Anisotropic magnetic systems with competing interlayer interactions

The magnetic ordering of the compounds RBaCuTO5+y where R is a rare earth ( Y or Pr) and T is a transition metal (Fe or Co) and 0<y<0.5 has been studie d by molecular field theory and the Monte Carlo simulation technique. We in troduce a model based on competition between weak ferromagnetic interlayer coupling and strong antiferromagnetic coupling induced by the presence of t he oxygen defects. We show that even for small y, three-dimensional long ra nge order is rapidly destroyed. (C) 1999 American Institute of Physics. [S0 021-8979(99)41208-3].