NEUTRON-DIFFRACTION STUDY OF THE MAGNETIC-ORDERING OF THE CU++ SPINS IN ND1.5BA1.5CU3O6+X

Elastic neutron scattering experiments performed on single crystals of Nd1.5Ba1.5Cu3O6+y reveal successive antiferromagnetic (AF) ordering of the Cu++ spins. The as grown single crystals show an AF structure characterized by a Neel temperature T(N1) approximately 390K and a magnetic wave vector (1/2 1/2 0) referring to the tetragonal structure of NdBa2Cu3O6. As the temperature is lowered below T(N2) approximately 150K, a spin reorientation develops and a second AF ordering with (1/2 1/2 1/2) wave vector is stabilized. When the samples are oxygenated the tetragonal symmetry and the Neel temperature T(N1) remain unchanged, whereas the spin reorientation at T(N2) is suppressed. The results indicate that the Nd/Ba substitution increases the stability of the tetragonal structure upon the oxygen content. This may induce new possibilities of local oxygen ordering that favour the presence of holes in the deficient layer.