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26 Mar 2001

Volume 78, Issue 13, pp. 1805-1950

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Low-loss YBa2Cu3O7 films on flexible, polycrystalline-yttria-stabilized zirconia tapes for cryoelectronic applications

K. S. Harshavardhan, H. M. Christen, S. D. Silliman, V. V. Talanov, S. M. Anlage, M. Rajeswari, and J. Claassen

Appl. Phys. Lett. 78, 1888 (2001); http://dx.doi.org/10.1063/1.1358845 (3 pages) | Cited 1 time

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High-temperature superconducting films on flexible, low-thermal conductivity, low-loss substrates offer a unique base for the development of cryoelectronic digital interconnects. Using an ion-beam-assisted pulsed-laser-deposition technique, we developed biaxially textured YBa2Cu3O7 (YBCO) films on flexible polycrystalline-yttria-stabilized zirconia (YSZ) substrates with the following materials properties: (i) in-plane x-ray Φ-scan full width at half maximum of ∼7°; (ii) transition temperatures (Tc) in the range of 88–89 K with transition widths (ΔTc) of ∼0.5 K; (iii) critical current densities (Jc) in the range 1.5–2×106 A/cm2 at 77 K, zero field; (iv) magnetic penetration depth (λ) of 284 nm at 77 K; and (v) surface resistance (Rs) of 700 μΩ at 77 K, 10 GHz. The low-microwave loss, biaxilly textured YBCO films combined with the low-thermal conductivity YSZ substrate could facilitate a variety of RF cryoelectronic applications. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
84.71.Mn Superconducting wires, fibers, and tapes
81.15.Fg Pulsed laser ablation deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.N- Response to electromagnetic fields

Thermal instability near planar defects in superconductors

A. Gurevich

Appl. Phys. Lett. 78, 1891 (2001); http://dx.doi.org/10.1063/1.1358361 (3 pages) | Cited 5 times

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It is shown that the local Joule heating due to planar defects, such as grain boundaries, microcracks, etc., can cause thermal instabilities, which limit the current-carrying capability of YBa2Cu3O7-coated conductors. Explicit instability criteria are obtained for a planar defect in a film and for a grain boundary. Thermal instabilities can be triggered by low-angle grain boundaries or planar defects, which block only a small fraction of the sample cross section. Hot spots near small defects and overheating of grain boundaries are essential for interpretation of experimental data on ac losses and E–J curves of polycrystals. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.25.Bt Thermodynamic properties
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects

Inverse magnetoresistance in chromium-dioxide-based magnetic tunnel junctions

A. Gupta, X. W. Li, and Gang Xiao

Appl. Phys. Lett. 78, 1894 (2001); http://dx.doi.org/10.1063/1.1356726 (3 pages) | Cited 47 times

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Magnetic tunnel junctions have been fabricated using half-metallic chromium-dioxide (CrO2) epitaxial film with a Co counterelectrode. The native insulating layer formed on the surface of CrO2 after air exposure is used as the tunneling barrier. These junctions exhibit nonlinear current–voltage characteristics, and the changes in junction resistance with applied field correspond to the coercivities of the two magnetic layers. The maximum observed magnetoresistance (MR) is about 8% at 4.2 K and has a negative sign, i.e., the resistance of the junction with parallel alignment of the electrodes is higher than with antiparallel alignment. This is opposite of what is normally observed with transition-metal electrodes and an Al2O3 barrier. Possible reasons for the inverse MR are discussed based on previous results on manganite/Co junctions. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Low-noise flux-gate magnetic-field sensors using ring- and rod-core geometries

R. H. Koch and J. R. Rozen

Appl. Phys. Lett. 78, 1897 (2001); http://dx.doi.org/10.1063/1.1358852 (3 pages) | Cited 10 times

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We have fabricated ring-core and single-domain rod-core flux-gate magnetic field sensors with 1/f noise levels at 1 Hz of 1.4 pT/math and 3.5 pT/math, respectively. These noise sensitivities were achieved by applying an electrical current through the core of the flux gate to magnetically bias the magnetic rotation of the core perpendicular to the easy-axis direction. We also found that in the rod-core sensor, the spatial correlation lengths of the magnetic fluctuations were 25 and 40 mm with and without the biasing current. The cross-power spectrum magnitude at 1 Hz was less than 200 fT/math. © 2001 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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