D. Ko et H. Oesterreicher, MAGNETIC AND ELECTRONIC-PROPERTIES OF SPECIALLY PROCESSED YBA2(CU0.95NI0.05)(3)O-Y, Journal of magnetism and magnetic materials, 158, 1996, pp. 661-662
We report on getter annealed YBa2(Cu0.95Ni0.05)(3)O-y which are parama
gnetic in a range from y = 6.1 to 6.8 with Curie-Weiss temperatures (T
heta) remaining near 0 K. Reoxidation of the most reduced materials pr
oduces superconductors with enhanced flux pinning followed in temperat
ure by a paramagnetic range with unusually large negative Theta approx
imate to -70 K indicative of Ni nanoclusters.