Magneto-Optical Properties of Amorphous Magnetic Thin Films

Tb-Fe amorphous films were found to be very promising materials for magneto-optical recording1), since they have (1) a large perpendicular magnetic anisotropy which ensures a recording density as high as 109 bits/cm2, (2) a Curie point TC of about 140°C which is reasonable from the view points of high thermal stability of written bits and of low laser power for Curie point writing, and (3) a very low medium noise due to the amorphous state. These films, however, have a magneto-optical Kerr rotation θk of only 0.25 degrees at room temperature, which is smaller than that for Gd-Fe and Gd-Co films. Therefore, many efforts have been made in Japan in order to increase θk of Tb-Fe films. Good results are obtained by replacing a part of Tb and/or Fe by Gd and/or Co. The maximum θk found so far is about 0.5 deg for quaternary films with a composition around (Gd0.5Td0.5)0.2(Fe0.7Co0.3)0.8, where θk is measured from the sub-strate (glass) side using light of λ=633 nm wave length.