Magnetoacoustic measurements on pure and Zn doped YBCO crystals

Investigations on the temperature dependence in the range from 4 to 100 K of the ultrasonic attenuation α(T, B) and the relative change Δv(T,B)/v of the sound velocity for various applied magnetic fields have been made. The ultrasonic attenuation α was measured by the pulse-echo technique and the relative change of the sound velocity Δv/v by a phase-comparison method. The measurements serve for the examination of the elastic behaviour of the flux line lattice (FLL) of pure and Zn doped YBCO crystals and YBCO/Ag composites. These crystals are important for applications as permanent magnets. In the framework of the thermally assisted flux flow model (TAFF) the activation energies U(B) were deduced from the ultrasonic data.