability changes were simulated using an extended magnetomechanical effect model which includes magnetocrystalline anisotropy K. The observed compositional dependence of stress sensitivity, which is related to λs/K, was reproduced in the simulations. This can be interpreted in terms of the effects of chemical substitution, which were found to increase magnetostriction but reduce the magnetocrystalline anisotropy within certain ranges of the substitute contents (near x=0.2 and y=0.4) and therefore accounts for the observed increase in stress sensitivities compared to pure cobalt ferrite.
Ultrasmall particle detection using a submicron Hall sensor
Authors: Kazakova O. , Panchal V. , Gallop J. , See P. , Cox D. C. , Spasova M. , Cohen L. F.
Published: April 2010

We demonstrate detection of a single FePt nanoparticle (diameter 150 nm, moment ∼107 μB) using an ultrasensitive InSb Hall sensor with the bar lateral width of 600 nm. The white noise of a typical nanodevice, SV1/2≈28 nV/√Hz, is limited only by two-terminal resistance of the voltage leads which results in a minimum field sensitivity of the device Bmin=0.87 μT/√Hz. To detect a single FePt bead, we employed a phase-sensitive method based on measuring the ac susceptibility change in a bead when exposed to a switched dc magnetic field. Such nano-Hall devices, enabling detection of potentially even smaller moments, are of considerable significance both for nanomagnetic metrology and high sensitivity biological and environmental detectors.
High sensitivity giant magnetoresistance magnetic sensor using oscillatory domain wall displacement
Authors: Wang G. A. , Nakashima S. , Arai S. , Kato T. , Iwata S.
Published: April 2010

A high sensitivity giant magnetoresistance (GMR) magnetic sensor has been demonstrated using the oscillatory domain wall displacing method. This sensor consists of a 30-μm-wide GMR element, CoFeB (10 nm)/Cu (2.2 nm)/CoFe (3 nm)/MnIr (10 nm), and a 100-μm-wide aluminum conducting wire placed onto the GMR element with an insulation layer between them. Domain walls in the free layer, whose easy axis is perpendicular to the length direction of GMR element, are oscillation-driven by a 140 kHz alternating magnetic field produced by an ac flowing through the aluminum conducting wire. The oscillatory wall displacement reduces the influence of wall coercivity and enables an output proportional to the external field. By applying a 1-kHz external field and separating the 1-kHz component from the amplified bridge signal using a band-pass filter, we successfully detected a magnetic field as small as 0.21 mOe (21 nT), which is much smaller than the wall coercivity of the free layer.
Reversibility and coercivity of Fe-alloy/Fe:SiO2 multilayers
Authors: Zhang Rui , Skomski Ralph , Yin Xiaolu , Liou Sy-Hwang , Sellmyer D. J.
Published: April 2010

Soft bilayer alloys were produced by depositing granular Fe:SiO2 onto transition-metal thin films. We have prepared series of samples using different soft-magnetic materials including permalloy (Ni80Fe20), hcp Co90Fe10, and amorphous Co60Fe20B20, all covered by a layer of superparamagnetic Fe particles in a silicon-oxide matrix. The thickness of transition-metal layer was fixed and the magnetic properties of the bilayer system were studied by varying the Fe:SiO2 layers thicknesses from 0 to 70 nm. The bilayer yields a moderate improvement of the soft-magnetic performance. The hysteresis loops show a pronounced twofold anisotropy in the film plane for permalloy and amorphous CoFeB, which is consistent with the presence of external magnetic field during processing. This indicates that the coercivity is controlled by the pinning of 180° domain walls and that the effect of the Fe particles on the hysteresis is mediated by the interaction with the domain-wall stray fields.
First-principles calculation on the Curie temperature of GdFeSi
Authors: Liu X. B. , Altounian Z.
Published: April 2010

Electronic structure and magnetic properties for GdFeSi have been studied theoretically from a first-principles density functional calculation. The energy band structure is calculated in a local spin density approximation (LSDA)+Hubbard U approach (LSDA+U). For Gd atoms, seven spin up 4f bands are fully occupied, while the spin down 4f hole levels are completely unoccupied and well above the Fermi level. The calculated magnetic moment of Gd is 7.20 μB, leading to a total magnetization of 7.1 μB per formula unit due to the small induced negative moments at Fe and Si atoms. The intersites exchange coupling parameters Jij of the Heisenberg model have been derived using a linear-response method based on the calculated band structure. The exchange coupling parameters for the nearest Gd–Gd pair (JGd–Gd) is 0.19 mRy. JGd–Gd decreases rapidly with increasing the intersites distance and shows a Ruderman-Kittel-Kasuya-Yoshida-like oscillation. The estimated Curie temperature is about 145 K from the calculated exchange coupling parameters based on the mean-field approximation, in good agreement with the experimental value (TCexp.=135 K).
Exchange bias in Pt doped NiMn thick films
Authors: Öner Y. , Özdemir M. , Kazan S. , Basaran A. C. , Aktas B. , Sato T.
Published: April 2010

Magnetization and electron spin resonance (ESR) measurements were carried out on a 1.2 at. % Pt doped NiMn thin film (8000 Å) in the temperature range of 5–200 K for both parallel (field parallel to the film surface) and perpendicular configurations. M versus H loops were recorded at selected temperatures. Magnetization curves in the parallel configuration differ from those in the perpendicular geometry in many respects, including the anisotropy fields derived from these curves, and the coercivity. In addition, the temperature dependences of the magnetization in a small negative field (−0.5 Oe) and several larger positive fields will also be reported. All of these phenomena can be understood by the coexistence of Mn-rich and Mn-deficient aggregated granular regions coupled antiferromagnetically. Furthermore, the exchange stiffness constant (D), bulk anisotropy constant, and surface anisotropy constant were deduced from ESR measurements. The fitted ESR parameters are in good agreement with the behavior deduced from magnetization.
The geometrical frustration properties of the antiferromagnetic Ni1−xFexGa2S4 (0.01≤x≤1)
Authors: Myoung Bo Ra , Kim Sam Jin , Lee Bo Wha , Kim Chul Sung
Published: April 2010

Ni 1 − x Fe x Ga 2 S 4  (0.01≤x≤1) has been studied by x-ray, Mössbauer spectroscopy, and superconducting quantum-interference device (SQUID) magnetometer. The samples were prepared by a standard solid-state reaction method. The crystal has a trigonal structure with space group P-3m1. The lattice constants a0, c0 and bond length dFe–S increase linearly with increasing Fe concentration. The Néel temperature (TN) for Ni1−xFexGa2S4 (0.01≤x≤1) increases with increase in Fe concentration, which is due to the short-range ordering in the undoped sample which changes into the long-range ordering with increase in Fe. The quadrupole splitting ΔEQ increases with Fe substitution in Mössbauer spectra in Ni1−xFexGa2S4 (0.01≤x≤1) at 4.2 K. We report that the spin configuration for geometrically frustrated Ni1−xFexGa2S4 (0.01≤x≤1) at 4.2 K has fluctuating incommensurate state by Mössbauer spectra spectroscopy.
Mg-doping effect on structural and magnetic properties on two-dimensional triangular lattice LiVO2
Authors: Li Yang , Wang Weipeng , Li Xiaoxiang , Liu Lihua , Wang Aihua , Chen Ning , Liu Yang , Cao Guohui
Published: April 2010

Transition metal compounds with two-dimensional triangular lattice, such as LiVO2, are of particular interest, because they exhibit peculiar structural and magnetic behavior involving the frustration present in these oxides. An orbital ordering transition occurs near 500 K, which leads to a suppression of magnetic moment below the phase transition temperature Tt. We synthesized a series of Mg-doped LiVO2 single-phase samples and reported their structural and magnetic properties. The samples were characterized by x-ray diffraction, scanning electron microscope, differential scanning calorimetry, electrical resistivity, magnetic susceptibility, and specific heat measurement. For Mg-doped samples Li1−xMgxVO2 (x=0, 0.05, 0.10, and 0.15), the structural analysis show that, with increasing x, the lattice constants change monotonously; in the a-b plane, the lattice expands; while in the c-axis direction, the lattice is compressed. Substitution of Li with Mg ions results in the degeneration of two-dimensional characteristics and the distortion of the VO6 block, which significantly influence magnetic properties. The magnetic phase transition temperature falls with increasing x. The Mg-dopants play an important role on breaking the original moment equilibrium and suppressing the magnetic frustration.
Complex magnetic order and spin chirality on the Kagomé lattices of BaMn2.49Ru3.51O11 and BaFe3.26Ti2.74O11
Authors: Shlyk L. , Parkin S. , De Long L. E.
Published: April 2010

Anomalies in the magnetization of single-crystal BaMn2.49Ru3.51O11 at temperatures T1=183 K, T2=171 K, and T3=128 K, signal complex magnetic order induced by competing ferro- and antiferromagnetic correlations and magnetic frustration within the Kagomé (hexagonal ab-) plane. The T2- and T3-anomalies and unconventional transverse magnetoresistance are observed only for applied field H directed in the Kagomé plane, suggesting a topological Hall effect is generated by nonzero scalar chirality of spins canted out of the Kagomé plane, but is suppressed in a collinear structure induced by only modest H⊥c. In contrast, the magnetic susceptibility of an isostructural BaFe3.26Ti2.74O11 single-crystal reveals magnetic transitions at T1=250 K and T2=85 K for H oriented both parallel and perpendicular to the c-axis. The rapid low-field increase of the magnetic moment at μoH<1 T, followed by nonsaturation with a near-linear increase at high fields, are typical of a canted antiferromagnet or ferrimagnet.
Geometry induced entanglement transitions in nanostructures
Authors: Coe J. P. , Abdullah S. , D’Amico I.
Published: April 2010

We model quantum dot nanostructures using a one-dimensional system of two interacting electrons. We show that strong and rapid variations may be induced in the spatial entanglement by varying the nanostructure geometry. We investigate the position-space information entropy as an indicator of the entanglement in this system. We also consider the expectation value of the Coulomb interaction and the ratio of this expectation to the expectation of the confining potential and their link to the entanglement. We look at the first derivative of the entanglement and the position-space information entropy to infer information about a possible quantum phase transition.
Phase formation and magnetotransport of alkali metal doped Na0.75CoO2 thermoelectric oxide
Authors: Jood P. , Peleckis G. , Wang X. L. , Dou S. X. , Yamauchi H. , Karppinen M.
Published: April 2010

Synthesis and characterization of bulk NaxCoO2 samples substituted by K and Rb is reported. Phase formation studies revealed a narrow stable region for Na-alkali metal-Co system. Whisker and platelike single crystalline structures have been found to form on the surface of the pellets in case of K doping. All samples were metallic and no characteristic anomaly in R-T curves was observed for Rb doped sample. Magnetoresistance measured has a pronounced positive response only for K-doped and pure NaxCoO2 phases, reaching 11% and 7% at 5 K temperature, respectively.
Extended dislocation-based pinning mechanism in superconducting YBa2Cu3O7 films
Authors: Pysarenko S. V. , Pan A. V. , Dou S. X. , Nigam R.
Published: April 2010

To describe the critical current density (Jc) as the function of applied magnetic field (Ba) in high quality YBa2Cu3O7 (YBCO) superconducting films, the vortex pinning mechanism along the structural domain boundaries of the films is developed. The boundaries, assumed to have low misorientation angles, are quantitatively considered to consist of individual edge dislocations acting as pinning wells, rather than a continuous boundary. This extended model accurately describes the experimental Jc(Ba) over the wide field and temperature ranges. Marginal deviations of the model from the experimental Jc(Ba) curves are observed at high fields and temperatures where thermally activated depinning is significant. This pinning model is verified to provide precise structural properties of the films which can be obtained by other considerations.
Synthesis of LiFeAs superconductor by electrochemistry at room temperature
Authors: Chen Ning , Qu Shaopeng , Li Yang , Liu Yang , Zhang Rui , Zhao Hailei
Published: April 2010

A new synthesis technique is developed to prepare LiFeAs superconductor at room temperature by using an electrochemical approach which differs from the traditional solid-state reaction at high temperature. Under the electrochemical drive, lithium ions in the solution are inserted into FeAs lattice to directly form LiFeAs on the surface of FeAs substrate at room temperature. The characterization of resulting LiFeAs samples indicates superconducting transition temperature at about 13 K, which is consistent with the reported results. This electrochemical technique offers a promising approach to prepare LiFeAs superconductors as well as thin films.
Landau theory of compressible magnets near a quantum critical point
Authors: Gehring Gillian A. , Ahmed Mahrous R.
Published: April 2010

Landau theory is used to investigate the behavior of a metallic magnet driven toward a quantum critical point by the application of pressure. The observed dependence of the transition temperature with pressure is used to show that the coupling of the magnetic order to the lattice diverges as the quantum critical point is approached. This means that a first order transition will occur in magnets (both ferromagnets and antiferromagnets) because of the coupling to the lattice. The Landau equations are solved numerically without further approximations. There are other mechanisms that can cause a first order transition so the significance of this work is that it will enable us to determine the extent to which any particular first order transition is driven by coupling to the lattice or if other causes are responsible.
Epitaxial growth and ferrimagnetic properties of Mn film on GaSb(100)
Authors: Feng Wuwei , Dung Dang Duc , Choi Jeongyong , Shin Yooleemi , Cho Sunglae
Published: April 2010

We report on the epitaxial stabilization and magnetic properties of Mn films on GaSb(100) using molecular beam epitaxy, a follow-up to our previous work on the growth of Mn films on GaAs(100) [Phys. Rev. B 79, 045309 (2009)]. A strong ferrimagnetic ordering was observed which was attributed to the largely expanded lattice parameter resulting from the lattice mismatch with substrate and the enhanced thermal energy with increasing growth temperature. The observed magnetic moment of 1.16μB/Mn atom was several times larger than that observed in the Mn/GaAs(100) films due to the lattice constant difference of substrates. The in-plane magnetoresistance behavior demonstrated the magnetic anisotropy that might result from the slightly distorted cubic structure of α-Mn phase under low-dimensional growth.
Diffraction-modified Kerr rotation from patterned garnet films
Authors: Baek Seungmin , Dokukin Maxim , Yayoi Kazuo , Baryshev Alexander , Inoue Mitsuteru
Published: April 2010

Bismuth-substituted yttrium iron garnet (Bi:YIG)-based two-dimensional (2D) magnetophotonic structures were fabricated on top of opal thin films. Autocloning approach was used to transpose 2D hexagonal symmetry of the opal (111) plane into sputtered Bi:YIG. Resultant 2D patterned Bi:YIG films had two realizations. As-sputtered films had a hemispherical profile of structural elements. These films were additionally etched to obtain films with a cone profile of scatterers. Optical and magneto-optical spectra of the films demonstrated resonances addressed to diffraction from the patterned Bi:YIG films. Structural parameters of these magneto-optical gratings were found to govern the magnitude of Kerr rotation.
Magnetostrictive effect in single crystal Fe1−xGax thin films
Authors: McClure Adam , Li H. , Idzerda Y. U.
Published: April 2010

The magnetic properties of single crystal Fe1−xGax thin films deposited on ZnSe/GaAs(001) and MgO(001) substrates by molecular beam epitaxy were investigated by vibrating sample magnetometry and angle dependent ferromagnetic resonance. Depositions on the ZnSe buffer layer feature a strong uniaxial anisotropy that scales with the thin film magnetostriction of the samples, while depositions on MgO(001) substrates result in a purely cubic anisotropy whose cubic anisotropy constant, K1, switches sign at a lower Ga concentration than is seen in bulk.
Magneto-optical imaging and coercivity mapping of GdFe spin-valve structures
Authors: Ishibashi Takayuki , Kosaka Terumasa , Naganuma Masayuki , Shioda Tatsutoshi , Aoshima Ken-ichi , Funabashi Nobuhiko , Machida Kenji , Kuga Kiyoshi , Shimidzu Naoki
Published: April 2010

GdFe spin-valve structures, Si/bottom electrode/TbFeCo/CoFe (1 nm)/Cu (6 nm)/GdFe (10 nm)/Ru, with dimensions of 20×20 μm2 were investigated by a magneto-optical imaging technique. In a parallel configuration, i.e., a configuration in which the magnetization directions of GdFe and TbFeCo layers are parallel, the coercivity (Hc) decreases when nucleation centers are present in the patterns. In the antiparallel configuration, although few nucleation centers are present the deviation in Hc is greater than that in the parallel configuration.
Magneto-optical effects in nanosandwich array with plasmonic structure of Au/[Co/Pt]n/Au
Authors: Du Guan Xiang , Mori Tetsuji , Suzuki Michiaki , Saito Shin , Fukuda Hiroaki , Takahashi Migaku
Published: April 2010

Nanodisk array with both sandwich structure of Au/[Co/Pt]n/Au and [Co/Pt]n were fabricated by electron-beam lithography combined with ion milling process. Optical transmittance spectra revealed the excitation of localized surface plasmon resonance (LSPR) in Au/[Co/Pt]n/Au nanosandwich array. Magneto-optical (MO) properties were measured by a micro-Faraday system with objective lens design and laser source. Faraday rotation angle for sandwich structure increased considerably compared to that of [Co/Pt]n, indicating enhancement in MO activity by excitation of LSPR. The optical and MO properties of nanosandwich array were fitted in the framework of average field approximation.
Morphology and magnetic properties of W-capped Co nanoparticles
Authors: Figueroa A. I. , Bartolomé J. , García L. M. , Bartolomé F. , Magén C. , Ibarra A. , Ruiz L. , González-Calbet J. M. , Petroff F. , Deranlot C.
Published: April 2010

Co–W nanoparticles formed by sequential sputtering of Co on amorphous alumina substrate and subsequent W capping are studied by high resolution and by scanning transmission electron microscopies, and by superconducting quantum interference device magnetometry. The analysis is focused on W nominal thickness dependence. Results suggest the formation of amorphous Co–W alloy nanoparticles, whose magnetic moment per Co atom is systematically reduced as the nominal thickness of W capping layer increases. The Co–W nanoparticles show superparamagnetic behavior. The activation energy for moment reversal and the effective anisotropy are obtained.
Permittivity and permeability of Fe(Tb) nanoparticles and their microwave absorption in the 2–18 GHz range
Authors: Han Z. , Li D. , Tong M. , Wei X. , Skomski R. , Liu W. , Zhang Z. D. , Sellmyer D. J.
Published: April 2010

The permittivity and permeability of the Tb-doped and undoped Fe core-shell nanoparticles were investigated for frequencies from 2 to 18 GHz. The particles were synthesized by arc discharge and contain some oxygen, probably in the form of Fe2O3, Fe3O4, and Tb2O3, whereas the core material is Fe. Both the electromagnetic materials constants and the morphology of the Fe nanoparticles are changed by Tb addition, which gives rise to the shifts to higher frequencies and thinner thicknesses of the maximum microwave absorption in the Tb-doped Fe nanoparticles.
Structure and magnetism of pseudobinary L1 alloy FePtM(M=Ir,Au)
Authors: Uebayashi Kazuhiko
Published: April 2010

We performed energy-band calculations for the L10 pseudobinary bulk alloy FePt1−xMx(M=Ir,Au) by using the linear muffin-tin orbital method with atomic sphere approximations. The exchange-correlation potential was treated within the generalized gradient approximation. The total energies for the ferromagnetic (FM) and three kinds of antiferromagnetic (AFM) states were estimated as a function of lattice ratio c/a∗. For 5d atom substitution, we adopted a virtual crystal approximation. On the basis of the minimum of the total energy, we present the following result: a change in magnetic state (FM-AFM) occurs around FePt1−xMx. It is pointed out that the magnetic state change also depends on the number of valence electrons.
Absolute calibration of LIDAR Thomson scattering systems by rotational Raman scattering
Authors: Scannell R. , Beurskens M. , Kempenaars M. , Naylor G. , Walsh M. , O’Gorman T. , Pasqualotto R.
Published: April 2010

Absolute calibration of LIDAR Thomson scattering systems on large fusion devices may be achieved using rotational Raman scattering. The choice of calibrating gas molecule presents different options and design trade-offs and is likely to be strongly dependent on the laser wavelength selected. Raman scattering of hydrogenic molecules produces a very broad spectrum, however, with far fewer scattered photons than scattering from nitrogen or oxygen at the same gas pressure. Lower laser wavelengths have the advantage that the Raman cross section increases, σRaman∝1/λ04, but the disadvantage that the spectral width of the scattered spectrum decreases, ΔλRaman∝λ02. This narrower spectrum makes measurement closer to the laser wavelength necessary. The design of the calibration technique presents a number of challenges. Some of these challenges are generic to all Thomson scattering systems. These include detecting a sufficient number of photoelectrons and designing filters that measure close to the laser wavelength while simultaneously achieving adequate blocking of the laser wavelength. An issue specific to LIDAR systems arises since the collection optics operates over a wide range of depth of field. This wide depth of field has the effect of changing the angle of light incident on the optical interference filter with plasma major radius. The angular distribution then determines the effective spectral transmission function of the interference filter and hence impacts on the accuracy of the absolute calibration. One method that can be used to increase absolute calibration accuracy is collecting both Stokes and anti-Stokes lines with optical filter transmission bands specifically designed to reduce systematic uncertainty.
Donor-donor binding in In2O3: Engineering shallow donor levels
Authors: Tang Li-Ming , Wang Ling-Ling , Wang Dan , Liu Jian-Zhe , Chen Ke-Qiu
Published: April 2010

Using first-principles band structure methods, we investigate the interactions between different donors in In2O3. Through the formation energy and transition energy level calculations, we find that an oxygen-vacancy creates a deep donor level, while an indium-interstitial or a tin-dopant induces a shallow donor level. The coupling between these donor levels gives rise to even shallower donor levels and leads to a significant reduction in their formation energies. Based on the analysis of the PBE0-corrected band structure and the molecular-orbital bonding diagram, we demonstrate these effects of donor–donor binding. In addition, total energy calculations show that these defect pairs tend to be more stable with respect to the isolated defects due to their negative binding energies. Thus, we may design shallow donor levels to enhance the electrical conductivity via the donor–donor binding.
Development of a scanning angle total internal reflection Raman spectrometer
Authors: McKee Kristopher J. , Smith Emily A.
Published: April 2010

A scanning angle total internal reflection (SATIR) Raman spectrometer has been developed for measuring interfacial phenomena with chemical specificity and high axial resolution perpendicular to the interface. The instrument platform is an inverted optical microscope with added automated variable angle optics to control the angle of an incident laser on a prism/sample interface. These optics include two motorized translation stages, the first containing a focusing lens and the second a variable angle galvanometer mirror. The movement of all instrument components is coordinated to ensure that the same sample location and area are probed at each angle. At angles greater than the critical angle, an evanescent wave capable of producing Raman scatter is generated in the sample. The Raman scatter is collected by a microscope objective and directed to a dispersive spectrometer and charge-coupled device detector. In addition to the collected Raman scatter, light reflected from the prism/sample interface is collected to provide calibration parameters that enable modeling the distance over which the Raman scatter is collected for depth profiling measurements. The developed instrument has an incident angle range of 25.5°–75.5°, with a 0.05° angle resolution. Raman scatter can be collected from a ZnSe/organic interface over a range of roughly 35–180 nm. Far from the critical angle, the achieved axial resolution perpendicular to the focal plane is approximately 34 nm. This is roughly a 30-fold improvement relative to confocal Raman microscopy.
Unusual dielectric response in B-site size-disordered hexagonal transition metal oxides
Authors: Choudhury Debraj , Venimadhav Adyam , Kakarla Chandrasekhar , Delaney Kris T. , Devi P. Sujatha , Mondal P. , Nirmala R. , Gopalakrishnan J. , Spaldin Nicola A. , Waghmare Umesh V. , Sarma D. D.
Published: April 2010

We discover that hexagonal holmium copper titanate (Ho2CuTiO6), has a unique and highly desirable combination of high dielectric constant, low losses, very small temperature coefficient, and low frequency dependence. Our first-principles calculations indicate that these exceptional properties result from a size-difference at the Cu/Ti B-site that suppresses the expected ferroelectric transition, combined with the dominance of intermediate-frequency polar vibrational modes in the dielectric response. Our results suggest that the use of such B-site disorder in alloys of hexagonal transition-metal oxides should generally result in similar robust dielectrics.
The equation of state and nonmetal–metal transition of benzene under shock compression
Authors: Wang Cong , Zhang Ping
Published: April 2010

We employ quantum molecular dynamic simulations to investigate the behavior of benzene under shock conditions. The principal Hugoniot derived from the equation of state is determined. We compare our first principles results with available experimental data and provide predictions of chemical reactions for shocked benzene. The decomposition of benzene is found under the pressure of 11 GPa. The nonmetal–metal transition, which is associated with the rapid C–H bond breaking and the formation of atomic and molecular hydrogen, occurs under the pressure around 50 GPa. Additionally, optical properties are also studied.
Size-consistent variational approaches to nonlocal pseudopotentials: Standard and lattice regularized diffusion Monte Carlo methods revisited
Authors: Casula Michele , Moroni Saverio , Sorella Sandro , Filippi Claudia
Published: April 2010

We propose improved versions of the standard diffusion Monte Carlo (DMC) and the lattice regularized diffusion Monte Carlo (LRDMC) algorithms. For the DMC method, we refine a scheme recently devised to treat nonlocal pseudopotential in a variational way. We show that such scheme—when applied to large enough systems—maintains its effectiveness only at correspondingly small enough time-steps, and we present two simple upgrades of the method which guarantee the variational property in a size-consistent manner. For the LRDMC method, which is size-consistent and variational by construction, we enhance the computational efficiency by introducing: (i) an improved definition of the effective lattice Hamiltonian which remains size-consistent and entails a small lattice-space error with a known leading term and (ii) a new randomization method for the positions of the lattice knots which requires a single lattice-space.
Heat fluctuations and phonon hydrodynamics in nanowires
Authors: Jou D. , Criado-Sancho M. , Casas-Vázquez J.
Published: April 2010

We evaluate the second moments of the fluctuations of the total longitudinal heat flux in cylindrical nanowires described by phonon hydrodynamics with boundary conditions accounting for phonon boundary collisions. It is found that the second moments exhibit an explicit dependence on the boundary conditions and, therefore, may provide a suitable tool for analyzing phonon boundary collisions. Furthermore, an analogous dependence is also manifested in the relative probability of forward and backward fluctuations of the heat flux in a nonequilibrium steady state, thus providing a complementary tool of research for phonon boundary collisions.
Computational investigation of the magneto-Rayleigh–Taylor instability in Z-pinch implosions
Authors: Yang Zhang , Jiming Wu , Zihuan Dai , Ning Ding , Cheng Ning , Yanzhong Yao , Delong Xiao , Shunkai Sun , Tongxiang Gu , Yi Cao , Jun Huang , Chuang Xue , Xiaojian Shu
Published: April 2010

The instability evolvement induced by single mode and random density seeds have been investigated by using the Magnetics Atom Radiation Electron Dynamics (MARED) code, which is a two dimensional, three temperature, radiation magnetohydrodynamic Lagrangian code developed for the Z-pinch implosion simulation. The instability development during each stage (linear, weak nonlinear, and nonlinear) and its corresponding characteristics are studied with single-mode seeds. The evolvement of the dominant mode and its final wavelength are revealed through the development of seeds composed of modes covering the “whole” spectrum or just a “band-type” range of it. In addition, the relationship between the initial perturbation amplitude and the final x-ray output are also discussed. Through these discussions, the MARED code is found able to reproduce the primary dynamic characteristics of the Z-pinch implosions and the development of the instability qualitatively agrees with the theoretical analyses and experimental observations, which shows us a modest expectation of the broad coverage of the future application.
A numerical study on the effects of cavitation on orifice flow
Authors: Dabiri S. , Sirignano W. A. , Joseph D. D.
Published: April 2010

Previous experimental studies have shown better atomization of sprays generated by high-pressure liquid injectors when cavitation occurs inside the nozzle. It has been proposed that the collapse of traveling cavitation bubbles increases the disturbances inside the liquid flow. These disturbances will later trigger the instabilities in the emerged jet and cause a shorter breakup distance. In this paper, effects of cavitation on increasing the disturbances in the flow through the orifice of an atomizer are studied. In previous cavitation models, spherical cavitation bubbles are considered. Here, the cavitation bubbles are allowed to deform as they travel through the orifice. Dynamics of the cavitation bubble, traveling in the separated shear layer in the orifice, is analyzed through a one-way coupling between the orifice flow and bubble dynamics. Effects of shear strain, normal strain, and pressure variation are examined. Three mechanisms are suggested that could be responsible for the increase in disturbances in the flow due to cavitation. These mechanisms are monopole, quadrupole, and vorticities generated during growth and collapse of cavitation bubbles. The effects of these mechanisms are estimated by postprocessing of the solutions to the Navier–Stokes equations to identify monopole and quadrupole behaviors.
Analytical expression for thermal conductivity of superlattices
Authors: Alvarez F. X. , Alvarez-Quintana J. , Jou D. , Viejo J. Rodriguez
Published: April 2010

The increasing interest in manufacturing nanoscale low thermal conductivity devices has made important to obtain simple expressions that can predict their transport properties. This is more necessary for superlattice structures, where size effects and interface resistance effects can make the models very cumbersome. In this work we propose a simple analytical expression that can predict in-plane and cross-plane values of thermal conductivity of superlattices from an approximate analytical expression that joins a model expansion of the Boltzmann equation with a combination of the acoustic mismatch model and diffuse mismatch model for thermal boundary resistance. The obtained values are compared to experimental data from AlAs/GaAs, Si/Ge, and Si/Si0.7Ge0.3 and a reasonable fit is obtained. Special attention is paid to the low thermal conductivity predicted in the Si/Ge large period range, which current microscale models fail to predict but which are approximately described in the present model.
Polarization induced control of single and two-photon fluorescence
Authors: Nag Amit , Goswami Debabrata
Published: April 2010

Modulation of two-photon absorption, two-photon fluorescence (TPF), as well as single-photon fluorescence (SPF), is shown through incident laser polarization for different fluorescent dyes. TPF intensity increases as the polarization changes from circular to linear irrespective of the dye, though the intensity and wavelength dependent studies of two-photon polarization ratio for any particular dye (e.g., Rhodamine 6G) reveal the nature of their excited state. SPF intensity of IR125 and IR144 dyes increases as the polarization changes from linear to circular. Thus, polarization studies indicate that in case of TPF, there is a preference toward the linear component while in case of SPF, the preference is toward the circular component of the incident laser beam.
Effect of excess Fe on the superconducting and magnetic properties of the FeTe0.70Se0.30 compound
Authors: Yadav C. S. , Paulose P. L.
Published: April 2010

We have studied the properties of stoichiometric FeTe0.7Se0.3 and the effect of Fe excess in this system. The excess Fe compound is shown to display spin glasslike order below 26 K. Microscopic studies using F57e Mössbauer spectroscopy show the gradual evolution of the magnetic hyperfine field below the spin glass order. The dc magnetization and hyperfine field distribution show that there is a strong moment on the Fe in this system.
Fast and reliable droplet transport on single-plate electrowetting on dielectrics using nonfloating switching method
Authors: Park Jun Kwon , Lee Seung Jun , Kang Kwan Hyoung
Published: April 2010

In a droplet transport based on electrowetting on dielectrics, the parallel-plate configuration is more popular than the single-plate one because the droplet transport becomes increasingly difficult without cover plate. In spite of the improved transport performance, the parallel-plate configuration often limits the access to the peripheral components, requesting the removal of the cover plate, the single-plate configuration. We investigated the fundamental features of droplet transport for the single-plate configuration. We compared the performance of several switching methods with respect to maximum speed of successive transport without failure and suggested nonfloating switching method which is inherently free from the charge-residue problem and exerts greater force on a droplet than conventional switching methods. A simple theory is provided to understand the different results for the switching methods.
Optical properties of II-VI colloidal quantum dot doped porous silicon microcavities
Authors: Qiao Hong , Guan Bin , Böcking Till , Gal Michael , Gooding J. Justin , Reece Peter J.
Published: April 2010

In this paper we report on the light emitting properties of mesoporous silicon vertical-cavity optical resonators with II-VI colloidal quantum dots selectively deposited in the cavity layer. Optical resonator structures exhibit reflectivity stop bands of several hundred nanometres and resonant modes with line-widths less than 3.5 nm. The observed modification of spectral and spatial emission properties of the quantum dots and tenfold enhancement at the resonance wavelength is consistent with cavity enhanced spontaneous emission. Using this hybrid fabrication approach we show that narrow band light emitting structures may be fabricated over a broad spectral region in the visible and near-infrared.
AlGaN based highly sensitive radio-frequency UV sensor
Authors: Chivukula Venkata , Ciplys Daumantas , Sereika Albertas , Shur Michael , Yang Jinwei , Gaska Remis
Published: April 2010

The response of the AlGaN based radio-frequency (rf) sensor to deep ultraviolet (UV) illumination was investigated. Illumination by UV light emitting diodes with wavelengths from 280 to 375 nm significantly decreased rf oscillator frequency due to change in the impedance of AlGaN-based metal-semiconductor-metal structure. The UV-induced frequency shift attains 400 kHz from the oscillator dark frequency of 144.5 MHz with the highest sensitivity of 40 kHz/(μW/cm2) at 280 nm wavelength and UV power density less than 7.4 μW/cm2. The AlGaN-based rf oscillator allows for a wireless visible-blind and solar-blind UV sensing.
Magnetization plateau and incommensurate spin modulation in Ca3Co2O6
Authors: Zhao Yang , Gong Shou-Shu , Li Wei , Su Gang
Published: April 2010

The magnetic properties of a trigonal prism unit of the spin-2 frustrated compound Ca3Co2O6 are studied by means of the density-matrix renormalization group method. A magnetization plateau at ms/3 (ms is the saturation magnetization) with ferrimagnetic structure is observed. By fitting the experimental data of magnetic curve, an estimation of the couplings gives J1=−26.84 K, J2=0.39 K, and J3=0.52 K. The local magnetic moments are unveiled to exhibit an incommensurate sinusoidally modulation along the three chains of the trigonal prism, which gives a strong theoretical support to the experimentally observed incommensurate partially disordered antiferromagnetic state for Ca3Co2O6. The present result suggests that the modulation indeed originates from the competition of antiferromagnetic and ferromagnetic couplings.
Stacked complementary metasurfaces for ultraslow microwave metamaterials
Authors: Navarro-Cía M. , Aznabet M. , Beruete M. , Falcone F. , El Mrabet O. , Sorolla M. , Essaaidi M.
Published: April 2010

We have experimentally realized at microwaves a dual-band ultraslow regime by constructing a metamaterial based upon the alternative stack of conventional- and complementary-split-ring-resonators-surfaces. The group delay reaches values larger than two orders of magnitude than those obtained when the electromagnetic wave propagates the same thickness in free-space. The ultraslow waves have been initially predicted by a numerical eigenmode analysis and finite-integration frequency domain simulations. Such ultraslow modes can be integrated into free-space technology for spatial delay lines, and traveling wave amplifier as well as sensors due to the enhanced interaction between different beams or radiation and matter.
IUPAC - NIST Solubility Data Series 66. Ammonium Phosphates
Authors: Eysseltová Jitka , Dirkse Thedford P.
Published: April 2010

The solubility of ammonium phosphate is reviewed. Many ammonium phosphates can be described in terms of the ternary system: NH3–PO5–H2O. However, this system differs from systems like the sulfates and halates in that it has a marked tendency to form condensed oligophosphate ions. The literature survey covers the period up to 1988.
Role of macroscopic particles in deep-sea oxygen consumption
Authors: Bochdansky Alexander B. , van Aken Hendrik M. , Herndl Gerhard J.
Published: April 2010

Macroscopic particles (>500 μm), including marine snow, large migrating zooplankton, and their fast-sinking fecal pellets, represent primary vehicles of organic carbon flux from the surface to the deep sea. In contrast, freely suspended microscopic particles such as bacteria and protists do not sink, and they contribute the largest portion of metabolism in the upper ocean. In bathy- and abyssopelagic layers of the ocean (2,000–6,000 m), however, microscopic particles may not dominate oxygen consumption. In a section across the tropical Atlantic, we show that macroscopic particle peaks occurred frequently in the deep sea, whereas microscopic particles were barely detectable. In 10 of 17 deep-sea profiles (>2,000 m depth), macroscopic particle abundances were more strongly cross-correlated with oxygen deficits than microscopic particles, suggesting that biomass bound to large particles dominates overall deep-sea metabolism.
microRNA 17/20 inhibits cellular invasion and tumor metastasis in breast cancer by heterotypic signaling
Authors: Yu Zuoren , Willmarth Nicole E. , Zhou Jie , Katiyar Sanjay , Wang Min , Liu Yang , McCue Peter A. , Quong Andrew A. , Lisanti Michael P. , Pestell Richard G.
Published: April 2010

microRNAs are thought to regulate tumor progression and invasion via direct interaction with target genes within cells. Here the microRNA17/20 cluster is shown to govern cellular migration and invasion of nearby cells via heterotypic secreted signals. microRNA17/20 abundance is reduced in highly invasive breast cancer cell lines and node-positive breast cancer specimens. Cell-conditioned medium from microRNA17/20–overexpressing noninvasive breast cancer cell MCF7 was sufficient to inhibit MDA-MB-231 cell migration and invasion through inhibiting secretion of a subset of cytokines, and suppressing plasminogen activation via inhibition of the secreted plasminogen activators (cytokeratin 8 and α-enolase). microRNA17/20 directly repressed IL-8 by targeting its 3′ UTR, and inhibited cytokeratin 8 via the cell cycle control protein cyclin D1. At variance with prior studies, these results demonstrated a unique mechanism of how the altered microRNA17/20 expression regulates cellular secretion and tumor microenvironment to control migration and invasion of neighboring cells in breast cancer. These findings not only reveal an antiinvasive function of miR-17/20 in breast cancer, but also identify a heterotypic secreted signal that mediates the microRNA regulation of tumor metastasis.