L.S. Kirschenbaum GMR Explanation Page

Last modified 10/3/98

Giant Magnetoresistance

Conventional magnetoresistance has been known for a number of years, since early low temperature solid state materials research started. When a magnetic field is applied to certain materials their resistance changes - Magnetoresistance. This effect is of a small percentage and was typically observed at very low temperatures.
Giant magnetoresistance was first discovered in 1987 by Fert, Grünberg, and Parkin. Unlike magnetoresistance, the percentage change in resistance was found to be quite large, and giant magnetoresistance was soon found in certain materials at room temperature. I measured the noise associated with giant magnetoresistance materials -- which is important since noisy materials would not be very useful for technological application. GMR offers a way in which magnetic fields may be detected merely by measuring the resistance of GMR materials; and blocks or stripes of these materials may be made quite small. Examples of devices using such small magnetic detectors might be:

blue bullet Computer hard drive read heads. Much smaller read heads would allow for 100x more data on the same size hard drive disk! These sensors are called "spin-valves" and are used in almost all hard drives today.
blue bullet Magnetic memory chips (MRAM). MRAM chips are currently under development at a number of companies.
blue bullet Magnetic transistors.
blue bullet Miniature velocity detectors -- a GMR sensor near a gear connected to a car's axle detects the gear's teeth which would comprise a tiny speed detector on every wheel of a car. {Seriously! Several automotive companies want to see this technology mature because the velocity detectors they have now are kind of...well, klunky, or so I've heard.}

How do hard drives work? See Quantum Corporation's description.
Alison Chaiken's Magnetoresistance Links
What units are used to measure magnetic fields?
Leif's GMR publications Page
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