Upper Critical Field Measurements by Pulsed Magnetic Fields in High-Tc Supoerconducting Oxides

Upper critical fields of high-T c superconducting oxides, La1.85Sr0.15CuO4-δ, Y0.4Ba0.6CuO y and YBa2Cu3O7-δ, were measured by magnetoresistance method under a pulsed magnetic field up to 60 T in a temperature region 4.2 K to T c. The H c2 (0) defined by the midpoint of the resistive transition are estimated to be 40, 90 and 148 tesla, for La1.85Sr0.15CuO4-δ, Y0.4Ba0.6CuO y and YBa2Cu3O7-δ, respectively.