Spin-1/2 quantum antiferromagnetic chains with tunable superexchange interactions found in BaCu2(Si1-xGex)(2)O-7

Synthesis, structure, and magnetic properties of a novel one-dimensional sp in-1/2 quantum antiferromagnetic (AF) system BaCu2(Si1-xGex)(2)O-7 (0 less than or equal to x less than or equal to 1) are reported. Contained in this system are corrugated CuO chains made of corner-sharing CuO4 squares with the dominant exchange interaction changing almost linearly between 290 K (x = 0) and 580 K (x = 1). Anomalies in susceptibility and specific heat, ind icative of the occurrence of a long-range AF ordering, are observed at 8.9 K (x = 0) and 8.6 K (x = 1), A rich magnetic phase diagram results from thi s strong composition dependence combined with the switching of the intercha in interaction changing from ferromagnetic (x = 0) to AF (x = 1), (C) 2001 Academic Press.