Giant magneto-resistance

See also: GMR

The giant magneto-resistance (in English, Giant Magneto-resistance Effect or GMR ) is a quantum effect observed in the structures of thin films made up of an alternation of layers Ferromagnétique S and nonmagnetic layers. It appears in the form of a significant decrease of the resistance observed under the application of a Magnetic field externe : with null field, the two adjacent ferromagnetic layers have a antiparallel Aimantation because they undergo a ferromagnetic Couplage weak. An external magnetic field induced a Inversion of magnetization: respective magnetizations of the two layers align and the resistance of the Multicouche decrease brutally.

The effect occurs because the Spin electron S of the nonmagnetic Métal is distributed in a parallel and antiparallel way equitably, and thus undergoes a magnetic Diffusion less important when the ferromagnetic layers are magnetized in a parallel way.

Discovered

Giant magneto-resistance was discovered in layers mono Cristal lines in 1988 by two indépendantes  teams;: that of Albert Fert, the University of Southern Paris - Orsay, and that carried out by Peter Grunberg of the Research center of Jülich (Rhineland-of-North-Westphalia, Germany). A research team of IBM carried out by Stuart Parkin carried out the same experiment on polycrystalline layers in 1989, thus opening the way with applications sufficiently not very expensive to consider commercial applications. In particular, one of the possible applications was the use of the GMR to carry out a Capteur Magnetic field, and thus to propose a new type of play-back head in the hard drives of Ordinateur S. the first device using giant magneto-resistance was marketed by IBM in December 1997. Since 1999 approximately, research relates on the use of nanofils organized into multi-layer, but also to the use of many types of nanostructurés materials (aggregates, nanoparticules trapped in dielectric substrates, etc)

October 9th, 2007, Albert Fert and Peter Grunberg jointly received the Nobel Prize of Physics for their discovery of giant magneto-resistance. This fundamental work allowed the development of a new research field in Nanotechnologie S, the Spintronique, or electronics of Spin, which exploits the quantum properties of the spin of the electron. The spintronic guide electrons while acting on the rotation of their spin instead of acting on their electric charge.

Various types of phenomena GMR

Giant magneto-resistance in the Multi-layer S

At least two layers Ferromagnétique S are separated by a ultra-thin film (approximately 1  Nanometer) of nonferromagnetic metal (for example, two layers of Iron separated by Chromium: Fe/Cr/Fe). For certain thicknesses, the Couplage RKKY between the adjacent ferromagnetic layers becomes a coupling antiferromagnétique : at the energy level, it becomes preferable for the adjacent layers that their respective magnetizations align in an antiparallel way. The electrical resistance of the device is normally larger in the antiparallel case, and the difference can reach several tens of pourcents to room temperature. In these devices, the transition course corresponds to the second antiferromagnetic peak in the antiferromagnetic-ferromagnetic oscillation of the Couplage RKKY.

Giant magneto-resistance was observed for the first time in a configuration Multicouche, and research related to mainly stackings of 10 layers or more.

Giant magneto-resistance spin-valve

Two layers Ferromagnétique S are separated by a nonmagnetic layer (approximately 3  Nm), but without Coupling RKKY. If the coercitive Force of both electrode S ferromagnetic is different, it is possible to commutate them independently. Thus, one can carry out a parallel or antiparallel alignment, and resistance must be larger in the antiparallel case. This system is sometimes called spin-valve , because it makes it possible to control the Spin electron S which forward.

Giant magneto-resistance by spin-valve is that which are of the most industrial interest and commercial  ; it is the configuration used in the hard drives.

Granular giant magneto-resistance

Granular giant magneto-resistance is a phenomenon occurring in the solid magnetic material precipitates in a nonmagnetic matrix. In practice, the granular GMR is only observed in matrices of Cuivre containing granules of Cobalt. The reason is that cobalt and copper are not Miscible S, and it is thus possible to create the solid precipitate by quickly cooling a mixture in cobalt and copper fusion. The size of the granules depends the speed of cooling and on post-annealing. The materials showing a granular giant magneto-resistance seem in 2005 pas able to reproduce effects also important only those presented by their formed counterparts of multi-layer.

Applications

The phenomenon of giant magneto-resistance is very much used in the play-back heads GMR of the modern hard drives. The nonvolatile magnetic storages (or MRAM) are another application.

Internal bonds

• Ferromagnetism

• Spintronique

References

• Magnetic properties off superlattices formed from ferromagnetic and anitferromagnetic materials , L.L. Hinchey & D.L. Millets, Physical Review B , 33 (5), 3329, March 1986.
• Layered Magnetic Structures: Obviousness for Antiferromagnetic Coupling off Fe Layers across Cr Interlayers , P. Grunberg, R. Schreiber, Y. Pang, Mr. B. Brodsky, & H. Sowers, Physical Review Letters , 57 (19), 2442, November 1986.
• Antiparallel coupling between Fe layers separated by has Cr interlayer: Dependence off the magnetization one the film thickness , C. Carbon and S.F. Alvarado, Physical Review B , 36 (4), 2433, August 1987.
• Giant Magneto-resistance off (001) Fe (001) Cr Magnetic Superlattices , Mr. NR. Baibich, J. Mr. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Eitenne, G. Creuzet, A. Friederich, & J. Chazelas, Physical Review Letters , 61 (21), 2472, November 1988.