In both crystals at 4.2 K, a trapped flux along the c axis is seen to inhibit the initial production of vortex flux by external fields (${\mathit{H}}_{\mathit{e}}$) in the a-b plane and to increase the retention of this vortex flux during subsequent cycling of ${\mathit{H}}_{\mathit{e}}$. Thus, the cross flux along c acts consistently as a pinning agent for the vortices aligned along a-b. The cross-flux effects in both these crystals are as pronounced as those observed in grain-oriented ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ [S. J. Park and J. S. Kouvel, Phys. Rev. B 48, 13 995 (1993)] and they persist undiminished to much larger cycling ranges of ${\mathit{H}}_{\mathit{e}}$ due to the stronger pinning of the cross flux itself.

• Received 19 July 1993

DOI:https://doi.org/10.1103/PhysRevB.48.13998