MAGNETIC-FIELD AND ORIENTATION DEPENDENCE OF VORTEX MOTION IN YBA2CU3O7 PRBA2CU3O7 MULTILAYERS/

We have studied the vortex motion in YBa2Cu3O7/PrBa2Cu3O7 (YBCO/PBCO) multilayers by measuring the magnetic field H and orientation dependen ce of the average activation energy (U) over bar. The (U) over bar of YBCO(24 Angstrom)/PBCO(96 Angstrom) multilayer system shows a logarith mic H dependence in the field region of 0.1-4 T. The H direction depen dence of (U) over bar shows that all (U) over bar versus H sin phi of experimental points fall on the same line, (U) over bar versus H(phi = 90 degrees), in the whole applied field and orientation regions. Here , phi is the angle between H and the film plane under the condition of H perpendicular to the transport current. These results suggest two d imensional vortex motion in the YBCO(24 Angstrom)/PBCO(96 Angstrom) mu ltilayers. The deviations from the log H dependence at low fields (H < 0.1 T) and high fields (H > 4 T) are observed. The deviation at low f ields is discussed on the basis of the interaction between vortices, T he H dependence of (U) over bar seems to follow a power-law behaviour in the high field. This suggests a possibility of coupling between the YBCO layers.