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25 Jun 2001

Volume 78, Issue 26, pp. 4065-4199

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Effect of sintering temperature under high pressure on the superconductivity of MgB2

C. U. Jung, Min-Seok Park, W. N. Kang, Mun-Seog Kim, Kijoon H. P. Kim, S. Y. Lee, and Sung-Ik Lee

Appl. Phys. Lett. 78, 4157 (2001); http://dx.doi.org/10.1063/1.1382632 (3 pages) | Cited 44 times

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We report on the effect of sintering temperature on the superconductivity of MgB2 pellets prepared under a high pressure of 3 GPa. The superconducting properties of the nonheated MgB2 were poor. However, as the sintering temperature increased, the superconducting properties were vastly enhanced, which was demonstrated by the narrow transition width for the resistivity and the low-field magnetization. The observed surface morphology using scanning electron microscopy showed that these changes were closely related to changes in the microscopic level such as the connectivity of the grains. © 2001 American Institute of Physics.
Show PACS
74.62.Fj Effects of pressure
74.72.-h Cuprate superconductors
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Microwave properties of superconducting MgB2

N. Hakim, P. V. Parimi, C. Kusko, S. Sridhar, P. C. Canfield, S. L. Bud’ko, and D. K. Finnemore

Appl. Phys. Lett. 78, 4160 (2001); http://dx.doi.org/10.1063/1.1379366 (3 pages) | Cited 11 times

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Measurements of 10 GHz microwave surface resistance, Rs, of dense MgB2 wire and pellet are reported. Significant improvements are observed in the wire with reduction of porosity. The data lie substantially above the theoretical estimates for a pure Bardeen–Cooper–Schrieffer s-wave superconductor. However, the Rs (20 K) of the wire is an order of magnitude lower than that of polycrystal YBa2Cu3O6.95 and matches with single-crystal YBa2Cu3O6.95. The results show promise for the use of MgB2 in microwave applications. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.F- Transport properties
74.25.N- Response to electromagnetic fields

High thermal stability of exchange-biased bilayers and bottom giant magnetoresistive spin valves using an α-Fe2O3 antiferromagnetic layer

Seongtae Bae, Jack H. Judy, P. J. Chen, William F. Egelhoff, and Shayne Zurn

Appl. Phys. Lett. 78, 4163 (2001); http://dx.doi.org/10.1063/1.1381031 (3 pages) | Cited 6 times

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The thermal stability of antiferromagnetic α-Fe2O3 exchange-biased bilayers and bottom giant magnetoresistive (GMR) spin valves has been investigated experimentally at various ambient temperatures. An α-Fe2O3 exchange-biased bilayer exhibited a high blocking temperature, Tb, of 390 °C, and a bottom spin valve showed stable GMR performance above 350 °C. The Tb of α-Fe2O3 exchange-biased bilayers depended strongly on the adjacent ferromagnetic material and the number of measurements. In addition, the increasing mean grain size and enhanced (104) and (110) crystalline texture of α-Fe2O3 increased Tb by up to 23%. © 2001 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects
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