MAGNETIC-BEHAVIOR OF THE OXYGEN-DEFICIENT PEROVSKITE PRBACUFEO5+Y

This article concerns the class of compounds RBaCuMO5 where R is a rar e earth (Y or Pr) and M is a transition metal (Fe or Co). The magnetic structure is associated with the Cu and M atoms which are surrounded by five oxygens. The dominant interaction is superexchange which rtsul ts in antiferromagnetic ordering within bilayers. The interaction betw een bilayers is believed to be much weaker than the intralayer couplin g. Neutron diffraction experiments determine the magnetic structure of these materials and also give evidence that the introduction of extra oxygen (e.g., PrBaCuFeO5+y) destroys the magnetic ordering if R=Pr. I t is believed that these extra oxygen atoms tend to go into the plane of the rare earth atoms; they provide an interlayer bridge between the Cu/M planes and most likely stronger coupling than in the compounds f ree of extra oxygen. We introduce a model based on competition between weak ferromagnetic interlayer coupling and strong antiferromagnetic c oupling induced by the presence of the oxygen defects. Monte Carlo sim ulations are used to investigate the conditions under which magnetic l ong range order (LRO) is destroyed. We find that different values of C u-Cu, M-M, and Cu-M interactions are important if LRO is to disappear over a wide range of y. (C) 1997 American Institute of Physics.