Specific heat near T sub N in (Pr,Nd,Sm,Gd, and Dy) Ba sub 2 Cu sub 3 O sub 7 - Evidence for spin-exchange-driven ordering.

Magnetic ordering at 2.2 K has been reported for Ba sub 2 Cu sub 3 O sub 7. In order to characterize the relevant magnetic interaction we have synthesized and measured the specific heat of polycrystalline ReBa sub 2 Cu sub 3 O sub 7, where Re = Pr, Nd, Sm, Gd, and Dy. The ordering temperatures are found to vary systematically with the deGennes factor, suggesting the dominance of spin-spin exchange over dipolar energies for these compounds. The field dependence of the specific heat peak for DyBa sub 2 Cu sub 3 O sub 7 implies the order is of antiferromagnetic nature.