Magnetic behavior of $\mathrm{Dy}{\left({\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x}\right)}_2$ and $\mathrm{Ho}{\left({\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x}\right)}_2$ compounds

The results of magnetic and Mössbauer-effect studies on $\mathrm{Dy}{\left({\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x}\right)}_2$ and $\mathrm{Ho}{\left({\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x}\right)}_2$ compounds between 4.2 and 1300 K are reported. The ferrimagnetic structure evidenced in the ordered range for $x>\mathrm{}0.1\mathrm{}$ is confirmed by the measurements above the Curie points. The thermal variation of the reciprocal susceptibilities obeys a Néel-type law. Using the molecular-field model, we deduce the magnitude of the magnetic interactions in the compounds. The effective iron moments and ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ hyperfine-field values decrease by increasing the nickel content. The deviation of these values from the simple dilution behavior are attributed to the variation of magnetic interactions in the system. Finally, we analyze the magnetic behavior of iron in the rare-earth compounds.