Using the techniques of muon spin rotation and torque magnetometry, we investigate the crossover field $B_{\mathrm{cr}}$ in ${\mathrm{Bi}}_{2.15}{\mathrm{Sr}}_{1.85}{\mathrm{Ca}}_1{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ at which the vortex lattice becomes disordered along the field direction. It is found that $B_{\mathrm{cr}}$ scales as the projection of the applied field along the perpendicular to the superconducting planes. This has the implication that a field large enough to give a disordered lattice when applied perpendicular to the planes, can give a well-ordered vortex-line lattice for angles of the field to the $c$ axis greater than a critical value.

• Received 11 July 1997

DOI:https://doi.org/10.1103/PhysRevB.57.1253