Magnetization rotation in YBCO thin films:: deviations from c-axis scaling

We report magnetization measurements on YBCO thin films performed with the applied field at various angles with respect to the c-axis at temperatures of 77 and 35 K. At low temperatures (T = 35 K) as the angle is increased the magnetization is observed to scale according to the component of field along the c-axis. However, for the higher temperature (T = 77 K) there are very strong deviations of the moment from this simple scaling and this clearly suggests that the critical state moment collapses rapidly as the angle is increased. The decrease of the moment is strong for higher fields and larger angles. We also conducted magnetization rotation measurements at 77 K whereby the M(theta) data were used to reconstruct the hysteresis curves, M(H). A comparison of actual and reconstructed M(H) curves indicates the same feature, i.e. collapse of the irreversible moment at higher fields when the applied field deviates away from the c-axis.