Giant magnetoresistance
The GMR effect (English giant magnetoresistance) or giant magnetoresistance is observed in structures consisting of alternating magnetic and non-magnetic thin films with a few nanometers thickness. The effect causes the electrical resistance of the structure of the mutual orientation of the magnetization of the magnetic layers is dependent, and that it is significantly higher than that of the magnetization in the same direction for magnetization in opposite directions.
Discovery
The effect was first discovered in 1988 by Peter Grünberg of the Jülich Research Center and Albert Fert of the University of Paris-Sud in of independent work, for which they were jointly awarded the 2007 Nobel Prize in Physics.
Explanation
The GMR effect is a quantum mechanical effect, which can be explained by the spin dependence of electron scattering at the interfaces. Electrons that can propagate well in one of the two ferromagnetic layers, because their spin is oriented favorably, are strongly scattered in the second ferromagnetic layer when it is magnetized in opposite directions. They pass through the second layer, but much easier when the magnetization having the same direction as in the first layer.
Application
If two layers of ferromagnetic material separated by a thin non-magnetic layer, then the magnetizations align in certain thicknesses of the intermediate layer in opposite directions. Even small external magnetic fields are sufficient, however, to switch this antiferromagnetic order again in the ferromagnetic order.
In connection with the GMR effect variations of the external magnetic field in suitable structures, therefore, cause large changes in electrical resistance of the structure.
The opportunities for using the effect in a sensor for a magnetic field ( and thus as a new type of read head in a computer disk), were quickly discovered by a project managed by Stuart Parkin IBM Research team by showing that the effect in polycrystalline layers occurs.
In the application of the effect today one distinguishes the following cases:
Commercial use
IBM introduced in December 1997, established the first commercial hard drive that used the GMR effect. Other applications are magnetic field sensors in automobiles.
The use of the effect in non-volatile storage media ( see MRAM) has not yet reached market maturity in 2010.