INFLUENCE OF THE LATTICE-PARAMETERS ON THE MAGNETIC-PROPERTIES OF THEWEAK FERROMAGNETIC RARE-EARTH CUPRATES (R,R')(2)CUO4

A systematic study of the magnetic properties of the T'-phase rare-ear th cuprates (R,R')(2)CuO4 (R,R' = rare earths) is presented. Attention is focused in those compounds with lattice parameters a = d(Cu-O(1)-C u) smaller than 3.91 Angstrom, where weak ferromagnetism (WF) is first detected. It is observed that. although a diminution of the Cu-O(1)-C u distance enhances monotonically the local WF component, it does not happen the same for the macroscopic WF characteristics, which reach a maximum at a(1) = 3.885 Angstrom, decreasing thereafter. The same poin t marks the onset for coercive fields in hi vers us H loops. The resul ts are interpreted in a framework which considers arrangements of oxyg en distortions within the CuO(1)(2) planes, origin of WF, as creating a non-unique WF component in those planes. (C) 1997 Elsevier Science B .V. All rights reserved.