Physics Nobel Prize Awarded for Hard Drive Breakthrough

from reporter Saswato R. Das:

Two physicists who discovered an effect that forever changed how humans would store electronic data â'' a discovery that enabled the now ubiquitous Apple iPod â'' have been awarded this yearâ''s Nobel Prize in Physics.

The Royal Swedish Academyâ''s decision to give scienceâ''s highest honor to Albert Fert of France and Peter Grÿnberg of Germany is acknowledgement of how the discovery of giant magnetoresistance, made independently by the two scientists in 1988, has revolutionized magnetic storage, making it possible to put vast amounts of data on tiny storage devices.

GMR (as giant magnetoresistance is referred to) is a physical effect that causes huge changes in electrical resistance when the magnetic field is changed ever so slightly. Harnessing it for hard drives has made possible media players that fit in the palm of oneâ''s hand yet contain thousands of songs.

â''It is thanks to this technology that it has been possible to miniaturize hard disks so radically in recent years,â'' said the Royal Swedish Academy of Sciences in the statement that announced the award.

Fert and Grÿnberg will share the prize, endowed by Swedish industrialist Alfred Nobel a little more than a century ago, and now worth about $1.5 million. The prize is awarded every year by the King of Sweden in Stockholm on December 10, the anniversary of Nobelâ''s death.

GMR was a chance discovery, and both Fert in France and Grÿnberg in Germany stumbled on it separately in 1988. As long as a century and a half ago, the British physicist Lord Kelvin observed that the electrical properties of pieces of iron change when placed in a magnetic field. This is ordinary magnetoresistanceâ''it is caused by the interaction of the magnetic field with the atoms in the pieces of iron.

Fert and Grunberg noticed that when they placed thin layers of magnetic materials such as iron and chromium separated by a thin layer of non-magnetic material in a magnetic field, they saw a very dramatic increase in magnetoresistance in the outer magnetic layers, much larger than what anyone had observed previously. The phenomenon came to be known as giant magnetoresistance.

It is an effect caused by a quantum property of the electrons in the two outer magnetic layers. Metals have a lot of free electrons, and electrons possess a quantum property called spin. If the spins in the magnetic layers are all pointing in the same direction, electrons having the same spin can pass through it easily. But electrons with opposite spins will get scattered.

Perturb one of the layers with a magnetic field, as would happen when reading a bit from a hard disk, and now all electrons trying to pass through are scatteredâ''the resistance jumps.

What was a laboratory curiosity evident only at very cold temperatures was harnessed to make better disk drives by Stuart Parkin of IBM, who realized that GMR had great potential. In a disk drive, information is stored digitally in the form of tiny magnetized domains. The more densely one can pack the domains, and the more sensitive they are, the better and smaller a disk drive one gets. Parkin and colleagues at IBM set about finding materials that were better suited to building commercial disk drives. In less than a decade, the first GMR-based disk drive was on the market. The result is that today information can be packed much more tightly than ever before. Hand in hand with Mooreâ''s law, GMR-disk drives have enabled electronic miniaturization as never before.

GMR disk drives in practice have very thin layers of the different magnetic and non magnetic materials. In fact, the layers are so thin that they are sometimes a few atoms across and measured in nanometers (a nanometer is one-billionth of a meter, or one-hundred thousanth the thickness of a human hair). Thus, â''GMR can also be considered one of the first real applications of the promising field of nanotechnology,â'' said the Nobel committee in its statement, labeling the physics prize this year as a nanotechnology prize.

GMR is also a key effect to the emerging research area of spintronics, which aims to build circuits based on electron spin. Fert has been an actively researching spintronics. His recent research, published in IEEE Transactions on Electron Devices (May 2007), has to do with developing a semiconductor-based spin transistor.


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