Conversion-electron Mössbauer spectroscopy studies in amorphous tb-fe films

We have carried out conversion-electron Mössbauer (CEM) spectroscopy studies in rf-sputtered amorphous ${\mathrm{Tb}}_x{\mathrm{Fe}}_{100-x}$ films with $x=20, 24, \mathrm{and} 25$. The samples present a well-defined uniaxial anisotropy $K_u$ on the order of 1 × ${10}^6$ erg ${\mathrm{cm}}^{-3\mathrm{}}$, and the magnetization is well aligned along the film normal as shown by rectangular hysteresis loops (both magnetization and polar Kerr). However, the analysis of the CEM spectra shows that the Fe moments deviate strongly from the film normal. The semiangle of the cone is calculated to be 35° for $x=20\mathrm{}$ and 25° for $x=24\mathrm{} \mathrm{and} 25$. Exchange coupling between Fe and Tb moments and the well-known tendency in some amorphous alloys to form antiferromagnetic coupling between Fe moments are offered as possible explanations for this result. Finally, the average hyperfine field for Fe is found to be 165 kOe with the high-field peak centered at around 190 kOe.