OBSERVATION OF 2D-3D TRANSITION IN TL2BA2CACU2OX

Magnetization curves of a Tl 2212 single crystal with T(c) = 107 K have been measured in fields perpendicular to the ab-plane and temperatures near T(c). Some qualitative changes in M versus H dependences have been observed at a temperature, T0, 6.5 K below T(c). They are tentatively interpreted as a manifestation of the 2D-3D crossover in the vortex dimensionality. The ordinary anisotropic mass model of GL theory has been argued to be applicable only at temperatures above T0 for which the anisotropy parameter, gamma, has been estimated to be 20 and the GL parameter kappa almost-equal-to 19.