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:
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.
Magnetic memory chips (MRAM). MRAM chips are currently under development
at a number of companies.
Magnetic transistors.
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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