Sr3CuPtxIr1-xO6 has been cited as an example of a one-dimensional quantum spin chain with competing ferromagnetic and antiferromagnetic interactions. We have measured the ac susceptibility of Sr3CuPtxIr1-xO6 with x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7, in magnetic fields of 0–60 kOe, and at temperatures down to 0.275 K. Our data show that the x=endpoint Sr3CuIrO6, exhibits long-range ferromagnetic order at T=20.1 K, contrary to results from dc susceptibility studies which indicated that it remained a one-dimensional ferromagnet to below 4 K. When platinum is substituted for iridium, antiferromagnetic couplings are introduced, and the susceptibility shows a diminishing signature of the three-dimensional ferromagnetic transition. Furthermore, the low-temperature susceptibility exhibits peaks which appear and evolve as x is increased. These results lead to a rich phase diagram in temperature and Pt concentration space. We find that the behavior of Sr3CuPtxIr1-xO6 cannot be simply described by the random quantum spin chain theories that were developed, in part, to address this system.
Published in Physical Review B, Volume 61, Issue 17, 2000, pages 594-600.
© 2000 The American Physical Society
PACS:75.40.Cx, 75.50.-y, 75.30.Kz, 75.50.Lk