Low Damage Smoothing of Magnetic Materials using Oblique Irradiation of Gas Cluster Ion Beam
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Low Damage Smoothing of Magnetic Materials using Oblique Irradiation of Gas Cluster Ion Beam Shigeru Kakuta1, 3, Shinji Sasaki1, 3, Kenji Furusawa1, 3, Toshio Seki3, Takaaki Aoki3 and Jiro Matsuo2 1 Storage Technology Research Center, Hitachi, Ltd., 292 Yoshida-cho Totsuka-ku Yokohama, 244-0817, Japan 2 Quantum Science and Engineering Center, Kyoto Univ., Gokasyo Uji, 611-0011, Japan 3 Collaborative Research Center of Nano-scale Machining with Advanced Quantum Beam Technology, Japan ABSTRACT Oblique irradiation using a gas cluster ion beam (GCIB) has been studied in order to achieve low-damage smoothing of magnetic materials. We investigated how the surface morphology and surface roughness depended on the angle of incidence. Quite smooth surfaces could be obtained using both normal and grazing-incidence irradiation. At incident angles larger than 45˚, periodic ripples were formed. The orientation of the ripples changed from perpendicular to parallel with respect to the GCIB when the incident angle exceeded a critical value. Surface roughening resulting from the formation of ripples was observed at incident angles between 45˚ and 65˚. Fluctuations in the Ni/Fe component ratio and the intermixing of oxygen from the native oxide were evaluated. As the angle of incidence increased, both the thickness of the layer in which the component ratio was fluctuating and the depth of oxygen intermixing decreased. As a result, it was determined that low-damage smoothing of magnetic materials could be performed by using grazing-incidence irradiation from a GCIB. INTRODUCTION As the areal density of hard disk drives (HDDs) has increased, the flying height of the magnetic recording head over the disk has been decreasing. In order to further reduce the flying height, a surface smoothing technology that induces minimal damage in magnetic materials is extremely important, since surface roughness and damage to surface layers decreases the sensitivity of the sensor. The goal of this study is to develop a method that enables damage-free and ultra-smooth surface processing of magnetic recording heads, which is a requirement for those wishing to manufacture such storage systems with high reliability. Traditionally, surface smoothing of magnetic recording heads has been performed by a polishing process using diamond abrasives. However, this polishing process is, by nature, liable to leave scratches on the surface, and these can cause severe damage to magnetic recording heads. Recently, a gas cluster ion beam (GCIB) technology has been proposed as a new surface smoothing technique [1]. Gas cluster ions are aggregations of a few to several thousands of atoms or molecules. Extremely low energy ion irradiation can easily be achieved, since atoms or molecules consisting of cluster ions share their kinetic energy. Therefore, GCIB technology can be utilized to obtain a low-damage and ultra-smooth surface finish on magnetic materials.
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EXPERIMENTAL Figure 1 shows a schematic diagram of the GCIB apparatus. The GCIB was generated by ad
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