We report direction dependent magnetization measurements in LSCO single crystals. The crystals were grown using traveling solvent floating zone method and where cut into rectangular needle-like shapes with the "c" direction parallel or perpendicular to the needle symmetry axis.The magnetic anisotropies were studied in details near the critical temperatures using a SQUID magnetometer.
The measurements were done at magnetic fields H < 1Oe which is lower than the critical field Hc1 at T -> Tc A difference in Tc of 0.65 K was observed between parallel and perpendicular direction of the optimally doped samples (x=0.15). Higher anisotropy of 2.9 K was observed in under doped samples (x=0.08). We confirmed that the effect is not caused by sample inhomogeneity, needle dimensions, cooling rates, or misalignment. Our results indicate that in term of volume fraction, there is a temperature region where LSCO behaves as a two dimensional superconductor.