Magnetic information-storage materials

Abstract

The purpose of this chapter is 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 magnetic random-access memory (MRAMmagneticrandom-access memory (MRAM)) technology. A wide range of magnetic materials is essential for the advance of magnetic recording both for heads and media, including high-magnetization soft-magnetic materials for write heads, antiferromagnetic alloys with high blocking temperatures and low corrosion propensity for pinning films in giant-magnetoresistive (GMRgiant magnetoresistance (GMR)) sensors and ferromagnetic alloys with large values of giant magnetoresistance. For magnetic recording media, the advances are in high-magnetization metal alloys with large values of switching coercivity. A significant limitation to magnetic recording is found to be the superparamagnetic effect and advances have been made 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 soon be replaced first by heat-assisted and later by bit-patterned magnetic recording in order to progress steadily toward areal densities well above 1012 bit ∕ in2 (1 Tbit ∕ in2 or 1000 Gbit ∕ in2). While an MRAM cell exploits some of the materials used in GMR sensors, its basic component is the magnetic tunneling junction in which magnetic films are coupled by a thin insulating film and conduction occurs by quantum mechanical tunneling. The status of MRAM cell technology and some closely related key problems are reviewed.