Search

Context. Characterizing the response of the upper Martian atmosphere to solar flares could provide important clues as to the climate evolution of the red planet in the early Solar System, when the extreme ultraviolet and soft X-ray radiation was substantially higher than the present-day level and when these events occurred more frequently. A critical process herein is the Martian atmospheric escape in the form of atomic C and N, as mainly driven by CO2/CO and N2 dissociation. Aims. This study is devoted to evaluating how these escape rates varied on the dayside of Mars during the X8.2 solar flare on 10 September 2017. Methods. The background Martian atmospheric structures, before, during, and after the flare, are constructed from the Neutral Gas and Ion Mass Spectrometer measurements made on board the Mars Atmosphere and Volatile Evolution spacecraft, from which the hot C and N production rate profiles via different photon and photoelectron impact channels and on different flare stages are obtained. They are combined with the respective escape probability profiles computed using a test particle Monte Carlo approach to derive the atomic C and N escape rates on the dayside of Mars. Results. Our calculations indicate that the pre-flare C and N escape rates are (1.3-1.4) × 1024 s-1 over the dayside of Mars. During the event, we find a modest decrease in the C escape rate of 8% about 1 h after the flare peak, followed by a recovery to the pre-flare level several hours later. However, an opposite trend is found for the N escape rate during the same period, which shows an increase of 20% followed by a recovery to the pre-flare level. Conclusions. The distinction between C and N in terms of the variation in the escape rate during the solar flare reflects the competition between two flare-induced effects: enhanced hot atom production via dissociation and enhanced collisional hindrance due to atmospheric expansion. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(S,Se)4 (CZTSSe) thin film deposited on flexible Mo foil substrate has advantage of high mass specific power and good ductility. However, a thick Mo(S,Se)2 interface layer is easily to be formed between CZTSSe and Mo foil substrate. The ohmic contact property of CZTSSe/Mo is deteriorated by the formation of Mo(S,Se)2. In this work, the Mo foil substrate was pre-annealed to inhibit the growth of Mo(S,Se)2 interface layer. CZTSSe thin films were prepared on the pre-annealed Mo foil substrate by sol-gel and selenization methods. The pre-annealing treatment of Mo foil substrate leads to the oxidation of Mo. During the high temperature selenization process, the MoOx acts as a buffer layer to suppress the formation of the Mo(S,Se)2 interface layer. With the increase of the pre-annealing temperature of the Mo foil substrate, the thickness of the Mo(S,Se)2 interface layer decreases, and the resistance of CZTSSe/Mo(S,Se)2/Mo structure decreases. The ohmic contact properties of CZTSSe/Mo can be improved by the pre-annealing treatment of metal Mo foil substrates. [ABSTRACT FROM AUTHOR]

Atmospheric escape is a central issue in understanding how Mars lost the habitability and it is critically controlled by the link between the atmosphere and the interplanetary space, i.e. the ionosphere. The predominant driver of the Martian ionospheric variability is the solar extreme ultraviolet radiation. To date, how the ionospheric electrons respond to this radiation has been well investigated, but the responses of various ion species are to be understood. Based on a multi-instrument data set from the Mars Atmosphere and Volatile Evolution, we report direct observations of quasi-periodical variations of photoelectrons and ions, with a common period of ≈27.2 d and almost in exact phase with the solar rotation. These diverse variations present remarkably different amplitudes. The ion density variation has a much larger amplitude than the solar flux variation and the electron density variation has a smaller amplitude. For comparison, the amplitude of the photoelectron intensity variation is nearly identical to that of the solar flux variation. The species-dependent solar rotation effects provide a good diagnostic of the upper atmospheric and ionospheric chemistry, urging reconsiderations of the solar-driven composition and variability of any planetary ionosphere. [ABSTRACT FROM AUTHOR]

A pure compressively strained La2/3Ca1/3MnO3 (LCMO) dead layer grown on (001)-oriented LaAlO3 substrate can show all the rich phenomenon of large bias field shift, coercive field enhancement, and high blocking temperature. The obtained exchange bias field (~350 Oe) and the enhanced coercivity of about 1160 Oe at 5K under 500 Oe cooling field are superior to that have been reported in LCMO-based ferromagnetic/antiferromagnetic superlattices or nanoscale systems. Our results clearly demonstrate that the inhomogeneous magnetic dead layer of LCMO can induce a strong exchange bias effect, which may be exploited as a very simple structure for spin-valve device application. [ABSTRACT FROM AUTHOR]

Effects of cation disorder and strain on the surface morphologies and transport properties of thin films with different A-site cation disorder, which was achieved by Y and Sr codoping into La2/3Ca1/3MnO3, have been investigated. A metal-insulator transition (MIT) was observed on all films except that on MgO, which indicates that large strain increases insulator phase. With increasing cation disorder, the resistivity increases while MIT and Curie temperature decrease, which reveal that cation disorder suppresses the long-range ferromagnetic metallic phase. The spin-glass state and ferromagnetic-metallic state coexist in low temperature. Cation disorder induces more insulator phases in the large strain films. A Kondo-like transport behavior was observed in the large cation disordered films. [ABSTRACT FROM AUTHOR]

La2/3Ca1/3MnO3 (LCMO)/YBa1.8Eu0.2Cu3O7 (YBECO) multilayers on yttrium-stabilized ZrO2 are fabricated. YBECO sublayer is well crystallized in c-axis orientation, while LCMO sublayer crystallized in (001) textured structure, which forms special mosaic structure. By magnetization measurements, we confirm that the cluster spin glass existed in LCMO/YBECO multilayers in low temperature, which may scatter the transport electrons. Superconductivity cannot be observed when thickness of YBECO layer is less than 24 nm. The magnetoresistance ratio depends on the thickness of YBECO layer. The magnetotransport properties of the multilayers make it very promising to provide a technological support for the heterostructure and superlattice of manganites and superconductors. [ABSTRACT FROM AUTHOR]

YBa2Cu3O7-δ (YBCO) powders with Gd2O3 additives are prepared by the solid state reaction method. X-ray diffraction with Rietveld refinements shows that both Gd2O3 and YBCO phases coexist in the products. With increasing additive content, the unit cell symmetry of YBCO phase remains unchanged but the grain size increases. The critical current density (Jc) exhibits a maximum at x=0.1 in YBCO+ xGd2O3 systems. Moreover, the addition of Gd2O3 in YBCO enhances Jc by applying the magnetic field, although the superconducting temperature (Tc) decreases slightly. We argue that the characteristic behavior of Jc may come from the counterbalance of two effects simultaneously, which was caused by the variation of superconductivity and the inhomogeneity of grain distribution in nanoscale. [ABSTRACT FROM AUTHOR]

Context. Photochemical escape of hot atoms is crucial to the long-term evolution of the Martian climate. For atomic C and N, photochemical escape is primarily driven by photodissociation (PD) of CO and N2. Aims. Combining the Mars Atmosphere and Volatile Evolution (MAVEN) measurements of atmospheric neutral densities and solar EUV/X-ray irradiance, we perform a state-of-the-art analysis of atomic C and N escape on Mars. Methods. For each MAVEN orbit, we calculated the hot C and N production rates in the dayside Martian upper atmosphere via PD, from which the escape rates are estimated using a simplified technique to parameterize the respective escape probabilities taking into account multiple collisions with ambient neutrals. Results. The mean C and N escape rates are 1 × 1024 s−1 and 9 × 1024 s−1, appropriate for low to moderate solar activity conditions, and thermospheric PD makes a larger contribution to the total N escape than to the total C escape. The above differences highlight the importance of nascent energy, with more energetic nascent escaping atoms able to survive collisions with ambient neutrals more easily, thus extending down to deeper regions of the atmosphere. Solar cycle variation in C and N escape is revealed by our analysis, whereas solar zenith angle variation is absent for both species. These results could be explained by the fact that the production of nascent escaping atoms responds to varying solar illumination angle at low altitudes where the escape probability is negligible, but responds to varying level of solar EUV/X-ray irradiance at high altitudes where the atmosphere is essentially collisionless. [ABSTRACT FROM AUTHOR]

The interface structure and magnetoresistance (MR) for the single spin valve (SV) of Co/Cu/Co structure with a NiO layer at the top or under the bottom were investigated. Glancing incident x-ray reflectivity and x-ray diffuse scatter studies show that the interface roughness of NiO on Co is much larger than that of Co on NiO. The large roughness may be one of the main factors of suppressing spin reflectivity. The interface between NiO and Co becomes more flat after annealing. Different temperature dependence of MR was observed for the top and the bottom SV. We attribute the above phenomena to the competition between the roughness and the exchange effects of the NiO/Co interface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

La0.67Ca0.33MnO3 (LCMO) thin films with the thickness varying from 200 to 500 Å have been deposited by magnetron sputtering on sapphire, SrTiO3, yttrium-stabilized ZrO2 substrates. A metal-to-insulator transition behavior was observed for all samples with the transition temperature and width varying with the substrate and the film thickness. A percolation model has been used to obtain the physical parameters on low-temperature metallic transport behavior and the adiabatic thermal small polaron hopping progress. The surface of the deposited films was measured by atomic force microscopy and grazing incidence x-ray specular and diffuse scattering. Fits to the data show the presence of a mixed layer between the substrate and the LCMO films the extent of which depends on the substrate used. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin Yba[SUB2]Cu[SUB3]O[SUB7-δ/La[SUB0.67]Ca[SUB0.33]MnO[SUB3] (YBCO/LCMO) films were grown on SrTiO[SUB3](STO)substrates by magnetron sputtering technique. The microstructures of the bilayers were characterized and a standard four-probe technique was applied to measure the resistivity of the samples. The interdiffusions at the YBCO/LCMO and LCMO/STO interfaces formed two transient layers with the thickness of about 3 and 2 nm, respectively. All the bilayers were well textured along the c axis. At low temperature, the superconductivity can only be observed when the thickness of YBCO is more than 25 nm. When the thickness of YBCO is less than 8 nm, the bilayers show only ferromagnetism. The superconductivity and ferromagnetism perhaps coexist in the bilayer with the YBCO thickness of 12.5 nm. These interesting properties are related to the interaction between spin polarized electrons in the manganites and the cooper pairs in the cuprates. [ABSTRACT FROM AUTHOR]

Reports on a study which demonstrated the use of sputtered silicon films in developing etching masks for gallium arsenide devices. Materials commonly used for etching masks; Preparation of the silicon films; Conclusion.

Context. Synthetic model atmosphere calculations are still the most commonly used tool when determining precise stellar parameters and stellar chemical compositions. Besides three-dimensional models that consistently solve for hydrodynamic processes, one dimensional models that use an approximation for convective energy transport play the major role. Aims. We use modern Balmer-line formation theory as well as spectral energy distribution (SED) measurements for the Sun and Procyon to calibrate the model parameter that describes the effciency of convection in our 1D models. Convection was calibrated over a significant range in parameter space, reaching from F-K along the main sequence and sampling the turno and giant branch over a wide range of metallicities. This calibration was compared to theoretical evaluations and allowed an accurate modeling of stellar atmospheres. Methods. We used Balmer-line fitting and SED fits to determine the convective effciency parameter α. Both methods are sensitive to the structure and temperature stratification of the deeper photosphere. Results. While SED fits do not allow a precise determination of the convective parameter for the Sun and Procyon, they both favor values significantly higher than 1.0. Balmer-line fitting, which we find to be more sensitive, suggests that the convective effciency parameter α is ≈2.0 for the main sequence and quickly decreases to ≈1.0 for evolved stars. These results are highly consistent with predictions from 3D models. While the values on the main sequence fit predictions very well, measurements suggest that the decrease of convective effciency as stars evolve to the giant branch is more dramatic than predicted by models. [ABSTRACT FROM AUTHOR]

Here, equal numbers of La and Mn ions are successfully introduced simultaneously in SrRuO3. With increasing La/Mn doping, all compositions crystallize in Pnma with the lattice constant, together with the RuO6 octahedral distortion, decreases. Ferromagnetism-to-spin glass magnetic behavior is observed at x ≥ 0.23. A metal–insulator transition (MIT) occurs at lower temperatures, resulting from the disordering of the metal mixture in the lattice. The retraction of the RuO6 octahedron increases the overlap of the Ru t2g–O 2p orbitals and broadens the Ru 4d bandwidth, leading to weaker electron–electron interactions, which may decrease the electronic and thermal conductivity. [ABSTRACT FROM AUTHOR]

Gd is successfully embedded into YBa2Cu3O7-δ by the solid state reaction. Rietveld refinements show that Gd replaces Cu in the unit cell. By magnetization and resistivity measurements, the effects of Gd-doping in YBCO on the critical current density Jc and the critical temperature Tc in YBa2Cu3O7-δ(YBCO) have been investigated. Jc varies with the applied field and the content of Gd and has a maximum at x = 0.03. The characteristic behavior of Jc with varying the Gd content can be explained in terms of the competition between two different effects caused by Gd-doping in YBCO: the inhomogeneity of grains distribution in nano-scale and the variation of superconductivity. [ABSTRACT FROM AUTHOR]

The composition of Mn0.05Si0.95 polycrystalline films on (001) Si substrate are prepared by vacuum deposition and post-crystallization processes. X-ray diffraction studies indicate that there are two phases coexist in the film: tetragonal, Mn4Si7 and diamond-like Si (Mn). The content of Si(Mn) phase increases with increasing the post-annealing temperature. Temperature dependence of the magnetization shows that there are two ferromagnetic phases with Curie temperature of around 50 K and near room temperature, which is confirmed by x-ray magnetic circular dichroism (XMCD). [ABSTRACT FROM AUTHOR]

No abstract received. [ABSTRACT FROM AUTHOR]

We have fabricated two sets of NiO-Co-Cu based spin valves by the magnetosputtering technique with different deposition parameters. Magnetoresistance (MR) measurements show that the MR value for the NiO layer under the bottom of Co/Cu/Co spin valve (BSV) is larger than that for the NiO layer at the top of Co/Cu/Co (TSV). The MR value of BSV decreases with increasing annealing temperature in air or in vacuum, which disappears at the blocking temperature of NiO, i.e., about 250 °C. There is maximum MR value for TSV annealing at a temperature range from room temperature to 350 °C. The different thermal behavior for BSV and TSV is explained by the competition between the interface roughness of NiO/Co, which was determined by the grazing incident X-ray reflectivity and X-ray diffuse scattering, and the coupling effect between Co layer and NiO layer. [ABSTRACT FROM AUTHOR]

La2/3Ca1/3MnO3 (LCMO) thin films with the thickness from 4 nm to 50 nm were fabricated by the off-axis magnetron sputtering technique. Single crystal (001) SrTiO3 (STO), (0001) sapphire (ALO), and (001) yttrium-stabilized ZrO2 (YSZ) were used as substrates. The surface morphology of thin films was characterized by atomic force microscope (AFM). The surface morphology of the thin films depends on the thickness. Thin films on STO substrates with the thickness less than 20 nm show a wave-like morphology, which indicates a two-dimension growth mode. With the thickness increases, some cracks and grains appear on the surface, which indicates the release of the lattice strain due to the lattice mismatch between the substrate and the films. The morphology became smoother with the thickness more than 30 nm, which indicates the full relaxation in strain for the film. The surface roughness and the average grain size increase with the thickness. The morphology for LCMO grows on ALO and YSZ show a rougher surface than that on STO. The rough surface morphology may indicate the wide metallic-to-insulating transition in transport properties. [ABSTRACT FROM AUTHOR]

A series of NiO-containing Co/Cu/Co spin valves with the thickness Co of 5 nm and Cu of 2 nm were fabricated by magnetron sputtering technique with different growth parameters. NiO layer with the thickness of 40 nm is used as a coupling layer. Magnetoresistance (MR) of the spin valve with NiO layer under the bottom of Co/Cu/Co (BSV) is larger than that of the spin valve with NiO layer at the top of Co/Cu/Co (TSV) at room temperature. The MR values can be improved with decreasing the sputtering rate of copper layer. The studies by in-situ grazing incident X-ray scattering on the annealing temperature dependence of MR show that the decrease of the interface roughness between Co and NiO may increase the MR value, while the decrease of the coupling effect between NiO and Co decreases the MR value. [ABSTRACT FROM AUTHOR]

The heterostructure La[sub 0.67]Ca[sub 0.33] MnO[sub 3]/YBa[sub 2]Cu[sub 3] O[sub 7-δ] (LCMO/YBCO) bilayers with a fixed LCMO thickness and varying YBCO thickness were deposited on (001)-oriented single crystal SrTiO[sub 3] (STO) substrate and its resistivity properties were investigated by standard four-probe technique without magnetic field applied. The X-ray diffraction (XRD) analysis shows that all the bilayers were well c-oriented grown. The resistivity measurement indicated that the bilayer's properties change from superconductivity to magnetism with the decrease of the thickness of the capping layer YBCO. There exists a critical thickness of YBCO, in which case the superconductivity and magnetism coexist in bilayer. We believe that the lattice strain and spin-polarized carriers injection are the main origin of the above-mentioned resistivity behavior. [ABSTRACT FROM AUTHOR]

The double-wave method is widely used in ferroelectric measurements to eliminate the effects of conductance and capacitance components while preserving the ferroelectric domain contribution. However, in polycrystalline ferroelectric material, the assumption of the evolution of domains by the double-wave method no longer applies due to the domain back switch of de-field, and the domain contribution calculated by the current subtraction method is also problematic. Therefore, we proposed a new method to calculate the charge contribution of conductance and eliminate the conductance interference in the hysteresis loop. Finally, the feasibility of this new method is verified in many typical polycrystalline ferroelectric materials. This work provides a path for the study of ferroelectric properties of some high conductivity materials. [ABSTRACT FROM AUTHOR]

With varying thickness of the spacer near the second oscillatory GMR peak in Co/Cu system, a series of glass/Fe/[Co/Cu][sub 20]/Co multilayers are prepared by magnetronsputtering technique. The MR values are relatively small. High angle X-ray diffraction shows that the copper crystallizes in fcc structure with (111) texture and the cobalt crystallizes in hcp structure with (002) preferential orientation. There is a mixed amorphous CoCu layer at the interface due to the diffusion between cobalt and copper, which may decrease the MR value. The thickness, the mass density for each sub-layer and the surfacial and interfacial roughnesses are refined from the X-ray specular reflectivity measurement. [ABSTRACT FROM AUTHOR]

The lattice strain distributions of epitaxial SrTiO3 films deposited on LaAlO3 were investigated by in situ x-ray diffraction at the temperature range of 25–300 K, grazing incident x-ray diffraction, and high resolution x-ray diffraction. The nearly linear temperature dependence of the out-of-plane lattice constant of SrTiO3 was observed in the measured temperature range. The depth distribution of the lattice strain at room temperature for SrTiO3 films includes the surface layer, strained layer, and interface layer. [ABSTRACT FROM AUTHOR]

This paper reports the effects of substrate-induced strain on the high-quality La0.5-xDyxCa0.5-ySryMnO3 (0≤x≤0.2) (LDCSMO) films grown on (00l) SrTiO3 (STO) substrate. LDCSMO films were epitaxially grown on the STO substrate along [001] direction. The lattice parameter c of the film increases relatively with the thickness increasing, and the in-plane tensile strain was controlled by varying the film thickness. The Raman results at room temperature show that the in-plane Mn-O bond stretching and MnO6 distortion were suppressed by the in-plane tensile strain with the thickness of film decreasing. The magnetic results show that the CO-AFM insulating phase and the weak FM phase coexist at low temperature, and spin-glass effect was found in all films. The ferromagnetic order and insulating state were enhanced by tensile strain in thinner film. This abnormal enhancement of insulating state may be ascribed to the disordering state due to the stronger FM and AFM competition and the dominated "dead layer" in thinner film. The improved FM ordering is resulted from the increased double-exchange interaction for the MnO6 distortion suppressed by the in-plane tensile strain in thinner film. These results indicate spin-phonon coupling could be manipulated by controlling strain in manganese oxide films. [ABSTRACT FROM AUTHOR]

Despite produced exclusively on the dayside, photoelectrons, as an important population of the Martian ionosphere, have also been observed on the nightside. Here we present a statistical survey of nightside photoelectrons using the suprathermal electron measurements, made by the Solar Wind Electron Analyzer onboard the Mars Atmosphere and Volatile Evolution. We find that nearly 30% of the available nightside suprathermal electron spectra show clear photoelectron signatures. Nightside photoelectrons have an occurrence rate that decreases with increasing solar zenith angle and they are characterized by a preferentially field‐aligned pitch angle distribution. Our analysis also suggests that nightside photoelectrons are less likely observed under the high solar wind condition. These observations are favorably interpreted by the scenario of photoelectron transport along cross‐terminator magnetic field lines, as supported by a simplified test particle model. Our study highlights a complex plasma environment near Mars modulated by both internal and external conditions. Plain Language Summary: Photoelectrons are an important population of a planetary upper atmosphere that plays a crucial role in ionization, heating, radiation, and escape. Despite that photoelectrons are ideally produced by solar radiation on the dayside only, they have also been observed on the nightside of a planet such as Mars. This study is devoted to a statistical survey of photoelectrons in the nightside Martian upper atmosphere, based on the state‐of‐the‐art measurements made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. A surprisingly large fraction of photoelectron energy spectra is identified on the nightside of Mars, occupying nearly 30% of the available nightside measurements. Meanwhile, substantial variations in the observations of nightside photoelectrons are suggested by the data, revealing that (1) their occurrence rate declines rapidly near and beyond the terminator; (2) their velocities are more likely parallel to the ambient magnetic field lines; and (3) they are less likely observed under high solar wind dynamic pressures. These observations could be interpreted by photoelectron transport along large‐scale magnetic field lines from their dayside source regions to the nightside, a scenario that is controlled by both internal and external conditions and thus provides a useful diagnostic of the ambient magnetic field configuration. Key Points: The photoelectron occurrence rate in the nightside Martian ionosphere decreases with increasing solar zenith angleNightside photoelectrons are observed to be preferentially field‐aligned, as a natural result of cross‐terminator transportNightside photoelectrons are more likely observed under low solar wind dynamical pressures [ABSTRACT FROM AUTHOR]

Perfect and defective surface structures for (001) SrTiO3 are determined in considering a supercell with 11 atomic layers using the first-principles calculations. The amplitude of the surface rumpling for the SrO-terminated surface is much larger than that for the TiO2-terminated surface, although both SrO- and TiO2-terminated surfaces are stable for a comparable range of the TiO2 chemical potential. The distance between the first and second planes compresses while that of the second and third planes expands due to the relaxation of the slab. The top sites of the oxygen atoms of SrO-termined surface and the fourfold symmetry hollow sites of TiO2-termined surface are favorable for Ti or Sr adsorbate. The relative stability of the defect species or reactions varies with the equilibrium conditions. The dominant surface defect is Ti substitutional defect and a TiO–TiO2 double layers may form at the surface, which has been confirmed by experiments. [ABSTRACT FROM AUTHOR]

The characteristics of novel reverse-biased waveguide phase modulators are reported. These devices, which use the translation of a depletion edge, have provided the highest efficiency figure of merit (56 °/Vmm) ever reported for a reverse-biased device. Furthermore, the speed of the device is only limited by the RC time constant. The investigated devices were GaAs/AlGaAs ridge waveguide modulators, a geometry which is well suited for integrated optoelectronics. [ABSTRACT FROM AUTHOR]

Describes the application of thin silicon (Si) films for selective area Si and zinc (Zn) diffusion into gallium arsenide and AlGaAs. Advantage of the Si film; Details on the Zn diffusion with the Si mask.

Molecular ferroelectric materials have been widely used in capacitors and sensors due to their low cost, light weight, flexibility and good biocompatibility. Organic–inorganic hybrid complexes, on the other hand, have received a great deal of attention in the luminescence field due to their low cost and simple preparation. The combination of ferroelectricity and photoluminescence in organic–inorganic hybrid materials not only leads to tunable optical properties, but also enriches potential applications of multifunctional ferroelectrics in optoelectronic devices. Here, we report a new luminescent ferroelectric material (1,3-dicyclohexylimidazole)2MnCl4 (DHIMC). Thermogravimetric analysis (TGA) was used to measure the mass change of the material at a measurement rate of 20 K min−1 from room temperature to 900 K, and we found that this material has good thermostability, which is up to 383 K. Meanwhile, UV-vis measurements showed that it is also a fluorescent material emitting a strong green fluorescence at the wavelength of 525 nm. The ferroelectricity of the crystal was determined by two different methods: the Sawyer–Tower method and the double-wave method (DWM). Particularly, the single crystal experiences a phase transition from the ferroelectric phase to the paraelectric phase during the heating/cooling process at 318 K/313 K and the space group changes from P1¯ (centrosymmetric) to P1 (non-centrosymmetric). This work will enrich multifunctional luminescent ferroelectric materials and their application in display and sensing. [ABSTRACT FROM AUTHOR]

Hexagonal yttrium manganite (YMnO3) and chromium doped yttrium manganite (YMn1 – xCrxO3) were prepared by the solid-state method. X-ray diffraction and Raman scattering were combined to explore the structural characterization. Structural analysis illustrates that the lattice is compressed and the tilt of the MO5 (M = Cr or Mn) bipyramid is decreased with an increase in Cr3+ concentration, leading to declining frustration. Magnetic measurement suggests both weak ferromagnetic (FM) and antiferromagnetic (AFM) orderings enhanced with the growth of doping concentration. Enhanced weak FM ordering may arise from breaking of the superexchange interaction and introduction of the double-exchange interaction inside the layers, and the increased AFM ordering is attributed to the improved coupling between neighboring planes that resulted from the structural distortion. Spin-phonon coupling is discussed to confirm the enhanced coupling between interplane Mn3+ moments. [ABSTRACT FROM AUTHOR]

Laser-induced femtosecond demagnetization, femtomagnetism, offers a potential route to develop faster magnetic storage devices. It is generally believed that the traditional spin-wave theory, which is developed for thermally driven slow demagnetization, cannot explain this rapid demagnetization by design. Here, we show that this traditional spin-wave theory, once augmented by laser-induced spin–orbit torque, provides a highly efficient paradigm for demagnetization, by capturing low-energy spin-wave excitation that is absent in existing mechanisms. Our paradigm is different from existing ones but does not exclude them. Microscopically, we find that optical spin–orbit torque generates massive spin waves across several hundred lattice sites, collapsing the long-range spin-spin correlation within 20 fs. Our finding does not only explain new experiments but also establishes an alternative paradigm for femtomagnetism. It is expected to have far-reaching impacts on future research. [ABSTRACT FROM AUTHOR]

Structure and transport properties of Eu-doped YBa2-xEuxCu3O7-δ (YBECO) have been studied. Eu is confirmed preferring to replace Ba at Ba sites. The averaged valence state of Eu, which is examined by x-ray photoemission spectroscopy, increases with increasing x. Eu doping in YBECO has a little influence on superconductivity in our studies, and the superconducting transition temperature Tc is almost unchanged. [ABSTRACT FROM AUTHOR]

We studied the microstructures, electronic, and magnetic properties on La-doped and La- and Ca-codoped YBa2Cu3O7-δ (YBCO). The superconducting transition temperature remains unchanged up to 10% for La-doped YBCO. The competition between electrons and holons was assumed according to the variation of Tc0 in La and Ca codopings in YBCO. The magnetoresistance (MR) effect is about 8%, which is observed obviously near the critical temperature and is independent of the content of La in La-doped YBCO. MR increases up to about 40% with the incorporation of Ca in La-doped YBCO. We present here possible explanations for the magnetoresistance effect in polycrystalline samples based on the microstructure and the increase of oxygen vacancies at grain-boundary interface. [ABSTRACT FROM AUTHOR]

Structural, magnetic, and calorimetric properties are reported for the La[sub 1-x]Pr[sub x]Ba[sub 2]Cu[sub 3]O[sub 7] solid solution. The structure remains orthorhombic with lattice parameter increases from a=0.3872, b=0.3927, and c=1.1709 nm for PrBa[sub 2]Cu[sub 3]O[sub 7] to a=0.3903, b=0.3944, and c=1.1801 nm for LaBa[sub 2]Cu[sub 3]O[sub 7]. Substitution of Pr for La depresses T[sub c] from 90 to 52 K for La[sub 0.5]Pr[sub 0.5]Ba[sub 2]Cu[sub 3]O[sub 7], which was reported to be a nonsuperconductor. The Pr antiferromagnetic ordering temperature T[sub N] decreases monotonically from 18 K for PrBa[sub 2]Cu[sub 3]O[sub 7] to 6 K for La[sub 0.8]Pr[sub 0.2]Ba[sub 2]Cu[sub 3]O[sub 7]. Thus there is a large range of coexistence of superconductivity and antiferromagnetism for 0.2≤x≤0.5. The superconductivity and anomalous Pr ordering will be discussed with the R[sub 1-x]Pr[sub x]Ba[sub 2]Cu[sub 3]O[sub 7] systems (R=Y, Nd-Lu). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The compressive LaMnO3+δ thin films with thickness of ~20 nm are grown on LaAlO3 (001) single crystal substrates under various oxygen environment. With decreasing oxygen pressure, the in-plane compressive strain is enhanced. It is found that the breathing mode (Q1) and the basal plane distortion mode (Q2) of MnO6 octahedron are suppressed, while the octahedral stretching mode (Q3) is promoted. The promoted Q3 switches the orbital order from x2-1/y2-1 to (x2-y2)+(z2-1) type. The ferromagnetic (FM) transition temperature Tc increases from 85 K to 105 K and the low-temperature magnetization increases greatly by 175%. The abnormal enhancement of magnetization with decreasing oxygen pressure is ascribed to the strain enlarged FM domains due to the decreased MnO6distortion and the switched orbital ordering. This result is advantageous to explain the novel phenomena in LaMnO3-related systems. [ABSTRACT FROM AUTHOR]

A type of micromachined rotating gyroscope with an electromagnetically levitated rotor is proposed. The working mechanism and the fabrication method based on MEMS technology of micromachined gyroscopes are described. The experiment showed that the vacuum package can increase the rotating speed of the rotor (diameter, 2.2 mm; thickness, 20 µm) from 800 to 4000 rpm. Possible reasons that resist further increase of rotating speed are air slip damping and electromagnetic damping. Sensing precision of 3°/s was obtained in the experiment. [ABSTRACT FROM AUTHOR]

In a novel stator structure, the levitated, stability and rotating coils of a micromotor with an electromagnetically levitated rotor are separated and of multi-loop. This micromotor has improved stability, levitation and rotation performance. With current of appropriate value and frequency in the coils, the rotor of 2.2 mm diameter and 20 μm thick is levitated to a height of 300 μm, and its rotating speed can reach 1400 rpm. [ABSTRACT FROM AUTHOR]

Silicon diffusion into AlxGa1-xAs (x=0–0.4) from a sputtered Si film is described. It is shown that both the diffusion rate and the surface concentration of Si decrease with increasing Al mole fraction. The diffusion behavior of Si in AlxGa1-xAs is discussed in terms of the binding energy of the Al–As bond and mixed crystal disorder. [ABSTRACT FROM AUTHOR]

A series of polycrystalline YMn1-xRuxO3 (0≤x≤0.2) samples were prepared by traditional solidstate reaction method. Effects of doping on the microstructures and magnetic properties were investigated. Microstructural results reveal that samples crystallize in a single hexagonal structure with P63cm group for x≤0.1. Lattice parameters a, c, and unit-cell volume of YMn1-xRuxO3 are found to increase with doping content, which are ascribed to the larger radius of Ru3+ than that of Mn3+. Weak ferromagnetism is found and is enhanced with increasing doping concentration x. The bond angles of Mn-O3-Mn and Mn-O4-Mn are changed in the opposite trends, which break the Mn-Mn exchange interaction, thus the antiferromagnetic ordering. The MnO5 bipyramid is found to be relieved and the trimerization of Mn ions is weakened. These structural modifications result in the increase of weak ferromagnetism ordering in samples. [ABSTRACT FROM AUTHOR]

SrTiO3 is a model of the perovskite-like compounds for structural transition which inducing the intriguing physical properties around the critical phase transition temperature TAFD (antiferrodistortive, abbrev. as AFD). Here we report that the electrical transport behavior is a new way to quantify Nb concentration for Nb-doped SrTiO3. The lattice parameter (c), phase transition temperature (TAFD), and the carrier concentration (n) of SrTiO3 may be manipulated by niobium doping. TAFD increases with increasing the niobium content in a rate of about 30 K per (wt%, i.e. niobium element's weight verses total weight) niobium and n in a rate of about 2.5 × 1020/cm3 per (wt%) niobium. [ABSTRACT FROM AUTHOR]

Background:Leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5), which is identified as a novel intestinal stem cell marker, is overexpressed in various tumours. In this study, we explore Lgr5 expression in gastric carcinoma and analyse its role in invasion, metastasis, and prognosis in carcinoma.Methods:A combination of immunohistochemistry, western blotting, and quantitative reverse transcription-polymerase chain reaction were used to detect mRNA and protein expression levels of Lgr5 and matrix metalloproteinase 2 (MMP2). Small interfering RNA against Lgr5 was designed, synthesised, and transfected into AGS cells. The effects of Lgr5 siRNA on cell invasion were detected by transwell invasion chamber assay and wound healing assay.Results:Leucine-rich repeat-containing G-protein-coupled receptor 5 expression was significantly higher in gastric carcinomas than in normal mucosa. Leucine-rich repeat-containing G-protein-coupled receptor 5 expression positively correlated with the depth of invasion, lymph node metastasis, distance of metastasis, and MMP2 expression levels. Multivariate analysis showed that Lgr5 had an independent effect on survival, and that it positively correlated with MMP2. Leucine-rich repeat-containing G-protein-coupled receptor 5 siRNAs inhibited Lgr5 mRNA and protein expression. Transwell assays indicated that these siRNAs resulted in significantly fewer cells migrating through the polycarbonate membrane, and wound healing assay also indicated that siRNAs decreased the migration of cells. Inhibition of Lgr5 resulted in a significant decrease in MMP2 and β-catenin levels compared with those in controls.Conclusions:Leucine-rich repeat-containing G-protein-coupled receptor 5 was correlated with invasion and metastasis. Leucine-rich repeat-containing G-protein-coupled receptor 5 inhibition could serve as a novel therapeutic approach. [ABSTRACT FROM AUTHOR]

The structural, electronic, and magnetic properties of (La2/3Sr1/3MnO3)m/(SrRuO3)n superlattices have been investigated based on the first principles calculations. An obvious Jahn-Teller distortion, which depends on m, n, appears in MnO6 octahedron in the superlattices. The stretch along c-axis of MnO6 octahedron at the interface lifts the Mn eg orbital degeneracy, with electrons preferring the lower energy 3z2 - r2 to the higher energy x2 - y2. Benefitting from the charge transfer at the interface, the still occupied x2 - y2 orbital can mediate a robust in-plane double exchange interaction. La2/3Sr1/3MnO3 block is ferromagnetic and metallic, even for the superlattice with m=n=1. [ABSTRACT FROM AUTHOR]

LaMnO3+δ films with various thicknesses were grown on LaAlO3 (001) single crystal substrate to investigate the effect of in-plane compressive strain (~-0.57%) on magnetic properties. All films exhibit a blocking temperature Tb at which the zero field cooled magnetization reaches a maximum, indicating the ferromagnetic (FM) nanoclusters are embedded in the background of antiferromagnetic (AFM) matrix. The onset temperature of FM transition Tc and Tb is increased by 24% and 89%, respectively, with the thickness decreasing from 82.4 nm to 9.2 nm. Simultaneously, the saturation magnetization greatly increases by 309%, which is ascribed to the strain-induced transition of AFM to FM phase due to the orbital order structure switching from x²- 1/y²-1 [A-type] to (x²- y²) + (z²- 1) [F-type]. [ABSTRACT FROM AUTHOR]

Polycrystalline samples YMn1-xAlxO3 with different Al doping concentration were synthesized by standard solid-state reaction. Effect of Al doping on the magnetic properties was studied. Magnetization measurements show that the magnetization increases, while the calculated frustration factor decreases with the doping content of Al3+ ion increasing. And the spin-glass behavior becomes more and more obvious with increasing the Al doping content. These results were ascribed to the broken exchange path between Mn ions by Al doping. [ABSTRACT FROM AUTHOR]

Polycrystalline manganite oxides with different A-site cation disorder were synthesized. The hole concentration and average radius of A-site cation are kept unchanged while the A-site cation disorder increases linearly by Y and Sr co-doped in La2/3Ca1/3 MnO3. All these samples exhibit a paramagnetic insulator to ferromagnetic (FM) metal transition, and the transition temperature TC and TMI decrease while the transition width increases with increasing the A-site cation disorder. TMI is usually 10 K higher than TC for the small cation disorder samples. However, with increasing the cation disorder, TMI is about 60 K lower than TC, and the resistivity increases in magnitude while the magnetization decreases. The metal-to-insulator transition for samples with small cation disorder can be well described by a percolative model, which indicates FM-metal state and antiferromagnetic insulator state assuredly coexist in the transition interval. It reveals that cation disorder suppresses the long-range FM-metal state which results in the phase separation behavior in samples with large cation disorder. [ABSTRACT FROM AUTHOR]

In this paper, with solid source molecular beam epitaxy technique, Si1-xGex(SiGe) virtual substrates were deposited on low-temperature-grown Si (LT-Si) buffer layer, which was doped with Sb. The strain in SiGe virtual substrate was characterized by high resolution X-ray diffraction. Results indicated that Sb-doping in LT-Si can effectively modulate the degree of strain relaxation in SiGe virtual substrate. The segregated Sb on the surface of LT-Si layer acts as surfactant and results in abrupt strain relaxation. [ABSTRACT FROM AUTHOR]

Y and Sr co-doped La2/3Ca1/3MnO3 films with different A-site cation disorder were deposited on Yttrium-stabilized ZrO2 (YSZ) single crystal substrate by modified off-axis rf magnetron sputtering technology. The influences of A-site cation disorder and biaxial strain on the surface morphologies and transport properties are discussed in detail. At high temperature, the mechanism of conduction is changed from the small polaron hopping model to the variable-range hopping model with increasing cation disorder, which reveals that cation disorder induces carrier localization. The Curie temperature and the magnetoresistance decrease with the increase of cation disorder. It reveals the variation of phase separation to be caused by the increasing cation disorder which suppresses the long-range FM metal state. [ABSTRACT FROM AUTHOR]

Two series of NiO-Co-Cu-Co based spin valves with the same nominal structure were grown by the magneton sputtering technique with different deposition parameters. Texture, surface and interfacial microstructures and the magnetic properties have been investigated in detail. X-ray diffraction, grazing incident X-ray reflectivity and transverse X-ray diffuse scattering were combined to analyze the microstructure of the multilayers. The results show that the texture of the multilayers is not a prerequisite factor for an exchange-bias (EB) field in NiO/Co/Cu/Co spin valves. And the EB effect is also independent of the average roughness at the interfaces. Large correlation lengths and two dimensions of the roughness at the interface are more advantageous for the EB effect. [ABSTRACT FROM AUTHOR]

Single phase of La1−xSrxCoO3 (LSCO) with 0.1 ≤ x ≤ 0.4 have been prepared by the solid-state reaction method. All samples have the R3̅c symmetry. There is no phase transition detected at the temperature range from 10 to 300 K. The variations of the local bond-lengths of Co—O in CoO6 octahedron and lattice parameter ar confirm that hole-doping stabilize the intermediate-spin (IS) state of Co ions. The magnetic phase diagram is well understood in terms of phase separation scenario. Qualitatively, hole-rich ferromagnetic (FM) clusters increasing in size and number with the increase in the concentration of Sr at the expensive of non-FM insulating matrix, and percolating at the vicinity of 0.15, are suggested to explain the onset of FM order and insulator–metal transition. In addition, the values of effective paramagnetic moment μeff also strongly prove the presence of IS spin state of Co in our system. Very small magnetoresistance (MR), 5% with 3 T magnetic field applied, is obtained. This MR response indicates that a distinct mechanism is likely to dominate in LSCO compared to that in mixed-valence manganites. [Copyright &y& Elsevier]