Effect of Co substitution for Fe on magnetic and magnetostrictive properties in Sm0.88Dy0.12(Fe1-xCox)2 compounds.

Abstract

Measurements of x-ray diffraction, magnetization, magnetostriction, and M\"ossbauer effect were made on a series of ${\mathrm{Sm}}_{0.88}$${\mathrm{Dy}}_{0.12}$(${\mathrm{Fe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${)}_{2}$ polycrystalline samples (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0). It was found that the system has the cubic ${\mathrm{MgCu}}_{2}$ structure over the whole range and the lattice constant decreases with increasing x. Initially, replacement of Fe results in a slight increase in both the saturation magnetization ${\mathit{M}}_{\mathit{S}}$ and Curie temperature ${\mathit{T}}_{\mathit{C}}$, while further substitution causes a decrease in ${\mathit{M}}_{\mathit{S}}$ and ${\mathit{T}}_{\mathit{C}}$ with x. Results of M\"ossbauer effect study at room temperature show that the easy axes of magnetization remain in the [111] direction for all the samples. The concentration dependence of the average hyperfine field, ${\mathit{H}}_{\mathrm{hf}}$ shows a similar trend as that of ${\mathit{M}}_{\mathit{S}}$ and ${\mathit{T}}_{\mathit{C}}$, exhibiting a maximum at x=0.4 due to the increase of the magnetic moment of the Fe atom caused by the adding of cobalt. The spin-orientation diagram in ${\mathrm{Sm}}_{0.88}$${\mathrm{Dy}}_{0.12}$(${\mathrm{Fe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$${)}_{2}$ was determined by measurements of M\"ossbauer effect and magnetization, showing that Co substitution lowers the spin-reorientation temperature. It was also found from x-ray measurement that the spontaneous magnetostriction ${\ensuremath{\lambda}}_{111}$ increased due to Co substitution, while monotonic decrease of the saturation magnetostriction ${\ensuremath{\lambda}}_{\mathit{s}}$ with Co content was observed and can be attributed to the increase of ${\ensuremath{\lambda}}_{100}$ with opposite sign to ${\ensuremath{\lambda}}_{111}$, which may be caused by the filling of the d band due to Co substitution. \textcopyright{} 1996 The American Physical Society.