Temperature dependence of the anisotropy in magnetic relaxation in YBa/sub 2/Cu/sub 3/O/sub 7-2/ thin films

The relaxation of diamagnetic magnetization in the c axis aligned YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films is studied as a function of orientation and temperature in the range of 5-50 K at H=0.2 T. The magnetization M(T,H) in the orientations H//c and H perpendicular to c and at all the temperatures is found to decrease logarithmically with time t. The activation energy for the movement of flux lines U is found to be 30-110 meV in the range 5-50 K. For H//c, U increases continuously with T, whereas for H perpendicular to c, U has two apparent maxima: at T=10 K and T>50 K. These results are discussed in terms of the thermally activated flux motion model.