${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer investigations on the ${\mathrm{Dy}}_{0.73}$${\mathrm{Tb}}_{0.27}$${\mathrm{Fe}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$ and ${\mathrm{Ho}}_{0.85}$${\mathrm{Tb}}_{0.15}$${\mathrm{Fe}}_{2\mathrm{-}\mathit{y}}$${\mathrm{Ni}}_{\mathit{y}}$ systems

${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer studies were carried out on the ${\mathrm{Dy}}_{0.73}$${\mathrm{Tb}}_{0.27}$${\mathrm{Fe}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$ and ${\mathrm{Ho}}_{0.85}$${\mathrm{Tb}}_{0.15}$${\mathrm{Fe}}_{2\mathrm{-}\mathit{y}}$${\mathrm{Ni}}_{\mathit{y}}$ systems (x=y=0, 0.5,1.0,1.5). The spectra were recorded in the temperature range 18–675 K. The variation of hyperfine field at 18 K with Ni concentration showed a maximum at x=0.5 as well as y=0.5 which has been attributed to the narrowing of the 3d bands by the substitution of Ni. The Curie temperatures were estimated for all values of x and y from the temperature dependence of the average hyperfine field, which followed the Brillouin function. A monotonic decrease in Curie temperature with Ni concentration is observed and this is attributed to the decrease in net transition-metal sublattice moment. From the Mössbauer spectra, spin reorientation transitions have been observed for compositions with x=y=0, 0.5, and 1.0.