Magnetostriction and magnetoacoustic measurements on pure and Zn-doped YBCO crystals

Magnetostriction hysteresis data reveal the presence of the fishtail effect in isothermal scans between 72 and 80 K. Thermal cycles in a constant magnetic field show the behaviour of pinning of flux lines in the different phases. Ultrasonic attenuation and the relative change of the sound velocity for various magnetic fields were measured. The aim is to examine the elastic behaviour of the flux line lattice. In the framework of the thermally assisted flux flow model the depinning temperature TD(B) and the activation energy U(B) were been deduced. The measurements on YBCO crystals are discussed and compared with investigations on YBCO/Zn + Ag composites. The magnetostrictive effects are verified by supplementary DC-magnetization measurements