The effective mass anisotropy ratio γ is generally determined relative to the main axes of a superconductor. Torque measurements with arbitrary field orientations, especially near the ab plane, are presented. The scaling of the apparent anisotropy ratio ${\gamma }_{\mathrm{app}}$ is verified also very close to the ab plane in the highly anisotropic ${\mathrm{La}}_{1.9}{\mathrm{Sr}}_{0.1}{\mathrm{CuO}}_4.$ This method allows a very precise determination of ${\gamma }_{\mathrm{ac}}$ and shows the importance of the field orientation for ab-plane measurements.

• Received 8 October 1998

DOI:https://doi.org/10.1103/PhysRevB.59.R717