The relentless demand for smaller, faster, cheaper, more capable computers continues to drive the development of devices for sensing and storing information. Over the past decade, manufacturers have exploited the phenomenon of giant magnetoresistance (GMR) to build sensors for reading data bits coded as tiny magnetized regions on disk drives. The higher sensitivity of these GMR read heads to magnetic fields has allowed a reduction in the bit size and hence an enormous increase in the storage capacity of magnetic hard disk drives. 1
One of the technologies on the horizon is the magnetic tunnel junction (MTJ). Dan Dahlberg at the University of Minnesota suspects that every hard-drive manufacturer has some kind of tunnel-junction sensor under development. Among it’s advantages, MTJs promise even higher sensitivities than GMR devices. Recent experiments now suggest that MTJs will not disappoint.
A GMR device comprises two layers of ferromagnetic material, such as cobalt, separated...
