Physicists win Nobel prize for hard work on hard drives

October 09, 2007

October 9, 2007 (ISNS)-If "giant magnetoresistance" is not the first word most people think of when they think about their cool new portable music players, perhaps they should. Without it, our wafer-thin iPods would be the size of Texas toast.

Giant magnetoresistance, or GMR for short, is the technology that has allowed laptops to shrink and storage bytes to boom. It enables computers to stuff more than a trillion bits of data on a storage cell the size of a fingernail-or, in terms of songs, all the music you've ever listened to in your life on a player no bigger than a keychain.

While GMR has been a driving technology behind our modern digital age, it has done so quietly. Until now, relatively few people outside of engineering circles had ever heard of it.

That may have ended today, however, when the Royal Swedish Academy of Sciences announced it will award the 2007 Nobel Prize in Physics jointly to Albert Fert of the Université Paris-Sud in France, and Peter Grünberg of Forschungszentrum Jülich, Germany for their early GMR work. In awarding this particular achievement, the academy marks the beginning of a new epoch as this is the first Nobel prize for a true form of "nanotechnology," which promises to revolutionize many areas of science and modern life.

What They Did

The work that led to this revolution began as basic research. Working independently, Fert and Grünberg both scrutinized the quantum properties of materials. As its name implies, giant magnetoresistance combines magnetism and electrical resistance; by the way, the "giant" refers to the fact that it's better than plain old magnetoresistance. What GMR did was to allow bits of information stored on a magnetic disk to be lifted up into the read head for decoding. The magnetic information had to be turned into an electrical form.

Information is stored on magnetic drives by virtue of the fact that these drives are made from metallic materials that can be manipulated with electric fields. Individual tiny areas on the surface of the drive can be polarized in a precise magnetic field and fixed like a very faint bar magnet, pointing north or south. This allows information in the form of individual bits (1 or 0) to be stored for later retrieval.

The "resistance" part of the name refers to the circuitry used to read the bits of information. Electrons flowing through a wire experience resistance, like water flowing through a partially clogged pipe. But this electrical resistance can be detected and used to relay electrical information.

The secret to this process is the readhead, which passes over the magnetic disk to electronically retrieve the information in tiny sectors or domains. The readhead of a modern hard drive is a tiny sensor consisting of a stack of layers of matter that are only a few atoms thick. Some of these layers are magnetic and some are not. What happens when this sensor passes above the hard drive's surface is that the information stored as tiny magnetic differences on the disk causes electrical resistance changes. These changes, in turn, create noticeable alterations in the electrical circuit. In this way, the magnetic information becomes electric information, to be sent off to a speaker or a screen, and a spinning disk churns out a digital song or movie.

The key to giant magnetoresistance is that the readheads are made of a sandwich of materials much more sensitive to magnetic differences than older magnetic-playback equipment. The MGR versions can read much smaller magnetic differences. This allows more information to be crammed into the same amount of space-much as you could fit more can fit more bodies onto an airplane by making the seats smaller and filling them with tinier people.

Once GMR became available in the 1990s, an added benefit was quickly realized. Its drives use less power, which allows extended battery life in the devices that use the technology, and providing and the people who use these devices more hours of unfettered entertainment.

The subtle magnetic-electric at work in magnetoresistance doesn't just help to make hand-held gizmos possible, though. It could also enable a new form of electronics called "spintronics," which relies on controlling the spin rather than the charge of an electron.

Spin is something that, like a magnet, can point up or down. Indeed, the magnetism we encounter in refrigerator magnets arises from the individual spins of electrons and nuclei in the atoms making up the magnet. Using or manipulating the spins of electrons as they flow through wires and into special "spin transistors" is a more recent development that promises to have new applications. Already in some niche markets spintronic-based magnetic random access memory (or MRAM) chips are in use.

The research done by scientists like Drs. Gruenberg and Fert helps to keep engineers ahead of "Moore's law," the idea asserted decades ago by Intel founder Gordon Moore, that the power of computers tends to double about every 18 months. Many energy analysts have predicted the end of this "law," since they couldn't see how scientists could keep coming up new technologies to keep the progress flowing. But thanks to Gruenberg and Fert's discovery of giant magnetoresistance, they have.

So you can think about them the next time you select a song on your iPod-whether Fergie, Creedence, or Frank.

American Institute of Physics

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