VARIATION OF ANTIFERROMAGNETIC PR ORDERING IN THE TL(BA1-XSRX)2PRCU2O7-DELTA SYSTEM

Structural, magnetic, calorimetric, and transport studies have been ma de on a synthesized Tl(1212) system of Tl(Ba1-xSrx)2PrCu2O7-delta(0 le ss-than-or-equal-to x less-than-or-equal-to 1). Based on x-ray Rietvel d refinement data, the bond length between Pr and oxygen in the adjace nt CuO2 layers increases with increasing x, even though the tetragonal lattice parameters decrease with progressive Sr substitution. This ma y result in a lower degree of hybridization between extended Pr 4f and O 2p pi orbitals and a corresponding reduction of superexchange magne tic coupling strength among Pr moments. Indeed, the anomalously high N eel temperature T(N)(Pr) decreases from 8.0-8.2 K for x = 0 to 3.6-4.2 K for x = 1. The magnetic entropy associated with this antiferromagne tic Pr ordering is estimated from specific-heat data, in which a heavy -fermion-like contribution also prevails.