A New Series of Magnetic Rare Earth Cuprates: RCu2O4 (R = La, Nd, Sm, and Eu)

The synthesis, crystal structure, and magnetic properties of a new series of isostructural rare earth cuprates, RCu{sub 2}O{sub 4} (R = La, Nd, Sm, and Eu), are reported. The highly oxidized materials with an average formal copper oxidation state of Cu{sup 2.5+} were isolated by precipitation from molten NaOH at 400{degree}C. Powder X-ray diffraction data for EuCu{sub 2}O{sub 4} combined with neutron diffraction data for NdCu{sub 2}O{sub 4} were used to determine the crystal structure and refine the structure by rietveld profile analysis. The lattice parameters for NdCu{sub 2}O{sub 4} in the non-standard monoclinic space group J2/a derived from the neutron data set are the following: a = 5.826(1) A, b = 9.703(1) A, c = 5.753(1) A, and {beta} = 92.341(1){degree}. The copper-oxygen network consists of a three-dimensional array of CuO{sub 4} distorted square planes that are cornered-shared; the Cu-O-Cu bond angle is approximately 115{degree}. These exhibit magnetic ordering of the copper spins as determined by a large increase in the magnetization as the temperature is lowered, the onset of which varies between 18 and 28 K, depending on R. While the negative Weiss constants for LaCu{sub 2}O{sub 4} and NdCu{sub 2}O{sub 4} indicate that the predominant interaction ismore » antiferromagnetic, the saturation moments of approximately 0.13 {mu}{sub B} per mol of RCu{sub 2}O{sub 4} indicate that there is a significant ferromagnetic component, possibly due to canting of the ordered copper moments 36 refs., 8 figs., 4 tabs.« less