Magnetic and conversion electron Mossbauer spectral study of amorphous thin films of DyxFe100-x and Dy20Fe80-yCoy

Amorphous thin films of DyxFe100-x and Dy20Fe80-yCoy, with various x and y values and of similar to 40 nm thickness, have been prepared by sputtering on polyimide films. Their magnetization curves and the Mossbauer spectra in dicate that at 295 K the iron moments are preferentially oriented parallel to the film in Dy2Fe98 and that Dy6Fe94 is paramagnetic. The DyxFe100-x thi n films, where x is 17, 20, 24, 29, 32, 35, and 37, show perpendicular magn etic anisotropies and moderate coercive fields of at most 150 kA/m, whereas the Dy20Fe80-yCoy thin films, where y is 8, 13, 16, and 20, thin films sho w stronger perpendicular anisotropies and larger coercive fields of similar to 400 kA/m. The introduction of cobalt into the amorphous thin films incr eases their coercive field and the perpendicular magnetic anisotropy. The M ossbauer spectra of the DyxFe100-x and Dy20Fe80-yCoy amorphous thin films c onsist of broadened sextets which have been analyzed with a distribution of hyperfine fields by assuming that the iron moments are oriented perpendicu lar to the plane of the film. Detailed fits of the Mossbauer spectrum of Dy 20Fe80 indicate that the cone angle of the iron magnetic moments cannot be determined with accuracy. The average hyperfine fields in the DyxFe100-x am orphous thin films are smaller than those in the crystalline dysprosium-iro n intermetallic compounds. The average hyperfine field increases from simil ar to 140 kOe in the DyxFe100-x films to similar to 220 kOe in the Dy20Fe80 -yCoy films, an increase which is in agreement with the increase in the sat uration magnetization. The x dependence of the isomer shift indicates that there is strong dysprosium-iron bonding, whereas the y dependence of the is omer shift reveals an enhancement of the d-electron localization. From earl ier x-ray magnetic circular dichroism results and the Mossbauer spectral re sults presented herein, iron magnetic moments of 0.87 or 0.67 mu (B), corre sponding to 2.9 or 2.8 holes in the iron 3d band, have been obtained for th e DyxFe100-x amorphous thin films with x greater or smaller than 27, respec tively. (C) 2001 American Institute of Physics.