Recent developments in magnetic tunnel junctions

The authors present various new phenomena in magnetic tunneling junction (MTJ). Since the interface and barrier structure play a significant role in determining the physical phenomena, they have employed various techniques to characterize this structure. For obtaining the barrier information, they have performed electron holography studies which directly show the energy profile with atomic resolution. The interdiffusion between different layers has been studied using high-resolution transmission electron microscopy, elemental mapping, and time-of-flight secondary ion mass spectrometry. With this structural information, the authors showed the existence of bulklike contribution in MTJ and determined the characteristic length. In addition, they also observed a conductance minimum anomaly which is much different from the normally observed zero bias anomaly. Large inversed TMR has also been observed at bias as high as 0.4 V in MTJs with an Al₂O₃-ZrO barrier. The authors have modified the Brinkman model by incorporating the voltage dependent density of states of the ferromagnetic electrodes, which successfully explains the bias dependence of the tunneling magnetoresistance (TMR), conductance minimum anomaly, and inversed TMR.