Light Rare Earth-Transition Metal Amorphous Films with Huge Perpendicular Magnetic Anisotropy. Magneto-optical Recording Media

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The aim of the present study is to investigate the magnetic and magneto-optical properties of light rare earth-transition metal amorphous films fabricated by r.f. sputtering, and also to obtain information for magneto-optical storage media.The followings may be summarized as the results;i) The vertically magnetized films with huge perpendicular magnetic anisotropy of the order of 10^7erg/cc at room temperature have been successfully obtained for (Nd,Pr)_x (Fe,Co)100_<-x> alloys with 10<less than or similar>x<less than or similar>50, when they were deposited onto glass substrates heated at about 150 to 280゜C.ii) The anisotropy constant K_u at 300K is maximum at x=40 for both Nd and Pr alloys.iii) The value of K_u increases with decreasing temperature and tends to decrease for temperatures less than about 70K. This result is consistent with those obtained form the magnetization curves in a high field of 150KOe.This can be closely related to the anisotropy dispersion.iv) The magneto-optical Kerr rotation angle O_k at 800 nm for these amorphous films is about 0.4-0.5゜, which is larger than that for those with heavy rare earths. The O_k increases with decreasing wavelength, which is in contrast to that for heavy rare earths. The addition of Tb with about 10 at% much improves both the magnetic and magneto-optical characteristics.In view of these results, light rare earth-transition metal amorphous films can be considered as potential candidates for magneto-optical recording storage media with better performance than those with heavy rare earths.