SYNTHESIS AND MAGNETIC-PROPERTIES OF THE R1-XCU2+XNB1-XO8-Y SYSTEM(XSR2)

We have carried out systematic studies involving synthesis of R1+xSr2- xCu2+xNb1-xO8-y (x=0.0-0.2), R=La, Pr, Nd, Sm, Eu, Gd, Dy and Y, and h ave investigated their magnetic properties. For R=La, Dy and Y, the ex pected RSr2Cu2NbO8-y (RSCNO) phase does not form. For R=Pr and Nd, onl y an off-stoichiometric composition yields the RSCNO single phase, Pr1 .2Sr1.8Cu2.2Nb0.8O8-y (Pr1.2SCNO) and Nd1.1Sr1.9Cu2.1Nb0.9O8-y (Nd1.1S CNO), respectively. In contrast, for R=Sm, Eu and Gd, the stoichiometr ic ratio results in monophasic material. Lattice parameters for Pr1.2S CNO, Nd1.1SCNO, SmSCNO, EuSCNO and GdSCNO are found to vary linearly w ith rare earth ionic size. Magnetic susceptibility, chi, for Pr1.2SCNO and GdSCNO, exhibits a magnetic ordering of the R sublattice. This oc curs at about 6 K for the former and at about 2.15 K for the latter. T he peak in the chi-T curve at 2.15 K for GdSCNO agrees well with the c usp (2.17 K) reported in heat capacity vs. temperature data. The effec tive paramagnetic moment, mu(eff), for the rare earth ion is deduced t o be 2.95 mu(B) in Pr1.2SCNO and 7.97 mu(B) in GdSCNO. This result for GdSCNO is consistent with that of heat capacity measurements which in dicate an entropy value corresponding to a Gd spin of 3.3. Magnetic su sceptibility results do not indicate a magnetic transition down to 1.8 K for the Nd1.1SCNO and SmSCNO compounds. The mu(eff) value is determ ined to be 3.42mu(B) for the former. Results on the abovementioned com pounds are discussed in the context of the related RBa2Cu2NbO8-y and R Ba2Cu3O7-y systems.