OXYGEN DEPENDENCE OF THE MAGNETIC ORDER OF ND IN NDBA2CU3O6+X

Neutron scattering and specific heat measurements have been carried ou t on a series of NdBa2Cu3O6+x powder samples with varying oxygen conce ntrations (x=0.94, 0.78, 0.45, 0.3, 0.13) in order to study the effect s of oxygen on the magnetic order of Nd. For our highest oxygenated su perconducting NdBa2Cu3O6.94 (T(c) = 92 K), three-dimensional (3D) long range order develops below T(N) congruent-to 0.53 K, with a spin conf iguration which is antiferromagnetic along all three crystallographic axes. For a small reduction of oxygen to x = 0.78, we observe drastic effects on the Nd order; 3D order is inhibited and only short range 2D correlations are found at low temperature. However, the 2D correlatio ns develop at a much higher temperature, near 1.5 K. At (nonsupercondu cting) x = 0.45, the 3D magnetic order is better developed at low temp erature, yet long range order still does not occur. For x = 0. 3, 3D l ong range magnetic order of the Nd ions is reestablished, developing b elow T(N) congruent-to 1.5 K, three times that of the fully oxygenated material. All of these ordering temperatures are much higher than wha t is expected based on dipolar interactions alone, and this coupled wi th our experimental results indicates that exchange interactions play an essential role, and are strongly influenced by the chain layer oxyg en.