Fishtail phenomenon in Ho-added PMP YBCO

The Y1-xHoxBa2Cu3Oy superconductors were fabricated by the powder melting process (PMP) method and the magnetic hysteresis loops of these samples were measured at different temperatures by a SQUID magnetometer (up to 7 T). Critical current density was calculated by the Bean critical state model. The results indicate that the fishtail effect is observed in Y0.6Ho0.4Ba2Cu3Oy below 60 K, while no fishtail can be found in Y0Ho0.2Ba2Cu3Oy until 30 K. The peak field at whichJc, reaches its maximum decreases with the increasing magnetic field. In the Y0.6Ho0.4Ba2Cu3Oy sample, the fishtail effect disappears when the temperature is raised to 77 K. In addition, after the Y0.6Ho0.4Ba2Cu3Oy sample was re-sintered at high temperature for a long time, the fishtail can be found in two field directions (Haa//C and H⊥C). It is considered that the paramagnetism in the sample may be responsible for the fishtail effect in Ho-added YBCO. Also, the cation disorder created by Ho addition may be another reason for the fishtail.