Effect of crystal symmetry on O '-phase weak ferromagnetism

Correlation between copper weak-ferromagnetic/canted-antiferromagnetic (WF/ CAF) order and structural symmetry of the Gd2-xRxCuO4 (R = Eu and Tb) syste ms is reported. With smaller rare earth ions, lattice mismatch between (Gd, R)(2)O-2 and CuO2 layers results in a small oxygen distortion in square Cu O2 plane. The distortion lowers the crystal symmetry from tetragonal T'- to an orthorhombic O'-phase. The weak ferromagnetism is a direct result of su ch a non-180 degrees alpha(Cu-O-Cu) coupling with CAF alignment and a WF sa turation moment m(s)(Cu2+) = mu(Cu2+) sin theta, with canting angle theta = (pi - alpha)/2. Magnetic and crystallographic data indicate that the magne tic moment m(T) and the canting angle theta decrease (increase) with larger (smaller) ion doping. (C) 2000 Elsevier Science B.V. All rights reserved.