Magnetic properties of rare earth nickelates for the Ln2 Ba Ni O5 family

Rare-earth nickelates Ln2 Ba Ni1-x Cux O5, Ln = Nd and Dy, and Dy2-x Yx Ba Ni O5 have been synthesized in order to investigate the effect of substitution of Ni by Cu and Dy by nonmagnetic Y on the magnetic properties of the nickelates. In Ln2 Ba Ni1-x Cux O5, the nickelate structure (x=0.0) changes to the cuprate structure (x=1.0) at a specific composition (x=0.3). The Neel temperature of Nd2 Ba Ni1-x Cux O5 decreases continuously with increase in x up to x=0.3 (TN = 18 K); when x > 0.3, the materials are paramagnetic down to 20 K. The effective magnetic moment (μ eff) in Nd2 Ba Ni1-x Cux O5 essentially corresponds to the contribution of the Nd ions. In Dy2-x Yx Ba Ni O5, the Neel temperature decreases from 40 K when x=0.0 to 24 K when x=1.5. The compositions with 1.5≤x<2 (including the x=1.95 composition) are paramagnetic down to 20 K, unlike Y2 Ba Ni O5 (x=2.0) which exhibits a TN of 370 K. Even the smallest concentration of paramagnetic Dy seems to destroy the antiferromagnetic Ni-O-Ni chains in Y2 Ba Ni O5. (authors). 10 refs., 7 figs., 1 tab