Improvement of Upper Critical Field in YBa2Cu3Oy Films by Substituting 3d Metal for Cu Sites Using Combinatorial Pulsed-laser Deposition

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Abstract It is well known that the critical upper field Bc2 is improved by shortening of the coherence length owing to the scattering of electrons in a superconductor. In order to improve of Bc2 in YBa2Cu3Oy (YBCO) films in our study, we substituted 3d metals (M = Zn, Co, Ni, Fe) for the Cu sites of the YBCO films. We used combinatorial pulsed-laser deposition to fabricate different YBa2(Cu1-xMx)3Oy films by continuously changing the amount of substitution metal x, from 0 to 0.01 on a single substrate using. As a result, the superconducting transition temperature Tc and critical current density Jc decreased with increasing amounts of all four variations of substitution metal M. For example, Tc was 82.5 K and Jc at 77 K was 0.15 MA/cm2 in the Co-substituted sample with x = 0.0091. For the substitution of Co and Ni, we confirmed that Bc2 was improved with increasing amount of substitute metal up to x = 0.01. Although Bc2(0 K) of a pure-YBCO film was 101 T, Bc2(0 K) of the Co-substituted sample with x = 0.0091 reached 272 T. On the other hand, the irreversibility field decreased by substituting Zn, Co, Ni, or Fe for Cu.