New Microstructural Model for Sputtered Co-Cr Magnetic Thin Films
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NEW MICROSTRUCTURAL MODEL FOR SPUTTERED Co-Cr MAGNETIC THIN FILMS
YOSHIRO NIIMURA AND MASAHIKO NAOE Tokyo Institute of Technology, Dept. of Electrical & Electronic Engineering 2-12-1, Oh-okayama, Meguro-ku, Tokyo 152, JAPAN
ABSTRACT Rapidly solidified Co-Cr thin films with a perpedicular magnetic anisotropy have been extensively investigated as one of the most promising media for perpendicular magnetic recording system. Most of these films used to be prepared by conventional RF diode sputtering and vacuum evaporation methods. We have developed the Facing Targets Sputtering apparatus which is able to deposite the magnetic thin films without the bombardment by high energy particles to the substrate along with the capabilities to deposit films under wide range of argon gas pressure at high deposition rate. It has been found that the texture and crystallographic structure of the sputtered films are primarily dependent on the argon gas pressure and the films prepared by the Facing Targets Sputtering exhibit quite different properties from the films prepared by conventional methods. The films deposited in the argon gas at the low pressure on the plasma-free substrate using the Facing Targets Sputtering are composed of the fine polyhedral grains packed densely from the initial growth layer to the surface layer of the film. They show exellent c-axis orientation of hcp crystallites, smoother surface textures and the superior perpendicular magnetic anisotropy as compared with the films composed of so-called columnar grains deposited in the argon gas at the higher pressures using the conventional RF diode sputtering. These results imply that the sputtering apparatus which is capable to deposit Co-Cr films in the argon gas at relatively lcw pressure is indispensable for the preparation of superior perpendicular magnetic recording media. Therefore, the Facing Targets Sputtering apparatus seems to be quite suitable for this purpose. Further, we have proposed a new micro structural model with fine polyhedral grains obtained by our sputtering method, because this model will have the ideal structural characteristics for ultra high density perpendicular magnetic recording.
INTRODUCTION In perpendicular magnetic recording system, the demagnetizing field approaches to zero with the shorter wave length and theoretically the ultimate linear recording density is limited only by the width of the 180° magnetic wall[l]. Rapidly solidified Co-Cr thin films have been considered to be one of tne most suitable media for this recording system. The perpendicular magnetic anisotropy of sputtered Co-Cr films have been supposed to be caused by the crystalline anisotropy with a perpendicular c-axis orientation of hcp crystallites in the filmt[2]. So-called columnar structures grown perpendicularly to the substrate plane have been observed among most of the films prepared by the RF diode sputtering and vacuum evaporation 3]. In general, it has been believed that these columnar structures are related to the perpendicular magnetic anisotropy of Co-Cr
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