Magnetic Interactions In YbBa Cu O (x = 7.0, 6.0) From Yb Mössbauer Measurements

(Received 19 October 1994, received in final form 19 December 1994, accepted 19 December 1994)

Abstract
The magnetic interactions in superconducting YbBa ₂Cu ₃O ₇ and non-superconducting YbBa ₂Cu ₃O ₆ have been examined using ¹⁷⁰Yb ³⁺ Mössbauer spectroscopy on grain-oriented samples. In YbBa ₂Cu ₃O ₇ where the Yb ³⁺ sublattice orders at 0.35 K and the saturated magnetic moment is 1.75  , the saturated molecular field is 0.4 T and it is directed perpendicular to the c-axis. In YbBa ₂Cu ₃O ₆, where the Cu(2) sublattice also orders, the average saturated molecular field on Yb ³⁺ is 0.2 T. It is disordered in direction and contains contributions from both the Yb ³⁺ and the Cu(2) ²⁺ sublattices. The presence of a Cu(2) ²⁺ derived molecular field shows the Yb ³⁺ ions are not at a center of magnetic inversion symmetry relative to the ordered Cu(2) ²⁺ moments.