First critical fields, critical currents and flux creep of TmBa2Cu3Ox and YBa2Cu3Ox superconducting single crystals

The twin walls influence on transition temperature and critical current density in YBa2Cu3Ox and TmBa2Cu3Ox single crystal was studied. The temperature dependence of resistivity shows that the untwinned region superconducting transition temperature exceeds the twinned volume Tc value by several degrees. The additional vortex pinning by twins at high temperatures T > 40-50 K was observed. The anomalous (and almost linear) increase of the magnetization hysteresis width, corresponding to the critical current density increase, was observed in single crystals. The effect was found to be strongly temperature and angular dependent. The absence of this anomaly in YBa2Cu3Ox samples suggests the magnetic origin of the critical current growth in magnetic field. (orig.)