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).
Click here for original story, A four-state magnetic tunnel junction for novel spintronics applications
Source: Phys.org