bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of film thickness on structural and magnetic properties of single crystalline Ba(Fe0.2Zr0.8)O3−δ thin films on (001)SrTiO3 substrates
Authors: Kanatani H. , Matsui T. , Hirao N. , Yamamoto H. , Baba Y. , Kume H. , Iwase A.
Published: May 2010

The epitaxially grown Ba(Fe0.2Zr0.8)O3−δ (BFZO) films with various thicknesses ranging from 30 to 170 nm were successfully synthesized on (001)SrTiO3 (STO) substrates by a pulsed laser-beam deposition method. The results of x-ray diffraction and transmission electron microscopy revealed that all the films exhibited the epitaxial relationship of (100)BFZO∥(100)STO and [100]BFZO∥[100]STO. In addition, 0.7% expansion of the a-axis lattice constant in the films with over 100 nm thickness was measured. Although all the BFZO films showed ferromagnetic and dielectric natures even at room temperature, the magnetization values were found to be significantly dependent upon the film thickness. The magnetization values of the films with a thickness over 100 nm films were fairly decreased rather than those of the smaller thickness films. In accordance with the x-ray photoelectron spectroscopy measurement, the decrease in the magnetization was mainly ascribed to the decreased number of the tetravalent Fe ions, which was caused by the relaxation of the misfit strain between the film and substrates.
Soft x-ray synchrotron radiation spectroscopy study of SrMn1−xRuxO3 perovskites (≤x≤1)
Authors: Kim D. H. , Lee S. M. , Kolesnik S. , Dabrowski B. , Park B.-G. , Kim J.-Y. , Lee Jieun , Min B. I. , Kang J.-S.
Published: May 2010

The electronic structures of SrMn1−xRuxO3 (0≤x≤1) have been investigated by employing soft x-ray absorption spectroscopy (XAS). The measured Mn 2p XAS spectra for SrMn1−xRuxO3 show that the valence states of Mn ions change monotonically from Mn4+ for x=0 to ∼Mn3+ for x=0.8, suggesting that the valence states of the substituted Ru ions are higher than 4+. The Ru 3p XAS spectra of SrMn1−xRuxO3 show the existence of pentavalent Ru5+ ions for the low x value. The measured O 1s XAS spectra also support these findings.
Magnetic phase diagram and magnetoelectric properties of Ho0.25Nd0.75Fe3(BO3)4
Authors: Chaudhury R. P. , Lorenz B. , Sun Y. Y. , Bezmaternykh L. N. , Temerov V. L. , Chu C. W.
Published: May 2010

The magnetic and magnetoelectric properties of a single crystal of Ho0.25Nd0.75Fe3(BO3)4 have been investigated along the main crystallographic directions. The spontaneous polarization starts increasing below the Neel temperature TN∼32 K and it displays a sudden drop at 4.8 K. This sharp decrease suggests the existence of a spin reorientation phase transition. In this compound, both spontaneous polarization and the polarization due to the magnetoelectric effect exist. Detailed study of the effect of magnetic field on the polarization and the spin rotation transition has been performed. Specific heat and magnetization measurements show characteristic anomalies at both magnetic transitions. The magnetic field (H)-temperature phase diagram has completely been resolved for H∥c and H∥a axes.
Critical scaling of transport properties in the phase diagram of iron pnictide superconductors KxSr1−xFe2As2 and KxBa1−xFe2As2
Authors: Gooch M. , Lv B. , Lorenz B. , Guloy A. M. , Chu C. W.
Published: May 2010

We present a systematic study of resistivity and thermoelectric power for iron pnictide systems KxSr1−xFe2As2 and KxBa1−xFe2As2 for 0<x<1. Both systems show a similar phase diagram with an antiferromagnetic (AFM) phase on the low-doping side and a superconducting dome-shaped phase at higher doping. The AFM phase intersects the superconducting phase boundary. The extrapolation of the AFM phase boundary to zero temperature defines a critical doping of xc∼0.4. We show that the electrical and thermoelectric transport properties above the superconducting Tc obey a characteristic temperature scaling behavior at xc. The crossover and scaling property indicates the existence of a (possibly hidden) magnetic quantum critical point in the phase diagram of the 122 iron pnictides. The results of this investigation prove the significance of magnetic fluctuations in iron pnictide superconductors.
Thermomagnetic irreversibility and magnetic short range ordering in Mn2.5Co0.5O4 tetragonal spinel thin films
Authors: Kuo K. M. , Chern G. , Li Y. Y. , Wang C. R.
Published: May 2010

Mn 2.5 Co 0.5 O 4 films are grown on MgO(001) and (011) substrate by molecular beam epitaxy. Detailed structural and magnetic analyses are carried out by x-ray diffraction and magnetization measurements. The reduction of the lattice parameter c/a* ratio and the enhancement of the Curie temperature (from 43 to 66 K), due to the weakening of the Jahn–Teller effect, are observed. In addition, thermomagnetic reversibility is observed at lower temperature and low external filed indicating the existence of local canting states. The randomness of Co cation and uniaxial anisotropy further enhance the local canting effect. An H-T phase diagram is mapped out, which indicates a short rang order state in the temperature 66–85 K separating the ferrimagentic and paramagnetic phases.
Diffraction line-shapes, Fermi surface nesting, and quantum criticality in antiferromagnetic chromium at high pressure (invited)
Authors: Jaramillo R. , Feng Yejun , Rosenbaum T. F.
Published: May 2010

We explore the behavior of the nested bandstructure of chromium as a function of temperature and pressure to the point where magnetism disappears. X-ray diffraction measurements of the charge order parameter suggest that the nesting condition is maintained at high pressure, where the spin density wave ground state is destabilized by a continuous quantum phase transition. By comparing diffraction line-shapes measured throughout the temperature-pressure phase diagram we are able to identify and describe three regimes: thermal near-critical, weak coupling ground state, and quantum critical.
Magnetotransport of La0.70Ca0.3−xSrxMnO3(Ag): A potential room temperature bolometer and magnetic sensor
Authors: Awana V. P. S. , Tripathi Rahul , Kumar Neeraj , Kishan H. , Bhalla G. L. , Zeng R. , Chandra L. S. Sharth , Ganesan V. , Habermeier H. U.
Published: May 2010

Here we report the optimized magnetotransport properties of polycrystalline La0.70Ca0.3−xSrxMnO3 and their composites with Ag. The optimization was carried out by varying the Sr and Ag contents simultaneously to achieve large temperature coefficient of resistance (TCR) as well as low field magnetoresistance (MR) at room temperature. Sharpest paramagnetic (PM)-ferromagnetic (FM) and insulator-metal (IM) transition is observed in the vicinity of the room temperature (TC≈300 K≈TIM) for the composition La0.70Ca0.20Sr0.10MnO3:Ag0.20. Partial substitution of larger Sr2+ ions at the Ca2+ ions sites controls the magnitude of the FM and IM transition temperatures, while the Ag induces the desired sharpness in these transitions. For the optimized composition, maximum TCR and MR are tuned to room temperature (300 K) with the former being as high as 9% and the later being ∼20% and ∼30% at 5 and 10 kOe magnetic fields respectively. Such sharp single peak (TCR∼9%) at room temperature can be used for the bolometric and infrared detector applications. The achievement of large TCR and low field MR at T∼300 K in polycrystalline samples is encouraging and we believe that further improvements can be achieved in thin films which by virtue of their low conduction noise are more suitable for device applications.
Faraday rotation of a magnetophotonic crystal with the dual-cavity structure
Authors: Goto Taichi , Baryshev Alexander V. , Tobinaga Kazuma , Inoue Mitsuteru
Published: May 2010

We demonstrated optical properties of a one-dimensional magnetophotonic crystal (MPC) which comprises two magnetic defects built into a dielectric multilayer. This MPC with the so-called dual-cavity structure exhibited resonant transmittance and enhancement of the Faraday rotation at a designed wavelength. A double peak that is intrinsic feature of dual cavities was observed in the spectrum of the Faraday rotation. However, the peak of resonant transmission had a bell-type shape. These results are in agreement with our theoretical consideration where a structural disorder in the experimental sample was taken into account.
Magnetic properties and magnetocaloric effects in antiferromagnetic ErTiSi
Authors: Shen Jun , Zhao Jin-Liang , Hu Feng-Xia , Wu Jian-Feng , Gong Mao-Qiong , Li Yang-Xian , Sun Ji-Rong , Shen Bao-Gen
Published: May 2010

Magnetic properties and magnetocaloric effects (MCEs) of the antiferromagnetic (AFM) ErTiSi compound with a Néel temperature TN=46 K are studied by magnetization measurements. Two successive magnetic transitions in the thermomagnetic M-T curves, an AFM-AFM transition followed by an AFM-paramagnetic transition with increasing temperature, are observed. ErTiSi undergoes a field-induced metamagnetic transition from AFM to FM state below TN. A sign change in MCE with increasing temperature or magnetic field in ErTiSi is observed near the critical field. The maximal value of magnetic entropy change ΔSm is −8.9 J/kg K around TN for a field change of 0–5 T. The modest ΔSm as well as no hysteresis loss around TN in ErTiSi may be useful for its application in magnetic refrigeration.
Magnetic field dependent neutron powder diffraction studies of Ru0.9Sr2YCu2.1O7.9
Authors: Nigam R. , Pan A. V. , Dou S. X. , Kennedy S. J. , Studer A. J. , Stuesser N.
Published: May 2010

Temperature and magnetic field dependent neutron diffraction has been used to study the magnetic order in Ru0.9Sr2YCu2.1O7.9. The appearance of (1/2, 1/2, 1/2), (1/2, 1/2, 3/2), and (1/2, 1/2, 5/2) peaks below TM=140 K manifests the antiferromagnetic order. Neutron diffraction patterns measured in applied magnetic fields from 0 to 6 T show the destruction of the antiferromagnetic order with increasing field. There is no evidence of spontaneous or field-induced long range ferromagnetic order. This latter result contradicts the vast majority of other experimental observations for this system.
Magnetic noise of a frozen ferrofluid
Authors: Komatsu K. , L’Hôte D. , Nakamae S. , Ladieu F. , Mosser V. , Kerlain A. , Konczykowski M. , Dubois E. , Dupuis V. , Perzynski R.
Published: May 2010

The magnetic noise of a frozen ferrofluid made of maghemite nanoparticles dispersed in glycerin is measured using a two-dimensional electron gas based quantum well Hall sensor (QWHS) with the spinning current technique. The frozen ferrofluid shows a superspin glass transition at 67 K. Below this glass transition temperature, the relation between the imaginary part of the ac susceptibility of a bulk ferrofluid sample and the magnetic noise measured with the QWHS gives an indication of a violation of the fluctuation dissipation theorem.
Visualization of the sensitivity of the magnetoencephalographic sensor array based on the three-dimensional modeling of cortical surface and volume conductor
Authors: Iwaki Sunao , Sutani Kouichi
Published: May 2010

Here, we present a system to visualize (i) the distribution of magnetoencephalographic (MEG) signal strength in the subject-specific measurement settings predicted by a realistic MEG signal generation model (forward model) and previously published results that are typically presented in the standardized brain coordinates, and (ii) the distribution of the sensitivity of arbitrary selected group of MEG sensors on the subject-specific cortical surface. The current results suggest that (a) our methods to predict MEG field distribution from a priori information about the possible “active” cortical regions obtained from standardized functional magnetic resonance imaging results are useful for determining the sensor sets of interest in the MEG studies for a specific subject under specific measurement condition, and that (b) visualization of the sensitivity of sensor groups could provide the approximate distribution of the MEG sources without solving the MEG inverse problem.
Competing anisotropies and temperature dependence of exchange bias in Co∣IrMn metallic wire arrays fabricated by nanoimprint lithography
Authors: Zhang Wei , Weiss Dirk N. , Krishnan Kannan M.
Published: May 2010

The magnetic behavior of exchange biased Co∣IrMn bilayer metallic wire arrays, fabricated by nanoimprint lithography, was studied and compared with identical thin film heterostructures. A significant uniaxial shape anisotropy, KU-shape, in addition to the unidirectional exchange anisotropy, KE, and the intrinsic uniaxial anisotropy, KU-intrinsic observed in the unpatterned film, was introduced in the wire arrays through wire patterning. The competing anisotropies were shown to modify the angular dependence of exchange bias, HEB, and coercivity, HC, for wire arrays. In addition, an asymmetric behavior is observed for both wire arrays and unpatterned film and is attributed to the noncollinear alignment of uniaxial and unidirectional anisotropies. Temperature dependence of HEB is different for the wire arrays from the unpatterned thin film. This and the large deviation from ideal cubic anisotropy in the antiferromagnet for the wire arrays are both in agreement with Malozemoff’s model of exchange bias.
Growth of highly textured manganese zinc ferrite films on glass substrates
Authors: Waqas H. , Huang X. L. , Ding J. , Fan H. M. , Ma Y. W. , Herng T. S. , Quresh A. H. , Wei J. Q. , Xue D. S. , Yi J. B.
Published: May 2010

Highly textured manganese zinc ferrite (Mn0.7Zn0.3Fe2O4) films have been successfully fabricated on glass substrates by pulse laser deposition at relatively low temperatures. Investigations indicated that the strain, which is induced by high deposition rate and the difference of thermal coefficient between the film and glass substrate, is attributed to the growth of textured structure. Growth of highly textured cobalt ferrite film was also achieved using the same method. This work provided a possible technique for fabricating high quality ferrite films on glass substrates.
Analysis on the exchange interactions in three metal-organic coordination network systems possessing one-dimensional magnetism
Authors: Danilovic Dusan , Hamida Youcef , Yuen Tan , Li Kunhao , Li Jing
Published: May 2010

The nature of the exchange interactions in three metal-organic coordination networks families is examined. These families have a general form ML2(bpy). Since (bpy) molecules are very long, our networks are reduced to effectively one-dimensional chain systems with very weak interchain interaction. The Bonner–Fisher and Fisher classical spin models are applied to fit the magnetic susceptibility data, and results of the fits are discussed. Metal ions inside MCl2(bpy) and M(N3)2(bpy) interact with ferromagnetic interactions and can be described with Fisher classical spin model, while metal ions in M(ox)(bpy) interact with antiferromagnetic interaction and it can be described with the Bonner–Fisher model. Fitting parameter J produced from our models has higher value in M(N3)2(bpy) than in MCl2(bpy) for the same M. It was found that the total spin value is dominant factor to the strength of the magnetic interaction.
Material parameters characterization for three-dimensional pyramidal cloak
Authors: Wu Qun , Zhang Kuang , Meng Fan-Yi , Fu Jia-Hui , Li Le-Wei
Published: May 2010

Arbitrarily three-dimensional (3D) pyramidal cloaks are proposed and designed theoretically based on the coordinate transformation. First, the general expressions of constitutive tensors of the cloaks are derived, and then there are some full-wave simulations which show that the cloak would bend incoming electromagnetic waves and guide them to propagate around inner region. Furthermore, the lossy cases are also considered and simulated. The results validate the constitutive tensors of the 3D pyramidal cloaks, and it is believed that the results are helpful for the practical design and analyze of the 3D cloaks.
High frequency magnetic field imaging by frequency modulated magnetic force microscopy
Authors: Saito Hitoshi , Lu Wei , Hatakeyama Kodai , Egawa Genta , Yoshimura Satoru
Published: May 2010

High frequency ac magnetic field from magnetic recording head was successfully imaged by using our newly developed frequency-modulated magnetic force microscopy (FM-MFM), which uses the frequency modulation of cantilever oscillation caused by applying ac magnetic field to a mechanically oscillated cantilever. The FM-MFM has been demonstrated and the experimental results show good agreement with our proposed models for FM-MFM. The amplitude and phase images of an ac magnetic field can be obtained separately by using the FM-MFM technique with a lock-in amplifier. By taking advantage of this technique, the present FM-MFM method opens a possibility to evaluate the magnetic field characteristics of magnetic recording head with high spatial resolution.
Magnetic properties of 3d transition metal wires on vicinal Cu(111) surfaces at finite temperature
Authors: Hashemi H. , Fischer G. , Hergert W. , Stepanyuk V. S.
Published: May 2010

One-dimensional transition metal (TM) nanowires can be formed on a stepped Cu(111) surface. The basic template is an embedded Fe chain at one-atom distance away from the upper edge of the monoatomic surface step, supplying the deposition of 3d TM chains from V to Co to form on top of the Fe chain. Density functional theory (DFT) is applied to calculate the magnetic properties of these TM-Fe wires. Exchange parameters are extracted from the DFT calculations. A classical Heisenberg model is used in Monte Carlo simulations to study finite temperature effects.
Quasiparticle density of states measurements in clean superconducting AlMn alloys
Authors: O’Neil G. C. , Schmidt D. R. , Tomlin N. A. , Ullom J. N.
Published: May 2010

Aluminum doped with Manganese (AlMn) forms a superconducting alloy with the transition temperature suppressed by the added manganese. We present quasiparticle density of states (DOS) measurements on superconducting AlMn alloys made by current-voltage measurements on normal-metal/insulator/superconductor tunnel junctions. The DOS remains Bardeen-Cooper-Schrieffer-like with a reduced gap, matching the predictions of Kaiser. However, we measure additional subgap states not predicted by Kaiser, and demonstrate that these subgap states will harm some potential applications.
Ion energy distribution near a plasma meniscus with beam extraction for multi element focused ion beams
Authors: Mathew Jose V. , Paul Samit , Bhattacharjee Sudeep
Published: May 2010

An earlier study of the axial ion energy distribution in the extraction region (plasma meniscus) of a compact microwave plasma ion source showed that the axial ion energy spread near the meniscus is small (∼5 eV) and comparable to that of a liquid metal ion source, making it a promising candidate for focused ion beam (FIB) applications [J. V. Mathew and S. Bhattacharjee, J. Appl. Phys. 105, 96101 (2009)]. In the present work we have investigated the radial ion energy distribution (IED) under the influence of beam extraction. Initially a single Einzel lens system has been used for beam extraction with potentials up to −6 kV for obtaining parallel beams. In situ measurements of IED with extraction voltages upto −5 kV indicates that beam extraction has a weak influence on the energy spread (±0.5 eV) which is of significance from the point of view of FIB applications. It is found that by reducing the geometrical acceptance angle at the ion energy analyzer probe, close to unidirectional distribution can be obtained with a spread that is smaller by at least 1 eV.
Modeling of electromigration on void propagation at the interface between under bump metallization and intermetallic compound in flip-chip ball grid array solder joints
Authors: Jen Ming-Hwa R. , Liu Lee-Cheng , Lai Yi-Shao
Published: May 2010

A void pattern in Sn4Ag0.5Cu solder joints under EM stressing was empirically obtained at the under bump metallization/intermetallic compound (UBM/IMC) interface. The pattern was associated with current crowding and consumption of the UBM layer. A kinetic model was employed and modified to describe the void propagation at UBM/IMC interface. Based on the continuity condition, the void growth velocity was calculated. The analytical results were in good agreement with the experimental data.
Measurement of laser heating in spin exchange optical pumping by NMR diffusion sensitization gradients
Authors: Parnell Steven R. , Deppe Martin H. , Ajraoui Salma , Parra-Robles Juan , Boag Stephen , Wild Jim M.
Published: May 2010

This paper details pulsed gradient NMR measurements of the H3e diffusion coefficient in sealed cells during spin exchange optical pumping. The potential of ultra low field magnetic resonance imgaing (MRI) and NMR for noninvasive measurement of cell pressure is demonstrated. Diffusion sensitization gradients allow measurement of the H3e diffusion coefficient from which the pressure and/or temperature of the gas can be determined during optical pumping. The pressure measurements were compared with neutron time of flight transmission measurements. Good agreement was observed between the temperature/pressure measurements and predictions based on Chapman–Enskog theory. The technique had sufficient sensitivity to observe the diffusion coefficient increasing with temperature in a sealed cell. With this method, evidence for laser heating of the H3e during optical pumping was found. The results show that NMR diffusion measurements allow noninvasive measurement of the cell temperature and/or pressure in an optical pumping setup. The method can be expanded using MRI to probe the spatial distribution of the diffusion coefficient. These techniques can be applied to the further investigation of polarization limiting effects such as laser heating.
Broadband optoacoustic measurements of ultrasound attenuation in severely plastically deformed nickel
Authors: Kozhushko Victor V. , Paltauf Günther , Krenn Heinz , Scheriau Stephan , Pippan Reinhard
Published: May 2010

Laser optoacoustics and immersion techniques allowed a broadband ultrasound spectroscopy which was used for measuring the attenuation of severely plastically deformed nickel. A disk shaped specimen of nickel of about 33 mm diameter and 2.5 mm thickness was prepared by the high pressure torsion method. The produced equivalent shear strain linearly increased from a minimum at the center up to 1000% at the edge, gradually refining the grain size distribution down to 200 nm. The metal water interface was illuminated by 5 ns laser pulses, generating longitudinal ultrasound pulses with a pronounced compression phase and a smooth spectrum covering the range from 0.1 up to 150 MHz. The laser beam spot diameter was 6 mm, yielding a maximum power density below 15 MW/cm2. The ultrasound passed through the sample thickness and a 2 mm layer of coupling water. The pulse was detected by a 25 μm thick piezoelectric foil transducer with a diameter of the sensitive area of 2 mm. The transient signals were locally measured at different radii of the specimen. The attenuation almost linearly increases with frequency while its absolute value decreases from the center to the edge of the specimen.
A cryogenic electrostatic trap for long-time storage of keV ion beams
Authors: Lange M. , Froese M. , Menk S. , Varju J. , Bastert R. , Blaum K. , López-Urrutia J. R. Crespo , Fellenberger F. , Grieser M. , von Hahn R. , Heber O. , Kühnel K.-U. , Laux F. , Orlov D. A. , Rappaport M. L. , Repnow R. , Schröter C. D. , Schwalm D. , Shornikov A. , Sieber T. , Toker Y. , Ullrich J. , Wolf A. , Zajfman D.
Published: May 2010

We report on the realization and operation of a fast ion beam trap of the linear electrostatic type employing liquid helium cooling to reach extremely low blackbody radiation temperature and residual gas density and, hence, long storage times of more than 5 min which are unprecedented for keV ion beams. Inside a beam pipe that can be cooled to temperatures <15 K, with 1.8 K reached in some locations, an ion beam pulse can be stored at kinetic energies of 2–20 keV between two electrostatic mirrors. Along with an overview of the cryogenic trap design, we present a measurement of the residual gas density inside the trap resulting in only 2×103 cm−3, which for a room temperature environment corresponds to a pressure in the 10−14 mbar range. The device, called the cryogenic trap for fast ion beams, is now being used to investigate molecules and clusters at low temperatures, but has also served as a design prototype for the cryogenic heavy-ion storage ring currently under construction at the Max-Planck Institute for Nuclear Physics.
Local spin injectors using GaAs tips under light excitation
Authors: Vu D. , Ramdani R. , Bansropun S. , Gérard B. , Gil E. , André Y. , Rowe A. C. H. , Paget D.
Published: May 2010

Local spin injectors using GaAs tips at the end of transparent cantilevers have been fabricated using a combination of epitaxial growth, etching processes and photolithographic techniques. The tip luminescence polarization is found to be small because of total internal light reflections of the luminescence inside the tip. However, measurements on planar films of similar doping along with a numerical solution of the spin and charge diffusion equations indicate that the injected spin polarization can be as high as 40% with corresponding electronic concentrations at the tip apex of the order of 1014 cm−3.
Simulations of direct-current air glow discharge at pressures ∼1 Torr: Discharge model validation
Authors: Mahadevan Shankar , Raja Laxminarayan L.
Published: May 2010

Computational simulations of air glow discharge phenomena in the pressure range typical of plasma actuator applications for high speed flow control are presented. The model is based on a self-consistent, multispecies, and multitemperature continuum description of the plasma. A reduced air plasma model suitable for multidimensional simulations with 11 species and 21 gas phase chemical reactions is validated against experimental results in the literature. The discharge model predicts experimentally observed glow mode discharge operation, the current-voltage characteristics of the discharge, and spatial profiles of the electron temperature and positive ion number densities. For pressures of order 1 Torr, O2+ and N2+ are the dominant positive ion species in the discharge, and the concentration of O− negative ion is comparable to electron concentration. The two-dimensional structure of the discharge is predicted by the model is found to be in agreement with qualitative observations from the experiments.
Ferromagnetic resonance and magnetoelastic demodulation in thin active films with an uniaxial anisotropy
Authors: Klimov A. , Ignatov Yu. , Tiercelin N. , Preobrazhensky V. , Pernod P. , Nikitov S.
Published: May 2010

The results of experimental and theoretical studies of ferromagnetic resonance (FMR) and magnetoelastic excitations near the spin reorientation transition (SRT) in an uniaxial TbCo2/FeCo layered nanostructure and a La0.7Sr0.3MnO3 film are reported. Experimental dependences of the amplitude of the reflected microwave signal versus the external magnetic field strength are presented in comparison with the theoretical ones. An increase in FMR reflectivity in the vicinity of SRT is clearly demonstrated. Low frequency magnetoelastic excitation of flexural vibrations of the samples by means of modulated microwave electromagnetic field is observed experimentally using a laser beam deflection technique. The increase in amplitude of vibrations at modulation frequency under combined FMR and SRT conditions is observed in agreement with the theory.
Phase properties of reflected light in photonic band gap
Authors: Dai Qiao-Feng , Lan Sheng , Wu Li-Jun , Wang He-Zhou
Published: May 2010

We find that the phase shifts of reflected light within band gap of two-dimensional photonic crystal (PC) are as follows: with frequency altering from the lower edge to the upper edge of first stop band, the reflection phase shift varies from −π to 0 for the PC’s unit cell with the high-index material near the center, while it varies from 0 to π for that with low-index material near the center. For the higher-order stop band, there exists a certain value of filling fraction, which makes the phase shifts in higher-order stop bands almost the same as that in the first stop band. When the filling fraction is far from that value, the phase shifts are significantly different. The further study on the Bloch modes demonstrates that their distribution of electric field and magnetic field determines the phase shifts. Moreover, we have found that, in the overlap area of transverse magnetic and transverse electric stop band, the phase difference between two polarizations of reflected light can remain invariant in a broad frequency region. Based on this property, the broadband and angle-insensitive phase retarders are designed. These interesting phase characteristics will bring about many potential applications.
Ab initio studies on atomic and electronic structures of black phosphorus
Authors: Du Yanlan , Ouyang Chuying , Shi Siqi , Lei Minsheng
Published: May 2010

The atomic and electronic properties of black phosphorus (BP), which has been recently shown to have potential application as anode material for lithium ion batteries, are studied via ab initio calculations. The calculations reveal that the interlayer interaction in BP is Van der Waals Keesom force, which is critical to the formation of the layered structure. Interestingly, we also found that the small band gap of bulk BP (0.19 eV) when compared with that of single layer BP (0.75 eV) is partly because of the interlayer Van der Waals interaction in BP. The change in a materials band structure because of Van der Waals interaction is rarely reported in literature.
Optical trapping and manipulation of magnetic holes dispersed in a magnetic fluid
Authors: Sun Ting , Fu Zhi-Cheng , Zhao Wei-Ren , Deng Hai-Dong , Dai Qiao-Feng , Wu Li-Jun , Lan Sheng , Gopal Achanta Venu
Published: May 2010

The optical trapping and manipulation of magnetic holes (MHs) dispersed in a magnetic fluid is systematically investigated. It is found that the gradient force, which tends to attract MHs to the beam center, can be completely counteracted by the repulsive force between MHs induced by a magnetic field. As a result, a depletion region is created at the laser beam spot for a sufficiently strong magnetic field. This phenomenon can be easily observed for large MHs with a diameter of 11 μm. However, it does not appear for MHs with a smaller diameter of 4.3 μm. It is revealed that the enhancement in the concentration of magnetic nanoparticles in the laser spot region as well as the clustering of these nanoparticles leads to a much stronger interaction between MHs when a magnetic field is applied. Consequently, the magnetic field strength necessary to create the depletion region is significantly reduced. We also find that the trapping behavior of MHs depends strongly on the thickness of the sample cells. For thin sample cells in which only one layer (or a two-dimensional distribution) of MHs is allowed, we can observe the creation of depletion region. In sharp contrast, MHs can be stably trapped at the center of the laser beam in thick sample cells even if a strong magnetic field is imposed. This phenomenon can be explained by the existence of a gradient in magnetic field strength along the direction perpendicular to the sample cells. Apart from individual MHs, we also investigate the movement of MH chains under the scattering force of the laser beam. It is observed that MH chains always move along the direction parallel to the magnetic field. This behavior can be easily understood when the anisotropy in viscosity caused by the applied magnetic field is considered.
Transport and magnetic properties of Mo2.5Ru0.5Sb7−xTex
Authors: Candolfi C. , Lenoir B. , Dauscher A. , Guilmeau E. , Hejtmánek J.
Published: May 2010

Transport properties including electrical resistivity, thermopower, and thermal conductivity of polycrystalline Mo2.5Ru0.5Sb7−xTex compounds for 0≤x≤1 have been investigated in the 2–1000 K temperature range. Additional information on the concentrations and the scattering mechanisms of the charge carriers as well as on the magnetic properties has been obtained through Hall effect and magnetic susceptibility measurements performed in the 5–300 K temperature range. The enhancement in the Te content results in a decrease in the carrier concentration which is at the origin of the simultaneous increase in the electrical resistivity and thermopower. A single parabolic band model with acoustic phonon scattering enables to explain the compositional and temperature dependence of the thermopower while such a simple model fails to adequately describe the electronic thermal conductivity. This characteristic together with the unusual dependence of the thermal conductivity upon alloying might be a direct consequence of strong phonons-dimers interactions displayed by Mo3Sb7. Magnetic susceptibility data demonstrate that the antiferromagnetically-coupled dimers tend to disappear as x is enhanced, lending further support to a crucial role played by these interactions to understand the thermal transport in these materials. Low thermal conductivity coupled with high thermopower values result in a high dimensionless figure of merit ZT∼0.70 at 1000 K in Mo2.5Ru0.5Sb6.5Te0.5 positioning this material as an interesting candidate for power generation applications.
The electronic structure and spin polarization of Fe3−xMnxSi and Fe3−yMnSiy alloys
Authors: Hamad Bothina , Khalifeh Jamil , Abu Aljarayesh Ibrahim , Demangeat Claude , Luo Hu-Bin , Hu Qing-Miao
Published: May 2010

First principle calculations using supercell approach and coherent potential approximation (CPA) are performed to investigate the electronic and magnetic structures of Fe3−xMnxSi and Fe3−yMnSiy alloys, where x,y=0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.5, 1.75, and 2.25. Using supercell calculations we obtained a metallic behavior for x=0, 0.25, and 0.5 in Fe3−xMnxSi alloys with spin polarizations of 24%, 39%, and 93%, respectively. The behavior starts to be half-metallic at x=0.75 with a small direct band gap that increases for higher concentrations of Mn. Among the half-metallic systems, only those of L21 structure at x=1 and 2 possess indirect band gaps along Γ-X symmetry line. The change of Si concentration in Fe3−yMnSiy structures retrieve the metallic behavior for all concentrations except y=1.25 that shows a half-metallic behavior with a direct band gap of 0.27 eV. We obtained a good agreement between supercell and CPA calculations for the values of the magnetic moment and the trends of the formation energies, which reveals the validity of the supercell approach in predicting the magnetic structure and the energetics of doped Heusler alloys.
Magnetic properties of granular CoCrPt:SiO2 films as tailored by Co+ irradiation
Authors: Tibus Stefan , Strache Thomas , Springer Felix , Makarov Denys , Rohrmann Hartmut , Schrefl Thomas , Fassbender Jürgen , Albrecht Manfred
Published: May 2010

We report on an approach to tailor the magnetic exchange in a conventional granular CoCrPt:SiO2 recording medium by irradiation with Co+ ions. Irradiation at low fluences enhances the intergranular exchange resulting in a narrowing of the switching field distribution (SFD). The modification of magnetic exchange coupling was evidenced by measuring the angular dependence of the switching field and is supported by an increase in the magnetic domain size. Further, micromagnetic simulations of a granular magnetic medium confirm the correlation between intergranular exchange and SFD. At high fluences, however, the irradiation damages lead to the degradation of the magnetic layer as magnetic anisotropy and saturation magnetization decrease. Ion irradiation simulations suggest that this is caused by strong intermixing at the grain and layer interfaces.
Metal grid/conducting polymer hybrid transparent electrode for inverted polymer solar cells
Authors: Zou Jingyu , Yip Hin-Lap , Hau Steven K. , Jen Alex K.-Y.
Published: May 2010

A simple method was developed using metal grid/conducting polymer hybrid transparent electrode to replace indium tin oxide (ITO) for the fabrication of inverted structure polymer solar cells. The performance of the devices could be tuned easily by varying the width and separation of the metal grids. By combining the appropriate metal grid geometry with a thin conductive polymer layer, substrates with comparable transparency and sheet resistance to those of ITO could be achieved. Polymer solar cells fabricated using this hybrid electrode show efficiencies as high as ∼3.2%. This method provides a feasible way for fabricating low-cost, large-area organic solar cells.
Effect of substrate annealing on the wetting of metastable BNi-2 ribbons by molten Sn
Authors: Shen Ping , Sun Jianxin , Yang Jun , Jiang Qichuan
Published: May 2010

Wetting of metastable BNi-2 substrates annealed at various temperatures (550–900 K) by molten Sn was investigated at a constant temperature of 550 K in a high vacuum using a modified sessile drop method. The spreading was the fastest for Sn on the amorphous substrate annealed at 550 K. With increasing annealing temperature, the wettability became worse, being the poorest for the substrate annealed at 750 K, and then improved. The wetting behavior was strongly affected by the structural and energetic changes from amorphous to nanocrystalline states, so were the atomic diffusion and interfacial reaction. The plausible correlations among the wetting behavior, the structural change, and the interfacial reaction were addressed.
Surface composition and electronic structure of the In4+xSn3−2xSbxO12 (≤x≤1) solid solution
Authors: O’Neil D. H. , Egdell R. G. , Edwards P. P.
Published: May 2010

The electronic structures of In4Sn3O12, In5SnSbO12 and the intermediate solid solution In4+xSn3−2xSbxO12 have been studied by x-ray photoemission spectroscopy. The surfaces were found be consistently rich in indium and deficient in tin, with the extent of the deviation from bulk stoichiometry decreasing with increasing cosubstitution of In and Sb for Sn. We find that the valence band structure of the In4+xSn3−2xSbxO12 solid solution evolves with the degree of cosubstitution and shows well-defined features that arise from the hybridization of O 2p states with In 5s, Sn 5s, and Sb 5s states. We determine the fundamental electronic gaps of In4Sn3O12 and In5SnSbO12 as 2.66 eV and 2.79 eV, respectively.
Phase transformation of Mg–Fe alloys
Authors: Yoneda Yasuhiro , Abe Hiroshi , Ohshima Takeshi , Uchida Hirohisa
Published: May 2010

An Mg–Fe alloy system prepared through mechanical alloying (MA) was structurally analyzed. MA can produce single-phase bcc alloys using Mg concentrations up to about 15 mol %. Use of conventional average structure analysis and x-ray pair-distribution function method enabled the long-range and short-range order structures of the Mg–Fe alloys to be bridged. The substituted Mg atoms were randomly arranged in the low-Mg composition but started to have an order structure. The partially ordered Mg–Fe alloy undergoes an austenitic (cubic) to martensitic (orthorhombic) phase change, as increasing Mg composition.
Nanoscale mechanical behavior of vanadium doped ZnO piezoelectric nanofiber by nanoindentation technique
Authors: Chen Y. Q. , Zheng X. J. , Mao S. X. , Li W.
Published: May 2010

The nanoscale mechanical behavior of Zn0.975V0.025O (V-ZnO) piezoelectric nanofibers by electrospinning was investigated using a nanoindenter in detail. After being calcined at 700 °C, V-ZnO nanofibers are of hexagonal wurtzite phase crystal structure, and the diameter and length are in the range of 50–300 nm and several tens to several hundreds of micrometers. The statistical average values of reduced modulus and hardness are 58.7±4.2 and 3.3±0.2 GPa for the nanofibers, and they decrease by 47.2% and 34.0% in comparison with those of bulk ZnO. It indicates that size effect of the mechanical behavior was obviously observed for the nanofibers, and the mechanism is discussed in conjunction with their high surface-to-volume ratio. Indentation depth-dependent reduced modulus and hardness properties were observed at indentation depth less than 18 nm, and it is attributed to the strain gradient effect during nanoindentation.
On regularity criteria of the Navier–Stokes equations in bounded domains
Authors: Kim Jae-Myoung
Published: May 2010

We present new regularity criteria of weak solutions to the Navier–Stokes equations in bounded domains of Rn, n=3,4. We prove that if a weak solution u=(u1,u2,…,un) satisfies uk∊Lx,tpk,qk with 2/qk+n/pk=1, n<pk⩽∞ for k=1,2,…,n−1 and ∂un/∂xn∊Lx,tl,m with 2/m+n/l=2, n/2<l⩽n, then u becomes smooth.
R
87
b
and C133s nuclear magnetic resonance study of the structural properties of mixed RbxCs2−xZnCl4 (x=, 1, and 2) crystals
Authors: Lim Ae Ran
Published: May 2010

The structures of mixed RbxCs2−xZnCl4 (x=0, 1, and 2) single crystals grown by using the slow evaporation method were determined with x-ray diffraction. In addition, the NMR spectra and the spin-lattice relaxation times, T1, of the R87b and C133s nuclei of the three crystals were determined by using nuclear magnetic resonance (NMR) spectroscopy. The spin-lattice relaxation times, T1, of the Cs-based compounds are very much longer than those of the Rb-based compounds. The differences between the T1 values of the Rb and Cs nuclei are due to the difference between their electric quadrupole moments. Further, we analyzed the crystallographic structures of these crystals by considering the occupation probabilities (Rb or Cs) of the two cationic sites. Our NMR experimental results confirm that there are two crystallographically inequivalent Rb sites, Rb(1) and Rb(2), in Rb2ZnCl4 and two crystallographically inequivalent Cs sites, Cs(1) and Cs(2), in Cs2ZnCl4. And, only one Rb site and only one Cs site in RbCsZnCl4 was obtained. The Cs and Rb occupation rates of each of the two available sites, A1 and A2, were determined from the NMR signals.
Effect of resonance in external radio-frequency circuit on very high frequency plasma discharge
Authors: Rauf Shahid , Chen Zhigang , Collins Ken
Published: May 2010

A fully electromagnetic plasma model for an asymmetric capacitively coupled plasma discharge is used to understand the interaction between the external radio-frequency (rf) distributed circuit and the plasma. The plasma is excited using a 150 MHz rf source connected to the top electrode, the bottom electrode is connected to a shorted transmission line, and the electrodes are separated from the chamber walls through dielectric rings. Under typical conditions, the electron density peaks in the center of the plasma chamber due to the standing electromagnetic wave and the rf current from the top electrode primarily returns through the bottom electrode. When the electrical length of the bottom transmission line is adjusted such that it presents a large (open-circuit) impedance at the plasma chamber interface, the rf return current shifts from the bottom electrode to the chamber wall. As a consequence, the peak in electron density also moves from the center of the chamber toward its outer periphery.
Vibration energy harvesting using highly (001)-oriented Pb(Zr,Ti)O3 thin film
Authors: Harigai Takakiyo , Adachi Hideaki , Fujii Eiji
Published: May 2010

Energy conversion from mechanical vibration into electric power was investigated using the piezoelectric Pb(Zr,Ti)O3 lead zirconate titanate (PZT) thin film with highly (001)-orientation. The piezoelectric d31 constant was found to be as large as −150 pC/N. The generated electric voltage under vibration acceleration of 45 m/s2 at 2450 Hz for the PZT/Si cantilever exceeded 2 V and the operation of light emitting diode lighting was demonstrated. The average output power of 100 μW was obtained at the impedance-matched load resistance of 2.2 kΩ. The generated power density of 50 μW/mm3 was much larger than that of conventional piezoelectric harvesters.
Three-electrode self-actuating self-sensing quartz cantilever: Design, analysis, and experimental verification
Authors: Chen C. Julian , Schwarz Alex , Wiesendanger Roland , Horn Oliver , Müller Jörg
Published: May 2010

We present a novel quartz cantilever for frequency-modulation atomic force microscopy (FM-AFM) which has three electrodes: an actuating electrode, a sensing electrode, and a ground electrode. By applying an ac signal on the actuating electrode, the cantilever is set to vibrate. If the frequency of actuation voltage closely matches one of the characteristic frequencies of the cantilever, a sharp resonance should be observed. The vibration of the cantilever in turn generates a current on the sensing electrode. The arrangement of the electrodes is such that the cross-talk capacitance between the actuating electrode and the sensing electrode is less than 10−16 F, thus the direct coupling is negligible. To verify the principle, a number of samples were made. Direct measurements with a Nanosurf easyPPL controller and detector showed that for each cantilever, one or more vibrational modes can be excited and detected. Using classical theory of elasticity, it is shown that such novel cantilevers with proper dimensions can provide optimized performance and sensitivity in FM-AFM with very simple electronics.
Surface plasmon polariton-assisted electron emission and voltage-controlled negative resistance of Al–Al2O3–Au diodes
Authors: Hickmott T. W.
Published: May 2010

Electrons are ejected from an Au surface when their energy exceeds the work function of Au, ϕAu, which is 5.2 eV. The threshold voltage for the onset of electron emission from Al–Al2O3–Au diodes that develop voltage-controlled negative resistance in their current-voltage characteristics is VEM≅2.4 V. The threshold voltage for electroluminescence (EL) is VEL=1.6–2.0 V. The interaction of electrons with surface plasmon polaritons (SPPs) produced at the Al2O3–Au interface by EL photons provides a mechanism by which electrons gain enough energy to surmount the work function barrier at the Au-vacuum interface when the applied voltage is less than 5.2 V. The interaction of EL photons with surface plasmons in Au is a new mechanism for creating SPPs.
Partial arsenic pressure and crystal orientation during the molecular beam epitaxy of GaAs on SrTiO3(001)
Authors: Cheng J. , Chettaoui A. , Penuelas J. , Gobaut B. , Regreny P. , Benamrouche A. , Robach Y. , Hollinger G. , Saint-Girons G.
Published: May 2010

A study of epitaxial growth of GaAs islands on (2×1) reconstructed SrTiO3(001) surface is presented. Under low arsenic partial pressures (PAs), GaAs islands are (001)-oriented, and increasing PAs leads to the progressive formation of (111)-oriented GaAs islands. This results from the competition between the formation of Ga–O and Ga–As bonds at the early stages of the growth, as supported by the analysis of the evolution of the island density with respect to PAs.