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Physics Nobel for a great discovery

To most of us, the ongoing information technology revolution has meant more powerful and lighter computers. A faster processor is only one part of the story. Equally important are the rapidly evolving technology of data storage capacity and the fast read-out capability of these systems. Ever-shrinking hard disks have made laptops slenderer and sleeker. They can now store hours of music and images in MP3 players, iPods, and other pocket-sized wonders of personal entertainme nt. Since the introduction of the disk drive in 1956, the density of information it can record has increased from 200 bits to 10 billion (or giga) bits crammed into one square centimetre. That is a 50-million-fold increase in half a century! This year’s Nobel Prize in Physics to France’s Albert Fert and Germany’s Peter Gruenberg is for their independent discovery, in the late-1980s, of a new effect called Giant Megnetoresistance (GMR) that has revolutionised hard disk technology. From the perspective of evolution of a new physical effect to an industrial scale technology, GMR storage devices are unique. IBM introduced the first 16.8-gigabyte GMR hard disk drive in 1997, less than a decade after the discovery. Indeed, GMR effect has been hailed as one of the first major applications of nanotechnology and ‘spintronics.’

Information is stored on a hard disk in the form of differently magnetised areas. As hard disks began to shrink, each magnetic area became correspondingly smaller. This made the magnetisation of each binary bit weaker and harder to read. With increasing bit density on hard disks, more sensitive read-out techniques were required. The discovery of GMR enabled that much-needed technological leap. An electron (of a flowing electric current) will encounter least resistance through a magnetic material whose electrons are similarly aligned and maximum resistance if they are oppositely aligned, but the change in resistance observed is only a few per cent. The application of this basic principle (of magnetoresistance) as technology for read-out heads occurred in the 1990s and was the direct predecessor of GMR. The latter effect, which displayed a resistance change up to 50 per cent and was therefore called ‘giant,’ was observed when tens of nanometre thick layers of magnetic and non-magnetic materials were sandwiched in an alternating magnetic configuration. Much like crossed polaroids, which block light completely, a crossed configuration of magnetic materials results in a steep increase in electrical resistance. This led to the development of rapid data read-out devices that are very sensitive to tiny variations in magnetisation on a hard disk. Given its huge impact and considering the exciting future of the application of spintronics, the discovery of GMR richly deserved the Nobel.

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