The effect is called giant magnetoresistance, but it enables amazing things at the miniature level. Two European scientists won the 2007 Nobel Prize in physics Tuesday for their discoveries of the phenomenon, which spurred some of computing’s most astonishing developments, from video-playing handheld devices to PCs whose storage capacity now seems all but limitlessHere’s how it works.
As a metal disk spins inside a hard drive, an arm with a sensitive electromagnetic head at its tip hovers over the disk, somewhat like the needle on a record player (though it doesn’t make contact). This head reads bits of data by registering the magnetic bearing of individual particles; it writes data by changing that magnetic orientation.
For disk drives to increase in capacity, those magnetic particles must become smaller, so more can be packed into the same amount of space. But these ever-tinier materials produce fainter magnetic signals, which means the read-write head in the disk drive has to become more sensitive.
What Fert and Gruenberg independently discovered was that extremely thin layers of alternating metals could detect remarkably weak changes in magnetism — and translate them into “giant” changes in electrical resistance.
In other words, the particles used in data storage could get much denser and still produce the electrical signals that computers read as ones or zeros as they do their business.
It took until 1997 for giant magnetoresistance (GMR) to get translated from Fert and Gruenberg’s raw science into a product for the disk market. That was led by IBM Corp., where researcher Stuart Parkin developed a way to incorporate Fert and Gruenberg’s findings into the cost-effective manufacturing process already used to produce disk drives.
One result can be measured in disk-drive density — the number of bits that can be squeezed into a given area. In the 1990s, disk density was generally improving about 60 percent a year. But GMR sparked a few years in which density doubled — a 100 percent rise — and costs still fell.