Synthesis and magnetism of Bi₂Sr₂RCu₂O_8+δ (R=Y, Pr, and Tb) systems

Abstract

The problems of making phase-pure Bi₂Sr₂RCu₂O_8+δsystems, with R=Y, Pr, and Tb, are discussed in detail, particularly in the case of Pr and Tb. Complete substitution of these three rare earths at the Ca site is realized in this system. The c lattice parameter of the rare-earth-containing material decreases in comparison with that of the pure undoped Bi₂Sr₂CaCu₂O_8+δ. On-site ionic size differences and increased oxygen content due to aliovalent substitution are the possible causes of the decreased c lattice parameter. Magnetic-susceptibility (Χ) measurements on these samples give an effective paramagnetic moment close to that of 3+ for Tb but intermediate between those of 3+ and 4+ for Pr. A change in slope in the Χ^-1 vs T curve for the Y compound at ~295 K and a dip in the same for the Pr compound at ~330 K may be indicative of the antiferromagnetic ordering of the Cu moments in these compounds.