That proved to be a sensitive detector of magnetic fields, like those used to store information on hard disks, and in 1997, IBM introduced the first hard disk that took advantage of giant magnetoresistance. Before then, the capacity of hard disks had increased by about 60 percent a year.
Since then, hard disk capacities have doubled every year, in large part because of the more sensitive read/write heads.
A structure known as a magnetic tunnel junction, first built by scientists at MIT in 1995, forms the basic component of MRAM. A junction consists of two magnetic layers separated by an insulator. The magnetic field of one magnetic layer always remains in one particular direction, the field in the other layer can be switched back and forth. When the fields oppose each other, little current flows across the junction, which represents a "0." When a field is switched in the one magnetic layer, resistance drops, representing a "1."
Because the atoms in the magnetic layers do not flip back and forth by themselves, the junction maintains its "0" or "1" state even when power is turned off. The speed of MRAM should be reasonably fast, if not quite as fast as the fastest of current technologies, and it is expected to be low-power.
"All of us have in mind the holy grail of memory," said Isaac of IBM. "We've shown that magnetic memory works. The physics of it work. The devices work."
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