Magnetic interaction between rare-earth moments in high-temperature superconductorsRBa2Cu3O7−x

It is shown on the basis of a simple model that a modified Ruderman-Kittel-Kasuya-Yosida interaction involving electrons at energies away from the Fermi level can stabilize the three-dimensional magnetic order of the rare-earth moments in R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$, where R=Gd and possibly Sm, Dy. The interaction favors antiferromagnetism.