MACROSCOPIC MAGNETIC-PROPERTIES OF NI AND ZN SUBSTITUTED YBA2CU3OX

We present a comparison between Ni and Zn substitutions in YBa2Cu3Ox. For x approximate to 1, besides the -12K/% decrease of T-c due to Zn, which is 3 times larger than with Ni, Zn induces a weak magnetic moment mu(eff) = 0.36 mu(B)/Zn while in the Ni case, mu(eff) = 1.5 mu(B)(S approximate to 1/2). In contrast, a deoxydization down to x approximate to 6.6 induces a larger increase of the local moment value for Zn than for Ni. The depression of T-c is 2 to 3 times larger than for x approximate to 1, in both cases. These results support the idea that Zn affects the local magnetic order of nearby Cu on the scale of the magnetic Cu correlation length, which varies with x. On the contrary, the magnetism associated with the Ni2+ ion seems to be more local.