GMR effect

of results of Fert et al.
Spin valve GMR

the GMR effect (English. Giant Magneto Resistance, dt. „Giant magneto-resistance “) is a quantum-mechanical effect, which is observed in thin film structures from alternating ferrousmagnetic and non-magnetic layers.

The effect shows up in a significant rise of the resistance of the structure, if two ferrousmagnetic levels contain electrons with spin moving in opposite directions (contrary to a lower resistance, if the two levels contain electrons with parallel spin).

The effect was from each other discovered first 1988 by Peter Grünberg of the research center Jülich and Albert Fert of the University of Paris south in independent work. The possibilities, which became effect in a sensor for a magnetic field to begin (and thus as a new type of read head in a computer non removable disk) fast by an IBM - research team by Stuart Parkin discovers. It made a replication the effect with polycrystallines layers. IBM manufactured the first commercial drive assembly, which used this effect in December 1997. Presently the research concentrates on the use of multilevel nano-wires (one larger sensitivity than those at present genutzen films offer).

It is appropriate to differentiate between two cases which are normally attributed both to the GMR:

  1. Two ferrousmagnetic levels are separate by a very thin (approximately 1 Nm) non-ferrousmagnetic Spacer (about Fe/Cr/Fe). Starting from a certain thickness the RKKY reciprocal effect between the two ferrous magnets ensures for the fact that a parallel or an antiparallel adjustment is energetically preferred. The electrical resistance of this unit is normally higher with an antiparallel adjustment, whereby the difference can reach some 10% at room temperature.
  2. Two ferrousmagnetic levels are separate by (approximately 3 Nm) a thin non-ferrousmagnetic Spacer without RKKY coupling. If the Koerzitivfelder of the two ferrousmagnetic electrodes is different, it is possible to change these independently. Therefore a parallel and an antiparallel adjustment can be achieved, whereby the resistance is again normally higher in the antiparallel case. Sometimes this construction unit is called also turning valve (spin valve).

Apart from application in non removable disks the GMR effect is used also in the non volatile storage technology Magneto resistive random ACCESS MEMORY and in magnetic field sensors of the automobile industry.

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