One of the promising applications of magnetic tunnel junctions (MTJs) is a magnetic random access memory (MRAM). The basic concept of MRAM is to use the magnetization direction in MTJs for information storage. “0” and “1” correspond to parallel and antiparallel magnetizations in a MTJ. The information bits can be written by passing a current through a MTJ, and they can be read out by measuring the resistance difference. The figure below shows schematically the architecture of MRAM. MRAM promises a high density, non-volatility and a low power consumption. The large TMR signal in MTJs also makes them attractive for magnetic-media read heads and other types of sensor applications.
Magnetic Tunnel Junction
A magnetic tunnel junction (MTJ) consists of two layers of magnetic metal, such as cobalt-iron, separated by an ultrathin layer of insulator, typically aluminum oxide with a thickness of about 1 nm. The insulating layer is so thin that electrons can tunnel through the barrier if a bias voltage is applied between the two metal electrodes. In MTJs the tunneling current depends on the relative orientation of magnetizations of the two ferromagnetic layers, which can be changed by an applied magnetic field. This phenomenon is called tunneling magnetoresistance (TMR).
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