Critical currents and pinning mechanisms in directionally solidified YBa2Cu3O7-Y2BaCuO5 composites

The superconducting properties of directionally solidified YBa2Cu3O7-Y2BaCuO5 composites, with critical currents above 10(5) A/cm(2) at 77 K and zero magnetic-field, are reported in a wide variety of samples having very different contents of Y2BaCuO5 (211 phase) precipitates with different particle size and magnetic fields up to 22 T The field, temperature, and composition dependence of the critical currents allow us to identify interfacial pinning by 211 precipitates as a very effective pinning mechanism. Nevertheless, single vortex interfacial pinning has a dominant-role only in a narrow region below about 1 T and temperatures 40 K less than or equal to T less than or equal to 80 K. In this region the system shows a behavior very akin to that observed in ion irradiated single crystals and described as correlated disorder. On lowering the temperature the thermal wandering of the vortex from secondary weak pinning centers decreases leading to a new single vortex pinning regime extending up to very high magnetic fields where a mixture of strong and weak pinning centers are active. On the other hand, increasing the magnetic field, the characteristic footprints of the small bundle and large bundle regimes are identified at intermediate temperatures. The former is found below the H-T line given by the maximum of the macroscopic Pinning force while the latter is observed above this line up to the irreversibility line. Finally, collecting all these results together a magnetic phase diagram of the mixed state of the YBa2Cu3O7-Y2BaCuO5 textured composites is proposed.