2-D AND 3-D MAGNETIC-ORDERING OF ER IN ERBA2CU3OX(6 LESS-THAN-OR-EQUAL TO 7)

Results of neutron-diffraction experiments on powder samples of ErBa2Cu3Ox with oxygen content x = 6.87, 6.64, 6.53, 6.40, 6.20 and 6.11 are presented. The superconducting compounds with x = 6.87, 6.64 and 6.53 exhibit three-dimensional (3-D) antiferromagnetic ordering of the Er moments with wave vector km = ( 1 2, 0, 1 2) and μ{norm of matrix}b below the Néel temperatures TN = 585(5), 530(5) and 460(5) mK, respectively. Their critical behavior near TN is 2-D in character, and short-range magnetic correlations can be measured up to about 1 K. In contrast, in the oxygen-deficient compounds with x = 6.40, 6.20 and 6.11 only 2-D antiferromagnetic correlations with ( 1 2, 0) grow at low T which saturate below about 200 mK. The suppression of 3-D antiferromagnetic order of Er upon oxygen removal coincides with the suppression of superconductivity, indicating the strong depression of the coupling between adjacent Cu(2)-O planes via Cu(1)-O "chains" near x = 6.45. © 1990.