Weak ferromagnetism in distorted T '-phase cuprates

Copper weak ferromagnetic or canted-antiferromagnetic order in distorted T ' -phase (orthorhombic O ' -phase) Gd2CuO4 and related Gd2-xRxCuO4 (R = rar e earth, Bi, or Bi/Ce) cuprates is reported. The weak ferromagnetism is the result of the small oxygen distortion in otherwise square CuO2 plane. Powd er X-ray Rietveld refinement analysis shows that the oxygen distortion angl e alpha (Cu-O-Cu) is directly related to the ionic size in Gd2CuO4-type cup rates. The correlation between the crystal symmetry, antiferromagnetism and weak ferromagnetism in T ' -phase cuprates is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.