What do missile guidance, keyhole surgery and position sensing in computer games have in common? They all represent applications of new giant magnetoresistance (GMR) sensors being developed by a number of UK universities.
These electronic devices are created by physicists exploiting the 'spin' or angular momentum property of the electron - a technique known as spintronics. It will have application in the development of robotics, fuel-handling systems, electronic engine control, anti-skid systems, missile guidance and post-operative care.
Spintronic devices have the advantage of being smaller, more versatile and more robust than those currently making up silicon chips and circuit elements. The spins of electronics can be oriented in one direction or the other: called spin up or spin down. When electron spins are aligned they create a large-scale net magnetic moment as seen in magnetic materials such as iron and cobalt. Magnetism is an intrinsic physical property associated with the spins of electronics in a material. It is already exploited in recording devices such as computer hard disks with data recorded and stored as tiny areas of magnetised iron and chromium oxide.
To access the information a 'read head' detects the minute changes in the magnetic field as the disk spins underneath it. This induces corresponding changes in the head's electrical resistance, an effect called magnetoresistance. GMR results from subtle electron-spin effects in ultra-thin multilayers of magnetic materials that cause huge changes in their electrical resistance when a magnetic field is applied. GMR is 200 times stronger than ordinary magnetoresistance.
Physicists have been quick to use these multilayer sandwiches of magnetic metal such as cobalt with a nonmagnetic metal filling such as silver to create spin valves that act as switches.
They have application as magnetic random access memory (MRAM) in computers. Used with silicon they are being developed as magnetic semiconductors and many other operations. Among UK universities now engaged in spintronic research are Oxford, Cambridge, Sheffield and York.
For further information, contact Dr Alice Larkin, Institute of Physics, at [email protected], or see www.iop.org
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