Evolution of Fishtail-effect with aging in pure and Ag-doped MG-YBCO

Abstract

$M(B)$-curves were experimentally investigated. Fishtail-effect (FE) was observed in MG YBa${}_2$Cu${}_3$O${}_{7-\delta }$ and YBa${}_2$Cu${}_{3-x}$Ag${}_x$O${}_{7-\delta }$ (at $x\approx$ 0.02) crystals in a wide temperature range 40 K $<T<$ 75 K at the orientation of magnetic field $\text{H}\parallel c$. It was obtained that the influence of bulk pinning on FE is more effective at low temperatures while the influence of surface barriers is more effective at high temperatures. The value $H_{max}$ for Ag-doped crystals is larger than for a pure one that due to the presence of additional pinning centers, above all on silver atoms.

3 pages, 4 figures