Critical current and microwave properties of YBCO films deposited on different metallic templates

It has been recently shown that the combination of dc and microwave regime measurements of the YBCO film transport properties is a powerful tool for vortex pinning investigation [1]. These techniques were successfully used for the study of pinning mechanisms on PLD-YBCO films with BaZrO3 (BZO) inclusions on SrTiO3 single crystal substrates [2]. In this contribution, YBCO films deposited by both pulsed laser ablation (PLD) and chemical techniques on metallic templates were investigated. Chemical-YBCO was deposited by low fluorine metallorganic precursor solution. On cube textured Ni-5at. %W metallic substrates two different buffer layer architectures CeO2/YSZ/CeO2 and CeO2/MgO were used as template for YBCO growth. In all cases high quality YBCO films were obtained showing critical temperature at 90 K. Critical current densities on patterned samples were measured by recording the I-V curves using the typical four probes methods in the maximum Lorentz force configurations. Magnetic field dependences of Jc at several temperatures were obtained. Critical current density in excess of 1 MA/cm2 at 77 K and self-field conditions were achieved in all cases. The microwave properties were measured by the dielectric resonator technique [3], operating at high frequency (48 GHz). The quality factor and the resonant frequency yielded a measure of the losses and of the reactance (screening) of the samples. The samples showed the superconducting transition in agreement with dc measurements: since the microwave field approximates, in this case, a bulk probe (the penetration depth is comparable to the sample thickness), this result indicates a homogeneous transition in the superconducting material (albeit some trace of lower-Tc phases can be spotted, as often revealed by microwave measurements of less-than-crystalline samples). An applied magnetic field up to ~1 T, directed perpendicular to the film plane, drove the samples in the vortex state. The vortex motion due to the microwave current induced additional resistive and reactive response. We derived the vortex-state parameters [4]: the flux-flow resistivity and the depinning frequency. The latter is independent on any calibration of the system [3], and thus is a very reliable indicator of the pinning strength. We compare the results obtained in the present YBCO-on-metal samples to the results obtained in PLD and Chemical-deposited YBCO/BZO. Finally, in order to gain information on both the depth and steepness of the pinning wells, we compare the pinning properties obtained at our very high driving frequency (mostly sensitive to the local steepness of the pinning well) to the experimental Jc (sensitive to the depth of the pinning wells). References: [1] V. Galluzzi, A. Augieri, L. Ciontea, G. Celentano, F. Fabbri, U. Gambardella, A. Mancini, T. Petrisor, N. Pompeo, A. Rufoloni, E. Silva, A. Vannozzi, IEEE Trans. Appl. Supercond. 17, 3628 (2007) [2] N. Pompeo, R. Rogai, E. Silva, A. Augieri, V. Galluzzi, G. Celentano, Journal of Applied Physics 105, 013927 (2009); A. Augieri, G. Celentano, V. Galluzzi, A. Mancini, A. Rufoloni, A. Vannozzi, A. Angrisani Armenio, T. Petrisor, L. Ciontea, S. Rubanov, E. Silva, and N. Pompeo, Journal of Applied Physics 108, 063906 (2010) [3] N. Pompeo, R.Marcon, E. Silva, J. Supercond. and Novel Magnetism 20, 71 (2007) [4] N. Pompeo, E. Silva, Physical Review B 78, 094503 (2008) Acknowledgements: This work has been carried out in the framework of EUROTAPES European Project funded in the FP7 program and in the framework of SURE:ARTYST Italian national project funded by MIUR.