51. Magnetic Information-Storage Materials

The purpose of this chapter to review the current status of magnetic materials used in data storage. The emphasis is on magnetic materials used in disk drives and in the emerging technology of the magnetic random-access memory (MRAM). A wide range of magnetic materials is essential for the advance of magnetic recording both for magnetic recording heads and media, including high-magnetization soft-magnetic materials for write heads, new antiferromagnetic alloys with high blocking temperatures and low susceptibility to corrosion for pinning films in giant-magnetoresistive (GMR) sensors and new ferromagnetic alloys with large values of giant magnetoresistance. For magnetic recording media, the advances are in high-magnetization metal alloys with large values of the switching coercivity. A significant limitation to magnetic recording is found to be the superparamagnetic effect and new advances in multilayer ferromagnetic films to reduce the impact of the effect, but also to allow high-density recording have been developed.

Perpendicular recording as compared to longitudinal recording is reviewed and it is shown that this technology will be the dominant recording technology in the future. The MRAM device uses some of the same materials as used in the GMR sensor, but the key technology is the magnetic tunneling junction in which soft-magnetic films are coupled by a thin insulating film and conduction is by quantum-mechanical tunneling. The status of the MRAM technology and some of the key problems are reviewed.