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17 Dec 2001

Volume 79, Issue 25, pp. 4073-4251

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Nonlinear effects in YBa2Cu3O7−x microstrip resonators on sapphire

A. G. Zaitsev, R. Schneider, G. Linker, F. Ratzel, R. Smithey, and J. Geerk

Appl. Phys. Lett. 79, 4174 (2001); http://dx.doi.org/10.1063/1.1425460 (3 pages) | Cited 13 times

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Power-induced nonlinear effects, i.e., the reduction of the quality factor, the distortion of the resonance peaks, and the two-tone intermodulation distortion (IMD), were experimentally examined by using 2.3 GHz microstrip resonators prepared from double-sided YBa2Cu3O7−x (YBCO) films on CeO2-buffered sapphire. The resonators exhibited advanced performance with an unloaded quality factor of 80 000 at 63 K up to a circulating power Pcirc of 0.5 W and an IMD third-order interception point estimated at Pcirc ≈ 400 W. We found that the nonlinear effects in these resonators were produced by the power-dependent surface resistance Rs of the YBCO films, whereas the variation of the surface reactance was negligible. Both the presence of the high-order IMD products and the dependence of their amplitude on the microwave power, indicate a Rs(H)∝cosh H relationship, where H is the amplitude of the microwave magnetic field at the film surface. Such a dependence agrees with the direct measurements of the power handling capability. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
85.25.Am Superconducting device characterization, design, and modeling
74.72.-h Cuprate superconductors
84.40.Az Waveguides, transmission lines, striplines

Oxygen-plasma effects of a La0.7Ca0.3MnO3−δ single crystal

H. S. Kim, C. H. Lee, Cheol Eui Lee, K. M. Kim, S. J. Noh, C. S. Hong, N. H. Hur, S. Y. Shim, and H.-C. Ri

Appl. Phys. Lett. 79, 4177 (2001); http://dx.doi.org/10.1063/1.1425085 (3 pages) | Cited 3 times

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A La0.7Ca0.3MnO3−δ single crystal was oxygen-plasma treated at 200 °C. Our electrical and magnetic measurements indicate that the oxygen-plasma treatment can be an effective low temperature method of oxygen stoichiometry modification of colossal magnetoresistance manganites. The oxygen plasma is also shown to introduce structural defects, whose effects are prominent near the Curie temperature (Tc), giving rise to anomalies in the resistivity and magnetic behaviors. © 2001 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
61.66.Bi Elemental solids
61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
52.77.-j Plasma applications
81.40.Rs Electrical and magnetic properties related to treatment conditions
72.15.Gd Galvanomagnetic and other magnetotransport effects

High-quality MgB2 films on boron crystals with onset Tc of 41.7 K

N. Hur, P. A. Sharma, S. Guha, Marta Z. Cieplak, D. J. Werder, Y. Horibe, C. H. Chen, and S.-W. Cheong

Appl. Phys. Lett. 79, 4180 (2001); http://dx.doi.org/10.1063/1.1427157 (3 pages) | Cited 21 times

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The simple binary compound, MgB2, has created enormous excitement, due to its remarkably high Tc (39 K), its exotic electronic and phononic structure, as well as its potential technological application. However, contrary to the initial expectation, worldwide efforts to enhance the Tc of this material by means of chemical doping and applying hydrostatic pressure have failed. Investigations of other diborides or related materials have also resulted in finding of lower Tcs. In this letter we report a slight, but significant enhancement of Tc in MgB2 films grown on boron crystals, which may stem from tensile-type strain. This finding opens up a new possibility for further optimizing Tc in MgB2 and perhaps in related materials. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.10.+v Occurrence, potential candidates
68.60.Bs Mechanical and acoustical properties
62.20.-x Mechanical properties of solids

Spin-glass behavior with short-range antiferromagnetic order in Nd2AgIn3

D. X. Li, S. Nimori, Y. Shiokawa, A. Tobo, H. Onodera, Y. Haga, E. Yamamoto, and Y. Ōnuki

Appl. Phys. Lett. 79, 4183 (2001); http://dx.doi.org/10.1063/1.1428114 (3 pages) | Cited 7 times

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We present experimental results of complex susceptibility, static magnetization, magnetic relaxation, specific heat, and electrical resistivity measurements on an intermetallic compound Nd2AgIn3. The results indicated that Nd2AgIn3 undergoes a spin-glass transition at a freezing temperature Tf = 12.6 K accompanied with the formation of short-range antiferromagnetic order. The mechanism of formation of spin-glass state in Nd2AgIn3 is different from that in diluted metallic spin-glass or uranium intermetallic compound. The existences of frustrated moments due to the triangles of nearest neighbors in Nd atomic layers and randomly distributed Ruderman–Kittle–Kasuya–Yosida interactions may be responsible for the spin glass state formed in Nd2AgIn3. © 2001 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Lk Spin glasses and other random magnets
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Synthesis of superconducting Mg/MgB2 composites

David C. Dunand

Appl. Phys. Lett. 79, 4186 (2001); http://dx.doi.org/10.1063/1.1427439 (3 pages) | Cited 8 times

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Composites consisting of Mg and MgB2 phases were fabricated by liquid-metal infiltration following two routes. First, a preform of MgB2 powders was pressure infiltrated at 800 °C with liquid Mg, which was subsequently solidified. Second, a preform of B powders was pressure infiltrated with liquid Mg at 700 °C, resulting in partial, in situ formation of the MgB2 phase. Subsequent annealing at 950 °C increased the content of MgB2 through reaction between B and Mg. All composites exhibited a pore-free structure with no significant additional phases and were superconducting near 39 K. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Sv Critical currents

Characteristics of interface-engineered Josephson junctions using a YbBa2Cu3Oy counterelectrode layer

H. Katsuno, S. Inoue, T. Nagano, and J. Yoshida

Appl. Phys. Lett. 79, 4189 (2001); http://dx.doi.org/10.1063/1.1428115 (3 pages) | Cited 21 times

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We have fabricated interface-engineered junctions with YbBa2Cu3Oy as the counterelectrode. The junctions fabricated on YBa2Cu3Oy base electrodes exhibited excellent Josephson characteristics with the 1σ-spread in Ic as low as 5.4% for 16 junctions with an average Ic of around 1 mA. We also confirmed that the 1σ in Ic correlates with the surface morphology of the base-electrode layer, indicating that further improvements in 1σ would be possible by advancing the thin-film growth technology. © 2001 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
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