Radio-frequency acoustic powder echoes in high-T c YBaCuO ceramics around the H-T phase boundary

Abstract

Intensity of rf acoustic powder echoes are studied around the H-T phase boundary in the superconducting state for powdered samples of YBaCuO prepared by the quench and melt growth (QMG) process and for conventional powder of YBa 2Cu 3O 7−δ. The echoes are fond to vanish at the critical field H C2 rather than the irreversibility field H irr for both of the samples. The intrinsic pinning rather than the pinning of fluxoids to defects seems to be important for the observation of rf acoustic powder echoes in the high-T c YBaCuO ceramics.