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8 Mar 1999

Volume 74, Issue 10, pp. 1355-1498

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Cation exchange: A scheme for synthesis of mercury-based high-temperature superconducting epitaxial thin films

J. Z. Wu, S. L. Yan, and Y. Y. Xie

Appl. Phys. Lett. 74, 1469 (1999); http://dx.doi.org/10.1063/1.123583 (3 pages) | Cited 31 times

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A cation-exchange process has been developed for growth of high-quality epitaxial thin films of highly volatile mercury-based high-temperature superconductors. By selecting epitaxial precursor matrices of TlyBa2CaCu2Ox (y = 1,2) and annealing them in Hg vapor, c-axis-oriented epitaxial HgBa2CaCu2O6+δ thin films with superior quality were formed through Tl and Hg-cation exchange. At 110 K, these films can carry supercurrent density close to 1 MA/cm2 which is nearly an order of magnitude higher than the best reported previously. This cation-exchange technique also provides a general scheme for synthesis of other volatile compounds with predesigned structure and composition. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena

Heterodyne detection of alternating magnetic fields with a resonating xylophone bar magnetometer

R. B. Givens, D. K. Wickenden, D. A. Oursler, R. Osiander, J. L. Champion, and T. J. Kistenmacher

Appl. Phys. Lett. 74, 1472 (1999); http://dx.doi.org/10.1063/1.123584 (3 pages) | Cited 6 times

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A resonating xylophone bar magnetometer has been utilized as the mixer in a heterodyne detector for variable-frequency alternating magnetic fields. To illustrate the range of this detection scheme, examples offered include the response to low frequency, sinusoidal magnetic fields at 2, 10, and 20 Hz and to high frequency sinusoidal magnetic fields in the MHz regime. In a final example, the response of the magnetometer to the field generated by a 20 Hz square wave has been compared to the Fourier components of an idealized square wave, with no apparent loss in sensitivity and a mean deviation from expected values of less than 0.5%. © 1999 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements

Local characterization of electronic transport in microcrystalline silicon thin films with submicron resolution

B. Rezek, J. Stuchlík, A. Fejfar, and J. Kočka

Appl. Phys. Lett. 74, 1475 (1999); http://dx.doi.org/10.1063/1.123585 (3 pages) | Cited 32 times

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Two-dimensional maps of dark conductivity with submicron resolution have been obtained on in situ prepared hydrogenated microcrystalline silicon (μc-Si:H) layers used for solar cells by atomic force microscopy with conductive cantilever. Comparison of the morphology and current image allows clear identification of Si crystallites. Pronounced current decrease has been detected at the grain boundaries. The technique was used to study initial stages of μc-Si:H growth, and we show how the incubation layer, detrimental for solar cells efficiency, can be minimized by pulsed excimer laser crystallization of the initial amorphous layer. © 1999 American Institute of Physics.
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73.61.Cw Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion
68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys

Preparation and characterization of Dy nanoparticles

N. B. Shevchenko, J. A. Christodoulides, and G. C. Hadjipanayis

Appl. Phys. Lett. 74, 1478 (1999); http://dx.doi.org/10.1063/1.123586 (3 pages) | Cited 9 times

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A technique of pure nanoparticle preparation has been explored by forming first small metal particles under high pressure sputtering and then embedding them into a sputtered film matrix. The tandem deposition method is used where the sputtered matrix is deposited at an argon pressure of 5 mTorr and the particles are formed within a specially designed gun at a pressure of 1 Torr and then deposited. The particle-matrix compositional limitations of reactivity and miscibility are thus reduced. The new technique was applied to dysprosium metal particles in an aluminum matrix. The absence of the antiferromagnetic transition for particles with sizes of 4–12 nm was observed. The 4 nm particles behaved superparamagnetically, while the larger 12 nm particles showed coercivities over twice as large as that of the bulk material at cryogenic temperatures. The success of the technique is demonstrated by having been able to carry out the study on the dysprosium-aluminum system that normally reacts, preventing the existence of pure Dy particles. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Step-edge magnetoresistance in La0.7Ca0.3MnO3 films

M. Ziese, G. Heydon, R. Höhne, P. Esquinazi, and J. Dienelt

Appl. Phys. Lett. 74, 1481 (1999); http://dx.doi.org/10.1063/1.123587 (3 pages) | Cited 44 times

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The magnetoresistance of step-edge structures in La0.7Ca0.3MnO3 films was investigated. Step-edge arrays with 200 steps of height 140–200 nm and step separation 20 μm along [110] were fabricated on LaAlO3 substrates by chemically assisted ion-beam etching. Thin La0.7Ca0.3MnO3 films were deposited on the structured substrates by pulsed-laser deposition. Measurements of the large low-field magnetoresistance, the dynamic conductance, and the anisotropic magnetoresistance lead to the proposal of a model of spin-polarized tunneling in a ferromagnet/spin-glass/ferromagnet geometry. © 1999 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Lk Spin glasses and other random magnets
81.15.Fg Pulsed laser ablation deposition
75.45.+j Macroscopic quantum phenomena in magnetic systems
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