Study on Bi-Substituted Garnet Films with Strong Magneto-Optical Activity and High Corrosion Resistance for Magneto-Optical Disc.

点击翻译按钮获取中文摘要

Highly Bi-substituted garnet film is a promising medium for magnetooptical (M-O) memory because of its strong M-O activity and high corrosion resistance. We have investigated optimum conditions to get the Bi-substituted garnet film with (1) a large amount of Bi and (2) good homogeneity in quality. In particular, (2) is an important factor on applying a polycrystalline film to M-O medium; inhomogeneity causes so-called media noise, responsible for light scatter at grain boundary and irregular shape in thermomagnetically written bit.The films were prepared on glass substrates by rf-diode sputtering, which were crystallized by post-deposition annealing or in situ during sputterdeposition. For (1), we have successfully got the films cotaining a large amount of Bi up to 2.9 at a relatively low temperature of 520゜C, For (2) we have proposed measures to reduce media noise. It is composed of two procedures; one is to make the grain boundary optically undiscernible, the other to prevent the written bit domain from diffusing in shape. We could attain the former by sputtering in pure Ar or Ar+H_2 gases, instead of Ar+O_2gas. The sputtering in reducing atmosphere distributes crystal imperfections, such as defects and dislocations, in the grains homogeneously. We could improve the latter by adding a small amount of W (<1.2 at.%) which increases domain wall coercivity inside the grains.We have further investigated the origin of magnetic anisotropy of Co-substituted garnet film suitable to M-O media. The films were epitaxially in situ grown by rf sputtering. The substitution of Co was found to markedly enhance the stress-induced magnetic anisotropy because of large magnetostriction due to octahedrally coordinated Co^<2+>.