A tunnel junction is a device consisting of two
conducting layers separated by an insulating layer. Classically,
the resistance for driving current across an insulating layer is
infinite; however, when the insulating layer is thin (~ 1-2
nanometers), charge carriers may tunnel through the insulating
layer, due to their quantum nature. When the conducting layers are
magnetic, a magnetic tunnel junction (MTJ), whose resistance
depends on the magnetic configurations, is obtained. Current MTJs
have only two resistance states as they support either parallel or
anti-parallel magnetic configurations of the two magnetic layers.
The two-state MTJ has been playing a central role in spintronics, a
branch of electronics that uses the magnetic moment associated with
the spin of the electron in addition to the electron charge used in
traditional electronics. Thus, for instance, the two-state MTJ is
the main building block of the magnetic random access memory
(MRAM).
A four-state magnetic tunnel junction for novel spintronics
applications
