MAGNETIC-INTERACTIONS IN YBBA2CU3OX (X=7.0, 6.0) FROM YB-170(3+) MOSSBAUER MEASUREMENTS

The magnetic interactions in superconducting YbBa2Cu3O7 and non-superc onducting YbBa2Cu3O6 have been examined using Yb-170(3+) Mossbauer spe ctroscopy on grain-oriented samples. In YbBa2Cu3O7 where the Yb3+ subl attice orders at 0.35 K and the saturated magnetic moment is 1.75 mu(B ), the saturated molecular field is 0.4 T and it is directed perpendic ular to the c-axis. In YbBa2Cu3O6, where the Cu(2) sublattice also ord ers, the average saturated molecular field on Yb3+ is 0.2 T. It is dis ordered in direction and contains contributions from both the Yb3+ and the Cu(2)(2+) sublattices. The presence of a Cu(2)(2+) derived molecu lar field shows the Yb3+ ions are not at a centre of magnetic inversio n symmetry relative to the ordered Cu(2)(2+) moments.