Anisotropy of flux trapping in ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{Y}}_{0.3}$${\mathrm{Ca}}_{0.7}$${\mathrm{Cu}}_3$${\mathrm{O}}_8$ single crystals

The angular dependence of magnetization of single crystals of ${\mathrm{Pb}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Y}}_{0.3}$ ${\mathrm{Ca}}_{0.7}$ ${\mathrm{Cu}}_{0.7}$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_8$ has been studied for various cooling procedures. A series of samples with different demagnetizing factors has been prepared. We succeeded in separating the material anisotropy from the sample shape anisotropy in the magnetization measurements. It is shown that the ‘‘field-cooled’’ magnetization is independent of the shape of the sample and reflects the anisotropy of the magnetic flux trapping. We observe that the vortices are most trapped in the direction parallel to the Cu-O planes. Our results are consistent with the anisotropy of the irreversibility line observed in high-${\mathit{T}}_{\mathit{c}}$ superconductors.