In-plane electrical transport properties of MgB2 single crystals grown under a high pressure of 4-6 GPa and temperature of 1400-1700 °C in the Mg-B-N system have been measured. For all specimens we found a sharp superconducting transition around 38.1-38.3 K with ΔTc(10-90%) within 0.2-0.3 K. Estimated resistivity value at 40 K is about 1 μΩ cm and the resistivity ratio ρ(273 K)/ρ(40 K) = 4.9±0.3. Results of measurements in magnetic field up to 5.5 T perpendicular to Mg and B planes (H⊥) and up to 9 T in parallel orientation (H∥) show temperature dependent anisotropy of the upper critical field with anisotropy ratio γ = Hc2∥/Hc2⊥ increasing from 2.2 close to Tc up to about 3 below 30 K. Strong deviation of the angular dependence of Hc2 from the anisotropic mass model has been also found.
|ジャーナル||Physica C: Superconductivity and its applications|
|出版ステータス||Published - 2002 10月 1|
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