ANOMALOUS PR ORDERING IN THE NEW TLBA2PRCU2O7-DELTA COMPOUND

Magnetic measurements on the new tetragonal Tl(1212) compound TlBa2PrCu2O7-delta (a = 3.910 angstrom and c = 12.53 angstrom) reveal an anomalously high antiferromagnetic Neel temperature T(N) congruent-to 8 K. This transition temperature is higher than T(N) = 2.2 K for isostructural TlBa2GdCu2O7-delta. Corroborative evidence comes from calorimetric studies, in which a magnetic entropy was obtained DELTAS congruent-to 0.5 Rln 2 between 2 and 10 K, as well as a sizeable linear term in specific heat comparable to those found in heavy-fermion systems. Through structural consideration, these observations can not only be correlated to the almost identical but still puzzling features of PrBa2Cu3O7-y, but also remove some ambiguity in the interpretation of earlier results.