Magnetic and Conversion Electron Mössbauer Spectral Study of Amorphous Thin Films of DyₓFe₁₀₀₋ₓ and Dy₂₀Fe_80-yCo_y

Amorphous thin films of Dy _x Fe _100-x and Dy ₂₀ Fe _80-y Co _y , with various x and y values and of ~40 nm thickness, have been prepared by sputtering on polyimide films. Their magnetization curves and the Mössbauer spectra indicate that at 295 K the iron moments are preferentially oriented parallel to the film in Dy ₂ Fe ₉₈ and that Dy ₆ Fe ₉₄ is paramagnetic. The Dy _x Fe _100-x thin films, where x is 17, 20, 24, 29, 32, 35, and 37, show perpendicular magnetic anisotropies and moderate coercive fields of at most 150 kA/m, whereas the Dy ₂₀ Fe _80-y Co _y thin films, where y is 8, 13, 16, and 20, thin films show stronger perpendicular anisotropies and larger coercive fields of ~400 kA/m. The introduction of cobalt into the amorphous thin films increases their coercive field and the perpendicular magnetic anisotropy. The Mössbauer spectra of the Dy _x Fe _100-x and Dy ₂₀ Fe _80-y Co _y amorphous thin films consist of broadened sextets which have been analyzed with a distribution of hyperfine fields by assuming that the iron moments are oriented perpendicular to the plane of the film. Detailed fits of the Mössbauer spectrum of Dy ₂₀ Fe ₈₀ indicate that the cone angle of the iron magnetic moments cannot be determined with accuracy. The average hyperfine fields in the Dy _x Fe _100-x amorphous thin films are smaller than those in the crystalline dysprosium-iron intermetallic compounds. The average hyperfine field increases from ~140 kOe in the Dy _x Fe _100-x films to ~220 kOe in the Dy ₂₀ Fe _80-y Co _y films, an increase which is in agreement with the increase in the saturation magnetization. The x dependence of the isomer shift indicates that there is strong dysprosium-iron bonding, whereas the y dependence of the isomer shift reveals an enhancement of the d-electron localization. From earlier x-ray magnetic circular dichroism results and the Mössbauer spectral results presented herein, iron magnetic moments of 0.87 or 0.67 µ _B , corresponding to 2.9 or 2.8 holes in the iron 3d band, have been obtained for the Dy _x Fe _100-x amorphous thin films with x greater or smaller than 27, respectively.