Nature of the magnetic order of Gd in superconducting and nonsuperconducting GdBa2Cu3O7- delta.

Abstract

Low-temperature ordered states of the Gd moments in ${\mathrm{GdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ have been investigated by the use of the Luttinger-Tisza method. It is shown that by taking into account the effect of the crystal field on the Gd ions, the gross features of the observed ordering can be understood if the dipole-dipole interaction is assumed to be predominant. However, the inclusion of weak superexchange interaction apprears necessary. It is shown that an antiferromagnetic state with the Gd moments lying along the c axis can be stabilized if a certain condition is met for the g tensor of the Gd ions.