Nanofilms in Giant Magnetoresistance Heads
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The magnetic hard disk drive has become the foremost data storage device for computer applications based on cost, capacity, performance, and miniature form factor. Although it is a mechanical, rotating disk storage device, power requirements are minimal, usually a few watts; reliability over a wide range of operating environments, from below 0°C to well over 100°C, is excellent; and costs are less than $0.01 per megabyte. Throughout its 46-year history, hard disk drives have been the recipient of significant technological innovations which have added to the usefulness of this device, and data density on the disk surface, areal density, has increased nearly 35 million times in this period.
The principal magnetic components in a drive are the media or disks, and a recording head that reads and writes data. These data are recorded in the form of magnetized regions on the media within a deposited thin film of magnetic alloy normally consisting of chromium, cobalt, platinum, and a fourth component as boron. Data are distributed geometrically on a series of concentric rings, or tracks, whose location has been predetermined by a process called formatting. Along these tracks, bits of data are magnetically written by an inductive element in the head, and subsequently sensed or read by the giant magnetoresistive element that is an integral part of the head structure.