Materials for Magnetic Data Storage: The Ongoing Quest for Superior Magnetic Materials
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Materials for
Magnetic Data Storage: The Ongoing Quest for Superior Magnetic Materials
Hans Coufal, Lisa Dhar, and C. Denis Mee, Guest Editors Abstract From its inception until today, and for the foreseeable future, magnetic data storage on disks and tape has provided constantly increased storage density. This has required not only constant innovation, but also major breakthroughs in magnetic materials, both for the media and the read head. Today’s disk and tape drives take advantage of novel nanoengineered composite magnetic materials and quantum mechanical processes. In this issue of MRS Bulletin, we present a number of review articles by some of the leaders in this rapidly moving field that highlight the key materials science accomplishments that have enabled the tremendous progress in hard disk drive and magnetic tape technologies. Individual articles describe the materials involved in stateof-the-art magnetic recording, advanced media for perpendicular magnetic recording, the materials challenges of achieving high performance in flexible media such as magnetic tape, the materials issues of read heads, and future avenues for magnetic storage beyond magnetic recording, such as nanowires and spintronics. Keywords: magnetic, magnetoresistance, memory, nanoscale, spintronic.
Half a century of progress in magnetic data storage has changed the world. Almost 50 years ago, on September 13, 1956, IBM announced the 305 RAMAC (random access method of accounting and control) computer system with the IBM 350, the world’s first disk drive. This novel way to store and retrieve data with a rotating disk enabled rapid “random” access to the data. The high cost of one recording and read head and the associated racks of electronics was amortized over 50 24-in. disks with a total of 5 Mbyte of storage capacity, resulting in an acceptable cost per bit.
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As shown in Figure 1, the storage density of hard disk drives (HDDs) has since then increased by eight orders of magnitude from these humble beginnings, first at a compounded growth rate of 25% per year, then 60%, followed by several years of 100%, to finally slow down a little bit in the last couple of years. At the same time, the cost has been declining exponentially (see Figure 2); today, storing data on a hard disk is substantially cheaper than storing the same information on paper. Disk drive design, while basically unchanged from its inception, required
breakthroughs in magnetic materials to enable the low-cost, large-capacity disk drives that have moved computers from the “glass houses” of the early days, which proudly showcased a company’s most prized possession behind a wall of windows, to portable applications such as laptops or iPods. Some of the drastic changes in the areal density curve of Figure 1 are due to breakthroughs in materials science that allowed the introduction of new technologies such as the thin-film head, the magnetoresistance head, and, finally, giant magnetoresistance and magnetic tunnel junction heads and the corresponding magnetic recording
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