As discovered earlier, a trapped flux along the c axis of the grain-oriented sample at 4.2 K inhibits the vortex flux produced by an increasing external field (${\mathit{H}}_{\mathit{e}}$) in the a-b plane. It is now found that when ${\mathit{H}}_{\mathit{e}}$ is subsequently cycled, the hysteresis loop shows a pronounced broadening, the remanent vortex-flux magnetization along a-b having increased to about twice its value in the absence of the cross flux along c. Thus, although the cross flux decreases steadily during the changes of ${\mathit{H}}_{\mathit{e}}$, it acts consistently as a pinning agent for the vortices aligned along a-b. However, for large cycling ranges of ${\mathit{H}}_{\mathit{e}}$, the pinning of the cross flux itself is sufficiently overcome that its effects on the vortex behavior in the a-b plane diminish.

• Received 10 March 1993

DOI:https://doi.org/10.1103/PhysRevB.48.13995