Non-Resonant Microwave Absorption in Nano Nickel Added YBCO Superconducting Powders: Line Shape and Hysteresis

Nonresonant Microwave Absorption (NRMA) or the low field microwave absorption' (LFMA) measurements on high quality Ni nanoparticle added YBCO powder (Ni-YBCO) were carried as a function of temperature. The NRMA signal has structure in its line shape. As the Ni-YBCO powder sample is warmed up from 20K towards Tc, a phase reversal of the signal occurred around 60K, indicating a cross over from 'normal' to 'anomalous' type of absorption. We believe that the phase reversal could be due to the pi-junction formation because of the nano nickle particles in the weaklinks between particles. Further, we observed strong low field hysteresis in NRMA. The low field hysteresis can be deduced from the boundary current response using Dulcic model. Our studies establish that, the addition of Nano Ni, can tune the microwave absorption properties and the low field hysteresis of NRMA. (C) 2018 Elsevier Ltd. All rights reserved.