Synthesis and magnetic properties of the R 1+ xSr 2− xNb 1− xO 8− y system

Abstract

We have carried out systematic studies involving synthesis of R 1+ x Sr 2− x Cu 2+ x Nb 1− x O 8− y ( x = 0.0−0.2), R = La, Pr, Nd, Sm, Eu, Gd, Dy and Y, and have investigated their magnetic properties. For R = La, Dy and Y, the expected RSr 2Cu 2NbO 8− y (RSCNO) phase does not form. For R = Pr and Nd, only an off-stoichiometric composition yields the RSCNO single phase, Pr 1.2Sr 1.8Cu 2.2Nb 0.8O 8− y (Pr 1.2SCNO) and Nd 1.1Sr 1.9Cu 2.1Nb 0.9O 8− y (Nd 1.1SCNO), respectively. In contrast, for R = Sm, Eu and Gd, the stoichiometric ratio results in monophasic material. Lattice parameters for Pr 1.2SCNO, Nd 1.1SCNO, SmSCNO, EuSCNO, and GdSCNO are found to vary linearly with rare earth ionic size. Magnetic susceptibility, χ, for Pr 1.2SCNO and GdSCNO, exhibits a magnetic ordering of the R sublattice. This occurs at about 6 K for the former and at about 2.15 K for the latter. The peak in the χ− T curve at 2.15 K for GdSCNO agrees well with the cusp (2.17 K) reported in heat capacity vs. temperature data. The effective paramagnetic moment, μ eff, for the rare earth ion is deduced to be 2.95μ B in Pr 1.2SCNO and 7.97 μ B in GDSCNO. This result for GdSCNO is consistent with that of heat capacity measurements which indicate an entropy value corresponding to a Gd spin of 3.3. Magnetic susceptibility results do not indicate a magnetic transition down to 1.8 K for the Nd 1.1SCNO and SmSCNO compounds. The μ eff value is determined to be 3.42μ B for the former. Results on the abovementioned compounds are discussed in the context of the related RBa 2Cu 2NbO 8− y and RBa 2Cu 3O 7− y systems.