VORTEX FLUCTUATIONS AND INTERLAYER COUPLING IN CUPRATES

The reversible magnetization (M) curves of HgBa2Cam-1CumO2m+2+delta (m =1, 2, and 3) at different H cross at a temperature T and M=M* as sug gested by various two-dimensional (2D) vortes-fluctuation models. Howe ver, the obtained M/T* was found to be independent of either m or the sheet density 1/s of the CuO2 blocks, where s is the size of the unit cell along the c axis, in contrast to the predictions of the models. A survey of published data shows a similar situation, i.e., M/T* in e ither Bi- or Ti-based compounds is independent on s. This observation suggests that the coupling between neighboring CuO2 blocks may be non- negligible in its effects on the magnetization, and that modifications to the existing 2D fluctuation models need to be made.