MAGNETIC-PROPERTIES OF YBA2(CU0.94ZN0.06)3OX (X=6.0 TO 7.0) STUDIED BY MOSSBAUER-SPECTROSCOPY ON SUBSTITUTED YB-170(3+)

We have used Yb-170 Mossbauer spectroscopy on Yb3+ diluted at the Y3+ sites to study YBa2(Cu0.94Zn0.06)3Ox. In the fully oxygenated sample, the presence of Zn2+ introduces a Korringa dependence of the Yb3+ paramagnetic relaxation mte, indicating an increase in the density of states at the Fermi level, which is visible both above and below T(c) (32 K). A molecular field coming from the Cu (2) is observed on all the Yb3+ probes in non-superconducting samples with x = 6.0 and 6.5 showing that at these oxygen levels, all the Cu(2)'s are locally magnetically correlated. For x = 6.88 (T(c) = 13 K), only some of the probes experience molecular fields suggesting there is phase separation between local magnetic and local non-magnetic superconducting regions. For x = 7.0, none of the Cu (2)'s are magnetically correlated. The general features of the oxygen-level dependence of the local magnetic properties are similar in the zinc-substituted and in the zinc-free samples, but magnetic ordering persists to higher oxygen levels when Zn2+ is present.