Antiferromagnetism and superconductivity in the presence of Ho moments inHoBa2Cu3Ox

Using the zero-field muon-spin-relaxation technique, we have observed a long-range magnetic ordering of Cu moments in a tetragonal insulator $\mathrm{Ho}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_x$ with $x\sim 6.2$. The magnitude of the internal field and its temperature dependence were found to be similar to those of Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.2}$. At temperatures below 3 K, freezing of the Ho magnetic moment was observed as in a 90-K superconductor Ho${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.9}$. These results imply that the effect of the magnetic rare-earth ${\mathrm{Ho}}^{3+}$ ions on the antiferromagnetism of the Cu ions is small, suggesting a relatively weak interaction between the Ho ions and the electrons in two-dimensional Cu-O planes.