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  • 1
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    Optical probing of MgZnO/ZnO heterointerface confinement potential energy levels (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-02-24
    Description: Low-temperature photoluminescence and reflectance measurements were employed to study the optical transitions present in two-dimensional electron systems confined at Mg x Zn 1– x O/ZnO heterojunctions. Transitions involving A- and B-holes and electrons from the two lowest subbands formed within the confinement potential are detected. In the studied density range of 2.0–6.5 × 10 11  cm −2 , the inter-subband splitting is measured and the first excited electron subband is shown to be empty of electrons.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 2
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    Magnetic anisotropy of single-crystalline Mn3Sn in triangular and helix-phase states (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-08-25
    Description: The magnetic structure and phase transitions in single-crystalline Mn 3 Sn with the D0 19 structure have been investigated by torque measurements and magnetic measurements. The results show that a triangular antiferromagnet (AFM) and a weak ferromagnet coexist above 270 K. At these temperatures, the torque measurements indicate a six-fold symmetry and another two-fold symmetry of the magnetic anisotropy. The [ 11 2 ¯ 0 ] direction is the lowest-energy state in the triangular configuration. At low temperatures, two AFM helix-phase states are found in an applied magnetic field ( H ): In one of them, the [ 11 2 ¯ 0 ] direction is the easiest deviation direction from the AFM state. In the other, it is the [0001] direction. The variation of the two states with temperature ( T ) and magnetic field is presented in an H-T phase diagram.
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    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 3
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    Abnormal magnetic ordering and ferromagnetism in perovskite ScMnO3 film (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-06-13
    Description: Bulk multiferroic ScMnO 3 is the stable hexagonal phase, and it is very difficult to prepare its perovskite orthorhombic phase even under high pressure. We fabricated the orthorhombic ScMnO 3 thin film by pulsed laser deposition through suitable substrate LaAlO 3 and found that nano-scale twin-like domains are naturally formed in the thin film. Magnetic properties of the orthorhombic ScMnO 3 thin films show that, besides normal antiferromagnetic ordering at 47 K, an anomalous magnetic transition occurs at 27 K for 60 nm film and at 36 K for 150 nm film only along the c-axis, which is absent in the ab-plane. Moreover, the second magnetic transition for both films is suppressed when the applied field increases from 1 kOe to 10 kOe. In addition, the ferromagnetism shows up in both films at 10 K, and saturation magnetization increases dramatically in 60 nm film compared with 150 nm film. We propose that the second magnetic transition might be more of lattice strain effect and also related to magnetism-induced ferroelectric polarization in orthorhombic RMnO 3 thin films and low-temperature ferromagnetic properties in our films originate from the nano-scale twin-like domain structure.
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    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 4
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    Design of novel dual-port tapered waveguide plasma apparatus by numerical analysis (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-07-12
    Description: Microwave plasma apparatus is often of particular interest due to their superiority of low cost, electrode contamination free, and suitability for industrial production. However, there exist problems of unstable plasma and low electron density in conventional waveguide apparatus based on single port, due to low strength and non-uniformity of microwave field. This study proposes a novel dual-port tapered waveguide plasma apparatus based on power-combining technique, to improve the strength and uniformity of microwave field for the applications of plasma. A 3D model of microwave-induced plasma (field frequency 2.45 GHz) in argon at atmospheric pressure is presented. On the condition that the total input power is 500 W, simulations indicate that coherent power-combining will maximize the electric-field strength to 3.32 × 10 5  V/m and improve the uniformity of distributed microwave field, which raised 36.7% and 47.2%, respectively, compared to conventional waveguide apparatus of single port. To study the optimum conditions for industrial application, a 2D argon fluid model based on above structure is presented. It demonstrates that relatively uniform and high-density plasma is obtained at an argon flow rate of 200 ml/min. The contrastive result of electric-field distribution, electron density, and gas temperature is also valid and clearly proves the superiority of coherent power-combining to conventional technique in flow field.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 5
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    Oxygen vacancy formation, crystal structures, and magnetic properties of three SrMnO3−δ films (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-08-05
    Description: The crystal structures and magnetic properties of the 40 nm brownmillerite SrMnO 2.5 film, perovskite SrMnO 3-δ film, and mixed-phase film have been systematically investigated. The features of the oxygen vacancy ordering superstructure in the brownmillerite SrMnO 2.5 film are observed from HRSTEM as follows: the dark stripes with a periodicity of four (110) planes of the cubic perovskite appearing at an angle of 45° with the substrate-film interface and extra reflection spots in fast Fourier transformation patterns along the (001) plane. When annealing the brownmillerite SrMnO 2.5 film under higher oxygen pressure, the top portion undergoes structure transition into perovskite SrMnO 3-δ as seen in the mixed-phase film consisting of the perovskite SrMnO 3-δ phase dominating at the top part and the brownmillerite SrMnO 2.5 phase dominating at the bottom part. The magnetic properties and Mn valences of the brownmillerite SrMnO 2.5 film indicate that this film, similar to the bulk, is antiferromagnetic with T N at 375 K. However, the strained tetragonal perovskite SrMnO 3-δ film exhibits ferromagnetic behavior with Curie temperature at 75 K and a saturation magnetization of 2.5μ B /Mn at 2 K. Moreover, the top perovskite SrMnO 3-δ phase of the mixed-phase film also exhibits ferromagnetic behavior evidenced by the existence of the exchange bias. We propose that the ferromagnetic properties in both the perovskite SrMnO 3-δ film and the top perovskite SrMnO 3-δ phase in the mixed-phase film originate from Mn 3+ –Mn 4+ double exchange coupling. However, the formation of Mn 3+ differs for the two samples in that it is caused by oxygen vacancies in the former and the distribution of oxygen content across the film during annealing in the latter.
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    Electronic ISSN: 1077-3118
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  • 6
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    Fast valve based on double-layer eddy-current repulsion for disruption mitigation in Experimental Advanced Superconducting Tokamak (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-05-14
    Description: A fast valve based on the double-layer eddy-current repulsion mechanism has been developed on Experimental Advanced Superconducting Tokamak (EAST). In addition to a double-layer eddy-current coil, a preload system was added to improve the security of the valve, whereby the valve opens more quickly and the open-valve time becomes shorter, making it much safer than before. In this contribution, testing platforms, open-valve characteristics, and throughput of the fast valve are discussed. Tests revealed that by choosing appropriate parameters the valve opened within 0.15 ms, and open-valve times were no longer than 2 ms. By adjusting working parameter values, the maximum number of particles injected during this open-valve time was estimated at 7 × 10 22 . The fast valve will become a useful tool to further explore disruption mitigation experiments on EAST in 2015.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 7
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    Magnetization reversal and coercivity of Fe3Se4 nanowire arrays (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-02-14
    Description: The microstructure and magnetic properties of Fe 3 Se 4 nanowire (NW) arrays in anodic aluminum oxide (AAO) porous membrane are studied. Cross-sectional SEM and plane-view TEM images show that the mean wire diameter ( d w ) and the center-to-center spacing ( D ) of Fe 3 Se 4 nanowires are about 220 nm and 330 nm, respectively. The field-cooled magnetization dependent on the temperature indicates a Curie temperature around 334 K for the Fe 3 Se 4 nanowires. The coercivities of Fe 3 Se 4 nanowires at 10 K, obtained from the in-plane and out-of-plane hysteresis loops, are as high as 22.4 kOe and 23.3 kOe, which can be understood from the magnetocrystalline anisotropy and the magnetization reversal process.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 8
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    The dynamics of short-scale turbulent fluctuations across low-intermediate-high-confinement transition with lower hybrid current drive in the EAST superconducting tokamak (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-02-07
    Description: Two different confinement transition discharges, the low-intermediate-high (L-I-H) and the low-intermediate-low (L-I-L) confinement transitions, respectively, have been obtained by lower hybrid current drive with lithium wall conditioning in the EAST superconducting tokamak. The dynamic features of short-scale turbulent fluctuations in the two discharges are investigated by a tangential CO 2 laser collective scattering system. It is found that the great changes of broadband fluctuations in amplitude and structure characteristics are closely related to the choice of the final transition to H-mode. These results could shed light on the understanding of the L-H transition mechanism.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 9
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    Demonstration of a GaAs-based 1550-nm continuous wave photomixer (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-01-17
    Description: An Er:GaAs-based 1550-nm CW photomixer is demonstrated. The related mechanism is extrinsic photoconductivity with optical absorption between the localized deep levels created by the Er and the extended states above the conduction band edge of GaAs. With the power boost made possible by a fiber-coupled erbium-doped-fiber amplifier, the Er:GaAs photomixers, operating at 1550 nm, radiate THz power levels easily measured by a Golay cell, and display a power spectrum having a −3 dB roll-off frequency of 307 GHz. This corresponds to a photocarrier lifetime of 520 fs, in good agreement with a previous measurement of the bandwidth of the same material in a photoconductive switch.
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    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 10
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    The tunable negative permittivity and negative permeability of percolative Fe/Al2O3 composites in radio frequency range (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-04-29
    Description: The electromagnetic properties including ac conductivity, permittivity, and permeability of percolative Fe/Al 2 O 3 composites, which were prepared by in-situ synthesis process, are investigated in the radio frequency range. There is an obvious percolation transition with the increase of iron contents. When iron content is beyond but near the percolation threshold, the negative permittivity and permeability are simultaneously obtained from 631 MHz to 1 GHz in sample FA30. Further increasing iron content, the Fano-like resonances are observed, and the resonance frequency where the permittivity changes from negative to positive shifts to lower frequency. In addition, the frequency region of negative permittivity and negative permeability are not overlapped any more. Hopefully, the percolative Fe/Al 2 O 3 composites with tunable negative permittivity and negative permeability can be used as electromagnetic wave absorber.
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    Electronic ISSN: 1077-3118
    Topics: Physics
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