Mössbauer Effect in ${\mathrm{Dy}}^{161}$ in Dy${\mathrm{Co}}_2$ and Dy${\mathrm{Ni}}_2$

The recoilless absorption spectra of the 26-keV $\gamma$ rays from ${\mathrm{Dy}}^{161m}$ in ${\mathrm{Dy}}^{161}$ situated in Dy${\mathrm{Ni}}_2$ and in Dy${\mathrm{Co}}_2$ were measured at various temperatures. A value of (-866±30) Mc/sec was found for the magnetic hyperfine constant ($g_0{\mu }_n{\mathrm{H}}_{\mathrm{eff}}$) of the ground state of ${\mathrm{Dy}}^{161}$ in Dy${\mathrm{Co}}_2$ at 4°K. This value is about 4% higher than the free-ion value calculated for the ${\mathrm{Dy}}_{+}^3$ ions in the fully magnetized state ($J_z=J$) from data on electron spin resonance in dilute salts. For ${\mathrm{Dy}}^{161}$ in Dy${\mathrm{Ni}}_2$, a value of (-818±30) Mc/sec was found for $g_0{\mu }_n{\mathrm{H}}_{\mathrm{eff}}$ at 4°K. This value corresponds to an ionic magnetic moment of ${(9.8\mathrm{}\pm 0.3)}_{\mathrm{\mu }\mathit{B}}$, which is higher than that obtained by magnetic measurements (${7.1}_{\mathrm{\mu }\mathit{B}}$) and indicates probably that the Ni sublattice contributes to the total magnetization by an antiferromagnetic coupling. The isomeric shifts of Dy metal, Dy${\mathrm{Fe}}_2$, Dy${\mathrm{Ni}}_2$, and Dy${\mathrm{Co}}_2$ absorbers were found to be the same within the experimental errors (1.9±0.2 mm/sec relative to ${\mathrm{Dy}}_2$ ${\mathrm{O}}_3$).