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 th
e magnetization is observed to scale according to the component of field al
ong the c-axis. However, for the higher temperature (T = 77 K) there are ve
ry strong deviations of the moment from this simple scaling and this clearl
y suggests that the critical state moment collapses rapidly as the angle is
increased. The decrease of the moment is strong for higher fields and larg
er angles. We also conducted magnetization rotation measurements at 77 K wh
ereby 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.