Low-temperature ordered states ofRBa2Cu3O7−δ(R=rare earth) due to dipole-dipole and exchange interactions

Low-temperature ordered states of the various R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (R=rare earth) compounds have been calculated using the Luttinger-Tisza method, taking into account both the dipole-dipole and exchange interactions among the rare-earth ions. It is found that dipolar interactions alone can explain all the observed orderings of these materials. As for the Ho compound below 0.1 K, its observed ordering can also be explained with appropriate values of exchange interactions and/or an appropriate ${\mathit{g}}_{\mathrm{\parallel }}$/${\mathit{g}}_{\mathrm{\perp }}$ ratio.