SINGLE ION PROPERTIES OF ER3+ IN YBA2CU3OX AND ER3+ ORDERING ARRANGEMENT IN ERBA2CU3OX (X-CONGRUENT-TO-7.0 AND 6.0) STUDIED BY ER-166 MOSSBAUER-SPECTROSCOPY

From Mossbauer measurements on Er-166(3+) diluted into YBa2Cu3Ox with x congruent-to 7.0 (superconducting) we obtain the hyperfine tensor and the g tensor of the Er3+ crystal field ground doublet: A(ab) = 1610, A(c) = 935 MHz, g(ab) = 8.0, g(c) = 4.5. When the Er3+ is diluted into a sample with x congruent-to 6.0 (non-superconducting) we find that it now experiences a molecular field of approximately 200 G attributed to a net exchange coupling with its magnetically ordered Cu(2) neighbours. The nonzero value for this field shows that the arrangement of the Cu(2) moments does not have inversion symmetry about the Er3+ ion. From Er-166(3+) measurements at 0.05 K on grain oriented ErBa2Cu3Ox (x congruent-to 7.0 and 6.0) we confirm that for x congruent-to 7.0 the ordered Er3+ magnetic moments are aligned close to directions perpendicular to the c-axis and we show that for x congruent-to 6.0 the additional Cu(2)-derived molecular field does not modify this alignment. We suggest however, that the appearance of this molecular field as the oxygen level is lowered below x congruent-to 6.4 could be a factor contributing to the known x dependence of the breakdown of the 3-dimensional correlations within the Er3+ sublattice. For the grain oriented samples we describe an X-ray diffraction analysis procedure which gives a comprehensive assessment of the quality of the grain orientation.