Development of FePt perpendicular magnetic recording media for thermally-assisted magnetic recording (TAMR)
National Institute for Materials Science
Dr. Kazuhiro Hono has succeeded in fabricating perpendicular magnetic films with extremely high coercivity (37 kOe), in which the nano-particles of an iron-platinum (FePt) alloy are densely dispersed with a very small size distribution.
Abstract
- Dr. Kazuhiro Hono, Managing Director of the Magnetic Materials Center at the National Institute for Materials Science (President: Sukekatsu Ushioda), together with Dr. Yukiko Takahashi, Senior Researcher, and Dr. Li Zhang, Postdoctoral Fellow have succeeded in fabricating perpendicular magnetic films with extremely high coercivity (37 kOe), in which the nano-particles of an iron-platinum (FePt) alloy are densely dispersed with a very small size distribution. Using these films, Dr. Barry C. Stipe and Dr. Michael Grobis at the San Jose Research Center of Hitachi Global Storage Technologies (HGST) have shown that thermally assisted magnetic recording with an areal density of 450 Gbit/in2 is possible. This value is comparable to the highest area densities achieved with the conventional perpendicular magnetic recording method used in current hard disk drives (HDD) and is the highest for thermally assisted magnetic recording (TAMR). This collaborative research has demonstrated the feasibility of high density TAMR on high coercivity FePt based perpendicular magnetic films, which has been proposed as one of thepromising next-generation ultra-high density magnetic recording system.
- The highest recording density of commercial HDDs is about 550 Gbit/in2. Since higher recording densities can reduce the size of HDDs and their power consumptions, various technological improvements have been made on the existing perpendicular magnetic recording method since its first commercialization in 2005. However, a recording density of about 1 Tbit/in2 is considered to be the limit with the existing method, and a transition to a new magnetic recording method is necessary to achieve a dramatic increase to the 4 Tbit/in2 level in the future. Thermally assisted magnetic recording (TAMR) has been proposed as one promising method to achieve higher recording densities. Although the development of TAMR head technology has been carried out by Hitachi Global Storage Technologies, a recording medium suitable for demonstrating high density TAMR recording has not been available. A suitable medium should be made of 4-6 nm ferromagnetic particles with minimal size distribution and a nearly perfect alignment of crystal orientations.
- The most critical issue for developing a TAMR recording medium has been how to achieve a chemically ordered structure from the FePt alloy nano-particles while maintaining a uniform size of 4-6 nm with the easy axis for magnetization perpendicular to the film plane. Since magnetically written information must be stored for over ten years, a ferromagnetic material with high magnetocrystalline anisotropy must be used so that the magnetization of nano-particles cannot be reversed by thermal energy. A chemically ordered FePt alloy in which the position of Fe and Pt atoms are specified in the face cubic centered structure satisfies such a requirement. However, the fabrication of FePt perpendicular magnetic films consisting of densely packed nano-particles with a small size distribution has been a challenge.
- In this collaborative research, the NIMS team succeeded in fabricating a nanostructure suitable for TAMR media using an FePt ordered alloy (particle size: 6 nm), and the HGST team showed the feasibility of the highest TAMR recording density using the head developed at HGST. The key to success was to co-sputter carbon with Fe and Pt. To achieve the chemically ordered structure, a small amount of Ag was added to the FePt alloy. Although the media was processed using a laboratory scale magnetron sputtering apparatus, this work has proved the feasibility of high density TAMR using the chemically ordered FePt alloy thin films.
- The results of this study will be presented at the 21st Magnetic Recording Conference (TRMC2010) to be held at the University of California, San Diego on August 16-18. The HGST part of this research was carried out as part of the NEDO project on the Development of Nanobit Technology for Ultra-High Density Magnetic Recording Project (Green IT Project).
Fig. 1 (Left) Transmission electron microscopy of the nano-particle-dispersed perpendicular magnetic film and (right) patterns of recording bits by the TAMR head.
