Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. Tunneling magnetoresistance (TMR) is a dramatic change of the tunneling current in magnetic tunnel junctions when relative magnetizations of the two ferromagnetic layers change their alignment. It is a magnetoresistive effect that occurs in a magnetic tunnel junction (MTJ), which is a component consisting of two ferromagnets separated by a thin insulator. TMR is a consequence of spin-dependent tunneling. The tunnel magnetoresistance (TMR) ratios were 80% at 2K and 48% at room temperature for the MTJ with the (100)-Co2FeSi bottom electrode.
Tunneling magnetoresistance effect in magnetic tunnel junctions (MTJs) is one of the most fundamental and important spintronic phenomena. If the insulating layer is thin enough (typically a few nanometres), electrons can tunnel from one ferromagnet into the other. Since this process is forbidden in classical physics, the tunnel magnetoresistance is a strictly quantum mechanical phenomenon. Thus, TMR effect in MTJs composed of (Ga, Mn).
Magnetic tunnel junctions are manufactured in thin film technology. It effect of changes in electrical resistance between two ferromagnetic regions, separated by a thin dielectric layer due to tunnelling of a spin-polarised carriers induced by the magnetic field. On an industrial scale the film deposition is done by magnetron sputter deposition; on a laboratory scale molecular beam epitaxy, pulsed laser deposition and electron beam physical vapor deposition are also utilized. The effect of tunnelling magnetoresistance is similar to that of giant magnetoresistance, but the ferromagnetic regions are separated by non-conductive insulating layers. The junctions are prepared by photolithography.
Tunneling magnetoresistance is a quantum mechanical effect which occurs when two ferromagnets are separated by a few atomic layers of insulator. Examples of systems using tunnel magnetoresistance include composites, in which ferromagnetic grains are arranged in an insulating matrix, and layered structures, in which magnetic layers are separated by thin dielectric layers. Recently, magnetoresistive random access memory (MRAM) has been created on the basis of tunnelling magnetic resistance. The conductance of such a tunneling junction can vary dramatically depending on whether the ferromagnets are alligned in parrallel or antiparallel. The effect is also used in the reading heads of hard drives. This effect is one of the main effects that can be practically implemented in spintronics devices.
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